Secondary battery, positive electrode active material and preparation method therefor, positive electrode sheet and electric device

Abstract

The present application relates to a secondary battery, a positive electrode active material and a preparation method therefor, a positive electrode sheet, and an electric device. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode active layer, and the positive electrode active layer comprising a positive electrode active material. In a particle size distribution curve of primary particles in the positive electrode active material, the full width at half maximum is denoted as WH, satisfying WH≤2.5 μm; and the average particle size of the primary particles in the positive electrode active material is denoted as D1, satisfying 1.3 μm≤D1≤3 μm.

Description

Secondary batteries, positive electrode active materials and their preparation methods, positive electrode sheets and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on January 27, 2025, with application number CN202510125623X, entitled "Secondary Battery, Positive Electrode Active Material and Preparation Method Thereof, Positive Electrode Sheet and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of secondary battery technology, and further to secondary batteries, positive electrode active materials and their preparation methods, positive electrode sheets and electrical devices. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] With the technological advancements in rechargeable batteries, lithium-ion batteries, in particular, are increasingly being used in smartphones, tablets, laptops, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. They are also widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants. As the application of rechargeable batteries at high voltages becomes more widespread, the requirements for their lifespan under high voltage conditions are becoming increasingly stringent. Summary of the Invention

[0006] According to various embodiments and examples of this application, this application provides a secondary battery, a positive electrode active material and a method for preparing the same, a positive electrode sheet, and an electrical device. The secondary battery exhibits significantly improved battery life under high voltage.

[0007] In a first aspect of this application, a secondary battery is provided, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material; the primary particles in the positive electrode active material have a narrow particle size distribution; the average particle size D1 of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0008] In some embodiments, a secondary battery is provided, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material;

[0009] In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm;

[0010] The average particle size of the primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3μm≤D1≤3μm.

[0011] In the positive electrode active material of secondary batteries, primary particles are the basic unit of particles.

[0012] For the positive electrode active materials of traditional rechargeable batteries, on the one hand, small-sized, large-specific-surface-area non-agglomerated primary particles are prone to large interfacial side reactions, which are easily amplified under high voltage, affecting battery life at high voltage, such as cycle and / or storage life. On the other hand, secondary particles in traditional positive electrode active materials are usually agglomerated from smaller nanoscale primary particles. Due to the relatively small contact area between adjacent primary particles, secondary particles are prone to cracking under stress at high voltage, forming fresh interfaces. This accelerates electrolyte consumption during high-voltage cycling and / or storage, thus deteriorating battery life.

[0013] In the secondary battery provided in the first aspect of this application, the half-width (W) of the peak value in the particle size distribution curve of the primary particles in the positive electrode active material is controlled. H Within the aforementioned range, the particle size distribution of primary particles in the positive electrode active material is made relatively uniform. Further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned range results in primary particles with relatively large micron-sized dimensions. This reduces, on the one hand, the content of small-sized, large-specific-surface-area non-agglomerated primary particles, significantly suppressing interfacial side reactions of the positive electrode active material under high voltage. On the other hand, when secondary particles formed by the agglomeration of primary particles exist in the positive electrode active material, controlling the average particle size and particle size distribution of the primary particles within the aforementioned range allows the secondary particles to have relatively large micron-sized dimensions. The relatively large micron-sized particles allow for a larger contact area between the primary particles in the secondary particles, resulting in stronger bonding between the primary particles under high voltage. This reduces the risk of cracking of the positive electrode active material under high voltage, decreases the generation of fresh interfaces, and slows down electrolyte consumption during high-voltage cycling and / or storage. Through these multiple effects, interfacial side reactions under high voltage can be significantly suppressed, reducing the risk of cracking of the positive electrode active material under high voltage, improving the structural stability of the positive electrode active material, and slowing down electrolyte consumption during high-voltage cycling and / or storage. Consequently, the battery life of the secondary battery under high voltage can be significantly improved.

[0014] The improvement described in any part of the context of this application is not intended to be limited by any theoretical constraints.

[0015] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0016] (ta1)1μm≤W H ≤2.5μm;

[0017] (ta2)1.4μm≤D1≤2.5μm.

[0018] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0019] (tb1)1.2μm≤W H ≤2.5μm;

[0020] (tb2)1.5μm≤D1≤2.4μm.

[0021] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). H Based on the condition that the positive electrode active material meets one or more of the characteristics (ta1), (ta2), (tb1) and (tb2), the distribution width and / or average particle size of the primary particles can be further controlled within a more suitable range, thereby improving the battery life under high voltage.

[0022] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). H Based on the condition that the particle size distribution curve of the primary particles in the positive electrode active material is ≤2.5μm and 1.3μm≤D1≤3μm, the half-maximum width (W) of the primary particles in the positive electrode active material can be further controlled. H Within the aforementioned optional range, it is beneficial to make the particle size distribution of primary particles in the positive electrode active material more uniform. On the one hand, it is more beneficial to reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles and reduce interfacial side reactions under high voltage. On the other hand, it is also more beneficial to improve the structural stability of secondary particles that may exist in the positive electrode active material under high voltage, which can better reduce the generation of fresh interfaces and slow down electrolyte consumption during high-voltage cycling and / or storage. Based on the aforementioned multiple effects, it is beneficial to better improve battery life under high voltage.

