High-strength lithium-ion secondary battery positive electrode active material and lithium-ion secondary battery using said positive electrode active material

Abstract

To obtain an excellent lithium ion secondary battery that has improved safety in addition to improved discharge capacity and durability, the present invention provides a positive electrode active material composed of a lithium nickel manganese cobalt aluminum composite oxide in which the mean particle size of primary particles and the mean particle size of secondary particles are controlled within optimum ranges while maintaining high particle strength and the sulfate concentration is suppressed. The present invention provides a positive electrode active material for a lithium ion secondary battery, which is used in the positive electrode of a lithium ion secondary battery and has an expansion amount of 104% or less, and which is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α (However, 0.95

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material for a high-strength lithium ion secondary battery, and a lithium ion secondary battery using the positive electrode active material. [Background technology]

[0002] In recent years, with the spread of portable electronic devices such as smartphones, tablets, and mini notebook computers, as well as hybrid and electric vehicles, there has been a rapid expansion in the need for development of small, lightweight lithium-ion secondary batteries with high energy density, as well as medium- and large-sized, high-output lithium-ion secondary batteries. These lithium ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, an electrolyte, etc., and the active materials used for the positive and negative electrodes are materials that can extract and insert lithium ions. Currently, research and development of lithium ion secondary batteries is being actively conducted, and among these, lithium ion secondary batteries that use layered or spinel type lithium metal composite oxides as the positive electrode material can obtain a high voltage of about 4V, and are being put into practical use as batteries with high energy density.

[0003] The main cathode materials proposed so far include lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium nickel manganese cobalt composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) and lithium manganese composite oxide (LiMn2O4) that uses manganese. Among these, lithium nickel manganese cobalt composite oxide (hereinafter, a lithium metal composite oxide mainly composed of lithium, nickel, manganese, and cobalt is also referred to as "NMC") has attracted attention as a material with good battery cycle characteristics, low resistance, and high output. As described above, it is also suitable for power sources for hybrid vehicles and electric vehicles that are subject to certain restrictions in the mounting space, and is regarded as important as an in-vehicle power source. For example, Patent Document 1 describes the properties of NMC, such as having a crystal structure of the α-NaFeO2 type, and Patent Document 2 describes that NMC in which sulfate radicals present in the form of lithium sodium sulfate (LiNaSO4) are washed with water and the concentration thereof is less than 0.1% is preferable. In Patent Document 3, when measured by the BET method, the specific surface area is 0.1 to 3 m 2 / g, the agglomerate size is larger than 6 μm as determined from the D50 value by the laser diffraction / scattering method, the diameter is 100 μm or less as determined from the D90 value, and the internal pores have a size of 0.3 μm < Dintra (internal pore diameter) < D50 value / 4 μm, and NMC having an internal pore volume of at least 0.08 ml / g is described as preferable. In addition, Patent Document 4 describes a method for producing NMC in which at least a part has a single crystal structure by subjecting lithium ions and other metal ions to a hydrothermal reaction in water in a supercritical or subcritical state, and Patent Document 5 describes a method for obtaining NMC with high capacity and high durability by performing firing for a long time of up to 50 hours. Furthermore, Patent Document 6 describes NMC composed of particles with a minimum crushing strength of more than 70 MPa when NMC is crushed for the purpose of improving the initial charge-discharge efficiency and cycle characteristics, and Patent Document 7 describes a production method in which a nickel manganese cobalt composite hydroxide (hereinafter, a metal composite hydroxide mainly composed of nickel, manganese, and cobalt is also referred to as "NMC precursor") is coprecipitated while continuously feeding a raw material solution into a reaction tank at 40 to 90°C and maintaining the pH at 9 to 11, and the NMC precursor is subjected to oxidative roasting at a temperature of 300 to 700°C, and NMC is obtained through a water washing and drying process.

