Positive electrode active material, method for preparing the same, and positive electrode and lithium

Abstract

The present invention relates to a positive electrode active material of a lithium-rich manganese-based oxide exhibiting improved capacity characteristics and excellent lifespan characteristics and rolling characteristics, and a method for preparing the same. The positive electrode active material includes a lithium-rich manganese-based oxide represented by the following Chemical Formula 1 and having a structure in which a rock salt-type lithium manganese oxide and a layered lithium transition metal oxide are mixed, wherein the lithium-rich manganese-based oxide may have a predetermined internal porosity. [Chemical Formula 1] Lia [NibCocMndMe] O2 is 1.00 lt in Chemical Formula 1; a, 0 < = b < = 0.53, 0 < = c < = 0.10, 0.47 < = d < = 1.00, 0 < = e < = 0.20, and M is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0020972 filed in the Korean Intellectual Property Office on February 16, 2023, and Korean Patent Application No. 10-2024-0022244 filed in the Korean Intellectual Property Office on February 16, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0003] The present invention relates to a positive electrode active material and a method for preparing the same. More specifically, the present invention relates to a positive electrode active material of a lithium-rich manganese-based oxide showing improved capacity characteristics and excellent life characteristics and rolling characteristics, a method for preparing the same, a positive electrode and a lithium secondary battery containing the same. Background Art

[0004] Lithium secondary batteries are generally composed of a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode and the negative electrode contain active materials capable of inserting and extracting lithium ions.

[0005] As the positive electrode active material of lithium secondary batteries, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese oxide (LiMnO 2 or LiMnO 4 etc.), lithium iron phosphate compounds (LiFePO 4 ) and the like. Among them, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high and the supply is unstable, making it difficult to commercially apply to large-capacity batteries. The structural stability of lithium nickel oxide is poor, which makes it difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide with a spinel structure has excellent stability, but has the problem of deteriorated capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed and used to compensate for the problems of lithium transition metal oxides containing only Ni, Co or Mn. Among them, it is known that oxides containing excess lithium and having a Mn content higher than the content of other metals except lithium (hereinafter referred to as "lithium-rich manganese oxides") can be used as high-capacity active materials to ensure high energy density, so research and interest in this field are increasing significantly.

[0006] However, in the case of lithium-rich manganese-based oxides, there are disadvantages such as high resistance of the electrode and insufficient capacity characteristics such as discharge capacity. In addition, lithium-rich manganese-based oxides have a structure in which a layered phase and a rock-salt phase are mixed. During the activation process of the rock-salt phase, a large amount of gas and excessive lithium ions may be generated. Such gas generation may cause deterioration of the positive electrode, which may lead to a decline in life characteristics.

[0007] Therefore, there is a continuous need to develop a positive electrode active material that contains a lithium-rich manganese-based oxide and exhibits excellent life characteristics and improved capacity characteristics. Summary of the Invention

[0008] Technical issues

[0009] An object of the present invention is to provide a positive electrode active material that contains a lithium-rich manganese-based oxide and thus exhibits improved capacity characteristics, excellent life characteristics, and rolling characteristics, and a method for preparing the same.

[0010] Another object of the present invention is to provide a positive electrode and a lithium secondary battery that contain a lithium-rich manganese-based oxide and thus exhibit improved discharge capacity, excellent life characteristics, and the like.

[0011] Technical Solution

[0012] In one aspect of the present invention, there is provided a positive electrode active material, which comprises:

[0013] A lithium-rich manganese-based oxide represented by the following Chemical Formula 1 and having a structure in which a rock-salt type lithium manganese oxide and a layered lithium transition metal oxide are mixed,

[0014] wherein the internal porosity of the lithium-rich manganese-based oxide is 2.5% to 13.0%,

[0015] [Chemical Formula 1]

[0016] Li a [Ni b Co c Mn d M e O 2

[0017] In Chemical Formula 1, 1.00 < a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and

[0018] M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0019] In Chemical Formula 1, 1.10 ≤ a ≤ 1.5, 0.10 ≤ b ≤ 0.40, 0 ≤ c ≤ 0.05, 0.47 ≤ d ≤ 0.80, 0 ≤ e ≤ 0.10.

[0020] In Chemical Formula 1, 1.12 < a < 1.18, 0.24 < b < 0.36, 0 < c < 0.10, 0.47 ≤ d < 0.63, 0 < e < 0.05, and

[0021] M can be at least one selected from Al, Mg, V, Ti, Zr, Nb, and W.

