Positive electrode active material precursor for secondary battery, and positive electrode active material

Abstract

A positive electrode active material precursor according to one embodiment of the present invention is a precursor containing a plurality of hydroxide particles, and can satisfy the following relational expression 1 in an XRD pattern obtained by Rietveld fitting according to the results of X-ray diffraction analysis using CuK [alpha] rays: 0.82 < = FWHM (102) < = 1.22, and can satisfy the following relational expression 1: 0.82 < = FWHM (102) < = 1.22. A positive electrode active material precursor according to one embodiment of the present invention is a precursor containing a plurality of oxide particles, and can satisfy the following relational expression 2 in an XRD pattern obtained by Rietveld fitting according to the results of X-ray diffraction analysis by CuK [alpha] rays: 127 < = XRD peak integral width / 4tan [theta] < = 137, in relational expression 1, x = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, y = 1, the FWHM (102) is the full width at half maximum (deg., 2 [theta]) of the (102) crystal plane at an XRD peak defined by a hexagonal lattice having an R-3m space group, and in the relational expression 2, the XRD peak integral width is the value obtained by dividing the area of the XRD peak by the height of the XRD peak, and [theta] is the Bragg angle of the peak.

Description

Technical Field

[0001] The present invention relates to a precursor of a positive electrode active material for a secondary battery and a positive electrode active material prepared from the precursor of the positive electrode active material. The precursor of the positive electrode active material relates to a precursor in the form of a hydroxide and a precursor in the form of an oxide. Background Art

[0002] With the development of portable mobile electronic devices such as smart phones, MP3 players, and tablet computers, the demand for secondary batteries capable of storing electric energy has increased explosively. In particular, with the emergence of electric vehicles, large and medium-sized energy storage systems, and portable devices that require high energy density, the demand for lithium secondary batteries is continuously increasing.

[0003] As a lithium composite oxide included in a positive electrode active material, a recently remarkable substance is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z )O 2 (In this case, x, y, and z are atomic fractions of respective independent oxide constituent elements, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, and 0 < x + y + z ≤ 1). Compared with the positive electrode active material LiCoO 2 actively studied and used in the past, since this positive electrode active material is used at a high voltage, it has the advantage of high output capacity, and since the Co content is relatively low, it has the advantage of low price.

[0004] However, with the insertion and extraction of lithium ions during charge and discharge, such a lithium composite oxide is accompanied by volume changes. During charge and discharge, there are problems such as a sharp volume change in the primary particles of the lithium composite oxide, or the generation of cracks in the secondary particles with repeated charge and discharge, or the collapse of the crystal structure or the phase change of the crystal structure.

[0005] In order to compensate for this disadvantage, as a positive electrode active material for a secondary battery, the demand for a nickel (Ni)-rich system - high nickel positive electrode active material in which the content of nickel (Ni) is 50 mol% or more relative to the total content of transition metals other than lithium (Li) has started to increase.

[0006] However, although such a nickel-rich positive electrode active material has the advantage of high energy density, with the increase in the Ni content, due to the increase in structural instability caused by Li / Ni cation mixing, physical fracture of internal particles due to microcracks, and the aggravation of electrolyte depletion, etc., there is a problem that the life characteristics deteriorate rapidly at room temperature and high temperature. Summary of the Invention

[0007] Technical issues

[0008] The present invention aims to control the physical properties of a cathode active material prepared by controlling the physical properties of cathode active material precursor particles, and improve life characteristics by applying the cathode active material to a secondary battery.

[0009] Technical Solution

[0010] The positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of hydroxide particles. According to the results of X-ray diffraction (XRD) analysis using CuKα rays, the XRD spectrum obtained by Rietveld fitting can satisfy the following equation 1.

[0011] Relationship 1: 0.82 ≤ FWHM (102) ≤1.22

[0012] In the above equation 1, the above FWHM (102) It refers to the full width at half maximum (FWHM (deg., 2θ)) of the (102) crystal plane at the XRD peak defined by the hexagonal lattice having the R-3m space group.

[0013] Furthermore, the cathode active material precursor according to one embodiment of the present invention is a precursor including a plurality of oxide particles, and according to the results of X-ray diffraction analysis using CuKα rays, the following equation 2 can be satisfied in the XRD spectrum obtained by Rietveld fitting.

[0014] Relationship 2: 127 ≤ XRD peak integral breadth / 4tanθ ≤ 137

[0015] In the above relational expression 2, the XRD peak integrated width is the value of "the area of ​​the XRD peak" divided by the "height of the XRD peak", and θ is the Bragg angle of the peak.