Prior Art Documents

[0004] [Patent Document 1] Patent Publication No. 2003-007298 [Patent Document 2] Patent Publication No. 13-273898 [Patent Document 3] Patent Publication No. 2003-505326 [Patent Document 4] Patent Publication No. 13-163700 [Patent Document 5] Patent Publication No. 2007-179917 [Patent Document 6] Patent Publication No. 2013-232318 [Patent Document 7] Patent Publication No. 2008-251191 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, it is known that in order to use a high-energy-density positive electrode active material and a high-density electrode to increase the capacity of a battery, the packing density of the positive electrode active material in the electrode is increased. However, when increasing the packing density, high pressure is applied to the positive electrode active material, and if the particle strength is weak, cracks will occur in the secondary particles and the electrical conductivity will decrease. In addition, the positive electrode active material expands and contracts repeatedly due to charging and discharging, and some of it expands due to irreversible reactions. For this reason, if the particle strength is weak, the secondary particles will break and the electrical conductivity will decrease, and the positive plate itself will expand, resulting in a decrease in battery performance. In addition, in the positive electrode coating process, high pressure is applied to the positive electrode active material, so if the particle strength is weak, the secondary particles will collapse, and the collapsed particles will adhere to the roll during roll pressing, resulting in a decrease in yield. Furthermore, even for collapsed particles that do not adhere to the roll, the lithium conductivity between the primary particles will be interrupted, leading to a deterioration in battery performance. As described above, the particle strength of the positive electrode active material is a very important factor in improving battery performance, such as increasing the capacity and durability of the battery, and in preventing a decrease in the yield rate. In contrast, the NMC described in Patent Documents 1 to 3 does not mention particle strength at all, and the capacity and durability are insufficient. Both of the manufacturing methods of NMC described in Patent Documents 4 and 5 require a large amount of energy and are not industrially preferable. In Patent Document 6, according to the examples shown, the crushing strength of the produced particles is about 75 to 85 MPa, and the particle strength is still low, so the effects of the initial charge / discharge efficiency and cycle characteristics are not sufficient. Furthermore, in Patent Document 7, the pH control value disclosed increases the amount of sulfate remaining in the NMC, and the battery performance decreases. Moreover, although the particle strength of NMC is improved by heat treating the NMC precursor, no attention is paid to this effect at all. In addition, the NMC precursor after oxidative roasting is washed with water, and while impurities such as sulfate are reduced, the impurities present at the grain boundaries are washed away, weakening the bond between the primary particles, which leads to a decrease in the particle strength of the secondary particles and worsening the battery performance. As described above, the NMCs described in Patent Documents 1 to 7 cannot be said to be positive electrode active materials that meet the needs of environmentally friendly automobiles, and positive electrode active materials with higher capacity and higher durability are required. In view of the above problems, an object of the present invention is to provide a lithium nickel manganese cobalt aluminum composite oxide and a method for producing the same, in which the average particle size of primary particles and the average particle size of secondary particles are controlled within optimal ranges while maintaining high particle strength, in order to obtain an excellent lithium ion secondary battery having improved safety in addition to improved discharge capacity and durability. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors conducted intensive research. As a result, in order to prevent the disintegration of NMC particles, which is a cause of capacity deterioration during cycling, and to obtain high durability, in the crystallization step, in addition to nickel, manganese, and cobalt, which are the main components of NMC, aluminum is added as an essential element, and element M is added as an optional element to produce an NMC precursor. The NMC precursor is then converted into a metal composite oxide (hereinafter, a metal composite oxide mainly composed of nickel, manganese, and cobalt is also referred to as an "NMC intermediate") in an oxidative roasting step. The metal composite oxide NMC intermediate is mixed with a lithium compound in a mixing step to form a lithium mixture. Then, when the lithium mixture is processed in a firing step, carbon dioxide is introduced and fired at a low oxygen concentration, and it was found that NMC with favorable particle strength, average particle size, and sulfate concentration can be obtained. By equipping with NMC having high capacity and high durability, it becomes possible to manufacture a lithium-ion secondary battery that improves cycle characteristics and suppresses swelling of the battery under high voltage, and the present invention has been completed. That is, a first aspect of the present invention, which is based on the above findings, is a cathode active material for a lithium-ion secondary battery that can suppress swelling of the battery under high voltage used in the cathode of a lithium-ion secondary battery, having the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α (where 0.95 < v < 1.22, 0.01 ≤ w ≤ 0.35, 0.01 ≤ x ≤ 0.50, 0.01 ≤ y ≤ 0.15, 0 ≤ z ≤ 0.10, 0 ≤ α ≤ 0.20, and M is one or more elements selected from V, Mg, Mo, Nb, Ti, Si, Zn, Cu, Fe), the particle strength of the lithium nickel manganese cobalt aluminum composite oxide mainly composed of agglomerated primary particles is 132 to 218 MPa, the average primary particle size is 0.1 μm or more and less than 0.5 μm, the average secondary particle size is 3 to 20 μm, and the sulfate concentration is 0.5 wt% or less When the positive electrode active material is used in a 2032-type lithium ion secondary battery having a positive electrode containing the positive electrode active material, the secondary battery has an initial discharge capacity of 155 to 175 mAh / g, a capacity retention rate of 75% or more, and a swelling amount indicating the degree of swelling of the battery, calculated by the following evaluation method, is 103.8% or less. A cathode active material for a lithium-ion secondary battery, characterized in that. [Expansion amount evaluation method] The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle) x 100 A second aspect of the present invention is a positive electrode active material for a lithium ion secondary battery that can suppress the swelling of the battery under high voltage used in the positive electrode of the lithium ion secondary battery, and has the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α (where 0.95 < v < 1.22, 0.01 ≤ w ≤ 0.35, 0.01 ≤ x ≤ 0.50, 0.01 ≤ y ≤ 0.15, 0 < z ≤ 0.10, 0 ≤ α ≤ 0.20, and M is represented by W), and the particle strength of the lithium nickel manganese cobalt aluminum composite oxide mainly composed of secondary particles in which primary particles are aggregated is 115 to 226 MPa, the average primary particle diameter is 0.1 μm or more and less than 0.5 μm, the average secondary particle diameter is 3 to 20 μm, and the sulfate concentration is 0.5% by weight or less When the positive electrode active material is used in a 2032-type lithium ion secondary battery having a positive electrode containing the positive electrode active material, the secondary battery has an initial discharge capacity of 155 to 175 mAh / g, a capacity retention rate of 75% or more, and a swelling amount indicating the degree of swelling of the battery, calculated by the following evaluation method, is 103.8% or less. It is a positive electrode active material for a lithium ion secondary battery, characterized in that it is so. [Expansion amount evaluation method] The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle) x 100

[0007] A third aspect of the present invention is a lithium ion secondary battery provided with a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to claim 1 or 2 Type 2032 lithium ion secondary battery In the above, the secondary battery The initial discharge capacity is 155 to 175 mAh / g, the capacity retention rate is 75% or more, The swelling amount indicating the degree of swelling of the battery is calculated by the following evaluation method, It is a lithium ion secondary battery characterized in that the swelling amount of the lithium ion secondary battery provided with a positive electrode containing the positive electrode active material is 103.8% or less. [Swelling amount evaluation method] The swelling amount of the small-sized rectangular lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle) x 100 Effect of the Invention

[0008] The positive electrode active material for lithium ion secondary batteries in the present invention is a lithium nickel manganese cobalt aluminum composite oxide, which is relatively inexpensive and easy to handle industrially, and has high capacity and durability. By using this, lithium ion secondary batteries with far superior battery characteristics to conventional ones can be obtained, and therefore its industrial value is extremely great. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic cross-sectional view of a coin battery used for evaluating battery characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] One embodiment of the present invention will be described in detail in the following order. 1. Positive electrode active material for lithium-ion secondary batteries 2. Manufacturing method of positive electrode active material for lithium-ion secondary batteries 3. Lithium-ion secondary battery The positive electrode active material for a lithium ion secondary battery and the manufacturing method thereof in the present invention are not limited to the following description, and the embodiments may be modified in various ways based on the knowledge of those skilled in the art without departing from the spirit of the present invention. 1. Positive electrode active material for lithium-ion secondary batteries In the embodiment of the present invention, the swelling amount Below 103.8% The positive electrode active material for lithium ion secondary batteries used in the positive electrode of the lithium ion secondary battery is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α(However, 0.95 < v < 1.22, 0.01 ≤ w ≤ 0.35, 0.01 ≤ x ≤ 0.50, 0.01 ≤ y ≤ 0.15, 0 ≤ z ≤ 0.10, 0 ≤ α ≤ 0.20, and M is one or more elements selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe), mainly composed of secondary particles in which primary particles are aggregated, the particle strength of the lithium nickel manganese cobalt aluminum composite oxide is 132 to 218 MPa, the average primary particle size is 0.1 μm or more and less than 0.5 μm, the average secondary particle size is 3 to 20 μm, and the sulfate concentration is 0.5% by weight or less. In addition, the positive electrode active material for the lithium ion secondary battery described above (1) A crystallization step of crystallizing a metal composite hydroxide by supplying and mixing at least a solution containing nickel, manganese, and cobalt, a solution containing aluminum, a solution containing an ammonium ion donor, an alkaline solution, and optionally a solution containing element M to a reaction tank.

[0011] (2) An oxidation roasting step of obtaining a metal composite oxide by oxidatively roasting the metal composite hydroxide obtained in the crystallization step at 400 to 900 °C.

[0012] (3) A mixing step of obtaining a lithium mixture by mixing the metal composite oxide obtained in the oxidation roasting step and a lithium compound.

