Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

In this invention, the molar ratio of Ni to all metal elements excluding Li is 50 mol% to 75 mol%, and the doping element M 1 A single-particle lithium nickel oxide doped with, and a coating element M formed on the single-particle lithium nickel oxide. 2 AON includes a coating layer containing and defined by formula (1) c+d The ratio is 3.5 to 4.2, R as defined by formula (2) is 0.5 or less, and the coating element M 2 The doping element M relative to the weight of 1 Weight ratio (M 1 / M 2 This relates to a positive electrode active material with a coefficient of 0.2 to 1.0, and to a positive electrode and lithium secondary battery containing the same.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, and more particularly to a positive electrode active material that can operate stably at 4.35V or higher and achieve high energy density, a positive electrode containing the same, and a lithium secondary battery. [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 its unstable supply make commercial application to high-capacity batteries difficult. 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 composite transition metal 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] Conventional lithium nickel cobalt manganese oxide typically consists of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide with this secondary particle form, particle cracking, where primary particles detach during the rolling process, is likely to occur during the manufacturing of the positive electrode, and cracks can develop inside the particles during the charge-discharge process. When particle cracking or cracking occurs in the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material, which in turn reduces its lifespan.

[0005] On the other hand, in the electric vehicle sector, there has recently been a demand for cells with high energy density to extend the driving range on a single charge. Accordingly, cells using high-nickel NCM cathode active material with a nickel content of 80 mol% or more, which has excellent capacity characteristics, have recently been developed for lithium secondary batteries for electric vehicles. However, when the nickel content in the cathode active material increases, the initial capacity characteristics improve, but when charge and discharge are repeated, the highly reactive nickel... +4 A large amount of ions are generated, causing structural breakdown of the positive electrode active material. This increases the degradation rate of the positive electrode active material, reducing its lifespan and compromising battery safety. This phenomenon worsens when the drive voltage is high.

[0006] Therefore, there is a need to develop lithium-ion secondary batteries that have high energy density and excellent lifespan characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems and provides a positive electrode active material that can be driven stably at high voltage to achieve high energy density and has excellent lifespan characteristics, as well as a positive electrode and lithium secondary battery to which this material is applied. [Means for solving the problem]

[0008] [1] The present invention relates to a single-particle type lithium nickel-based oxide in which the Ni content is 50 mol% to 75 mol% and is doped with a doping element M 1 and a coating layer formed on the single-particle type lithium nickel-based oxide and containing a coating element M 2 . The present invention provides a positive electrode active material including: AON c+d defined by the following formula (1) is 3.5 to 4.2, R defined by the following formula (2) is 0.5 or less, and the weight ratio of the doping element M 2 to the coating element M 1 (M 1 / M 2 ) is 0.2 to 1.0. Formula (1): AON c+d = {Σ (oxidation number of M 1 element × mole fraction of M 1 element) + Σ (oxidation number of M 2 element × mole fraction of M 2 element)} / (sum of mole fractions of M 1 element and M 2 element) Formula (2): R = | AON d - AON c | In the above formula (2), AON d is the average oxidation number of the doping element M 1 defined by the following formula (2-1), and AON c is the average oxidation number of the coating element M 2 defined by the following formula (2-2). Formula (2-1): AON d = Σ (oxidation number of M 1 [[ID=5​​]] element × mole fraction of M 1 element) / (sum of mole fractions of M 1 element) Formula (2-2): AON c = Σ (oxidation number of M 2 element × mole fraction of M 2 element) / (sum of mole fractions of M 2 element)

[0009] [[ID=​​​​​​​70]][2] The present invention is as described in [1] above, wherein the doping element M 1The present invention provides a positive electrode active material which is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo.

[0010] [3] The present invention relates to the doping element M in the above [1] or [2]. 1 The present invention provides a positive electrode active material which consists of two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo.

[0011] [4] The present invention relates to at least one of the above [1] to [3], wherein the doping element M 1 The present invention provides a positive electrode active material containing one or more elements selected from Y, Sr, Ti, and Nb, and Zr.

[0012] [5] The present invention relates to at least one of the above [1] to [4], wherein the coating element M 2 The present invention provides a positive electrode active material which is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0013] [6] The present invention relates to at least one of the above [1] to [5], wherein the coating element M 2 The present invention provides a positive electrode active material which consists of two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0014] [7] The present invention relates to at least one of the above [1] to [6], wherein the coating element M 2 This provides a positive electrode active material containing Al and W.

[0015] [8] In at least one of the above [1] to [7], the present invention relates to the average oxidation state of the doping element represented by formula (2-1) AON. d The present invention provides a positive electrode active material with a value of 2.5 to 5.5.

[0016] [9] The present invention relates to at least one of the above [1] to [8], wherein the average oxidation state of the coating element represented by formula (2-2) is AON. c The present invention provides a positive electrode active material with a value of 2.5 to 5.5.

[0017]

[10] The present invention provides a positive electrode active material in which, in at least one of the above [1] to [9], R as defined by formula (2) is 0.01 to 0.30.

[0018]

[11] The present invention relates to at least one of the above [1] to

[10] , wherein the doping element M 1 The present invention provides a positive electrode active material that is present in an amount of 500 ppm to 10,000 ppm relative to the total weight of the positive electrode active material.

[0019]

[12] The present invention relates to at least one of the above [1] to

[11] , wherein the coating element M 2 The present invention provides a positive electrode active material that is present in an amount of 500 ppm to 10,000 ppm relative to the total weight of the positive electrode active material.

[0020]

[13] In at least one of the above [1] to

[12] , the present invention provides a positive electrode active material represented by the following [Chemical Formula 1], the single-particle lithium nickel oxide. [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2 In the above [Chemical Formula 1], M 1 It contains one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1 ≤ x ≤ 0.1, 0.5 ≤ a ≤ 0.75, 0 <b<0.5、0<c<0.5、0<d≦0.2である。

[0021]

[14] The present invention provides a positive electrode active material in which, in at least one of the above [1] to

[13] , the average particle size of the single-particle lithium nickel oxide nodules is 0.8 μm to 4 μm.

