Transition metal precursor for preparation of cathode active material

Abstract

The present invention provides a transition metal precursor for preparation of a cathode active material in the form of secondary particles in which primary particles are aggregated, the transition metal precursor being characterized by comprising Mn and at least one additive element selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W, wherein a specific volume represented by the following formula is 20-200 cm3 / g. Specific volume (cm3 / g) = (average particle diameter of secondary particles) Х (specific surface area of secondary particles).

Description

Transition metal precursors for manufacturing positive electrode active materials

[0001] The present invention relates to a transition metal precursor for manufacturing a positive electrode active material in the form of secondary particles in which primary particles are aggregated, and relates to a transition metal precursor containing a specific additive element and Mn and having a specific volume that satisfies a condition within a specific range.

[0002] As concerns about environmental issues have recently emerged, secondary batteries are expanding into medium- to large-scale fields such as transportation, such as electric vehicles, and power storage devices, such as energy storage systems (ESS). However, securing high efficiency, high capacity, and stability remain challenges for the industry.

[0003] Lithium transition metal composite oxides are used as positive electrode active materials for lithium secondary batteries. In particular, lithium-cobalt oxide (LCO) initially received attention due to its high operating voltage and excellent capacity characteristics, but it has the disadvantage of having very poor crystal structure and thermal characteristics due to delithiation.

[0004] To replace these, lithium-manganese or lithium-nickel composite metal oxides have been developed, and composite metal oxides with a high Ni content in particular are attracting attention due to their high reversible capacity.

[0005] However, lithium-nickel oxide has thermal instability and poses a risk of decomposition, rupture, and ignition under external forces when charged. Therefore, active research is underway to improve its stability. These stability issues in cathode active materials can directly impact the safety of secondary batteries, necessitating a fundamental solution.

[0006] In this regard, in the past, the Mn content in the composition of the precursor for the positive electrode active material was increased to pursue increased durability, but in this case, problems of increased resistance and decreased efficiency inevitably occurred.

[0007] Therefore, there is a high need in the industry for new technologies that can solve these problems at once.

[0008] The present invention aims to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0009] The inventors of the present invention, after repeated in-depth research and various experiments, have confirmed that by including a specific additive element in a transition metal precursor for manufacturing a cathode active material containing Mn to increase durability, the size of primary particles increased by Mn is reduced and the specific volume is set to satisfy a specific range, problems such as BET decrease and subsequent increase in resistance and decrease in efficiency characteristics can be solved, and thus the present invention has been completed.

[0010] Therefore, the transition metal precursor according to the present invention is a transition metal precursor for manufacturing a cathode active material in the form of secondary particles in which primary particles are aggregated.

[0011] Contains Mn and at least one additional element selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo and W;

[0012] The specific volume expressed by the following formula is 20 to 200 cm 3 It is characterized by / g.

[0013] Specific volume (cm) 3 / g) = (average particle size of secondary particles) Х (specific surface area of ​​secondary particles)

[0014]

[0015] The inventors of the present application have focused on the enlargement of the primary particle size by Mn and the resulting decrease in the specific surface area as the cause of the increased durability of the precursor containing Mn and the trade-off battery characteristics according to the constituent elements, and have proposed, in order to solve the problems described above through the addition of an additive element that reduces the primary particle size, the inclusion of a specific additive element and the limitation of the range of the particle size ratio obtained therefrom as defined above.

[0016]

[0017] Generally, the cathode active material for lithium secondary batteries is a lithium composite transition metal oxide manufactured by calcining a "transition metal raw material" containing a transition metal and a "lithium raw material" containing lithium at high temperatures in air and an oxidizing atmosphere.

[0018] Transition metal raw materials may be in the form of, for example, oxides, hydroxides, oxyhydroxides, various salts, etc. of transition metals, and lithium raw materials may be in the form of, for example, lithium carbonates, hydroxides, etc.

[0019] The term “precursor” or “transition metal precursor” in the present invention means the above “transition metal raw material.”

[0020] As explained above, when the precursor contains Mn, primary particle growth is promoted and durability is improved, but the specific surface area decreases and resistance and efficiency characteristics deteriorate due to the increase in the size of the primary particles, so the present invention solves the above problem by using an additive element that reduces the size of the primary particles.

[0021] The additive elements described above are transition metal precursors that can reduce the size of primary particles without participating in oxidation-reduction reactions during the charge-discharge process of manufacturing positive electrode active materials. That is, when an additive element is added to a precursor containing Mn, the average particle diameter of primary particles contained within secondary particles of the same particle diameter becomes smaller compared to a precursor without an additive element.

[0022] Therefore, by adding an additive element that reduces the size of the primary particles, the precursor has relatively smaller primary particles and a high BET specific surface area compared to conventional precursors under conditions where the average particle diameter of the secondary particles is substantially the same as that of conventional precursors. This allows for overcoming problems such as BET degradation, resulting in increased resistance, and decreased efficiency characteristics, which are problems of conventional precursors containing Mn.

[0023] The additive element may be evenly distributed throughout the precursor particle, primarily distributed in a specific region, or distributed only in a specific region. Furthermore, the effect of the additive element is exerted in the region where it is present, and its degree is proportional to the amount of the additive element.

