Secondary battery, electric device and positive electrode active material

Abstract

A secondary battery, an electric device and a positive electrode active material. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte containing an organic solvent and a lithium salt, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode membrane layer located on at least one surface of the positive electrode current collector; the positive electrode membrane layer comprises a positive electrode active material; the positive electrode active material comprises a lithium transition metal oxide; the lithium transition metal oxide comprises nickel, cobalt, and at least one of manganese and aluminum; in the lithium transition metal oxide, the molar content of nickel is 85 mol% or more with respect to all the metal elements other than lithium; and in a DTG curve obtained by heating the positive electrode active material at a heating rate of 10ºC / min, the absolute value of the peak value of the derivative weight loss of the positive electrode active material is less than 7% / min.

Description

Secondary battery, power consuming device, and positive electrode active material

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202410657760.3, filed on May 24, 2024, entitled “Secondary battery, power consuming device, and positive electrode active material”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a secondary battery, a power consuming device, and a positive electrode active material. BACKGROUND

[0004] In recent years, with the increasingly wide range of applications of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power, and solar power stations, and in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance, and storage performance, etc.

[0005] The performance of a secondary battery is closely related to the positive electrode active material. Among them, high-nickel positive electrode active materials are considered to be the best choice to meet the requirement of high energy density. However, with the increase of nickel content in the positive electrode active material, its thermal stability becomes poor. Therefore, how to improve the thermal stability of high-nickel positive electrode active materials and further improve the performance of secondary batteries is a technical problem to be solved.

[0006] SUMMARY

[0007] In order to achieve the above-mentioned purpose, the present disclosure provides a secondary battery, a power consuming device, and a positive electrode active material. The secondary battery uses a positive electrode active material with high thermal stability, and the secondary battery has improved storage performance and cycle performance.

[0008] The first aspect of the present disclosure provides a secondary battery, comprising: a positive electrode tab, a negative electrode tab, a separator disposed between the positive electrode tab and the negative electrode tab, and an electrolyte comprising an organic solvent and a lithium salt, the positive electrode tab comprising a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising a nickel element and a cobalt element, and comprising at least one of a manganese element and an aluminum element, in the lithium transition metal oxide, the molar content of the nickel element relative to all metal elements excluding lithium is 85 mol% or more, and in a differential thermogravimetric curve obtained by warming the positive electrode active material at a warming rate of 10°C / min, the absolute value of the peak value of the heat loss rate of change is less than 7% / min. In the present disclosure, by making the absolute value of the peak value of the heat loss rate of change less than 7% / min, the heat loss rate can be inhibited from suddenly rising, the thermal stability of the positive electrode active material with an ultra-high nickel content (Ni content of 85 mol% or more) can be improved, the occurrence of gas generation can be reduced, and the storage performance and cycle performance of the battery can be further improved. In some embodiments, the molar content of the nickel element relative to all metal elements excluding lithium is 90 mol% or more. By making the molar percentage of the nickel element in the above range, the positive electrode active material has a high energy density.

[0009] In some embodiments, the absolute value of the peak value of the heat loss rate of change is less than or equal to 6.1% / min. By making the peak value of the heat loss rate of change of the positive electrode active material in the above range, the thermal stability of the positive electrode active material is further improved.

[0010] In some embodiments, the absolute value of the peak value of the heat loss rate of change is less than or equal to 5.6% / min. By making the peak value of the heat loss rate of change of the positive electrode active material in the above range, the thermal stability of the positive electrode active material is further improved.

[0011] In some embodiments, in a thermogravimetric analysis, the total weight loss of the positive electrode active material during warming from 0°C to 600°C is set as m1, the weight loss during warming from 220°C to 360°C is set as m2, and m1 and m2 satisfy the following relationship: 40%≤m2 / m1≤75%. By making the proportion of the weight loss during warming from 220°C to 360°C in the total weight loss (m2 / m1) in the above range, the heat loss of the positive electrode active material in the temperature range from 220°C to 360°C is small, which is conducive to reducing the heat accumulated in this temperature range and improving the thermal stability of the positive electrode active material.

[0012] In some embodiments, m2 is 0.5%-12%. By making m2 in the above range, the heat loss of the positive electrode active material in the temperature range from 220°C to 360°C is small, which is conducive to reducing the heat accumulated in this temperature range and improving the thermal stability of the positive electrode active material.

[0013] In some embodiments, m1 is 1% to 18%. By setting m1 in the above range, the positive electrode active material has less thermal weight loss in the temperature range of 0°C to 600°C, which is advantageous for improving the thermal stability of the positive electrode active material.

[0014] In some embodiments, in the thermogravimetric analysis, the positive electrode active material has a weight loss rate of greater than 1% and less than or equal to 18% at 600°C. In some embodiments, in the thermogravimetric analysis, the positive electrode active material has a weight loss rate of 10% to 18% at 600°C. Thereby, the thermal stability of the positive electrode active material can be further improved.

[0015] In some embodiments, in the thermogravimetric analysis, the positive electrode active material has a weight loss rate of 10% to 12% at 300°C. Thereby, the thermal stability of the positive electrode active material can be further improved.

[0016] In some embodiments, in the thermogravimetric analysis, the positive electrode active material has a weight loss rate of 0.01% to 0.5% at 200°C. Thereby, the thermal stability of the positive electrode active material can be further improved.

[0017] In some embodiments, the differential thermogravimetric curve is obtained by testing the positive electrode active material under a nitrogen atmosphere from 0°C to 600°C.

[0018] In some embodiments, in the differential thermogravimetric curve, a peak of the rate of change of thermal weight loss occurs in the range of 200°C to 280°C.

[0019] In some embodiments, in the differential thermogravimetric curve, a peak of the rate of change of thermal weight loss occurs in the range of 220°C to 240°C.

[0020] In some embodiments, in the differential thermogravimetric curve, the peak area of the peak of the rate of change of thermal weight loss is 12.0% to 17.0%.

[0021] In some embodiments, in the differential thermogravimetric curve, the half-peak width of the peak of the rate of change of thermal weight loss is 5°C to 25°C.

[0022] In some embodiments, for the oxygen released in the thermogravimetric analysis of the positive electrode active material, the peak value of the mass spectrometry peak in the mass spectrometry curve obtained by mass spectrometry analysis is less than or equal to 5×10 -10 A. The peak value of the mass spectrometry peak in the above range indicates that the amount of oxygen released by the positive electrode active material is small, and the thermal stability of the positive electrode active material is further improved.

[0023] In some embodiments, in the mass spectrum curve, the peak value of the mass spectrum peak occurs in the range of 200°C to 280°C. By satisfying the above condition for the peak value of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0024] In some embodiments, in the mass spectrum curve, the peak value of the mass spectrum peak occurs in the range of 220°C to 240°C. By satisfying the above condition for the peak value of the mass spectrum peak, the thermal stability of the positive electrode active material is further improved.

[0025] In some embodiments, the area of the mass spectrum peak is 1.2×10 -9 A·℃ to 50×10 -9 A·℃. By satisfying the above condition for the peak area of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0026] In some embodiments, the half-peak width of the mass spectrum peak is 10°C to 20°C. By satisfying the above condition for the half-peak width of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0027] In some embodiments, in the X-ray diffraction spectrum of the positive electrode active material, the ratio of the peak intensity I(003) of the 003 plane to the peak intensity I(104) of the 104 plane is 1.2-1.7. By making I(003) / I(104) in the above range, the lithium transition metal oxide in the positive electrode active material has a better layered structure, which is conducive to improving the thermal stability of the positive electrode active material.