[0016] As one embodiment, the particles contained in the positive electrode active material may be first particles having an average particle size (D50) of 8 μm or more, and may further include second particles having an average particle size (D50) of 7 μm or less.

[0017] As one embodiment, the positive electrode active material precursor including the oxide particles may be prepared from the positive electrode active material precursor including the hydroxide particles.

[0018] As one embodiment, the average porosity A of the positive electrode active material particles contained in the positive electrode active material may be 5%≤A≤7%.

[0019] As one embodiment, the positive electrode active material particles contained in the positive electrode active material may include first particles having an average particle size (D50) of 8 μm or more, and second particles having an average particle size (D50) of 7 μm or less.

[0020] As one embodiment, the positive electrode active material particles contained in the positive electrode active material may include a coating oxide occupying at least a portion of one or more of the surface of the secondary particles or the grain boundary between the primary particles and the surface of the primary particles.

[0021] The positive electrode according to one embodiment of the present invention may include the positive electrode active material described above.

[0022] A secondary battery according to one embodiment of the present invention may include the above-mentioned positive electrode active material.

[0023] Effects of the Invention

[0024] As an effect, the present invention can control the physical properties of a cathode active material prepared by controlling the physical properties of cathode active material precursor particles, and can improve life characteristics by applying the cathode active material thereof to a secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The cross-sectional SEM images of the positive electrode active materials of the examples and comparative examples of the present invention are shown.

[0026] Figure 2 The results of measuring the particle strength of oxide precursors of Examples of the present invention and Comparative Examples are shown.

[0027] Figure 3 The results of measuring the change rate of the average particle size (D50) of the oxide precursors of the examples of the present invention and the comparative examples after pressurization are shown. DETAILED DESCRIPTION

[0028] Expressions such as "comprising" and the like used in this specification should be understood as open-ended terms implying the possibility of including other structures.

[0029] The terms "preferred" and "preferably" used in this specification refer to embodiments of the present invention that can provide specified advantages under specified circumstances. However, other embodiments are not intended to be excluded from the scope of the present invention.

[0030] Furthermore, unless otherwise indicated in the context, singular forms used in the specification and the appended claims may be intended to include plural forms as well.

[0031] On the other hand, the following technical features relate to an embodiment for achieving the above-mentioned desired effects of the present invention.

[0032] That is, the positive electrode active material precursor particles and the positive electrode active material particles according to one embodiment of the present invention include the technical features of one embodiment described below, and thus when applied to a secondary battery, the battery characteristics can be significantly improved.

[0033] The present invention relates to a positive electrode active material precursor and a positive electrode active material for a secondary battery. The type of the secondary battery of the present invention is not limited, as long as it is a battery that can convert external electrical energy into chemical energy and store it for reuse. As a more preferred embodiment, the present invention may relate to a positive electrode active material precursor and a positive electrode active material for a lithium ion secondary battery.

[0034] First, the cathode active material precursor of the present invention will be described.

[0035] On the other hand, in this specification, the cathode active material precursor including a plurality of hydroxide particles may be named “hydroxide precursor”, and the cathode active material precursor including a plurality of oxide particles may be named “oxide precursor” for explanation.

[0036] The cathode active material precursor according to one embodiment of the present invention is a precursor including a plurality of hydroxide particles. According to the results of X-ray diffraction analysis using CuKα rays, the XRD pattern obtained by Rietveld fitting can satisfy the following equation 1.

[0037] Relationship 1: 0.82 ≤ FWHM (102) ≤1.22,

[0038] In the above equation 1, the above FWHM (102) It refers to the full width at half maximum of the (102) crystal plane at the XRD peak defined by the hexagonal lattice with the R-3m space group.

[0039] In the present invention, during the XRD analysis process, the full width at half maximum (FWHM) value may produce deviations or errors depending on various variables such as the conditions of the analysis equipment, the X-ray source, and the measurement conditions. Therefore, correction is performed using the full width at half maximum of a corundum disc as a standard sample.

[0040] In the present invention, the corundum grinding disc used is a NIST corundum grinding disc.

[0041] In the present invention, X-ray diffraction analysis is performed by using CuKα radiation. The measurement was performed using a Bruker D8 Advance diffractometer at a step size (° / step) of 0.01° / step and a measurement time of 0.05 s / step.

[0042] As an embodiment, in the above equation 1, FWHM (102) It may be 0.9 or more or 1.1 or less.

[0043] As one embodiment, the hydroxide particles may include nickel.