[0023] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). HBased on the condition that the average particle size (D1) of the primary particles in the positive electrode active material is ≤2.5μm and 1.3μm≤D1≤3μm, further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned selectable range is beneficial to give the primary particles in the positive electrode active material a more suitable micron-scale size. This is more conducive to reducing the content of small-sized, large-specific-surface-area non-agglomerated primary particles, better reducing interfacial side reactions under high voltage and improving the stability of the CEI film (the solid electrolyte interfacial film of the positive electrode can be called the CEI film). At the same time, it is also more conducive to improving the structural stability of secondary particles that may exist in the positive electrode active material under high voltage, which can better reduce the generation of fresh interfaces and slow down electrolyte consumption during high-voltage cycling and / or storage. Based on the aforementioned multiple effects, it is beneficial to better improve the battery life under high voltage.

[0024] On the other hand, by suppressing the generation of fresh interfaces under high voltage, it is also beneficial to resist the increase in impedance, suppress the deterioration of battery dynamics, and promote the discharge capacity of positive electrode active materials and improve battery rate performance.

[0025] When the primary particle size in the positive electrode active material is relatively large, the specific surface area of ​​the positive electrode active material is relatively small. This may reduce the intercalation / deintercalation area of ​​active ions, thus affecting the intercalation / deintercalation rate. It also leads to a longer solid-phase transport path for active ions and an increased diffusion time. During high-rate discharge, active ions may not have enough time to fully deintercalate in a short period of time, which may be detrimental to the discharge capacity and rate performance of the positive electrode active material. By controlling the primary particles in the positive electrode active material to have a suitable micron-scale size (e.g., 1.3μm≤D1≤3μm, further such as 1.4μm≤D1≤2.5μm, and even further such as 1.5μm≤D1≤2.4μm), it is beneficial to achieve good discharge capacity and rate performance of the positive electrode.

[0026] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

[0027] By controlling the particle size distribution curve of the primary particles in the positive electrode active material to be a single-peak curve, it is beneficial to improve the uniformity of the particle size distribution of the primary particles in the positive electrode active material.

[0028] In some embodiments, the D of the positive electrode active material v The ratio of 50 to the average particle size of the primary particles in the positive electrode active material is denoted as R1, which satisfies 1≤R1≤3.

[0029] In some implementations, 1.5 ≤ R1 ≤ 2.2.

[0030] By using the D of the positive electrode active material v 50 (can be written as D) v 50 AThe ratio of the average particle size (D1) of the primary particles in the positive electrode active material to the average particle size (R1 = D) v 50 A Controlling / D1) within the aforementioned range helps to make the median particle size of the positive electrode active material particles close to the average particle size of the primary particles, which are the basic unit of particles. This helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and reduce the content of secondary particles, which are agglomerates of primary particles. Correspondingly, it increases the proportion of non-agglomerated primary particles. Since there is no interface between primary particles in secondary particles inside the non-agglomerated primary particles, they can better resist volume stress changes and cracking risks under high voltage. This makes the positive electrode active material have better structural stability under high voltage, which is more conducive to improving battery life under high voltage.

[0031] In some embodiments, the positive electrode active material comprises non-agglomerated primary particles; the mass percentage of the non-agglomerated primary particles in the positive electrode active material is denoted as f. M The proportion of the non-agglomerated primary particles in the positive electrode active material is denoted as f. N ;

[0032] The positive electrode active material satisfies one or more of the following characteristics:

[0033] (tc1)40%≤f M ≤100%;

[0034] (tc2)60%≤f N ≤100%.

[0035] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0036] (td1)55%≤f M ≤100%;

[0037] (td2)80%≤f N ≤100%.

[0038] By measuring the mass ratio (f) of non-agglomerated primary particles in the positive electrode active material M The proportion of non-agglomerated primary particles in the positive electrode active material (f) N By controlling one or two of the above-mentioned parameters within the specified range, the proportion of non-agglomerated primary particles can be controlled within a more suitable range, enabling the positive electrode active material to better resist volume stress changes and cracking risks under high voltage, thus exhibiting better structural stability and further improving battery life under high voltage.

[0039] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0040] (te1)80%≤f M <100%;

[0041] (te2)90%≤f N <100%.

[0042] By measuring the mass ratio (f) of non-agglomerated primary particles in the positive electrode active material M The proportion of non-agglomerated primary particles in the positive electrode active material (f) N If one or two of the above conditions are controlled within a higher range, and there are still agglomerated primary particles in the positive electrode active material, the proportion of non-agglomerated primary particles can be controlled within a higher range, which is more conducive to improving the structural stability of the positive electrode active material under high voltage, and thus more conducive to improving the battery life under high voltage.