[0013] (4) A firing step of obtaining a lithium metal composite oxide by firing the lithium mixture obtained in the mixing step at 700 to 1000 °C while controlling the oxygen concentration to 0.1 to 20% by volume. Obtained by the production method having these steps (1) to (4), and the treatment is performed in the order of steps (1) to (4). In the crystallization step (1), an NMC precursor is generated by adding aluminum as an essential element and element M as an optional element in addition to the main NMC components nickel, manganese, and cobalt. The resulting NMC precursor is converted into a metal composite oxide in the oxidation roasting step (2). The resulting NMC intermediate is mixed with a lithium compound in the mixing step (3) to form a lithium mixture. When the resulting lithium mixture is treated in the calcination step (4), carbon dioxide is introduced and calcined at a low oxygen concentration, resulting in NMC with preferred particle strength, average particle size, and sulfate ion concentration. As described above, by incorporating NMC, which has high capacity and high durability, into a battery as a positive electrode active material, it is possible to manufacture lithium-ion secondary batteries that are far superior to those using conventional technology, such as by improving cycle characteristics and suppressing battery swelling under high voltage. <Composition> Nickel is an element that contributes to improving battery capacity. In order to obtain high capacity, the range of "1-wxyz" indicating the nickel content is preferably 0.30 to 0.95, more preferably 0.35 to 0.80, and particularly preferably 0.40 to 0.60. If the value of "1-wxyz" is less than 0.30, the battery capacity decreases, while if it exceeds 0.95, the electronic conductivity increases too much, causing thermal runaway due to short circuit, etc., and there is a risk that the safety of the battery cannot be sufficiently ensured. Manganese is an element that contributes to improving thermal stability. In order to obtain better thermal stability, the range of "w" indicating the manganese content is preferably 0.01 to 0.35, more preferably 0.10 to 0.30, and particularly preferably 0.15 to 0.30. If the value of "w" is less than 0.01, no improvement in thermal stability is observed, while if it exceeds 0.35, the amount of manganese eluted during operation at high temperatures increases, causing a problem of reduced cycle characteristics. Cobalt is an element that contributes to improving cycle characteristics. By including an appropriate amount of cobalt in the positive electrode active material, it is possible to provide good cycle characteristics and high durability without impairing the initial discharge capacity. The range of "x" indicating the cobalt content is preferably 0.01 to 0.50, more preferably 0.10 to 0.35, and particularly preferably 0.15 to 0.35. If the value of "x" is less than 0.01, sufficient cycle characteristics cannot be obtained and the capacity retention rate after cycling decreases, while if it exceeds 0.50, the cost burden increases. Aluminum is an element that suppresses excessive electronic conductivity and contributes greatly to ensuring safety. In order to ensure excellent safety, the value of "y" indicating the aluminum content is preferably 0.01 to 0.15, more preferably 0.05 to 0.10, and particularly preferably 0.06 to 0.08. If the value of "y" is less than 0.01, no improvement in safety is observed, while if it exceeds 0.15, aluminum segregates inside the particles, inhibiting the conductivity of lithium ions and causing a problem of reduced cycle characteristics. Furthermore, the NMC of the present invention can contain an element M as an option. By containing the element M in the positive electrode active material, it is possible to further improve the battery characteristics, such as the durability of the lithium ion secondary battery. The element M can be one or more elements selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe. The element M is appropriately selected according to the application of the lithium ion secondary battery as well as the required performance. The range of "z", which indicates the content of the element M that is optionally added, is preferably 0 to 0.10, more preferably 0.02 to 0.08, and particularly preferably 0.04 to 0.06. If the value of "z" exceeds 0.10, the efficiency of the redox reaction decreases, and therefore the battery capacity also decreases. In addition, as described later, the element M can be crystallized together with nickel, manganese, cobalt, and aluminum in the crystallization step and uniformly dispersed in the particles of the resulting NMC precursor, or it can be coated on the particle surface of the NMC precursor after the crystallization step. Furthermore, it is possible to mix the lithium compound together with the NMC intermediate in the mixing step, and these methods may be used in combination. In any case where any method is used, it is necessary to adjust the content so as not to deviate from the composition in the general formula above.

[0014] The method for evaluating the composition is not particularly limited, and the composition can be determined by a chemical analysis method such as acid decomposition-ICP (inductively coupled plasma) emission spectrometry. <Particle strength> The particle strength is 100 to 230 MPa, preferably 132 to 226 MPa. If the particle strength is less than 115 MPa, many "cracks" may occur in the NMC particles after charging and discharging, causing a decrease in capacity and swelling of the battery. On the other hand, if the particle strength exceeds 226 MPa, the filling property may become poor when preparing a positive electrode film of a battery, and the positive electrode film may not be prepared. In addition, if a positive electrode film with poor filling property is subjected to a charge and discharge cycle, the capacity decrease becomes large and the cycle characteristics become extremely poor.

[0015] The method for evaluating particle strength is not particularly limited, and for example, it can be determined by measuring each particle using a microcompression tester. <Average particle size> The primary particle average particle size is preferably 0.1 μm or more and less than 0.5 μm. This makes it possible to obtain high battery capacity and high cycle characteristics when used in a battery positive electrode. If the primary particle average particle size is less than 0.1 μm, high cycle characteristics may not be obtained, while if it exceeds 0.5 μm, the battery capacity and output characteristics may decrease, and sufficient battery characteristics may not be obtained. The secondary particle average particle size is preferably 3 to 20 μm, and more preferably 6 to 12 μm. This makes it possible to achieve high battery capacity and high packing ability for the positive electrode when used in a battery positive electrode. If the secondary particle average particle size is less than 3 μm, high packing ability for the positive electrode may not be obtained, while if it exceeds 20 μm, the battery capacity and output characteristics may decrease, and sufficient battery characteristics may not be obtained. The method for evaluating the average particle size is not particularly limited, and it can be determined, for example, from a volume-based distribution measured using a laser diffraction / scattering method. <Sulfate root concentration> The sulfate concentration is preferably 0.5% by weight or less, more preferably 0.3% by weight or less, and particularly preferably 0.1% by weight or less. If the sulfate concentration exceeds 0.5% by weight, the diffusion of lithium ions is hindered, resulting in a decrease in the battery capacity, and the sulfate itself is easily dissolved. Since lithium hardly contributes to the charge / discharge reaction, the battery must use an extra negative electrode material to cover the irreversible capacity of the positive electrode material. As a result, the capacity per weight or volume of the battery as a whole is reduced, and excess lithium accumulates in the negative electrode as irreversible capacity, which is problematic from the standpoint of safety.