[0024] When the additive element is distributed only in a specific region within the precursor particle or is mainly distributed in a specific region, the degree of expression of the primary particle reduction effect differs depending on the region of the precursor particle, and accordingly, the average particle diameter of the primary particle can be reduced, but the particle size distribution of the primary particle becomes wide, making it difficult to improve the electrochemical properties to the desired level.

[0025] Therefore, preferably, the additive element can be uniformly distributed throughout the precursor particle, where “uniform” means that when the additive element is distributed inside the particle, it is preferable that the content in all regions is constant, but due to technical limitations, a slight gradient of increase and / or decrease in the content in some regions is permitted.

[0026] When the additive elements are distributed relatively uniformly within the precursor particles, the degree of primary particle reduction is uniform in each region of the precursor particles, narrowing the particle size distribution of the primary particles and improving reproducibility.

[0027]

[0028] For reference, in the present invention, the form in which the additive element is included in the precursor may be the same in that the additive element is ultimately present in the positive electrode active material, but there is a clear difference compared to the case in which the additive element is included in the positive electrode active material by mixing the additive element raw material with the transition metal precursor and the lithium raw material and then firing it as in the past.

[0029] In general, in a cathode active material in which primary particles are aggregated into secondary particles, the overall size of the primary and secondary particles depends on the sizes of the primary and secondary particles in the transition metal precursor before firing. Therefore, if the primary particle size in the transition metal precursor is large, the primary particle size in the cathode active material cannot be small. Therefore, when additive elements are included in the mixed state of raw materials for firing as in the past, they cannot substantially contribute to a change in particle size, and thus cannot bring about a reduction in the primary particle size as intended in the present invention.

[0030] In addition, since the additive elements included in the conventional form exist in the form of a physical mixture with the already manufactured transition metal precursor and lithium raw material, it is difficult to distribute them uniformly within the precursor even when fired at high temperatures. In addition, since the transition metal precursor according to the present invention is manufactured by simultaneously chemically reacting the transition metal raw material and the additive element raw material during manufacturing, there is a clear difference from the conventional precursor just before firing, in which the additive elements are unevenly distributed due to simple physical mixing.

[0031] On the other hand, as in the present invention, if the additive element is controlled to be included in the transition metal precursor before mixing with the lithium raw material, the additive element can be evenly distributed throughout the precursor and the final product, the positive electrode active material, to exhibit a uniform effect throughout the particles, and ultimately, the size distribution of the primary particles can be manufactured more uniformly.

[0032]

[0033] The primary particles of the transition metal precursor according to the present invention generally have a rod or needle shape, as the plate-like primary particles of the typical precursor are reduced in size by the addition of an additive element. Furthermore, the reduction in the average particle diameter of these primary particles shortens the migration path of Li ions when manufacturing a cathode active material using the precursor, which can be effective in improving electrochemical characteristics.

[0034] For reference, the transition metal precursor that reduces the primary particle size by controlling the manufacturing environment such as pH and ammonia input during precursor manufacturing does not exhibit the above effect. The side of the plate-shaped precursor only shows a rod or needle shape, and does not affect the movement path of Li ions.

[0035]

[0036] In the above precursor stage, when the longer length of the shape is defined as the major axis and the shorter length as the minor axis, the "average particle diameter of the primary particles" in the present invention is defined as the length of the minor axis. Therefore, in the present invention, the "size reduction of the primary particles" due to the addition of the additive element can be said to mean that the average particle diameter of the primary particles, i.e., the minor axis, becomes shorter. However, since there are cases where the major axis also becomes shorter as the minor axis becomes shorter, resulting in an overall decrease in the size of the primary particles, the "size reduction of the primary particles" does not mean that only the minor axis of the primary particles becomes shorter.

[0037] Fig. 1a is a schematic diagram of a conventional transition metal precursor, and Fig. 1b is a schematic diagram of a transition metal precursor according to the present invention. For reference, the sizes of the precursor secondary particles shown in Figs. 1a and 1b are identical.

[0038] Compared to Fig. 1a, Fig. 1b shows that the sizes of the secondary particles are approximately the same, but the primary particles are generally smaller and have shorter minor axis lengths. Fig. 1a illustrates the concept of the average particle diameter of the primary particles defined in the present invention, as previously described.

[0039] The average particle size of these primary particles can be calculated by measuring the particle sizes of a large number of primary particles after processing them so that the cross-section of the secondary particles can be observed, and then calculating the average value, or by directly measuring the particle size from an SEM image of the secondary particles, or by calculating it mechanically using an FE-SEM, and various other methods can be considered.

[0040] Meanwhile, the secondary particles generally have a spherical shape, and their average particle diameter is defined as the D50 value according to the cumulative particle size distribution.

[0041]

[0042] As defined above, the transition metal precursor of the present invention has a specific volume of 20 to 200 cm, expressed by the following formula: 3 / g can satisfy the condition.

[0043] Specific volume (cm) 3 / g) = (average particle size of secondary particles) × (specific surface area of ​​secondary particles)

[0044] The above specific volume refers to the product of the surface area per unit mass of the precursor, measured using the BET method, and the average particle diameter of the secondary particles. Therefore, the specific volume is a parameter that can determine the volume per unit mass of the precursor.

[0045] In general, the specific surface area is an indicator of improving the reactivity with a lithium compound before heat treatment to manufacture a precursor into an active material, or the electrolyte contact area of ​​the active material after heat treatment. The specific surface area of ​​the precursor is improved due to the reduction in the primary particle size by the additive element according to the present invention. However, various factors, such as the average particle size of secondary particles in addition to the average particle size of the primary particles, are involved in the specific surface area of ​​the precursor, and it cannot be determined that the increase in BET is simply due to the reduction in the primary particle size of the additive element.