[0022]

[15] The present invention relates to at least one of the above [1] to

[14] , wherein the D of the positive electrode active material 50 We provide a positive electrode active material with a size of 3 μm to 8 μm.

[0023]

[16] The present invention provides a positive electrode comprising a positive electrode active material comprising at least one of the above [1] to

[15] .

[0024]

[17] The present invention provides a lithium secondary battery including the positive electrode according to

[16] .

[0025]

[18] The present invention provides a lithium secondary battery in which the lithium secondary battery has a charge cutoff voltage of 4.35V or higher, as described in

[17] above. [Effects of the Invention]

[0026] The positive electrode active material according to the present invention contains a single-particle type lithium nickel oxide with a small contact area with the electrolyte, thereby minimizing side reactions with the electrolyte and suppressing gas generation and reduction in lifespan due to side reactions with the electrolyte.

[0027] Furthermore, since the positive electrode active material according to the present invention uses a lithium nickel-based oxide with a nickel content of 50 mol% to 75 mol%, it has high reactivity. +4 The low ion content improves the structural stability of the positive electrode active material, preventing rapid degradation of the positive electrode active material even when driven at high voltages of 4.35V or higher.

[0028] Furthermore, as with the positive electrode active material according to the present invention, when the average oxidation state and content of the doping element and coating element are adjusted to a specific range, the stability of the crystal structure and surface structure of the positive electrode active material is improved, and rapid degradation of the positive electrode active material can be suppressed when driven at high voltages of 4.35V or higher. Therefore, when the positive electrode active material according to the present invention is applied, it is possible to stably drive at high voltages of 4.35V or higher and realize a secondary battery with excellent capacity characteristics and life characteristics. [Modes for carrying out the invention]

[0029] 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.

[0030] In this invention, "single-particle type" refers to a particle consisting of 30 or fewer nodules, and is a concept that includes single particles consisting of one nodule and pseudo-single particles which are composites of 2 to 30 nodules.

[0031] The aforementioned "nodule" is a lower particle unit that constitutes a single particle or a pseudo-single particle, and can 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.

[0032] In this invention, "secondary particle" refers to a particle formed by the aggregation of multiple primary particles, for example, several tens to several hundred primary particles. Specifically, a secondary particle may be an aggregate of 31 or more primary particles.

[0033] In this invention, "particle" is a concept that includes one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0034] In the present invention, the average particle size (D) of the nodule or primary particle mean ) refers to the arithmetic mean of these particles, calculated after measuring the particle size of nodules or primary particles observed from images taken with a scanning electron microscope or electron backscatter diffraction (EBSD) pattern analyzer. For example, the particle size of the nodules or primary particles can be measured after manufacturing an electrode using the positive electrode active material powder to be measured, obtaining a cross-section by ion milling (HITACHI IM-500, accelerating voltage 6kV) of the electrode before rolling, and then measuring it with an FE-SEM (JEOL JSM7900F) under conditions of accelerating voltage 15kV and WD15mm, on a scale of approximately 400±10 primary particles.

[0035] In this invention, "average particle size D 50 "50% of the volume of the cumulative particle size distribution of the powder being measured" refers to the particle size corresponding to 50% of the cumulative volume, and can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then measured by obtaining a volume cumulative particle size distribution graph and determining the particle size corresponding to 50% of the cumulative volume.

[0036] In this invention, the "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mini II manufactured by BEL Japan.

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

[0038] positive electrode active material The positive electrode active material according to the present invention has a Ni content of 50 mol% to 75 mol%, and contains at least one doping element M1 A single-particle lithium nickel oxide doped with, and at least one coating element M formed on the single-particle lithium nickel oxide. 2 Includes a coating layer containing the following.

[0039] In the case of lithium nickel oxides in secondary particle form, where 31 to several hundred primary particles aggregate, the contact area with the electrolyte is large, and fine particles are generated due to particle cracking during the rolling process of the positive electrode, resulting in many side reactions with the electrolyte and the generation of gas during these side reactions. In contrast, single-particle lithium nickel oxides have fewer nodules constituting the particles, resulting in fewer interfaces within the particles and a smaller contact area with the electrolyte. As a result, particle cracking is less during rolling, and compared to secondary particles, there are fewer side reactions with the electrolyte, and consequently, the amount of gas generated is significantly less. Therefore, when single-particle lithium nickel oxides are used as positive electrode active materials, superior lifetime characteristics can be obtained compared to secondary particles.

[0040] However, single-particle lithium nickel oxides have longer lithium migration paths within the particles and fewer interfaces between nodules that serve as lithium ion migration paths, compared to conventional secondary-particle lithium nickel oxide particles. This reduces lithium mobility, resulting in lower battery capacity and inferior output characteristics. Therefore, high-voltage operation is necessary to realize high-capacity batteries.

[0041] While lithium-ion secondary batteries using lithium nickel oxide can achieve relatively stable performance when the charge cutoff voltage is 4.3V or lower, it is known that when the charge cutoff voltage exceeds 4.35V, side reactions with the electrolyte worsen, transition metal ions dissolve, and battery performance deteriorates rapidly. This deterioration in performance is further exacerbated at higher temperatures.

[0042] Conventionally, to solve these problems, a method has been used in which metal oxides such as Al or boron are coated on the surface of lithium nickel oxide to reduce contact with the electrolyte. However, since the coating layer is electrically inactive, when a coating layer is formed on the surface of lithium nickel oxide, the resistance of the positive electrode active material increases, and the increase in resistance worsens as the thickness of the coating layer increases. In particular, in the case of single-particle lithium nickel oxide, the resistance tends to be high, so when a conventional coating layer is applied to the surface, the problem of output reduction due to increased resistance becomes even more serious.

[0043] The inventors of this invention have conducted extensive research to solve these problems and have found that by applying doping and coating to single-particle lithium nickel oxide with a nickel content of 50 mol% to 75 mol%, and by adjusting the average oxidation states of the doping element and coating element to satisfy the conditions of the following formulas (1) and (2), and by adjusting the ratio of the doping element content to the coating element to 0.2 to 1, the crystal structure and surface structure of the positive electrode active material can be stably maintained even under high voltages of 4.35 V or higher, thereby achieving excellent capacitance and lifetime characteristics, and thus completing the present invention.