[0043] In some embodiments, the D of the positive electrode active material v 50 is 2μm to 6μm.

[0044] In some embodiments, the D of the positive electrode active material v 50 is 2.8μm to 4.5μm.

[0045] The half-width (W) of the primary particle size distribution curve in the synergistically controlled positive electrode active material H Based on the average particle size (D1) of the primary particles in the positive electrode active material, further improvements are made to the D1 of the positive electrode active material. v Controlling the 50 within the aforementioned range helps to make the particle size in the positive electrode active material more appropriate, which helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and can increase the proportion of non-agglomerated primary particles. Since there is no interface between primary particles in the secondary particles inside the non-agglomerated primary particles, it can better resist volume stress changes and cracking risks under high voltage, so that the positive electrode active material has better structural stability under high voltage and can better improve battery life under high voltage.

[0046] Through the D of the positive electrode active material v Further control of 50 can further reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles in the positive electrode active material, which is more conducive to reducing interfacial side reactions under high voltage, and thus more conducive to improving battery life under high voltage.

[0047] On the other hand, by using the D of the positive electrode active material vControlling the content of 50 within the aforementioned range also helps to control the content of large-diameter secondary particles formed by the agglomeration of primary particles to be low. Therefore, the problem of large-diameter secondary particles in agglomeration cracking under high voltage, which leads to the formation of fresh interfaces, is suppressed. This helps to reduce the increase in impedance caused by the formation of fresh interfaces and improves the battery dynamic performance.

[0048] In some embodiments, the SPAN value of the positive electrode active material is 0.7 to 1.8; wherein, SPAN = (D v 90-D v 10) / D v 50.

[0049] In some embodiments, the SPAN value of the positive electrode active material is 0.85 to 1.35.

[0050] By controlling the SPAN value of the positive electrode active material within the aforementioned range, it is beneficial to make the particle size in the positive electrode active material more uniform and the particle size distribution narrower. This helps to reduce the content of small-sized non-agglomerated primary particles, reduce interfacial side reactions under high voltage, and also helps to reduce the content of large-sized secondary particles. This reduces the negative impact of secondary particle cracking under high voltage on battery life. Through the aforementioned multiple effects, it is beneficial to significantly improve battery life under high voltage.

[0051] In some embodiments, the positive electrode active material includes a lithium composite metal oxide, which includes lithium, non-lithium metal elements, and oxygen; the non-lithium metal elements include transition metal elements.

[0052] In some embodiments, the lithium composite metal oxide includes one or more of lithium nickel-based oxides, lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and modified versions of any of the aforementioned cathode active materials; wherein the modified version includes one or more of doping elements and coating elements.

[0053] Introducing lithium nickel-based oxides into the positive electrode active material can help improve energy density.

[0054] Introducing lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and other cathode active materials into the cathode active materials can improve the structural stability of the cathode active materials under high voltage and extend the battery life under high voltage.

[0055] In some embodiments, the lithium composite metal oxide comprises a lithium nickel-based oxide, which contains Li, a non-lithium metal element, and O, wherein the non-lithium metal element includes Ni; the lithium nickel-based oxide satisfies one or more of the following characteristics:

[0056] (t1) The atomic molar ratio of Ni element to non-lithium metal elements in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1;

[0057] (t2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.6 ≤ x2 ≤ 1.2;

[0058] (t3) The lithium nickel-based oxide contains Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.6 ≤ x3 ≤ 2.1.

[0059] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics:

[0060] (i) 0.5 ≤ q1 ≤ 0.99;

[0061] (ii) 0.5 ≤ q2 ≤ 0.99;

[0062] (iii) 0.5 ≤ q3 ≤ 0.99;

[0063] (iv) The lithium nickel-based oxide contains Co element, and the atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3, optionally 0.02 ≤ q4 ≤ 0.3;

[0064] (v) The lithium nickel-based oxide contains Mn element, and the atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5, optionally 0.01 ≤ q5 ≤ 0.5;

[0065] (vi) The mass percentage of the lithium nickel-based oxide in the lithium composite metal oxide is 80% - 100%.

[0066] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics:

[0067] (ti) 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99;

[0068] (tii) 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99;

[0069] (tiii) 0.8 ≤ x2 ≤ 1.1;

[0070] (tiv) 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99;

[0071] (tv) 1.8 ≤ x3 ≤ 2.06;

[0072] (tvi) The lithium nickel-based oxide contains Co, where 0.05 ≤ q4 ≤ 0.2;

[0073] (tvii) The lithium nickel-based oxide contains Mn element, 0.02≤q5≤0.38;

[0074] (tviii) The lithium nickel-based oxide accounts for 90% to 100% of the mass of the lithium composite metal oxide.

[0075] By controlling the nickel content of the lithium nickel-based oxide in the positive electrode active material, the crystal structure stability of the positive electrode active material is improved under high voltage, which is more conducive to improving the battery life under high voltage.

