Method for producing a positive electrode active material

Abstract

The present invention relates to a method of preparing a positive electrode active material, the method including the steps of forming a pre-sintered product by mixing a transition metal precursor having a nickel content of 70 atm% or more and a lithium raw material and performing primary sintering, and forming a lithium composite transition metal oxide by performing secondary sintering on the pre-sintered product, wherein the primary sintering is performed such that a spinel phase ratio of the pre-sintered product is in the range of 7% to 16%.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2020-0103341, filed on August 18, 2020, the disclosure of which is incorporated herein by reference.

[0002] The present application relates to a method of preparing a positive electrode active material, and more particularly, to a method of preparing a nickel-rich positive electrode active material having excellent capacity retention and resistance characteristics. BACKGROUND

[0003] Recently, as technology development and demand for mobile devices and electric vehicles increase, demand for secondary batteries as energy sources has significantly increased. Among these secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0004] Lithium transition metal composite oxides have been used as positive electrode active materials for lithium secondary batteries, and among these oxides, lithium cobalt composite metal oxides, such as LiCoO2, having high operating voltage and excellent capacity characteristics have been mainly used. However, LiCoO2 has poor thermal properties due to instability of the crystal structure caused by delithiation. In addition, since LiCoO2 is relatively expensive, there is a limitation in using a large amount of LiCoO2 as a power source for applications such as electric vehicles.

[0005] Lithium manganese composite metal oxides (LiMnO2 or LiMn2O4), lithium iron phosphate compounds (LiFePO4 or the like), or lithium nickel composite metal oxides (LiNiO2 or the like) have been developed as materials to replace LiCoO2. Among these materials, research and development of lithium nickel composite metal oxides, which can easily achieve a high-capacity battery due to high reversible capacity of about 200 mAh / g, have been more actively conducted. However, LiNiO2 has limitations in that the thermal stability of LiNiO2 is poorer than that of LiCoO2, and when internal short-circuiting occurs due to external pressure in a charged state, the positive electrode active material itself is decomposed, thereby causing a battery to rupture and catch fire. Therefore, as a method of improving low thermal stability while maintaining the excellent reversible capacity of LiNiO2, lithium transition metal oxides in which a part of nickel (Ni) is replaced with cobalt (Co), manganese (Mn), or aluminum (Al) have been developed.

[0006] For lithium ion batteries using lithium transition metal oxides, particularly nickel-rich lithium transition metal oxides as positive electrode active materials, since the amount of nickel oxidation increases due to high nickel content in the same voltage range, the amount of lithium ion movement increases, and as a result, there are limitations in terms of positive electrode stability reduction and secondary battery life characteristics deterioration.

[0007] Accordingly, there is a need to develop a Ni-rich positive electrode active material having excellent lifespan characteristics. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] One aspect of the present application provides a method of preparing a nickel-rich positive electrode active material, which can improve lifespan characteristics by controlling sintering conditions in the preparation process of the nickel-rich positive electrode active material.

[0010] TECHNICAL SOLUTION

[0011] According to one aspect of the present application, there is provided a method of preparing a positive electrode active material, the method including the steps of:

[0012] forming a pre-sintered product by mixing a transition metal precursor having a nickel content of 70 at% or more and a lithium raw material and performing primary sintering; and

[0013] forming a lithium composite transition metal oxide by performing secondary sintering on the pre-sintered product,

[0014] wherein the primary sintering is performed such that a spinel phase ratio of the pre-sintered product is in the range of 7% to 16%.

[0015] If necessary, after forming the pre-sintered product, the method can further include a step of measuring crystal phase information of the pre-sintered product and / or a step of pulverizing or classifying the pre-sintered product.

[0016] The transition metal precursor and the lithium raw material can be mixed in an amount such that a molar ratio of lithium:transition metal is in the range of 1.04:1 to 1.1:1.

[0017] Preferably, the transition metal precursor can be a compound represented by Formula 1 or Formula 2 below, and the lithium raw material can be LiOH·H2O.

