Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode includes a positive electrode active material having a lithium metal oxide core part and a coating layer, the lithium metal oxide core part is doped with Mo, the coating layer contains Al, and expression 1 is satisfied. [Expression 1] 0.47 ≤ T2 / T1 ≤ 1 (in expression 1, T2 is a low-temperature discharge capacity under a predetermined condition, T1 is a discharge capacity at room temperature, and the low-temperature discharge condition and the room-temperature discharge condition refer to the capacities measured when a charged cell is maintained at a low temperature for a predetermined period of time and is then discharged at the respective temperatures.)

Description

lithium secondary battery

[0001] The present invention relates to a lithium secondary battery, and specifically to a lithium secondary battery having charge transfer resistance characteristics.

[0002] The present invention claims priority based on Korean Patent Application No. 10-2024-0191459 filed on December 19, 2024, the entire contents of said application incorporated herein by reference.

[0003] High energy density and excellent lifespan characteristics are essential for lithium-ion batteries. Lithium manganese-rich layered cathode active materials (Li) being researched as next-generation cathode materials 1+x M 1-x O2 is attracting attention as a candidate for next-generation cathode active materials due to its very high charge / discharge capacity.

[0004] However, because oxygen oxidation / reduction reactions are utilized, oxygen gas is generated during the initial charge; as oxygen is removed from the lattice and vacancies for lithium ions are created, irreversible capacity increases. Furthermore, structural changes occur from layered structures to spinel or rock salt structures, leading to problems of capacity and voltage reduction. In addition, Mn 4+ The presence of a large number of ions results in low electrical conductivity and rate characteristics. To solve the above problems, coating the surface of the material is essential, and this can improve performance.

[0005] The objective of the present invention is to provide a lithium secondary battery having excellent rate characteristics and low-temperature performance by introducing doping and a surface coating layer into the positive electrode active material.

[0006] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising: a lithium metal oxide core portion represented by the following chemical formula 1; and a coating layer located on the surface of the lithium metal oxide core portion; wherein the coating layer comprises Al, and the wt% content of Al is 500 to 2000 ppm with respect to 100 wt% of the lithium metal oxide core portion.

[0007] [Chemical Formula 1]

[0008] Li 1+x [(Ni a Mn b M c ) 1-t Mo t ] 1-x O2

[0009] (In the above Chemical Formula 1, M comprises Co, Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof, and 0 < x ≤ 0.5, 0.20 ≤ a ≤ 0.40, 0.60 ≤ b ≤ 0.80, 0 ≤ c ≤ 0.1, a+b+c=1, and 0 < t ≤ 0.5.)

[0010] The wt% content of the above Mo may be 1,000 to 5,000 ppm with respect to 100 wt% of the total metal (Me) excluding lithium.

[0011] The above-mentioned positive active material has a rolled density of 2.5 to 5 g / cm³ under a pressure of 6 ton. 3 It could be.

[0012] The above positive active material has a fine particle generation rate of 6 to 9.3% under a pressure of 6 ton, and the fine particle may have an average particle size (D50) of 1 μm or less.

[0013] The above positive active material may have a porosity of 10 to 43% under a pressure of 6 ton.

[0014] The above coating layer may include an island coating layer comprising a plurality of attached particles spaced apart from each other.

[0015] The above island coating layer may have a coverage rate of 25 to 75 area%.

[0016] The thickness of the above island coating layer may be 5 to 120 nm.

[0017] The specific surface area (BET) of the above positive active material is 0.5 to 5 m 2 / g can be.

[0018] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising: (S1) a step of preparing a precursor containing Ni and Mn; (S2) a step of dry-mixing the precursor, a Li raw material, and a Mo-containing raw material and then calcining them to form a lithium metal oxide core; and (S3) a step of dry-mixing the lithium metal oxide core and an Al-containing raw material and then calcining them to form a coating layer. In step (S2), the Mo-containing raw material is introduced such that the wt% content of the Mo is 1,000 to 5,000 ppm relative to 100 wt% of the precursor.

[0019] In step (S2) above, the Mo-containing raw material may include one or more selected from MoO3, MoO2, MoO2Cl2 and other raw materials containing Mo.

[0020] In the above step (S2), the average particle size (D50) of the Mo-containing raw material may be 50 to 800 nm.

[0021] In step (S3) above, the Al-containing raw material can be introduced such that the wt% content of the Al is 500 to 2000 ppm with respect to 100 wt% of the lithium metal oxide core.

[0022] In step (S3) above, the Al-containing raw material may include one or more selected from Al2O3, Al(OH)3, and other raw materials containing Al.

[0023] The above (S2) step may be performed by firing at a temperature of 600°C or higher.

[0024] The above step (S3) can be performed by firing at a temperature of 300 to 500°C.

[0025] The above firing can be carried out in an atmospheric or O2 atmosphere.

[0026] Another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; and an electrolyte; wherein the positive electrode comprises a positive electrode active material composed of a lithium metal oxide core portion and a coating layer, the lithium metal oxide core portion is doped with Mo, and the coating layer comprises Al.

[0027] [Equation 1]

[0028] 0.47 ≤ T2 / T1 ≤ 1

[0029] (In the above Equation 1, T2 is the low-temperature discharge capacity under specific conditions, and T1 is the discharge capacity at room temperature, and

[0030] The above low-temperature discharge condition and the above room-temperature discharge condition refer to the capacity when a charged cell is maintained at a low temperature for a predetermined period of time and then discharged at each respective temperature.)

[0031] The above lithium secondary battery may have a charge transfer resistance (R1) of 20 to 32 Ω measured after one cycle under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C.

[0032] The ratio of R1 to the charge transfer resistance (R) measured after formation of the above lithium secondary battery at a voltage of 4.65 V, a temperature of 45°C, and 0.1 C may be less than 0.48.

[0033] The above lithium secondary battery may have a charge transfer resistance (R50) of 10 to 23 Ω measured after 50 cycles under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C.

[0034] The ratio of R50 to the charge transfer resistance (R) measured after formation at a voltage of 4.65 V, a temperature of 45°C, and 0.1 C may be less than 0.33.

[0035] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can secure high capacity and excellent lifespan characteristics by suppressing surface side reactions through Mo doping and Al coating.

[0036] A method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention can manufacture a positive electrode active material for a lithium secondary battery having the aforementioned advantages, with a simple process and low cost by using dry mixing.

[0037] Figure 1 is a scanning electron microscope (SEM) image of Example 1 and Comparative Example A1.

[0038] Figure 2 is a TEM (transmission electron microscopy) image of Example 1.

[0039] Figure 3 is a graph of electrochemical impedance spectroscopy (EIS) measurements in the charged states of Example 1, Comparative Examples B1 and B3 to B6.

[0040] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0041] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0042] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0043] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0044] Also, unless otherwise specified, 1 ppm means 0.0001 wt%.

[0045] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0046] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0047]

[0048] Cathode active material for lithium secondary batteries

[0049] In one embodiment of the present invention, a positive electrode active material for a lithium secondary battery is provided, which secures high capacity and excellent lifespan characteristics by suppressing surface side reactions through Mo doping and Al coating.

[0050] In one embodiment, a positive electrode active material for a lithium secondary battery comprises a lithium metal oxide core portion represented by the following chemical formula 1; and a coating layer located on the surface of the lithium metal oxide core portion; wherein the coating layer comprises Al, and the wt% content of Al may be 500 to 2000 ppm with respect to 100 wt% of the active material.