[0022] In the lithium-rich manganese-based oxide, the rock-salt type lithium manganese oxide can contain Li 2 MnO 3 , and it can have a structure in which a layered lithium transition metal oxide containing nickel, cobalt, and manganese is mixed therewith. The lithium-rich manganese-based oxide can be represented by the following Chemical Formula 2:

[0023] [Chemical Formula 2]

[0024] XLi 2 MnO 3 · (1-X)Li[Ni 1-y-z-w Mn y Co z M w O 2

[0025] In Chemical Formula 2,

[0026] 0.2 ≤ X ≤ 0.5, 0.4 ≤ y < 1, 0 ≤ z ≤ 0.1, 0 ≤ w ≤ 0.2, and

[0027] M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0028] The positive electrode active material has a secondary particle shape in which a plurality of primary particles with a particle size of 50 nm to 200 nm are agglomerated, and the D 50 of the secondary particles can be 2 to 10 μm.

[0029] In another aspect of the present invention, a method for preparing a positive electrode active material is provided, and the method includes the following steps:

[0030] (A) Mixing a lithium-rich manganese-based transition metal hydroxide precursor containing nickel, cobalt, and manganese with a lithium raw material; and

[0031] (B) Firing the mixture at a temperature above 600 °C to form a lithium-rich manganese-based oxide represented by Chemical Formula 1.

[0032] In the method of preparing a positive electrode active material, the lithium-rich manganese-based transition metal hydroxide precursor may be a compound represented by the following Chemical Formula 1a:

[0033] [Chemical formula 1a]

[0034] Ni b Co c Mn d M e (OH) 2

[0035] In Chemical Formula 1a, 0≤b≤0.53, 0≤c≤0.10, 0.47≤d≤1.00, 0≤e≤0.20, and

[0036] M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0037] In addition, the lithium-rich manganese-based transition metal hydroxide precursor can be formed by co-precipitating a transition metal raw material, such as a manganese raw material, a nickel raw material, a cobalt raw material, etc., at pH 9.5 to 12.

[0038] In addition, in the method of preparing the positive electrode active material, the firing may be performed at a temperature of 600 to 1000°C.

[0039] The lithium-rich manganese-based oxide prepared in this manner can be represented by Chemical Formula 2.

[0040] In still another aspect of the present invention, a positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode are provided.

[0041] Beneficial Effects

[0042] The positive electrode active material according to the present invention includes a lithium-rich manganese-based oxide having an internal porosity within a specific range, thereby improving the contact state between the positive electrode active material particles, and having a relatively large specific surface area, which makes it easy for the electrolyte to penetrate into the positive electrode active material. As a result, the positive electrode active material can exhibit capacity characteristics such as lower resistance and improved discharge capacity compared to the existing lithium-rich manganese-based oxide.

[0043] In addition, since the internal porosity is optimized, after the positive electrode is rolled, the positive electrode active material of the present invention can show excellent contact and filling characteristics between active material particles, which can not only suppress side reactions and gas generation, but also suppress particle cracking during rolling. As a result, the degradation of the positive electrode active material can be suppressed during the charge and discharge process of the battery, thereby showing excellent life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a photograph showing a state in which cross-sectional image data of positive electrode active material particles are extracted from an electron microscope photograph of a positive electrode cross section using a digital conversion technique to analyze the internal porosity of the positive electrode active material.

[0045] Figure 2 This is a photograph showing a state in which a particle region, an internal pore region, and an internal crack region are divided from cross-sectional image data of a positive electrode active material particle and extracted into image data, thereby analyzing the internal porosity of the positive electrode active material. DETAILED DESCRIPTION

[0046] The terms or words used in this specification and the appended claims should not be construed as limited to the ordinary meaning or dictionary meaning, but should be interpreted in accordance with the meaning and concept consistent with the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to appropriately describe the inventor's own invention in the best manner.

[0047] In the present invention, "secondary particles" refer to particles formed by agglomeration of tens to hundreds of primary particles. More specifically, secondary particles are agglomerates of 50 or more primary particles.

[0048] In the present invention, when "particles" are described, any or all of single particles, quasi-single crystals, primary particles, nodules, and secondary particles may be included.

[0049] In addition, in the present invention, "D 50 " refers to the particle size corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material. The average particle size D 50 It can be measured by laser diffraction. For example, the average particle size can be measured by the following steps: dispersing the positive electrode active material powder in a dispersion medium, introducing the resultant into a commercially available laser diffraction particle size analyzer (e.g., MT 3000 of Microtrac), irradiating with ultrasonic waves at a frequency of about 28 kHz and an output of 60 W, obtaining a volume-cumulative particle size distribution diagram, and then determining the particle size corresponding to 50% of the cumulative volume.

[0050] Hereinafter, the "internal porosity" can be calculated by arithmetic mean after the following steps: using a scanning electron microscope (SEM) to obtain a SEM image of the positive electrode cross section, selecting a particle having a predetermined particle size, for example, equal to D 50 The particle size or D 50 The positive electrode active material particles with a particle size of ± 0.1 μm were analyzed by SEM images, and the ratio of the pore area to the cross-sectional area of ​​the positive electrode active material particles was measured.