[0044] As one embodiment, the hydroxide particles may further include one or more selected from cobalt (Co), aluminum (Al), and manganese (Mn).

[0045] As one embodiment, the hydroxide particles may be represented by the following Chemical Formula 1.

[0046] Chemical formula 1:

[0047] Ni x Co y M 1-x-y (OH) 2

[0048] In the above Chemical Formula 1, M is selected from the group consisting of Zr, Mn, Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.5≤x≤1.0, 0.0≤y≤0.4, and 0.0≤1-xy≤0.4.

[0049] As one embodiment, the hydroxide particles may be represented by the following Chemical Formula 1-1.

[0050] Chemical formula 1-1:

[0051] Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ (OH) 2

[0052] In the above chemical formula 1-1, M1 is Al or Mn, M2 is selected from the group consisting of Zr, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.5≤x'≤1.0, 0.0≤y'≤0.4, 0.0≤z'≤0.4, 0.0≤1-x'-y'-z'≤0.4.

[0053] As one embodiment, in the above Chemical Formula 1 and / or Chemical Formula 1-1, x and / or x' representing the molar percentage of nickel relative to the total molar percentage of transition metals may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, it may be a high nickel hydroxide in which x and / or x' is 0.8 or more or 0.9 or more.

[0054] As one embodiment, in the above Chemical Formula 1 and / or Chemical Formula 1-1, y and / or y' representing the molar percentage of cobalt relative to the total molar percentage of transition metals may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0055] The positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of oxide particles. According to the results of X-ray diffraction analysis using CuKα rays, the XRD pattern obtained by Rietveld fitting can satisfy the following equation 2.

[0056] Relationship 2: 127 ≤ XRD peak integral width / 4tanθ ≤ 137

[0057] In the above relational expression 2, the XRD peak integrated width is a value obtained by dividing the "XRD peak area" by the "XRD peak height".

[0058] In the above relational expression 2, since the value of "XRD peak integrated width / 4tanθ" is derived from the intrinsic value of the sample, it does not matter whether any peak of any surface of the sample is selected for measurement. As an example, the value of "XRD peak integrated width / 4tanθ" can be a value measured at the peak of the (200) crystal plane.

[0059] The above-mentioned “XRD peak area” and “XRD peak height” refer to values ​​corrected to subtract the background, and the background correction is performed by a common method.

[0060] The above θ is the Bragg angle of the peak.

[0061] As one embodiment, in the above-mentioned relational expression 2, “XRD peak integrated width / 4tanθ” may be 129 or more or 135 or less.

[0062] As one embodiment, the oxide particles may include nickel (Ni).

[0063] As one embodiment, the oxide particles may further include one or more selected from cobalt (Co), aluminum (Al), and manganese (Mn).

[0064] As one embodiment, the oxide particles may be represented by the following Chemical Formula 2.

[0065] Chemical formula 2:

[0066] Ni x Co y M 1-x-y O 2

[0067] In the above Chemical Formula 2, M is selected from the group consisting of Zr, Mn, Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.5≤x≤1.0, 0.0≤y≤0.4, and 0.0≤1-xy≤0.4.

[0068] As one embodiment, the oxide particles may be represented by the following Chemical Formula 2-1.

[0069] Chemical formula 2-1:

[0070] Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ O 2

[0071] In the above chemical formula 2-1, M1 is Al or Mn, M2 is selected from the group consisting of Zr, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.5≤x'≤1.0, 0.0≤y'≤0.4, 0.0≤z'≤0.4, 0.0≤1-x'-y'-z'≤0.4.

[0072] As one embodiment, in the above Chemical Formula 2 and / or Chemical Formula 2-1, x and / or x' representing the molar percentage of nickel relative to the total molar percentage of transition metals may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, it may be a high nickel hydroxide in which x and / or x' is 0.8 or more or 0.9 or more.

[0073] As one embodiment, in the above Chemical Formula 2 and / or Chemical Formula 2-1, y and / or y' representing the molar percentage of cobalt relative to the total molar percentage of transition metals may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0074] On the other hand, the oxide precursor can be prepared by oxidizing the hydroxide precursor.

[0075] More specifically, the oxide precursor may be prepared by oxidizing the hydroxide precursor through heat treatment. In this case, the heat treatment temperature may be 300°C to 500°C.

[0076] As one embodiment, the positive electrode active material precursor may be in a unimodal form, and the average particle size (D50) of the positive electrode active material precursor particles may be 1 μm to 30 μm, more preferably, 8 μm to 20 μm.

