Secondary battery

Abstract

The present invention relates to a secondary battery comprising: a cathode including a cathode active material; an electrolyte; and an anode, wherein, in the secondary battery, the capacity change rate with respect to a termination voltage change represented by formula 1 below is 1 (Volt-1) or less. [Formula 1] (second capacity - first capacity) / {second capacity X (second termination voltage - first termination voltage)} In formula 1, the second capacity is a discharge capacity measured after charging to a second termination voltage, the first capacity is a discharge capacity measured after charging to a first termination voltage, the second termination voltage is selected in a range of 4.15 V-4.25 V, the first termination voltage is selected in a range of 4.05 V-4.15 V, and the difference between the second termination voltage and the first termination voltage (second termination voltage - first termination voltage) is 0.05 V or more.

Description

secondary battery

[0001] The present invention relates to a secondary battery with a small rate of change in capacity according to a change in voltage.

[0002] With the increasing technological development and demand for various electronic devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, those featuring high energy density and voltage, long cycle life, and low self-discharge rates have been commercialized and are widely used. Consequently, there is a growing demand from the industry to improve the performance of rechargeable batteries.

[0003] As part of efforts to improve the performance of secondary batteries, attention is focused on introducing layered high-nickel lithium transition metal composite oxides as cathode active materials. In such cathode active materials, a phenomenon occurs where nickel occupies the space within the lithium layer. This nickel occupancy rate in the lithium layer (Ni Li ) causes a change in the H2 / H3 phase transition behavior, and as a result, the electrochemical properties of the lithium secondary battery, such as charge / discharge capacity, may change.

[0004] In the case of NCM-based layered cathode active materials, the cathode potential can vary even at the same cell voltage due to factors such as electrode thickness, the ratio of active material to conductive material, binder content, electrolyte composition, the type of cathode and / or anode, or the thickness of the electrode and / or electrolyte layer during the electrode and cell manufacturing process. Such variations in cathode potential can lead to differences in design capacity, causing deviations from expected specifications, or result in changes to cell performance and lifespan depending on the balance with the anode.

[0005] In other words, considering the design precision and quality control aspects of secondary batteries, cells with minimal capacity change even when the anode potential shifts are advantageous. However, conventional technology manufactures cathode materials without considering this, ultimately leading to various quality issues during the cell manufacturing process.

[0006] The present invention is designed to solve the above problems and aims to provide a secondary battery comprising a positive electrode active material containing a lithium transition metal oxide, wherein the difference in capacity according to changes in the charging terminal voltage is reduced.

[0007] Accordingly, the purpose is to reduce capacity deviations caused by other variables that may intervene in the design and / or manufacturing process of the secondary battery, thereby improving the precision of the initial design and providing a secondary battery that has relatively consistent quality even under changes in external conditions.

[0008] The present invention relates to a secondary battery comprising a positive electrode including a positive active material; an electrolyte; and a negative electrode, wherein the secondary battery has a capacity change rate with respect to a terminal voltage change represented by the following Equation 1 of 1 (Volt -1 This relates to a secondary battery with a value of ) or less.

[0009] [Equation 1]

[0010] (2nd capacitance - 1st capacitance) / {2nd capacitance × (2nd terminal voltage - 1st terminal voltage)}

[0011] In the above formula, the second capacity is the discharge capacity measured after charging to the second terminal voltage, and the first capacity is the discharge capacity measured after charging to the first terminal voltage; the second terminal voltage is selected from a range of 4.15 V or more to 4.25 V or less, and the first terminal voltage is selected from a range of 4.05 V or more to 4.15 V or less, and the difference between the second terminal voltage and the first terminal voltage (second terminal voltage - first terminal voltage) is 0.05 V or more.

[0012] In one embodiment, the first capacity is measured by CC charging at a first C-rate up to the first terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a second C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less; the second capacity is measured by CC charging at a third C-rate up to the second terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a fourth C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less, and the discharge voltages at the time of measuring the first capacity and the second capacity are the same, and the first C-rate, the second C-rate, the third C-rate, and the fourth C-rate may each be values ​​independently selected in the range of 0.1 C or more to 0.5 C or less.

[0013] In one embodiment, the secondary battery has a capacity change rate with respect to the terminal voltage change represented by Equation 1 of 0.9 (Volt -1 ) or more to 1 (Volt -1 It may be less than )

[0014] In one embodiment, the positive electrode active material may comprise a lithium transition metal oxide containing 80 mol% or more of nickel (Ni).

[0015] In one embodiment, the positive active material may have a molar ratio of lithium to a transition metal (Ni, Co, Mn, or a dopant substituted at the transition metal site) of 0.9 or more and less than 1.

[0016] In one embodiment, the positive electrode active material may comprise a lithium transition metal oxide represented by any one of the following chemical formulas 1 to 3.

[0017] [Chemical Formula 1]

[0018] Li (1-a) (Ni x M 1(1-x) )M 2 y O2

[0019] [Chemical Formula 2]

[0020] Li (1-a) (Ni x M 1 (1-x) ) 1-y M 2 y O2

[0021] [Chemical Formula 3]

[0022] Li (1-a-y) (Ni x M 1 (1-x) )M 2 y O2

[0023] In the above chemical formulas 1 to 3, M 1 is at least one selected from Co and Mn, and M 2 is at least one selected from Al, Zr, B, W, Mo, Cr, Ta, Nb, Mg, Ce, Hf, La, Ti, Sr, Ba, F, P, S, Na, Si, Sb, V, and Y, and 0 <a<0.1, 0.8≤x≤1, 0≤y≤0.1이다.

[0024] In one embodiment, the positive electrode active material comprises a lithium layer and a transition metal layer, and the lithium layer may have at least a portion of the lithium sites occupied by nickel.

[0025] In one embodiment, the nickel occupancy rate (Ni) of the lithium layer Li ) may be 0.003 or more to 0.015 or less.

[0026] In one embodiment, the positive active material may have a Curie-Weiss temperature of 0 K or higher and 19 K or lower.

[0027] In one embodiment, the Curie-Weiss temperature of the positive active material may be 3 K or higher and 10 K or lower.

[0028] In one embodiment, the positive active material has a lattice volume of 101.5 Å. 3 From 101.6 Å or more 3 It may be less than

[0029] The secondary battery of the present invention can provide a secondary battery in which the difference in charge / discharge capacity is reduced even when the charge termination voltage changes. Accordingly, capacity deviations caused by variables that may intervene in the design and / or manufacturing process of the secondary battery can be reduced, and the battery can maintain relatively consistent quality even with changes in external conditions.