[0051] [Chemical Formula 1]

[0052] Li 1+x [(Ni a Mn b M c ) 1-t Mo t ] 1-x O 2-y

[0053] (In the above Chemical Formula 1, M comprises Co, Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof, and 0 < x ≤ 0.2, 0.20 ≤ a ≤ 0.40, 0.60 ≤ b ≤ 0.80, 0 ≤ c ≤ 0.1, a+b+c=1, 0 < t ≤ 0.5, 1.8 ≤ y ≤ 2.2.)

[0054] The above lithium metal oxide core may contain Li in an amount corresponding to 1+x, where x may be 0 < x < 0.5. If x deviates from the upper limit of the aforementioned range, lifespan characteristics may be degraded due to reduced phase stability, and if x corresponds to 0, the capacity characteristics cannot be improved due to an excess of lithium content.

[0055] The above core portions may independently contain Li in an amount corresponding to 1+x, wherein x may be 0 < x ≤ 0.5. By satisfying the aforementioned range, capacity characteristics can be improved compared to existing NCM or NCA containing Li in an amount corresponding to 1. In this case, due to the higher Li content, O participates in oxidation and reduction reactions during the insertion and extraction of Li, thereby supplementing the oxidation and reduction of Ni, Mn, and Co to ensure chemical stability. If x exceeds the upper limit of the aforementioned range, lifespan characteristics may be degraded due to reduced phase stability, and if x corresponds to 0, the effect of improving capacity characteristics due to excess lithium content cannot be achieved.

[0056] The lithium metal oxide core may contain Ni in an amount corresponding to a, i.e., 0.20 ≤ a ≤ 0.40. If a exceeds the upper limit of the aforementioned range, the amount of oxidation-reduction reaction decreases, which may degrade capacity and output characteristics. Additionally, if a exceeds the lower limit of the aforementioned range, the amount of oxidation-reduction reaction becomes excessive, which may lead to a problem where lifespan characteristics deteriorate.

[0057] The lithium metal oxide core portion may contain Mn in an amount corresponding to b, i.e., 0.60 ≤ b ≤ 0.80. If b exceeds the upper limit of the aforementioned range, the amount of oxidation-reduction reaction is excessive, which degrades lifespan characteristics and may cause problems such as Mn leaching. Additionally, if b exceeds the lower limit of the aforementioned range, production costs increase, the stability of the cathode active material decreases, and capacity may decrease.

[0058] The lithium metal oxide core may contain M, an other metal element, in an amount corresponding to c, i.e., 0 ≤ c ≤ 0.1. The content of M may be appropriately selected and controlled to improve the battery effect within a range that does not degrade electrochemical properties. In this case, M may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

[0059] The lithium metal oxide core portion may contain Mo, a doping metal, in an amount corresponding to t, i.e., 0 < t ≤ 0.5. Specifically, t may be greater than 0 and less than 0.5 mol%, greater than 0 and less than 0.45 mol%, greater than 0 and less than 0.4 mol%, 0.05 to 0.5 mol%, 0.05 to 0.45 mol%, 0.05 to 0.4 mol%, 0.1 to 0.5 mol%, 0.1 to 0.45 mol%, 0.1 to 0.4 mol%, 0.15 to 0.5 mol%, 0.15 to 0.45 mol%, or 0.15 to 0.4 mol%.

[0060] By satisfying the aforementioned range of the mol% content of Mo, the Mo is Ni 2+ Increasing the ion presence ratio increases the capacity expression, and proper cation mixing occurs after charging, Li + Even if ions escape, the interlayer structure does not collapse, which can improve the battery's lifespan characteristics.

[0061] If the mol% content of Mo exceeds the upper limit of the aforementioned range, the Li interlayer distance becomes shorter and cation mixing phenomena intensify because the radius of Mo ions is larger than the radius of Ni and / or Mn, making it impossible to obtain the aforementioned advantages. Furthermore, if it exceeds the lower limit of the aforementioned range, problems may arise such as a decrease in the rolling density of the cathode active material and the specific capacity of the battery.

[0062] In this specification, the total metal (Me) excluding lithium refers to Ni, Mn, M, and Mo. The total metal (Me) excluding lithium may be included in the lithium metal oxide core portion in an amount corresponding to 1-x. For further explanation regarding x, refer to the section on the content of Li mentioned above.

[0063] The coating layer may be located on the lithium metal oxide core portion. The coating layer may improve structural stability by including Al as a coating metal to suppress surface side reactions.

[0064] The wt% content of the above Al may be 500 to 2000 ppm with respect to 100 wt% of the above lithium metal oxide core part. Specifically, 500 to 1900 ppm, 500 to 1800 ppm, 500 to 1700 ppm, 500 to 1600 ppm, 500 to 1500 ppm, 600 to 2000 ppm, 600 to 1900 ppm, 600 to 1800 ppm, 600 to 1700 ppm, 600 to 1600 ppm, 600 to 1500 ppm, 700 to 2000 ppm, 700 to 1900 ppm, 700 to 1800 ppm, 700 to 1700 ppm, 700 to 1600 ppm, 700 to 1500 ppm, 800 to 2000 ppm, 800 to 1900 It may be ppm, 800 to 1800 ppm, 800 to 1700 ppm, 800 to 1600 ppm, 800 to 1500 ppm, 900 to 2000 ppm, 900 to 1900 ppm, 900 to 1800 ppm, 900 to 1700 ppm, 900 to 1600 ppm, 900 to 1500 ppm, 1000 to 2000 ppm, 1000 to 1900 ppm, 1000 to 1800 ppm, 1000 to 1700 ppm, 1000 to 1600 ppm, 1000 to 1500 ppm.

[0065] By satisfying the aforementioned range of the wt% content of Al, side reactions such as oxidation-reduction on the surface of the cathode active material are mitigated, and at the same time, charge transfer is not hindered, thereby lowering the charge transfer resistance and improving the battery's capacity and low-temperature performance. If the wt% content of Al deviates from the upper limit of the aforementioned range, the charge transfer resistance increases, and Li + Problems may arise where ion mobility is reduced and the battery's capacity decreases due to it being a light element compared to transition metals. Additionally, if the value falls outside the lower limit of the aforementioned range, the aforementioned advantages cannot be obtained.

[0066] In addition, a portion of the above Al may be included by partially doping it inside and outside the lithium metal oxide core.

[0067] In one embodiment, the wt% content of Mo may be 1,000 to 5,000 ppm with respect to 100 wt% of the total metal (Me) excluding lithium. Specifically, 1000 to 4700 ppm, 1000 to 4400 ppm, 1000 to 4100 ppm, 1000 to 3800 ppm, 1000 to 3500 ppm, 1100 to 5000 ppm, 1100 to 4700 ppm, 1100 to 4400 ppm, 1100 to 4100 ppm, 1100 to 3800 ppm, 1100 to 3500 ppm, 1200 to 5000 ppm, 1200 to 4700 ppm, 1200 to 4400 ppm, 1200 to 4100 ppm, 1200 to 3800 ppm, 1200 to 3500 ppm, 1300 to 5000 ppm, 1300 to 4700 ppm, 1300 to 4400 ppm, 1300 to 4100 ppm, 1300 to 3800 ppm, 1300 to 3500 ppm, 1400 to 5000 ppm, 1400 to 4700 ppm, 1400 to 4400 ppm, 1400 to 4100 ppm, 1400 to 3800 ppm, 1400 to 3500 ppm, 1500 to 5000 ppm, 1500 to 4700 ppm, 1500 to 4400 ppm, 1500 to 4100 ppm, 1500 to 3800 ppm, 1500 to 3500 ppm, It may be 1500 to 3300 ppm, 1500 to 3100 ppm, 1500 to 2900 ppm, 1600 to 3500 ppm, 1600 to 3300 ppm, 1600 to 3100 ppm, 1600 to 2900 ppm, 1700 to 3500 ppm, 1700 to 3300 ppm, 1700 to 3100 ppm, or 1700 to 2900 ppm.

