Cathode active material for secondary battery

Abstract

The present invention provides a cathode active material comprising a transition metal and a dopant, wherein the dopant comprises W, and selectively comprises at least one element selected from the group consisting of alkaline earth metals, transition metals of Group 3 to Group 12, post-transition metals and metalloids of Group 13 to Group 15, non-metals of Group 14 to Group 16, and lanthanide elements.

Description

Cathode active material for secondary batteries

[0001] The present invention relates to a cathode active material for a secondary battery, and more particularly, to a cathode active material that provides an overall high particle strength, a small particle size, and a dense internal structure by including tungsten and optionally a predetermined element as a dopant, thereby minimizing particle destruction during the manufacturing process or use of a secondary battery.

[0002] With the rapid development of mobile devices over the past several decades, secondary batteries have also been rapidly developing, and recently, the application areas of secondary batteries have expanded further, including electric vehicles, power tools, bicycles, and ESS.

[0003] In general, among lithium secondary batteries, non-aqueous electrolyte secondary batteries are widely used, and recently, development of all solid-state secondary batteries is also actively underway.

[0004] The process of manufacturing these lithium secondary batteries necessarily involves a "pressing process." This process involves mixing raw materials and pressing them at a specific pressure using equipment such as a roll press to increase the mutual contact between the active material, binder, and conductive material, which are components of the electrode mixture, thereby improving electrical properties and simultaneously increasing energy density.

[0005] However, the high pressure applied during the pressing process causes particle breakage, which is a major cause of deterioration in battery characteristics. In particular, in the case of all-solid-state secondary batteries, since the electrolyte is applied in a solid rather than liquid form, the pressing process is performed at higher pressure to improve interfacial contact with the positive electrode active material. Consequently, the particle breakage problem is more pronounced compared to non-aqueous electrolyte secondary batteries.

[0006] Therefore, there is a significant need in the industry for new technologies that can solve these problems.

[0007] The present invention aims to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0008] The inventors of the present invention, after repeated in-depth research and various experiments, have confirmed that when a cathode active material is manufactured by essentially including tungsten (W) as a dopant and optionally including specific element(s), the crystal grain size becomes smaller, the structure becomes denser, and the particle strength significantly increases, thereby suppressing the particle breakage phenomenon that may occur during the pressing process of battery manufacturing and the use (repeated charging and discharging) of the manufactured battery and maintaining high contact force, thereby making it possible to manufacture a secondary battery, particularly an all-solid-state battery, with excellent characteristics, and have completed the present invention.

[0009] Therefore, the positive electrode active material according to the present invention is

[0010] Contains transition metals and dopants,

[0011] The above dopant is characterized in that it includes tungsten (W), and optionally includes at least one element selected from the group consisting of alkaline earth metals, transition metals of groups 3 to 12, post-transition metals and metalloids of groups 13 to 15, non-metals of groups 14 to 16, and lanthanide elements.

[0012] The above tungsten (W) has the property of increasing the strength of the manufactured positive electrode active material when included as a dopant. Furthermore, the inclusion of W as a dopant tends to decrease the particle size of the manufactured positive electrode active material, which provides a denser structure when primary particles combine to form secondary particles, further enhancing particle strength.

[0013] Specifically, a grain is a collection of crystals with the same orientation within an active material particle, and the area where these grains come into contact with each other is called a grain boundary. As the grains become smaller, the number of contact interfaces increases, resulting in an increase in grain boundaries, which inhibits dislocation movement of the grains. This requires more force to deform the crystal structure of the positive electrode active material, thereby increasing particle strength.

[0014] Moreover, W tends to induce the formation of small, thin-shaped particles, which, when aggregated, form a radial particle morphology, thereby providing a more regular and dense aggregate structure, as can be seen in Fig. 2b. Therefore, this regular and dense aggregate structure is more stable against the applied external force and / or the inherent phenomenon of repeated shrinkage and expansion compared to an irregular aggregate structure, thereby contributing to the enhancement of particle strength.

[0015] However, if the grain size is too small, the number of grain boundaries that are relatively weak in brittleness increases, so it is necessary to form an appropriate grain size, and accordingly, it may be necessary to form an appropriate grain size with an appropriate doping amount. In addition, if the W doping amount is too large, the excess W may form a resistive layer, like a coating, on the particle surface.