[0076] In some embodiments, the lithium composite metal oxide includes one or more lithium nickel cobalt manganese-based oxides and modified lithium nickel cobalt manganese-based oxides, wherein the modified oxides include one or more doping elements and coating elements.

[0077] In lithium nickel cobalt manganese-based oxides, nickel can increase energy density, cobalt can reduce cation mixing, enhance material structural stability and rate performance, and manganese can stabilize the layered structure of lithium nickel cobalt manganese-based oxide materials, but these effects are not limited to those described above.

[0078] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0079] (tf1) The positive electrode active material includes doping elements, which include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb;

[0080] (tf2) The positive electrode active material includes coating elements located on the particle surface, and the coating elements include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0081] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0082] (tf1') The positive electrode active material includes doping elements, and the doping elements include one or both of Zr and W;

[0083] (tf2') The positive electrode active material includes a coating element located on the particle surface, and the coating element includes Ti.

[0084] By introducing one or more doping and coating elements into the positive electrode active material, the positive electrode active material can be modified in one or more ways, either through doping or coating. Taking the introduction of doping elements as an example, as a non-limiting example, introducing doping elements (such as Zr, W, etc.) can improve the bonding force between transition metal elements and O atoms in the positive electrode active material, thereby improving lattice stability during lithium insertion / extraction and enhancing the stability of the positive electrode active material. Taking the introduction of coating element Ti as an example, it facilitates the formation of an oxide coating layer, hindering direct contact between the electrolyte and the positive electrode material, thus reducing interfacial side reactions.

[0085] In some embodiments, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active layer, the negative electrode active layer including the negative electrode active material, the negative electrode active material including one or more of carbon-based materials and silicon-based materials.

[0086] In some embodiments, the negative electrode active material includes graphite.

[0087] The negative electrode active material in the negative electrode sheet can be one of the aforementioned types, but is not limited to these.

[0088] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0089] In some embodiments, the charging cutoff voltage of the secondary battery is greater than or equal to 4.2V;

[0090] Optionally, the charging cut-off voltage of the secondary battery is greater than or equal to 4.3V;

[0091] Alternatively, the charging cutoff voltage of the secondary battery is 4.2V to 4.5V, and more preferably 4.3V to 4.5V.

[0092] In a second aspect of this application, a method for preparing a positive electrode active material is provided. The obtained positive electrode active material can be used as a positive electrode active material in the secondary battery described in the first aspect of this application or as part of the raw material for the positive electrode active material in the secondary battery described in the first aspect of this application.

[0093] In some embodiments, a method for preparing a positive electrode active material is provided, which includes the following steps:

[0094] The positive electrode active material solid precursor and lithium source are mixed to obtain a preliminary mixture. The preliminary mixture is subjected to a first sintering and a first crushing, and then subjected to a second sintering and a second crushing to prepare the positive electrode active material.

[0095] The temperature at which the first sintering is performed is higher than the temperature at which the second sintering is performed.

[0096] In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm;

[0097] The average particle size of the primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3μm≤D1≤3μm.

[0098] By subjecting the initial mixture, including a solid precursor of positive electrode active material and a lithium source, to multiple sintering and crushing processes, the solid precursor can be lithiated in the first sintering to form the target crystal structure of the positive electrode active material. The first crushing can reduce particle agglomeration. The second sintering can achieve particle morphology repair, reduce defects, and promote the fusion of fine particles. The second crushing can further reduce particle agglomeration. Thus, a positive electrode active material with moderate particle size and uniform particle size distribution can be prepared.

[0099] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0100] (1) The positive electrode active material includes doping elements, and the initial mixture also includes raw materials containing the doping elements;

[0101] (2) The positive electrode active material includes a coating element, and the preparation method of the positive electrode active material includes at least one of a first coating step and a second coating step. The first coating step is carried out simultaneously with the second sintering, and the second coating step is achieved by a third sintering after the second crushing.

[0102] Depending on the target composition of the positive electrode active material, one or more of the doping elements and coating elements can be selectively introduced during the preparation process.

[0103] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0104] (tg1) The positive electrode active material includes doping elements, which include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb;

[0105] (tg2) The positive electrode active material includes a doping element, and the initial mixture also includes a raw material containing the doping element; the raw material containing the doping element includes one or more of the following: oxides, hydroxides, carbonates and phosphates containing the doping element;

[0106] (tg3) The positive electrode active material includes coating elements, which include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na;

[0107] (tg4) The raw materials providing the coating element include one or more of oxides, hydroxides, carbonates and phosphates containing the coating element;

[0108] (tg5) The temperature for the first sintering is 900℃~980℃;

[0109] (tg6) The first sintering time is 5h to 15h;

[0110] (tg7) The temperature for the second sintering is 700℃~800℃;

[0111] (tg8) The second sintering time is 4h to 12h;

[0112] (tg9) The second sintering step is carried out in the presence of a first coating agent, which includes one or more of oxides, hydroxides, carbonates and phosphates of a first coating element, and the first coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0113] By controlling one or more parameters in the preparation process within the aforementioned range, it is beneficial to better regulate the particle size and particle size distribution of primary particles in the positive electrode active material.