[0068] By satisfying the aforementioned range of the wt% content of Mo, the binding energy between the Mo element and the O element is greater than the binding energy between the Ni element and / or the Mn element and the O element, thereby reducing the interlayer (slab) distance of the Ni element and / or the Mn element and expanding the interlayer distance of Li, Li + The movement of ions can be facilitated. This reduces charge transfer resistance, thereby improving the battery's capacity and low-temperature performance. If the wt% content of Mo exceeds the upper limit of the aforementioned range, the Li interlayer distance becomes shorter and cation mixing intensifies because the radius of Mo ions is larger than the radius of Ni and / or Mn, making it impossible to obtain the aforementioned advantages. Furthermore, if it exceeds the lower limit of the aforementioned range, problems may arise such as a decrease in the rolling density of the cathode active material and the battery's capacity.

[0069] In one embodiment, the positive electrode active material for a lithium secondary battery has a rolled density of 2.5 to 5 g / cm³ under a pressure of 6 ton. 3 It may be. Specifically, 2.5 to 4.7 g / cm³ 3 , 2.5 to 4.4 g / cm³ 3 , 2.5 to 4.1 g / cm³ 3 , 2.5 to 3.9 g / cm³ 3 , 2.5 to 3.8 g / cm³ 3 , 2.6 to 5 g / cm² 3 , 2.6 to 4.7 g / cm³ 3 , 2.6 to 4.4 g / cm³ 3 , 2.6 to 4.1 g / cm³ 3 , 2.6 to 3.9 g / cm³ 3 , 2.6 to 3.8 g / cm³ 3 , 2.7 to 5 g / cm² 3 , 2.7 to 4.7 g / cm³ 3 , 2.7 to 4.4 g / cm³ 3 , 2.7 to 4.1 g / cm³ 3, 2.7 to 3.9 g / cm³ 3 , 2.7 to 3.8 g / cm³ 3 , 2.8 to 5 g / cm² 3 , 2.8 to 4.7 g / cm³ 3 , 2.8 to 4.4 g / cm³ 3 , 2.8 to 4.1 g / cm³ 3 , 2.8 to 3.9 g / cm³ 3 , 2.8 to 3.8 g / cm³ 3 , 3.0 to 5 g / cm² 3 , 3.0 to 4.7 g / cm³ 3 , 3.0 to 4.4 g / cm³ 3 , 3.0 to 4.1 g / cm³ 3 , 3.0 to 3.9 g / cm³ 3 , 3.0 to 3.8 g / cm³ 3 , 3.1 to 5 g / cm³ 3 , 3.1 to 4.7 g / cm³ 3 , 3.1 to 4.4 g / cm³ 3 , 3.1 to 4.1 g / cm³ 3 , 3.1 to 3.9 g / cm³ 3 , 3.1 to 3.8 g / cm³ 3 , 3.2 to 5 g / cm² 3 , 3.2 to 4.7 g / cm³ 3 , 3.2 to 4.4 g / cm³ 3 , 3.2 to 4.1 g / cm³ 3 , 3.2 to 3.9 g / cm³ 3 , 3.2 to 3.8 g / cm³ 3 It could be.

[0070] The above rolling density is a numerical range achieved by doping Mo, a heavy element relative to the transition metal, and satisfying the aforementioned range of rolling density can improve the specific capacity of the battery. If the above rolling density exceeds the upper limit of the aforementioned range, cracks may occur in the positive electrode active material, leading to problems such as degraded lifespan characteristics due to electrolyte penetration and surface degradation; if it exceeds the lower limit of the aforementioned range, the specific capacity of the battery may decrease and the energy density may be reduced.

[0071] In one embodiment, the positive electrode active material for a lithium secondary battery may have a fine particle generation rate of 6 to 9.3% under a pressure of 6 ton. In this case, the fine particle refers to one having an average particle size (D50) of 1 μm or less. Specifically, the above fine powder generation rates are 6 to 9%, 6 to 8.8%, 6 to 8.6%, 6 to 8.4%, 6 to 8.2%, 6.2 to 9.3%, 6.2 to 9%, 6.2 to 8.8%, 6.2 to 8.6%, 6.2 to 8.4%, 6.2 to 8.2%, 6.4 to 9.3%, 6.4 to 9%, 6.4 to 8.8%, 6.4 to 8.6%, 6.4 to 8.4%, 6.4 to 8.2%, 6.6 to 9.3%, 6.6 to 9%, 6.6 to 8.8%, 6.6 to 8.6%, 6.6 to 8.4%, 6.6 to 8.2%, 6.8 It may be up to 9.3%, 6.8 to 9%, 6.8 to 8.8%, 6.8 to 8.6%, 6.8 to 8.4%, 6.8 to 8.2%, 7 to 9.3%, 7 to 9%, 7 to 8.8%, 7 to 8.6%, 7 to 8.4%, 7 to 8.2%, 7.2 to 9.3%, 7.2 to 9%, 7.2 to 8.8%, 7.2 to 8.6%, 7.2 to 8.4%, 7.2 to 8.2%.

[0072] By satisfying the aforementioned range of fine particle generation rates, the shape of the positive electrode active material particles is maintained during the battery manufacturing and operation processes, which can help improve energy density and secure battery capacity. If the fine particle generation rate exceeds the upper limit of the aforementioned range, the shape of the positive electrode active material particles may be damaged, leading to a deterioration in lifespan characteristics. Furthermore, since a lower fine particle generation rate is advantageous for battery performance, the specification of the present invention should not be interpreted as limiting the fine particle generation rate to the lower limit of the aforementioned range.

[0073] In one embodiment, the positive electrode active material for a lithium secondary battery may have a porosity of 10 to 43% under a pressure of 6 ton. Specifically, 10 to 40%, 10 to 37%, 10 to 34%, 10 to 31%, 10 to 29%, 10 to 27%, 12 to 43%, 12 to 40%, 12 to 37%, 12 to 34%, 12 to 31%, 12 to 29%, 12 to 27%, 13 to 43%, 13 to 40%, 13 to 37%, 13 to 34%, 13 to 31%, 13 to 29%, 13 to 27%, 14 to 43%, 14 to 40%, 14 to 37%, 14 to 34%, 14 to 31%, 14 to 29%, 14 to 27%, 14 to 43%, 14 to 40%, 14 to 37%, 14 to 34%, 14 to 31%, 14 to 29%, 14 to 27% there is.

[0074] By satisfying the aforementioned range, the above porosity can help form the aforementioned rolling density. If the above porosity deviates from the upper and lower limits of the aforementioned range, the aforementioned advantages cannot be achieved.

[0075] In one embodiment, the coating layer of the positive electrode active material for a lithium secondary battery may include an island coating layer comprising a plurality of attached particles spaced apart from each other. The island coating layer has the aforementioned coating metal Al as its main component, and in this specification, "main component" means that it accounts for 60 wt% or more of the compounds within the coating layer. Since the positive electrode active material for a lithium secondary battery includes the island coating layer, compared to a structure in which the entire lithium metal oxide core is coated, Li + Battery performance can be improved by properly maintaining the ion transport pathways. The specific coverage rate and effects regarding this are described below.

[0076] In one embodiment, the island coating layer may have an average coverage rate of 25 to 75 area%. Specifically, it may be 25 to 72 area%, 30 to 75 area%, 30 to 72 area%, 35 to 75 area%, or 35 to 72 area%.

