Secondary battery, electric device, and positive electrode active material

Abstract

The application provides a secondary battery, a power consumption 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 comprising an organic solvent and a lithium salt. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material. The positive electrode active material comprises a lithium transition metal oxide. The lithium transition metal oxide comprises a nickel element and a cobalt element, and comprises 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 except lithium. In a DTG curve obtained by warming the positive electrode active material at a warming rate of 10 DEG C / 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. The secondary battery has improved storage performance and cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, an electrical device, and a positive electrode active material. Background Technology

[0002] In recent years, with the increasingly wide range of applications, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their energy density, cycle performance, and storage performance.

[0003] The performance of secondary batteries is closely related to the cathode active material. Among them, high-nickel cathode active materials are considered the best choice to meet the requirements of high energy density. However, as the nickel content in the cathode active material increases, its thermal stability deteriorates. Therefore, how to improve the thermal stability of high-nickel cathode active materials, and thus improve the performance of secondary batteries, is an urgent technical problem to be solved. Summary of the Invention

[0004] To achieve the above objectives, this application provides a secondary battery, an electrical device, and a positive electrode active material. The secondary battery employs a positive electrode active material with high thermal stability, and thus exhibits improved storage and cycle performance.

[0005] The first aspect of this application provides a secondary battery, comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte comprising an organic solvent and a lithium salt. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium transition metal oxide. The lithium transition metal oxide includes nickel and cobalt, and includes at least one of manganese and aluminum. In the lithium transition metal oxide, the molar content of nickel is 85 mol% or more relative to all metal elements other than lithium. In the differential thermogravimetric curve obtained by heating the positive electrode active material at a heating rate of 10 °C / min, the absolute value of the peak value of the rate of change of thermal weight loss is less than 7% / min. This application achieves this by ensuring that the absolute value of the peak value of the rate of thermal weight loss is less than 7% / min, thereby suppressing sudden drops in the rate of thermal weight loss, improving the thermal stability of ultra-high nickel (Ni content ≥ 85 mol%) cathode active materials, reducing gas generation, and ultimately improving the battery's storage and cycle performance. In some embodiments, the molar content of nickel relative to all metal elements except lithium is ≥ 90 mol%. The molar percentage of nickel within the aforementioned range results in a high energy density for the cathode active material.

[0006] In some embodiments, the absolute value of the peak value of the thermogravimetric change rate is less than or equal to 6.1% / min. By keeping the peak value of the thermogravimetric change rate of the positive electrode active material within the above range, the thermal stability of the positive electrode active material is further improved.

[0007] In some embodiments, the absolute value of the peak value of the thermogravimetric change rate is less than or equal to 5.6% / min. By keeping the peak value of the thermogravimetric change rate of the positive electrode active material within the above range, the thermal stability of the positive electrode active material is further improved.

[0008] In some embodiments, during thermogravimetric analysis, the percentage of total weight loss of the positive electrode active material during the process of heating from 0°C to 600°C is defined as m1, and the percentage of weight loss during the process of heating from 220°C to 360°C is defined as m2. The relationship between m1 and m2 is: 40% ≤ m2 / m1 ≤ 75%. Ensuring that the percentage of weight loss during the heating from 220°C to 360°C (m2 / m1) is within the above range results in less thermal weight loss of the positive electrode active material in the temperature range of 220°C to 360°C, which helps to reduce the accumulated heat in this temperature range and improve the thermal stability of the positive electrode active material.

[0009] In some embodiments, m2 is 0.5%-12%. Keeping m2 within this range results in less thermal weight loss of the positive electrode active material in the temperature range of 220°C to 360°C, which helps reduce the accumulated heat in this temperature range and improves the thermal stability of the positive electrode active material.

[0010] In some embodiments, m1 is 1%-18%. Keeping m1 within this range results in less thermal weight loss of the positive electrode active material in the temperature range of 0°C to 600°C, which is beneficial for improving the thermal stability of the positive electrode active material.

[0011] In some embodiments, during thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and less than 18%. In some embodiments, during thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is 10% to 18%. This further improves the thermal stability of the positive electrode active material.

[0012] In some embodiments, the weight loss rate of the positive electrode active material at 300°C is 10% to 12% in thermogravimetric analysis. This further improves the thermal stability of the positive electrode active material.

[0013] In some embodiments, the weight loss rate of the positive electrode active material at 200°C is 0.01% to 0.5% in thermogravimetric analysis. This further improves the thermal stability of the positive electrode active material.

[0014] In some embodiments, the differential thermogravimetric curve is obtained by heating from 0°C to 600°C under a nitrogen atmosphere.

[0015] In some embodiments, the peak value of the rate of thermal weight loss appears in the differential thermogravimetric curve in the range of 200°C to 280°C.

[0016] In some embodiments, the differential thermogravimetric curve shows a peak value for the rate of thermal weight loss in the range of 220°C to 240°C.

[0017] In some embodiments, the peak area of ​​the peak of the rate of change of thermal weight loss in the differential thermogravimetric curve is 12.0% to 17.0%.

[0018] In some embodiments, the half-width of the peak of the rate of thermal weight loss in the differential thermogravimetric curve is between 5°C and 25°C.

[0019] In some embodiments, the peak value of the mass spectrometry curve obtained by mass spectrometry analysis of the oxygen released during thermogravimetric analysis of the positive electrode active material is less than or equal to 5 × 10⁻⁶. -10 A. The peak values ​​of the mass spectrometry are within the above range, indicating 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.

[0020] In some embodiments, the peak value of the mass spectrometry peak appears in the range of 200°C to 280°C in the mass spectrometry curve. By making the peak value of the mass spectrometry peak meet the above conditions, the amount of oxygen generated by the positive electrode active material is small under high temperature conditions (e.g., 200°C-300°C), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0021] In some embodiments, the peak values ​​of the mass spectrometry peaks are located in the range of 220°C to 240°C in the mass spectrometry curve. By ensuring that the peak values ​​of the mass spectrometry peaks meet the above conditions, it is beneficial to further improve the thermal stability of the positive electrode active material.