[0044] The positive electrode active material according to the present invention has an oxidation state AON as defined by the following formula (1). c+d However, it is 3.5 to 4.2, preferably 3.5 to 4.0.

[0045] Formula (1): AON c+d ={Σ(M 1 Oxidation number of an element × M 1 (Mole fraction of the element) + Σ(M 2 Oxidation number of an element × M 2 (Mole fraction of an element) / (M 1 Elements and M 2 (The sum of the mole fractions of the elements)

[0046] M 1 Element and / or M 2When multiple elements that are different from each other are used as elements, the average oxidation number is the value obtained by multiplying the oxidation number of each element by the mole fraction of each element, summing the results, and then dividing the sum by the sum of the mole fractions of the doping element and the coating element. For example, M 1 Element a and element b are used as elements, M 2 If elements c and d are used as elements, the average oxidation number of the doping element and coating element is calculated as {(oxidation number of element a × mole fraction of element a) + (oxidation number of element b × mole fraction of element b) + (oxidation number of element c × mole fraction of element c) + (oxidation number of element d × mole fraction of element d)} / (mole fraction of element a + mole fraction of element b + mole fraction of element c + mole fraction of element d).

[0047] On the other hand, M 1 Elements and M 2 If an element has two or more oxidation states, the oxidation state is calculated using the oxidation state in which each element is in its most stable state. For example, the oxidation state of Al is 3, Mg is 2, Ti is 4, Nb is 5, Sr is 2, Zr is 4, W is 6, Y is 3, and B is 3.

[0048] On the other hand, in formula (1) above, M 1 Mole fraction of elements and M 2 The mole fraction of each element was calculated by dividing the weight ratio (in ppm) of each element in the positive electrode active material by the atomic weight of each element, i.e., weight ratio of each element (ppm) / atomic weight of each element. Here, M in the positive electrode active material 1 and M 2 The weight ratio of elements can be measured using the inductively coupled plasma (ICP) method.

[0049] According to the inventors' research, the AON c+d It was found that when a positive electrode active material satisfying the range of 3.5 to 4.2 is applied, the deterioration of the electrochemical properties of the secondary battery is minimized, and the high-voltage endurance is significantly improved. In contrast, the AON of the positive electrode active material c+dIt was found that when the value is less than 3.5 or greater than 4.2, the degradation of the positive electrode active material accelerates during high-voltage operation, leading to a decrease in capacitance and an increase in resistance.

[0050] The positive electrode active material according to the present invention has an R value defined by the following formula (2) of 0.50 or less, preferably 0.01 to 0.50, and more preferably 0.01 to 0.30.

[0051] Formula (2): R=|AON d -AON c |

[0052] In the above formula (2), AON d M is the doping element defined by the following formula (2-1). 1 This is the average oxidation number of AON. c The coating element M is defined by the following formula (2-2). 2 This is the average oxidation number of [the element].

[0053] Formula (2-1): AON d =Σ(M 1 Oxidation number of an element × M 1 (Mole fraction of an element) / (M 1 (The sum of the mole fractions of the elements)

[0054] Formula (2-2): AON c =Σ(M 2 Oxidation number of an element × M 2 (Mole fraction of an element) / (M 2 (The sum of the mole fractions of the elements)

[0055] In equations (2-1) and (2-2) above, M 1 and M 2 The oxidation states and mole fractions of the elements are as described in equation (1). That is, the oxidation state is the oxidation state at which each element is in its most stable state, and the mole fraction is the value obtained by dividing the weight ratio (unit: ppm) of each element in the positive electrode active material by the atomic weight of each element.

[0056] When R represented by the formula (2) satisfies the above range, the crystal structure and surface structure of the positive electrode active material can be stably maintained. During high-voltage driving, the deterioration of the active material is suppressed, and the resistance characteristics and high-temperature life characteristics are improved. Doping element M 1 of the average oxidation number AON d and the coating element M 2 of the average oxidation number AON c When the difference R therebetween exceeds 0.5, due to the difference in the average oxidation numbers of the doping element and the coating element, the resistance increases at the interface between the lithium nickel-based oxide and the coating layer, and during high-voltage driving, the life characteristics may deteriorate due to the collapse of the crystal structure or surface structure.

[0057] Said AON c+d , AON c and AON d are values that vary depending on the types and contents of the doping element and the coating element. During the production of the positive electrode active material, by adjusting the types and contents of the doping element and the coating element, AON c+d , AONc and AON d can be adjusted to a desired range.

[0058] The positive electrode active material according to the present invention has a weight ratio (M 2 / M 1 ) of the doping element M 1 to the coating element M 2 of 0.2 to 1.0, preferably 0.3 to 1.0, more preferably 0.5 to 1.0. When M 1 / M 2 exceeds 1.0, the capacity of the positive electrode active material decreases, and during high-voltage driving, the surface stability of the positive electrode active material decreases and the gas generation amount increases. When it is less than 0.2, the resistance of the positive electrode active material increases, and during high-voltage driving, the crystal structure collapses and the deterioration of the active material may occur rapidly.

[0059] On the other hand, the doping element M 1 can include an element having an oxidation number of 2 to 6. Specifically, the doping element M[[ID=]] 1The doping element M can be one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, preferably two or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and more preferably two or more selected from the group consisting of Ti, Mg, Al, Zr, Sr, Nb, and Y. Even more preferably, the doping element M 1 This may include one or more elements selected from Y, Sr, Ti, and Nb, and Zr. More preferably, the doping element M 1 The doping element M may include Zr and Y. 1 When Zr and Y are the same, the molar ratio of Y to Zr (Y / Zr) can be 0.1 or more and 5 or less, preferably 0.2 or more and 2 or less, and more preferably 0.3 or more and 0.8 or less.