[0051] The specific embodiments of the present invention will be described in detail below.

[0052] Positive electrode active material

[0053] The positive electrode active material according to one aspect of the present invention may include a lithium-rich manganese-based oxide represented by the following Chemical Formula 1 and having a structure in which a rock-salt type lithium manganese oxide and a layered lithium transition metal oxide are mixed therein.

[0054] [Chemical Formula 1]

[0055] Li a [Ni b Co c Mn d M e O 2

[0056] In Chemical Formula 1, M may be at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. Preferably, M may be at least one selected from Al, W, Mg, V, Ti, Zr, and Nb.

[0057] On the other hand, a is the molar ratio of Li in the lithium-rich manganese-based oxide, which may be 1.00 < a, 1.10 ≤ a ≤ 1.5, or 1.12 < a < 1.18. When a satisfies the above range, high-capacity characteristics and high energy density per unit volume can be achieved.

[0058] b is the molar ratio of Ni in the lithium-rich manganese-based oxide, which may be 0 ≤ b ≤ 0.53, 0.10 ≤ b ≤ 0.40, or 0.24 < b < 0.36.

[0059] c is the molar ratio of Co in the lithium-rich manganese-based oxide, which may be 0 ≤ c ≤ 0.10, 0 ≤ c ≤ 0.05, or 0 < c < 0.10. When c exceeds 0.1, it is difficult to ensure high capacity, gas generation, and deterioration of the positive electrode active material become aggravated, which may lead to deterioration of life characteristics.

[0060] d is the molar ratio of Mn in the lithium-rich manganese-based oxide, which may be 0.47 ≤ d ≤ 1.00, 0.47 ≤ d ≤ 0.80, or 0.47 ≤ d < 0.63. When d is less than 0.47, the ratio of the rock-salt phase becomes too small, so the capacity improvement effect is not significant.

[0061] e is the molar ratio of the additional element M in the lithium-rich manganese-based oxide, which may be 0 ≤ e ≤ 0.20, 0 ≤ e ≤ 0.10, or 0 < e < 0.05. When the content of the additional element is too high, this may have an adverse effect on the capacity of the active material.

[0062] The lithium-rich manganese oxide has a mixture of layered lithium transition metal oxide and rock salt type lithium manganese oxide (Li 2 MnO 3 ) structure, wherein an excess of lithium ions are generated while the rock salt phase is activated during the initial activation process. In addition, an oxygen redox reaction occurs during the activation process of the rock salt phase, and this excess lithium ion generation and oxygen redox reaction can help improve the capacity of the positive electrode active material. However, a large amount of gas may be generated during the activation process of the rock salt phase, which may lead to degradation of the positive electrode and degradation of the life characteristics. In addition, a disadvantage of lithium-rich manganese oxides is that it relatively increases the resistance of the positive electrode, resulting in insufficient discharge capacity.

[0063] The results of the inventors' ongoing research indicate that the above disadvantages can be solved by including a lithium-rich manganese oxide having a specific range of internal porosity. More specifically, the optimization of the internal porosity improves the contact state between the positive electrode active material particles, while the relatively large specific surface area facilitates the penetration of the electrolyte into the positive electrode active material. As a result, it is confirmed that the positive electrode active material exhibits improved discharge capacity and low resistance compared to the existing lithium-rich manganese oxide.

[0064] In addition, since the positive electrode active material optimizes the internal porosity, it can show excellent contact and filling characteristics between the active material particles after the positive electrode is rolled, and can also suppress particle cracking during the rolling period. In addition, side reactions and gas generation during activation can be suppressed. As a result, the degradation of the positive electrode can be suppressed during the charge and discharge process of the battery, thereby showing excellent life characteristics.

[0065] Therefore, in one aspect, the internal porosity of the lithium-rich manganese oxide can be 2.5% to 13.0%, or 3.0% to 12.0%, or 4.0% to 11.0%. If the internal porosity is too low, the electrolyte penetration may not be smooth due to the reduction in the specific surface area of ​​the positive electrode active material, and the capacity characteristics such as discharge capacity may be insufficient, or the resistance of the positive electrode may increase. On the contrary, if the internal porosity is too high, many cracks may appear in the positive electrode active material particles during the rolling of the positive electrode. In addition, the occurrence of side reactions during the activation process of the rock salt phase increases, which may lead to the degradation of the positive electrode and the decline of the life characteristics.

[0066] On the other hand, the lithium-rich manganese-based oxide can be represented by the following chemical formula 2:

[0067] [Chemical formula 2]

[0068] X Li 2 MnO 3 · (1-X)Li[Ni 1-y-z-w Mny Co z M w ]O 2

[0069] In Chemical Formula 2, M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0070] X refers to the rock salt phase (Li 2 MnO 3 ) ratio, which can be 0.2≤X≤0.5, 0.25≤X≤0.5 or 0.25≤X≤0.4. 2 MnO 3 ) satisfies the above range, high capacity characteristics can be achieved.