[0030] In addition, the present invention has the advantage of being able to minimize the rate of change in capacity due to changes in the charging terminal voltage by including a positive electrode active material having specific physical properties, and thereby provide a secondary battery having specifications expected during the design and / or manufacturing process or satisfying the intended performance.

[0031] Figure 1 is a graph showing the relationship between the lattice volume and the Curie-Weiss temperature of the positive electrode active material prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 according to Experimental Example 1 of the present invention.

[0032] FIG. 2 is a graph showing the relationship between lattice volume and capacity change rate for secondary batteries prepared with positive active materials prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 according to Experimental Example 2 of the present invention.

[0033] FIG. 3 is a graph showing the relationship between the Curie-Vice temperature and the rate of change in capacity for secondary batteries prepared with the positive active materials prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 according to Experimental Example 2 of the present invention.

[0034] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0035] Therefore, the configurations of the embodiments described in this specification are merely one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application. In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0036] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Thus, for example, a composition comprising compound A may include compounds other than A. However, the term "comprising" also encompasses, in a more restrictive sense as a specific embodiment thereof, "essentially / essentially composed of" and "composed of," so that, for example, a "composition comprising compound A" may also be (essentially / essentially) composed of compound A.

[0037] In this regard, terms such as “to have” or “to possess,” as described in this specification, are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0038] In this specification, when any layer is described as being located "on" or "between" another arbitrary layer, this includes not only cases where any layer is in contact with another arbitrary layer, but also cases where another layer or material, etc., exists between the two layers.

[0039] Where in this specification a quantity, concentration, or other value or parameter is given as an enumeration of a range, a preferred range, a preferred upper limit, and a preferred lower limit, it should be understood that any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the range is disclosed separately, specifically discloses all ranges that may be formed. Where a range of numerical values ​​is mentioned in this specification, unless otherwise stated, for example, without limiting terms such as greater than or less than, the range is intended to include its endpoint value and all integers and fractions within that range. The scope of the invention is not intended to be limited to the specific value mentioned when defining the range.

[0040] Among the physical properties mentioned in this specification, if the measured temperature affects the property, the property is measured at room temperature unless specifically otherwise specified. The term "room temperature" refers to a natural temperature that has not been heated or cooled, and may mean, for example, any temperature within the range of about 10°C to 30°C, about 23°C, or about 25°C. Furthermore, unless specifically otherwise specified, the unit of temperature in this specification is °C.

[0041] In addition, among the physical properties mentioned in this specification, if the measured pressure affects the physical property, unless otherwise specifically defined, the physical property is measured at atmospheric pressure, that is, at about 1 atmosphere.

[0042] The present invention relates to a secondary battery.

[0043] The present invention relates to a secondary battery comprising a positive electrode including a positive active material; an electrolyte; and a negative electrode, wherein the secondary battery has a capacity change rate with respect to a terminal voltage change represented by the following formula 1, which is 1 (Volt -1 It may be less than )

[0044] [Equation 1]

[0045] (2nd capacitance - 1st capacitance) / {2nd capacitance × (2nd terminal voltage - 1st terminal voltage)}

[0046] In the above formula, the second capacity is the discharge capacity measured after charging to the second terminal voltage, and the first capacity is the discharge capacity measured after charging to the first terminal voltage; the second terminal voltage is selected from a range of 4.15 V or more to 4.25 V or less, and the first terminal voltage is selected from a range of 4.05 V or more to 4.15 V or less, and the difference between the second terminal voltage and the first terminal voltage (second terminal voltage - first terminal voltage) is 0.05 V or more.

[0047] The capacity change rate with respect to the change in terminal voltage represented by Equation 1 above is calculated by normalizing the difference in capacity when measuring the charge / discharge capacity of a secondary battery with different terminal voltages as a ratio to the difference in terminal voltages, and then normalizing it to a second capacity value. A secondary battery verified to have a low capacity change rate can have a small capacity deviation even when the potential of the positive electrode changes due to various reasons during manufacturing or operation. In other words, the secondary battery of the present invention can have relatively stable and consistent quality even with various variables or external factors that appear during the design and / or manufacturing process, and thus has the advantage of obtaining a secondary battery of the expected specifications with a high yield.

[0048] In this specification, "terminal voltage" may refer to the upper limit voltage of charging or the termination voltage of charging when charging / discharging a secondary battery. In a secondary battery, CC (Constant Current) charging refers to a method of charging to a specified constant A (ampere) by continuously flowing a constant current, and CV (Constant Voltage) charging refers to a charging mode that maintains a constant voltage and charges to a specified V (volt). Generally, when charging a secondary battery, it can be charged using the CC / CV method. In such CC / CV charging, charging begins in CC mode, and as the voltage rises and reaches a constant voltage, the charging switches to CV mode, gradually reducing the current amount while charging at a constant voltage until the current (I) reaches a set value, at which point the charging is terminated. The above-mentioned terminal voltage may refer to the voltage at which the charging mode switches from CC charging mode to CV charging mode. Alternatively, for example, it may refer to a voltage arbitrarily set by the user to terminate charging in CC charging mode, or an arbitrary constant voltage set during charging in CV charging mode.

[0049] The above second capacity may be the discharge capacity measured after charging to the second terminal voltage.

[0050] The above first capacity may be the discharge capacity measured after charging to the first terminal voltage.

[0051] The first capacity above may be measured, for example, by CC charging at a first C-rate up to the first terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a second C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less.

[0052] The second capacity may be measured, for example, by CC charging at a third C-rate up to the second terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a fourth C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less.

[0053] The first C-rate, second C-rate, third C-rate, and fourth C-rate represent a charge / discharge rate at which a secondary battery is charged or discharged, and the first C-rate, second C-rate, third C-rate, and fourth C-rate may be identical or different from each other and may each be independently selected within a range of 0.1 C or more to 0.5 C or less.

[0054] The first C-rate and the second C-rate can be selected to have the same value.

[0055] The above third C-rate and the above fourth C-rate can be selected to have the same value.

[0056] The first C-rate and the third C-rate can be selected to have the same value.

[0057] The above second C-rate and the above fourth C-rate can be selected to have the same value.

[0058] The first C-rate and the third C-rate are identical to each other, the second C-rate and the fourth C-rate are identical to each other, and the first C-rate and the second C-rate may be identical to each other.

[0059] In addition, the first C-rate and the third C-rate are identical to each other, the second C-rate and the fourth C-rate are identical to each other, and the first C-rate and the second C-rate may be different from each other.