[0077] By satisfying the aforementioned range for the coverage rate of the island coating layer, the lithium oxide core portion can be properly coated to effectively reduce charge transfer resistance and exhibit improved electrochemical properties according to the coating layer. If the coverage rate exceeds the upper limit of the aforementioned range, due to excessive coating, Li + Hindering the movement of ions may lead to problems such as increased resistance and reduced capacitance and output characteristics. Furthermore, if the value exceeds the lower limit of the aforementioned range, the aforementioned advantages, reduced resistance growth rate, and effects regarding capacitance and output characteristics cannot be achieved.

[0078] In this specification, the average coverage rate of the island coating layer can be measured by the following method. First, the coverage rate of the island coating layer for a single positive electrode active material particle can be obtained by taking the ratio (%) of the area of ​​the island coating layer to the total surface area of ​​the positive electrode active material visible when the positive electrode active material is observed with a scanning electron microscope (SEM) at 5000x magnification. Next, the average coverage rate of the island coating layer can be obtained by taking the average of the coating layer coverage rates obtained by the above method for any 30 positive electrode active material particles within the positive electrode active material powder.

[0079] In one embodiment, the thickness of the island coating layer may be 5 to 120 nm. Specifically, it may be 5 to 100 nm, 5 to 80 nm, 5 to 60 nm, 5 to 40 nm, 8 to 120 nm, 8 to 100 nm, 8 to 80 nm, 8 to 60 nm, 8 to 40 nm, 10 to 120 nm, 10 to 100 nm, 10 to 80 nm, 10 to 60 nm, 10 to 40 nm, 11 to 120 nm, 11 to 100 nm, 11 to 80 nm, 11 to 60 nm, and 11 to 40 nm.

[0080] By satisfying the aforementioned range for the thickness of the island coating layer, surface side reactions are mitigated, and charge transfer resistance is lowered without hindering charge transfer, thereby improving the battery's capacity and low-temperature performance. The thickness of this coating layer can be appropriately achieved by controlling the amount of coating raw material input, the mixing method, and the coating heat treatment temperature during the manufacturing process.

[0081] If the thickness of the above-mentioned island coating layer exceeds the upper limit of the aforementioned range, Li due to excessive coating +Hindering the movement of ions may lead to problems such as increased resistance and reduced capacitance and output characteristics. Furthermore, if the value exceeds the lower limit of the aforementioned range, the aforementioned advantages, reduced resistance growth rate, and effects regarding capacitance and output characteristics cannot be achieved.

[0082] In this specification, the average thickness of the island coating layer can be measured by the following method. First, the thickness of the island coating layer for a single positive active material particle can be obtained by taking the average of the thicknesses of 30 randomly attached particles visible when the cross-section of the positive active material particle is observed with a transmission electron microscopy (TEM) at a magnification of 500,000. Next, the average thickness of the island coating layer can be obtained by taking the average of the coating layer thicknesses obtained by the above method for 30 randomly selected positive active material particles within the positive active material powder.

[0083] In one embodiment, the average particle size (D50) of the positive electrode active material for a lithium secondary battery may be 1 to 15 μm. Specifically, it may be 1 to 13 μm, 1 to 11 μm, 1 to 10 μm, 3 to 15 μm, 3 to 13 μm, 3 to 11 μm, 3 to 10 μm, 5 to 15 μm, 5 to 13 μm, 5 to 11 μm, 5 to 10 μm, 7 to 15 μm, 7 to 13 μm, 7 to 11 μm, and 7 to 10 μm.

[0084] By satisfying the aforementioned range, the above average particle size (D50) satisfies Li +It is possible to improve ion mobility and reduce charge transfer resistance. If the average particle size (D50) exceeds the upper limit of the aforementioned range, the high resistance of the lithium excess oxide material itself hinders the mobility of atoms within the battery, which may lead to problems such as reduced capacity and output characteristics. Furthermore, if it exceeds the lower limit of the aforementioned range, adverse reactions with the electrolyte may intensify, leading to problems such as degraded lifespan characteristics.

[0085] In one embodiment, the specific surface area (BET) of the positive electrode active material for a lithium secondary battery is 0.5 to 5 m² 2 It can be / g. Specifically, 0.5 to 4.5 m 2 / g, 0.5 to 4 m 2 / g, 0.5 to 3.5 m 2 / g, 1 to 5 m 2 / g, 1 to 4.5 m 2 / g, 1 to 4 m 2 / g, 1 to 3.5 m 2 / g, 1.5 to 5 m 2 / g, 1.5 to 4.5 m 2 / g, 1.5 to 4 m 2 / g, 1.5 to 3.5 m 2 / g, 2 to 5 m 2 / g, 2 to 4.5 m 2 / g, 2 to 4 m 2 / g, 2 to 3.5 m 2 / g can be.

[0086] As the above specific surface area satisfies the aforementioned range, the electrolyte penetrates smoothly into the cathode active material, allowing Li to + Rate characteristics can be secured by improving ion mobility. If the above specific surface area exceeds the upper limit of the aforementioned range, side reactions with the electrolyte may intensify, leading to a decrease in lifespan characteristics. Additionally, if it exceeds the lower limit of the aforementioned range, it becomes difficult for the electrolyte to penetrate, making it impossible to achieve the aforementioned advantages.

[0087]

[0088] Method for manufacturing a positive electrode active material for a lithium secondary battery

[0089] In another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery having the aforementioned characteristics and advantages is provided.

[0090] In one embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery comprises: (S1) a step of preparing a precursor containing Ni and Mn; (S2) a step of dry-mixing the precursor, a Li raw material, and a Mo-containing raw material and then calcining them to form a lithium metal oxide core; and (S3) a step of dry-mixing the lithium metal oxide core and an Al-containing raw material and then calcining them to form a coating layer to produce a positive electrode active material; wherein in step (S2), the Mo-containing raw material may be added such that the wt% content of the Mo is 1,000 to 5,000 ppm relative to 100 wt% of the precursor.

[0091] In step (S1) above, the precursor may contain Ni in an amount of 0.20 to 0.40 mol%. If the mol% of Ni deviates from the upper limit of the aforementioned range, the amount of oxidation-reduction reaction decreases, which may degrade capacity and output characteristics. Additionally, if it deviates from the lower limit of the aforementioned range, the amount of oxidation-reduction reaction becomes excessive, which may lead to a problem where lifespan characteristics degrade.

[0092] In addition, the above precursor may contain Mn in an amount of 0.60 to 0.80 mol%. If the mol% of Mn exceeds the upper limit of the aforementioned range, the amount of oxidation-reduction reaction is excessive, which degrades lifespan characteristics and may cause problems such as Mn leaching. Furthermore, if it exceeds the lower limit of the aforementioned range, the production cost increases, the stability of the cathode active material decreases, and the capacity may decrease.

[0093] The above precursor may further include other metal element M in an amount of 0 to 0.1 mol%. The content of M can be appropriately selected and controlled to improve the cell effect within a range that does not degrade electrochemical properties. In this case, M may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

[0094] The particle size of the above precursor may be 1 to 100 μm. The particle size of this precursor is a factor directly related to the particle size of the positive electrode active material to be manufactured, and further explanation regarding this can be found in the section on the average particle size (D50) of the positive electrode active material for the lithium secondary battery mentioned above.

[0095] In the above step (S2), the Li raw material may be LiOH, Li2CO3, etc., with a particle size of 10 μm. However, it is not limited thereto, and modifications can be made based on the common sense of a person skilled in the art as long as they perform the aforementioned function and do not impair the purpose of the present invention.