[0077] Furthermore, as another more preferred embodiment, in the positive electrode active material precursor of the present invention, the hydroxide particles and / or oxide particles contained in the above-mentioned positive electrode active material precursor may be first particles having an average particle size (D50) of 8 μm or more or 10 μm or more, and the above-mentioned positive electrode active material precursor may be a bimodal form further comprising second particles having an average particle size (D50) of 7 μm or less or 5 μm or less.

[0078] In this manual, D 50 It is the particle size at 50% of the cumulative distribution of particle sizes according to the area, and can be measured by a laser diffraction method. Specifically, the powder to be tested can be dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device to measure the difference in diffraction patterns according to the particle size when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0079] As one embodiment, when the above-mentioned positive electrode active material precursor is in a bimodal form, when the weight of the first particles contained in the above-mentioned positive electrode active material precursor is set to w1, and the weight of the second particles contained in the above-mentioned positive electrode active material precursor is set to w2, w1 / w2 can be 1.5 to 9.0 or 2.0 to 4.0.

[0080] Next, the positive electrode active material of the present invention will be described.

[0081] The positive electrode active material according to one embodiment of the present invention may be prepared from the above-mentioned hydroxide precursor and / or oxide precursor.

[0082] As one embodiment, the positive electrode active material may be prepared by mixing the hydroxide precursor and a lithium compound and performing a heat treatment.

[0083] Also, the positive electrode active material may be prepared by mixing the oxide precursor and a lithium compound and performing a heat treatment.

[0084] On the other hand, the positive electrode active material may include a plurality of lithium composite oxide particles.

[0085] As one embodiment, the lithium composite oxide particles may contain nickel.

[0086] As one embodiment, the lithium composite oxide particles may further include one or more selected from the group consisting of cobalt, aluminum, and manganese.

[0087] As one embodiment, the lithium composite oxide particles may be represented by the following Chemical Formula 3.

[0088] Chemical formula 3:

[0089] Li a Ni x Co y M 1-x-y O 2

[0090] In the above Chemical Formula 3, M is selected from the group consisting of Zr, Mn, Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.9≤a≤1.2, 0.5≤x≤1.0, 0.0≤y≤0.4, and 0.0≤1-xy≤0.4.

[0091] As one embodiment, the lithium composite oxide particles may be represented by the following Chemical Formula 3-1.

[0092] Chemical formula 3-1:

[0093] Li a’ Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ O 2

[0094] In the above chemical formula 3-1, M1 is Al or Mn, M2 is selected from the group consisting of Zr, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr and combinations thereof, and 0.9≤a'≤1.2, 0.5≤x'≤1.0, 0.0≤y'≤0.4, 0.0≤z'≤0.4, 0.0≤1-x'-y'-z'≤0.4.

[0095] As one embodiment, in the above Chemical Formula 3 and / or Chemical Formula 3-1, a and / or a' representing the molar percentage of lithium relative to the total molar percentage of transition metals other than lithium may be greater than 0.9, greater than 1.0, less than 1.2, less than 1.1, or less than 1.05.

[0096] As one embodiment, in the above Chemical Formula 3 and / or Chemical Formula 3-1, x and / or x' representing the molar percentage of nickel relative to the total molar percentage of transition metals other than lithium may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, it may be a high nickel oxide in which x and / or x' is 0.8 or more or 0.9 or more.

[0097] As one embodiment, in the above Chemical Formula 3 and / or Chemical Formula 3-1, y and / or y' representing the molar percentage of cobalt relative to the total molar percentage of transition metals other than lithium may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0098] The crystal structure of the positive electrode active material particles in one embodiment of the present invention may be hexagonal α-NaFeO 2 (R-3m space group).

[0099] As an embodiment, the average porosity A of the positive electrode active material particles contained in the positive electrode active material may be 5%≤A≤7%, or 5%≤A≤6%.

[0100] In the present invention, porosity is defined as "pore area / total particle cross-sectional area".

[0101] The above-mentioned “total particle cross-sectional area” refers to the cross-sectional area passing through the center of the secondary particle, and is measured including both the material area and the pore area.

[0102] The above-mentioned "pore area" refers to the area of ​​the "pores" on the cross section passing through the center of the secondary particle.

[0103] The above-mentioned “pores” refer to spaces between primary particles constituting secondary particles and / or spaces between crystallites, and include both open pores and closed pores.

[0104] On the other hand, the inventors of the present invention have confirmed that the FWHM of the hydroxide precursor can be controlled. (102) The average porosity of the positive electrode active material particles contained in the positive electrode active material is controlled by using a value.