[0046] Meanwhile, since the specific volume is determined by the average particle size of the secondary particles as well as the specific surface area of ​​the precursor, under the same condition of the average particle size of the secondary particles, the higher the specific volume value, the higher the specific surface area of ​​the primary particles constituting the secondary particles, and it can be judged that the secondary particles have relatively smaller primary particles.

[0047] In addition, considering the mass per unit volume, i.e. density, which is the reciprocal of the specific surface area, the conventional precursor containing Mn has a specific volume of 20 cm, with the primary particles constituting the secondary particles being enlarged. 3 / g, and the precursor in which the primary particle size expansion is suppressed by the additive element according to the present invention has a specific volume that satisfies the above range, so that the overall specific surface area of ​​the primary particles and secondary particles is high.

[0048] On the other hand, the primary particle is so reduced that its specific volume is 200 cm 3 If it is greater than / g, the specific surface area can be improved, but the particle strength of the secondary particles can be reduced by the primary particles close to the fine particles, which is not desirable.

[0049] Preferably, the specific volume may be in the range of 50 to 180, and more preferably in the range of 80 to 150.

[0050] The above range can be subdivided according to the average particle size of the secondary particles, and the specific volume of the small particle precursor having an average particle size of 2 to 8 ㎛ of the secondary particles is 20 to 50 cm 3 / g is preferable, and the specific volume of the medium / large particle size precursor having an average particle size of 8 to 20 ㎛ of secondary particles is 70 to 200 cm 3 / g is preferable.

[0051] If the average particle size of each secondary particle is outside the specified range, the effect of suppressing the size expansion of the primary particle may be excessive or insufficient, making it difficult to achieve the purpose of the present invention.

[0052] One of the technical features of the present invention is to control the average particle diameter and specific volume of primary particles using additive elements. In addition to the additive elements presented in the present invention, methods for controlling the average particle diameter and specific volume of primary particles (such as changing the manufacturing environment) are known. However, as can be confirmed from the results of the examples and comparative examples described below, simply controlling the average particle diameter and specific volume of primary particles without additive elements does not achieve the desired level of electrochemical performance when manufacturing a transition metal precursor into a cathode active material.

[0053]

[0054] In one specific example, the transition metal precursor of the present invention may comprise a composition represented by the following chemical formula 1.

[0055] Ni a Mn b D1 c (OH)2(1)

[0056] In the above formula,

[0057] 0.6≤a<1, 0 <b≤0.3, 0<c≤0.1이고,

[0058] D1 is at least one element selected from Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W.

[0059] Preferably,

[0060] a+b+c=1,

[0061] It can be 0.65≤a<0.85, 0.15≤b≤0.3, 0.01≤c≤0.05.

[0062]

[0063] In another specific example, the transition metal precursor of the present invention may comprise a composition represented by the following chemical formula 2.

[0064] Ni a' (Co x Mn 1-x ) b' D2 c' (OH)2(2)

[0065] In the above formula,

[0066] 0.6≤a'<1, 0 <x≤0.05, 0<b'≤0.30, 0<c'≤0.1이고,

[0067] D2 is at least one element selected from Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W.

[0068] Compared to Chemical Formula 1, since it contains more Co, when some of the Mn content in the precursor is replaced with Co, the resistance and efficiency characteristics due to the added element are significantly improved, and there is an effect of improving battery conductivity.

[0069] However, if too much Mn is substituted with Co, no significant improvement in electrochemical properties due to the added element can be induced, so the Co content in the precursor may be appropriately 5 mol% or less based on the entire transition metal.

[0070] It may be possible to suppress primary particle expansion by simply replacing part of the Mn content of the main component with Co without adding additional elements, but in this case, it may be difficult to expect an increase in reactivity when manufacturing the precursor into an active material, and this can also be confirmed in the experimental results for Comparative Example 7 described later.

[0071] Preferably,

[0072] a'+b'+c'=1,

[0073] 0.65≤a'<0.85, 0.01≤x≤0.05, 0.15≤b'≤0.3, 0.01≤c'≤0.05.

[0074]

[0075] Among the elements listed above, Al may be particularly preferable as an additive element in the transition metal precursor of the present invention. Al having a small ionic radius 3+ Al has a stable primary particle structure without participating in oxidation-reduction reactions, so it can improve electrochemical properties even in small amounts. 3+ This is because it suppresses performance degradation due to Ni movement within this crystal structure.

[0076]

[0077] In one specific example, it may contain less than 30 mol% of Mn based on the total transition metal content, and may contain 2,000 to 8,000 ppm of the additive element.

[0078] As the Mn content increases, the effect of increasing the size of the primary particles increases, and the amount of additive elements required to suppress this also increases. However, as the amount of additive elements that reduce the size of the primary particles increases, fine particle control becomes difficult, and electrochemical characteristics may actually deteriorate.

[0079] When Mn is contained in an amount of 30 mol% or more, the primary particles become excessively enlarged, and the amount of additive elements required to reduce them to a desired level exceeds the level that can be differentially controlled. Therefore, the upper limit of Mn that the precursor can contain may be 30 mol%, as defined above, and preferably 25 mol%. In a nickel-based precursor containing Mn, the Ni content decreases as the Mn content increases, and therefore, if the Mn content exceeds the above range, the desired charge / discharge capacity cannot be secured.