[0060] The voltage selected within the range of 1.5 V or more to 3.5 V or less is a concept that includes discharge voltage, discharge termination voltage, and / or discharge end voltage, and may refer to the minimum voltage for discharge during the charging and discharging of a secondary battery. That is, it may refer to the voltage at the point where discharge ends when discharging the secondary battery after charging it. For example, it may mean that discharge ends at the moment the voltage selected within the range is reached while performing CC / CV discharge after charging the secondary battery. The voltage selected within the range of 1.5 V or more to 3.5 V or less may preferably be a value selected within the range of 1.8 V or more to 3.0 V or less, more preferably a value selected within the range of 2.0 V or more to 2.6 V or less, or a value selected within the range of 2.0 V or more to 3.5 V or less.

[0061] When measuring the discharge capacity at a voltage lower than 1.5 V, the electrode plates or leads of the secondary battery may melt and be damaged, and over-discharge may occur, resulting in a dangerous condition. On the other hand, when measuring the discharge capacity at a voltage higher than the 3.5 V range, the discharge terminates prematurely, causing a problem where the capacity becomes smaller.

[0062] The above second terminal voltage can be selected in the range of 4.15 V or more to 4.25 V or less.

[0063] The above first terminal voltage can be selected in the range of 4.05 V or more to 4.15 V or less.

[0064] The second terminal voltage may be selected from a range higher than the first terminal voltage.

[0065] The difference between the second terminal voltage and the first terminal voltage (second terminal voltage - first terminal voltage) may be 0.05 V or more, and preferably 0.05 V or more to 0.2 V or less.

[0066] The second capacity above may refer to a second discharge capacity measured by CC charging at a third C-rate up to a second terminal voltage selected in the range of 4.15 V or more to 4.25 V or less, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a fourth C-rate up to a voltage selected in the range of 1.5 V or more to 3.5 V or less.

[0067] The above first capacity may refer to a first discharge capacity measured by CC charging at a first C-rate until the current (I) reaches less than 0.05 C after CC charging to a first terminal voltage selected in the range of 4.05 V or more to 4.15 V or less, and then CC discharging at a second C-rate to a voltage selected in the range of 1.5 V or more to 3.5 V or less.

[0068] The discharge voltage at the time of measuring the second capacity and / or the first capacity may be the same as each other.

[0069] The measurement of the first and second capacities may be performed after the step of activating the secondary battery. At this time, the step of activating the secondary battery may be performed according to a generally known activation process for secondary batteries, and, for example, may be performed in a CC / CV charging mode by setting the first terminal voltage or the second terminal voltage as the charging terminal voltage and in a CC discharge mode by setting any voltage selected in the range of 1.5 V or more to 3.5 V or less as the discharge terminal voltage, but is not limited thereto.

[0070] The above secondary battery has a capacity change rate of 1 (Volt with respect to the terminal voltage change represented by Equation 1). -1) It may be less than or equal to. When the above capacity change rate satisfies the above range, it means that the difference in capacity relative to the change in terminal voltage is small, and a secondary battery satisfying the above range may mean that the capacity change rate with respect to the change in terminal voltage is small. Therefore, when the capacity change rate with respect to the change in terminal voltage satisfies the above range, a secondary battery having consistent quality even with changes due to external influences occurring during the design and / or manufacturing process can be provided.

[0071] The rate of change in capacity with respect to the change in terminal voltage represented by Equation 1 above is 0.9 (Volt -1 ) or more to 1 (Volt -1 It may be ) or less, specifically 0.9 (Volt -1 ) or more to 0.99 (Volt -1 ) or less, 0.91 (Volt -1 ) or more to 0.96 (Volt -1 ) or less, 0.91 (Volt -1 ) or more to 0.95 (Volt -1 ) or less, or 0.91 (Volt -1 ) or more to 0.94 (Volt -1 It may be less than )

[0072] As described above, the secondary battery is characterized by a low rate of change in capacity due to changes in terminal voltage, and accordingly, the capacity deviation due to differences in terminal voltage is also reduced. The secondary battery can have a reduced capacity deviation due to differences in terminal voltage without being affected by various variables occurring during the design and / or manufacturing process of the secondary battery, and ultimately, can maintain relatively stable and consistent performance even under changes in the external environment.

[0073] The above secondary battery may satisfy the capacity deviation represented by the following Equation 2 between the second capacity measured after charging to the second terminal voltage and the first capacity measured after charging to the first terminal voltage.

[0074] [Equation 2]

[0075] |(2nd capacity - 1st capacity) / 1st capacity| ≤ 0.1

[0076] Specifically, the second capacity may be measured by, for example, CC charging at a third C-rate up to the second terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a fourth C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less.

[0077] The first capacity may be measured, for example, by CC charging at a first C-rate up to the first terminal voltage, CV charging until the current (I) reaches less than 0.05 C, and then CC discharging at a second C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less. The second terminal voltage may be selected from a higher range than the first terminal voltage, and the second capacity may be equal to or greater than the first capacity.

[0078] In addition, the above secondary battery may satisfy the capacity deviation expressed by Equation 3 below between the second capacity measured after charging to the second terminal voltage and the first capacity measured after charging to the first terminal voltage.

[0079] [Equation 3]

[0080] |(2nd capacity - 1st capacity) / 2nd capacity| ≤ 0.1

[0081] The first C-rate, the second C-rate, the third C-rate, and the fourth C-rate may each be independently selected within the range of 0.1 C to 0.5 C.

[0082] The above-mentioned details may be applied in the same way to the first C-rate, second C-rate, third C-rate, and fourth C-rate.

[0083] As described above, when the secondary battery of the present invention satisfies a capacity deviation of 0.1 or less calculated by the difference between the second capacity and the first capacity with respect to the first capacity and / or the second capacity, the secondary battery can have relatively stable and consistent quality even with various variables or external factors appearing during the design and / or manufacturing process.

[0084] The above-mentioned positive active material may include a lithium transition metal oxide containing 80 mol% or more of nickel (Ni). Specifically, the above-mentioned positive active material may include a lithium transition metal oxide, and the positive active material may include a lithium transition metal oxide in which the nickel composition is 80 mol% or more relative to the total molar amount of the transition metal among the lithium transition metal oxides, and may include a positive active material having a lattice volume and a Curie-Weiss temperature in a specific range by adjusting the input ratio of lithium and transition metal precursors.

[0085] The above lithium transition metal oxide may include a layered structure.

[0086] In addition, the lithium transition metal oxide may include a high-nickel lithium transition metal oxide.

[0087] In this specification, "layered structure" may mean that the positive electrode active material has a structure comprising a lithium layer and a transition metal layer. In this specification, "high-nickel" may mean that nickel (Ni) is included in, for example, 80 mol% or more with respect to the total transition metal in the lithium transition metal composite oxide, and in other examples, 85 mol% or more, or 90 mol% or more.