[0028] In some embodiments, the lithium transition metal oxide further comprises a doping element, and the doping element comprises at least one of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti. By introducing the above-mentioned doping element, it is conducive to further improving the thermal stability of the positive electrode active material.

[0029] In some embodiments, the content of the doping element is 3000 ppm or less with respect to the lithium transition metal oxide. By controlling the content of the doping element in the above range, it is conducive to improving the specific capacity and cycle performance of the battery.

[0030] In some embodiments, the lithium transition metal oxide comprises Li a Ni b Co c Mn d M 1(1-b-c-d) O n and / or Li e Ni f Co g Al h M 2 (1-f-g-h) O n , Li a Ni b Co c Mn d M 1 (1-b-c-d) O n , 0.5≤a≤1.2, 0.85≤b≤0.99, 0≤c≤0.1, 0≤d≤0.05, 1.9≤n≤2.2, M 1 comprising one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, Li e Ni f Co g Al h M 2 (1-f-g-h) O n , 0.5≤e≤1.2, 0.85≤f≤0.99, 0≤g≤0.1, 0≤h≤0.05, 1.9≤n≤2.2, M 2 comprising one or more of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, Ti.

[0031] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: (1) the volume average particle size Dv50 of the positive electrode active material is 8.5 μm to 12 μm; (2) the specific surface area BET of the positive electrode active material is 0.35 m 2 / g to 0.65 m 2 / g; (3) the powder compaction density of the positive electrode active material under a pressure of 3000 N is 3.0 g / cm 3 to 3.5 g / cm 3 ; (4) the tap density of the positive electrode active material is 2.9 g / cm 3 to 3.5 g / cm 3 ; (5) the delithiation capacity of the positive electrode active material is 210 mAh / g to 225 mAh / g.

[0032] In some embodiments, the positive electrode active material comprises a substrate and a coating layer arranged on at least part of the surface of the substrate; the substrate comprises a lithium transition metal oxide. The coating layer is coated on the surface of the lithium transition metal oxide, which can reduce the side reaction between the lithium transition metal oxide and the electrolyte, thereby improving the thermal stability of the positive electrode active material.

[0033] In some embodiments, the coating layer comprises an outer layer and an inner layer disposed between the outer layer and the substrate; the inner layer comprises at least one of P, Al, Ca, Ti elements; the outer layer comprises at least one of Y element, Al element. By disposing the inner and outer layers of the coating layer, the structural stability of the coating layer can be improved, and the probability of side reactions between the electrolyte and the lithium transition metal oxide can be reduced, thereby further improving the thermal stability of the positive electrode active material.

[0034] In some embodiments, the inner layer comprises P element, and the outer layer comprises Y element and Al element. The coating containing phosphorus element (phosphate) can improve the ion conductivity of the surface of the positive electrode active material while reducing the contact with the electrolyte, which is conducive to further improving the thermal stability of the positive electrode active material.

[0035] In some embodiments, in the positive electrode active material, the molar ratio of lithium element to phosphorus element is 1:0.001-0.004. By controlling the molar ratio of lithium element to phosphorus element within the above range, the phosphate can better form a coating layer with appropriate thickness on the surface of the substrate, which can effectively protect the surface interface stability of the positive electrode active material, improve the stability of the positive electrode active material, and minimize the impact of the coating on ion transmission.

[0036] The second aspect of the present disclosure provides a power device comprising the secondary battery of the first aspect.

[0037] The third aspect of the present disclosure provides a positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising a nickel element and a cobalt element, and comprising at least one of a manganese element and an aluminum element, in the lithium transition metal oxide, the molar content of the nickel element is 85 mol% or more with respect to all metal elements excluding lithium, and in a differential thermal gravimetric curve obtained by warming the positive electrode active material at a warming rate of 10°C / min, the absolute value of the peak value of the thermal weight loss rate is less than 7% / min. The positive electrode active material of the present disclosure can inhibit the sudden drop of the thermal weight loss rate, has excellent thermal stability, reduces the occurrence of gas production, and can improve the storage performance and cycle performance of the battery.

[0038] In some embodiments, the molar content of the nickel element is 90 mol% or more with respect to all metal elements excluding lithium. By making the molar percentage of the nickel element within the above range, the positive electrode active material has a high energy density.

[0039] In some embodiments, the absolute value of the peak value of the thermal weight loss rate is less than or equal to 6.1% / min. By making the peak value of the thermal weight loss rate of the positive electrode active material within the above range, the thermal stability of the positive electrode active material is further improved.

[0040] In some embodiments, the absolute value of the peak of the rate of change of thermal weight loss is less than or equal to 5.6% per minute. By having the peak of the rate of change of thermal weight loss of the positive electrode active material in the above range, the thermal stability of the positive electrode active material is further improved.

[0041] In some embodiments, in the thermal gravimetric analysis, the total weight loss of the positive electrode active material from 0°C to 600°C is set as m1, and the weight loss from 220°C to 360°C is set as m2, and m1 and m2 satisfy the following relationship: 40%≤m2 / m1≤75%.

[0042] In some embodiments, m2 is 0.5%-12%. In this way, the positive electrode active material has less thermal weight loss in the temperature interval of 220°C to 360°C, which is conducive to reducing the heat accumulated in this temperature interval and improving the thermal stability of the positive electrode active material. In some embodiments, m1 is 1%-18%. In this way, the positive electrode active material has less thermal weight loss in the temperature interval of 0°C to 600°C, which is conducive to improving the thermal stability of the positive electrode active material.

[0043] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and is 18% or less. In this way, the thermal stability of the positive electrode active material can be further improved.

[0044] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 300°C is 10%-12%. In this way, the thermal stability of the positive electrode active material can be further improved.

[0045] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 200°C is 0.01%-0.5%. In this way, the thermal stability of the positive electrode active material can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0047] FIG. 2 is an exploded view of the battery cell according to an embodiment of the present disclosure.

[0048] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0049] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0050] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present disclosure.

[0051] FIG. 6 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0052] FIG. 7 is a thermogravimetric-temperature curve of the positive electrode active material prepared in Example 1 of the present disclosure.

[0053] FIG. 8 is a rate of change of thermogravimetry-temperature curve of the positive electrode active material prepared in Example 1 of the present disclosure.

[0054] FIG. 9 is a mass spectrum of the positive electrode active material prepared in Example 1 of the present disclosure.

[0055] BRIEF DESCRIPTION OF DRAWINGS

[0056] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: top cap assembly. DETAILED DESCRIPTION

[0057] Hereinafter, specific embodiments of the secondary battery, the power using device, and the positive electrode active material of the present disclosure are specifically disclosed with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters well known, repeated description of actually identical structures are omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter described in the present disclosure.

[0058] The "range" disclosed in the present disclosure is defined in the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing any real combination of numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand manner of describing these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] If there is no special indication, all the embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0060] If there is no special indication, all the technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0061] If there is no special indication, the terms used in the present disclosure have the commonly understood meanings understood by those skilled in the art.

[0062] If there is no special indication, the values of the parameters mentioned in the present disclosure can be measured by various test methods commonly used in the art, for example, can be measured according to the test methods given in the present disclosure.