[0022] In some embodiments, the area of ​​the mass spectrometry peak is 1.2 × 10⁻⁶. -9 A·℃ to 50×10 -9 A·℃. By ensuring that the peak area of ​​the mass spectrometry peak meets the above conditions, the amount of oxygen generated by the positive electrode active material is reduced under high temperature conditions (e.g., 200℃-300℃), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0023] In some embodiments, the half-width at half-maximum (WHM) of the mass spectrometer peak is 10°C to 20°C. By ensuring that the WHM of the mass spectrometer peak meets the above condition, the amount of oxygen generated by the positive electrode active material is reduced under high-temperature conditions (e.g., 200°C-300°C), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0024] In some embodiments, the ratio of the peak intensity I(003) on the 003 plane to the peak intensity I(104) on the 104 plane in the X-ray diffraction pattern of the positive electrode active material is 1.2-1.7. By keeping I(003) / I(104) within the above range, the lithium transition metal oxide in the positive electrode active material has a better layered structure, which is beneficial to improving the thermal stability of the positive electrode active material.

[0025] In some embodiments, the lithium transition metal oxide further includes a dopant element, which includes at least one selected from Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti. Introducing these dopant elements helps to further improve the thermal stability of the cathode active material.

[0026] In some embodiments, the content of the dopant element relative to the lithium transition metal oxide is 3000 ppm or less. Controlling the content of the dopant element within this range is beneficial for improving the specific capacity and cycle performance of the battery.

[0027] In some embodiments, the lithium transition metal oxide includes 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 In the given condition, 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 one or more combinations of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, and Li e Ni f Co g Alh M 2 (1-f-g-h) O n In the given condition, 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 It includes one or more combinations of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, and Ti.

[0028] 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 m². 2 / g to 0.65m 2 / g; (3) The compacted density of the positive electrode active material under a pressure of 3000N is 3.0g / cm³. 3 Up to 3.5g / cm 3 (4) The tap density of the positive electrode active material is 2.9 g / cm³. 3 Up to 3.5g / cm 3 (5) The lithium removal capacity of the positive electrode active material is 210 mAh / g to 225 mAh / g.

[0029] In some embodiments, the positive electrode active material includes a substrate and a coating layer disposed on at least a portion of the surface of the substrate; the substrate includes the lithium transition metal oxide. The coating layer coats the surface of the lithium transition metal oxide, which can reduce side reactions between the lithium transition metal oxide and the electrolyte, thereby improving the thermal stability of the positive electrode active material.

[0030] In some embodiments, the coating layer includes an outer layer and an inner layer disposed between the outer layer and the substrate; the inner layer includes at least one element selected from P, Al, Ca, and Ti; and the outer layer includes at least one element selected from Y and Al. By providing two coating layers, the structural stability of the coating layer can be improved, and the probability of side reactions between the electrolyte and lithium transition metal oxides can be reduced, thereby further improving the thermal stability of the positive electrode active material.

[0031] In some embodiments, the inner layer includes phosphorus (P), and the outer layer includes phosphorus (Y) and aluminum (Al). Coating with phosphorus (phosphate) can improve the ion-conducting ability of the positive electrode active material surface while reducing contact with the electrolyte, which is beneficial for further improving the thermal stability of the positive electrode active material.

[0032] In some embodiments, the molar ratio of lithium to phosphorus in the positive electrode active material is between 1:0.001 and 0.004. By controlling the molar ratio of lithium to phosphorus within this range, it is beneficial for phosphate to form a coating layer of suitable thickness on the substrate surface. This effectively protects the surface and interfacial stability of the positive electrode active material, improves its stability, and minimizes the impact of the coating on ion transport.

[0033] A second aspect of this application provides an electrical device, including the secondary battery of the first aspect.

[0034] A third aspect of this application provides a positive electrode active material comprising a lithium transition metal oxide, wherein the lithium transition metal oxide comprises nickel and cobalt, and includes at least one of manganese and aluminum. In the lithium transition metal oxide, the molar content of nickel is 85 mol% or more relative to all metal elements except lithium. In the differential thermogravimetric curve obtained by heating the positive electrode active material at a heating rate of 10 °C / min, the absolute value of the peak value of the rate of change of thermal weight loss is less than 7% / min. The positive electrode active material of this application can suppress sudden drops in thermal weight loss rate, exhibits excellent thermal stability, reduces gas generation, and improves the storage performance and cycle performance of the battery.

[0035] In some embodiments, the molar percentage of nickel is 90 mol% or more relative to all metal elements except lithium. By keeping the molar percentage of nickel within the above range, the positive electrode active material exhibits a high energy density.

[0036] In some embodiments, the absolute value of the peak value of the thermogravimetric change rate is less than or equal to 6.1% / min. By keeping the peak value of the thermogravimetric change rate of the positive electrode active material within the above range, the thermal stability of the positive electrode active material is further improved.

[0037] In some embodiments, the absolute value of the peak value of the thermogravimetric change rate is less than or equal to 5.6% / min. By keeping the peak value of the thermogravimetric change rate of the positive electrode active material within the above range, the thermal stability of the positive electrode active material is further improved.

[0038] In some embodiments, during thermogravimetric analysis, the percentage of total weight loss of the positive electrode active material during the process of heating from 0°C to 600°C is defined as m1, and the percentage of weight loss during the process of heating from 220°C to 360°C is defined as m2. The relationship between m1 and m2 is as follows: 40% ≤ m2 / m1 ≤ 75%.