[0071] y is a layered phase (LiM'O 2 ) in the present invention, which can be 0.4≤y<1, 0.4≤y≤0.8 or 0.4≤y≤0.7.

[0072] z is a layered phase (LiM'O 2 ) is a molar ratio of Co in ZnO, which may be 0≤z≤0.1, 0≤z≤0.08, or 0≤z≤0.05. When z exceeds 0.1, gas generation and degradation of the positive electrode active material become more severe, which leads to a decrease in life characteristics.

[0073] w is a layered phase (LiM'O 2 ) may be 0≤w≤0.2, 0≤w≤0.1 or 0≤w≤0.05.

[0074] In addition, the positive electrode active material of one aspect of the present invention may be in the form of secondary particles in which a plurality of primary particles are agglomerated. In this case, the particle size of the primary particles may be 50 nm to 200 nm, or 60 nm to 180 nm, or 70 nm to 150 nm, and the average particle size D of the secondary particles may be 200 nm to 180 nm, or 200 nm to 150 nm. 50 It may be 2 μm to 10 μm, or 3 μm to 9 μm, or 4 μm to 7 μm.

[0075] At this time, the particle size of the primary particles may be proportional to the particle size of the precursor for preparing the lithium-rich manganese-based oxide, and can be regarded as a factor in achieving the above-mentioned internal porosity. If the particle size of the primary particles is too large, the internal porosity may be reduced, and if the particle size of the primary particles is too small, the internal porosity may be excessively increased.

[0076] In addition, since the positive electrode active material having a secondary particle shape has the above-mentioned D50 range, so excellent electrode density can be achieved after rolling and capacity characteristics can be improved. 50 If D is too small, it will be difficult to achieve high rolling density, which may reduce the rolling characteristics and energy density. 50 If it is too large, the lithium mobility of the positive electrode active material may decrease, and the resistance of a lithium secondary battery containing the same may increase.

[0077] Method for preparing positive electrode active material

[0078] Next, a method for preparing the above-mentioned positive electrode active material will be described.

[0079] According to another aspect of the present invention, a method for preparing a positive electrode active material comprises the following steps:

[0080] (A) mixing a lithium-rich manganese-based transition metal hydroxide precursor with a lithium raw material; and

[0081] (B) firing the mixture at a temperature of 600° C. or higher to form a lithium-rich manganese-based oxide represented by Chemical Formula 1.

[0082] In a more specific embodiment, the lithium-rich manganese-based transition metal hydroxide precursor may be a compound represented by the following Chemical Formula 1a, and may have a particle size corresponding to or proportional to the primary particles of the lithium-rich manganese-based oxide described above,

[0083] [Chemical formula 1a]

[0084] Ni b Co c Mn d M e (OH) 2

[0085] In Chemical Formula 1a, 0≤b≤0.53, 0≤c≤0.10, 0.47≤d≤1.00, 0≤e≤0.20, and

[0086] M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0087] As confirmed by the following examples, in order to obtain the appropriate primary particle size (e.g., 50 nm to 200 nm) of the above-mentioned lithium-rich manganese-based oxide, the preparation process of the lithium-rich manganese-based transition metal hydroxide precursor can be controlled to optimize the primary particle size of the precursor, and the firing temperature of the mixture of such precursor and lithium raw material can be adjusted to above 600° C., or 600 to 1000° C., or 750 to 950° C. As a result, it was confirmed that one aspect of the positive electrode active material having the above-mentioned internal porosity can be prepared.

[0088] At this time, if the primary particle size of the precursor and the lithium-rich manganese oxide is too small or the firing temperature is too low, a positive electrode active material with excessive internal porosity may be prepared. On the contrary, if the primary particle size of the precursor and the lithium-rich manganese oxide is too large or the firing temperature is too high, a positive electrode active material with excessive internal porosity may be prepared.

[0089] In a more specific embodiment, in order to achieve the appropriate precursor and lithium-rich manganese oxide primary particle size and internal porosity, the lithium-rich manganese transition metal hydroxide precursor can be formed by coprecipitating each transition metal raw material such as manganese raw material, nickel raw material, cobalt raw material (and raw material of additional element M) under the conditions of pH 9.5 to 12 or pH 9.5 to 11.5. During such a coprecipitation reaction, if the pH becomes too low, the internal porosity of the positive electrode active material may become too small, and if the pH becomes too high, the internal porosity may become too large.

[0090] By controlling the above-mentioned general conditions, a positive electrode active material of one aspect including the lithium-rich manganese-based oxide represented by Chemical Formula 1 and / or Chemical Formula 2 and satisfying a predetermined internal porosity may be prepared.