[0063] The performance of the secondary battery is closely related to the thermal stability of the positive electrode active material. In the current design of positive electrode active material, in order to obtain a higher energy density, high-nickel positive electrode active materials are usually used. However, during the operation of the battery, the high temperature inside the battery causes the above-mentioned materials to undergo phase transition, resulting in the reduction of transition metal ions (for example, Ni 4+ , Ni 3+ , Co 4+ , Co 3+ ) and the generation of gas (for example, oxygen). The higher the nickel content, the faster the above-mentioned phase transition will be. In particular, ultra-high nickel positive electrode active materials (in particular, Ni content of 85 mol% or more) have poorer thermal stability than low-nickel materials, are more prone to decomposition at high temperatures, and have serious gas generation problems, which affect the cycle performance and storage performance of the battery.

[0064] Based on this, the present disclosure proposes a secondary battery and a power utilization device. The present invention and optional embodiments are described in more detail below.

[0065] The first aspect of the present disclosure provides a secondary battery. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte comprising an organic solvent and a lithium salt, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material; the positive electrode active material comprises a lithium transition metal oxide, the lithium transition metal oxide comprises nickel element and cobalt element, and comprises at least one of manganese element and aluminum element, in the lithium transition metal oxide, the molar content of the nickel element is 85 mol% or more relative to all metal elements excluding lithium, and in the differential thermal gravimetric curve of the positive electrode active material obtained at a heating rate of 10℃ / min, the absolute value of the peak value of the thermal weight loss rate of the positive electrode active material is less than 7% / min.

[0066] In the present disclosure, by making the absolute value of the peak of the heat weight loss rate less than 7% / min, the heat weight loss rate can be inhibited from suddenly rising, the thermal stability of the positive electrode active material with ultra-high nickel content (Ni content of 85 mol% or more) can be improved, the generation of gas can be reduced, and the storage performance and cycle performance of the battery can be further improved.

[0067] In the present disclosure, in the lithium transition metal oxide, the molar percentage content of the nickel element is 85 mol% or more with respect to all metal elements other than lithium. For example, the molar percentage content of the nickel element is 85 mol%, 86 mol%, 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, or a value between any two of the values, but is not limited thereto. Preferably, the molar percentage content of the nickel element is 90 mol% or more. The molar percentage of the nickel element in the above range allows the positive electrode active material to have a high energy density.

[0068] In the present disclosure, the thermogravimetric analysis on the positive electrode active material can be performed, for example, as follows: 10 mg to 20 mg of a positive electrode active material sample powder is taken, dried to remove moisture, placed in a thermal analysis crucible, the temperature range for testing is set to 0°C-600°C, the temperature rise rate is set to 10°C / min, and the sample is placed in a thermogravimetric analyzer to obtain a thermogravimetric analysis curve (TG curve). Then, the first derivative of each point on the TG curve with respect to the time coordinate is taken to obtain a differential thermogravimetric curve (DTG curve). The DTG curve shows the change in the heat weight loss rate with time, and the lower the heat weight loss rate, the better the thermal stability of the positive electrode active material.

[0069] In the present disclosure, the heat weight loss rate of the positive electrode active material in the DTG curve shows one inverted peak, and the absolute value of the peak is less than 7% / min. For example, the peak of the heat weight loss rate of the positive electrode active material is -6.9% / min, -6.8% / min, -6.5% / min, -6.3% / min, -6.2% / min, -6.1% / min, -6% / min, -5.6% / min, -5% / min, -4% / min, -3% / min, -2% / min, -1% / min, or a value between any two of the values. Preferably, the absolute value of the peak of the heat weight loss rate is 6.1% / min or less, and more preferably, the absolute value of the peak of the heat weight loss rate is 5.6% / min or less. By making the peak of the heat weight loss rate of the positive electrode active material in the above range, the thermal stability of the positive electrode active material is further improved.

[0070] In some embodiments, the DTG curve is tested under nitrogen atmosphere from 0°C to 600°C. In some embodiments, in the DTG curve, a peak of the rate of thermal weight loss occurs in the range of 200°C to 280°C, for example, the peak occurs at 200°C, 210°C, 220°C, 230°C, 240°C, or a value between any two of the values. Preferably, the peak occurs in the range of 220°C to 240°C.

[0071] In some embodiments, the peak area of the peak of the rate of thermal weight loss is 12.0% to 17.0%. For example, the peak area of the peak of the rate of thermal weight loss is 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, or a value between any two of the values.

[0072] In some embodiments, the half-peak width of the peak of the rate of thermal weight loss is 5°C to 25°C. For example, the half-peak width of the peak of the rate of thermal weight loss is 5°C, 10°C, 15°C, 20°C, 25°C, or a value between any two of the values.

[0073] In some embodiments, the total weight loss of the positive electrode active material from 0°C to 600°C is denoted as m1, and the weight loss from 220°C to 360°C is denoted as m2, and the m1 and the m2 satisfy the following relationship: 40%≤m2 / m1≤75%. For example, m2 / m1 is 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a value between any two of the values.

[0074] It is found that the side reaction of the positive electrode active material mainly occurs in the temperature range of 220°C to 360°C, and most of the thermal weight loss occurs in this temperature range, and the weight decreases significantly in this temperature range, and the weight loss increases. In the present disclosure, by making the weight loss from 220°C to 360°C account for 40% to 75% of the total weight loss (m2 / m1), the thermal weight loss of the positive electrode active material in the temperature range of 220°C to 360°C is small, which is beneficial to reduce the heat accumulated in this temperature range and improve the thermal stability of the positive electrode active material. In some embodiments, preferably, the m1 and the m2 satisfy the following relationship: 40%≤m2 / m1≤55%, thereby further improving the thermal stability of the positive electrode active material.

[0075] In some embodiments, the m1 is greater than 1% and is 18% or less, for example, m1 is 3%, 6%, 9%, 12%, 15%, 16.87%, 18% or a value between any two of these values. By having m1 in the above range, the positive electrode active material has less thermal weight loss in the temperature interval of 0°C to 600°C, which is beneficial to improve the thermal stability of the positive electrode active material.

[0076] In some embodiments, the m2 is 0.5% to 12%, for example, m2 is 0.5%, 1%, 3%, 6%, 9%, 10.95%, 12% or a value between any two of these values. By having m2 in the above range, the positive electrode active material has less thermal weight loss in the temperature interval of 220°C to 360°C, which is beneficial to reduce the heat accumulated in this temperature interval and improve the thermal stability of the positive electrode active material.

[0077] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and is 18% or less. For example, the weight loss rate of the positive electrode active material at 600°C is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a value between any two of these values. Preferably, the weight loss rate of the positive electrode active material at 600°C is 10% to 18%.

[0078] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 300°C is 10% to 12%. For example, the weight loss rate of the positive electrode active material at 300°C is 10%, 11%, 12% or a value between any two of these values.

[0079] In some embodiments, in the thermal gravimetric analysis, the weight loss rate of the positive electrode active material at 200°C is 0.01% to 0.5%. For example, the weight loss rate of the positive electrode active material at 200°C is 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or a value between any two of these values.

[0080] In some embodiments, for the oxygen released by the positive electrode active material in the thermal gravimetric analysis, the peak value (maximum value of ion current intensity) of the mass spectrum peak in the mass spectrum curve obtained by mass spectrometry is less than or equal to 5×10 -10 A (ampere), wherein the mass spectrum curve is a mapping relationship of the intensity of ion current (lon Current ) and temperature, and the ion current is the ion current generated by the oxygen released by the positive electrode active material during mass spectrometry. The peak value (lon CurrentThe smaller the value of the peak value of the mass spectrum peak in the mass spectrum curve is, the less oxygen released by the positive electrode active material at the current temperature, and the better the thermal stability of the positive electrode active material. The peak value of the mass spectrum peak in the above range indicates that the positive electrode active material releases less oxygen, and the thermal stability of the positive electrode active material is further improved.