[0016] Therefore, the doping amount of W may preferably be in the range of 8000 to 14000 ppm, may be in the range of 10000 to 14000 ppm, and may particularly preferably be in the range of 11000 to 13000 ppm. Such a W doping amount may be excessive compared to the doping amount of the cathode active material generally applied to a non-aqueous electrolyte battery. This can be understood as applying a doping amount specialized for an all-solid-state battery by securing particle strength through relatively excessive W doping, since a higher particle strength is required in an all-solid-state battery than in a non-aqueous electrolyte battery.

[0017]

[0018] In one desirable example,

[0019] The alkaline earth metal is one or more elements selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra;

[0020] The above group 3 to group 12 transition metal is at least one element selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, Re, Os, Ir, Pt, Au, and Hg;

[0021] The transition metals and metalloids of Groups 13 to 15 are at least one element selected from the group consisting of Al, Ga, In, Sn, Tl, Pb, Bi, Po, B, Si, Ge, As, Sb, Te, and At;

[0022] The non-metallic elements in Groups 14 to 16 are at least one element selected from the group consisting of C, P, S, and Se;

[0023] The above lanthanide element may be one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0024] Preferably, the dopant other than W may be one or more elements selected from the group consisting of Zr, Ti, B, P, Al, Si, Mg, Zn, and V, more preferably one or more elements selected from the group consisting of Ti and Al, and particularly preferably Ti.

[0025]

[0026] Titanium (Ti) as a dopant inhibits grain growth during the production of cathode active materials, resulting in a smaller grain size compared to undoped or doped materials with other elements. Furthermore, Ti possesses a stronger bonding affinity with oxygen than watts (W), enabling it to form a more stable structure. It also possesses lower electronegativity than nickel, cobalt, and manganese (Ni), yet possesses a higher bonding energy when combined with oxygen.

[0027] However, despite these characteristics, when doped with Ti alone, it does not satisfy the particle size variation conditions set in the present invention, and there are certain limitations to its use, especially in all-solid-state batteries, as can be confirmed in the experimental examples described below, so a combination with W is necessary.

[0028] The doping amount of the above Ti may be, for example, in the range of more than 0 to 6000 ppm or less, preferably in the range of 2000 to 5500 ppm, more preferably in the range of 2500 to 5000 ppm, and particularly preferably in the range of 4000 to 5000 ppm.

[0029]

[0030] In the positive electrode active material according to the present invention, the transition metal may be, for example, Ni, Co, Mn, etc., and the elemental composition of the positive electrode active material may be expressed by, for example, the following chemical formula 1.

[0031] Li a M b D c Ox (1)

[0032] In the above formula

[0033] M is one or more of Ni, Co, and Mn,

[0034] D is one or more of the dopants exemplified above,

[0035] 0.9≤a≤2.0, 0 <b≤1, 0≤c≤0.5, 0<x≤8의 조건을 만족한다.

[0036] In particular, M may have an elemental composition that essentially includes Ni and its content is 60% or more, preferably 80% or more, and more preferably 85% or more, based on the total mole of M.

[0037]

[0038] In one preferred example, W assists in the formation of agglomerated particles having a radial shape, and Ti assists in the formation of particles having a relatively small crystal size, so that composite doping of W and Ti can result in relatively dense active material particles.

[0039] In non-aqueous electrolyte batteries, the more pores on the outer surface of the active material, the larger the contact area with the electrolyte, which can lead to faster ion exchange. However, in all-solid-state batteries, contact with the solid electrolyte is not achieved in the pores on the outer surface of the active material, which leads to a problem in that the contact area available for ion exchange is reduced. Therefore, by complex doping with W and Ti, it is possible to control the formation of a shape in which the internal pores of the active material particles are significantly reduced, as confirmed by the relatively large decrease in the internal pores of the particles in the cross-sectional SEM image of Figure 3b.

[0040]

[0041] In one preferred example, the positive electrode active material of the present invention can be set such that, when measuring the cumulative particle size distribution (PSD), the change rate (%) of the volume fraction of particles smaller than 3 μm after the press execution is 100% or less, based on the change rate before the press execution of 4 tons.

[0042] The PSD change amount of particles (fine powder) less than 3 ㎛ set as above can be understood as a necessary condition for suppressing the amount of fine powder generation by high particle strength despite press execution.