[0114] In some embodiments, the solid precursor of the positive electrode active material satisfies one or more of the following characteristics:

[0115] (tj1) The X-ray diffraction pattern of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 15° to 25°;

[0116] (tj2) The X-ray diffraction pattern of the solid precursor of the positive electrode active material shows (001) crystal plane diffraction peaks, and the full width at half maximum (FWH) of the (001) crystal plane diffraction peaks is denoted as FWDH. (001) Where 0.35≤FWDH (001) ≤0.70, optionally, 0.35≤FWDH (001) ≤0.64;

[0117] (tj3) The D of the solid precursor of the positive electrode active material v 50 is 2.5μm~4.5μm;

[0118] (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m². 2 / g~35m 2 / g;

[0119] (tj5) The SPAN value of the solid precursor of the positive electrode active material is 0.4 to 1.5; where SPAN = (D v 90-D v 10) / D v 50.

[0120] In some embodiments, the solid precursor of the positive electrode active material satisfies one or more of the following characteristics:

[0121] (tk1)0.35≤FWDH (001) ≤0.64;

[0122] (tk2) The D of the solid precursor of the positive electrode active material v 50 is 3.0μm~4.2μm;

[0123] (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6m². 2 / g~30m 2 / g;

[0124] (tk4) The SPAN value of the solid precursor of the positive electrode active material is 0.60 to 1.30.

[0125] The position of the diffraction peaks in the X-ray diffraction pattern of the solid precursor of the positive electrode active material can be used to determine the formation of the (001) crystal plane. The solid precursor of lithium nickel cobalt manganese-based oxide positive electrode active materials typically has a layered structure, and the (001) crystal plane is the crystal plane perpendicular to the stacking direction of the layered structure. The "half-maximum width at half maximum (FWDH)" of the (001) crystal plane can be used as a metric. (001) Characterizing the crystallinity of the solid precursor of the positive electrode active material, a lower FWDH (001) This corresponds to a higher degree of crystallinity. By using FWDH... (001) By controlling the process within the aforementioned range, the solid precursor of the positive electrode active material can achieve a more suitable crystallinity, resulting in more suitable hardness of the sintered particles. This is beneficial for reducing the generation of micro-powder or fine particles during the crushing process. Therefore, based on the aforementioned multiple sintering and multiple crushing processes, further combined control of the FWDH of the solid precursor of the positive electrode active material is necessary. (001) Within the aforementioned range, it is beneficial to better control the particle size and particle size distribution of the primary particles in the prepared positive electrode active material, so that the size of the primary particles in the positive electrode active material is more moderate and the particle size concentration is higher.

[0126] By using a solid precursor of a positive electrode active material with relatively high crystallinity to prepare a positive electrode active material, and then preparing a positive electrode sheet and a secondary battery, the amount of transition metal dissolved in the positive electrode active material is reduced during the lithium insertion / extraction process under high voltage, the amount of transition metal deposition in the negative electrode is reduced, the thickening of the solid electrolyte interphase (SEI) film of the negative electrode is suppressed, the loss of active lithium is reduced, and the life deterioration of the battery under high voltage can be suppressed.

[0127] By controlling the FWDH of the solid precursor of the positive electrode active material (001) D of solid precursors for positive electrode active materials v 50. Having one or more parameters, such as the specific surface area of ​​the positive electrode active material solid precursor and the SPAN value of the positive electrode active material solid precursor, within the aforementioned range is beneficial for controlling the average particle size (D1) and particle size distribution (e.g., W) of the primary particles. H ), D of positive electrode active material v 50 and SPAN value, R1 (D of positive electrode active material) v One or more parameters, such as the ratio of 50 to the average particle size D1 of the primary particles, are within a more suitable range and are not limited to any theory. For example, this can be more beneficial in reducing the contact area between the positive electrode active material and the electrolyte, more beneficial in reducing the occurrence of positive electrode-electrolyte interface side reactions under high voltage, more beneficial in reducing metal dissolution of the positive electrode, and more beneficial in improving the structural stability of the positive electrode active material under high voltage, thereby improving battery life under high voltage. For example, when the positive electrode active material contains manganese, it is also beneficial in reducing manganese dissolution.