[0081] In some embodiments, the peak value of the mass spectrum peak appears in the range of 200°C to 280°C in the mass spectrum curve. In some embodiments, the peak value of the mass spectrum peak appears in the range of 220°C to 240°C. For example, the peak value of the mass spectrum peak appears at 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or a value between any two values. By satisfying the above conditions for the peak value of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0082] In some embodiments, the area of the mass spectrum peak is 1.2×10 -9 A·℃ to 50×10 -9 A·℃. For example, the area of the mass spectrum peak is 1.2×10 -9 A·℃, 10×10 -9 A·℃, 20×10 -9 A·℃, 30×10 -9 A·℃, 40×10 -9 A·℃, 50×10 -9 A·℃, or a value between any two values. By satisfying the above conditions for the peak area of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0083] In some embodiments, the half-peak width of the mass spectrum peak is 10°C-20°C. For example, the half-peak width of the mass spectrum peak is 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, or a value between any two values. By satisfying the above conditions for the half-peak width of the mass spectrum peak, the amount of oxygen generated by the positive electrode active material under high temperature conditions (for example, 200°C-300°C) is small, which is conducive to further improving the thermal stability of the positive electrode active material.

[0084] In some embodiments, the ratio of the peak intensity I(003) of the 003 plane to the peak intensity I(104) of the 104 plane in the X-ray diffraction pattern of the positive electrode active material is 1.2-1.7. For example, I(003) / I(104) is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or a value between any two of the above values. By making I(003) / I(104) in the above range, the lithium transition metal oxide in the positive electrode active material has a better layered structure, which is beneficial to the improvement of the thermal stability of the positive electrode active material.

[0085] In some embodiments, the lithium transition metal oxide further comprises a doping element, which comprises at least one of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti. By introducing the above-mentioned doping element, it is beneficial to further improve the thermal stability of the positive electrode active material.

[0086] In some embodiments, the content of the above-mentioned doping element is less than or equal to 3000 ppm with respect to the lithium transition metal oxide. For example, the content of the doping element can be 3000 ppm, 2000 ppm, 1000 ppm, 500 ppm, 200 ppm, 100 ppm, 0 ppm, or a value between any two of the above values, but is not limited thereto. By controlling the content of the doping element in the above range, it is beneficial to improve the specific capacity and cycle performance of the battery.

[0087] In the present disclosure, "lithium transition metal oxide" refers to an oxide composed of metallic lithium and a transition metal element. The lithium transition metal oxide mentioned in the present disclosure includes but is not limited to lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), etc.

[0088] In some embodiments, the chemical formula of the above-mentioned lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M 1 (1-b-c-d) O n , 0.5≤a≤1.2, 0.85≤b≤0.99, 0≤c≤0.1, 0≤d≤0.05, 1.9≤n≤2.2, M 1 comprises a combination of one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti.

[0089] In some embodiments, the chemical formula of the above-mentioned lithium nickel cobalt aluminum oxide is Li e Ni f Co g Al h M 2(1-f-g-h) O n , 0.5≤e≤1.2, 0.85≤f≤0.99, 0≤g≤0.1, 0≤h≤0.05, 1.9≤n≤2.2, M 2 comprising a combination of one or more of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, Ti.

[0090] For example, the lithium transition metal oxide includes Li(Ni 0.93 Co 0.06 Mn 0.01 ) 0.991 W 0.004 Zr 0.005 O2, Li(Ni 0.93 Co 0.06 Mn 0.01 ) 0.994 Ta 0.001 Zr 0.005 O2, etc.

[0091] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: (1) the volume average particle size Dv50 of the positive electrode active material is 8.5 μm to 12 μm. (2) the specific surface area BET of the positive electrode active material is 0.35 m 2 / g to 0.65 m 2 / g. (3) the powder compaction density of the positive electrode active material under a pressure of 3000 N is 3.0 g / cm 3 to 3.5 g / cm 3 . (4) the tap density of the positive electrode active material is 2.9 g / cm 3 to 3.5 g / cm 3 . (5) the delithiation capacity of the positive electrode active material is 210 mAh / g to 225 mAh / g.

[0092] In the present disclosure, the volume distribution particle size Dv50 of a material is the meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage reaching 50%, and can be measured by instruments and methods known in the art. For example, GB / T 19077-2016 can be referred to, and a laser particle size analyzer can be used for measurement. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0093] In the present disclosure, the specific surface area of a material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be tested by using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated by using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area pore size analyzer of Micromeritics, USA.

[0094] In the present disclosure, the tap density of a material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by using an electronic pressure testing machine (for example, a UTM7305 electronic pressure testing machine) according to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is added into a mold with a bottom area of 1.327 cm 2 , and is pressed to 3000 N, kept for 30 s, then released, kept for 10 s, and then recorded and calculated to obtain the tap density of the material under a pressure of 3000 N.

[0095] In the present disclosure, the tap density of a material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by using an electronic pressure testing machine (for example, a UTM7305 electronic pressure testing machine) according to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is added into a mold with a bottom area of 1.327 cm

[0096] In the present disclosure, the tap density of a material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by using an electronic pressure testing machine (for example, a UTM7305 electronic pressure testing machine) according to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is added into a mold with a bottom area of 1.327 cm

[0097] In some embodiments, the positive electrode active material comprises a substrate and a coating layer arranged on at least part of the surface of the substrate, wherein the substrate comprises a lithium transition metal oxide. In this embodiment, the coating layer is coated on the surface of the lithium transition metal oxide, which can reduce the side reaction between the lithium transition metal oxide and the electrolyte, thereby improving the thermal stability of the positive electrode active material.

[0098] In some embodiments, the coating layer comprises an outer layer and an inner layer arranged between the outer layer and the substrate; the inner layer comprises at least one of phosphorus, aluminum, calcium and titanium elements; and the outer layer comprises at least one of Y and Al. By arranging the inner and outer coating layers, the structural stability of the coating layer can be improved, and the probability of side reaction between the electrolyte and the lithium transition metal oxide can be reduced, thereby further improving the thermal stability of the positive electrode active material.

[0099] In some embodiments, the inner layer comprises a P element, and the outer layer comprises a Y element and an Al element. The coating containing the phosphorus element (phosphate) can improve the ion conductivity of the surface of the positive electrode active material while reducing the contact with the electrolyte, which is beneficial to further improve the thermal stability of the positive electrode active material.

[0100] In some embodiments, the molar ratio of lithium element to phosphorus element in the positive electrode active material is 1:0.001-0.004. For example, the molar ratio of lithium element to phosphorus element is 1:0.001, 1:0.002, 1:0.003, 1:0.004, or a value between any two of the above values, but is not limited thereto. By controlling the molar ratio of lithium element to phosphorus element within the above range, the phosphate can better form a coating layer with an appropriate thickness on the surface of the substrate, which can effectively protect the surface interface stability of the positive electrode active material, improve the stability of the positive electrode active material, and minimize the impact of the coating on ion transport.

[0101] In addition, for the preparation method of the positive electrode active material of the present disclosure, the following method can be used, which comprises the following steps.