[0088] The above-mentioned cathode active material has a molar ratio of transition metals (including Ni, Co, Mn, or dopant elements substituted at transition metal sites) to lithium (Li) in its structure that is greater than 1 (Li / Metal ratio < 1), which is a different value from the input ratio. Since the input ratio includes byproducts and impurities such as LiOH and Li2CO3, the input ratio alone cannot accurately represent structural and electrochemical properties. Generally, the Li / transition metal ratio in terms of input ratio is greater than 1, but considering the amount of lithium (Li) impurities and doping elements substituted at transition metal sites, the Li / transition metal ratio of the cathode active material alone may be less than 1.

[0089] The above-mentioned positive electrode active material may have a molar ratio of lithium (Li) to transition metals (including Ni, Co, Mn, or dopant elements substituted at transition metal sites) of 0.9 or more to less than 1. Preferably, the molar ratio of lithium to transition metals may be 0.91 or more to less than 1, or 0.92 or more to less than 1; specifically, it may be 0.95 or more to less than 1, 0.96 or more to less than 1, or 0.97 or more to less than 1. If the molar ratio of lithium to transition metals within the structure of the above-mentioned positive electrode active material exceeds the above range, the nickel occupancy rate of the lithium layer (Ni Li ) may increase, and conversely, if it is below the above range, the nickel occupancy rate (Ni) of the lithium layer Li ) may decrease.

[0090] The above positive active material may include a lithium transition metal oxide represented by any one of the following chemical formulas 1 to 3.

[0091] [Chemical Formula 1]

[0092] Li (1-a) (Ni x M 1 (1-x) )M 2 y O2

[0093] [Chemical Formula 2]

[0094] Li (1-a) (Ni x M 1 (1-x) ) 1-y M 2 y O2

[0095] [Chemical Formula 3]

[0096] Li (1-a-y) (Ni x M 1 (1-x) )M 2 y O2

[0097] In the above chemical formulas 1 to 3, M 1 is at least one selected from Co and Mn, and M 2 is at least one selected from Al, Zr, B, W, Mo, Cr, Ta, Nb, Mg, Ce, Hf, La, Ti, Sr, Ba, F, P, S, Na, Si, Sb, V, and Y, and 0 <a<0.1, 0.8≤x≤1, 0≤y≤0.1이다.

[0098] The above positive active material may include an NCM-based lithium transition metal oxide, or M 2 It may include a lithium transition metal oxide doped with a doping element such as NCMA. When the positive electrode active material is doped, it may include a quaternary lithium transition metal oxide such as NCMA.

[0099] The above positive active material comprises a lithium layer and a transition metal layer, and the lithium layer may have at least a portion of the lithium sites occupied by nickel.

[0100] The above positive active material is Ni 2+ The ionic radius (0.69 Å) of Li in an octahedral environment + Since it is similar to the ionic radius (0.76 Å), Ni 3+ A small amount of Ni reduced in 2+Nickel can easily occupy lithium sites and replace the lithium in the lithium layer. Accordingly, nickel occupies at least a portion of the lithium layer, and the nickel occupancy rate of this lithium layer (Ni Li Depending on ), it can affect the phase transition occurring during the charge / discharge process, particularly the H2 / H3 phase transition behavior. Since the nickel included in the lithium layer has a pillar effect that controls the collapse of the lithium layer during the phase transition process, it is necessary to ensure that nickel occupies an appropriate amount within the lithium layer. For example, the nickel occupancy rate (Ni) of the lithium layer Li As ) increases, the H2 / H3 transition peak appears at higher voltages, and the voltage plateau (V H2 / H3 ) may increase, and conversely, the nickel occupancy (Ni) of the lithium layer may increase. Li As ) decreases, the H2 / H3 transition peak appears at a lower voltage, and the voltage plateau (V H2 / H3 ) may decrease. Based on this trend, the charge / discharge capacity of the battery can be optimized by adjusting the voltage value at which the H2 / H3 phase transition occurs according to the upper charge / discharge voltage limit of the secondary battery. The above H2 / H3 phase transition refers to a phase transition from the second hexagonal phase to the third hexagonal phase, and can induce crack formation and gas generation. Therefore, the nickel occupancy rate (Ni of the lithium layer) Li The electrochemical characteristics of the battery, including its charge / discharge capacity, can be achieved as intended only if the H2 / H3 phase transition is properly controlled.

[0101] The above positive active material may have a Curie-Weiss temperature (CW temperature) of 0 K or higher and 19 K or lower. Preferably, the above positive active material may have a Curie-Weiss temperature of 3 K or higher and 18 K or lower, and more preferably, 4 K or higher and 12 K or lower. Alternatively, the Curie-Weiss temperature of the above positive active material may be, for example, 3 K or higher and 10 K or lower.

[0102] As the above Curie-Weiss temperature decreases, the lattice volume may decrease. As the Curie-Weiss temperature of the above positive active material satisfies the above range, the positive active material has a specific lattice volume, and accordingly, the rate of change in capacity and / or capacity deviation due to the change in the terminal voltage may decrease.

[0103] The above Curie-Weiss temperature may be measured by a superconducting quantum interference device (SQUID), but is not limited thereto; any device or method capable of measuring the Curie-Weiss temperature of a secondary battery positive electrode active material may be used without limitation.

[0104] The above positive active material has a lattice volume of 101.5 Å. 3 From 101.6 Å or more 3 It may be less than or equal to. Specifically, the lattice volume is 101.5 Å. 3 From 101.6 Å or more 3 It may be less than or equal to 101.55 Å 3 From 101.6 Å or more 3 Below, more specifically, 101.5 Å 3 From 101.57 Å to 101.57 Å 3 It may be less than or equal to 101.55 Å. 3 From 101.57 Å to 101.57 Å 3 It may be less than

[0105] When the lattice volume of the above positive active material satisfies the above range, the molar ratio of lithium to transition metal in the structure of the above positive active material may be reduced, and as described above, the molar ratio of lithium to transition metal in the structure of the above positive active material may be less than 1.

[0106] The above lattice volume may be measured by X-ray powder diffraction (XRD), but is not limited thereto; any instrument or method capable of measuring the lattice volume of a secondary battery positive electrode active material may be used without limitation.

[0107] The above-mentioned positive active material has (1) (Ni average oxidation number)*(concentration) and (2) Ni defects (Ni in the Li layer) within its structure Li It may be due to the competitive effect of ). In this case, the lattice volume represents (1) (Ni average oxidation number)*(concentration) within the structure, and the Curie-Weiss temperature is (2) Ni defects (Ni in the Li layer Li This can represent ). This competitive effect gradually converged (saturated) in a specific range, and the inventors were able to identify a secondary battery with a small rate of change in capacity (or small capacity deviation) depending on the terminal voltage difference.