[0060] The doping element M relative to the total weight of the positive electrode active material 1 The total content can be 500 ppm to 10,000 ppm, preferably 1,000 ppm to 10,000 ppm, and more preferably 1,500 ppm to 8,000 ppm. Doping element M 1 When the content of the doping element satisfies the aforementioned range, the capacity reduction of the positive electrode active material can be minimized and high-voltage durability can be improved. If the doping element content is too high, the amount of transition metal may decrease, potentially negatively affecting the capacity, and if it is too low, the effect of improving high-voltage durability will be reduced.

[0061] On the other hand, in the present invention, the doping element M 1 AON is the average oxidation state of the doping element defined by the following formula (2-1). d However, it is preferable that it be 2.5 or higher, 3.0 or higher, 3.3 or higher, 3.4 or higher, or 3.5 or higher, and preferably 5.5 or lower, 5.0 or lower, 4.0 or lower, or 3.9 or lower. Specifically, the AON c This can be 2.5-5.5, 3.0-5.0, 3.3-4.0, 3.4-3.9, or 3.5-3.9. Formula (2-1): AON d =Σ(M 1 Oxidation number of an element × M 1 (Mole fraction of an element) / (M 1 (The sum of the mole fractions of the elements)

[0062] In the above formula (2-1), M 1 The oxidation number and mole fraction of an element have the meanings explained in equation (1). Doping element M 1 When the average oxidation number of satisfies the above range, the stability of the crystal structure of the positive electrode active material is increased, and the effect of suppressing the degradation of the active material during high-voltage operation can be obtained.

[0063] On the other hand, the coating element M 2 This can include elements with oxidation states of 2 to 6. Specifically, the coating element M 2 It may contain one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, preferably two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and more preferably two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W. Even more preferably, the coating element M 2 It may include Al and W.

[0064] With respect to the total weight of the positive electrode active material, the coating element M 2 The total content can be 500 to 10,000 ppm, preferably 1,000 to 10,000 ppm, and more preferably 1,500 to 8,000 ppm. Coating element M 2 When the content of the coating element satisfies the aforementioned range, the increase in resistance is minimized, and an improvement in high-voltage durability can be obtained. If the content of the coating element is too high, the insertion / deinsertion of lithium ions may be suppressed, which may increase resistance, and if it is too low, the effect of suppressing transition metal elution will decrease when driven at high voltage.

[0065] On the other hand, in the present invention, the coating element is defined by the average oxidation state of the coating element AON as shown in formula (2-2) below. c However, it is preferable that it be 2.5 or higher, 3.0 or higher, 3.3 or higher, 3.4 or higher, or 3.5 or higher, and preferably 5.5 or lower, 5.0 or lower, 4.0 or lower, or 3.9 or lower. Specifically, the AON c This can be 2.5-5.5, 3.0-5.0, 3.3-4.0, or 3.4-3.9.

[0066] Formula (2-2): AON c =Σ(M 2 Oxidation number of an element × M 2 (Mole fraction of an element) / (M 2 (The sum of the mole fractions of the elements)

[0067] In the above formula (2-2), M 2 The oxidation number and mole fraction of the elements have the same meaning as explained in equation (1). Coating element M 2 When the average oxidation number of satisfies the above range, the surface structure stability of the positive electrode active material is improved, contact between electrolytes is suppressed, and the effect of suppressing degradation of the active material during high-voltage driving can be obtained.

[0068] The positive electrode active material according to the present invention has a Ni content of 50 mol% to 75 mol%, preferably 50 mol% to 70 mol%, and doping element M 1 Contains single-particle lithium nickel oxide doped with M. 1 This is as stated above.

[0069] As described above, when a single-particle lithium nickel oxide with a relatively low nickel content is used as the positive electrode active material, side reactions with the electrolyte are suppressed under high voltage conditions, reducing gas generation and enabling the realization of excellent lifespan characteristics.

[0070] In the case of single-particle lithium nickel oxides with a relatively low nickel content, the structural stability at high voltages is higher compared to lithium nickel oxides with a high nickel content or those with a secondary particle form, thus minimizing the degradation of life characteristics when driven at high voltages. Specifically, the higher the nickel content in the lithium nickel oxide, the more reactive the nickel... +4 The increased ion content reduces the structural stability of the positive electrode active material during charging and discharging, leading to rapid degradation of the positive electrode. This phenomenon worsens under high-voltage operation. Therefore, in this invention, by using a lithium nickel-based oxide with a low Ni content of 75 mol% or less, it is possible to suppress the reduction in lifespan due to degradation of the active material under high-voltage operation. However, if the Ni content is too low, the capacity characteristics will deteriorate, so the Ni content of the lithium nickel-based oxide is preferably around 50 mol% to 75 mol%.

[0071] Specifically, the single-particle lithium nickel oxide can be a lithium transition metal oxide containing nickel, manganese, and cobalt, and can be represented, for example, by the following [Chemical Formula 1].

[0072] [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0073] In the above [Chemical Formula 1], M 1 It may contain one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. 1 When elements are included, the structural stability of lithium nickel oxide particles is improved, and excellent life characteristics can be achieved when driven at high voltage. Preferably, the M 1The elements may include one or more selected from the group consisting of Ti, Mg, Al, Zr, and Y, and more preferably two or more selected from the group consisting of Ti, Mg, Al, Zr, and Y.

[0074] The aforementioned 1+x represents the lithium molar ratio within the lithium nickel oxide and can be -0.1 ≤ x ≤ 0.1, 0 ≤ x ≤ 0.1, or 0 ≤ x ≤ 0.07. When 1+x satisfies the above range, a stable layered crystal structure can be formed.

[0075] The value 'a' represents the molar ratio of nickel to the total metals other than lithium in the lithium nickel oxide, and can be 0.5 ≤ a ≤ 0.75, 0.55 ≤ a ≤ 0.75, or 0.55 ≤ a ≤ 0.70. When 'a' satisfies the above range, stable operation at high voltage and high capacity can be achieved.