[0039] In some embodiments, m2 is 0.5%-12%. Therefore, the positive electrode active material experiences less thermal weight loss in the temperature range of 220°C to 360°C, which helps reduce the accumulated heat in this temperature range and improves the thermal stability of the positive electrode active material. In some embodiments, m1 is 1% to 18%. Therefore, the positive electrode active material experiences less thermal weight loss in the temperature range of 0°C to 600°C, which helps improve the thermal stability of the positive electrode active material.

[0040] In some embodiments, during thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and less than 18%. This further improves the thermal stability of the positive electrode active material.

[0041] In some embodiments, the weight loss rate of the positive electrode active material at 300°C is 10%-12% in thermogravimetric analysis. This further improves the thermal stability of the positive electrode active material.

[0042] In some embodiments, the weight loss rate of the positive electrode active material at 200°C is 0.01%-0.5% in thermogravimetric analysis. This further improves the thermal stability of the positive electrode active material. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0044] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0045] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0048] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0049] Figure 7 Thermogravimetric-temperature curve of the positive electrode active material prepared in Example 1 of this application.

[0050] Figure 8 The thermogravimetric change rate-temperature curve of the positive electrode active material prepared in Example 1 of this application.

[0051] Figure 9 This is a mass spectrum of the positive electrode active material prepared in Example 1 of this application.

[0052] Explanation of reference numerals in the attached figures

[0053] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, power-consuming device, and positive electrode active material of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in this application.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0059] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0060] The performance of a secondary battery is closely related to the thermal stability of the positive electrode active material. In current positive electrode active material designs, high-nickel positive electrode active materials are typically used to achieve higher energy density. However, the high internal temperatures during battery operation cause these materials to undergo phase transitions, leading to the introduction of transition metal ions (e.g., Ni). 4+ Ni 3+ Co 4+ Co 3+ The nickel content is reduced, producing gas (e.g., oxygen). Higher nickel content accelerates this phase transition. In particular, ultra-high nickel cathode active materials (especially those with a Ni content of 85 mol% or higher) have poorer thermal stability compared to low-nickel materials, are more prone to decomposition at high temperatures, and exhibit severe gas production problems, affecting the battery's cycle performance and storage performance.

[0061] Based on this, this application proposes a secondary battery and an electrical device. The invention and its optional embodiments will be described in more detail below.

[0062] The first aspect of this application provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrode, and an electrolyte comprising an organic solvent and a lithium salt. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a lithium transition metal oxide, which includes nickel and 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 relative to all metal elements except lithium. Furthermore, in the differential thermogravimetric curve obtained by heating the positive electrode active material at a heating rate of 10 °C / min, the absolute value of the peak value of the rate of change of thermal weight loss of the positive electrode active material is less than 7% / min.

[0063] In this application, by making the absolute value of the peak value of the thermal weight loss rate less than 7% / min, it is possible to suppress the sudden drop in thermal weight loss rate, improve the thermal stability of ultra-high nickel (Ni content above 85mol%) cathode active material, reduce gas generation, and thus improve the storage performance and cycle performance of the battery.

[0064] In this application, the molar percentage of nickel in the lithium transition metal oxide is 85 mol% or more relative to all metal elements except lithium. For example, the molar percentage of nickel is 85 mol%, 86 mol%, 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, or any range of two such values, but is not limited thereto. Preferably, the molar percentage of nickel is 90 mol% or more. A molar percentage of nickel within the above range results in a high energy density in the positive electrode active material.

[0065] In this application, thermogravimetric analysis (TGA) is performed on the positive electrode active material, for example, as follows: 10 mg to 20 mg of positive electrode active material sample powder is taken, dried to remove moisture, and placed in a thermogravimetric analysis crucible. The test temperature range is set to 0℃-600℃, and the heating rate is set to 10℃ / min. The sample is then 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 axis is taken to obtain the differential thermogravimetric curve (DTG curve). The DTG curve shows the change in the rate of thermal weight loss over time; a lower rate of thermal weight loss indicates better thermal stability of the positive electrode active material.

[0066] In this application, the thermogravimetric change rate of the positive electrode active material in the DTG curve exhibits an inverted peak, with the absolute value of the peak value being less than 7% / min. For example, the peak value of the thermogravimetric change rate of the positive electrode active material is a value within the range of -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 any two of these values. Preferably, the absolute value of the peak value of the thermogravimetric change rate is less than 6.1% / min, and more preferably, the absolute value of the peak value is less than 5.6% / min. By ensuring that the peak value of the thermogravimetric change rate of the positive electrode active material is within the above range, the thermal stability of the positive electrode active material is further improved.

[0067] In some embodiments, the DTG curve is obtained by heating from 0°C to 600°C under a nitrogen atmosphere. In some embodiments, the DTG curve shows a peak in the rate of thermogravimetric change in the range of 200°C to 280°C, for example, the peak occurs between 200°C, 210°C, 220°C, 230°C, 240°C, or any two of these values. Preferably, the peak occurs in the range of 220°C to 240°C.

[0068] In some embodiments, the peak area of ​​the rate of thermal weight loss is between 12.0% and 17.0%. For example, the peak area of ​​the rate of thermal weight loss is a value between 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, or any two of these values.

[0069] In some embodiments, the half-width at half-maximum (WHM) of the peak of the rate of thermal weight loss is between 5°C and 25°C. For example, the WHM of the peak of the rate of thermal weight loss is a value between 5°C, 10°C, 15°C, 20°C, 25°C, or any two of these values.

[0070] In some embodiments, the percentage of total weight loss of the positive electrode active material during the process of heating from 0°C to 600°C is defined as m1, and the percentage of weight loss during the process of heating from 220°C to 360°C is defined as m2. The relationship between m1 and m2 is: 40% ≤ m2 / m1 ≤ 75%. For example, m2 / m1 can be a value between 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or any two of these values.