[0096] In step (S2) above, the Li raw material can be introduced such that the mol% of Li relative to the precursor is greater than 1 and less than or equal to 1.5. However, if the value exceeds the upper limit of the aforementioned range, the residual lithium increases, which may lead to an increase in the amount of gas generated due to side reactions with hydrogen fluoride (HF), etc., within the battery. Additionally, if the value exceeds the lower limit of the aforementioned range, there may be a problem of reduced capacity due to a lack of Li in the cathode active material.

[0097] In step (S2) above, the Mo raw material may be added such that the wt% content of Mo is 1,000 to 5,000 ppm relative to 100 wt% of the precursor. Further explanation regarding this can be found in the section on the wt% content of Mo relative to 100 wt% of the total metal (Me) excluding the aforementioned lithium.

[0098] The above step (S2) can be dry mixed and calcined to dope the Mo into the lithium metal oxide core. Unlike wet doping, this dry doping does not involve the process of mixing the doping metal into a solvent, transferring it to the oxide surface, and then volatilizing the solvent, which has the advantage of simplifying the process and reducing process costs.

[0099] The above step (S3) can form a coating layer containing Al on the lithium metal oxide core by dry mixing and firing. Compared to wet coating, this dry coating allows for the easy formation of the aforementioned island coating layer on the core, thereby simplifying the process, reducing process costs, and facilitating the manufacture of the aforementioned positive electrode active material for a lithium secondary battery.

[0100] In one embodiment, in step (S2), the Mo-containing raw material may include one or more selected from MoO3, MoO2, MoO2Cl2, and other raw materials containing Mo. However, it is not limited thereto, and modifications can be made based on the common sense of those skilled in the art as long as they perform the aforementioned functions and do not impair the purpose of the present invention.

[0101] In one embodiment, the average particle size (D50) of the Mo-containing raw material in step (S2) may be 50 to 800 nm. Specifically, it may be 50 to 700 nm, 50 to 600 nm, 100 to 800 nm, 100 to 700 nm, 100 to 600 nm, 200 to 800 nm, 200 to 700 nm, or 200 to 600 nm.

[0102] In one embodiment, in step (S3), the Al-containing raw material may be introduced such that the wt% content of Al is 500 to 2000 ppm with respect to 100 wt% of the lithium metal oxide core. Further explanation regarding this can be found in the section regarding the wt% content of Al with respect to 100 wt% of the lithium metal oxide core.

[0103] In one embodiment, in step (S3), the Al-containing raw material may include one or more materials selected from Al2O3, Al(OH)3, and other raw materials containing Al. However, it is not limited thereto, and modifications can be made based on the common sense of those skilled in the art as long as they perform the aforementioned functions and do not impair the purpose of the present invention.

[0104] In one embodiment, step (S2) may be performed by calcination at a temperature of 600°C or higher. This is for doping Mo into the lithium metal oxide core using the Mo-containing raw material, and specifically, the temperature range may be 600 to 1000°C, 600 to 950°C, 700 to 1000°C, 700 to 950°C, 800 to 1000°C, or 800 to 950°C. By satisfying the aforementioned calcination temperature range, Mo is uniformly doped into the inside and outside of the lithium metal oxide core, thereby improving lifespan characteristics and reducing charge transfer resistance, which can improve the battery's capacity and low-temperature performance.

[0105] If the above-mentioned firing temperature deviates from the upper limit of the aforementioned range, the primary particles of the positive electrode active material become single particles due to sintering, and the specific surface area decreases, so the aforementioned advantages cannot be achieved. In addition, if it deviates from the lower limit of the aforementioned range, Mo is not properly doped into the lithium metal oxide core, and the resulting effect may be negligible.

[0106] In one embodiment, step (S3) may be performed at a temperature of 300 to 500°C. This is for forming the coating layer with the Al-containing raw material, and specifically, it may be 300 to 450°C, 350 to 500°C, or 350 to 450°C.

[0107] By satisfying the aforementioned range of the calcination temperature, the type of compound in the coating layer, the shape of the coating layer, and the average thickness can be appropriately obtained within the range according to the present invention, thereby enabling the aforementioned advantages to be achieved. If the calcination temperature deviates from the upper limit of the aforementioned range, problems may arise in which the added Al-containing raw material does not form a coating layer but is doped into the lithium metal oxide core or separated into a secondary phase (segregation). Furthermore, if the temperature deviates from the lower limit of the aforementioned range, the coating layer is not formed smoothly, and the effects of improving electrochemical properties and suppressing surface side reactions through the coating layer may be negligible.

[0108] At this time, the above-mentioned sintering may be performed for 1 to 10 hours. Specifically, it may be 1 to 8 hours, 2 to 7 hours, or 3 to 6 hours. By satisfying the above-mentioned ranges for the sintering time, the type of compound in the coating layer, the shape of the coating layer, and the average thickness, etc., can be appropriately obtained within the range according to the present invention, thereby enabling the aforementioned advantages to be achieved.

[0109] If the above-mentioned calcination temperature deviates from the upper limit of the aforementioned range, the added Al-containing raw material may not form a coating layer and may instead be doped into the lithium metal oxide core or segregated into a secondary phase. Additionally, if the above-mentioned temperature deviates from the lower limit of the aforementioned range, the coating layer may not form smoothly, resulting in minimal effects for improving electrochemical properties and suppressing surface side reactions through the coating layer.

[0110] In one embodiment, the firing in steps (S2) and / or (S3) may be carried out in an air atmosphere or an O2 atmosphere. However, this is not limited thereto, and modifications can be made by the common sense of those skilled in the art as long as they perform the aforementioned functions and do not impair the purpose of the present invention.

[0111]

[0112] lithium secondary battery

[0113] In another embodiment of the present invention, a lithium secondary battery having excellent rate characteristics and low-temperature performance is provided by reducing charge transfer resistance through the aforementioned positive electrode active material.

[0114] In one embodiment, the lithium secondary battery comprises a positive electrode; a negative electrode; and an electrolyte; wherein the positive electrode comprises a positive active material composed of a lithium metal oxide core and a coating layer, wherein the lithium metal oxide core is doped with Mo and the coating layer comprises Al, and the charge transfer resistance (R1) measured after one cycle under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C may be 20 to 32 Ω.

[0115] For a further explanation of the above-mentioned positive electrode active material, refer to the section on the positive electrode active material for lithium secondary batteries described above.

[0116] The above R1 is a charge transfer resistance measured after charging for one cycle under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C, and specifically may be 20 to 30 Ω, 20 to 29 Ω, 20 to 28 Ω, 21 to 32 Ω, 21 to 30 Ω, 21 to 29 Ω, 21 to 28 Ω, 22 to 32 Ω, 22 to 30 Ω, 22 to 29 Ω, 22 to 28 Ω, 23 to 32 Ω, 23 to 30 Ω, 23 to 29 Ω, 23 to 28 Ω, 24 to 32 Ω, 24 to 30 Ω, 24 to 29 Ω, and 24 to 28 Ω.

[0117] By satisfying the aforementioned range, the specific capacity and low-temperature performance of the battery can be improved. If the above R1 deviates from the upper limit of the aforementioned range, Li + The mobility of ions is reduced, so the aforementioned advantages cannot be realized. Furthermore, since a smaller R1 is advantageous for battery performance, the specification of the present invention should not be interpreted as limiting R1 to the lower limit of the aforementioned range.