[0102] Step (1): A mixed solution containing Ni element, Co element and Mn element is prepared by mixing Ni, Co and Mn in a molar ratio of x:y:(1-x-y), wherein x≥0.85. Under a certain pump speed, the mixed solution, sodium carbonate and ammonia water are added to a reaction kettle, the pH in the reaction kettle is controlled between 11-14, and the temperature is controlled between 50°C-70°C. Co-precipitation reaction is carried out to make the precursor particles grow to a target Dv50=8.5-12 μm. After the reaction is completed, washing and drying are carried out to obtain an ultra-high nickel ternary material precursor.

[0103] In the present disclosure, as substances capable of providing Ni element, for example, but not limited to, nickel carbonate, nickel hydroxide, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate, and nickel oxalate, etc.

[0104] In the present disclosure, as substances capable of providing Co element, for example, but not limited to, cobalt carbonate, cobalt hydroxide, cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt oxalate, etc.

[0105] In the present disclosure, as substances capable of providing Mn element, for example, but not limited to, manganese dioxide, electrolytic manganese dioxide, and trimanganese tetraoxide, etc.

[0106] The reaction temperature in the co-precipitation reaction described above can be 50-70°C, for example, the reaction temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, or a value between any two of the values in the range. The reaction time is 24-48h. For example, the reaction time can be 24h, 28h, 32h, 36h, 40h, 44h, 48h, or a value between any two of the values in the range.

[0107] The co-precipitation reaction described above is carried out in an environment with a pH of 11-14, for example, the pH of the reaction environment is 11, 12, 13, 14, or a value between any two of the values in the range, but is not limited thereto.

[0108] Step (2): mixing the ultra-high nickel ternary material precursor obtained in step (1), a lithium source, and a doping element M source to obtain a mixture, and performing sintering treatment at a high temperature to obtain a lithium transition metal oxide.

[0109] In some embodiments, the lithium source is a substance capable of providing lithium elements, for example, the lithium source includes at least one of lithium hydroxide (LiOH·H2O), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium oxalate (LiC2O4), lithium acetate (CH3COOLi), but is not limited thereto. The molar ratio of the lithium source to the metal of the ternary material precursor described above is Li / Me 1.0-1.2:1, Me is the total molar amount of Ni, Co, and Mn elements.

[0110] In some embodiments, the doping element M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti. In some embodiments, as a source of the doping element M, as long as it is a substance capable of providing the doping element M described above, it is not particularly limited. For example, it can be sodium carbonate, zirconium hydroxide, zirconium oxide, zirconium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, titanium oxide, titanium hydroxide, titanium carbonate, tungsten oxide, tungsten hydroxide, tungsten carbonate, niobium oxide, niobium hydroxide, niobium carbonate, tantalum hydroxide, tantalum carbonate, strontium hydroxide, strontium oxide, strontium carbonate, strontium phosphate, calcium hydroxide, calcium oxide, calcium carbonate, calcium phosphate, aluminum oxide, aluminum hydroxide, yttrium oxide, yttrium hydroxide, etc.

[0111] In some embodiments, the sintering temperature and sintering time of the above sintering are not particularly limited. For example, the sintering temperature can be 500-800°C. Specifically, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 720°C, 800°C, or a value between any two of the above values, and preferably 720°C. The sintering time can be 5-16h, for example, it can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, or a value between any two of the above values, and preferably 14h.

[0112] Step (3): mixing the lithium transition metal oxide obtained in step (2) with a phosphate salt, and sintering at a sintering temperature of 400-650°C for 5-11h.

[0113] Preferably, the phosphate salt comprises Li X Al 0.5 Ti 1.5 (PO4)3, wherein x = 1.5-5. For example, x is 1.5, 2, 3, 4, 5, or a value between any two of the above values, but is not limited thereto. Further preferably, it comprises LiAl 0.5 Ti 1.5 (PO4)3. By using a phosphate salt coating, the ion conductivity of the surface of the positive electrode active material can be improved while reducing contact with the electrolyte, which is conducive to further improving the thermal stability of the positive electrode active material. In the material obtained after this sintering, the molar ratio of lithium to phosphorus is 1:0.001-0.004. For example, it is 1:0.001, 1:0.002, 1:0.003, 1:0.004, or a value between any two of the above values, but is not limited thereto.

[0114] In this step, the sintering temperature is 400-650°C. For example, it can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, or a value between any two of the above values, and preferably 600°C. The sintering time is 5-11h, for example, it can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, or a value between any two of the above values, and preferably 6.5h.

[0115] Step (4): adding the product obtained in step (3) above to pure water, stirring for 3-5min, and filtering and drying.

[0116] Step (5): mixing the substance obtained in step (4) above with an Al source and a Y source, and sintering at high temperature to obtain the positive electrode active material of the present disclosure.

[0117] In the present disclosure, the aluminum source is a substance capable of providing an aluminum element, for example, the aluminum source can include at least one of aluminum oxide, aluminum hydroxide. The yttrium source is a substance capable of providing a yttrium element, for example, the yttrium source can include at least one of yttrium oxide, yttrium hydroxide.

[0118] In some embodiments, the molar ratio of the substance obtained in the above step (4) to the Al element, the Y element is 1:0.005-0.01:0.005-0.01, for example, the molar ratio is 1:0.005:0.005, 1:0.01:0.005, 1:0.005:0.01 or a value between any two values in the range. In some embodiments, the component of the cladding layer close to the inner layer of the substrate includes Li x Al 0.5 Ti 1.5 (PO4) 3， wherein x is 1.5-5. The outer layer of the cladding layer away from the substrate includes at least one of the Al element, the Y element. Preferably, the outer layer of the cladding layer away from the substrate includes Al 18 Y 14 O 48 .

[0119] In this step, the sintering temperature can be 250℃-400℃, for example, it can be 250℃, 300℃, 350℃, 400℃ or a value between any two values in the range, preferably 300℃. The sintering time can be 5h-12h, for example, it can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h or a value between any two values in the range, but not limited to this. Preferably, it can be 6h-10h, more preferably 8h.

[0120] It should be noted that the chemical formula of the lithium transition metal oxide given in the present disclosure is the chemical formula of the material used in the battery preparation process. In the positive electrode sheet, the secondary battery, the electric device, due to the processes such as formation and cycling, the elements in the above chemical formula can be lost, as understood by those skilled in the art. For example, due to the processes such as cycling, the oxygen element in the positive electrode active material is lost, so the measured oxygen content in the positive electrode active material is reduced. In addition, due to the processes such as formation and cycling, lithium ions are consumed, so the measured lithium content in the positive electrode active material is reduced.

[0121] In addition, the secondary battery and the electric device of the present disclosure are described below with appropriate reference to the accompanying drawings.

[0122] The term "secondary battery" referred to herein means a battery cell, a battery module, or a battery pack. Each is explained below.

[0123] Generally, a secondary battery cell includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During charging and discharging of the battery, active ions are intercalated and deintercalated between the positive electrode tab and the negative electrode tab. The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab. The separator is disposed between the positive electrode tab and the negative electrode tab and functions to prevent short circuiting of the positive and negative electrodes while allowing ions to pass through.

[0124] Positive electrode tab

[0125] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the present disclosure.

[0126] In some embodiments, the positive electrode current collector has two opposing surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0127] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0129] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and drying, cold-pressing, or the like.

[0131] Negative electrode sheet

[0132] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0133] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0134] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As a metal foil, for example, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material can also be used. These negative electrode active materials can be used alone or in combination with two or more.

[0136] In some embodiments, the negative electrode film layer can also optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0137] In some embodiments, the negative electrode film layer can also optionally include a conductive agent. The conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] In some embodiments, the negative electrode film layer can also optionally include other additives, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0139] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0140] Electrolyte

[0141] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present disclosure and can be selected as needed.