[0071] Studies have found that side reactions in positive electrode active materials mainly occur within the temperature range of 220℃ to 360℃, and most of the thermal weight loss occurs within this temperature range, resulting in a significant decrease in weight and increased weight loss. In this application, by ensuring that the weight loss from heating from 220℃ to 360℃ accounts for 40% to 75% of the total weight loss (m2 / m1), the thermal weight loss of the positive electrode active material within the 220℃ to 360℃ temperature range is reduced, which helps to decrease the accumulated heat in this temperature range and improve the thermal stability of the positive electrode active material. In some embodiments, preferably, m1 and m2 satisfy the following relationship: 40% ≤ m2 / m1 ≤ 55%, which further helps to improve the thermal stability of the positive electrode active material.

[0072] In some embodiments, m1 is greater than 1% and less than 18%, for example, m1 is a value between 3%, 6%, 9%, 12%, 15%, 16.87%, 18%, or any two of these values. Keeping m1 within the above range results in less thermal weight loss of the positive electrode active material in the temperature range of 0°C to 600°C, which is beneficial for improving the thermal stability of the positive electrode active material.

[0073] In some embodiments, m2 is 0.5% to 12%, for example, m2 is a value between 0.5%, 1%, 3%, 6%, 9%, 10.95%, 12%, or any two of these values. Keeping m2 within the above range results in less thermal weight loss of the positive electrode active material in the temperature range of 220°C to 360°C, which helps to reduce the accumulated heat in this temperature range and improve the thermal stability of the positive electrode active material.

[0074] In some embodiments, during thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is greater than 1% and less than 18%. For example, the weight loss rate of the positive electrode active material at 600°C is a value between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or any two of these values. Preferably, the weight loss rate of the positive electrode active material at 600°C is between 10% and 18%.

[0075] In some embodiments, the weight loss rate of the positive electrode active material at 300°C in thermogravimetric analysis 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 ranges.

[0076] In some embodiments, the weight loss rate of the positive electrode active material at 200°C in thermogravimetric analysis 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 within a range of any two values.

[0077] In some embodiments, the peak value (maximum ion current intensity) of the mass spectrometry curve obtained by mass spectrometry analysis of the oxygen released during thermogravimetric analysis of the positive electrode active material is less than or equal to 5 × 10⁻⁶. -10 A (Ampere), where the mass spectrum curve represents the intensity of the ion current (lon). Current The mapping relationship between temperature and ion current, where the ion current is the ion current generated by oxygen released from the positive electrode active material during mass spectrometry analysis. Peak value (lon) Current The smaller the value of ), the less oxygen is released by the positive electrode active material at the current temperature, and the better the thermal stability of the positive electrode active material. If the peak value of the mass spectrometry peak is within the above range, it indicates that the positive electrode active material releases less oxygen, further improving its thermal stability.

[0078] In some embodiments, the peak value of the mass spectrometry curve appears in the range of 200°C to 280°C. In some embodiments, the peak value appears in the range of 220°C to 240°C. For example, the peak value appears in the range of 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or any two of these values. By ensuring that the peak value of the mass spectrometry curve meets the above conditions, the amount of oxygen generated by the positive electrode active material is reduced under high temperature conditions (e.g., 200°C-300°C), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0079] In some embodiments, the area of ​​the mass spectrometry peak is 1.2 × 10⁻⁶. -9 A·℃ to 50×10 -9 A·℃. For example, the area of ​​the mass spectrometry peak is 1.2 × 10⁻⁶. -9 A·℃, 10×10 -9 A·℃, 20×10 -9 A·℃, 30×10 -9 A·℃, 40×10 -9 A·℃, 50×10 -9 A·℃ or any value within a range of two values. By ensuring that the peak area of ​​the mass spectrometry peak meets the above conditions, the amount of oxygen produced by the positive electrode active material is reduced under high temperature conditions (e.g., 200℃-300℃), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0080] In some embodiments, the half-width at half-maximum (WHM) of the mass spectrometer peak is 10°C-20°C. For example, the WHM of the mass spectrometer peak is a value between 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, or any two of these values. By ensuring that the WHM of the mass spectrometer peak meets the above conditions, the amount of oxygen generated by the positive electrode active material is reduced under high-temperature conditions (e.g., 200°C-300°C), which is beneficial to further improving the thermal stability of the positive electrode active material.

[0081] 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 a value between 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or any two of these values. By keeping I(003) / I(104) within the above range, the lithium transition metal oxide in the positive electrode active material has a better layered structure, which is beneficial to improving the thermal stability of the positive electrode active material.

[0082] In some embodiments, the lithium transition metal oxide further includes a dopant element, wherein the dopant element includes at least one selected from Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti. Introducing the above-mentioned dopant elements is beneficial for further improving the thermal stability of the cathode active material.

[0083] In some embodiments, the content of the dopant element relative to the lithium transition metal oxide is less than or equal to 3000 ppm. For example, the content of the dopant element can be 3000 ppm, 2000 ppm, 1000 ppm, 500 ppm, 200 ppm, 100 ppm, 0 ppm, or any value within a range of two such values, but is not limited thereto. By controlling the content of the dopant element within the above range, it is beneficial to improve the specific capacity and cycle performance of the battery.

[0084] In this application, "lithium transition metal oxide" refers to an oxide composed of metallic lithium and transition metal elements. The lithium transition metal oxides mentioned in this application include, but are not limited to, lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA).

[0085] 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 It includes one or more combinations of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti.

[0086] 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 It includes one or more combinations of Mg, Na, Zr, Y, Ca, W, Nb, Ta, Sr, and Ti.

[0087] For example, lithium transition metal oxides include 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.

[0088] 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 m². 2 / g to 0.65m 2 / g. (3) The compacted density of the positive electrode active material under a pressure of 3000N is 3.0 g / cm³. 3 Up to 3.5g / cm 3 (4) The tap density of the positive electrode active material is 2.9 g / cm³. 3 Up to 3.5g / cm 3 (5) The delithiation capacity of the positive electrode active material is 210 mAh / g to 225 mAh / g.