[0108] Nickel occupancy (Ni) of the above lithium layer Li ) may be 0.003 or more to 0.015 or less.

[0109] In this specification, "occupancy rate of nickel in the lithium layer (Ni Li ")" may refer to the mole fraction of nickel within the lithium layer. This nickel content can be measured through Rietveld refinement via XRD measurement. In this specification, "lithium" or "nickel" implies the inclusion of ions.

[0110] The above positive electrode active material is the nickel occupancy rate (Ni) of the lithium layer. Li ) may be 0.004 or more to 0.014 or less, or 0.004 or more to 0.013 or less, and more preferably 0.005 or more to 0.012 or less. The cathode active material may include nickel occupying the lithium layer in a predetermined range as described above, while simultaneously satisfying the aforementioned lattice volume and Curie-Weiss temperature range. This is significant in that it allows for easy verification and control at the cathode active material level of the control of H2 / H3 phase transition behavior and the securing of accurate secondary battery capacity according to the design purpose. The nickel occupancy rate of the lithium layer (NiLi ) can be controlled, for example, by adjusting the synthesis conditions of the cathode active material (e.g., Li / transition metal molar ratio, calcination temperature, and / or calcination time, etc., but not limited thereto).

[0111] The Curie-Vice temperature of the above-mentioned cathode active material can be controlled to a desired temperature range by finely adjusting the input ratio of Li and transition metal precursors during the manufacture of the cathode active material. However, the lattice volume and Curie-Vice temperature are not necessarily set to the same value simply because the input ratio of Li and transition metal precursors is the same; they may vary depending on various factors and / or environmental conditions, such as equipment, precursor quality, mass production process, presence / content of impurities, and temperature or humidity during synthesis.

[0112] The physical and electrochemical properties of the synthesized positive electrode active material can be analyzed and determined through the structural and / or magnetic properties of the positive electrode active material product after synthesis. In other words, the characteristics of the positive electrode active material are not determined solely by the input ratio of Li and the transition metal precursor.

[0113] The above secondary battery can achieve a capacity change rate according to the terminal voltage difference required by the secondary battery at a desired level by using a positive electrode active material in which the lattice volume and / or the Curie-Weiss temperature satisfy the aforementioned ranges. Therefore, it becomes possible to identify and control the most efficient process variables from materials such as the positive electrode active material to the final battery stage, and thereby design a secondary battery with optimized performance and excellent stability.

[0114] The secondary battery of the present invention may include a positive electrode, an electrolyte, and a negative electrode.

[0115] The above-mentioned positive electrode may include a positive current collector and a positive active material layer located on at least one surface of the positive current collector, and the positive active material layer may include the aforementioned positive active material. The positive active material layer may further include a conductive material, a binder and / or additives, etc.

[0116] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and may be made of, for example, copper (Cu), nickel (Ni), aluminum (Al), vanadium (V), gold (Au), platinum (Pt), chromium (Cr), iron (Fe), zinc (Zn), indium (In), germanium (Ge), lithium (Li), magnesium (Mg), stainless steel (e.g., SUS), titanium (Ti), cobalt (Co), or an alloy thereof.

[0117] The anode current collector may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the anode current collector to increase the adhesion of the anode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. The anode current collector may be omitted depending on the case.

[0118] The above conductive material is used to impart conductivity to the electrode, and can be used without special restrictions as long as it has electronic conductivity without causing chemical changes. 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, carbon fiber, carbon nanotube, carbon nanofiber; metal powder or metal fiber such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide or 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. The above conductive material may typically be included in an amount of 1% or more to 30% or less with respect to the total weight of the anode active material layer.

[0119] The above 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 (PVA), polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 1% or more to 30% or less with respect to the total weight of the positive active material layer.

[0120] The above anode may additionally include additives. The above additives may further include, for example, fillers, coating agents, dispersants, thickeners, ion conductivity aids, etc., and any known material generally used in electrodes may be used without limitation.

[0121] The above-mentioned anode may be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, comprising the above-mentioned anode active material and optionally a binder, a conductive material and / or additives, onto an anode current collector, followed by drying and rolling. In this case, the composition for forming the anode active material layer may further include a solvent, and the types and contents of the above-mentioned anode active material, binder, conductive material, and additives are as described above.

[0122] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (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 is sufficient to dissolve or disperse the above-mentioned cathode active material, conductive material, binder, etc., considering the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0123] The above anode may also 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.

[0124] In addition to the aforementioned configuration, the anode may further include known configurations that can be included in the anode of a lithium secondary battery.

[0125] In the above secondary battery, the negative electrode may include a negative current collector and a negative active material layer located on at least one surface of the negative current collector. In another example, the negative electrode may be a negative electrode for an anodeless battery in which the negative active material layer, such as a lithium metal layer, is not included immediately after battery manufacturing, but is formed through battery charging.

[0126] 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 (e.g., SUS), aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated or coated with carbon, nickel, titanium, or silver, or aluminum-cadmium alloy may be used.

[0127] The above-mentioned negative current collector can typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities can be formed on the surface of the negative current collector to strengthen the bonding force of the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0128] The above-mentioned cathode active material layer may optionally include a binder, a conductive material, and / or additives, etc., together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, for example, by applying a cathode forming composition containing the cathode active material, etc., onto a cathode current collector and drying it, or by casting the cathode forming composition onto a separate support and then laminating the film obtained by peeling it off from the support onto the cathode current collector. The above-mentioned cathode forming composition may further include a solvent, and the solvent may be selected from examples of solvents included in the aforementioned anode forming composition.

[0129] 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, or amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Ag, Au, In alloys, Si alloys, Sn alloys, or Al alloys; and SiO₂ β Examples include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, or lithium vanadium oxide (0<β≤2); or composites comprising the metal compound and carbonaceous material, 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 negative electrode active material. Furthermore, the carbon material may include 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, or high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. Furthermore, the binder and conductive material described above may be applied in the same manner as previously explained for the anode, and the binder and conductive material included in the cathode may be identical to or different from the binder and conductive material included in the anode. Additionally, the cathode active material layer may be omitted depending on the case.

[0130] In the above secondary battery, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery, but is not limited to these.

[0131] The above electrolyte may include, for example, an organic solvent and / or a lithium salt.

[0132] 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 or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol or isopropyl alcohol; R-CN (R is C2 to C 20Nitriles such as (which are hydrocarbon groups with a straight, branched, or cyclic structure and may include double bond-directing rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are 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 the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 can simultaneously satisfy high dielectric constant and low viscosity characteristics and achieve excellent ionic conductivity characteristics, thereby resulting in excellent performance of the electrolyte.