[0076] The above b represents the molar ratio of cobalt among the total metals other than lithium in the lithium nickel oxide, and 0 <b<0.5、0.05≦b≦0.25または0.1≦b≦0.30であることができる。

[0077] The aforementioned c represents the molar ratio of manganese among the total metals other than lithium in the lithium nickel oxide, and 0 <c<0.5、0.05≦c≦0.25または0.1≦c≦0.30であることができる。

[0078] The above d is M, which is the total metal other than lithium in the lithium nickel oxide. 1 This indicates the molar ratio of elements, where 0 ≤ d ≤ 0.2, 0 ≤ d ≤ 0.1, or 0 <d≦0.1であることができる。M 1 When the molar ratio of the elements satisfies the aforementioned range, both the structural stability and capacity of the positive electrode active material can be improved.

[0079] On the other hand, the single-particle lithium nickel oxide preferably contains 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15. This is because if the number of nodules constituting the lithium nickel oxide exceeds 30, particle cracking increases during electrode manufacturing, and the occurrence of internal cracks due to the expansion / contraction of nodule volume increases during charging and discharging, which can reduce the improvement effect on high-temperature lifetime characteristics and high-temperature storage characteristics.

[0080] On the other hand, the nodules can have an average particle size of 0.8 μm to 4.0 μm, preferably 0.8 μm to 3 μm, and more preferably 1.0 μm to 3.0 μm. When the average particle size of the nodules satisfies the above range, particle cracking can be minimized during electrode manufacturing, and the increase in resistance can be suppressed more effectively. Here, the average particle size of the nodules refers to the value obtained by measuring the particle size of each nodule observed in the SEM image obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0081] The positive electrode active material according to the present invention is formed on the single-particle lithium nickel-based oxide, and is coated with the element M 2 Includes a coating layer containing [a specific component].

[0082] Preferably, the coating layer is Li-M 2 -O solid solution may be included. 2 As stated above, the coating element M 2 It may contain one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo, and may contain two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W. More preferably, the coating element M 2 This may include Al and W. When these elements are included, side reactions with the electrolyte on the surface of the positive electrode active material particles can be effectively suppressed.

[0083] Coating element M2 two types of elements (for convenience, M 2a M 2b If it includes the above M 2a The average oxidation value is 2 to 3, and the above M 2b The average oxidation value can be 4 to 6. 2b M for 2a Mole ratio (M 2a / M 2b ) can be 1 or more and 10 or less, preferably 2 or more and 6 or less, more preferably 2.5 or more and 4 or less.

[0084] The aforementioned Li-M 2 When the -O solid solution is Li-Al-WO, the molar ratio of Al to W (Al / W) can be 1 or more and 10 or less, preferably 2 or more and 6 or less, and more preferably 2.5 or more and 4 or less. When this range is met, HF products due to side reactions of lithium salts in the electrolyte can be effectively suppressed, and the capacity characteristics and resistance characteristics of the battery can be improved.

[0085] On the other hand, the positive electrode active material is D 50 The particle size can be 3.0 μm to 8.0 μm, preferably 3.0 μm to 7.5 μm. More preferably, it is about 3.5 μm to 7.5 μm. D of lithium nickel oxide 50 If it is too small, the processability during electrode manufacturing will decrease, the impregnation of the electrolyte will decrease, and the electrochemical properties may be increased or decreased. 50 If the value is too large, the resistance increases, leading to a problem of reduced output characteristics.

[0086] Furthermore, the positive electrode active material is D 50 The degree of single particle formation, which is the ratio of the average particle size of the nodules to the total particle size, can be 0.1-1, 0.2-0.8, 0.3-0.9, or 0.4-0.8. When the degree of single particle formation of the positive electrode active material satisfies the above range, the lifetime characteristics and gas generation suppression effect are further improved at high temperatures and / or high voltages.

[0087] The positive electrode active material according to the present invention has a BET specific surface area of ​​0.3 m². 2 / g~1.5m2 / g, preferably 0.4m 2 / g~1.3m 2 / g, more preferably 0.5m 2 / g~1.0m 2 It can be / g. When the BET specific surface area of ​​the positive electrode active material satisfies the above range, it has better capacity characteristics and lifetime characteristics. If the BET specific surface area is too small, there is insufficient reaction area with the electrolyte, making it difficult to achieve sufficient capacity. If it is too large, the adhesive strength may be low during electrode manufacturing, or side reactions with the electrolyte may be accelerated during electrode operation, making it difficult to ensure lifetime characteristics.

[0088] Method for manufacturing positive electrode active material Next, a method for producing a positive electrode active material according to the present invention will be described.

[0089] The method for producing a positive electrode active material according to the present invention comprises (1) a transition metal precursor, a lithium raw material, and M 1 (1) Mixing doping raw materials containing elements and firing to produce single-particle lithium nickel oxide, and (2) the single-particle lithium nickel oxide and M 2 The process includes the steps of mixing a coating raw material containing an element and heat-treating it to form a coating layer on the surface of the single-particle lithium nickel oxide.

[0090] Here, the doping raw material and the coating raw material satisfy formulas (1) and (2), and the coating element M 2 Doping element M 1 Weight ratio (M 1 / M 2 The amount added is such that the ratio becomes 0.2 to 1.0.

[0091] First, a transition metal precursor in which nickel content is 50 mol% to 75 mol% of the total metals other than lithium, a lithium raw material, and a doping element M 1 Doping material substances containing (where M 1This involves mixing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Zr, Sr, W, Ta, Nb, and Mo, and then calcining the mixture to produce a single-particle lithium nickel oxide containing 30 or fewer nodules.

[0092] The transition metal precursor can be a cathode active material precursor commonly used in the art. For example, the transition metal precursor can be purchased and used as a commercially available precursor such as nickel-cobalt-manganese hydroxide or nickel-cobalt-manganese oxide, or it can be manufactured and used by a precursor manufacturing method well known in the art, such as coprecipitation or spray pyrolysis.

[0093] The lithium raw material can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and one or more of these can be used as a mixture.

[0094] As the doping raw material, oxides, hydroxides, sulfides, oxyhydroxides, halides, or mixtures thereof containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Zr, Sr, W, Ta, Nb, and Mo can be used.