[0128] In some embodiments, the prepared positive electrode active material satisfies one or more of the following characteristics (tm1) and (tm2):

[0129] The positive electrode active material prepared by (tm1) is the positive electrode active material defined in the first aspect of this application;

[0130] (tm2) The prepared cathode active material includes lithium nickel-based oxide, the lithium nickel-based oxide contains Li element, non-lithium metal element and O element, the non-lithium metal element includes Ni element, and the lithium nickel-based oxide satisfies one or more of the following characteristics (tn1), (tn2), (tn3), (tn4) and (tn5): (tn1) The atomic molar ratio of Ni element to the non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1; (tn2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.98 ≤ x2 ≤ 1.02; (tn3) The lithium nickel-based oxide contains Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.96 ≤ x3 ≤ 2.04; (tn4) The atomic molar ratio of Co element to the non-lithium metal element in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3; (tn5) The atomic molar ratio of Mn element to the non-lithium metal element in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5.

[0131] In the third aspect of the present application, a cathode active material is provided, and the cathode active material includes primary particles;

[0132] In the particle size distribution curve of the primary particles in the cathode active material, the full width at half maximum is denoted as W H , satisfying W H ≤ 2.5 μm;

[0133] The average particle size of the primary particles in the cathode active material is denoted as D1, satisfying 1.3 μm ≤ D1 ≤ 3 μm.

[0134] This cathode active material can be used to prepare the secondary battery of the first aspect of the present application, and can significantly improve the battery life of the secondary battery at high voltages. Without being limited to any theory, reference can be made to the description in the first aspect of the present application.

[0135] In some embodiments, the cathode active material includes the cathode active material prepared by the preparation method of the cathode active material described in the second aspect of the present application, or the cathode active material defined in the first aspect of the present application (i.e., having the same characteristics as the cathode active material in the secondary battery of the first aspect).

[0136] In the fourth aspect of the present application, a cathode electrode sheet is provided, which includes a cathode active layer, and the cathode active layer includes a cathode active material;

[0137] In the particle size distribution curve of the primary particles in the cathode active material, the full width at half maximum is denoted as W H , satisfying W H ≤ 2.5 μm;

[0138] The average particle size of the primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3μm≤D1≤3μm.

[0139] By introducing the aforementioned positive electrode active material into the positive electrode active layer of the positive electrode sheet, the advantages of the aforementioned positive electrode active material can be realized, improving the battery life of the secondary battery under high voltage, including cycle and / or storage life.

[0140] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0141] (to1) The positive electrode active material includes the positive electrode active material prepared by the preparation method of the positive electrode active material described in the second aspect of this application;

[0142] (to2) The positive electrode active material is the positive electrode active material defined in the first aspect of this application;

[0143] (to3) The positive electrode is the positive electrode as defined in the first aspect of this application.

[0144] In a fifth aspect of this application, an electrical device is provided, comprising at least one of the secondary battery described in the first aspect of this application, a positive active material prepared by the method for preparing the positive active material described in the second aspect of this application, a positive active material described in the third aspect of this application, and a positive electrode sheet described in the fourth aspect of this application.

[0145] Details of one or more embodiments or examples of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0146] To better describe and illustrate the embodiments, examples, or models provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments, examples, or models, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0147] Figure 1 is a particle size distribution curve of primary particles in a positive electrode active material in one embodiment of this application. The statistical range of primary particles includes non-agglomerated primary particles and primary particles that may exist in secondary particles. The horizontal axis is the particle size of primary particles, and the vertical axis is the number of primary particles of different sizes.

[0148] Figure 2 is a scanning electron microscope (SEM) image of the solid precursor of the positive electrode active material in one embodiment of this application.

[0149] Figure 3 is an X-ray diffraction (XRD) pattern of a solid precursor for preparing a positive electrode active material in one embodiment of this application. The horizontal axis is 2θ (unit is ° (degree)) and the coordinate axis is intensity (au) (intensity (au)).

[0150] Figure 4 is a SEM image of the positive electrode active material in one embodiment of this application.

[0151] Figure 5 is a schematic diagram of a battery cell according to one embodiment of this application.

[0152] Figure 6 is an exploded view of a battery cell according to an embodiment of this application, as shown in Figure 5.

[0153] Figure 7 is a schematic diagram of a battery device according to an embodiment of this application.

[0154] Figure 8 is a schematic diagram of a battery pack according to one embodiment of this application.

[0155] Figure 9 is an exploded view of the battery pack of one embodiment of this application shown in Figure 8.

[0156] Figure 10 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0157] Explanation of reference numerals in the attached drawings: 1, battery pack; 2, upper casing; 3, lower casing; 4, battery assembly; 5, individual battery cell; 51, housing; 52, electrode assembly; 53, cover plate; 6, electrical device. Detailed Implementation

[0158] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments and examples of the secondary battery, positive electrode active material, preparation method thereof, positive electrode sheet, and electrical device of this application. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical 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 of the claims.

[0159] The "range" disclosed in this application can be 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, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently and can be combined arbitrarily; 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0160] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0161] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0162] In this application, the terms "multiple," "various," "multiple items," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more (greater than or equal to) two. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0163] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0164] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0165] Those skilled in the art will understand that, unless otherwise specified, the order in which the steps are written in the various embodiments or methods of this application does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if method M includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0166] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if 'a' includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3," and features or solutions where "a includes not only a1, a2, and a3, but also other members."