[0016] The method for evaluating the sulfate concentration is not particularly limited. For example, the total sulfur content of NMC is analyzed by a combustion infrared absorption method or an acid decomposition-ICP emission spectrometry method, and the total sulfur content is calculated as the sulfate concentration (SO 2- ) can be calculated by converting it into 2. Manufacturing method of positive electrode active material for lithium-ion secondary batteries The method for producing NMC in the present invention includes the following steps (1) to (4), which are carried out in the order of steps (1) to (4). Through these steps, a lithium nickel manganese cobalt aluminum composite oxide can be obtained that maintains high particle strength, has an average primary particle size and an average secondary particle size within optimal ranges, and has a reduced sulfate concentration. (1) Crystallization process Usually, when preparing NMC precursor by crystallization, continuous crystallization is used. This method allows easy and large-scale preparation of NMC precursor with uniform composition. Generally, NMC precursor particles obtained by crystallization are mainly composed of secondary particles formed by aggregation of primary particles. However, this continuous crystallization method has a problem that the particle size distribution of the obtained NMC precursor particles tends to be a relatively wide normal distribution, and particles with uniform particle size are not necessarily obtained. When NMC is prepared using NMC precursor particles with a wide particle size distribution as a raw material, fine powders less than 3 μm may be mixed in when a lithium-ion secondary battery is assembled, which is likely to cause deterioration of cycle characteristics. In addition, if the particle size distribution becomes uneven, the reaction resistance increases, which may have a negative effect on the battery output. Therefore, in the crystallization process, it is preferable to obtain an NMC precursor with a narrow particle size distribution by, for example, clearly separating the "nucleation" stage and the "particle growth" stage to achieve uniform particle size. <Nucleation stage> First, water-soluble nickel salt, manganese salt, and cobalt salt are dissolved in water in a predetermined ratio to prepare raw material solution A containing nickel, manganese, and cobalt. The nickel salt, manganese salt, and cobalt salt used here are preferably sulfates. Next, water-soluble aluminum salt is dissolved in water in a predetermined ratio to prepare raw material solution B containing aluminum. The aluminum salt used here is preferably an aluminate rather than a sulfate. Next, the prepared raw material solutions A and B and a solution containing an ammonium ion donor such as ammonia water are supplied to a crystallization reaction tank while stirring, and a reaction solution is formed in the reaction tank, and an alkaline solution such as a sodium hydroxide solution is supplied at the same time to control the pH of the reaction solution to be constant. A solution containing element M may be added to raw material solutions A and B, but if the addition of this solution causes precipitation, it is supplied to the reaction tank simultaneously from a route separate from that of each raw material solution. By controlling the amount of alkaline solution added so as to maintain a constant pH, it becomes possible to selectively generate minute "nuclei" of the NMC precursor in the formed reaction solution. The pH of the reaction solution (based on a liquid temperature of 25°C) is preferably 12.0 or higher, and more preferably controlled to 12.0 to 14.0. This allows minute "nuclei" of the NMC precursor to be selectively generated in the reaction solution. If the pH is less than 12.0, the growth of the "nuclei" also occurs at the same time, leading to an insufficient total number of "nuclei", resulting in coarse particle sizes and a wide particle size distribution. The total number of "nuclei" can be controlled by the pH and ammonium ion concentration during nucleation, and the amount of each raw material solution supplied. The ammonium ion concentration of the reaction solution is preferably kept constant within the range of 3 to 15 g / L. When the ammonium ion concentration becomes unstable, the solubility of metal ions also changes, inhibiting the formation of regular NMC precursor particles and making it easier for gel-like "nuclei" to form, which tends to lead to a broad particle size distribution. Furthermore, when the ammonium ion concentration is less than 3 g / L, it does not function as a complexing agent, while when it exceeds 15 g / L, the NMC precursor particles are formed too densely, and the final product NMC also has a dense structure, which is likely to reduce the specific surface area, which is not preferable. The temperature of the reaction solution is preferably set to 35 to 60° C. If the temperature is lower than 35° C., the solubility of the metal ions supplied is insufficient, nucleation occurs easily, and control of nucleation becomes difficult. On the other hand, if the temperature exceeds 60° C., the volatilization loss of ammonia is promoted, so the concentration of ammonium ions as a complexing agent decreases, and the solubility of the metal ions is insufficient as described above. In addition, the crystallization time in the nucleation stage can be set arbitrarily depending on the intended average particle size of the NMC precursor particles. <Particle growth stage> In the particle growth stage, the pH of the reaction solution (based on a liquid temperature of 25°C) is controlled to a range of 10.5 to 12.0, and an alkaline solution is supplied into the reaction tank to set the pH lower than that in the nucleation stage. By controlling the pH within this range after the nucleation stage, only the growth of the "nuclei" generated in the nucleation stage is preferentially caused, and new nucleation is suppressed, thereby narrowing the width of the particle size distribution in the NMC precursor particles. If the pH is less than 10.5, the production efficiency deteriorates due to an increase in metal ions remaining in the reaction solution, while if it exceeds 12.0, not only particle growth but also nucleation progresses, so the particle size distribution tends to become wide. In addition, when sulfate is used in the raw material solution, the concentration of sulfate radicals remaining in the NMC precursor particles becomes high, which is not preferable. The ammonium ion concentration and temperature of the reaction solution may be controlled within the same range as in the nucleation stage. In addition, after the nucleation step or during the particle growth step, a portion of the reaction solution can be discharged from the reaction tank to increase the concentration of the NMC precursor particles in the reaction solution, and then the particle growth can be continued. This allows the particle size distribution of the NMC precursor particles to be narrowed and the particle density to be increased. In addition, by controlling the atmosphere in the reaction tank in the nucleation stage and particle growth stage, it is possible to control the particle structure of the NMC precursor and therefore the MNC. That is, by controlling the oxygen concentration in the reaction tank, the size of the primary particles constituting the NMC precursor particles can be adjusted, and the denseness of the NMC precursor particles can be adjusted. Therefore, by lowering the oxygen concentration in the reaction tank and creating a non-oxidizing atmosphere, the denseness of the NMC precursor particles increases, and the finally obtained NMC also becomes dense and has a solid structure. On the other hand, by increasing the oxygen concentration in the reaction tank and creating an oxidizing atmosphere, the denseness of the NMC precursor particles decreases, and the finally obtained NMC has a hollow structure or a porous structure. In particular, by controlling the reaction tank to an oxidizing atmosphere in the early stages of the nucleation stage and particle growth stage, and then to a non-oxidizing atmosphere, the denseness of the center of the NMC precursor particles can be reduced and the denseness of the outer periphery can be increased. The positive electrode active material obtained from such NMC precursor particles has a hollow structure with a sufficiently large hollow portion. The size of the hollow portion can be controlled by adjusting the time during which the oxidizing atmosphere is maintained and the time during which the non-oxidizing atmosphere is maintained. (2) Oxidation roasting process The oxidizing roasting step is a step in which the NMC precursor obtained in the crystallization step is heated in an oxidizing atmosphere at a temperature of 400 to 900°C for 3 to 10 hours to obtain an NMC intermediate. The retention time at the oxidizing roasting temperature is preferably 3 to 10 hours, more preferably 5 to 7 hours. If it is less than 3 hours, the average primary particle size of the NMC intermediate becomes small, so that the average primary particle size of the final product NMC becomes 0.1 μm or less, resulting in a decrease in particle strength. On the other hand, if it exceeds 10 hours, the specific surface area of ​​the NMC intermediate becomes 2.0 m 2 / g or less, the reactivity between lithium and the transition metal deteriorates in the subsequent firing step, the battery capacity decreases, and the productivity deteriorates due to the extended firing time.