[0095] The mixing of the transition metal precursor, lithium raw material, and doping raw material can be carried out by solid-phase mixing or liquid-phase mixing. When the components are mixed by solid-phase mixing, the calcination process can be performed without a separate drying process. When the components are mixed by liquid-phase mixing, the mixed components are spray-dried before the calcination process.

[0096] Next, the mixture can be subjected to a calcination treatment. The calcination may be carried out in an air or oxygen atmosphere. The calcination is carried out at a temperature and time suitable for the formation of lithium nickel oxide into single-particle form. The calcination temperature may vary depending on the Ni content and may be, for example, 700°C to 1000°C, 750°C to 1000°C, or 850°C to 980°C, but is not limited thereto.

[0097] The firing time can be, for example, 10 to 30 hours, 15 to 30 hours, or 20 to 28 hours, but is not limited to these.

[0098] Next, the lithium nickel-based oxide is coated with element M. 2 The material is mixed with a coating raw material containing the above, and then heat-treated to form a coating layer on the surface of the lithium composite transition metal oxide particles.

[0099] The formation of the coating layer can be carried out using methods well known in the art, such as wet coating, dry coating, plasma coating, or ALD (Atomic Layer Deposition).

[0100] The aforementioned wet coating method can be carried out, for example, by adding a suitable solvent such as ethanol, water, methanol, or acetone to a lithium nickel oxide and a coating raw material, and then mixing until the solvent is gone.

[0101] The aforementioned dry coating method is a method of mixing lithium nickel oxide and coating raw material in a solid phase without a solvent, and for example, grinder mixing or mechanofusion can be used.

[0102] The coating raw material may be an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, carboxylate, or combination thereof, containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Zr, Sr, W, Ta, Nb, and Mo.

[0103] The aforementioned heat treatment temperature is M 2 The temperature can be adjusted as appropriate depending on the type of element; for example, heat treatment can be performed at temperatures of 200°C to 900°C, 250°C to 800°C, or 300°C to 700°C, but is not limited thereto. The heat treatment can be performed for 2 to 25 hours, 5 to 20 hours, or 8 to 18 hours, but is not limited thereto.

[0104] positive electrode Next, the positive electrode of the present invention will be described.

[0105] The positive electrode according to the present invention includes the positive electrode active material according to the present invention as described above, and may further include a positive electrode conductive material and a positive electrode binder as needed. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive material and a positive electrode binder. On the other hand, the positive electrode active material is as described above, and a detailed explanation is omitted.

[0106] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0107] On the other hand, the positive electrode active material can be included in an amount of 93% to 99% by weight, preferably 95% to 98% by weight, and more preferably 95% to 97% by weight, of the total weight of the positive electrode active material layer, i.e., the sum of the positive electrode active material, positive electrode conductive material, and positive electrode binder. When the content of the positive electrode active material satisfies the above range, a high energy density can be achieved.

[0108] Next, the positive electrode conductive material is used to impart conductivity to the positive electrode and can be used without particular limitations in a battery that does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used individually or in mixtures of two or more.

[0109] The positive electrode conductive material can be included in an amount of 0.1% to 10% by weight, preferably 0.5% to 8% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the positive electrode active material layer.

[0110] Next, the positive electrode 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 positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used.

[0111] The positive electrode binder may be present in an amount of 0.5% to 5% by weight, preferably 1% to 4% by weight, and more preferably 1% to 3% by weight, relative to the total weight of the positive electrode active material layer.

[0112] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent to produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it; or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0113] On the other hand, the solvent for the positive electrode slurry can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, used individually or in combination of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0114] negative electrode The lithium secondary battery according to the present invention includes a negative electrode comprising a negative electrode active material, a negative electrode conductive material, and a negative electrode binder. Specifically, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0115] 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, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0116] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these mixtures can be used.

[0117] On the other hand, both low-crystalline carbon and high-crystalline carbon can be used as carbonaceous materials. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0118] Preferably, the negative electrode active material may consist of a carbon-based negative electrode active material, which may include, for example, natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, or a combination thereof. More preferably, the carbon-based negative electrode active material may include natural graphite and artificial graphite.

[0119] The carbon-based negative electrode active material has an average particle size D 50 However, the particle size can be 2 μm to 30 μm, preferably 5 μm to 30 μm.

[0120] The negative electrode active material can be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, relative to the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, an excellent energy density can be achieved.

[0121] Next, the negative electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes and has electronic conductivity in the battery it is used in. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used.

[0122] The negative electrode conductive material can typically be included in an amount of 0.1% to 10% by weight, preferably 0.5% to 8% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the negative electrode active material layer.

[0123] The negative electrode binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used.

[0124] The negative electrode binder may be present in an amount of 1% to 10% by weight, preferably 1% to 8% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the negative electrode active material layer.

[0125] On the other hand, in the lithium secondary battery according to the present invention, the negative electrode active material layer may be a single-layer structure or a multilayer structure of two or more layers. For example, the negative electrode may include a first negative electrode active material layer formed on at least one surface of the negative electrode current collector and containing a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material. Here, the first negative electrode active material and the second negative electrode active material may consist of carbon-based negative electrode active materials, such as natural graphite, artificial graphite, or a combination thereof.

[0126] On the other hand, in the case of a multilayer structure in which the negative electrode active material layer consists of two or more layers, the type and / or content of the negative electrode active material, binder, and / or conductive material in each layer can differ from one another.

[0127] For example, the weight ratio of natural graphite to the total weight of negative electrode active material in the first negative electrode active material layer (lower layer) can be made higher than the weight ratio of natural graphite to the total weight of negative electrode active material in the second negative electrode active material layer (upper layer), and the weight ratio of artificial graphite to the total weight of negative electrode active material in the second negative electrode active material layer can be made higher than the weight ratio of artificial graphite to the total weight of negative electrode active material in the first negative electrode active material layer.

[0128] Alternatively, the weight ratio of the conductive material to the total weight of the second negative electrode active material layer (upper layer) can be made higher than the weight ratio of the conductive material to the total weight of the first negative electrode active material layer (upper layer).

[0129] In this way, by forming the negative electrode active material layer in a multilayer structure and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and output characteristics, can be further improved.