[0142] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0143] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0144] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0145] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0146] Separator film

[0147] In some embodiments, a separator film is further included in the battery cell. The type of the separator film is not particularly limited in the present disclosure, and any known porous separator film having good chemical stability and mechanical stability can be used.

[0148] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0149] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly through a winding process or a stacking process.

[0150] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0151] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0152] The shape of the battery cell is not particularly limited in the present disclosure, and the battery cell can be cylindrical, square, or any other shape. For example, FIG. 1 is a battery cell 5 having a square structure as an example.

[0153] In some embodiments, referring to FIG. 2, the outer package can include a shell 51 and a top cover assembly 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0154] In some embodiments, the battery cell can be assembled into a battery module, and the number of the battery cells included in the battery module can be one or more, and a person skilled in the art can select according to the application and capacity of the battery module.

[0155] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in series along a length direction of the battery module 4. Of course, the plurality of battery cells 5 can be arranged in any other manner. The plurality of battery cells 5 can be fixed by fasteners.

[0156] Optionally, the battery module 4 can further include a housing having an accommodation space in which the plurality of battery cells 5 are accommodated.

[0157] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0158] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0159] In addition, a second aspect of the present disclosure provides a power utilization device including the secondary battery provided by the present disclosure. The secondary battery can be used as a power source of the power utilization device or as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0160] As the power utilization device, the battery cell, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0161] FIG. 6 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0162] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinness, and the battery cell can be used as a power source.

[0163] Embodiments

[0164] Hereinafter, an embodiment of the present disclosure will be described. The embodiment described below is exemplary and for the purpose of explanation of the present disclosure and is not to be understood as a limitation of the present disclosure. In the embodiment, a specific technique or condition not mentioned is performed in accordance with a technique or condition described in a document in the art or in accordance with a product manual. The reagent or apparatus not mentioned by the manufacturer is a general product available on the market.

[0165] Example 1

[0166] Preparation of positive active material

[0167] Step (1): Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of Ni:Co:Mn = 93:6:1 to obtain a mixed solution. The mixed solution, sodium carbonate, and ammonia water were added to a reaction kettle, and the pH of the mixed solution in the reaction kettle was controlled at 12 and the temperature was controlled at 61°C to perform a co-precipitation reaction, so that the particle growth of the precursor reached a target Dv50 = 10 pm. After the reaction was completed, washing and drying were performed to obtain an ultra-high nickel ternary material precursor (Ni 0.93 Co 0.06 Mn 0.01 (OH)2).

[0168] Step (2): The above precursor and Li(OH)2 were mixed in a molar ratio of 1:1.05, and then WO3 and ZrO2 were added to the mixture to make the molar ratio of Li:W:Zr = 1:0.003:0.005. Then, the mixed powder was added to a sintering furnace, and the temperature was maintained at 720°C for 14 h. After that, the temperature was decreased to room temperature at a rate of 5°C / min to obtain a lithium transition metal oxide (Li(Ni 0.93 Co 0.06 Mn 0.01 ) 0.992 W 0.003 Zr 0.005 O2).

[0169] Step (3): The lithium transition metal oxide obtained in step (2) was crushed and mixed with lithium aluminum titanium phosphate (LiAl 0.5 Ti 1.5 (PO4)3) to make the molar ratio of lithium element to phosphorus element = 1:0.001. Then, the mixed powder was added to a sintering furnace and sintered. The sintering temperature was 600°C, and the temperature was maintained for 6.5 h. After that, the temperature was decreased to room temperature at a rate of 5°C / min.

[0170] Step (4): 300 g of the powder obtained in step (3) was added to 300 mL of deionized water and stirred for 5 min. Then, the solid powder was obtained by filtration, and then dried at 60°C with air blowing.

[0171] Step (5): The powder obtained in step (4) was added into a sintering furnace and mixed with Al2O3 and Y2O3 to make the molar ratio of lithium element, aluminum element and yttrium element 1:0.009:0.007. The mixed powder was sintered at 300°C for 8h, and then cooled to room temperature at a rate of 1.5°C / min to obtain the positive electrode active material of Example 1.

[0172] Preparation of a secondary battery

[0173] (a) Preparation of a positive electrode tab

[0174] The positive electrode active material prepared above, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methyl pyrrolidone (NMP) at a mass ratio of 98:0.5:1.5, and then stirred and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated on an aluminum foil, and then dried and cold-pressed to obtain a positive electrode tab.

[0175] (b) Preparation of a negative electrode tab

[0176] The artificial graphite, the hard carbon, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR) and the thickening agent sodium carboxymethyl cellulose (CMC) were added into a deionized water solvent at a mass ratio of 90:5:2:2:1, and then stirred and mixed uniformly. The mixture was then coated on both sides of a copper foil, and then dried and cold-pressed to obtain a negative electrode tab.

[0177] (c) Preparation of an electrolyte

[0178] The electrolyte was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC), wherein the volume ratio of EC, DEC and DMC was 1:1:1. LiPF6 was then dissolved in the organic solvent, and the concentration of LiPF6 was 1 mol / L.

[0179] (d) Preparation of a battery

[0180] The separator film (a polyethylene film with a thickness of 13μm), the negative electrode tab and the positive electrode tab were stacked in the order of “separator film-negative electrode tab-separator film-positive electrode tab”, and then processed and molded. The battery was then packaged in an aluminum plastic bag, injected with the electrolyte, and then packaged after formation to obtain a soft package battery.

[0181] Measurement of the positive electrode active material

[0182] (a) Measurement of TG and DTG

[0183] The positive electrode active material prepared in Example 1 was tested by thermogravimetric mass spectrometer TGA-MS (SDT 650 + Discovery MS) to obtain a thermogravimetric analysis curve (TG curve) by heating the positive electrode active material from 0°C to 600°C at a heating rate of 10°C / min, as shown in Figure 7.

[0184] As can be seen from Figure 7, the main part of the total weight loss occurs in the temperature interval of 220°C to 360°C, m1 in the process of heating from 0°C to 600°C is 16.87%, and m2 in the process of heating from 220°C to 360°C is 11.37%. m2 / m1 = 67.40%.

[0185] Then, the first derivative of each point on the TG curve with respect to the time coordinate was taken to obtain a differential thermogravimetric curve (DTG curve), as shown in Figure 8. In Figure 8, a peak appears in the temperature interval of 220°C to 240°C, and the peak value of the thermal weight loss rate is -5.1% / min.

[0186] (b) Determination of oxygen mass spectrum

[0187] The TGA-MS (SDT 650 + Discovery MS) was used to test the TGA and the mass spectrum test was performed simultaneously to obtain Figure 9.

[0188] As shown in Figure 9, the abscissa is the test temperature, and the ordinate is the intensity of the ion current (lon Current ), and the tested gas is oxygen in the gas released by the positive electrode active material during the thermal weight loss test. The larger the value of the ion current intensity, the more oxygen is released by the positive electrode active material at the current temperature, indicating that the positive electrode active material decomposes more severely at the current temperature, indicating that the thermal stability is worse. The smaller the value of the ion current intensity, the less oxygen is released by the positive electrode active material at the current temperature, indicating that the thermal stability of the positive electrode active material is better. As can be seen from Figure 9, a peak appears in the temperature interval of 220°C to 360°C, and the corresponding value of the ion current intensity (lon Current ) is 127.5 x 10 -12 A.