[0091] On the other hand, in the preparation method of the other aspect, as the lithium raw material, for example, a lithium-containing carbonate (such as lithium carbonate), a hydrate (such as lithium hydroxide hydrate (LiOH·H 2 O) etc.), hydroxides (e.g. lithium hydroxide), nitrates (e.g. lithium nitrate (LiNO 3 ) etc.), chlorides (e.g. lithium chloride (LiCl) etc.), etc., of which one may be used alone or a mixture of two or more may be used.

[0092] In addition, as described above, the lithium-rich manganese-based transition metal hydroxide precursor of Chemical Formula 1a can be prepared by a coprecipitation process at a predetermined pH. At this time, it can be prepared by the following steps: dissolving each transition metal raw material in a solvent to prepare a metal solution, then mixing the metal solution, an ammonium cation complexing agent and an alkaline compound such as sodium hydroxide, and then performing a coprecipitation reaction. In addition, if necessary, an oxidant or oxygen can also be added during the coprecipitation reaction.

[0093] In addition, the transition metal raw material can be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal raw material can be NiO, NiCO 3 ·2Ni(OH) 2 ·4H 2 O、NiC 2 O 2 ·2H 2 O.Ni(NO 3 ) 2 6H 2 O、NiSO 4 、NiSO 4 6H 2 O、Mn 2 O 3 、MnO 2 , Mn 3 O 4 、MnCO 3 、Mn(NO 3 ) 2 、MnSO 4 ·H 2 O, manganese acetate, manganese halide, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt halide, etc.

[0094] The ammonium cation complexing agent may be selected from NH 4 OH, (NH 4 ) 2 SO 4 NH 4 NO 3 NH 4 Cl, CH 3 COONH 4 and (NH 4 ) 2 CO 3 At least one of .

[0095] The alkaline compound may be selected from NaOH, KOH and Ca(OH) 2A precursor in the form of a hydroxide can be obtained using such a basic compound, and a precursor having an appropriate primary particle size can be prepared by controlling the pH during the coprecipitation reaction.

[0096] On the other hand, after preparing a lithium-rich manganese transition metal hydroxide precursor, such a precursor can be mixed with a lithium raw material and fired. At this time, the precursor and the lithium raw material can be mixed in a certain amount so that the molar ratio of all transition metals (such as Ni, Co, Mn, etc.): Li is 1:1.05~1:2, or 1:1.1~1:1.8, or 1:1.25~1:1.8.

[0097] In addition, the firing step can be carried out in air or an oxygen atmosphere, for example, in an atmosphere containing 20% ​​to 100% by volume of oxygen. In addition, in order to effectively prepare the positive electrode active material with a predetermined internal porosity in one aspect by growing the primary particles, the firing is carried out at a temperature of 600° C. or above, or 600 to 1000° C., or 750 to 950° C. for 5 to 30 hours, 7 to 25 hours, or 9 to 20 hours.

[0098] If the firing temperature is too low or the firing time is too short, a positive electrode active material with excessive internal porosity may be prepared. On the contrary, if the firing temperature is too high or the firing time is too long, a positive electrode active material with excessive internal porosity may be prepared.

[0099] positive electrode

[0100] Next, a positive electrode including the above-mentioned positive electrode active material will be described.

[0101] The positive electrode comprises the positive electrode active material of one aspect described above. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material of one aspect. Since the positive electrode active material has been described above, its detailed description will be omitted, and only the remaining constituent elements will be described in detail below.

[0102] The positive electrode collector may contain a highly conductive metal, and the positive electrode active material layer is easy to adhere, but there is no particular limitation as long as it is non-reactive within the voltage range of the battery. As the positive electrode collector, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc., may be used. The thickness of the positive electrode collector may generally be 3 μm to 500 μm, and the positive electrode collector may have fine concave-convex shapes formed on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode collector may be used in different forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabric structures.

[0103] The positive electrode active material layer may include a positive electrode active material and optionally a conductive material and a binder as needed.

[0104] At this time, the content of the positive electrode active material may be 80 wt % to 99 wt %, more specifically 90 wt % to 98 wt %, based on the total weight of the positive electrode active material layer.

[0105] The conductive material is used to impart conductivity to the electrode, and the conductive material can be used without particular limitation as long as it has electronic conductivity and does not cause chemical changes in the battery to be configured. Specific examples thereof include graphite, such as natural graphite and artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them can be used alone or a mixture of two or more of them can be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material can be 0.01% to 10% by weight, preferably 0.1% to 9% by weight, and more preferably 0.1% to 5% by weight.