[0017] When the oxidizing roasting temperature is less than 400°C, the average primary particle diameter of the NMC intermediate becomes small, the average primary particle diameter of the NMC becomes less than 0.1 μm, and the particle strength decreases. On the other hand, when the oxidizing roasting temperature exceeds 900°C, the specific surface area of ​​the NMC intermediate becomes 2.0 m 2 / g, the reactivity between lithium and the transition metal deteriorates in the firing step, resulting in a decrease in battery capacity and a decrease in productivity due to an extension of the firing time. The oxidizing roasting atmosphere is an oxidizing atmosphere, and the oxygen concentration is preferably 18 to 100% by volume. That is, it is preferable to carry out the roasting in an air atmosphere and in an oxygen stream. Considering the cost, it is particularly preferable to carry out the roasting in an air stream. If the oxygen concentration is less than 18% by volume, the oxidation is insufficient, which may cause abnormal growth of primary particles.

[0018] The heating furnace used for the oxidizing roasting is not particularly limited as long as it can be used in an air atmosphere and an oxygen stream, but an electric furnace that does not generate gas is preferable, and a batch or continuous heating furnace is used. In addition, a rotary kiln or a fluidized roasting furnace, which have good gas replacement properties, heat exchange efficiency, and productivity, are particularly preferable from an industrial perspective. (3) Mixing process The mixing step is a step of obtaining a lithium mixture by mixing a lithium compound with the NMC intermediate obtained in the oxidation roasting step so that the ratio (Li / Me) of the number of lithium (Li) atoms to the total number of atoms (Me) of metal elements excluding lithium is 0.95 to 1.20. If Li / Me is less than 0.95, the reaction resistance of the positive electrode in a lithium ion secondary battery using the obtained NMC increases, resulting in low battery output. On the other hand, if Li / Me exceeds 1.20, the initial discharge capacity of the obtained NMC decreases and the reaction resistance of the positive electrode also increases.

[0019] The lithium compound is not particularly limited, but lithium hydroxide, lithium carbonate, or a mixture thereof can be suitably used. Considering ease of handling and stability of quality, it is more preferable to use lithium carbonate.

[0020] It is preferable to thoroughly mix the NMC intermediate and the lithium compound. A general mixer can be used for the mixing operation. For example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, etc. can be used, and the NMC intermediate particles should be thoroughly mixed with the lithium compound so as not to be destroyed. (4) Firing process The sintering process is a process in which the lithium mixture obtained in the mixing process is heated at a temperature of 700 to 1000 ° C for 5 to 20 hours in a low-oxygen atmosphere in which carbon dioxide is introduced and the oxygen concentration is lower than that in air, thereby obtaining the final product NMC. If the sintering temperature is less than 700 ° C, the reaction between the NMC intermediate and the lithium compound is difficult to proceed, lithium diffusion into the NMC intermediate is insufficient, excess lithium and unreacted NMC intermediate remain, and the crystal structure is not fully aligned, resulting in a decrease in battery capacity and output characteristics. On the other hand, if the sintering temperature exceeds 1000 ° C, intense sintering occurs between the NMC particles, forming sintered masses that hinder particle size adjustment by crushing treatment, generating particles of 20 μm or more, significantly worsening the battery's packing ability and causing a decrease in battery capacity. The time for which the firing temperature is maintained is preferably 5 to 20 hours, and more preferably 5 to 10 hours. If the time is less than 5 hours, the production of NMC becomes insufficient, while if the time exceeds 20 hours, severe sintering occurs between NMC particles, resulting in a decrease in battery capacity and a deterioration in productivity due to the extended firing time.

[0021] The firing atmosphere is a low-oxygen atmosphere, and it is preferable to flow carbon dioxide and control the oxygen concentration to 0.1 to 20% by volume. If the oxygen concentration exceeds 20% by volume, the crystallinity of NMC may not be uniform, and improvement in particle strength may not be observed. By growing crystals in a low-oxygen atmosphere, the crystallinity is greatly improved, and improvement in particle strength has been confirmed in normal firing times. This is because oxygen deficiencies occur in parts of the heating furnace due to the low oxygen concentration, but the crystallinity is rapidly improved starting from the oxygen deficiency parts, which is thought to contribute to the improvement of particle strength.

[0022] The heating furnace used for firing is not particularly limited as long as it can be used in a low-oxygen atmosphere, but an electric furnace that does not generate gas is preferable, and a batch-type or continuous-type heating furnace is used.

[0023] Under the above firing conditions, the generation of sintered masses due to intense sintering of the obtained NMC particles is suppressed, but slight sintering may occur. In such a case, a crushing step for crushing the obtained NMC particles can be further provided. As a crushing method, a known means can be used, for example, a pin mill or a hammer mill. In this case, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles. 3. Lithium-ion secondary battery Next, a lithium ion secondary battery using the NMC produced according to the embodiment of the present invention as a positive electrode active material will be described. The lithium ion secondary battery (hereinafter also referred to as "secondary battery") includes the same components as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. (1) Components <Positive electrode> The above-mentioned NMC is used as a positive electrode active material to prepare a positive electrode for a lithium ion secondary battery, for example, in the following manner.

[0024] First, the conductive material and the binder are mixed with the NMC according to this embodiment, and further, activated carbon and a solvent for viscosity adjustment, etc. are added as necessary, and these are kneaded to prepare a positive electrode composite paste. At that time, the mixing ratio of each in the positive electrode composite paste is also an important factor that determines the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode composite excluding the solvent is 100 parts by mass, the NMC content can be 60 to 95 parts by mass, the conductive material content can be 1 to 20 parts by mass, and the binder content can be 1 to 20 parts by mass, similar to the positive electrode of a general lithium ion secondary battery. In particular, in order to obtain a battery with a high capacity, it is more preferable to prepare a highly filled positive electrode with an NMC content of 90 to 95 parts by mass.

[0025] The obtained positive electrode composite paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to evaporate the solvent. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. In this manner, a sheet-shaped positive electrode can be produced. The sheet-shaped positive electrode is cut to an appropriate size according to the intended battery and used to produce the battery. The method for producing the positive electrode is not limited to the above, and other methods may be used.

[0026] As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

[0027] The binder serves to bind the NMC particles together, and examples of the binder that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, and polyacrylic acid.

[0028] In addition, if necessary, a solvent for dispersing NMC, conductive material, and activated carbon and dissolving the binder can be added to the positive electrode mixture, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity. When manufacturing a sheet-shaped positive electrode, the positive electrode mixture paste is rolled and stretched, but in manufacturing a high-capacity secondary battery, a strong roll pressure is applied to improve the packing property, which may cause the NMC particles to crack and the cycle characteristics to deteriorate. However, if the NMC whose particle strength is adjusted to 100 to 230 MPa in the present invention is used as the positive electrode active material, it is possible to prevent particle cracking of the positive electrode active material and a decrease in the packing rate during electrode production. In addition, the battery may swell due to particle cracking of the positive electrode active material, but by using the above-mentioned NMC as the positive electrode active material, the swelling can be suppressed. <Negative electrode> For the negative electrode, metallic lithium or lithium alloys can be used. In addition, a negative electrode active material capable of absorbing and desorbing lithium ions can be mixed with a binder, and an appropriate solvent can be added to make a paste of the negative electrode mixture, which can be applied to the surface of a metal foil collector such as copper, dried, and compressed to increase the electrode density as necessary.