[0043]

[0044] The inventors of the present application have confirmed through analysis of various experiments that the change in D25 in PSD measurement can be used as a standard indicator of the amount of differential generation linked to particle strength.

[0045] Therefore, in one preferred example, after the press run, the D25 change amount can be set to a range of 0.5 μm or less, and more preferably, the D25 change rate can be set to a range of 15% or less, based on the 4 ton press run before the positive electrode active material.

[0046]

[0047] On the other hand, D5, D25, and D50 can be utilized together based on PSD measurements.

[0048] Specifically, as the difference between D50 and D5 ('D50-D5') increases, the distribution of particles in the differential region becomes broader, so the particle size becomes non-uniform and more dispersed, whereas as D50-D5 decreases, the particle size becomes uniform and the distribution of particles in the differential region becomes denser.

[0049] It can be interpreted that as D25 increases, the number of particles in the differential region decreases, and conversely, as D25 decreases, the number of particles in the differential region increases.

[0050] Based on this, it can be interpreted that the smaller the (D50-D5) / D25 before press execution, the more uniformly the particles in the fine-grained region of the manufactured active material are distributed. For example, the (D50-D5) / D25 of the positive electrode active material can be set to 0.5 or less.

[0051] Experimentally confirmed, it may be desirable for the change rate of (D50-D5) / D25 before / after press execution for the positive electrode active material to be less than 40%.

[0052] The above contents are experimentally proven in Experimental Example 3 described later.

[0053]

[0054] The present invention also provides a secondary battery comprising a positive electrode active material. The general structure and manufacturing method of secondary batteries are well known in the art, and therefore, a detailed description thereof is omitted herein.

[0055] The secondary battery according to the present invention may preferably be in the form of an all-solid-state battery.

[0056] As previously explained, in the case of an all-solid-state battery, the pores in the outer surface layer of the active material make contact with the solid electrolyte difficult, resulting in a decrease in performance. However, the cathode active material of the present invention has a shape in which the pores inside the active material particles are significantly reduced, thereby increasing contact with the solid electrolyte and providing excellent particle strength, and thus can be preferably used in an all-solid-state battery.

[0057] As described above, the cathode active material according to the present invention has high particle strength, a small crystal grain size, and a dense structure due to a specific dopant, thereby suppressing particle breakage that may occur during the pressing process of battery manufacturing and the charge / discharge use of the manufactured battery, thereby providing a secondary battery with excellent characteristics, and furthermore, by providing a shape in which the outer layer pores, etc. are greatly reduced, it has the effect of being particularly suitable for use in an all-solid-state battery.

[0058] Figure 1a is a SEM image of positive electrode active material particles according to Comparative Example 1;

[0059] Figure 1b is a cross-sectional SEM image of the positive electrode active material particles according to Comparative Example 1;

[0060] Figure 2a is a SEM image of positive electrode active material particles according to Example 3;

[0061] Figure 2b is a cross-sectional SEM image of the positive electrode active material particles according to Example 3;

[0062] Figure 3a is a SEM image of positive electrode active material particles according to Example 7;

[0063] Figure 3b is a cross-sectional SEM image of the positive electrode active material particles according to Example 7;

[0064] Figure 4 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Comparative Example 1 in Experimental Example 2;

[0065] Figure 5 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Example 3 in Experimental Example 2;

[0066] Figure 6 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Example 6 in Experimental Example 2;

[0067] Figure 7 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Example 7 in Experimental Example 2;

[0068] Figure 8 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Example 10 in Experimental Example 2;

[0069] Figure 9 is a graph showing the change in PSD according to the pressure applied to the positive electrode active material according to Example 11 in Experimental Example 2.

[0070] Hereinafter, the present invention will be described in more detail with reference to drawings according to embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0071]

[0072] [Comparative Example 1]

[0073] Caustic soda and ammonia were added to a 500 L cylindrical reactor to adjust the initial pH to 11.5 to 12.0. Then, when a metal salt aqueous solution with a ratio of Ni:Co:Mn of 90:6:4 was continuously supplied together with the caustic soda and ammonia aqueous solutions to proceed with the reaction, the pH of the composite in the reactor was adjusted to 11.5 to 12.0, and the ammonia concentration in the reactor was adjusted to 6000 to 8000 ppm. The synthesis was carried out by co-precipitation reaction at 60°C for 34 hours with a stirring speed of 420 rpm.