[0133] 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-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, 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 above additives may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte. The above lithium salt may be used without special limitations as long as it is a compound capable of providing lithium ions used in a secondary battery.

[0134] For example, the above lithium salt is Li as a cation. + It includes, and as anion, F- , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , BF6 - , SF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , F3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may include at least one selected from a group consisting of

[0135] Specifically, the lithium salts mentioned above are LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10Examples include at least one selected from the group consisting of LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single substance or a mixture of two or more selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0136] The concentration of the lithium salt may be included in the electrolyte at a concentration of 0.1 M or more to 4 M or less, specifically at 0.1 M or more to 2 M or less, and more specifically at 0.8 M or more to 1.6 M or less. When the concentration of the lithium salt is included within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can move effectively, thereby improving the output characteristics of the secondary battery.

[0137] The above electrolyte may include a solid electrolyte, and if the solid electrolyte is included, the solid electrolyte can take the place of the separator, so the separator may not be included.

[0138] The above solid electrolyte may include, for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, polymer-based solid electrolytes, or halide-based solid electrolytes, but is not limited thereto.

[0139] The above sulfide-based solid electrolyte contains sulfur atoms (S), has ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may have electronic insulation properties. The above sulfide-based solid electrolyte preferably contains at least Li, S, and P as elements and has lithium ion conductivity, but may include other elements other than Li, S, and P depending on the purpose or case.

[0140] Specific sulfide-based solid electrolytes include, for example, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2OP2S5, Li2S-LiBr-P2S5, Li2SLi2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2SGa2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2SSiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2SSiS2-Li3PO4, or Li 10 GeP2S 12 The back can be used.

[0141] As the above oxide-based solid electrolyte, for example, Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7](LLTO), Li xb La yb Zr zb Mbb mb O nb(Mbb is at least one element among Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, xb satisfies 5≤xb≤10, yb satisfies 1≤yb≤4, zb satisfies 1≤zb≤4, mb satisfies 0≤mb≤2, and nb satisfies 5≤nb≤20), Li xc B yc Mcc zc O nc (Mcc is at least one element among C, S, Al, Si, Ga, Ge, In, and Sn, xc satisfies 0≤xc≤5, yc satisfies 0≤yc≤1, zc satisfies 0≤zc≤1, and nc satisfies 0≤nc≤6), Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd (However, 1≤xd≤3, 0≤yd≤1, 0≤zd≤2, 0≤ad≤1, 1≤md≤7, 3≤nd≤13), Li (3-2xe) Mee xe DeeO(xe represents a number between 0 and 0.1, and Mee represents a divalent metal atom. Dee represents a halogen atom or a combination of two or more halogen atoms), Li xf Si yf O zf (1≤xf≤5, 0 <yf≤3, 1≤zf≤10), Li xg S yg O zg (1≤xg≤3, 0 <yg≤2, 1≤zg≤10), Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li6BaLa2Ta2O 12 , Li3PO (4-3 / 2w) N w (w is w<1), Li having a LISICON (Lithium superionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La having a perovskite-type crystal structure 0.55Li 0.35 LiTi2P3O having a TiO3, NASICON (Sodium(Na) superionic conductor) type crystal structure 12 , Li 1+xh+yh (Al, Ga) xh (Ti, Ge) 2-xh Si yh P3- yh O 12 (where 0≤xh≤1, 0≤yh≤1), Li7La3Zr2O having a garnet-type crystal structure 12 Examples include (LLZO). Alternatively, phosphorus compounds containing Li, P, and O may also be used. Examples include lithium phosphate (Li3PO4), LiPON in which some of the oxygen in lithium phosphate is substituted with nitrogen, LiPOD1 (where D1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au, etc.). Alternatively, LiA1ON (where A1 is at least one selected from Si, B, Ge, Al, C, and Ga, etc.) may also be used.

[0142] The above polymer-based solid electrolyte includes polymer materials that are ion-conducting materials and are typically used as solid electrolyte materials for all-solid-state batteries, but is not specifically limited thereto. The above polymer-based solid electrolyte may include, for example, polyether-based polymers, polycarbonate-based polymers, acrylate-based polymers, polysiloxane-based polymers, phosphazene-based polymers, polyethylene oxide (PEO), polyethylene derivatives, alkylene oxide derivatives, phosphate ester polymers, polyaisation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, or polymers containing ionic dissociators. Alternatively, the above polymer-based solid electrolyte may include, as a polymer resin, a branched copolymer, a comb-like polymer, and a cross-linked polymer resin, etc., in which an amorphous polymer such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane, and / or phosphazene is copolymerized as a comonomer to a polyethylene oxide (PEO) main chain.

[0143] The above solid electrolyte may include a gel-type polymer electrolyte. The above gel-type polymer electrolyte comprises an organic electrolyte containing a lithium salt and a polymer resin, wherein the organic electrolyte comprises 60 to 400 parts by weight per 100 parts by weight of the polymer resin. The polymer resin applied to the gel-type polymer electrolyte is not limited to specific components, but may include, for example, polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA) systems, polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), or poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP).

[0144] In addition, the secondary battery may optionally include a separator. Meanwhile, if the electrolyte includes the aforementioned solid electrolyte, the secondary battery may not include a separate separator because the solid electrolyte acts as a separator, but is not limited thereto.

[0145] In the above secondary battery, the 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 limitations as long as it is generally used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of ions in the electrolyte 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. The separator may be omitted in some cases.

[0146] The above secondary battery may be pouch-type, prismatic-type, or cylindrical, and its shape and size may be applied without restriction as long as it is a commonly used secondary battery.

[0147] Additionally, the secondary battery may further include a case capable of sealing the electrode assembly, such as a container, pouch, pack, or module, for housing the electrode assembly comprising the positive electrode, electrolyte, and negative electrode. The case may optionally further include a sealing member.

[0148] In the following, the present invention is described in detail with reference to examples to specifically explain the disclosure of the present invention as described above and the intended functions and effects of the present invention. However, the examples may be modified in various different forms, and the scope of this specification is not to be interpreted as being limited only to these examples. It is emphasized that the examples are provided to represent the present invention and to explain it more specifically to those skilled in the art.

[0149]

[0150] Examples

[0151] Preparation Example 1. Preparation of positive electrode active material

[0152] Positive electrode active material precursor Ni 0.85 Co 0.05 Mn 0.10 Lithium source LiOH was added to (OH)2 and mixed so that the Li / transition metal molar ratio was 1.02, and 31 wt% B2O and 31 wt% K2CO were added and mixed. The mixed powder was introduced into a calcination furnace. Subsequently, primary calcination was performed at 400°C under an oxygen atmosphere for 4 hours. Afterward, the powder, which had undergone grinding, washing, and drying processes, was mixed with 30.1 wt% H3BO and secondary calcined at 690°C to 710°C under an air atmosphere for 6 hours to obtain a lithium transition metal composite oxide-based cathode active material.