[0118] In one embodiment, the ratio of R1 to the charge transfer resistance (R) may be less than 0.48 after the lithium secondary battery is formed under a voltage of 4.65 V, a temperature of 45°C, and 0.1 C. Specifically, it may be greater than 0 and less than 0.47, greater than 0 and less than 0.46, greater than 0 and less than 0.45, greater than 0 and less than 0.44, greater than 0 and less than 0.43, or greater than 0 and less than 0.42. This takes into account the actual operating environment of the lithium secondary battery and can be understood as a value comparing the charge transfer resistance (R) immediately after formation with the charge transfer resistance (R1) at room temperature of 25°C, which is the temperature at which the subsequent cycle proceeds.

[0119] By satisfying the aforementioned range, it can be predicted that the battery performance will be excellent even in the actual operating environment of the lithium secondary battery. If the above ratio deviates from the upper limit of the aforementioned range, the aforementioned advantage cannot be obtained. Furthermore, since maintaining battery performance with respect to temperature changes is excellent as the above ratio decreases, the specification of the present invention should not be interpreted as limiting the lower limit of the above ratio.

[0120] In one embodiment, the charge transfer resistance (R50) of the lithium secondary battery measured after charging for 50 cycles under a voltage of 4.4 V, a temperature of 25°C, and 0.33 C may be 10 to 23 Ω. Specifically, 10 to 22 Ω, 10 to 21 Ω, 10 to 20 Ω, 10 to 19 Ω, 11 to 23 Ω, 11 to 22 Ω, 11 to 21 Ω, 11 to 20 Ω, 11 to 19 Ω, 12 to 23 Ω, 12 to 22 Ω, 12 to 21 Ω, 12 to 20 Ω, 12 to 19 Ω, 13 to 23 Ω, 13 to 22 Ω, 13 to 21 Ω, 13 to 20 Ω, 13 to 19 Ω, 14 to 23 Ω, 14 to 22 Ω, 14 to 21 Ω, 14 to 20 Ω, 14 to 19 Ω, 15 to It can be 23 Ω, 15 to 22 Ω, 15 to 21 Ω, 15 to 20 Ω, or 15 to 19 Ω.

[0121] By satisfying the aforementioned range, the specific capacity and low-temperature performance of the battery can be improved. If the above R50 deviates from the upper limit of the aforementioned range, Li + The mobility of ions is reduced, so the aforementioned advantages cannot be realized. Furthermore, since a smaller R50 is advantageous for battery performance, the specification of the present invention should not be interpreted as limiting R50 to the lower limit of the aforementioned range.

[0122] In one embodiment, the ratio of R50 to the charge transfer resistance (R) may be less than 0.33 after the lithium secondary battery is formed under a voltage of 4.65 V, a temperature of 45°C, and 0.1 C. Specifically, it may be greater than 0 and less than 0.32, greater than 0 and less than 0.31, greater than 0 and less than 0.30, greater than 0 and less than 0.29, or greater than 0 and less than 0.28. This takes into account the environment in which the actual lithium secondary battery operates and can be understood as a value comparing the charge transfer resistance (R) immediately after formation with the charge transfer resistance (R50) at room temperature of 25°C, which is the temperature at which the subsequent cycle proceeds.

[0123] By satisfying the aforementioned range, it can be predicted that the battery performance will be excellent even in the actual operating environment of the lithium secondary battery. If the above ratio deviates from the upper limit of the aforementioned range, the aforementioned advantage cannot be obtained. Furthermore, since maintaining battery performance with respect to temperature changes is excellent as the above ratio decreases, the specification of the present invention should not be interpreted as limiting the lower limit of the above ratio.

[0124] The above charge transfer resistance is measured through EIS (electrochemical impedance spectroscopy), and EIS refers to a method of analyzing electrochemical reactions occurring at electrodes by modeling them.

[0125] In one embodiment, the lithium secondary battery can satisfy the following Equation 1 when charged.

[0126] [Equation 1]

[0127] 0.47 ≤ T2 / T1 ≤ 1

[0128] In the above Equation 1, T2 is the low-temperature discharge capacity under a predetermined condition, and T1 is the discharge capacity at room temperature. The low-temperature discharge condition and the room temperature discharge condition refer to the capacity when a charged lithium secondary battery is discharged at each temperature after being maintained at a low temperature for a predetermined period of time. Equation 1 can be understood as a numerical value representing the performance of a lithium secondary battery at a low temperature.

[0129] Specifically, the charged lithium secondary battery may be in a charged state after undergoing a formation process and then proceeding with one cycle under a voltage of 4.4 to 4.5 V, a temperature of 25°C, and 0.2 C. Additionally, the condition of maintaining the charged lithium secondary battery at a low temperature for a predetermined period may be a temperature range of -10 to 0°C, -8 to 0°C, -6 to 0°C, -10 to -2°C, -8 to -2°C, or -6 to -2°C, and the low temperature storage time may be 1 to 6 hours, 1 to 5 hours, 2 to 6 hours, or 2 to 5 hours.

[0130] In addition, the predetermined conditions under which T2 is measured may be a constant power (CP) of 3.7 Wh, a temperature of -5°C, and a temperature of 0.2°C, and the predetermined conditions under which T1 is measured may be a constant power (CP) of 3.7 Wh, a temperature of 25°C, and a temperature of 0.2°C.

[0131] Specifically, the above Equation 1 may be 0.47 to 1, 0.5 to 1, 0.55 to 1, 0.58 to 1, 0.6 to 1, 0.62 to 1, or 0.64 to 1. As the above Equation 1 satisfies the aforementioned range, the charge transfer resistance is low, so Li + The increased mobility of ions allows the lithium secondary battery to maintain a high capacity even at low temperatures of -10 to 0°C.

[0132] If the above ratio deviates from the lower limit of the aforementioned range, a problem may arise in which the capacity is significantly reduced when discharged at low temperatures. Furthermore, as the above Equation 1 approaches 1, the maintenance of battery performance at low temperatures is excellent; therefore, the specification of the present invention should not be interpreted as limiting the upper limit of the above ratio.

[0133] In one embodiment, the lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte. The lithium secondary battery may optionally further include a battery container that accommodates an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0134] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising the aforementioned positive electrode active material for a lithium secondary battery.

[0135] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0136] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0137] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive active material layer.

[0138] In addition, the conductive material is used to impart conductivity to the electrode, and can be used without special limitations as long as it possesses electronic conductivity without causing chemical changes in the battery being constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% relative to the total weight of the positive electrode active material layer.

[0139] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0140] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0141] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0142] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0143] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0144] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0145] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0146] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0147] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0148] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0149] The above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0150] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0151] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0152] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0153] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0154] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0155]

[0156] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0157]

[0158] Examples

[0159] Example 1

[0160] (1) Preparation of positive electrode active material for lithium secondary batteries

[0161] Precursor Ni prepared using a co-precipitation reaction 0.35 Mn 0.65 (OH)2 and the Li raw material LiOH·H2O were weighed and mixed so that the Li / Me ratio was 1.33, and then dry-mixed with MoO3. Subsequently, a lithium metal oxide core was formed by calcining at 850°C for 10 hours under an atmospheric atmosphere. At this time, the amount of MoO3 added was such that the wt% content of Mo was 1500 ppm relative to 100 wt% of the precursor. Subsequently, the lithium metal oxide core and Al2O3 were dry-mixed, and then a coating layer was formed by calcining at 400°C for 5 hours under an atmospheric atmosphere to produce a positive electrode active material. At this time, the amount of Al2O3 added was such that the wt% content of Al was 500 ppm relative to 100 wt% of the positive electrode active material.

[0162] (2) Manufacturing of lithium secondary batteries

[0163] The slurry for electrode manufacturing was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF1100) in a ratio of 92.5 : 3.5 : 4 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content concentration was approximately 30%. The prepared slurry was coated onto a 15 μm thick Al foil using a doctor blade, dried, and then rolled. At this time, the electrode loading amount was approximately 14 mg / cm². 2 It was.