[0074] The precursor manufactured above and LiOH were mixed in a 10L mixer (Nippon Coke & Engineering) at a Li / Me=1.01 ratio under the set conditions of 100 to 500 rpm / 15 min, and then calcined at 700°C for 30 hours to obtain Ni. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured. The grain size of the manufactured positive electrode active material was 202 nm.

[0075]

[0076] [Comparative Example 2]

[0077] Ni doped with 3000 ppm of Al was prepared under the same conditions as Comparative Example 1, except that Al2O3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0078]

[0079] [Comparative Example 3]

[0080] Ni doped with 4500 ppm of Ti was prepared under the same conditions as in Comparative Example 1, except that TiO2 was added when mixing the precursor and LiOH. 0.90 Co0.06 Mn 0.04 The positive electrode active material was manufactured.

[0081]

[0082] [Comparative Example 4]

[0083] Ni doped with 6000 ppm of W was prepared under the same conditions as in Comparative Example 1, except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0084]

[0085] [Example 1]

[0086] Ni doped with 8000 ppm of W was prepared under the same conditions as in Comparative Example 1, except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0087]

[0088] [Example 2]

[0089] Ni doped with 10000 ppm of W was prepared under the same conditions as in Comparative Example 1, except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0090]

[0091] [Example 3]

[0092] Ni doped with 12000 ppm of W was prepared under the same conditions as Comparative Example 1 except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 A positive electrode active material was manufactured. The crystal grain size of the manufactured positive electrode active material was 49 nm.

[0093]

[0094] [Example 4]

[0095] Ni doped with 14000 ppm of W was prepared under the same conditions as in Comparative Example 1, except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0096]

[0097] [Comparative Example 5]

[0098] Ni doped with 16000 ppm of W was prepared under the same conditions as in Comparative Example 1, except that WO3 was added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0099]

[0100] [Comparative Example 6]

[0101] Ni doped with 6000 ppm of W and 1000 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0102]

[0103] [Example 5]

[0104] Ni doped with 12000 ppm of W and 1000 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0105]

[0106] [Example 6]

[0107] Ni doped with 12000 ppm of W and 3000 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 A positive electrode active material was manufactured. The crystal grain size of the manufactured positive electrode active material was 44 nm.

[0108]

[0109] [Example 7]

[0110] Ni doped with 12000 ppm of W and 4500 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 A positive electrode active material was manufactured. The crystal grain size of the manufactured positive electrode active material was 44 nm.

[0111]

[0112] [Example 8]

[0113] Ni doped with 12000 ppm of W and 6000 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0114]

[0115] [Example 9]

[0116] Ni doped with 12000 ppm of W and 10000 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that WO3 and TiO2 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0117]

[0118] [Example 10]

[0119] Ni doped with 12000 ppm of W and 3000 ppm of Al was prepared under the same conditions as Comparative Example 1, except that WO3 and Al2O3 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0120]

[0121] [Example 11]

[0122] Ni doped with 12000 ppm of W and 5000 ppm of Al was prepared under the same conditions as Comparative Example 1, except that WO3 and Al2O3 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0123]

[0124] [Example 12]

[0125] Ni doped with 12000 ppm of W, 4500 ppm of Ti and 3000 ppm of Al was prepared under the same conditions as Comparative Example 1, except that WO3, TiO2 and Al2O3 were added when mixing the precursor and LiOH. 0.90 Co 0.06 Mn 0.04 The positive electrode active material was manufactured.

[0126]

[0127] [Example 13]

[0128] Ni doped with 12000 ppm of W and 4500 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that a metal salt solution with a ratio of 80:10:10 of Ni:Co:Mn was used, WO3 and TiO2 were added when mixing the precursor and LiOH, and firing was performed at 780°C. 0.80 Co 0.10 Mn 0.10 The positive electrode active material was manufactured.

[0129]

[0130] [Example 14]

[0131] Ni doped with 12000 ppm of W and 4500 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that a metal salt solution with a ratio of Ni:Co:Mn of 70:15:15 was used, WO3 and TiO2 were added when mixing the precursor and LiOH, and firing was performed at 780°C. 0.70 Co 0.15 Mn 0.15 The positive electrode active material was manufactured.