[0130] The negative electrode can be manufactured by a conventional negative electrode manufacturing method. For example, the negative electrode can be manufactured by mixing a negative electrode active material, a negative electrode binder, and / or a negative electrode conductive material in a solvent to produce a negative electrode slurry, applying the negative electrode slurry onto a negative electrode current collector, and then drying and rolling it; or by casting the negative electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto a negative electrode current collector.

[0131] On the other hand, the solvent for the negative electrode slurry can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, used individually or in combination of two or more. The amount of solvent used should be sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0132] electrolyte The electrolyte may include an organic solvent and a lithium salt.

[0133] The aforementioned 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 aforementioned 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), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which 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.

[0134] The lithium salt can be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, 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 in the range of 0.1M to 3.0M, more preferably 0.1M to 2.0M, and more preferably 0.5M to 1.5M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0135] In addition to the electrolyte components, the electrolyte may further contain additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. For example, the additives may include various additives used in the art, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bisoxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorobisoxalate phosphate (LiDFBP), and lithium tetrafluorooxalate phosphate (LiTF OP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propanesultone (PS), propensultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonite (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyldi(pro-2-i-1-nyl)phosphate (EDP), 5-methyl-5-propargyloxylcarbonyl-1,3-dioxan-2-one (MPOD), etc., can be used alone or in combination, but are not limited thereto. The additives may be present in an amount of 0.1% to 10% by weight, preferably 0.1% to 5% by weight, relative to the total weight of the electrolyte.

[0136] Separator The lithium secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode, if necessary. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator that is normally used in lithium secondary batteries, and is particularly preferred if it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as 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 nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0137] On the other hand, the lithium secondary battery preferably has a charge cutoff voltage of 4.35V or higher, preferably 4.35V to 5V, and more preferably 4.35V to 4.5V. When the charge cutoff voltage satisfies the above range, a high energy density can be achieved. The energy density of a lithium secondary battery is affected not only by the capacity of the active material used but also by the drive voltage range. In particular, when lithium nickel cobalt manganese oxide is used as the positive electrode active material, a higher drive voltage can be achieved. However, when the drive voltage is high, side reactions with the electrolyte increase during charging and discharging, and the structural collapse of the positive electrode active material occurs rapidly, leading to a problem of rapid deterioration of the life characteristics. This problem is even more pronounced in high-nickel lithium nickel cobalt manganese oxide with a high nickel content. For this reason, conventionally, when lithium nickel cobalt manganese oxide is used as the positive electrode active material, it has been common to use it with a drive voltage of 2.0V to 4.3V. However, in this invention, by applying a positive electrode active material that is doped and coated with a single-particle lithium nickel-based oxide having a Ni content of 50 to 75 mol% or less to satisfy specific conditions, it is possible to maintain excellent life characteristics even when driven at a high voltage with a charge cutoff voltage of 4.35V or higher.

[0138] The lithium secondary battery according to the present invention can be usefully applied in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs). Because the lithium secondary battery according to the present invention can be driven at high voltage, achieve high energy density, and exhibit excellent safety in the event of thermal runaway, it can be particularly useful in the field of electric vehicles.

[0139] According to another embodiment of the present invention, a battery module and a battery pack including the lithium secondary battery according to the present invention as a unit cell are provided.

[0140] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0141] 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 a variety of different forms and is not limited to the embodiments described herein.

[0142] Example 1 Transition metal hydroxide Ni 0.6 Co 0.1 Mn 0.3 (OH)2, Li2CO3 as a lithium-containing raw material, and ZrO2 and Y2O3 as doping raw materials were mixed in amounts such that the Zr and Y content was 2800 ppm and 1400 ppm, respectively.

[0143] The mixture was calcined at 940°C for 20 hours, then the calcined product was mixed with ultrapure water in a 1:1 weight ratio and washed for 20 minutes, followed by filtration using a vacuum filter. After filtration, the mixture was dried at 130°C under vacuum conditions to produce single-particle lithium nickel oxide doped with Zr and Y.

[0144] The aforementioned single-particle lithium nickel oxide was mixed with Al2O3 and WO3 as coating raw materials in amounts that resulted in Al and W content of 1400 ppm and 2900 ppm, respectively. Next, the mixture was heat-treated at 400°C for 15 hours to form a coating layer on the positive electrode active material (D 50 We manufactured a sample (3.8 μm).

[0145] As described above, the manufactured positive electrode active material, positive electrode conductive material, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95:2:3 to produce a positive electrode slurry. Here, carbon nanotubes were used as the positive electrode conductive material.

[0146] The positive electrode slurry was applied to an aluminum current collector sheet, dried, and then rolled to produce the positive electrode.

[0147] An electrode assembly was manufactured by interposing a separator between the positive electrode and the lithium metal negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte was injected to manufacture a lithium secondary battery cell.

[0148] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that during the production of the positive electrode active material, Al2O3 and WO3 were mixed as coating raw materials in amounts that resulted in Al and W content of 1800 ppm and 3800 ppm, respectively.

[0149] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that, during the production of the positive electrode active material, ZrO2 and SrO were used as doping materials instead of ZrO2 and Y2O3, in amounts that resulted in Zr and Sr content of 3500 ppm and 800 ppm, respectively.

[0150] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that during the production of the positive electrode active material, ZrO2 and Y2O3 were mixed as doping raw materials in amounts that resulted in Zr and Y content of 1200 ppm and 1400 ppm, respectively, and Al2O3 and WO3 were mixed as coating raw materials in amounts that resulted in Al and W content of 1500 ppm and 1000 ppm, respectively.

[0151] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that ZrO2 and Y2O3 were mixed as doping raw materials in amounts that resulted in Zr and Y content of 1200 ppm and 500 ppm, respectively, during the production of the positive electrode active material, and Al2O3 and WO3 were mixed as coating raw materials in amounts that resulted in Al and W content of 500 ppm and 4200 ppm, respectively.

[0152] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that, during the production of the positive electrode active material, ZrO2 and MgO were mixed in amounts such that the Zr and Mg contents were 1500 ppm and 1500 ppm, respectively, instead of ZrO2 and Y2O3 as doping raw materials, and Al2O3 and H3BO3 were mixed in amounts such that the Al and B contents were 1500 ppm and 500 ppm, respectively, instead of Al2O3 and WO3 as coating raw materials.