[0018] [Formula 1]

[0019] Ni a Co b Mn c (OH)2

[0020] [Formula 2]

[0021] Ni a Co b Mn c OOH

[0022] In Formula 1 and Formula 2, 0.7≤a<1, 0.01≤b<0.3, 0.01≤c<0.3.

[0023] The primary sintering can be performed at a temperature range of 580°C to 680°C, and the secondary sintering can be performed at a temperature range of 700°C to 850°C.

[0024] M can be further mixed before the primary sintering 1 The raw material (wherein M 1 is at least one selected from aluminum (Al), silicon (Si), boron (B), tungsten (W), molybdenum (Mo), magnesium (Mg), vanadium (V), titanium (Ti), zinc (Zn), gallium (Ga), indium (In), ruthenium (Ru), niobium (Nb), tantalum (Ta), tin (Sn), strontium (Sr), lanthanum (La), cerium (Ce), praseodymium (Pr), and zirconium (Zr), and in this case, the M 1 The raw material can be aluminum hydroxide.

[0025] The lithium complex transition metal oxide prepared according to the preparation method of the present application can be a compound represented by the following Formula 3.

[0026] [Formula 3]

[0027] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0028] In Formula 3, 0≤x≤0.1, 0.7≤a<1, 0.01≤b<0.3, 0.01≤c<0.3, 0≤d<0.3, a+b+c+d=1,

[0029] M 1 is at least one selected from Al, Si, B, W, Mo, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Ta, Sn, Sr, La, Ce, Pr, and Zr.

[0030] Advantageous effects

[0031] Since the method of preparing a positive active material according to the present application improves the reactivity of lithium and transition metal precursors and the crystallinity of the final product by adjusting the primary sintering conditions so that the spinel phase content of the pre-sintered product is within a specific range, the method can prepare a nickel-rich positive active material having excellent lifespan characteristics.

[0032] In addition, the method of preparing a positive active material according to the present application, since the secondary sintering is performed after removing moisture and unnecessary gas during the primary sintering process, the density of the positive active material is increased, and the effect of improving the crystallinity can be obtained. DETAILED DESCRIPTION

[0033] Based on the principle that the inventor can appropriately define the meaning of the words or terms to best interpret the invention, it should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and should also be understood as having a meaning consistent with their meaning in the relevant technical context and the technical concept of the invention.

[0034] Because extensive research has been conducted to improve the initial capacity and lifetime characteristics of nickel-rich (Ni) cathode active materials, the inventors have discovered that, in the preparation process of Ni-rich cathode active materials, after a pre-sintered product is formed by a first sintering, a second sintering is performed. However, if the spinel ratio in the crystal phase of the pre-sintered product meets a specific range during the first sintering, the initial capacity and lifetime characteristics of the Ni-rich cathode active material can be improved, thus completing the present invention.

[0035] The invention will be described in more detail below.

[0036] The method for preparing a positive electrode active material according to the present invention comprises the following steps: (1) forming a pre-sintered product by mixing a transition metal precursor with a nickel content of 70 atm% or more and a lithium raw material and performing a first sintering; and (2) forming a lithium composite transition metal oxide by performing a second sintering on the pre-sintered product, wherein the first sintering is performed such that the spinel ratio of the pre-sintered product is in the range of 7% to 16%. After forming the pre-sintered product, if necessary, the method may further include a step of measuring the crystal phase information of the pre-sintered product and / or a step of pulverizing or classifying the pre-sintered product.

[0037] In the following text, each step of the method for preparing the positive electrode active material according to the present invention will be described in detail.

[0038] Step (1): One-time sintering step

[0039] First, the transition metal precursor and lithium raw material are mixed and sintered once to form a pre-sintered product.

[0040] In this case, the transition metal precursor may be a hydroxide or hydroxy oxide containing nickel, manganese and cobalt, wherein the amount of nickel relative to all transition metals may be more than 70 atm%, preferably 80 atm% to 99 atm, more preferably 80 atm% to 95 atm.