[0132]

[0133] [Example 15]

[0134] Ni doped with 12000 ppm of W and 4500 ppm of Ti was prepared under the same conditions as Comparative Example 1, except that a metal salt solution with a ratio of Ni:Co:Mn of 60:20:20 was used, WO3 and TiO2 were added when mixing the precursor and LiOH, and firing was performed at 780°C. 0.60 Co 0.20 Mn 0.20 The positive electrode active material was manufactured.

[0135]

[0136] [Experimental Example 1] - Morphology of positive electrode active material

[0137] SEM images and cross-sectional SEM images of the positive electrode active materials manufactured in Comparative Example 1, Example 3, and Example 7, respectively, were obtained and are shown in Figures 1 to 3.

[0138] In each image, the large particles with curved surfaces are secondary particles, and each secondary particle has a structure in which small-sized primary particles are aggregated. Therefore, the surface curvature of the secondary particles can be understood to be caused by the primary particles, and the surface curvature shape can be seen to decrease in the order of FIG. 1a, FIG. 2a, and FIG. 3a, which means that the primary particles decrease in the order mentioned above.

[0139] Based on this, compared to the positive electrode active material of Comparative Example 1 (Figs. 1a and 1b), it can be seen that the positive electrode active material of Example 3 (Figs. 2a and 2b) doped solely with W forms a radial particle structure when primary particles aggregate to form secondary particles.

[0140] In addition, the positive electrode active material of Example 7 doped with W and Ti (Figs. 3a and 3b) can be seen to have a smaller primary particle size and filled pores between particles compared to the positive electrode active material of Example 3 doped solely with W (Figs. 2a and 2b), which increases contact with other components and improves particle strength.

[0141]

[0142] [Experimental Example 2] - Measurement of particle size distribution changes before and after pressing

[0143] For the particles of the positive electrode active material manufactured in each of the comparative examples and examples above, the unit area (cm) was measured using Autopellet 3887.NE.L (Carver) 2 ) was applied with a pressure of 4 tons, and the particle size distribution (D5, D25, D50) before and after pressing was measured, and the results are shown in Table 1 below.

[0144]

[0145] As shown in Table 1 above, the upper area (cm 2 ) As a pressure of 4 tons is applied, the particle sizes become smaller overall, and this particle size reduction is confirmed to be greater in the active materials of the comparative examples.

[0146]

[0147] In addition, the change in PSD (particle size distribution) according to the application of 4 ton pressure in the positive electrode active materials manufactured in Comparative Example 1 and Examples 3, 6, 7, 10, and 11, respectively, is shown in FIGS. 4 to 9, and the decrease in particle size is also clearly confirmed. However, the positive electrode active material of Comparative Example 1 (FIG. 4) shows a different change pattern from the Examples (FIGS. 5 to 9) in that the amount of fine particles generated by the application of pressure is significantly higher.

[0148]

[0149] Meanwhile, based on the measurement results in Table 1 above, the change amount and change rate of particle size in D5, D25, and D50 were calculated, respectively, and the change amount and change rate of (D50-D5) / D25 were calculated before and after press execution, and the results are shown in Table 2 below.

[0150]

[0151] As shown in Table 2 above, it can be seen that the change in D25 after the press execution is 0.5 ㎛ or less and the change rate is 15% or less compared to before the press execution in the positive active materials of all examples.

[0152] In addition, when analyzing PSD before press execution, it can be confirmed that the positive electrode active materials of the examples have (D50-D5) / D25 of 0.5 or less, and the difference change rate after press execution with respect to (D50-D5) / D25 before press execution is 40% or less.

[0153] The positive electrode active material of Comparative Example 3 satisfies the range in which the amount of change in D25 is 0.5 ㎛ or less and the rate of change is 15% or less, but does not satisfy the condition in which (D50-D5) / D25 before press execution is 0.5 or less and the condition in which the rate of change in (D50-D5) / D25 before and after press execution is 40% or less.