[0080]

[0081] In one specific example, the mol% content ratio of the additive element and Mn in the secondary particle may be in the range of 1:15 to 1:3.

[0082] With regard to the optimal ratio of Mn and additive elements, when the content ratio is less than 1:15, the content of additive elements relative to Mn contained in the precursor is low, so primary particle expansion cannot be sufficiently suppressed, and thus a significant improvement in specific surface area cannot be obtained.

[0083] Conversely, when the content ratio is greater than 1:3, an excessive amount of additive elements is added compared to the Mn containing precursor, which excessively reduces the primary particle size, making fine particle control difficult and deteriorating the electrochemical characteristics due to the excessive amount of additive elements acting as resistance, which is not desirable.

[0084]

[0085] Since Ni may be important in terms of capacity increase, it may be included as an essential transition metal as described above in Chemical Formulas 1 and 2, and may have a content of 65 to 85 mol% based on the total transition metal content.

[0086] As the Ni content increases, the Mn content decreases and the primary particles become smaller, so a High-Ni precursor with a Ni content exceeding 85 mol% may have sufficiently small primary particles, but problems such as thermal stability and the risk of decomposition, rupture, and ignition due to external force in a charged state may arise, so it may be desirable to include it at 85 mol% or less. In addition, under the condition that the Ni content exceeds 85 mol%, the effect of reducing the primary particle size of the additive element is limited, and it may rather act as an impurity, making it difficult to expect a performance improvement effect.

[0087]

[0088] In one specific example, the average particle diameter of the primary particles may be in the range of 50 to 250 nm, the average particle diameter of the secondary particles may be in the range of 8 to 20 μm, and the specific surface area of ​​the precursor may be in the range of 7 to 20 m 2 / g can be in the range.

[0089]

[0090] First, with respect to the average particle size of the primary particles, in general, the primary particles of a precursor containing Mn without a separate additive element are expanded to the level of 300 to 800 nm, which reduces the specific surface area. However, in the present invention, the primary particles are reduced to the level of 50 to 250 nm by the additive element, so that the durability due to Mn can be secured, while the electrochemical characteristics can be improved by controlling the specific surface area. When the average particle size of the primary particles is smaller than 50 nm, the particle strength of the precursor secondary particles may be excessively deteriorated due to the primary particles close to fine particles, and conversely, when the average particle size of the primary particles is larger than 250 nm, the specific surface area cannot be improved to the desired level, which is not preferable. However, when the average particle size of the primary particles satisfies the above range, it is difficult for the electrochemical characteristics to reach the desired level when manufacturing a transition metal precursor as a cathode active material, and when the range of the average particle size of the primary particles is achieved by the additive element, the performance can be significantly improved.

[0091]

[0092] In addition, with respect to the average particle size of the secondary particles, when the size of the secondary particles is less than 4 ㎛, it is difficult to suppress the size expansion of the primary particles by the additive element, so the efficiency may be slightly improved, but it is difficult to secure resistance characteristics, while when the size of the secondary particles exceeds 20 ㎛, the packing density of the active material may decrease due to the increase in porosity, which may result in a decrease in capacity, and therefore is not preferable. A particularly preferable range may be a range of 8 to 20 ㎛ as defined above.

[0093] Meanwhile, with regard to the specific surface area of ​​the precursor, a conventional precursor containing Mn but not containing additive elements has an enlarged primary particle size of 4 to 8 m 2 / g represents the specific surface area, and the factor that usually has the greatest influence on the specific surface area is the particle size. By reducing the primary particles by adding elements while maintaining the size of the secondary particles at the desired level, the specific surface area of ​​the precursor can be improved to the above numerical range. In this regard, when the specific surface area is 7 m 2 / g or less, it is difficult to solve the problem of the prior art in which the resistance and efficiency characteristics deteriorate because the primary particle expansion suppression effect is minimal. On the other hand, if the specific surface area is 20 m 2 / If it exceeds g, the area in contact with the electrolyte when manufacturing the precursor as an active material becomes excessively large, which may be undesirable as the long-term life characteristics deteriorate.

[0094]

[0095] In one specific example, the transition metal precursor according to the present invention may have a ratio of the average particle diameter (Ds) of the secondary particles to the average particle diameter (Dp) of the primary particles (Ds / Dp) of 20 to 150.

[0096] When the average particle size ratio of the primary and secondary particles satisfies the above range, the size of the primary particles is smaller than that of the conventional precursor, so that a high specific surface area can be secured for the entire precursor particle.

[0097] If the additive element is added in excessive amounts, the primary particles may be excessively reduced, and as a result, if the average particle size ratio is less than 20, the average particle size of the primary particles may be excessively small compared to the secondary particles, which may weaken the particle strength. Conversely, if the additive element is added in small amounts, the primary particle reduction effect is minimal, and as a result, if the average particle size ratio is greater than 150, the resistance and efficiency characteristics may be reduced due to the enlargement of the primary particles, which is not desirable.

[0098] Preferably, the average particle size ratio (Ds / D p ) may be in the range of 30 to 130, and more preferably in the range of 40 to 110.

[0099]

[0100] In another specific example, the transition metal precursor according to the present invention is characterized by a grain size of the (101) plane measured by XRD of 15 nm or less.