[0153] Preparation Example 2. Preparation of positive electrode active material

[0154] In the above Preparation Example 1, the cathode active material was prepared in the same manner as in Preparation Example 1, except that the Li / transition metal input ratio was adjusted to 1.03 instead of 1.02.

[0155] Preparation Example 3. Preparation of positive electrode active material

[0156] In the above Preparation Example 1, the cathode active material was prepared in the same manner as in Preparation Example 1, except that the Li / transition metal input ratio was adjusted to 1.04 instead of 1.02.

[0157] Preparation Example 4. Preparation of positive electrode active material

[0158] In the above Preparation Example 1, the cathode active material was prepared in the same manner as in Preparation Example 1, except that the Li / transition metal input ratio was adjusted to 1.05 instead of 1.02.

[0159] Comparative Manufacturing Example 1. Preparation of positive electrode active material

[0160] In the above Preparation Example 1, the cathode active material was prepared in the same manner as in Preparation Example 1, except that the Li / transition metal input ratio was adjusted to 1.01 instead of 1.02.

[0161]

[0162] Experimental Example 1.

[0163] The lattice volume, Curie-weiss temperature, and nickel occupancy in the lithium layer of the cathode active materials prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 were measured using the following measurement method, and the results are shown in Table 1 below.

[0164] Figure 1 shows the relationship between the lattice volume and the Curie-Weiss temperature of the positive electrode active materials prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1.

[0165]

[0166] Lattice volume

[0167] XRD measurements were performed using a Bruker D8 Endeavor instrument (Cu target 40kV, 40 mA; Lynxeye-XE-T 1D detector). The measurement conditions were set to a fixed divergence slit of 0.5°, 2θ=10–125°, Δ2θ=0.016°, and time per step of 0.4s. Depending on the micro-deformation or crystallinity of the powder sample, the slit spacing, 2θ measurement range, Δ2θ interval, and time per step can be adjusted to suit the sample. For the same powder sample, sampling was performed three times, and the average and deviation values ​​were calculated. Subsequently, the lattice constants a and c and the lattice volume V were determined from the XRD measurement data using the TOPAS program.

[0168] For the R-3m crystal group, the lattice constants a, c, and lattice volume, and the crystalline size and microstrain were calculated using the Rietveld method with a fundamental parameter approach that takes into account measurement equipment information.

[0169] Curie-weiss temperature

[0170] Magnetic susceptibility was measured in the range of 5 to 300 K using an MPMS instrument from Quantum Design. The magnetic field and measurement temperature steps may vary depending on the sample measurement conditions, and in this evaluation example, a magnetic field of 1 Tesla was applied, and the measurement temperature steps were measured at intervals of 5 K. In Preparation Examples 1 to 4 and Comparative Preparation Example 1, no rapid increase in magnetic susceptibility due to ferromagnetic impurities was observed.

[0171] Meanwhile, if other magnetic impurities are present, the magnetic susceptibility can be described by a general formula including the impurities as follows (see Stephen Blundell, Magnetism in Condensed Matter).

[0172] χ m cgs[emu / mol / Oe]=M / H=χ sample +(χ T +χ0) impurity = C / (T-θ CW ) + C T / T+χ0

[0173] The magnetic susceptibility of the sample of interest and the magnetic susceptibility of the impurities may be mixed, and the magnetic susceptibility of the impurities is a temperature-dependent magnetic susceptibility C that follows the Curie-Weiss law. T It can be distinguished by / T and χ0, which has low temperature dependence.

[0174] By taking the inverse magnetic susceptibility of this magnetic susceptibility and plotting it against temperature, a line with a constant slope and y-intercept can be drawn in the temperature range above the magnetic phase transition temperature. By removing the influence of impurities on the magnetic susceptibility and calculating the slope a and y-intercept b of the inverse magnetic susceptibility with respect to the magnetic susceptibility of the sample, the effective magnetic moment and the Curie-Weiss temperature can be determined.

[0175] 1 / χ=(T-θ CW ) / C=1 / C*T-θ CW / C=aT+b

[0176] Effective magnetic moment μ eff =2.827sqrt(χ m cgs T)≒2.827sqrt(C)=2.827sqrt(1 / a)

[0177] Curie Vise temperature

[0178] θ CW =-b*C

[0179]

[0180] The Curie-Weiss temperature represents the average strength of magnetic interactions in magnetic materials, and in high-nickel layered active materials, the Curie-Weiss temperature has a positive value (predominance of ferromagnetic interactions) when the nickel occupancy in the lithium layer is high. In this case, as the nickel occupancy decreases, the positive Curie-Weiss temperature tends to decrease. The change in Curie-Weiss temperature according to the nickel occupancy in the lithium layer is more sensitive than the change in effective magnetic moment, and unlike in the case of Rietveld structural analysis, it has less dependence on the crystal structure model. Therefore, by observing the changes in XRD lattice constants and Curie-Weiss temperature, it is possible to synthesize samples with controlled nickel occupancy within the lithium layer in a complementary manner.

[0181] Nickel occupancy in the lithium layer (Ni Li )

[0182] Assuming an ideal simple crystal structure model, lithium in a LiMO2 unit cell occupies the Wyckoff position 3a (0 0 0), transition metals such as Al and M occupy 3b (0 0 0.5), and oxygen occupies 3c (0 0 z). In actual synthesis of high-nickel cathode active materials, Ni 2+ Ga Li + Having a radius similar to, some Ni 3+ Ga Ni 2+ As it is reduced to Ni 2+ Ga Li + It can occupy a position. In this case, the substituted lithium may exist in a different form outside the LiMO2 unit cell or occupy a transition metal layer, so a crystal structure model in which Wyckoff position 3a is mainly occupied by lithium and some nickel, and 3b is mainly occupied by nickel and some lithium (Li 1-x Ni 2+ x ) 3a (Ni 3+ 1-y Li y ) 3bRietveld analysis was performed using O2 as the initial model. In this case, the partial nickel occupancy x at position 3a and the partial lithium occupancy y at position 3b do not need to be the same in the crystal structure model. In this evaluation example, the lithium occupancy y at position 3b was fitted as 0, and the crystal structure model was simplified (Li 1-x Ni 2+ x ) 3a (M) 3b The O2 (M=Ni, Co, Mn, Al, etc.) model was used. Using this XRD measurement and analysis method, the nickel occupancy within the lithium layer was precisely measured with deviations in lattice constants a=0.0002Å, c=0.001Å, and lattice volume V=0.01Å.