[0189] Test of battery performance

[0190] (a) Test of gas production performance

[0191] The obtained soft package battery was charged to 4.25V at 0.33C, and then placed in a temperature environment of 70°C for 50 days. Then, the volume of the gas was tested as the gas production of the soft package battery, denoted as Q, and the capacity at that time was measured, denoted as D50, and the gas production per unit capacity at 50 days was Q / D50.

[0192] (b) Test of 25°C cycle performance

[0193] At 25°C, charge at 0.33C to 4.25V, then constant voltage charge at 4.25V until current < 0.05mA, stand for 5min, then discharge at 0.33C to 2.8V, get capacity D1. Repeat the previous process, record the capacity of soft pack battery after 100 cycles D100.

[0194] 100 cycles capacity retention rate = D100 / D1.

[0195] (c) 60°C storage performance test

[0196] Charge the soft pack battery at 0.33C to 4.25V, then constant voltage charge at 4.25V until current < 0.05mA, stand for 5min, then discharge at 0.33C to 2.8V, capacity is recorded as D0, then charge at 0.33C to 4.25V, store in a temperature environment of 60°C, store for 30 days, discharge at 0.33C to 2.8V, capacity is recorded as D30.

[0197] 60°C storage for 30 days capacity retention rate = D30 / D0.

[0198] Example 2

[0199] Prepare the positive electrode active material according to the similar method of Example 1, except that:

[0200] In step (2), replace WO3 with Ta2O5, and replace ZrO2 with Sb2O3, and the molar ratio of Li, Ta, and Sb is 1:0.01:0.006.

[0201] In addition, prepare the soft pack battery by the same method as Example 1 and test it. The results are shown in Table 2 below.

[0202] Example 3

[0203] Prepare the positive electrode active material according to the similar method of Example 1, except that:

[0204] In step (2), after adding WO3 and ZrO2, the molar ratio of Li, W, and Zr is 1:0.005:0.005.

[0205] In addition, prepare the soft pack battery by the same method as Example 1 and test it. The results are shown in Table 2 below.

[0206] Example 4

[0207] Prepare the positive electrode active material according to the similar method of Example 1, except that:

[0208] In step (2), WO3 was replaced with Ta2O5, and after adding Ta2O5 and ZrO2, the molar ratio of Li, Ta, and Zr was 1:0.01:0.005.

[0209] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 2 below.

[0210] Example 5

[0211] The cathode active material was prepared in the same manner as in Example 1, except that:

[0212] In the sintering process of step (5), Al2O3 and Y2O3 were not added.

[0213] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 2 below.

[0214] Example 6

[0215] The cathode active material was prepared in the same manner as in Example 1, except that:

[0216] In step (1), nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of Ni:Co:Mn = 90:5:5 to obtain a mixed solution.

[0217] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 2 below.

[0218] Example 7

[0219] The cathode active material was prepared in the same manner as in Example 1, except that:

[0220] In step (1), nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of Ni:Co:Al = 90:5:5 to obtain a mixed solution.

[0221] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 2 below.

[0222] Comparative Example 1

[0223] The cathode active material was prepared in the same manner as in Example 1, except that:

[0224] In step (3), lithium aluminum titanium phosphate (LiAl 0.5 Ti 1.5 (P04)3) was not added.

[0225] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0226] Table 1

[0227] Table 2

[0228] As can be seen from the data in Tables 1 and 2 above, the absolute value of the peak value of the thermal weight loss rate of the positive electrode active material in Examples 1-7 is less than 7% / min, the positive electrode active material has improved thermal stability and low gas production, and the batteries in Examples 1-7 have improved storage performance and cycle performance.

[0229] Example 8

[0230] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0231] In step (2), WO3, ZrO2 and Ta2O5 are added, and the molar ratio of Li, W, Ta and Zr is 1:0.004:0.005:0.002.

[0232] In step (3), the lithium transition metal oxide obtained in step (2) is crushed and then reacted with lithium aluminum phosphate (LiAl). 0.5 Ti 1.5 (PO4)3), so that the molar ratio of Li to P is 1:0.004.

[0233] In step (5), Al2O3 and Y2O3 are added during the sintering process to make the molar ratio of Li, Al and Y 1:0.01:0.01.

[0234] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 4 below.

[0235] Example 9

[0236] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0237] In step (2), WO3 is replaced with Ta2O5 and ZrO2 is replaced with Sb2O3. After adding ZrO2 and Ta2O5, the molar ratio of Li, Ta and Zr is 1:0.008:0.006.

[0238] In step (3), the lithium transition metal oxide obtained in step (2) is crushed and then reacted with lithium aluminum phosphate (LiAl). 0.5 Ti 1.5 (PO4)3), so that the molar ratio of Li to P is 1:0.003.

[0239] The sintering process of step (5) adds Al2O3 and Y2O3, so that the molar ratio of Li, Al, and Y is 1:0.01:0.008.

[0240] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 4 below.

[0241] Example 10

[0242] The positive electrode active material was prepared in a similar manner to Example 1, except that:

[0243] In step (2), WO3 and ZrO2 were added, so that the molar ratio of Li, W, and Zr was 1:0.001:0.001.

[0244] The sintering process of step (5) adds Al2O3 and Y2O3, so that the molar ratio of Li, Al, and Y is 1:0.005:0.005.

[0245] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 4 below.

[0246] Example 11

[0247] The positive electrode active material was prepared in a similar manner to Example 1, except that:

[0248] In step (2), WO3 and ZrO2 were added, so that the molar ratio of Li, W, and Zr was 1:0.001:0.001.

[0249] The sintering process of step (5) adds Al2O3 and Y2O3, so that the molar ratio of Li, Al, and Y is 1:0.005:0.005.

[0250] In addition, pouch batteries were prepared and tested in the same manner as in Example 1. The results are shown in Table 4 below.

[0251] Table 3

[0252] Table 4

[0253] From the data in Tables 1 and 4 above, it can be seen that, compared to Example 5, the m2 / m1 of the positive electrode active material in Examples 8-11 is in the range of 40%-75%, the thermal stability of the positive electrode active material is further improved, the gas production is further reduced, and the batteries of Examples 8-11 have further improved storage performance and cycle performance.

[0254] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having a constitution substantially the same as the technical idea, which achieves the same effects, within the scope of the technical solution of the present disclosure are included in the technical scope of the present disclosure.

Claims

1. A secondary battery comprising: a positive electrode tab, a negative electrode tab, a separator disposed between the positive electrode tab and the negative electrode tab, and an electrolyte including an organic solvent and a lithium salt, the positive electrode tab including a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a lithium transition metal oxide including a nickel element and a cobalt element, and including at least one of a manganese element and an aluminum element, a molar content of the nickel element with respect to all metal elements excluding lithium being 85 mol% or more in the lithium transition metal oxide, an absolute value of a peak of a rate of change of thermal weight in a differential thermogravimetric curve obtained by temperature increasing the positive electrode active material at a temperature increasing rate of 10°C / min being less than 7% / min. A molar content of the nickel element with respect to all metal elements excluding lithium is 90 mol% or more. An absolute value of the peak of the rate of change of thermal weight is less than or equal to 6.1% / min. An absolute value of the peak of the rate of change of thermal weight is less than or equal to 5.6% / min. In a thermogravimetric analysis, a total weight loss of the positive electrode active material in a process of temperature increasing from 0°C to 600°C is set as m1, and a weight loss in a process of temperature increasing from 220°C to 360°C is set as m2, the m1 and the m2 satisfy the following relationship: 40%≤m2 / m1≤75%.