[0089] In this application, the volumetric particle size distribution (Dv50) of the material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0090] In this application, the specific surface area of ​​the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0091] In this application, the powder compaction density of the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined by referring to GB / T 24533-2009 using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine). An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2In the mold, pressure is applied to 3000N, held for 30s, then depressurized and held for 10s. The compaction density of the powder under 3000N pressure is then recorded and calculated.

[0092] In this application, the tap density of the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a measuring cylinder of 25mL.

[0093] In this application, the lithium delithiation capacity of the material has a meaning known in the art and can be tested using methods known in the art.

[0094] In some embodiments, the positive electrode active material includes a substrate and a coating layer disposed on at least a portion of the surface of the substrate, wherein the substrate includes a lithium transition metal oxide. In this embodiment, the coating layer coats the surface of the lithium transition metal oxide, which can reduce side reactions between the lithium transition metal oxide and the electrolyte, thereby improving the thermal stability of the positive electrode active material.

[0095] In some embodiments, the coating layer includes an outer layer and an inner layer disposed between the outer layer and the substrate; the inner layer includes at least one element selected from phosphorus, aluminum, calcium, and titanium; and the outer layer includes at least one element selected from Y and Al. By providing two coating layers, the structural stability of the coating layer can be improved, and the probability of side reactions between the electrolyte and lithium transition metal oxides can be reduced, thereby further improving the thermal stability of the positive electrode active material.

[0096] In some embodiments, the inner layer includes phosphorus (P) and the outer layer includes phosphorus (Y) and aluminum (Al). Coating with phosphorus (phosphate) can improve the ion-conducting ability of the positive electrode active material surface while reducing contact with the electrolyte, which is beneficial for further improving the thermal stability of the positive electrode active material.

[0097] In some embodiments, the molar ratio of lithium to phosphorus in the positive electrode active material is 1:0.001-0.004. For example, the molar ratio of lithium to phosphorus can be 1:0.001, 1:0.002, 1:0.003, 1:0.004, or any value within a range of two such values, but is not limited thereto. By controlling the molar ratio of lithium to phosphorus within the above range, it is beneficial for phosphate to form a coating layer of suitable thickness on the substrate surface, which can effectively protect the surface and interface stability of the positive electrode active material, improve the stability of the positive electrode active material, and minimize the impact of coating on ion transport.

[0098] In addition, the preparation method of the positive electrode active material of this application can be, for example, the following method, which includes the following steps.

[0099] Step (1): Prepare a mixed solution containing Ni, Co, and Mn elements by mixing them in a molar ratio of x:y:(1-xy), where x ≥ 0.85. Add the mixed solution, sodium carbonate, and ammonia to the reactor at a certain pump speed, controlling the pH in the reactor between 11 and 14 and the temperature between 50℃ and 70℃ to carry out a co-precipitation reaction, allowing the precursor particles to grow to the target Dv50 = 8.5 μm-12 μm. After the reaction is complete, wash and dry to obtain the ultra-high nickel ternary material precursor.

[0100] In this application, the substances that can provide Ni may include, but are not limited to, nickel carbonate, nickel hydroxide, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate, and nickel oxalate.

[0101] In this application, substances capable of providing Co may include, but are not limited to, cobalt carbonate, cobalt hydroxide, cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt oxalate.

[0102] In this application, the substances that can provide Mn may include, but are not limited to, manganese dioxide, electrolytic manganese dioxide, and manganese tetroxide.

[0103] In the above coprecipitation reaction, the reaction temperature can be between 50℃ and 70℃. For example, the reaction temperature can be 50℃, 55℃, 60℃, 65℃, 70℃, or any value within a range of two such values. The reaction time is 24h-48h. For example, the reaction time can be 24h, 28h, 32h, 36h, 40h, 44h, 48h, or any value within a range of two such values.

[0104] The coprecipitation 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 any range between two of these values, but is not limited thereto.

[0105] Step (2): The ultra-high nickel ternary material precursor, lithium source and doping element M source obtained in step (1) are mixed to obtain a mixture, and sintered at high temperature to obtain lithium transition metal oxide.

[0106] In some embodiments, the lithium source is a substance capable of providing lithium, such as lithium hydroxide (LiOH·H2O), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium oxalate (LiC2O4), and lithium acetate (CH3COOLi), but not limited thereto. The metal molar ratio Li / Me of the lithium source and the ternary material precursor is 1.0-1.2:1, where Me is the total molar amount of Ni, Co, and Mn elements.

[0107] In some embodiments, the dopant element M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti. In some embodiments, the source of the dopant element M is any substance capable of providing the aforementioned dopant element M, and there is no particular limitation. 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.

[0108] In some embodiments, the sintering temperature and sintering time are not particularly limited. For example, the sintering temperature can be 500℃-800℃. Specifically, it can be 500℃, 550℃, 600℃, 650℃, 700℃, 720℃, 800℃, or any value within a range of two such values, preferably 720℃. The sintering time can be 5h-16h, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, or any value within a range of two such values, preferably 14h.

[0109] Step (3): Mix the lithium transition metal oxide obtained in step (2) with phosphate and sinter at a sintering temperature of 400-650℃ for 5-11 hours.

[0110] Preferably, the phosphate includes Li X Al 0.5 Ti 1.5 (PO4)3, where x = 1.5-5. For example, x can be a value between 1.5, 2, 3, 4, 5, or any two values, but is not limited thereto. More preferably, it includes LiAl. 0.5 Ti 1.5(PO4)3. Phosphate coating improves the ion-conductivity of the positive electrode active material surface while reducing contact with the electrolyte, thus enhancing its thermal stability. In the sintered material, the molar ratio of lithium to phosphorus is 1:0.001-0.004. For example, it can be 1:0.001, 1:0.002, 1:0.003, 1:0.004, or any range of two values, but is not limited to these.