[0101] The size of the primary particles can be controlled by changing the conditions of the manufacturing process during precursor manufacturing, but if the primary particles are reduced by changing the manufacturing method without adding elements, the grain size of the (101) plane measured by XRD is large. In general, the main method for controlling the average particle size of the primary particles is to control the process conditions during manufacturing by the coprecipitation method, such as changing the pH, temperature, and ammonia concentration. In this case, the grain size of the (101) plane measured by XRD is overgrown.

[0102] On the other hand, when the primary particle size is reduced by an additive element as in the present invention, the crystal grain size of the (101) plane is relatively small, so the interfacial resistance is reduced, and the capacity and output can be improved.

[0103]

[0104] The present invention also provides a cathode active material manufactured using the above transition metal precursor and a secondary battery including such cathode active material.

[0105] Since the manufacturing and composition of positive electrode active materials and the structure and manufacturing method of secondary batteries are well known in the art, a detailed description thereof is omitted in this specification.

[0106] As described above, the transition metal precursor for manufacturing a cathode active material according to the present invention has the effect of solving problems such as BET decrease, increase in resistance, and decrease in efficiency characteristics caused when Mn is included to increase durability in a precursor containing Ni for increasing capacity, for example, by including a specific additive element that reduces the size of primary particles.

[0107] Figure 1a is a schematic diagram of a conventional transition metal precursor;

[0108] FIG. 1b is a schematic diagram of a transition metal precursor according to one embodiment of the present invention;

[0109] Figure 2 is an SEM image of the transition metal hydroxide powder of Comparative Example 1 obtained in Experiment 1;

[0110] Figure 3 is a SEM image of the transition metal hydroxide powder of Example 1 obtained in Experiment 1;

[0111] Figure 4 is a SEM image of the transition metal hydroxide powder of Example 2 obtained in Experiment 1;

[0112] Figure 5 is an XRD graph provided in Experimental Example 3.

[0113] Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0114]

[0115] Comparative Example 1

[0116] A metal salt aqueous solution with a composition of Ni:Mn=75:25 was continuously supplied to a 30L CSTR reactor together with ammonia water and caustic soda water, and the ammonia concentration in the reactor was adjusted to 4,000 to 7,000 ppm and the pH to 12.1 to 12.6, respectively. Then, co-precipitation was performed for 2 hours under conditions of a stirring speed of 600 rpm and a reaction temperature of 60°C, to produce precursor seed to core particles having an average particle size of 5.5 to 6 μm.

[0117] Afterwards, a metal salt aqueous solution of the same composition was continuously supplied together with ammonia water and caustic soda aqueous solution, thereby lowering the pH to 11.4 to 11.7 and the ammonia concentration to 3,000 to 5,000 ppm, and increasing the particle size until the average particle diameter became 10 ㎛ to manufacture the final precursor.

[0118] The manufactured precursor was dried at 120°C for 20 hours through filtering and washing, and a secondary particle-shaped composite transition metal hydroxide powder with an average particle diameter of 10 μm was manufactured as a precursor.

[0119] The manufactured powder was photographed using a scanning electron microscope (SEM), and it was confirmed that the average particle diameter of the precursor primary particles was approximately 0.5 ㎛.

[0120]

[0121] Comparative Example 2

[0122] A metal salt aqueous solution having the same composition as Comparative Example 1 was continuously supplied while adjusting the ammonia concentration in the reactor to 4500 to 6000 ppm and pH to 12.6 to 13.0, and co-precipitation was performed for 2 hours under the conditions of a stirring speed of 800 rpm and a reaction temperature of 60°C, thereby producing seed particles having a D50 of 1.9 μm. Afterwards, the pH was lowered to 11.4 to 11.7 and the ammonia concentration to 3000 to 5000 ppm, thereby producing a composite transition metal hydroxide powder in the form of secondary particles having an average particle diameter of 4 μm as a precursor. It was confirmed by scanning electron microscopy (SEM) that the average particle diameter of the precursor primary particles was about 0.3 μm.

[0123]

[0124] Comparative Example 3

[0125] A transition metal hydroxide powder having an average particle size of primary particles of 0.25 ㎛ and an average particle size of secondary particles of 10 ㎛ was manufactured under the same experimental conditions as Comparative Example 1, except that the molar ratio (Ni:Mn) of the metal salt solution was adjusted to 85:15.

[0126]

[0127] Comparative Example 4

[0128] A transition metal hydroxide powder having an average particle size of 0.2 ㎛ of primary particles and an average particle size of 10 ㎛ of secondary particles was manufactured under the same experimental conditions as Comparative Example 1, except that the molar ratio (Ni:Mn) of the metal salt solution was adjusted to 90:15.

[0129]

[0130] Comparative Example 5

[0131] A transition metal hydroxide powder having an average particle size of 0.2 ㎛ of primary particles and an average particle size of 10 ㎛ of secondary particles was manufactured under the same experimental conditions as Comparative Example 1, except that the molar ratio (Ni:Mn) of the metal salt solution was adjusted to 95:05.

[0132]

[0133] Comparative Example 6

[0134] A transition metal hydroxide powder having an average particle size of 0.15 ㎛ of primary particles and an average particle size of 10 ㎛ of secondary particles was manufactured under the same experimental conditions as Comparative Example 1, except that the molar ratio (Ni:Mn) of the metal salt solution was adjusted to 75:25.