[0153] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that, during the production of the positive electrode active material, ZrO2 and Nb2O3 were mixed as doping raw materials in amounts such that the Zr and Nb content was 1500 ppm and 1200 ppm, respectively, and Al2O3 and WO3 were mixed as coating raw materials in amounts such that the Al and W content was 500 ppm and 3000 ppm, respectively.

[0154] Comparative Example 5 During the production of lithium nickel oxides, Ni is used as a transition metal hydroxide. 0.6 Co 0.1 Mn 0.3 Ni instead of (OH)2 0.86 Co 0.08 Mn 0.06 A lithium secondary battery was manufactured in the same manner as in Example 1, except that (OH)2 was used and single-particle lithium nickel oxide was produced by firing at 890°C for 20 hours.

[0155] Comparative Example 6 A lithium secondary battery was manufactured using the same method as in Example 1, except that during the production of the lithium nickel oxide, a calcination process was performed at 820°C for 20 hours to produce secondary particle type lithium nickel oxide.

[0156] Using formulas (1) to (3), the average oxidation state of the doping elements AON of Examples 1 to 3 and Comparative Examples 1 to 6 was determined. d , Coating element average oxidation state AON c and the average oxidation state of the doping and coating elements AON c+d The calculation was performed, and the results are shown in Table 1 below.

[0157] [Table 1]

[0158] Experimental Example 1 Each lithium secondary battery manufactured in Examples 1-5 and Comparative Examples 1-12 was charged to 4.35V at 45°C with a rate of 0.5C, and then discharged to 2.5V at a rate of 1.0C. This constituted one charge-discharge cycle. After 50 charge-discharge cycles, the capacity retention rate and resistance increase rate were measured. The measurement results are shown in Table 2 below.

[0159] [Table 2]

[0160] Referring to Table 2 above, it can be confirmed that the secondary batteries of Examples 1 to 5 have superior lifespan characteristics compared to the secondary batteries of Comparative Examples 1 to 12.

Claims

1. The Ni content is 50 mol% to 75 mol%, and the doping element M １ Single-particle lithium nickel oxide doped with, Formed on the aforementioned single-particle lithium nickel oxide, coating element M ２ A coating layer including, AON is defined by the following formula (1) ｃ＋ｄ The range is 3.5 to 4.

2. R, defined by the following formula (2), is 0.5 or less. The aforementioned coating element M ２ The doping element M relative to the weight of １ Weight ratio (M １ / M ２ ) is between 0.2 and 1.0, Formula (1): AON ｃ＋ｄ = {Σ (M １ oxidation number of element × M １ mole fraction of element) + Σ (M ２ oxidation number of element × M ２ mole fraction of element)} / (M １ element and M ２ sum of mole fractions of elements) Equation (2): R = |AON ｄ - AON ｃ | In the above formula (2), AON ｄ M is the doping element defined by the following formula (2-1). １ This is the average oxidation number of AON. ｃ The coating element M is defined by the following formula (2-2). ２ This is the average oxidation number of, Formula (2-1): AON ｄ =Σ(M) １ Oxidation number of an element × M １ (Mole fraction of an element) / (M １ (The sum of the mole fractions of the elements) Formula (2-2): AON ｃ =Σ(M) ２ Oxidation number of an element × M ２ (Mole fraction of an element) / (M ２ (The sum of the mole fractions of the elements) This is the positive electrode active material.

2. The doping element M １ The positive electrode active material according to claim 1, wherein the positive electrode active material is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo.

3. The doping element M １ The positive electrode active material according to claim 1, wherein the positive electrode active material is two or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo.

4. The doping element M １ The positive electrode active material according to claim 1, wherein it comprises one or more elements selected from Y, Sr, Ti, and Nb, and Zr.

5. The aforementioned coating element M ２ The positive electrode active material according to claim 1, wherein the positive electrode active material is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

6. The aforementioned coating element M ２ The positive electrode active material according to claim 1, wherein the positive electrode active material is two or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

7. The aforementioned coating element M ２ The positive electrode active material according to claim 1, comprising Al and W.

8. The average oxidation state of the doping element represented by formula (2-1) is AON. ｄ The positive electrode active material according to claim 1, wherein the ratio is 2.5 to 5.

5.

9. The average oxidation state of the coating element represented by the above formula (2-2) is AON. ｃ The positive electrode active material according to claim 1, wherein the ratio is 2.5 to 5.

5.

10. The positive electrode active material according to claim 1, wherein R, as defined by formula (2), is 0.01 to 0.

30.

11. The doping element M １ The positive electrode active material according to claim 1, wherein it is contained in an amount of 500 ppm to 10,000 ppm relative to the total weight of the positive electrode active material.

12. The aforementioned coating element M ２ The positive electrode active material according to claim 1, wherein it is contained in an amount of 500 ppm to 10,000 ppm relative to the total weight of the positive electrode active material.

13. The aforementioned single-particle lithium nickel oxide is represented by the following [Chemical Formula 1], [Chemical formula 1] Li １＋ｘ [Ni ａ Co ｂ Mn ｃ M １ ｄ ]O ２ In the above [Chemical Formula 1], M １ The positive electrode active material according to claim 1, wherein the element comprises one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and satisfies -0.1 ≤ x ≤ 0.1, 0.5 ≤ a ≤ 0.75, 0 < b < 0.5, 0 < c < 0.5, and 0 < d ≤ 0.

2.

14. The positive electrode active material according to claim 1, wherein the average particle size of the nodules of the single-particle lithium nickel oxide is 0.8 μm to 4 μm.

15. The D of the positive electrode active material ５０ The positive electrode active material according to claim 1, wherein the diameter is 3 μm to 8 μm.

16. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 15.

17. A lithium secondary battery comprising the positive electrode described in claim 16.

18. The lithium secondary battery according to claim 17, wherein the lithium secondary battery has a charge cutoff voltage of 4.35V or higher.

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