[0029] As the negative electrode active material, for example, a material containing lithium such as metallic lithium or a lithium alloy, a calcined body of an organic compound such as natural graphite, artificial graphite, and phenolic resin capable of absorbing and desorbing lithium ions, and a powder of a carbon material such as coke can be used. In this case, as with the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. <separator> The separator is sandwiched between the positive electrode and the negative electrode, and has the function of separating the positive electrode and the negative electrode and retaining the electrolyte. As such a separator, for example, a thin membrane such as polyethylene or polypropylene having a large number of fine pores can be used, but there is no particular limitation as long as it has the above-mentioned function. <Non-aqueous electrolyte> The non-aqueous electrolyte solution is a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent. The organic solvent may be one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, either alone or in combination.

[0030] The supporting salt may be LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, or a composite salt thereof. The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, or the like. <Lithium-ion secondary battery> The lithium ion secondary battery according to the embodiment of the present invention can be formed into various shapes such as a cylindrical shape, a laminated shape, etc. In any shape, the positive electrode and the negative electrode are laminated with a separator interposed therebetween to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte solution, the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and the battery is sealed in a battery case to complete the lithium ion secondary battery. <Characteristics of non-aqueous electrolyte secondary batteries> As described above, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention uses the NMC according to the embodiment as a positive electrode active material, and thus has excellent battery capacity, output characteristics, and cycle characteristics by reducing the negative electrode resistance. Moreover, this lithium ion secondary battery is superior not only in particle strength but also in thermal stability and safety, even when compared with secondary batteries using conventional NMC particles as a positive electrode active material.

[0031] Fig. 1 is a schematic cross-sectional view of a coin battery used to evaluate battery characteristics. For example, when a 2032-type coin battery shown in Fig. 1 is constructed using the NMC according to the embodiment of the present invention as a positive electrode active material, the initial discharge capacity can be increased to 155 mAh / g or more, the capacity retention rate at 500 cycles to 75% or more, and the swelling rate can be increased to 100% or more by keeping the particle strength within the claimed range. Below 103.8% It is possible to do so. <Application> As described above, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention is excellent in battery capacity, output characteristics, and cycle characteristics, and can be suitably used as a power source for small portable electronic devices (smartphones, tablets, mini notebook computers, etc.) that require a high level of these characteristics. In addition, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention is also excellent in safety, and not only can it be made smaller and have a higher output, but it can also simplify expensive protection circuits, so it can be suitably used as a power source for transportation equipment that is limited by its mounting space. EXAMPLES

[0032] The present invention will be specifically described using examples, but the technical scope of the present invention is not limited by these examples. In addition, all of the reagents used in the manufacture of NMC (positive electrode active material) and lithium ion secondary batteries in the present examples are special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. The evaluation methods in the examples (and comparative examples) are as follows, and the evaluation results obtained are shown in Table 1. (1)NMC (positive electrode active material) 1) Composition The composition was determined by thermally decomposing 1 g of the sample with an inorganic acid, adjusting the volume to 100 ml with pure water to obtain an analytical specimen solution, which was then appropriately diluted and measured using an ICPE-9000 multi-type ICP optical emission spectrometer (manufactured by Shimadzu Corporation). 2) Particle strength The particle strength was measured by applying a load to one NMC particle with an indenter using a micro strength evaluation tester MCT-500 (manufactured by Shimadzu Corporation), and calculating the particle strength at the time of destruction. Specifically, the NMC particle was placed on a silicon plate, its position was finely adjusted to match the center of the indenter, and the indenter was brought into contact with the NMC particle so as not to apply a large load, and the measurement was performed. The measurement conditions were a test force of 150 mN and a loading speed of 2.0 mN / sec, and the average value of 10 particles was calculated. 3) Average particle size The average particle size was determined from the volume distribution measured using a laser diffraction / scattering particle size distribution analyzer, Microtrac MT3300EX2 (manufactured by Microtrac BEL Co., Ltd.) The average particle size of primary particles and the average particle size of secondary particles were separately measured by adjusting the ultrasonic irradiation intensity of the sample. 4) Sulfate root concentration The sulfate radical content was determined by analyzing the total sulfur content using acid decomposition-ICP emission spectrometry, and the total sulfur content was calculated by dividing the total sulfur content by the sulfate radical (SO4 2- The measurement was performed using a multi-type ICP emission spectrometer, ICPE-9000 (manufactured by Shimadzu Corporation). (2) Lithium-ion secondary battery 1)Initial discharge capacity The initial discharge capacity was measured by leaving the coin battery or small rectangular battery for about 24 hours after production, and after the open-circuit voltage (OCV) had stabilized, applying a current density of 0.1 mA / cm to the positive electrode. 2 The capacity was measured when the battery was charged to a cut-off voltage of 4.3 V, and after a 1-hour rest, discharged to a cut-off voltage of 3.0 V. A multi-channel voltage / current generator R6741A (manufactured by Advantest Corporation) was used to measure the discharge capacity. 2) Cycle characteristics The above-mentioned charge / discharge test was repeated, and the capacity retention rate after 500 cycles was calculated by measuring the 500th discharge capacity relative to the initial discharge capacity. 3) Amount of swelling The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (battery thickness after 500 cycles) / (battery thickness at 1st cycle) × 100