[0135]

[0136] Comparative Example 7

[0137] A transition metal hydroxide powder having an average particle size of 0.15 ㎛ of primary particles and an average particle size of 10 ㎛ of secondary particles was manufactured under the same experimental conditions as Comparative Example 1, except that the molar ratio (Ni:Co:Mn) of the metal salt solution was adjusted to 75:02:23.

[0138]

[0139] Example 1

[0140] A 30L CSTR reactor was continuously supplied with a metal salt aqueous solution with a composition of Ni:Mn=75:25 and 3000 ppm of Al together with ammonia water and caustic soda aqueous solution to control the ammonia concentration in the reactor to 4,000 to 7,000 ppm and the pH to 12.1 to 12.6, respectively. Then, the mixture was co-precipitated for 2 hours under the conditions of a stirring speed of 600 rpm and a reaction temperature of 60℃, thereby producing precursor seed particles with an average particle size of 5.5 to 6 ㎛. Thereafter, a metal salt aqueous solution with the same composition was continuously supplied together with ammonia water and caustic soda aqueous solution to control the pH downward to 11.4 to 11.7 and the ammonia concentration downward to 3,000 to 5,000 ppm, and the particle size was increased until the average particle size became 10 ㎛, thereby producing the final precursor.

[0141] The manufactured precursor was dried at 120°C for 20 hours through filtering and washing, and a secondary particle-shaped composite transition metal hydroxide powder with an average particle diameter of 10 μm was manufactured as a precursor.

[0142] The manufactured powder was photographed using a scanning electron microscope (SEM) and confirmed that the average particle size of the precursor primary particles was approximately 0.1 ㎛.

[0143]

[0144] Example 2

[0145] Transition metal hydroxide powder having an average particle size of 0.1 μm for primary particles and an average particle size of 10 μm for secondary particles was manufactured under the same experimental conditions as Example 1 except that the Al input amount was adjusted to 6000 ppm.

[0146]

[0147] Example 3

[0148] Transition metal hydroxide powder having an average particle size of 0.1 μm for primary particles and an average particle size of 10 μm for secondary particles was manufactured under the same experimental conditions as Example 1 except that the Al input amount was adjusted to 7500 ppm.

[0149]

[0150] Example 4

[0151] A metal salt aqueous solution having the same composition as Example 2 was continuously supplied to a reactor while adjusting the ammonia concentration in the reactor to 4500 to 6000 ppm and pH to 12.6 to 13.0, and co-precipitation was performed for 2 hours under the conditions of a stirring speed of 800 rpm and a reaction temperature of 60°C to produce seed particles having a D50 of 1.9 μm. Afterwards, the pH was lowered to 11.4 to 11.7 and the ammonia concentration to 3000 to 5000 ppm, thereby producing a composite transition metal hydroxide powder having an average particle size of 4 μm as a precursor for secondary particles. It was confirmed by scanning electron microscopy (SEM) that the average particle size of the primary particles was about 0.1 μm.

[0152]

[0153] Example 5

[0154] A transition metal hydroxide powder having an average particle size of 0.1 μm for primary particles and an average particle size of 10 μm for secondary particles was manufactured under the same experimental conditions as Example 2, except that the molar ratio (Ni:Co:Mn) of the metal salt solution was adjusted to 75:02:23.

[0155]

[0156] Example 6

[0157] A transition metal hydroxide powder having an average particle size of 0.15 μm for primary particles and an average particle size of 4 μm for secondary particles was manufactured under the same experimental conditions as Example 4, except that the molar ratio (Ni:Co:Mn) of the metal salt solution was adjusted to 75:02:23.

[0158]

[0159] Example 7

[0160] A transition metal hydroxide powder having an average particle size of 0.1 μm for primary particles and an average particle size of 10 μm for secondary particles was manufactured under the same experimental conditions as Example 2, except that the molar ratio (Ni:Co:Mn) of the metal salt solution was adjusted to 75:05:25.

[0161]

[0162] Example 8

[0163] A transition metal hydroxide powder having an average particle size of 0.1 μm for primary particles and an average particle size of 10 μm for secondary particles was manufactured under the same experimental conditions as Example 2, except that the molar ratio (Ni:Co:Mn) of the metal salt solution was adjusted to 90:00:10.

[0164]

[0165] Lithium secondary battery manufacturing

[0166] The transition metal hydroxide powders manufactured in each of the above comparative examples and examples were mixed with LiOH so that the molar ratio of Li and Metal was 1.03 to prepare a Li-transition metal mixed precursor powder, and then the powder was calcined at 750°C with air flowing for 18 hours to manufacture a cathode active material.

[0167] The positive electrode active material manufactured above was mixed with Super-P as a conductive agent and PVdF as a binder in a solvent, N-methylpyrrolidone, at a weight ratio of 98:5:2 to manufacture a positive electrode active material slurry, which was then applied onto an aluminum current collector. After drying at 120°C, it was rolled to manufacture an electrode. An electrode assembly was manufactured by using lithium metal as an anode together with the positive electrode manufactured above and interposing a porous polyethylene film as a separator therebetween, and the electrode assembly was placed inside a battery case, and an electrolyte was injected into the battery case to manufacture a lithium secondary battery. At this time, the electrolyte used was lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate (EC / DMC mixing volume ratio = 1:1).