[0106] In addition, the binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the collector. Its specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers whose hydrogen is replaced by Li, Na or Ca, or various copolymers thereof, and any one of them may be used alone or a mixture of two or more thereof. Based on the gross weight of the positive electrode active material layer, the content of the binder may be 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, more preferably 1% by weight to 10% by weight.

[0107] Lithium secondary battery

[0108] Next, a lithium secondary battery according to the present invention will be described.

[0109] A lithium secondary battery includes a positive electrode, a negative electrode located opposite to the positive electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0110] Except for this, the positive electrode is the same as described above, so its detailed description will be omitted and only the remaining constituent elements will be described in detail below.

[0111] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0112] There is no particular limitation on the negative electrode collector, as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or copper or stainless steel, aluminum-cadmium alloy, etc., whose surface is treated with carbon, nickel, titanium, silver, etc., can be used. In addition, the thickness of the negative electrode collector can generally be 3 μm to 500 μm. In addition, similar to the positive electrode collector, the negative electrode collector can have fine concave-convex shapes formed on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode collector can be used in different forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabric structures.

[0113] The negative electrode active material layer contains a negative electrode active material and optionally a binder and a conductive material.

[0114] As the negative electrode active material, a compound capable of reversibly inserting and deinserting lithium can be used. Specific examples thereof may include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber or amorphous carbon; (semi)metallic materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; (semi)metallic oxides capable of doping and dedoping lithium, such as SiO β (0<β<2), SnO 2 , vanadium oxides and lithium vanadium oxides; composites containing (semi) metal materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one of them can be used alone or a mixture of two or more thereof. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon include soft carbon and hard carbon. Typical examples of high-crystalline carbon include irregular, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch carbon fibers, mesophase carbon microbeads, high-temperature heat-treated carbon such as mesophase pitch and coke derived from petroleum or coal tar pitch.

[0115] The content of the negative electrode active material may be 80 wt % to 99 wt %, 82 wt % to 99 wt %, or 84 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0116] The binder is a component that helps to bind the conductive material, the active material and the current collector, and is generally added in an amount of 0.1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber or various copolymers thereof.

[0117] The conductive material is a component that further improves the conductivity of the negative electrode active material, and the content may be 1 wt % to 30 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, for example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0118] The negative electrode active material layer can be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing the negative electrode active material and optional binder and conductive material in a solvent onto a negative electrode collector, followed by drying. Alternatively, the negative electrode active material layer can be prepared by casting the negative electrode slurry composition on a separate support, and then laminating the film peeled off from the support on the negative electrode collector.

[0119] On the other hand, in lithium secondary batteries, the separator is used to separate the negative electrode from the positive electrode and provide a mobile path for lithium ions. Any separator can be used without particular restriction, as long as it is commonly used as a separator in a lithium secondary battery. In particular, it is preferred to have a high moisture retention capacity for the electrolyte and a separator with low resistance to the movement of electrolyte ions. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure of more than two layers thereof. In addition, a typical porous nonwoven fabric can be used, such as a nonwoven fabric formed by a high melting point glass fiber, a polyethylene terephthalate fiber, etc. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used with a single layer or a multilayer structure.

[0120] In addition, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., all of which can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0121] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0122] Any organic solvent can be used without particular limitation, as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as an organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile such as R-CN (wherein R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolanes; or cyclopentane sulfone. Among these solvents, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant (e.g., ethylene carbonate or propylene carbonate) and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) which can improve the charge and discharge performance of the battery.

[0123] The lithium salt can be used without particular limitation as long as it can provide the lithium ions used in the lithium secondary battery. Specifically, the anion of the lithium salt can be selected from F - , Cl - Br - ,I - 、NO 3 - 、N(CN) 2 - , BF 4 - CF 3 CF 2 SO 3 - ,(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - CF 3 CF 2 (CF3 ) 2 CO - ,(CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - ,(CF 3 SO 2 ) 3 C - CF 3 (CF 2 ) 7 SO 3 - CF 3 CO 2 - , CH 3 CO 2 - 、SCN - ,(CF 3 CF 2 SO 2 ) 2 N - As the lithium salt, LiPF 6 、LiClO 4 、LiAsF 6 , LiBF 4 、LiSbF 6 、LiAlO 4 、LiAlCl 4 、LiCF 3 SO 3 ,LiC 4 F 9 SO 3 、LiN(C 2 F 5 SO 3 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 、LiCl、LiI、LiB(C 2 O 4 ) 2The lithium salt may be used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, more preferably 1.0 M to 2.0 M. When the concentration of the lithium salt is included within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can be efficiently moved.

[0124] In order to improve the life characteristics of the battery, inhibit the decrease in battery capacity and improve the discharge capacity of the battery, in addition to the electrolyte components, the electrolyte may also contain one or more additives, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum chloride, etc. At this time, the content of the additive may be 0.1 to 10 parts by weight based on the total weight of the electrolyte.