[0033] (Reference example 1) <Crystallization process> First, a 60L reaction tank was filled with water to half its volume, and the temperature inside the tank was set to 40°C while stirring in an air atmosphere. An appropriate amount of 25% by weight sodium hydroxide solution and 25% by weight ammonia water were added to adjust the pH of the liquid in the tank (based on a liquid temperature of 25°C) to 12.8 and the ammonium ion concentration to 10g / L. Next, a 2.0mol / L raw material solution (metal element molar ratio Ni:Co:Mn=55:20:25) in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved and mixed was fed at 0.13L / min to prepare a reaction solution. At the same time, a 25% by weight sodium hydroxide solution and 25% by weight ammonia water were added at a constant rate to control the pH to 12.8 (nucleation pH) and perform crystallization for 2 minutes and 30 seconds. Thereafter, nitrogen gas was supplied to reduce the oxygen concentration in the reaction tank to 2% by volume or less, while the supply of the 25% by mass sodium hydroxide solution was temporarily stopped until the pH reached 11.6 (nucleus growth pH). After the pH reached 11.6, the supply of the 25% by mass sodium hydroxide solution was adjusted according to the amount of sodium aluminate solution added and resumed. Crystallization was continued for 4 hours while controlling the pH at 11.6, and then the crystallization was completed. After the crystallization was completed, the product was washed with water, filtered, and dried to obtain Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC precursor represented by (OH)2 was obtained. <Oxidation roasting process> The NMC precursor obtained in the crystallization process was placed in a magnesia heating vessel and treated in a closed electric furnace under the conditions of an oxidizing roasting temperature of 400°C and an oxidizing roasting time of 5 hours in an air atmosphere. The oxidizing roasted product was then cooled to room temperature to obtain Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC intermediate represented by O was obtained. <Mixing process> The NMC intermediate obtained in the oxidation roasting process and lithium carbonate weighed so that the Li / Me ratio was 1.03 were thoroughly mixed using a shaker mixer TURBULA-Type T2C (manufactured by Willy & Bachofen (WAB)) to obtain a lithium mixture. <Firing process> The lithium mixture obtained in the mixing process was placed in a magnesia heating container, and a closed electric furnace was used to supply carbon dioxide into the furnace at a rate of 0.5 to 20 L / min. The oxygen concentration in the furnace was kept at 18% by volume to maintain a low-oxygen atmosphere. The firing temperature was set to 850°C and the firing time was set to 10 hours. The fired product was then cooled to room temperature and crushed to produce the Li 1.03 Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC (positive electrode active material) represented by O2 was obtained. <Battery Construction> 52.5 mg of the obtained NMC, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were weighed and mixed, and molded to a thickness of 100 μm at a pressure of 100 MPa to prepare a positive electrode (electrode for evaluation) (1) shown in FIG. 1. Furthermore, this positive electrode (1) was dried at 120 ° C for 12 hours using a vacuum dryer, and then a 2032-type coin battery using the positive electrode (1) was prepared in a glove box in an argon gas atmosphere with a dew point controlled at -80 ° C. For the negative electrode (2), lithium metal or carbon with a thickness of 1 mm was used, and for the electrolyte, a mixture of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 mol of lithium perchlorate (LiClO4) as a supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. For the separator (3), a polyethylene porous film with a thickness of 25 μm was used. The 2032 type coin battery also had a gasket (4) and a wave washer (5), and was assembled into a battery with a positive electrode can (6) and a negative electrode can (7).

[0034] (Reference example 2) The same procedure as in Example 1 was carried out except for the following conditions. <Oxidation roasting process> The oxidizing roasting temperature was set to 500°C.

[0035] [Example 3] <Crystallization process> First, a 60L reaction tank was filled with water to half its volume, and the temperature inside the tank was set to 40°C while stirring in an air atmosphere. An appropriate amount of 25% by weight sodium hydroxide solution and 25% by weight ammonia water were added to adjust the pH of the liquid in the tank (based on a liquid temperature of 25°C) to 12.8 and the ammonium ion concentration to 10g / L. Next, a 2.0mol / L raw material solution (metal element molar ratio Ni:Co:Mn=55:20:25) in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved and mixed was fed at 0.13L / min to prepare a reaction solution. At the same time, a 25% by weight sodium hydroxide solution and 25% by weight ammonia water were added at a constant rate to control the pH to 12.8 (nucleation pH) and perform crystallization for 2 minutes and 30 seconds. Thereafter, nitrogen gas was supplied to reduce the oxygen concentration in the reaction tank to 2% by volume or less, while the supply of the 25% by mass sodium hydroxide solution was temporarily stopped until the pH reached 11.6 (nucleus growth pH). After the pH reached 11.6, the supply of the 25% by mass sodium hydroxide solution was adjusted according to the amount of sodium aluminate solution added and resumed. Crystallization was continued for 4 hours while controlling the pH at 11.6, and then the crystallization was completed. After the crystallization was completed, the product was washed with water, filtered, and dried to obtain Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC precursor represented by (OH)2 was obtained. <Oxidation roasting process> The NMC precursor obtained in the crystallization process was placed in a magnesia heating vessel and treated in a closed electric furnace under the conditions of an oxidizing roasting temperature of 600°C and an oxidizing roasting time of 5 hours in an air atmosphere. The oxidizing roasted product was then cooled to room temperature to obtain Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC intermediate represented by O was obtained. <Mixing process> The NMC intermediate obtained in the oxidation roasting process and lithium carbonate weighed so that the Li / Me ratio was 1.03 were thoroughly mixed using a shaker mixer TURBULA-Type T2C (manufactured by Willy & Bachofen (WAB)) to obtain a lithium mixture. <Firing process> The lithium mixture obtained in the mixing process was placed in a magnesia heating container, and a closed electric furnace was used to supply carbon dioxide into the furnace at a rate of 0.5 to 20 L / min. The oxygen concentration in the furnace was kept at 18% by volume to maintain a low-oxygen atmosphere. The firing temperature was set to 850°C and the firing time was set to 10 hours. The fired product was then cooled to room temperature and crushed to produce the Li 1.03 Ni 0.54 Mn 0.24 Co 0.19 Al 0.03 The NMC (positive electrode active material) represented by O2 was obtained. <Battery Construction> 52.5 mg of the obtained NMC, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were weighed and mixed, and molded to a thickness of 100 μm at a pressure of 100 MPa to prepare a positive electrode (electrode for evaluation) (1) shown in FIG. 1. Furthermore, this positive electrode (1) was dried at 120 ° C for 12 hours using a vacuum dryer, and then a 2032-type coin battery using the positive electrode (1) was prepared in a glove box in an argon gas atmosphere with a dew point controlled at -80 ° C. For the negative electrode (2), lithium metal or carbon with a thickness of 1 mm was used, and for the electrolyte, a mixture of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 mol of lithium perchlorate (LiClO4) as a supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. For the separator (3), a polyethylene porous film with a thickness of 25 μm was used. The 2032 type coin battery also had a gasket (4) and a wave washer (5), and was assembled into a battery with a positive electrode can (6) and a negative electrode can (7).

[0036] [Example 4] The same procedure as in Example 3 was carried out except for the following conditions. <Firing process> The oxygen concentration in the furnace was set to 0.2% by volume.

[0037] [Example 5] The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> The oxidizing roasting temperature was set to 700°C.

[0038] [Example 6] The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> The oxidation roasting temperature was set to 800°C.

[0039] (Reference example 7) The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> The oxidizing roasting temperature was set to 900°C.

[0040] [Example 8] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03.

[0041] [Example 9] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> The oxidizing roasting temperature was set to 600°C.

[0042] [Example 10] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y Mz O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> The oxidizing roasting temperature was set to 600°C. <Firing process> The oxygen concentration in the furnace was set to 0.2% by volume.

[0043] [Example 11] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> The oxidation roasting temperature was set to 800°C.

[0044] [Example 12] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> The element M is molybdenum or niobium, and the general formula is Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The molybdenum and niobium were added in equal amounts so that the total Z value was 0.03. <Oxidation roasting process> The oxidation roasting temperature was set to 800°C.