[0041] Specifically, the transition metal precursor may be a compound represented by Formula 1 or Formula 2.

[0042] [Formula 1]

[0043] Ni a Co b Mn c (OH)2

[0044] [Equation 2]

[0045] Ni a Co b Mn c OOH

[0046] In Equations 1 and 2, 0.7 ≤ a < 1, 0.01 ≤ b < 0.3, and 0.01 ≤ c < 0.3.

[0047] a represents the atomic ratio of nickel in all transition metals in the transition metal precursor, wherein a can satisfy 0.7≤a<1, preferably 0.8≤a≤0.99, and more preferably 0.8≤a≤0.95.

[0048] b represents the atomic ratio of cobalt in all transition metals in the transition metal precursor, wherein b can satisfy 0.01≤b<0.3, preferably 0.01≤b<0.2, and more preferably 0.01≤b≤0.15.

[0049] c represents the atomic ratio of manganese in all transition metals in the transition metal precursor, wherein c can satisfy 0.01≤c<0.3, preferably 0.01≤c<0.2, and more preferably 0.01≤c≤0.15.

[0050] As lithium feedstock, lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O) etc.), hydroxides (e.g., lithium hydroxide etc.), nitrates (e.g., lithium nitrate (LiNO3) etc.) or chlorides (e.g., lithium chloride (LiCl) etc.) can be used, but among them, the lithium feedstock can be LiOH·H2O in particular.

[0051] Ideally, the transition metal precursor and lithium feedstock can be mixed in amounts such that the lithium:transition metal molar ratio is in the range of 1.04:1 to 1.1:1, preferably 1.05:1 to 1.1:1, and more preferably 1.06:1 to 1.1:1. When the lithium:transition metal molar ratio is less than 1.04:1, the electrochemical performance of the cathode active material may deteriorate because the degree of cation mixing becomes severe and the hexagonal crystal arrangement of the lattice structure is disrupted. When the lithium:transition metal molar ratio is greater than 1.1:1, excess lithium may not be inserted into the lattice structure of the cathode active material but remains as an impurity on the surface, causing gelation during cathode slurry preparation. This not only makes it difficult to form a uniform slurry but also increases the amount of gas generated during battery operation, potentially reducing stability and long-term lifespan.

[0052] In this invention, the first sintering is performed such that the spinel content in the pre-sintered product is in the range of 7% to 16%, for example, 8% to 15%. According to the inventors' research, when the spinel content of the pre-sintered product meets the above range, excellent effects on improved lifetime characteristics can be obtained, and specifically, a significant effect on improved electrical resistance characteristics can be achieved.

[0053] The spinel ratio of the pre-sintered product varies depending on complex factors such as sintering temperature, sintering time, type of raw materials used, and mixing ratio of raw materials. Therefore, in order to control the spinel ratio of the pre-sintered product within the above-mentioned range, it is necessary to take into account the type of raw materials used and the mixing ratio of raw materials to appropriately adjust the sintering temperature or sintering time.

[0054] Specifically, in this invention, the primary sintering can be carried out at a temperature range of 580°C to 680°C, for example, 600°C to 650°C, for 1 hour to 15 hours, for example, 3 hours to 10 hours. When the primary sintering temperature and sintering time meet the above ranges, the ratio of the formed spinel phase is within the desired range.

[0055] Furthermore, sintering can be performed in an air atmosphere or an oxygen atmosphere. Compared to sintering in an inert atmosphere, sintering in an air atmosphere or an oxygen atmosphere promotes the precursor oxidation reaction.