[0168]

[0169] Experimental Example 1: SEM Image

[0170] SEM images were obtained for the transition metal hydroxide powders manufactured in Comparative Example 1 and Examples 1 and 2, respectively, under the following measurement conditions and are shown in FIGS. 2 to 4. FIG. 2 is an SEM image of the transition metal hydroxide powder of Comparative Example 1, FIG. 3 is an SEM image of the transition metal hydroxide powder of Example 1, and FIG. 4 is an SEM image of the transition metal hydroxide powder of Example 2.

[0171] [SEM measurement conditions]

[0172] - Model: HITACHI (S-4800)

[0173] - Resolution: 1.0㎚ 15㎸, 1.5㎚ 1㎸

[0174] - Magnification: x10,000

[0175] - Electron gun: Cold-cathode field emission type electron gun

[0176] - Accelerating voltage: 10~15㎸

[0177] - Detector: SE (BSE)

[0178]

[0179] First, when comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the primary particles are significantly smaller due to the added element. In addition, when comparing Examples 1 and 2, it can be seen that the primary particles become smaller when the content of the added element (Al) increases from 3000 ppm (Example 1) to 6000 ppm (Example 2).

[0180]

[0181] Experimental Example 2: Evaluation of Powder Characteristics and Electrochemical Properties

[0182] The specific surface area (BET) and tap density (TD) of the transition metal hydroxide powders manufactured in Comparative Examples 1 to 7 and Examples 1 to 8 were measured, and the specific volume obtained by multiplying the average particle diameter of the secondary particles by the surface area is shown in Table 1 below.

[0183] In addition, charge and discharge were performed under the condition of 0.1C for each lithium secondary battery manufactured above, and the resistance was calculated by dividing the applied current by the voltage change between 0 and 70 seconds from the start of discharge (V / I=R). In addition, the efficiency was measured by repeating 100 times at 45℃ under the conditions of 0.5C charge and 1.0C discharge for each lithium secondary battery manufactured above. The charge and discharge conditions were constant current (CC) / constant voltage (CV) in the voltage range of 4.3 to 2.7 V. The results are shown in Table 2 below.

[0184]

[0185]

[0186] Referring to the experimental results in Tables 1 and 2 above, the following facts can be confirmed.

[0187] First, referring to Comparative Examples 1 and 2, in a precursor containing Mn, when the particle size of the primary particle is small, the BET increases and the electrochemical characteristics improve (resistance decreases, efficiency increases), and referring to Comparative Examples 3 to 5, as the Mn content increases (as the Ni content decreases), the BET tends to gradually decrease due to the expansion of the primary particle, and there is a tendency for resistance to increase and efficiency to decrease accordingly, which is consistent with the tendency for the Mn content and the particle size of the primary particle to be proportional.

[0188] Second, referring to Comparative Example 6, the primary particles can be reduced by controlling the manufacturing method without a separate additive element, and the BET increases slightly because the primary particles become smaller, but compared to the examples, the performance improvement effect is inferior to the primary particle size reduction through the additive element, and referring to Comparative Example 7, a slight size reduction can be achieved by replacing some of the Mn content with Co (2 mol%) without an additive element, but no significant performance improvement effect can be obtained.

[0189] Third, referring to Examples 1 to 3, the effects according to the added element Al and its content can be confirmed, and the size reduction effect of the precursor primary particles due to Al, the increase in BET, and the increase in electrochemical characteristics can be confirmed, and it is shown that the electrochemical characteristics are superior to those of the same composition (Comparative Example 1) simply by adding Al. In particular, since the electrochemical characteristics are slightly deteriorated when the Al content is lower or higher than 6,000 ppm, the optimal Al content is understood to be around 6,000 ppm.

[0190] Fourth, referring to Example 4, Example 4 is an example in which the effect of adding Al to a small-sized precursor (4 μm) can be confirmed. Compared to a small-sized precursor (Comparative Example 2) of the same composition, it can be confirmed that it exhibits better electrochemical characteristics. However, compared to medium-sized precursors (Comparative Example 1 and Example 2), the small-sized precursor shows a relatively narrow range of improvement in electrochemical characteristics. These results in the small-sized precursor can be confirmed to be similar in Example 6 in which some of the Mn content was replaced with Co. When Examples 4 and 6 and other examples are comprehensively compared, it can be interpreted that the electrochemical performance is commonly improved by the added elements regardless of the average particle size of the secondary particles of the precursor, but the extent is more remarkable in medium / large-sized precursors.

[0191] Fifth, referring to Examples 5 and 6, these Examples are Examples in which a portion (2 to 5 mol%) of the Mn content is replaced with Co. In the case of Example 5, which is a medium-sized precursor, it can be confirmed that the small amount of Co further amplifies the effect of improving the electrochemical properties of the added element compared to Example 2, and when compared with Comparative Example 7 which has the same composition without the added element, it can be confirmed that a significant effect of improving the properties by Al is exhibited. In addition, in the case of Example 6, which is a small-sized precursor, it can be confirmed that performance is improved by substituting a portion of the Mn with Co compared to Example 3.

[0192] Sixth, referring to Example 7, which is an example in which a portion of the Ni content is replaced with Co while the Mn content is the same as in Example 4, it can be confirmed that although a small amount of Co improves the resistance characteristics, a slight decrease in the efficiency characteristics occurs due to a decrease in the Ni content.