[0183]

[0184] Experimental Example 2. Secondary Battery Manufacturing and Discharge Capacity Evaluation

[0185] An anode slurry was prepared by mixing an NCM-based anode active material (Ni 90%), a conductive material (MWCNT), and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.0 : 1.0 : 2.0. The anode slurry was applied to one surface of a 15 μm thick aluminum current collector sheet at a concentration of 25 mg / cm² 2 A positive electrode active material layer with a thickness of 160 μm was formed by applying a loading amount, then dried at 160 ℃, and rolled to manufacture a positive electrode.

[0186] A cathode slurry was prepared by mixing natural graphite, a conductive material (Super-C65), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 97:1:1:1. The cathode slurry was applied to the other side of a copper current collector sheet at a ratio of 14 mg / cm² 2 A cathode active material layer with a thickness of 175 μm was formed by applying a loading amount, then drying at 100°C and rolling to manufacture a cathode.

[0187] A jelly-roll type electrode assembly was manufactured by interposing a PE separator with a 14 μm thickness between the anode and cathode manufactured as described above, stacking them in the order of separator / anode / separator / cathode, and then winding them. At this time, the electrode assembly was manufactured by arranging the anode active material layer and the cathode active material layer so as to face the separator. The electrode assembly manufactured as described above was inserted into a cylindrical battery can, and an electrolyte was injected to manufacture a 21700 cylindrical lithium secondary battery.

[0188] To evaluate the capacity of the 21700 cylindrical battery, two consecutive cycles are performed. The first cycle involves CC charging at 0.5 C to 4.2 V, CV charging until I < C / 20, and then CC discharging at 0.5 C to 3.0 V. The second cycle involves CC charging at 0.5 C to 4.1 V, CV charging ending when I < C / 20, and then CC discharging at 0.5 C to 3.0 V. All capacity tests were performed using a 10 A cycler (PECC05-10: Wonik PNE) in a chamber maintained at 40 ℃. The produced 21700 batteries were stored for 2 hours to reach thermal equilibrium prior to testing.

[0189] The capacity change rate evaluated from this is shown in Table 1 below. For the secondary battery prepared in Experimental Example 2, the relationship between grid volume and capacity change rate is shown in Figure 2, and the relationship between Curie-weiss temperature and capacity change rate is shown in Figure 3.

[0190] Nickel occupancy rate (Ni) in the separated lithium layer Li )Curie-Weiss temperature (K) Lattice volume (Å) 3 )Rate of change in capacity (Volt -1 Manufacturing Example 10.7% or less 17.1 101.5 97 80.946 Manufacturing Example 20.7% or less 11.4 101.5 6 980.947 Manufacturing Example 30.7% or less 9.5 101.5 6 720.912 Manufacturing Example 40.7% or less 2.9 2 101.5 7 40.957 Comparative Manufacturing Example 1 Approx. 1% 19.3 101.6 47 31.033

Claims

A secondary battery comprising a positive electrode including a positive electrode active material; an electrolyte; and a negative electrode, The above secondary battery has a capacity change rate of 1 with respect to the terminal voltage change represented by the following Equation 1 (Volt -1 Secondary battery with less than ) [Equation 1] (2nd capacitance - 1st capacitance) / {2nd capacitance × (2nd terminal voltage - 1st terminal voltage)} In the above formula, the second capacity is the discharge capacity measured after charging to the second terminal voltage, and the first capacity is the discharge capacity measured after charging to the first terminal voltage. The second terminal voltage is selected from a range of 4.15 V or more to 4.25 V or less, the first terminal voltage is selected from a range of 4.05 V or more to 4.15 V or less, and the difference between the second terminal voltage and the first terminal voltage (second terminal voltage - first terminal voltage) is 0.05 V or more. In Article 1, The above first capacity is measured by CC charging at the first C-rate up to the above first terminal voltage, CV charging until the current (I) value reaches less than 0.05 C, and then CC discharging at the second C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less. The second capacity is measured by CC charging at the third C-rate up to the second terminal voltage, CV charging until the current (I) value reaches less than 0.05 C, and then CC discharging at the fourth C-rate up to a selected voltage in the range of 1.5 V or more to 3.5 V or less. The discharge voltages during the measurement of the first and second capacities are identical to each other, and A secondary battery in which the first C-rate, the second C-rate, the third C-rate, and the fourth C-rate are each independently selected within a range of 0.1 C or more to 0.5 C or less. In Article 1, The above secondary battery has a capacity change rate of 0.9 (Volt with respect to the terminal voltage change represented by Equation 1 above). -1 ) or more to 1 (Volt -1 A secondary battery that is less than or equal to ) In Article 1, A secondary battery in which the positive electrode active material comprises a lithium transition metal oxide containing 80 mol% or more of nickel (Ni). In Article 1, A secondary battery in which the above-mentioned positive active material has a molar ratio of lithium to a transition metal (Ni, Co, Mn, or a dopant substituted at the transition metal site) of 0.9 or more and less than 1. In Article 1, A secondary battery wherein the positive active material comprises a lithium transition metal oxide represented by any one selected from Chemical Formulas 1 to 3 below: [Chemical Formula 1] Li (1-a) (Ni x M 1 (1-x) )M 2 y O2 [Chemical Formula 2] Li (1-a) (Ni x M 1 (1-x) ) 1-y M 2 y O2 [Chemical Formula 3] Li (1-a-y) (Ni x M 1 (1-x) )M 2 y O2 In the above chemical formulas 1 to 3, M 1 is at least one selected from Co and Mn, and M 2 is at least one selected from Al, Zr, B, W, Mo, Cr, Ta, Nb, Mg, Ce, Hf, La, Ti, Sr, Ba, F, P, S, Na, Si, Sb, V, and Y, and 0 <a<0.1, 0.8≤x≤1, 0≤y≤0.1이다. In Article 1, A secondary battery, wherein the positive electrode active material comprises a lithium layer and a transition metal layer, and the lithium layer has at least a portion of the lithium sites occupied by nickel. In Article 7, Nickel occupancy (Ni) of the above lithium layer Li A secondary battery in which ) is 0.003 or more to 0.015 or less. In Article 1, The above positive active material is a secondary battery having a Curie-Weiss temperature of 0 K or higher and 19 K or lower. In Article 1, A secondary battery having a Curie-Weiss temperature of the positive electrode active material of 3 K or more and 10 K or less. In Article 1, The above positive active material has a lattice volume of 101.5 Å. 3 From 101.6 Å or more 3 A secondary battery that is less than or equal to the following.

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