[0105] Furthermore, the inventors of the present invention have confirmed that the average porosity of the positive electrode active material particles contained in the positive electrode active material can be controlled by controlling the value of "XRD peak integrated width / 4tanθ" of the oxide precursor.

[0106] Furthermore, the inventors of the present invention have confirmed that when the hydroxide precursor satisfies the above-mentioned relationship 1, and the oxide precursor prepared by oxidizing it satisfies the above-mentioned relationship 2, the life characteristics can be significantly improved by controlling the average porosity of the positive electrode active material particles contained in the positive electrode active material prepared from its oxide precursor.

[0107] The positive electrode active material particles contained in the positive electrode active material may be secondary particles formed by agglomeration of a plurality of primary particles.

[0108] As one embodiment, the primary particles may include one or more crystallites.

[0109] The secondary particles may be in the form of multiple particles or polycrystalline particles including two or more primary particles.

[0110] As a more preferred embodiment, the grain boundary density of the secondary particles calculated by the following formula 1 may be 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, 0.90 or more, or 0.95 or more.

[0111] Formula 1:

[0112] Grain boundary density = the number of grain boundaries between the primary particles located on the straight line / the number of the primary particles located on the straight line

[0113] The above-mentioned “grain boundary density” is calculated from the primary particles and grain boundaries between the primary particles located on a straight line passing through the center of the secondary particle and crossing along the minor axis direction in the cross-sectional image of the above-mentioned particle photographed by a scanning electron microscope (SEM).

[0114] For example, in the case of a non-agglomerated single particle composed of a single primary particle, the grain boundary density calculated by the above formula 1 may be 0. Also, when two primary particles are agglomerated, the grain boundary density calculated by the above formula 1 may be 0.5.

[0115] In this case, the above-mentioned grain boundary density refers to the average value of corresponding straight lines when 10 straight lines are drawn arbitrarily.

[0116] As one embodiment, the positive electrode active material may be in a unimodal form, and the average particle size (D50) of the positive electrode active material particles may be 1 μm to 30 μm, more preferably, 8 μm to 20 μm.

[0117] Furthermore, as another more preferred embodiment, in the positive electrode active material of the present invention, the above-mentioned positive electrode active material particles can be first particles having an average particle size (D50) of 8 μm or more or 10 μm or more, and the positive electrode active material can be a bimodal form also comprising second particles having an average particle size (D50) of 7 μm or less or 5 μm or less.

[0118] As an embodiment, in the case where the positive electrode active material is in a bimodal form, when the weight of the first particle contained in the positive electrode active material is set to w1, and the weight of the second particle contained in the positive electrode active material is set to w2, w1 / w2 may be 1.5 to 9.0 or 2.0 to 4.0. The present invention can increase the energy density by using small particles existing in the pores between large particles in a bimodal positive electrode active material having such a mixing ratio, and can solve the problem of reduced battery characteristics caused by changes in the average particle size deviation between large particles and small particles.

[0119] As one embodiment, when the positive electrode active material of the present invention is in a bimodal form, the first particles as large particles may be secondary particles formed by agglomeration of primary particles.

[0120] As one embodiment, the primary particles of the first particles as large particles may include one or more crystallites.

[0121] The secondary particles of the above-mentioned first particles as large particles may be in the form of multiple particles or in the form of polycrystalline particles including a plurality of primary particles.

[0122] As one embodiment, the grain boundary density of the first particles as large particles calculated by the above formula 1 may be 0.95 or more.

[0123] As one embodiment, the second particle as a small particle may be in the form of a single particle including one primary particle, and may be in the form of a single crystal when the primary particle is composed of one crystallite.

[0124] As another embodiment, the second particles as small particles may be in the form of multiple particles or polycrystalline particles including two or more primary particles.

[0125] As one embodiment, the grain boundary density of the second particles as small particles calculated by the following formula 1 may be 0.98 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0126] As one embodiment, the positive electrode active material particles contained in the positive electrode active material may include a coating oxide occupying at least a portion of one or more of the surface of the secondary particles or the grain boundary between the primary particles and the surface of the primary particles.

[0127] As one embodiment, the coating oxide may be represented by the following Chemical Formula 4.

[0128] Chemical formula 4:

[0129] Li p M3 q O r

[0130] In the above chemical formula 4, M3 is one or more selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, and 0≤p≤10,0 <q≤8,2≤r≤13。

[0131] As an example, in the above chemical formula 4, M3 refers to a coating element, and the above coating oxide may be an oxide in which lithium and an element represented by M3 are combined, or an oxide of M3.