[0111] In this step, the sintering temperature is 400℃-650℃. For example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or any value within a range of two values, preferably 600℃. The sintering time is 5h-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 any value within a range of two values, preferably 6.5 hours.

[0112] Step (4): Add the product obtained in step (3) above to pure water and stir for 3-5 minutes, then filter and dry.

[0113] Step (5): Mix the material obtained in step (4) with Al source and Y source, and sinter at high temperature to obtain the positive electrode active material of this application.

[0114] In this application, the aluminum source is a substance capable of providing aluminum, for example, the aluminum source may include at least one of aluminum oxide and aluminum hydroxide. The yttrium source is a substance capable of providing yttrium, for example, the yttrium source may include at least one of yttrium oxide and yttrium hydroxide.

[0115] In some embodiments, the molar ratio of the substance obtained in step (4) to Al and Y elements is 1:0.005-0.01:0.005-0.01, for example, a molar ratio of 1:0.005:0.005, 1:0.01:0.005, 1:0.005:0.01, or any value within a range of two such values. In some embodiments, the component of the coating layer near the inner layer of the substrate includes Li. x Al 0.5 Ti 1.5 (PO4) 3， Where x is 1.5-5. The outer layer of the coating layer away from the substrate includes at least one of Al and Y elements. Preferably, the outer layer of the coating layer away from the substrate includes Al. 18 Y 14 O 48 .

[0116] In this step, the sintering temperature can be between 250℃ and 400℃, for example, it can be 250℃, 300℃, 350℃, 400℃, or any value within a range of two such values, preferably 300℃. The sintering time can be between 5h and 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 any value within a range of two such values, but is not limited thereto. Preferably, it can be 6h to 10h, more preferably 8h.

[0117] It should be noted that the chemical formulas of lithium transition metal oxides given in this application are the chemical formulas of materials used in the battery manufacturing process. In positive electrode sheets, secondary batteries, and electrical devices, due to processes such as formation and cycling, those skilled in the art will understand that elements in the above chemical formulas may be lost. For example, in positive electrode sheets, secondary batteries, and electrical devices, oxygen elements are lost in the positive electrode active material due to cycling processes, resulting in a decrease in the measured oxygen content of the positive electrode active material. Additionally, lithium ions are consumed during formation and cycling processes, resulting in a decrease in the measured lithium content of the positive electrode active material.

[0118] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0119] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0120] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0121] Positive electrode sheet

[0122] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of this application.

[0123] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0124] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0126] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0128] Negative electrode sheet

[0129] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0130] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0131] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0132] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0133] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may 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).

[0134] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0135] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0136] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0137] electrolytes

[0138] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0139] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0140] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0141] In some embodiments, the solvent may 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, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0142] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0143] Separating membrane

[0144] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0145] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0146] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0147] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0148] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0149] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0150] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0151] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0152] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0153] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0154] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0155] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0156] Furthermore, a second aspect of this application provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0157] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0158] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0159] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0160] Example

[0161] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0162] Example 1

[0163] Preparation of positive electrode active materials

[0164] Step (1): Mix nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of Ni, Co, and Mn of 93:6:1 to obtain a mixed solution. Add the mixed solution, sodium carbonate, and ammonia to a reaction vessel, control the pH of the mixed solution in the reaction vessel at 12, and the temperature at 61℃ to carry out a co-precipitation reaction, so that the precursor particles grow to the target Dv50 = 10μm. After the reaction is completed, wash and dry to obtain the ultra-high nickel ternary material precursor (Ni).0.93 Co 0.06 Mn 0.01 (OH)2).

[0165] Step (2): The above precursor and Li(OH)2 were mixed at a molar ratio of 1:1.05, and then WO3 and ZrO2 were added and mixed to make the molar ratio of Li, W and Zr 1:0.003:0.005. The mixed powder was then added to a sintering furnace and held at 720°C for 14 hours. After that, the temperature was lowered to room temperature at a cooling rate of 5°C / min to obtain lithium transition metal oxide (Li(Ni)2). 0.93 Co 0.06 Mn 0.01 ) 0.992 W 0.003 Zr 0.005 O2).

[0166] Step (3): After crushing the lithium transition metal oxide obtained in step (2), react it with lithium aluminum phosphate (LiAl). 0.5 Ti 1.5 (PO4)3) to make the molar ratio of lithium to phosphorus 1:0.001 fully mixed. The mixed powder is added to a sintering furnace for sintering at 600℃ for 6.5h, and then cooled to room temperature at a rate of 5℃ / min.

[0167] Step (4): Add 300g of the powder obtained in step (3) to 300mL of deionized water and stir for 5min. Then filter to obtain solid powder and dry it at 60℃.

[0168] Step (5): Add the powder obtained in step (4) into a sintering furnace and mix it thoroughly with Al2O3 and Y2O3 so that the molar ratio of lithium, aluminum and yttrium is 1:0.009:0.007. Sinter the mixed powder at 300°C for 8 hours and cool it to room temperature at a rate of 1.5°C / min to obtain the positive electrode active material of Example 1.

[0169] Preparation of secondary batteries

[0170] (a) Preparation of the positive electrode sheet

[0171] The above-prepared positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 98:0.5:1.5. After thorough stirring and mixing, a positive electrode slurry was obtained. The positive electrode slurry was then uniformly coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0172] (b) Preparation of negative electrode sheet

[0173] Artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are added to a deionized water solvent in a mass ratio of 90:5:2:2:1 and thoroughly mixed. The mixture is then coated onto both sides of a copper foil and subjected to drying, cold pressing, and other processes to obtain the negative electrode sheet.

[0174] (c) Preparation of electrolyte

[0175] 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 above organic solvent at a concentration of 1 mol / L.