[0154]

[0155] Referring to the results in Tables 1 and 2 together, it can be seen that as the W doping amount increases from 8000 ppm (Example 1) to 12000 ppm (Example 3), the particle size change decreases and decreases somewhat in the section from 12000 ppm (Example 3) to 14000 ppm (Example 4). The small particle size change of D25 even after pressing means that the particle strength is high. In addition, the particle size change increases further in the section from 14000 ppm (Example 4) to 16000 ppm (Comparative Example 5), and the W doping amount that increases like this forms a coating layer on the particle surface, which acts as a resistive layer and causes the problem of increased resistance. The difference in the characteristics of the secondary battery according to the above can also be confirmed in the experimental results of Experimental Example 4 described below.

[0156]

[0157] In addition, when Ti was used together with W as a dopant (Examples 5 to 9), the particle size change was further reduced, and in particular, the result of Example 7, in which the W doping amount was 12,000 ppm and the Ti doping amount was 4,500 ppm, was the best. However, looking at the result of Comparative Example 6, in which the W doping amount was 6,000 ppm and the Ti doping amount was 1,000 ppm, it was confirmed that the W doping amount did not satisfy a certain level, so the desired positive electrode active material particle structure and density were not achieved, and the change rate was large before and after the press execution, and accordingly, when applied to an all-solid-state battery, the battery characteristics were significantly deteriorated, as can be confirmed in Experimental Example 4 described later.

[0158] On the other hand, even when the W doping amount is above a certain level, when the Ti doping amount reaches 10,000 ppm, there is no significant difference in the change in particle size despite the increased doping amount, and rather, as excessive dopants occupy the transition metal site, the battery characteristics such as capacity are lowered. This can also be confirmed in the experimental results of Experimental Example 4 on the characteristics of secondary batteries.

[0159]

[0160] Finally, the experimental results of Examples 13 to 15 demonstrated that the combination of W and Ti as dopants is still effective even when the Ni content is changed.

[0161]

[0162] [Experimental Example 3] - Measurement of PSD Differential Domain Change

[0163] Generally, when a cathode active material that has been subjected to a large amount of fine powder by pressing is applied to a battery, the battery characteristics deteriorate. Therefore, if the change in fine powder before and after pressing can be appropriately controlled by improving the particle strength, it can contribute to improving the battery characteristics. Although there is no set standard for defining the fine powder region, the present invention defines particles with a particle size of less than 3 μm as fine powder, and aims to provide a cathode active material with improved particle strength by measuring the change in fine powder before and after pressing.

[0164] Based on the above, for the particles of the positive electrode active material manufactured in each of the comparative examples and examples, S3500 (Microtrac) was used under the condition of 'particle characteristics: refractive index 1.55', and the unit area (cm 2 ) was applied with a pressure of 4 tons, and the change in the volume fraction of particles with a diameter of less than 3 ㎛ before and after compression was measured, and the results are shown in Table 3 below.

[0165]

[0166] As shown in Table 3 above, it can be seen that the change rate (%) of the volume fraction of particles smaller than 3 μm after the press execution is 100% or less compared to before the press execution for the positive active materials of all examples.

[0167] This is in contrast to the positive active materials of the comparative examples in which the change rate exceeds 100%, and the low change rate in the positive active materials of the examples means that the particle strength is correspondingly increased.

[0168]

[0169] [Experimental Example 4] - Battery Characteristics Evaluation

[0170] (Manufacturing of all-solid-state secondary batteries)

[0171] To manufacture an all-solid-state secondary battery, the cathode active material, solid electrolyte (Li6PS5Cl), and conductive material (Super-P) manufactured in the comparative examples and examples were dry mixed at a weight ratio of 70:25:5 to prepare a cathode active material composite. Li foil and In foil were used as counter electrodes (cathode).

[0172] An all-solid-state secondary battery with a diameter of 10 mm consisting of a load collector and a mold was manufactured as follows.

[0173] First, a solid electrolyte (Li6PS5Cl) was pressurized to 17 MPa to form an SE layer (solid electrolyte layer). Next, the above-mentioned positive electrode active material composite was applied to one side of the SE layer, and a counter electrode (Li foil, In foil) was used on the other side of the SE layer to manufacture an electrode assembly, which was then compressed to 24 MPa to manufacture an all-solid-state secondary battery.