[0164] A CR2032 coin cell was manufactured using an electrolyte of 1 M LiPF6 in EC:EMC=3:7 (vol%) with 3.0 vol% FEC added relative to the total amount of the electrolyte, a PP separator, and a lithium anode (200 μm, Honzo metal).

[0165]

[0166] Examples 2 to 5

[0167] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that the input amounts of MoO3 and Al2O3 were varied as shown in Table 1 below.

[0168] Mo Doping Content (ppm) Mo Doping Content (mol%) Al Coating Content (ppm) Example 1 15000.1599500 Example 2 20000.21321000 Example 3 25000.26651500 Example 4 30000.31982000 Example 5 35000.37312000

[0169] (In Table 1 above, Mo doping content (ppm) refers to the wt% content of Mo relative to 100 wt% of the precursor, and Mo doping content (mol%) refers to the mol% content of Mo relative to 100 mol% of the precursor.)

[0170] Comparative Example A - Change in Mo and Al content

[0171] Comparative Example A1

[0172] Precursor Ni prepared using a co-precipitation reaction 0.35 Mn 0.65 (OH)2 and the Li raw material LiOH·H2O were weighed and mixed so that the Li / Me ratio was 1.33, and then calcined at 850°C for 10 hours under an atmospheric atmosphere to prepare a positive electrode active material. A lithium secondary battery was prepared by carrying out the same procedure as in Example 1.

[0173]

[0174] Comparative Examples A2 and A3

[0175] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that the input amounts of MoO3 and Al2O3 were different, and the wt% content of Mo and Al was different as shown in Table 2 below.

[0176] Mo Doping Content (ppm) Mo Doping Content (mol%) Al Coating Content (ppm) Comparative Example A 1000 Comparative Example A 220000 0.21325000 Comparative Example A 320000 0.213210000

[0177] (In Table 2 above, Mo doping content (ppm) refers to the wt% content of Mo relative to 100 wt% of the precursor, and Mo doping content (mol%) refers to the mol% content of Mo relative to 100 mol% of the precursor.)

[0178] Comparative Example B - Change in coating material

[0179] Comparative Example B1

[0180] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Comparative Example A1.

[0181]

[0182] Comparative Example B2

[0183] A positive electrode active material and a lithium secondary battery were prepared by carrying out the same procedure as in Example 1, except that the amount of MoO3 added was such that the wt% content of Mo was 2000 ppm relative to 100 wt% of the precursor, and no coating layer was formed.

[0184]

[0185] Comparative Examples B3 to B6

[0186] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that MoO3 was added such that the wt% content of Mo was 2000 ppm relative to 100 wt% of the precursor, and H3BO3, Co(OH)2, ZrO2, and Ta2O5 were added instead of Al2O3 such that the wt% content of B, Co, Zr, and Ta was 500 ppm relative to 100 wt% of the lithium metal oxide core. This is summarized in Table 3 below.

[0187] Mo Doping Content (ppm) Mo Doping Content (mol%) Coating Material Coating Content (ppm) Comparative Example B100-0 Comparative Example B220000.2132-0 Comparative Example B320000.2132B500 Comparative Example B420000.2132Co500 Comparative Example B520000.2132Zr500 Comparative Example B620000.2132Ta500

[0188] (In Table 3 above, Mo doping content (ppm) refers to the wt% content of Mo relative to 100 wt% of the precursor, and Mo doping content (mol%) refers to the mol% content of Mo relative to 100 mol% of the precursor.)

[0189] Experimental Example A - Examples and Comparative Example A

[0190] (1) Particle size measurement

[0191] The particle size of Example and Comparative Example A was measured using a Microtrac particle size analyzer, and the results are shown in Table 4 below. Since both Example and Comparative Example A were manufactured from precursors of the same particle size under the same calcination conditions, it can be seen that the average particle size (D50) has a similar value.

[0192] D10 (μm) D50 (μm) D90 (μm) SPAN Example 1 3.049.0914.031.21 Example 2 3.019.0714.021.21 Example 3 3.029.0814.011.21 Example 4 3.029.0714.011.21 Example 5 3.069.0814.041.21 Comparative Example A 1 3.029.0714.021.21 Comparative Example A 2 3.079.0914.061.21 Comparative Example A 3 3.079.0914.061.21

[0193] (2) Measurement of coating layer thickness and shape

[0194] Figure 1 is a scanning electron microscope (SEM) image of Example 1 and Comparative Example A1.

[0195] Looking at Fig. 1, it can be seen that the surface of Example 1 in the left image and Comparative Example A1 in the right image are different. Through this, it can be seen that Example 1 has a coating layer composed of Al formed on it, unlike Comparative Example A1.

[0196] Figure 2 is a TEM (transmission electron microscopy) image of Example 1.

[0197] Looking at Figure 2, the left image shows that Mo is uniformly present inside and outside the positive electrode active material particles. Through this, it can be inferred that the lifespan characteristics are improved by uniformly penetrating inside and outside the lithium metal oxide core rather than forming a coating layer with Mo.

[0198] In addition, the image on the right shows that Al has formed a coating layer on some areas of the surface of the positive active material particles. This is in the form of the aforementioned island coating layer, and it can be inferred that forming an island coating layer by adding Al in an appropriate amount as defined in the present invention is more advantageous for reducing charge transfer resistance than forming a coating layer that covers the entire surface by adding an excessive amount of Al.

[0199] In addition, as previously mentioned, the average thickness of the island coating layer was measured through Fig. 2 and is shown in Table 4 below. Through this, it can be seen that, as in Examples 1 to 5, when the Al content is added at 500 to 2000 ppm, a coating layer thickness capable of exhibiting the aforementioned advantages is formed.

[0200] Coating layer thickness (nm) Example 1 12 Example 2 16 Example 3 22 Example 4 28 Example 5 32 Comparative Example A 10 Comparative Example A 2 126 Comparative Example A 3 241

[0201] (3) Measurement of rolling density, fine powder generation rate and porosity

[0202] For the example and comparative example A, 3 g of positive electrode active material powder was placed in a 1 cm diameter mold, and the rolling density, fine particle generation rate, and porosity were measured using a hydraulic press under a pressure of 6 ton and are shown in Table 6 below. Through this, it can be confirmed that the example with Mo doping and Al coating has a high rolling density, a low fine particle generation rate, and a low porosity. Looking at the rolling density and porosity in Table 6 below, it can be seen that they are inversely proportional to each other; this can be understood as the voids within the positive electrode active material being reduced as it is compressed under a pressure of 6 ton, thereby achieving a high rolling density. Through this, it can be seen that a positive electrode active material capable of exhibiting the aforementioned advantages was manufactured when the wt% content of Mo is 1500 to 3500 ppm and the Al content is 500 to 2000 ppm.

[0203] 6 ton lower rolled density (g / cm³) 3 Fine powder generation rate (%) under 6 ton Porosity (%) under 6 ton Example 1 3.24 7.18 26.4 Example 2 3.41 7.12 22.0 Example 3 3.56 7.48 19.2 Example 4 3.62 7.82 17.3 Example 5 3.74 8.18 14.7 Comparative Example A 1 2.41 9.52 45.1 Comparative Example A 2 2.49 9.31 43.4 Comparative Example A 3 2.44 9.58 44.6

[0204] (4) Measurement of electrochemical properties

[0205] The electrochemical characteristics of the lithium secondary batteries of Example and Comparative Example A were measured under the conditions shown in Table 7 below. Through this, it can be confirmed that the lithium secondary battery containing a positive electrode active material having the content defined in the present invention exhibits excellent rate characteristics and life characteristics at both a high temperature of 45°C and a room temperature of 25°C. In particular, it can be seen that the life characteristics of the Example are superior, as the 50-cycle capacity retention rate is at least 4%p higher than that of Comparative Example A.