[0176] (d) Battery fabrication

[0177] The separator (a 13μm thick polyethylene film), the negative electrode, and the positive electrode are stacked in the order of "separator-negative electrode-separator-positive electrode", processed and shaped, packaged in an aluminum-plastic bag, injected with electrolyte, sealed and formed to obtain a soft-pack battery.

[0178] Determination of positive electrode active materials

[0179] (a) Determination of TG and DTG

[0180] The positive electrode active material prepared in Example 1 was heated from 0°C to 600°C at a heating rate of 10°C / min using a thermogravimetric mass spectrometer (TGA-MS) (SDT650+Discovery MS). The thermogravimetric analysis curves (TG curves) were obtained, as shown below. Figure 7 As shown.

[0181] Depend on Figure 7 It can be seen that the main part of the total weight loss occurs in the temperature range of 220℃ to 360℃. During the process of heating from 0℃ to 600℃, m1 accounts for 16.87%, and during the process of heating from 220℃ to 360℃, m2 accounts for 11.37%. m2 / m1 = 67.40%.

[0182] Then, taking the first derivative of each point on the TG curve with respect to the time coordinate yields the differential thermogravimetric curve (DTG curve), as shown below. Figure 8 As shown, in Figure 8 In the temperature range of 220℃ to 240℃, a peak appears, and the peak value of the rate of change of thermal weight loss is -5.1% / min.

[0183] (b) Determination of oxygen mass spectrometry

[0184] Thermogravimetric mass spectrometry (TGA-MS) (SDT 650 + Discovery MS) was used to perform TGA and mass spectrometry tests simultaneously, yielding the results.Figure 9 .

[0185] like Figure 9 As shown, the horizontal axis represents the test temperature, and the vertical axis represents the intensity of the ion current (lon). Current The gas tested is oxygen released from the positive electrode active material during the thermogravimetric analysis (TGA) test. A higher ion current intensity indicates that more oxygen is released from the positive electrode active material at that temperature, suggesting more vigorous decomposition and poorer thermal stability. Conversely, a lower ion current intensity indicates that less oxygen is released from the positive electrode active material at that temperature, suggesting better thermal stability. Figure 9 As can be seen, a peak occurs in the temperature range of 220℃-360℃, corresponding to an ion current intensity (lon). Current The value is 127.5 × 10 -12 A.

[0186] Battery performance testing

[0187] (a) Gas production performance test

[0188] The resulting pouch cell was charged to 4.25V at 0.33C and then stored at 70℃ for 50 days. The volume of gas produced was then measured as the gas production of the pouch cell, denoted as Q, and the current capacity was measured, denoted as D50. The gas production per unit capacity after 50 days was Q / D50.

[0189] (b) Cyclic performance test at 25°C

[0190] Under constant temperature conditions of 25℃, the battery was charged at 0.33C to 4.25V, then charged at 4.25V at a constant voltage until the current was ≤0.05mA. After resting for 5 minutes, the battery was discharged at 0.33C to 2.8V to obtain the capacity D1. The previous process was repeated for 100 cycles, and the capacity D100 of the pouch battery was recorded.

[0191] Capacity retention rate after 100 cycles = D100 / D1.

[0192] (c) Storage performance test at 60°C

[0193] The soft-pack battery was charged to 4.25V at 0.33C, then charged at 4.25V with a constant voltage until the current was ≤0.05mA. After standing for 5 minutes, it was discharged to 2.8V at 0.33C. The capacity was recorded as D0. After that, it was charged to 4.25V at 0.33C and stored at 60℃ for 30 days. Then it was discharged to 2.8V at 0.33C. The capacity was recorded as D30.

[0194] Capacity retention rate after 30 days of storage at 60℃ = D30 / D0.

[0195] Example 2

[0196] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0197] In step (2), WO3 is replaced with Ta2O5 and ZrO2 is replaced with Sb2O3, and the molar ratio of Li, Ta and Sb is 1:0.01:0.006.

[0198] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0199] Example 3

[0200] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0201] In step (2), after adding WO3 and ZrO2, the molar ratio of Li, W and Zr is 1:0.005:0.005.

[0202] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0203] Example 4

[0204] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0205] In step (2), WO3 is replaced with Ta2O5, and after adding Ta2O5 and ZrO2, the molar ratio of Li, Ta and Zr is 1:0.01:0.005.

[0206] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0207] Example 5

[0208] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0209] No Al2O3 or Y2O3 is added during the sintering process in step (5).

[0210] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0211] Example 6

[0212] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0213] In step (1), nickel sulfate, cobalt sulfate and manganese sulfate are mixed in a molar ratio of 90:5:5 for Ni, Co and Mn to obtain a mixed solution.

[0214] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0215] Example 7

[0216] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0217] In step (1), nickel sulfate, cobalt sulfate and manganese sulfate are mixed in a molar ratio of Ni, Co and Al of 90:5:5 to obtain a mixed solution.

[0218] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0219] Comparative Example 1

[0220] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0221] Lithium titanium aluminum phosphate (LiAl) is not added in step (3). 0.5 Ti 1.5 (PO4)3).

[0222] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 2 below.

[0223] Table 1

[0224]

[0225] Table 2

[0226]

[0227] 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.

[0228] Example 8

[0229] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0230] 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.

[0231] 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.

[0232] 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.

[0233] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 4 below.

[0234] Example 9

[0235] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0236] 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.

[0237] 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.

[0238] In step (5), Al2O3 and Y2O3 are added during the sintering process to make the molar ratio of Li, Al and Y 1:0.01:0.008.

[0239] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 4 below.

[0240] Example 10

[0241] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0242] In step (2), WO3 and ZrO2 are added so that the molar ratio of Li, W and Zr is 1:0.001:0.003.

[0243] In step (5), Al2O3 and Y2O3 are added during the sintering process to make the molar ratio of Li, Al and Y 1:0.005:0.006.

[0244] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 4 below.