[0056] Although not strictly necessary, prior to a single sintering step, in addition to the transition metal precursor and lithium feedstock, an element (Mn) selected from aluminum (Al), silicon (Si), boron (B), tungsten (W), molybdenum (Mo), magnesium (Mg), vanadium (V), titanium (Ti), zinc (Zn), gallium (Ga), indium (In), ruthenium (Ru), niobium (Nb), tantalum (Ta), tin (Sn), strontium (Sr), lanthanum (La), cerium (Ce), praseodymium (Pr), and zirconium (Zr) may be further mixed (Mn). 1 M of the element 1 Raw materials. M is further mixed before primary sintering. 1 Given the raw materials, it is possible to prepare materials doped with M. 1 M contained in raw materials 1 A positive electrode active material of an element. For example, the M... 1 Raw materials can contain M 1 Acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides of an element (i.e., at least one metallic element selected from Al, Si, B, W, Mo, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Ta, Sn, Sr, La, Ce, Pr, and Zr). In M 1In the case of Al, the M 1 The raw material can be aluminum hydroxide.

[0057] After the pre-sintered product is formed by the above method, if necessary, an additional step of measuring the crystal phase information of the pre-sintered product can be performed.

[0058] For example, the step of measuring the crystal phase information of the pre-sintered product can be performed by collecting a sample of the pre-sintered product and then measuring the spinel ratio in the crystal phase by performing X-ray diffraction (XRD) analysis. That is, the spinel ratio can be calculated by using XRD data measured for the pre-sintered product and by measuring the intensity contribution of each phase, which is refined by Rietveld, for both the cubic phase (NiO / LiN2O4) and the layered phase (LiNiO2).

[0059] After measuring the crystal phase information of the pre-sintered product as described above, a positive electrode active material with excellent initial capacity and lifetime characteristics can be prepared by secondary sintering when the spinel ratio of the pre-sintered product is in the range of 7% to 16%.

[0060] Furthermore, after the first sintering, if necessary, the preparation method of the present invention may also include a step of pulverizing and / or classifying the pre-sintered product. When the additional step of pulverizing and / or classifying the pre-sintered product is performed, the moisture and gases generated during the first sintering process can be removed, and the mixing process can be carried out more effectively. Therefore, the sintering uniformity in the second sintering process is improved, and the quality uniformity of the finally prepared positive electrode active material can be improved.

[0061] Step (2): Secondary sintering step

[0062] Next, the pre-sintered product is subjected to secondary sintering to form a lithium composite transition metal oxide.

[0063] The secondary sintering is intended to transform the spinel phase of the pre-sintered product into a layered phase, wherein the secondary sintering can be carried out at a temperature 100°C to 200°C higher than the primary sintering temperature, for example, at a temperature 100°C to 180°C higher than the primary sintering temperature.

[0064] When the difference between the secondary sintering temperature and the primary sintering temperature is less than 100℃, the spinel phase cannot smoothly transform into a layered phase. However, when the difference between the secondary sintering temperature and the primary sintering temperature is greater than 200℃, the positive electrode active material particles are severely agglomerated, making it difficult to disperse them during the preparation of the positive electrode slurry and to coat the positive electrode slurry to a uniform thickness, which may reduce processability.

[0065] Specifically, the secondary sintering can be carried out in a temperature range of 700°C to 850°C, preferably 700°C to 800°C, and more preferably 720°C to 800°C.

[0066] The secondary sintering can be carried out for 1 hour to 15 hours, for example, 3 hours to 10 hours.

[0067] Furthermore, secondary sintering can be performed in an air atmosphere or an oxygen atmosphere. Compared to sintering in an inert atmosphere, secondary sintering in an air atmosphere or an oxygen atmosphere promotes precursor oxidation, crystal growth, and phase transformation.

[0068] The lithium composite transition metal oxide prepared according to the preparation method of the present invention can be a compound represented by the following formula 3.

[0069] [Formula 3]

[0070] Li 1+x [Ni a Co b Mn c M 1 d O2

[0071] In Equation 3, M 1 It is at least one element selected from Al, Si, B, W, Mo, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Ta, Sn, Sr, La, Ce, Pr, and Zr.

[0072] 1+x represents the atomic ratio of lithium to all transition metals, where x satisfies 0≤x≤0.1, preferably 0.04≤x≤0.1, more preferably 0.05≤x≤0.1, for example 0.06≤x≤0.1.