2. The secondary battery according to claim 1, wherein The m2 is 0.5% to 12%.

3. The secondary battery according to claim 1 or 2, wherein The m1 is 1% to 18%.

4. The secondary battery according to any one of claims 1 to 3, wherein In a thermogravimetric analysis, a weight loss rate of the positive electrode active material at 600°C is greater than 1% and is 18% or less.

5. The secondary battery according to any one of claims 1 to 4, wherein In a thermogravimetric analysis, a weight loss rate of the positive electrode active material at 600°C is 10% to 18%.

6. The secondary battery according to claim 5, wherein In a thermogravimetric analysis, a weight loss rate of the positive electrode active material at 300°C is 10% to 12%.

7. The secondary battery according to claim 5 or 6, wherein In a thermogravimetric analysis, a weight loss rate of the positive electrode active material at 200°C is 0.01% to 0.5%.

8. The secondary battery according to any one of claims 1 to 7, wherein The differential thermogravimetric curve is obtained by testing temperature increasing from 0°C to 600°C under a nitrogen atmosphere.

9. The secondary battery according to any one of claims 1 to 8, wherein In the differential thermogravimetric curve, a peak of the rate of change of thermal weight occurs in a range of 200°C to 280°C.

10. The secondary battery according to any one of claims 1 to 9, wherein In the differential thermogravimetric curve, a peak of the rate of change of thermal weight occurs in a range of 220°C to 240°C.

11. The secondary battery according to any one of claims 1 to 10, wherein In the differential thermogravimetric curve, a peak area of a peak of the rate of change of thermal weight is 12.0% to 17.0%.

12. The secondary battery according to any one of claims 1 to 11, wherein In the differential thermogravimetric curve, a half-peak width of the peak of the rate of change of thermal weight is 5°C to 25°C.

13. The secondary battery according to any one of claims 1 to 12, wherein In the mass spectrum curve, a peak of the mass spectrum peak occurs in a range of 200°C to 280°C.

14. The secondary battery according to any one of claims 1 to 13, wherein In the mass spectrum curve, a peak of the mass spectrum peak occurs in a range of 220°C to 240°C.

15. The secondary battery according to any one of claims 1 to 14, wherein A half-peak width of the mass spectrum peak is 10°C to 20°C.

16. The secondary battery according to any one of claims 1 to 15, wherein In an X-ray diffraction spectrum of the positive electrode active material, a ratio of a peak intensity of a 003 plane to a peak intensity of a 104 plane is 1.2-1.

7.

17. The secondary battery according to any one of claims 1 to 16, wherein In the mass spectrum curve obtained by performing mass spectrometry on the oxygen released in the thermogravimetric analysis of the positive electrode active material, the peak value of the mass spectrum peak is less than or equal to 5 x 10 -10 A.

18. The secondary battery according to claim 17, wherein ​ 19. The secondary battery according to claim 17 or 18, wherein ​ 20. The secondary battery according to any one of claims 17 to 19, wherein The area of the mass spectrum peak is 1.2 x 10 -9 A·℃ to 50 x 10 -9 A·℃.

21. The secondary battery according to any one of claims 17 to 20, wherein ​ 22. The secondary battery according to any one of claims 1 to 21, wherein ​ 23. The secondary battery according to any one of claims 1 to 22, wherein The lithium transition metal oxide further includes a doping element including at least one of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, Ti.

24. The secondary battery according to claim 23, wherein The content of the doping element is 3000 ppm or less relative to the lithium transition metal oxide.

25. The secondary battery according to any one of claims 1 to 24, wherein The lithium transition metal oxide comprises Li a Ni b Co c Mn d M 1 (1-b-c-d) O n and / or Li e Ni f Co g Al h M 2 (1-f-g-h) O n , Li a Ni b Co c Mn d M 1 (1-b-c-d) O n wherein 0.5≤a≤1.2, 0.85≤b≤0.99, 0≤c≤0.1, 0≤d≤0.05, 1.9≤n≤2.2, M 1 including a combination of one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, Li e Ni f Co g Al h M 2 (1-f-g-h) O n wherein 0.5 < e < 1.2, 0.85 < f < 0.99, 0 < g < 0.1, 0 < h < 0.05, 1.9 < n < 2.2, M 2 comprises a combination of one or more of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, Ti.

26. The secondary battery according to any one of claims 1 to 25, wherein The positive electrode active material satisfies at least one of the following conditions: (1) the volume average particle diameter Dv50 of the positive electrode active material is 8.5 μm to 12 μm, (2) the specific surface area BET of the positive electrode active material is 0.35 m 2 / g to 0.65 m 2 / g, (3) the powder compaction density of the positive electrode active material under a pressure of 3000 N is 3.0 g / cm3or more 3 to 3.5 g / cm3 3 , (4) the tap density of the positive electrode active material is 2.9 g / cm 3 to 3.5 g / cm 3 , (5) the delithiation capacity of the positive electrode active material is 210 mAh / g to 225 mAh / g.

27. The secondary battery according to any one of claims 1 to 26, wherein The positive electrode active material includes a base including the lithium transition metal oxide and a coating layer provided on at least part of the surface of the base.

28. The secondary battery of claim 27, wherein, The coating layer includes an outer layer and an inner layer provided between the outer layer and the base, The inner layer includes at least one of P, Al, Ca, Ti elements, The outer layer includes at least one of Y element, Al element.

29. The secondary battery of claim 28, wherein, The inner layer includes P element, and the outer layer includes Y element and Al element.

30. The secondary battery according to claim 28 or 29, wherein In the positive electrode active material, the molar ratio of lithium element to phosphorus element is 1:0.001-0.

004.

31. An electric device including the secondary battery according to any one of claims 1 to 30.

32. A positive electrode active material including a lithium transition metal oxide including a nickel element and a cobalt element, and including at least one of a manganese element and an aluminum element, In the lithium transition metal oxide, the molar content of the nickel element is 85 mol% or more relative to all metal elements other than lithium, In a differential thermogravimetric curve obtained by temperature increasing of the positive electrode active material at a temperature increasing rate of 10°C / min, the absolute value of the peak of the rate of change of the thermal weight loss is less than 7% / min. The molar content of the nickel element is 90 mol% or more relative to all metal elements other than lithium.

33. The positive electrode active material according to claim 32, wherein The absolute value of the peak of the rate of change of the thermal weight loss is less than or equal to 6.1% / min.

34. The positive electrode active material according to claim 32 or 33, wherein The absolute value of the peak of the rate of change of the thermal weight loss is less than or equal to 5.6% / min.

35. The positive electrode active material according to any one of claims 32 to 34, wherein In a thermogravimetric analysis, the total weight loss of the positive electrode active material during temperature increasing from 0°C to 600°C is set as m1, and the weight loss during temperature increasing from 220°C to 360°C is set as m2, and the m1 and the m2 satisfy the following relationship: 40%≤m2 / m1≤75%.

36. The positive electrode active material according to any one of claims 32 to 35, wherein The m2 is 0.5% to 12%.

37. The positive electrode active material according to claim 36, wherein The m1 is 1% to 18%.

38. The positive electrode active material according to claim 36 or 37, wherein In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and is 18% or less.

39. The positive electrode active material according to any one of claims 32 to 38, wherein, In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 300°C is 10% to 12%.

40. The positive electrode active material according to any one of claims 32 to 39, wherein, In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 200°C is 0.01% to 0.5%.

41. The positive electrode active material according to any one of claims 32 to 40, wherein ​

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