[0045] (Reference example 13) The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> Vanadium and magnesium are used as the element M, and the general formula is Li v Ni 1-w-x-y-z Mn w Co xAl y M z O 2+α The vanadium and magnesium were added in equal amounts so that the total Z value was 0.06.

[0046] [Example 14] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> The element M is titanium or silicon, and the general formula is Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The titanium and silicon were added in equal amounts so that the total Z value was 0.06. <Oxidation roasting process> The oxidation roasting temperature was set to 800°C.

[0047] [Example 15] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> The element M is zinc, copper, or iron, and the general formula is Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The zinc, copper and iron were added in equal amounts so that the total Z value was 0.09.

[0048] [Comparative Example 1] The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> No oxidation roasting was performed. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0049] [Comparative Example 2] The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> The oxidizing roasting temperature was set to 300°C. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0050] [Comparative Example 3] The same procedure as in Example 3 was carried out except for the following conditions. <Oxidation roasting process> The oxidizing roasting temperature was set to 1000°C. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0051] [Comparative Example 4] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> No oxidation roasting was performed. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0052] [Comparative Example 5] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> The oxidizing roasting temperature was set to 300°C. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0053] [Comparative Example 6] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> As the element M, tungsten is represented by the general formula: Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The amount was added so that the Z value was 0.03. <Oxidation roasting process> The oxidizing roasting temperature was set to 1000°C. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0054] [Comparative Example 7] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> The element M is molybdenum or niobium, and the general formula is Li v Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The molybdenum and niobium were added in equal amounts so that the total Z value was 0.03. <Oxidation roasting process> No oxidation roasting was performed. <Firing process> The inside of the furnace was made into a high temperature atmosphere (oxygen concentration exceeding 20% ​​by volume).

[0055] [Comparative Example 8] The same procedure as in Example 3 was carried out except for the following conditions. <Crystallization process> The element M is zinc, copper, or iron, and the general formula is Liv Ni 1-w-x-y-z Mn w Co x Al y M z O 2+α The zinc, copper and iron were added in equal amounts so that the total Z value was 0.09. <Oxidation roasting process> No oxidation roasting was performed. <Firing process> The inside of the furnace was filled with air (oxygen concentration exceeding 20% ​​by volume).

[0056] [Table 1]

[0057] [comprehensive evaluation] As can be seen from Table 1 above, the NMC of each Example had good particle strength, average primary particle diameter, average secondary particle diameter, and sulfate concentration because the conditions such as the oxidizing roasting temperature and the baking atmosphere in the manufacturing process were all within the preferred range. This result shows that an optimal positive electrode active material for lithium ion secondary batteries has been developed to obtain an excellent lithium ion secondary battery with improved safety in addition to discharge capacity and durability. Therefore, when a lithium ion secondary battery was produced using the NMC of each Example and its characteristics were evaluated, the initial discharge capacity was 155 mAh / g or more, the capacity retention rate in the cycle characteristics was 75% or more, and the swelling rate was 104% or less, which were also very good values. In contrast, the NMCs of Comparative Examples 1 to 8 did not undergo an oxidizing roasting step in the manufacturing process, or the oxidizing roasting temperature and other conditions were not favorable, so that the particle strength, average primary particle diameter, average secondary particle diameter, and sulfate concentration were all insufficient. Moreover, when lithium ion secondary batteries were produced using the NMCs of Comparative Examples 1 to 8 and their characteristics were evaluated, the initial discharge capacity, capacity retention rate in cycle characteristics, and swelling rate were all far inferior to those of the Examples. [Explanation of symbols]

[0058] 1 Positive electrode (electrode for evaluation) 2 negative electrode (lithium metal or carbon) 3. Separator 4 Gasket 5 Wave Washer 6 Positive electrode can 7 Anode can

Claims

1. A positive electrode active material for a lithium ion secondary battery that can suppress battery swelling under high voltage and is used in a positive electrode of the lithium ion secondary battery, General formula: Li ｖ Ni １－ｗ－ｘ－ｙ－ｚ Mn ｗ Co ｘ A ｙ M ｚ O ２＋α (wherein 0.95<v<1.22, 0.01≦w≦0.35, 0.01≦x≦0.50, 0.01≦y≦0.15, 0≦z≦0.10, 0≦α≦0.20, and M is one or more elements selected from V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe), the particle strength of the lithium nickel manganese cobalt aluminum composite oxide mainly composed of secondary particles formed by agglomeration of primary particles is 132 to 218 MPa, the average particle size of the primary particles is 0.1 μm or more and less than 0.5 μm, the average particle size of the secondary particles is 3 to 20 μm, and the concentration of sulfate ions is 0.5 wt % or less, A positive electrode active material for a lithium ion secondary battery, characterized in that, when used in a 2032-type lithium ion secondary battery having a positive electrode containing the positive electrode active material, the secondary battery has an initial discharge capacity of 155 to 175 mAh / g, a capacity retention rate of 75% or more, and a swelling amount indicating the degree of swelling of the battery, calculated by the following evaluation method, is 103.8% or less. [Expansion amount evaluation method] The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle)×100

2. A positive electrode active material for a lithium ion secondary battery that can suppress battery swelling under high voltage and is used in a positive electrode of the lithium ion secondary battery, General formula: Li ｖ Ni １－ｗ－ｘ－ｙ－ｚ Mn ｗ Co ｘ A ｙ M ｚ O ２＋α (wherein 0.95<v<1.22, 0.01≦w≦0.35, 0.01≦x≦0.50, 0.01≦y≦0.15, 0<z≦0.10, 0≦α≦0.20, and M is W), the particle strength of the lithium nickel manganese cobalt aluminum composite oxide mainly composed of secondary particles formed by agglomeration of primary particles is 115 to 226 MPa, the average particle size of the primary particles is 0.1 μm or more and less than 0.5 μm, and the average particle size of the secondary particles is a particle size of 3 to 20 μm, a sulfate concentration of 0.5% by weight or less, and when used in a 2032-type lithium ion secondary battery having a positive electrode containing the positive electrode active material, the secondary battery has an initial discharge capacity of 155 to 175 mAh / g, a capacity retention rate of 75% or more, and a swelling amount, which indicates the degree of swelling of the battery and is calculated by the following evaluation method, is 103.8% or less. [Expansion amount evaluation method] The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle)×100

3. A 2032-type lithium ion secondary battery having a positive electrode containing the positive electrode active material for lithium ion secondary batteries according to claim 1 or 2, wherein the initial discharge capacity of the secondary battery is 155 to 175 mAh / g, the capacity retention rate is 75% or more, The swelling amount, which indicates the degree of swelling of the battery, is calculated by the following evaluation method: A lithium ion secondary battery having a positive electrode containing the positive electrode active material, characterized in that the amount of swelling of the lithium ion secondary battery is 103.8% or less. [Expansion amount evaluation method] The amount of swelling of the small prismatic lithium ion battery was calculated using the following formula. Swelling amount (%) = (Battery thickness after 500 cycles) / (Battery thickness at 1st cycle)×100

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