[0132] As an example, the coating oxide may be Li p Co q O r , Li p W q O r , Li p Zr q O r , Li p Ti q O r , Li p Ni q O r , Li p Al q O r , Li p Mo q O r 、Co q O r 、Al q O r , W q O r 、Zr q O r 、Ti q O r, B q O r , Li p (W / Ti) q O r , Li p (W / Zr) q O r , Li p (W / Ti / Zr) q O r , Li p (W / Ti / B) q O r , but not limited to this.

[0133] The coating oxide may include a concentration gradient portion where the molar concentration of the element contained in the coating oxide changes. As an example, when the coating oxide includes lithium, the molar concentration of lithium may change. And, as an example, the molar concentration of one or more of M3 contained in the coating oxide may change.

[0134] As one embodiment, when the coating oxide occupies at least a portion of the surface area of ​​the outermost primary particle forming the secondary particle, the concentration gradient portion may decrease or increase from the surface of the outermost primary particle forming the secondary particle toward the center of the secondary particle, or first increase and then decrease.

[0135] Furthermore, the concentration gradient portion may decrease or increase, or first increase and then decrease, from the surface of the primary particle forming the outermost periphery of the secondary particle toward the center of the primary particle.

[0136] As one embodiment, when the coating oxide occupies at least a portion of the surface region of the primary particle that does not form the outermost periphery of the secondary particle, it may decrease or increase, or first increase and then decrease, from the surface of the primary particle toward the center of the primary particle.

[0137] The coating oxide of one embodiment of the present invention improves the battery output characteristics due to high ion conductivity and protects the surface of the lithium composite oxide, thereby further improving the battery life. In addition, it can effectively reduce the residual lithium present on the surface of the lithium composite oxide and prevent side reactions caused by unreacted residual lithium.

[0138] The preparation method of the positive electrode active material precursor and the positive electrode active material according to one embodiment of the present invention is not limited as long as they have the above-mentioned technical features. However, as a more preferred embodiment, they can be prepared as follows.

[0139] First, a hydroxide precursor can be prepared.

[0140] Next, the prepared hydroxide precursor may be heat-treated to prepare an oxide precursor.

[0141] Next, the prepared oxide precursor and lithium compound may be mixed and heat-treated to prepare a positive electrode active material.

[0142] On the other hand, the technical characteristics of the positive electrode active material precursor may be related to the average technical characteristics of a plurality of positive electrode active material precursor particles contained in the positive electrode active material precursor.

[0143] Furthermore, the technical characteristics of the positive electrode active material may be related to the average technical characteristics of a plurality of positive electrode active material particles contained in the positive electrode active material.

[0144] On the other hand, the meaning of “≤”, “above” or “below” described in the present invention can be replaced by the meaning of “<”, “greater than” or “less than”.

[0145] A positive electrode according to one embodiment of the present invention includes the positive electrode active material described above.

[0146] In addition to using the above-mentioned positive electrode active material, the above-mentioned positive electrode can have a known structure and be prepared according to a known preparation method. The binder, the conductive material and the solvent are not particularly limited as long as they can be used for the positive electrode collector of the secondary battery.

[0147] A secondary battery according to one embodiment of the present invention includes the above-mentioned positive electrode active material.

[0148] Specifically, the secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and an electrolyte between the positive electrode and the negative electrode, but there is no particular limitation as long as it can be used as a secondary battery.

[0149] Hereinafter, embodiments of the present invention will be described in more detail.

[0150] Example 1

[0151] (a) Preparation of hydroxide precursor

[0152] The seeds of the large hydroxide particle precursor and the small hydroxide particle precursor designed with an atomic ratio of Ni:Co:Al=95:4:1 (atomic percentage) were synthesized by a co-precipitation method using nickel sulfate, cobalt sulfate and aluminum sulfate.

[0153] While the above-mentioned hydroxide large particle precursor seeds were being synthesized, stirring was performed at 400 rpm, and then the reactor was transferred and stirred at 600 rpm.

[0154] (b) Preparation of oxide precursors

[0155] The prepared large hydroxide particle precursor and small hydroxide particle precursor were heated at a rate of 2° C. per minute and sintered at 400° C. for 6 hours for oxidation to be converted into oxide precursors.

[0156] The average particle size (D50) of the converted large oxide particle precursor is 15.0 μm, and the average particle size (D50) of the prepared small oxide particle precursor is 3.0 μm.