[0193] Seventh, referring to Example 8, Example 8 is an example containing a high content of Ni, and when compared with Comparative Example 4, although there is a performance improvement effect due to the addition of Al, it can be confirmed that the improvement effect is inferior to Examples 1 to 7 due to the high content of Ni.

[0194] Eighth, when comparing Example 2 and Comparative Example 1, it can be confirmed that the specific volume of Example 2 is high, which means that the size of the primary particles existing in the secondary particles of the same particle size is larger in the Example than in the Comparative Example.

[0195]

[0196] Experimental Example 3: XRD Measurement

[0197] XRD analysis was performed on the transition metal hydroxide powders manufactured in Comparative Example 6 and Example 2, respectively, under the following measurement conditions, and the results are shown in Fig. 5.

[0198] <XRD 측정 조건>

[0199] - Power source: CuKα (pre-focus), wavelength: 1.541836Å

[0200] - Operating axis: 2θ / θ, Measurement method: Continuous, Counting unit: cps

[0201] - Start angle: 10.0°, End angle: 80.0°, Number of accumulations: 1

[0202] - Sampling width: 0.01°, Scan speed: 1.3° / min

[0203] - Voltage: 40kV, Current: 40mA

[0204] - Divergence slit: 0.2mm, divergence species limiting slit: 10mm

[0205] - Scatter slit: open, receiving slit: open

[0206] - Offset angle: 0°

[0207] - Goniometer radius: 285mm, optical system: focusing method

[0208] - Attachment: ASC-48 - Slit: Slit for D / teX Ultra

[0209] - Detector: D / teX Ultra

[0210] - Incident Monochrome: CBO

[0211] - Ni-Kβ filter: None

[0212] - Rotation speed: 30rpm

[0213]

[0214] In general, precursors for positive electrode active materials are arranged in a structure similar to a monoclinic system, and the representative main peaks that can be confirmed in the monoclinic system are (001), (100 or 010), and (101), where the (010) plane is the plane related to the behavior of Li.

[0215] When conducting XRD analysis of the precursor, a peak close to β-Ni(OH)2 can be obtained, and when referring to Figure 5, the peak occurring around 18 degrees indicates the intensity for the (001) plane, the peak occurring around 33 degrees indicates the intensity for the (100) plane, and the peak occurring around 38 degrees indicates the intensity for the (101) plane.

[0216]

[0217] Referring to Table 1 described above, the particle sizes of the primary particles of Example 2 and Comparative Example 6 are similar, but referring to FIG. 5, the XRD measurement results show that Example 2 has a (101) plane grain size of 15 nm or less, that is, 12.24 nm, whereas Comparative Example 6 has a grain size of 32.90 nm, which is approximately 2.5 times higher than that of Example 2. In other words, although the particle sizes of the primary particles are similar, there is a large difference in the orientation of crystallinity, so it is difficult to expect the precursor of Comparative Example 6 to have the same battery characteristic improvement effect as the precursor of Example 2.

[0218]

[0219] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. As a transition metal precursor for manufacturing a cathode active material in the form of secondary particles in which primary particles are aggregated, Contains Mn and at least one additional element selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo and W; The specific volume expressed by the following formula is 20 to 200 cm 3 A transition metal precursor characterized by / g: Specific volume (cm) 3 / g) = (average particle size of secondary particles) Х (specific surface area of ​​secondary particles).

2. A transition metal precursor according to claim 1, characterized in that it comprises a composition represented by the following chemical formula 1: There is no a Mn b D1 c (OH)2(1) In the above formula, 0.6≤a<1, 0 <b≤0.3, 0<c≤0.1이고, D1 is at least one element selected from Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W.

3. A transition metal precursor according to claim 1, characterized in that it comprises a composition represented by the following chemical formula 2: Ni a' (What x Mn 1-x ) b' D2 c' (OH)2(2) In the above formula, 0.6≤a'<1, 0 <x≤0.05, 0<b'≤0.30, 0<c'≤0.1이고, D2 is at least one element selected from Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W.

4. A transition metal precursor according to claim 1, characterized in that the additive element is Al.

5. A transition metal precursor characterized in that it comprises less than 30 mol% of Mn based on the total transition metal content in the first paragraph and comprises 2,000 to 8,000 ppm of the additive element.

6. A transition metal precursor, characterized in that the mol% content ratio of the additive element and Mn in the secondary particle is 1:15 to 1:3 in the first paragraph.

7. A transition metal precursor according to claim 1, characterized in that it contains 65 to 85 mol% of Ni based on the total transition metal content.

8. A transition metal precursor according to claim 1, characterized in that the average particle diameter of the primary particles is 50 to 250 nm.

9. A transition metal precursor according to claim 1, characterized in that the average particle diameter of the secondary particles is 8 to 20 ㎛.

10. In the first paragraph, the specific surface area is 7 to 20 m 2 A transition metal precursor characterized by being / g.

11. In the 9th paragraph, the average particle diameter (D) of the primary particles p ) average particle diameter of secondary particles (D s ) of the ratio (D) s / D p ) is in the range of 20 to 150.

12. A transition metal precursor characterized in that the grain size of the (101) plane measured by XRD in the first paragraph is 15 nm or less.

13. A cathode active material characterized by being manufactured using a transition metal precursor according to Article 1.

14. A secondary battery characterized by including a positive electrode active material according to Article 13.

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