[0245] Example 11

[0246] The positive electrode active material was prepared using a method similar to that in Example 1, with the difference being:

[0247] In step (2), WO3 and ZrO2 are added so that the molar ratio of Li, W and Zr is 1:0.001:0.001.

[0248] In step (5), Al2O3 and Y2O3 are added during the sintering process to make the molar ratio of Li, Al and Y 1:0.005:0.005.

[0249] In addition, pouch cells were prepared using the same method as in Example 1 and tested. The results are shown in Table 4 below.

[0250] Table 3

[0251]

[0252] Table 4

[0253]

[0254] As can be seen from the data in Tables 1 and 4 above, compared with Example 5, the thermal stability of the positive electrode active material in Examples 8-11 is further improved in the range of m2 / m1 of 40%-75%, and the gas production is further reduced. The batteries of Examples 8-11 have further improved storage performance and cycle performance.

[0255] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and function as the technical concept within the scope of this application are included in the technical scope of this application.

Claims

1. A secondary battery characterized by comprising: The positive electrode sheet, the negative electrode sheet, the separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte solution including an organic solvent and a lithium salt, The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material. The positive electrode active material includes 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, and 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. In a differential thermogravimetric curve obtained by temperature increasing of the positive electrode active material at a temperature increase rate of 10°C / min, the absolute value of the peak value of the heat loss rate change is less than 7% / min. The molar content of the nickel element is 90 mol% or more with respect to all metal elements excluding lithium.

2. The secondary battery according to claim 1, characterized by The absolute value of the peak value of the heat loss rate change is less than or equal to 6.1% / min.

3. The secondary battery according to claim 1 or 2, characterized by The absolute value of the peak value of the heat loss rate change is less than or equal to 5.6% / min.

4. The secondary battery according to any one of claims 1 to 3, characterized by In a thermogravimetric analysis, the total weight loss of the positive electrode active material during temperature increase from 0°C to 600°C is set as m1, and the weight loss during temperature increase from 220°C to 360°C is set as m2, and the m1 and the m2 satisfy the following relationship: 40%≤m2 / m1≤75%.

5. The secondary battery according to any one of claims 1 to 4, characterized by, The m2 is 0.5% to 12%.

6. The secondary battery according to claim 5, characterized by The m1 is 1% to 18%.

7. The secondary battery according to claim 5 or 6, characterized by 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.

8. The secondary battery according to any one of claims 1 to 7, characterized by, In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 600°C is 10% to 18%.

9. The secondary battery according to any one of claims 1 to 8, characterized by, In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 300°C is 10% to 12%.

10. The secondary battery according to any one of claims 1 to 9, characterized by In a thermogravimetric analysis, the weight loss rate of the positive electrode active material at 200°C is 0.01% to 0.5%.

11. The secondary battery according to any one of claims 1 to 10, characterized by The differential thermogravimetric curve is obtained by testing from 0°C to 600°C under a nitrogen atmosphere.

12. The secondary battery according to any one of claims 1 to 11, characterized by In the differential thermogravimetric curve, the peak value of the heat loss rate change occurs in the range of 200°C to 280°C.

13. The secondary battery according to any one of claims 1 to 12, characterized by, In the differential thermogravimetric curve, the peak value of the heat loss rate change occurs in the range of 220°C to 240°C.

14. The secondary battery according to any one of claims 1 to 13, characterized by In the differential thermogravimetric curve, the peak area of the peak of the heat loss rate change is 12.0% to 17.0%.

15. The secondary battery according to any one of claims 1 to 14, characterized by In the differential thermogravimetric curve, the half-peak width of the peak of the heat loss rate change is 5°C to 25°C.

16. The secondary battery according to any one of claims 1 to 15, characterized by In the mass spectrum curve, the peak value of the mass spectrum peak occurs in the range of 200°C to 280°C.

17. The secondary battery according to any one of claims 1 to 16, characterized by 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 .

18. The secondary battery according to claim 17, characterized by In the mass spectrum curve, the peak value of the mass spectrum peak occurs in the range of 220°C to 240°C.

19. The secondary battery according to claim 17 or 18, characterized by The half-peak width of the mass spectrum peak is 10°C to 20°C.

20. The secondary battery according to any one of claims 17 to 19, characterized by, 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, characterized by In the X-ray diffraction spectrum of the positive electrode active material, the ratio of the peak intensity of the 003 plane to the peak intensity of the 104 plane is 1.2-1.

7.

22. The secondary battery according to any one of claims 1 to 21, characterized by ​ 23. The secondary battery according to any one of claims 1 to 22, characterized by 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, characterized by 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, characterized by 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 comprising 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, characterized by 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 positive electrode active material has a powder compaction density of 3.0 g / cm3 or more under a pressure of 3000 N 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, characterized by The positive electrode active material includes a base including the lithium transition metal oxide and a coating layer provided on at least a part of the surface of the base.

28. The secondary battery according to claim 27, characterized by 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 according to claim 28, characterized by 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, characterized by In the positive electrode active material, the molar ratio of lithium element to phosphorus element is 1:0.001-0.

004.

31. An electrical device, comprising: A secondary battery including the positive electrode active material according to any one of claims 1 to 30.

32. A positive electrode active material, characterized by comprising: 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 value of the rate of change of thermal weight loss is less than 7% / min.

33. The positive electrode active material according to claim 32, characterized by The molar content of the nickel element is 90 mol% or more relative to all metal elements other than lithium.

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

35. The positive electrode active material according to any one of claims 32 to 34, characterized by, The absolute value of the peak value of the rate of change of thermal weight loss is less than or equal to 5.6% / min.

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

37. The positive electrode active material according to claim 36, characterized by The m2 is 0.5% to 12%.

38. The positive electrode active material according to claim 36 or 37, characterized by The m1 is 1% to 18%.

39. The positive electrode active material according to any one of claims 32 to 38, characterized by, 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.

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

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

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