[0073] a represents the atomic ratio of nickel in all transition metals in the lithium composite transition metal oxide, wherein a can satisfy 0.7≤a<1, preferably 0.8≤a≤0.99, and more preferably 0.8≤a≤0.95.

[0074] b represents the atomic ratio of cobalt in all transition metals in the lithium composite transition metal oxide, wherein b can satisfy 0.01≤b<0.3, preferably 0.01≤b<0.2, and more preferably 0.01≤b≤0.15.

[0075] c represents the atomic ratio of cobalt in all transition metals in the lithium composite transition metal oxide, wherein c can satisfy 0.01≤c<0.3, preferably 0.01≤c<0.2, and more preferably 0.01≤c≤0.15.

[0076] d represents the M in the lithium composite transition metal oxide. 1 The atomic ratio of the elements, where d can satisfy 0≤d<0.3, preferably 0≤d≤0.2.

[0077] Furthermore, in Equation 3, a+b+c+d=1.

[0078] The positive electrode active material prepared according to the method of the present invention has better capacity retention and resistance characteristics than conventional nickel-rich positive electrode active materials.

[0079] Example

[0080] The invention will now be described in detail with reference to specific embodiments. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments described herein. Rather, these exemplary embodiments are provided so that the description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0081] Example 1

[0082] Adding the transition metal precursor Ni 0.88 Co 0.05 Mn 0.07 Al(OH)2 and LiOH·H2O were mixed to make the molar ratio of Li:transition metal 1.07:1. After mixing Al(OH)3, the mixture was sintered at 600°C in an oxygen atmosphere for 5 hours to prepare a pre-sintered product. The pre-sintered product was then pulverized using an air classifier mill (ACM).

[0083] The spinel ratio was measured by Ritwald refinement analysis of the XRD data, which was obtained by X-ray diffraction analysis (Bruker D4 Endeavor) of the pre-sintered product using HighScore software.

[0084] As a result of the measurements, it was found that the proportion of spinel in the crystal phase of the pre-sintered product was 13.5%.

[0085] Next, lithium composite transition metal oxide LiNi was prepared by secondary sintering the pre-sintered product at 765°C in an oxygen atmosphere for 5 hours. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2. After pulverizing, washing and drying the lithium composite transition metal oxide, the lithium composite transition metal oxide powder is mixed with 0.1% by weight of H3BO3 and heat-treated in air at 295°C for 5 hours to prepare B-coated positive electrode active material powder.

[0086] Example 2

[0087] The pre-sintered product and the positive electrode active material powder were prepared in the same manner as in Example 1, but the sintering temperature during the preparation of the pre-sintered product was 650°C. It was found that the spinel content in the crystal phase of the pre-sintered product was 9.0%.

[0088] Example 3

[0089] The pre-sintered product and the positive electrode active material powder were prepared in the same manner as in Example 1, but the molar ratio of Li to transition metal was 1.09:1 during the preparation of the pre-sintered product. It was found that the spinel content in the crystal phase of the pre-sintered product was 12.0%.

[0090] Comparative Example 1

[0091] The pre-sintered product and positive electrode active material powder were prepared in the same manner as in Example 1, but the sintering temperature was 550°C during the preparation of the pre-sintered product. It was found that the spinel content in the crystal phase of the pre-sintered product was 18.2%.

[0092] Comparative Example 2

[0093] The pre-sintered product and the positive electrode active material powder were prepared in the same manner as in Example 1, but the sintering temperature was 700°C during the preparation of the pre-sintered product. It was found that the spinel content in the crystal phase of the pre-sintered product was 6.2%.

[0094] Comparative Example 3

[0095] The pre-sintered product and the positive electrode active material powder were prepared in the same manner as in Example 1, but the molar ratio of Li to transition metal was 1.03:1 during the preparation of the pre-sintered product. It was found that the spinel content in the crystal phase of the pre-sintered product was 16.2%.