[0206] 0.1 C, 45℃ 0.1 C 25℃ 0.33 C, 25℃ Charging Capacity (mAh / g) Discharging Capacity (mAh / g) Discharging Capacity (mAh / g) Discharging Capacity (mAh / g) 50 Cycle Capacity Retention Rate (%) Example 1 298.7 275.8 215.2 202.7 97.2 Example 2 299.0 276.4 215.5 203.0 97.4 Example 3 299.2 276.5 215.7 203.2 97.2 Example 4 299.4 276.7 216.2 203.7 97.0 Example 5 299.8 277.1 216.5 204.1 96.8 Comparative Example A 1 294.6 274.0 214.2 196.6 93.7 Comparative Example A2290.1269.8211.8193.791.4 Comparative Example A3283.2260.1205.7189.590.2

[0207] Experimental Example B - Examples and Comparative Example B

[0208] (1) Measurement of charge transfer resistance

[0209] Figure 3 is a graph of electrochemical impedance spectroscopy (EIS) measurements in the charged states of Example 1, Comparative Examples B1 and B3 to B6.

[0210] EIS was measured for the lithium secondary batteries of Example 1 and Comparative Example B and is shown in Table 8 below. In this case, R is the charge transfer resistance value immediately after formation under a voltage of 4.65 V, a temperature of 45°C, and 0.1 C, and R1 and R50 are the charge transfer resistance values ​​measured after 1 cycle of charging and discharging under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C, and 50 cycles of charging and discharging under 0.33 C, respectively, and then recharging.

[0211] Through this, it can be confirmed that a lithium secondary battery containing a positive electrode active material with a coating layer formed with Al, as in Example 1, has a lower charge transfer resistance value compared to Comparative Example B, which does not form a coating layer or has coating layers formed with B, Co, Zr, and Ta, respectively. In other words, it can be inferred that forming a coating layer with Al can exhibit the aforementioned advantages by lowering the charge transfer resistance value compared to other coating materials.

[0212] In this case, R1 / R and R50 / R serve as criteria for comparing performance in an environment where the actual lithium secondary battery is operated, and through this, it can be inferred that the embodiment of the present invention can maintain excellent performance even in an actual operating environment as described above.

[0213] R (Ω)R1 (Ω)R1 / RR50 (Ω)R50 / R Example 1 66.64 27.94 0.42 18.69 0.28 Comparative Example B 173.82 41.28 0.563 3.10.45 Comparative Example B 270.673 8.51 0.542 3.32 0.33 Comparative Example B 369.813 6.48 0.52 26.14 0.37 Comparative Example B 469.683 6.07 0.52 24.91 0.36 Comparative Example B 568.243 2.78 0.48 27.44 0.40 Comparative Example B 668.723 5.70.52 25.45 0.37

[0214] (2) Measurement of electrochemical properties

[0215] The electrochemical characteristics of the lithium secondary batteries of Example 1 and Comparative Example B were measured at a voltage of 4.4 V and a temperature of 25°C and are shown in Table 9 below. Through this, it can be confirmed that the lithium secondary battery containing a positive electrode active material with an Al coating layer formed thereon, as in the example of the present invention, has high rate characteristics and lifespan characteristics.

[0216] 0.1 C Discharge Capacity (mAh / g) 0.33 C Discharge Capacity (mAh / g) 0.33 C / 0.1 C (%) Example 1 2 16.2 20 3.5 9 4.1 Comparative Example B 1 2 11.8 19 6.6 9 2.8 Comparative Example B 2 2 13.1 19 9.1 9 3.4 Comparative Example B 3 2 15.1 20 0.4 9 3.1 Comparative Example B 4 2 15.4 20 1.3 9 3.5 Comparative Example B 5 2 15.8 20 1.9 9 3.6 Comparative Example B 6 2 15.9 20 1.8 9 3.5

[0217] (3) Low temperature performance measurement

[0218] A 2 Ah lithium secondary battery prepared with the positive active material of Example 1 and Comparative Example B was charged after one cycle at a voltage of 4.4 to 4.5 V, a temperature of 25°C, and 0.2 C after formation, then stored in a low-temperature chamber maintained at -5°C for 4 hours, and subsequently discharged at a constant power (CP) of 3.7 Wh and 0.2 C. At this time, the discharge capacity was measured at room temperature of 25°C and low temperature of -5°C, respectively, and is shown in Table 10 below. Through this, it can be confirmed that the lithium secondary battery containing the positive active material with an Al coating layer maintains excellent performance even at low temperatures.

[0219] 25℃ Discharge Capacity (Ah) - 5℃ Discharge Capacity (Ah) Formula 1 (T2 / T1) Example 1 2.0 1.3 0.650 Comparative Example B1 1.7 10.5 20.301 Comparative Example B2 1.7 60.7 20.409 Comparative Example B3 1.7 80.7 50.421 Comparative Example B4 1.8 10.7 80.431 Comparative Example B5 1.9 40.9 10.469 Comparative Example B6 1.8 90.8 50.450

[0220]

[0221] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

It includes an anode; a cathode; and an electrolyte, The above-mentioned positive electrode comprises a positive electrode active material composed of a lithium metal oxide core and a coating layer, and The above lithium metal oxide core is doped with Mo, and The above coating layer includes Al, and Satisfying Equation 1 below, Lithium secondary battery. [Equation 1] 0.47 ≤ T2 / T1 ≤ 1 (In the above Equation 1, T2 is the low-temperature discharge capacity under specific conditions, and T1 is the discharge capacity at room temperature, and The above low-temperature discharge condition and the above room-temperature discharge condition refer to the capacity when a charged cell is maintained at a low temperature for a predetermined period of time and then discharged at each respective temperature.) In paragraph 1, A charge transfer resistance (R1) of 20 to 32 Ω measured after one cycle under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C, Lithium secondary battery. In paragraph 2, The ratio of the above R1 to the charge transfer resistance (R) measured after formation under a voltage of 4.65 V, a temperature of 45°C, and 0.1 C is less than 0.48 Lithium secondary battery. In paragraph 1, A charge transfer resistance (R50) of 10 to 23 Ω measured after 50 cycles under a voltage of 4.4 V, a temperature of 25°C, and 0.1 C, Lithium secondary battery. In paragraph 4, The ratio of the above R50 to the charge transfer resistance (R) measured after formation under a voltage of 4.65 V, a temperature of 45°C, and 0.1 C is less than 0.33 Lithium secondary battery. In paragraph 1, The above lithium metal oxide core portion is represented by the following chemical formula 1, Lithium secondary battery. [Chemical Formula 1] Li 1+x [(Ni a Mr b M c ) 1-t Mo t ] 1-x O2 (In the above Chemical Formula 1, M comprises Co, Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof, and 0 < x < 0.5, 0.20 ≤ a ≤ 0.40, 0.60 ≤ b ≤ 0.80, 0 ≤ c ≤ 0.1, a+b+c=1, and 0 < t ≤ 0.5.) In paragraph 1, The wt% content of the above Mo is 1,000 to 5,000 ppm with respect to 100 wt% of the total metal (Me) excluding lithium, Lithium secondary battery. In paragraph 1, The wt% content of the above Al is 500 to 2000 ppm with respect to 100 wt% of the above lithium metal oxide core portion, Lithium secondary battery.

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