[0174]

[0175] (Manufacturing of liquid electrolyte secondary batteries)

[0176] In the comparative examples and examples above, Li metal was used as the positive electrode active material and the negative electrode, respectively, and a porous polyethylene film as a separator was interposed between them to manufacture an electrode assembly, and after positioning the electrode assembly inside a battery case, an electrolyte was injected into the inside of the battery case to manufacture a liquid electrolyte secondary battery.

[0177] At this time, as the electrolyte, 1.0 M lithium hexafluorophosphate (LiPF6) was dissolved in an organic solvent containing ethylene carbonate / dimethyl carbonate / diethyl carbonate (EC / DMC / DEC mixed volume ratio 1 / 2 / 1) and vinylene carbonate (VC: 2 wt%).

[0178]

[0179] (charge-discharge test)

[0180] The all-solid-state secondary batteries and liquid electrolyte secondary batteries manufactured above were aged at room temperature for 12 hours, and then a charge-discharge test was performed, and the results are shown in Table 4 below. The capacity evaluation was based on 200 mAh / g at a 0.1C rate, and the charge-discharge conditions were constant current (CC) / constant voltage (CV) in the voltage range of 4.25 to 2.5 V.

[0181]

[0182] As shown in Table 4 above, it can be confirmed that the positive electrode active materials according to the examples have better overall battery characteristics than the positive electrode active materials of the comparative examples in the secondary batteries manufactured using them, and in particular, the difference in effectiveness is very large in all-solid-state secondary batteries.

[0183]

[0184] Anyone with ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims

1. Contains transition metals and dopants, A cathode active material characterized in that the dopant comprises W, and optionally comprises at least one element selected from the group consisting of alkaline earth metals, transition metals of groups 3 to 12, post-transition metals and metalloids of groups 13 to 15, non-metals of groups 14 to 16, and lanthanide elements.

2. A cathode active material characterized in that the doping amount of W in the first paragraph is in the range of 8000 to 14000 ppm.

3. A cathode active material characterized in that the doping amount of W in the second paragraph is in the range of 11000 to 13000 ppm.

4. In paragraph 1, The alkaline earth metal is one or more elements selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra; The above group 3 to group 12 transition metal is at least one element selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, Re, Os, Ir, Pt, Au, and Hg; The transition metals and metalloids of Groups 13 to 15 are at least one element selected from the group consisting of Al, Ga, In, Sn, Tl, Pb, Bi, Po, B, Si, Ge, As, Sb, Te, and At; The non-metallic elements in Groups 14 to 16 are at least one element selected from the group consisting of C, P, S, and Se; A cathode active material characterized in that the lanthanide element is at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

5. A cathode active material characterized in that, in the first paragraph, the dopant comprises at least one element selected from the group consisting of Zr, Ti, B, P, Al, Si, Mg, Zn, and V in addition to W.

6. A cathode active material according to claim 5, characterized in that the dopant comprises W and Ti.

7. A cathode active material characterized in that the doping amount of Ti in the 6th paragraph is in the range of more than 0 to 6000 ppm or less.

8. A cathode active material according to claim 7, characterized in that the doping amount of Ti is in the range of 2500 to 5000 ppm.

9. In the fifth paragraph, the W assists in the formation of radially agglomerated particles, and the Ti assists in the formation of particles with a relatively small crystal grain size, so that a cathode active material is formed of relatively dense active material particles through composite doping of W and Ti.

10. A positive electrode active material characterized in that, in the first paragraph, when measuring the cumulative particle size distribution (PSD), the change rate (%) of the volume fraction of particles less than 3 ㎛ after the press execution is 100% or less based on the change rate before the press execution of 4 tons.

11. A positive electrode active material according to claim 1, characterized in that the change in D25 after the press execution is 0.5 ㎛ or less based on the time before the 4 ton press execution for the positive electrode active material.

12. A positive electrode active material characterized in that, in the first paragraph, the D25 change rate is 15% or less after the press execution based on the time before the 4 ton press execution for the positive electrode active material.

13. A positive electrode active material according to claim 1, characterized in that (D50-D5) / D25 of the positive electrode active material is 0.5 or less.

14. A positive electrode active material characterized in that the change rate of (D50-D5) / D25 before / after press execution for the positive electrode active material in the first paragraph is 40% or less.

15. A secondary battery characterized by including a positive electrode active material according to Article 1.

16. A secondary battery characterized in that it is an all-solid-state battery according to claim 15.

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