[0096] Experimental Example

[0097] Each of the positive electrode active materials, conductive materials (FX35), and binders (a mixture of KF9700 and BM730H in a weight ratio of 1.35:0.15) prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were mixed in N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then rolled to a porosity of 24% to prepare individual positive electrodes.

[0098] A lithium (Li) metal disk is used as the negative electrode.

[0099] After fabricating an electrode assembly by placing a separator between the positive and negative electrodes, a lithium secondary battery is fabricated by placing the electrode assembly in a battery case and then injecting an electrolyte into the case. In this case, an electrolyte is used as the electrolyte, wherein 1M LiPF6 is dissolved in an organic solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 3:3:4.

[0100] Each lithium secondary battery prepared as described above was charged at 25°C with a constant current of 0.1C to 4.25V (cutoff current 0.05C) in constant current / constant voltage (CC / CV) mode, and then discharged to 3.0V in CC mode to measure the initial discharge capacity. In this case, 1C = 200mA / g was set.

[0101] In addition, the charge and discharge cycles were repeated 30 times at a constant current of 0.33C within the range of 3.0V to 4.25V at 45°C to measure the capacity retention rate and the rate of increase in resistance relative to the resistance 60 seconds after the start of discharge in each cycle. The measurement results are shown in Table 1 below.

[0102] [Table 1]

[0103]

[0104] Referring to [Table 1], for secondary batteries that used the positive electrode active materials of Examples 1 to 3 (prepared by performing a single sintering such that the spinel ratio of the pre-sintered product was 7% to 16%), it can be confirmed that after 30 cycles, the capacity retention rate was higher and the resistance increase rate was lower compared to secondary batteries that used the positive electrode active materials of Comparative Examples 1 to 3 (prepared such that the spinel ratio of the pre-sintered product was less than 7% or greater than 16%).

Claims

1. A method for preparing a positive electrode active material, the method comprising the following steps: A pre-sintered product is formed by mixing a transition metal precursor with a nickel content of 70 atm% or higher and a lithium feedstock, followed by a single sintering process; and Lithium composite transition metal oxides are formed by secondary sintering of the pre-sintered product. The first sintering is performed such that the spinel content of the pre-sintered product is in the range of 7% to 16%. The first sintering is carried out in a temperature range of 580°C to 680°C. The secondary sintering is carried out at a temperature 100°C to 200°C higher than the primary sintering temperature. The secondary sintering is carried out in a temperature range of 700°C to 850°C. The transition metal precursor and the lithium feedstock are mixed in amounts such that the lithium:transition metal molar ratio is in the range of 1.04:1 to 1.1:

1. The aluminum hydroxide is further mixed with the transition metal precursor with a nickel content of 70 atm% or more and the lithium raw material. The lithium composite transition metal oxide mentioned above is a compound represented by Formula 3: [Formula 3] Li 1+x [Ni a Co b Mr c M 1 d ]O2 in, In equation 3, 0 ≤ x ≤ 0.1, 0.7 ≤ a < 1, 0.01 ≤ b < 0.3, 0.01 ≤ c < 0.3, 0 ≤ d < 0.3, and a + b + c + d = 1. M 1 It is at least one element selected from Al, Si, B, W, Mo, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Ta, Sn, Sr, La, Ce, Pr, and Zr.

2. The method according to claim 1, further comprising, after forming the pre-sintered product, a step of measuring the crystal phase information of the pre-sintered product.

3. The method according to claim 1, further comprising, after forming the pre-sintered product, a step of pulverizing or classifying the pre-sintered product.

4. The method according to claim 1, wherein the transition metal precursor is a compound represented by formula 1 or formula 2: [Formula 1] Ni a What b Mn c (OH)2 [Equation 2] Ni a Co b Mr c OOH in, In Equations 1 and 2, 0.7 ≤ a < 1, 0.01 ≤ b < 0.3, and 0.01 ≤ c < 0.

3.

5. The method according to claim 1, wherein the lithium raw material is LiOH·H2O.

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