[0157] (c) Preparation of positive electrode active material

[0158] The prepared oxide large particle precursor and oxide small particle precursor were weighed to a weight ratio of 70:30, and then LiOH (Li / (Ni+Co+Al) molar ratio = 1.05) was added and mixed, and then kept in a sintering furnace. 2 The temperature was raised to 800°C at a rate of 2°C per minute and the heat treatment was performed for 12 hours.

[0159] Distilled water was added to the lithium composite oxide prepared by heat treatment, and 1.5 weight percent of NaOH was added relative to the lithium composite oxide. Then, 5.0 weight percent of cobalt sulfate aqueous solution was added so that the amount of cobalt in the cobalt sulfate aqueous solution was 3.0 mole percent relative to the metal elements other than lithium in the lithium composite oxide, and stirred to coat the surface of the lithium composite oxide particles. After the reaction was completed, it was dried at a temperature of 120° C. for 12 hours.

[0160] The dried product is kept in a calcining furnace. 2 The temperature was raised to 700° C. at a rate of 2° C. per minute while maintaining a humid atmosphere, and a heat treatment was performed at 700° C. for 12 hours to obtain a bimodal positive electrode active material.

[0161] Comparative Example 1

[0162] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (a) of Example 1, stirring was performed at 600 rpm in a single reactor without transferring the reactor when synthesizing the large hydroxide particle precursor seed.

[0163] Comparative Example 2

[0164] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (a) of Example 1, stirring was performed at 400 rpm in a single reactor without transferring the reactor when synthesizing the large hydroxide particle precursor seed.

[0165] Preparation of lithium secondary batteries

[0166] The positive electrode slurry was prepared by dispersing 92 weight percent of the positive electrode active material prepared according to the above embodiments to the comparative examples, 4 weight percent of artificial graphite, and 4 weight percent of polyvinylidene fluoride (PVDF) binder into 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on an aluminum film having a thickness of 15 μm and vacuum dried at a temperature of 135° C. to prepare a positive electrode for a lithium secondary battery.

[0167] For the positive electrode, lithium foil was used as a counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and LiPF in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 was used. 6 The button cell is prepared using electrolyte.

[0168] Experimental Example 1

[0169] For the positive electrode active materials of the above-mentioned embodiments and comparative examples, a cross section was obtained by polishing at a current of 380 μA for 1 hour and 30 minutes using a cross section polisher. A cross-sectional SEM image of the positive electrode active material particles was obtained at a voltage of 2 kV using a JSM-7610FPlus (JEOL) field emission scanning electron microscope (FE-SEM), and then shown in Figure 1 middle.

[0170] Experimental Example 2

[0171] The FWHM of the hydroxide precursors of the above examples and comparative examples was measured. (102) Value (X). The determination method is as described above.

[0172] Furthermore, the XRD peak broadening / 4tanθ value (Y) of the oxide precursors of the above-mentioned Examples and Comparative Examples was calculated. The measurement method is as described above.

[0173] And, the average porosity of the positive active material of the above-mentioned embodiment and comparative example is calculated. The porosity is calculated by cross-section processing using a focused ion beam (FIB) (gallium ion source) so that it passes through the center of the particle, and then taking the obtained cross-section SEM image, and measuring the area of ​​the darker part representing the pore from the above-mentioned SEM image.

[0174] The above results are shown in Table 1 below.

[0175] Table 1

[0176]

[0177] Experimental Example 3

[0178] The battery characteristics of the lithium secondary batteries of the above-described Examples and Comparative Examples were measured and the results are shown in Table 2 below.

[0179] For the charge / discharge capacity measurement, the initial discharge capacity was measured and the efficiency was calculated by a charge / discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at a temperature of 25° C. and a voltage range of 3.0 V to 4.25 V at a discharge rate of 0.2 C.

[0180] The life span was determined by charging and discharging the same lithium secondary battery 50 times at 45°C and a driving voltage range of 3.0V to 4.3V at 1C / 1C, and then measuring the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity (capacity retention).

[0181] For the DC-IR analysis, the battery charged and discharged at 45°C was charged to a state of charge (SOC) of 100% and then the resistance was measured. Then, the battery was charged and discharged 50 times in the same manner as the life measurement, and the resistance was measured under the same measurement conditions.

[0182] For constant current constant voltage (CCCV) analysis, the time required to charge to the maximum drive voltage -0.05V at 1C at a temperature of 45°C by constant current (CC) is used as the CC charging time, and then the time required to fully charge to the maximum drive voltage by constant voltage (CV) is used as the CV charging time to determine the charging time. Then, charge / discharge is performed 50 times in the same manner as the life measurement, and then the charging time is measured under the same measurement conditions.