[0125] The lithium secondary battery including the positive electrode active material of one aspect described above stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, and can therefore be used in portable devices such as mobile phones, notebook computers and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0126] Therefore, according to another embodiment, a battery module including a lithium secondary battery as a unit cell, and a battery pack including the same are provided.

[0127] The battery module or battery pack may be used as a power source for one or more medium to large devices such as power tools, electric vehicles such as electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0128] Hereinafter, the embodiments of the present invention are described in detail so that those skilled in the art to which the present invention belongs can easily implement the embodiments. However, the present invention can be modified into other various forms, and its scope is not limited to the embodiments described herein.

[0129] Examples and Comparative Examples

[0130] Example 1

[0131] Manganese sulfate and nickel sulfate were dissolved in a molar ratio of manganese: nickel of 65:35 to obtain a mixed salt solution (metal solution) with a concentration of 2 mol / L, and sodium hydroxide (alkaline compound) was dissolved to obtain a precipitant solution. In addition, ammonia water was dissolved at a certain concentration to obtain a complexing agent solution. The precipitant solution, complexing agent solution and mixed salt solution were added to the reactor in parallel, and reacted for 20 hours at a temperature of 45°C, a pH value of 9.5 and a stirring speed of 700 rpm. The slurry was filtered and washed, and the filter cake was dried and sieved at 105°C to prepare Ni 0.35 Mn 0.65 (OH) 2 precursor.

[0132] Ni 0.35 Mn 0.65 (OH) 2 The precursor and lithium hydroxide (LiOH) were added to a Henschel mixer (700 L) so that the molar ratio of Li: transition metal (Ni + Mn) was 1.3:1, and mixed at 300 rpm for 20 minutes. The mixture was placed in an alumina crucible with a size of 330 mm × 330 mm and fired at 850°C for 10 hours in an oxygen atmosphere to prepare the positive electrode active material of Example 1. It was confirmed that the positive electrode active material of Example 1 had 0.3 {Li 2 MnO 3}∙0.7{Li[Ni 0.5 Mn 0.5 ]O 2}, and has a secondary particle shape in which a plurality of primary particles having a particle size of 50 nm to 200 nm are agglomerated, and the secondary particles have a D 50 5 μm.

[0133] Example 2

[0134] The positive electrode active material of Example 2 was prepared in the same manner as in Example 1, except that the pH during the precursor preparation was controlled to 11.5, and the firing temperature for preparing the positive electrode active material was adjusted to 750°C.

[0135] Comparative Example 1

[0136] The positive electrode active material of Comparative Example 1 was prepared in the same manner as in Example 1, except that the pH during the precursor preparation was controlled to 9, and the firing temperature for preparing the positive electrode active material was adjusted to 1050°C.

[0137] Preparation example: Preparation of positive electrode and lithium secondary battery

[0138] The positive electrode active material of the embodiment or comparative example: single-walled carbon nanotube: PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 96.0:1.0:3.0 to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum current collector sheet, dried, and rolled to prepare a positive electrode.

[0139] A negative electrode slurry was prepared by mixing graphite negative electrode active material: single-walled carbon nanotube: styrene butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 96.2:0.8:2:1. The negative electrode slurry was coated on a copper current collector sheet, dried, and rolled to prepare a negative electrode.

[0140] On the other hand, the positive electrode and the negative electrode were prepared by adjusting the loading amount so that the ratio of the discharge capacity of the negative electrode to the discharge capacity of the positive electrode (N / P ratio) was 115%.

[0141] A polyethylene separator was inserted between the positive electrode and the negative electrode prepared as above to prepare an electrode assembly. The electrode assembly was inserted into a battery case, and then an electrolyte was injected therein, charged at a constant current of 0.1 C at 45° C. until reaching 4.6 V, and discharged at a constant current of 0.1 C to 2.0 V. The activation process was performed in this way to prepare a lithium secondary battery.

[0142] Experimental Example 1: Cross-sectional observation of positive electrode active material and measurement of internal porosity

[0143] The cross section of the positive electrode obtained by using the positive electrode active material of Examples 1 and 2 or Comparative Example 1 in the preparation example was analyzed using a scanning electron microscope. The cross-sectional image data of the positive electrode active material particles were extracted from the SEM image of the cross section of the positive electrode using a digital conversion technique. As a reference, Figure 1 A photograph showing cross-sectional image data of positive electrode active material particles extracted from a cross-sectional SEM image of a positive electrode prepared using the positive electrode active material of Example 1 is shown.

[0144] In such cross-sectional image data of the positive electrode active material particles, a particle size equal to D 50 Or particle size D 50 Image data of 2500 positive electrode active material particles with a diameter of ±0.1 μm. The particle region, internal pore region, and internal crack region are divided from the image data of each particle and extracted as image data (see Figure 2 ).