[0167] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0168] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0169] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0170] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0171] In this document, the term "suitable" in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the technical solution that enables the implementation of this application.

[0172] In this document, terms such as "preferred," "better," "more suitable," "ideal," "good," and "superior" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0173] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0174] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0175] In the description of this application, it should be understood that the terms "length", "width", "thickness", "height", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0176] In this application, unless otherwise expressly specified and limited, the terms "connected," "linked," etc., should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0177] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0178] In this application, the term "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0179] In this application, when a unit is specified for a data range, if it is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the units for the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature and size are interpreted in the same way.

[0180] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "less than or equal to", and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently represented as ">", and "less than" can be equivalently represented as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be considered as providing two additional solutions: "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be considered as providing two additional solutions: "less than" and "equal to".

[0181] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0182] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0183] With the increasing prevalence of rechargeable batteries, their high-voltage performance is receiving more and more attention to meet the growing demand for longer driving ranges. Increasing the operating voltage of a rechargeable battery can increase energy storage while maintaining the same battery volume or weight, thereby extending driving time. However, at high voltages, the positive electrode active material is prone to the extraction or insertion of a large number of active ions. During cycling and / or storage at high voltages, the positive electrode active material is susceptible to intensified interfacial side reactions, and the risk of cracking increases, leading to a deterioration in battery life under high voltage conditions.

[0184] To improve the structural stability of cathode active materials under high voltage and thus enhance battery life, non-agglomerated primary particles can be selected as cathode active materials. Compared to secondary particles formed by the agglomeration of primary particles, non-agglomerated primary particles lack the interfaces between primary particles within secondary particles. This allows non-agglomerated primary particles to better resist volumetric stress changes and cracking risks under high voltage, resulting in better structural stability. Secondary particles, on the other hand, have interfaces between multiple primary particles, leading to a relatively higher risk of cracking under high voltage. Cracked particles form fresh interfaces; during cycling and / or storage at high voltage, these fresh interfaces further react with the electrolyte to form a new solid electrolyte interphase (CEI) film (the CEI film of the cathode), consuming lithium, increasing impedance, and ultimately degrading battery life.

[0185] However, non-agglomerated primary cathode materials tend to introduce small-sized non-agglomerated primary particles. These small particles have a relatively large specific surface area, resulting in a larger interfacial area with the electrolyte and more interfacial side reactions. These side reactions are easily exacerbated at high voltages, thus worsening battery life at high voltages. Increasing the size of the non-agglomerated primary particles typically requires raising the sintering temperature and / or extending the sintering time in the manufacturing process. This can easily lead to increased agglomeration of primary particles, resulting in an increased content of secondary particles. Furthermore, these small secondary particles are difficult to separate from the similarly sized non-agglomerated primary particles. This makes improving the battery life of secondary batteries at high voltages quite challenging.

[0186] According to various embodiments and examples of this application, this application provides a secondary battery, a positive electrode active material and a method for preparing the same, a positive electrode sheet, and an electrical device. The secondary battery exhibits significantly improved battery life under high voltage.

[0187] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. 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 of ions between the positive and negative electrodes. A secondary battery may also include a separator, positioned between the positive and negative electrodes, primarily to prevent short circuits while allowing ions to pass through. Alternatively, a solid electrolyte membrane can be used between the positive and negative electrode layers to conduct active ions and isolate the positive and negative electrodes, thus preventing short circuits.

[0188] In this application, unless otherwise specified, "electrode active material layer" includes at least one of the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive active material layer or the negative active material layer. It is understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material. In this application, "electrode active material layer" may also be referred to as "active material layer," "positive active material layer" may also be referred to as "positive active layer," and "negative active material layer" may also be referred to as "negative active layer."

[0189] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions. When a battery cell or secondary battery is charged, active ions are extracted from the positive electrode and inserted into the negative electrode via the electrolyte; conversely, when a battery cell or secondary battery is discharged, active ions are extracted from the negative electrode and inserted into the positive electrode.

[0190] In this application, the term "negative electrode sheet" includes a negative electrode active layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0191] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0192] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0193] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0194] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0195] In a first aspect of this application, a secondary battery is provided, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material; the primary particles in the positive electrode active material have good uniformity in particle size distribution, and the primary particles in the positive electrode active material have a moderate average particle size. This secondary battery exhibits significantly improved battery life at high voltages.

[0196] In some embodiments, a secondary battery is provided, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material;

[0197] In the particle size distribution curve of primary particles in the positive electrode active material, the half-peak width is denoted as W. H Satisfying W H ≤2.5μm;

[0198] The average particle size of the primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3μm≤D1≤3μm.

[0199] In this application, unless otherwise specified, "primary particles" in the positive electrode active material refer to the basic particle unit in the positive electrode active material. It is understood that primary particles exist in the positive electrode active material. In the positive electrode active material, primary particles can exist in a non-agglomerated state, or multiple primary particles can form aggregates. Non-agglomerated primary particles can be called "non-agglomerated primary particles," and aggregates formed by multiple primary particles can be called "secondary particles."