[0183] In this case, the constant current constant voltage value is (CC charging time) / (CC charging time+CV charging time)*100(%).

[0184] Table 2

[0185]

[0186] According to Table 2, it can be confirmed that the life characteristics of Example 1 are significantly improved compared with Comparative Examples 1 and 2. This can be understood as the result of controlling the FWHM of the hydroxide precursor. (102) The porosity of the positive electrode active material is controlled by controlling the XRD peak integrated width / 4tanθ value (Y) of the oxide precursor, thereby improving the life characteristics of the lithium secondary battery.

[0187] Experimental Example 4

[0188] The results of measuring the particle strength of the oxide precursors of the above-mentioned examples and comparative examples are shown in FIG. Figure 2 middle.

[0189] The oxide precursor particles are dropped onto a glass plate and the particle strength is measured by gradually applying pressure using a particle strength tester to measure the force at which the particles break.

[0190] according to Figure 2 It can be confirmed that the particle strength of Example 1 is significantly improved compared with Comparative Examples 1 and 2. This can be understood as the result of controlling the FWHM of the hydroxide precursor. (102) The XRD peak integrated width / 4tanθ value (Y) of the oxide precursor is controlled to ensure the stability of the crystal structure, thereby improving the particle strength.

[0191] Experimental Example 5

[0192] The results of measuring the change rate of the particle size (D50) after pressurization of the oxide precursors of the above-mentioned Examples and Comparative Examples are shown in FIG. Figure 3 middle.

[0193] The particle size change rate is determined as follows.

[0194] Particle size change rate = (P0-P1) / P0*100(%)

[0195] In the above, P0 is D50 of the oxide precursor particles, and P1 is D50 measured after the oxide precursor particles were pressurized at 8.5 tons for 30 seconds.

[0196] according to Figure 3 It can be confirmed that the change rate of the particle size (D50) after pressurization in Example 1 is significant compared with Comparative Examples 1 and 2. This can be understood as the result of controlling the FWHM of the hydroxide precursor. (102) The XRD peak integrated width / 4tanθ value (Y) of the oxide precursor is controlled to ensure the stability of the crystal structure, so that the oxide precursor breaks under pressure above the ultimate strength instead of shrinking into the empty space, and the particle size (D50) change rate after pressurization increases.

Claims

1. A positive electrode active material precursor, characterized in that: comprising a plurality of hydroxide particles, According to the results of X-ray diffraction analysis using CuKα rays, the following relationship 1 is satisfied in the XRD pattern obtained by Rietveld fitting: Relationship 1: 0.82 ≤ FWHM (102) ≤1.22, In the above equation 1, the above FWHM (102) It refers to the full width at half maximum of the (102) crystal plane at the XRD peak defined by the hexagonal lattice with the R-3m space group.

2. A positive electrode active material precursor, characterized in that: Contains multiple oxide particles, According to the results of X-ray diffraction analysis using CuKα rays, the following relationship 2 is satisfied in the XRD pattern obtained by Rietveld fitting: Relationship 2: 127≤XRD peak integral width / 4tanθ≤137, In the above relational expression 2, the XRD peak integrated width is the value of "the area of ​​the XRD peak" divided by the "height of the XRD peak", and θ is the Bragg angle of the peak.

3. The positive electrode active material precursor according to any one of claims 1 to 2, characterized in that The particles are first particles having an average particle size D50 of 8 μm or more, The second particles having an average particle size D50 of 7 μm or less are also included.

4. A positive electrode active material, characterized in that Prepared from the positive electrode active material precursor according to any one of claims 1 to 2.

5. The positive electrode active material according to claim 4, characterized in that The average porosity A of the positive electrode active material particles contained in the positive electrode active material is 5%≤A≤7%.

6. The positive electrode active material according to claim 4, characterized in that The positive electrode active material particles contained in the positive electrode active material are first particles having an average particle size D50 of 8 μm or more. The second particles having an average particle size D50 of 7 μm or less are also included.

7. The positive electrode active material according to claim 4, characterized in that The positive electrode active material particles contained in the positive electrode active material include a coating oxide occupying at least a part of one or more of the surface of the secondary particles or the grain boundary between the primary particles and the surface of the primary particles.

8. A positive electrode, characterized in that Contains the positive electrode active material according to claim 4.

9. A secondary battery, characterized in that: Contains the positive electrode active material according to claim 4.

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