[0145] The porosity was calculated by measuring the area percentage of the pore area relative to the total cross-sectional area of ​​the positive electrode active material particles from these image data. The internal porosity of the positive electrode active material of the example or comparative example was calculated from the arithmetic mean of the porosity of 2500 particles.

[0146] The internal porosity of the positive electrode active material of each example and comparative example is shown in Table 1 below.

[0147]

[0148] Experimental Example 2: Evaluation of electrochemical characteristics

[0149] The lithium secondary battery prepared with the positive electrode active material of the embodiment or comparative example was subjected to a charge and discharge test at 25°C, 0.1°C and 0.33°C in a voltage range of 4.4 V to 2.5 V. The discharge capacity was evaluated from the results of such charge and discharge tests, and the evaluation results are shown in Table 2 below. In addition, while repeating the charge and discharge test for more than 50 cycles, the capacity retention rate during 50 charge and discharge cycles was measured and evaluated. The results are shown together in Table 2 below.

[0150]

[0151] Referring to Table 2, it was confirmed that the positive electrode active materials of Examples 1 and 2 in which the internal porosity was optimized showed excellent capacity retention ratios comparable to that of Comparative Example 1, while also showing improved discharge capacity.

Claims

1. A positive electrode active material, the positive electrode active material comprising: A lithium-rich manganese-based oxide represented by the following Chemical Formula 1 and having a structure in which a rock-salt type lithium manganese oxide and a layered lithium transition metal oxide are mixed therein, wherein an internal porosity of the lithium-rich manganese-based oxide is 2.5% to 13.0%, [Chemical Formula 1] Li a [Ni b Co c Mr d M e ]O2 In Chemical Formula 1, 1.00 < a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

2. The positive electrode active material according to claim 1, wherein: In Chemical Formula 1, 1.10 ≤ a ≤ 1.5, 0.10 ≤ b ≤ 0.40, 0 ≤ c ≤ 0.05, 0.47 ≤ d ≤ 0.80, 0 ≤ e ≤ 0.

10.

3. The positive electrode active material according to claim 1, wherein: In Chemical Formula 1, 1.12 < a < 1.18, 0.24 < b < 0.36, 0 < c < 0.10, 0.47 ≤ d < 0.63, 0 < e < 0.05, and M is at least one selected from Al, Mg, V, Ti, Zr, Nb, and W.

4. The positive electrode active material according to claim 1, wherein the rock-salt type lithium manganese oxide contains Li2MnO3.

5. The positive electrode active material according to claim 1, wherein the lithium-rich manganese-based oxide is represented by the following Chemical Formula 2: [Chemical Formula 2] X Li2MnO3· (1-X)Li[Ni 1-y-z-w Mr y Co z M w ]O2 In Chemical Formula 2, 0.2 ≤ X ≤ 0.5, 0.4 ≤ y < 1, 0 ≤ z ≤ 0.1, 0 ≤ w ≤ 0.2, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

6. The positive electrode active material according to claim 1, wherein the positive electrode active material has a secondary particle shape in which a plurality of primary particles having a particle size of 50 nm to 200 nm are aggregated, and The D of the secondary particles 50 It is 2 μm to 10 μm.

7. A method for preparing the positive electrode active material according to claim 1, the method comprising the following steps: (A) Mixing a lithium-rich manganese-based transition metal hydroxide precursor with a lithium raw material; and (B) Firing the mixture at a temperature of 600 °C or higher to form a lithium-rich manganese-based oxide represented by the following Chemical Formula 1, [Chemical Formula 1] Li a [Ni b Co c Mr d M e ]O2 In Chemical Formula 1, 1.00 < a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

8. The method for preparing a positive electrode active material according to claim 7, wherein the lithium-rich manganese-based transition metal hydroxide precursor is represented by the following Chemical Formula 1a: [Chemical Formula 1a] No b What c Mn d M e (OH)2 In Chemical Formula 1a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr. 9 . The method for preparing a positive electrode active material according to claim 7 , wherein the lithium-rich manganese-based transition metal hydroxide precursor is formed by co-precipitating a transition metal raw material at a pH of 9.5 to 12. 10 . The method for preparing a positive electrode active material according to claim 7 , wherein the firing is performed at a temperature of 600° C. to 1000° C.

11. The method for preparing a positive electrode active material according to claim 7, wherein the lithium-rich manganese-based oxide is represented by the following Chemical Formula 2: [Chemical formula 2] X Li2MnO3· (1-X)Li[Ni 1-y-z-w Mr y Co z M w ]O2 In Chemical Formula 2, 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.2, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr. 12 . A positive electrode comprising the positive electrode active material according to claim 1 .

13. A lithium secondary battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, The positive electrode comprises a positive electrode active material layer, and the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 6.

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