[0200] In some embodiments of this application, the positive electrode active material includes non-agglomerated primary particles.

[0201] The purpose of some embodiments of this application is to reduce the agglomeration ratio of primary particles, that is, to increase the proportion of non-agglomerated primary particles and reduce the proportion of secondary particles.

[0202] In this application, unless otherwise specified, in the "particle size distribution curve of primary particles in positive electrode active material", the horizontal axis corresponds to the particle size of primary particles in positive electrode active material, and the vertical axis corresponds to the frequency of occurrence of each particle size or the proportion of the number of primary particles in the statistics. Unless otherwise specified, "particle size of primary particles" refers to the maximum diameter of primary particles in each direction.

[0203] Unless otherwise stated in this application, the statistical range of primary particles in the "particle size distribution curve of primary particles in positive electrode active material" includes both non-agglomerated and agglomerated primary particles. Taking a positive electrode active material that includes both non-agglomerated primary particles and secondary particles as an example, the statistical range of the "particle size distribution curve of primary particles in positive electrode active material" includes both the particle size of non-agglomerated primary particles and the particle size of primary particles in secondary particles.

[0204] In this application, unless otherwise specified, the "half-peak width" in the "particle size distribution curve of primary particles in the positive electrode active material" corresponds to the half-peak width of the main peak. Unless otherwise specified, the "main peak" refers to a peak whose percentage of the integrated area under the peak relative to the sum of the integrated areas of the curve exceeds 50%, and can be further selected as a peak whose percentage of the integrated area under the peak relative to the sum of the integrated areas of the curve is 80% to 100%. When the particle size distribution curve of primary particles in the positive electrode active material is a single-peak curve, that single peak is the main peak.

[0205] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

[0206] In this application, unless otherwise specified, in the "particle size distribution curve of primary particles in positive electrode active material", "half-peak width" refers to the width between the two particle size boundaries corresponding to half the peak height of the distribution curve. The "half-peak width in the particle size distribution curve of primary particles in positive electrode active material" can be denoted as "W". H The half-width at half-maximum (HWHM) reflects the concentration of the primary particle size distribution. The smaller the HWHM value, the narrower the particle size distribution, the better the particle size uniformity, and the more concentrated the particle size distribution. Conversely, the larger the HWHM value, the wider the particle size distribution, the greater the particle size difference, and the more particles deviating from the average particle size, with a higher proportion of smaller and larger primary particles.

[0207] The particle morphology of the positive electrode active material can be used to statistically analyze the particle size and distribution of primary particles in the positive electrode active material, and a "particle size distribution curve of primary particles in the positive electrode active material" can be plotted. The particle morphology of the positive electrode active material can be obtained using scanning electron microscopy (e.g., ZEISS Sigma 300, JEOL scanning electron microscope, Axia Chemi SEM scanning electron microscope, etc.). The sample to be tested can be obtained by laying a powder sample of the positive electrode active material on conductive adhesive. Non-limitingly, SEM testing can refer to JY / T(001)-1996. One or more regions are randomly selected in the sample to be tested for scanning, and based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed. Non-limitingly, the magnification of a single scanned region can be, for example, 1000X, but is not limited to this. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning.

[0208] Unless otherwise specified, based on the particle morphology image of the positive electrode active material, the "particle size of primary particles in the positive electrode active material" is taken as the maximum diameter of the primary particles in each of the two dimensions in the morphology image. For example, the maximum diameter of the primary particles in each of the two dimensions in the SEM image can be taken.

[0209] Without limitation, the particle size distribution curve of primary particles in the positive electrode active material can be plotted and analyzed using the LIBMAS lithium-ion battery material microscopic intelligent analysis system.

[0210] In this application, the test sample of the "positive electrode active material" in a secondary battery can be obtained by disassembling the battery, removing the positive electrode sheet, and extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted powder sample is then dried to obtain a powder sample. The obtained powder sample can be used for SEM testing or other tests, such as laser particle size analysis. Furthermore, the powder material extracted from the positive electrode active layer can be sintered to remove organic components, thereby obtaining a powder sample of the positive electrode active material.

[0211] For example, the preparation of powder samples of positive electrode active materials can be carried out by the following method: disassemble the battery, take out the positive electrode sheet, soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape the powder material of the positive electrode active layer, soak the powder material extracted from the positive electrode active layer with a solvent (such as N-methylpyrrolidone (NMP) etc.) to dissolve organic components such as binders in the solvent (ultrasonic dispersion and other methods can also be combined to promote dissolution), wash and filter, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collect the centrifuged precipitate to obtain the test powder of positive electrode active material.

[0212] In this application, unless otherwise specified, the statistical range of primary particles referred to as "average particle size (which can be denoted as D1)" is the same as that of "particle size distribution curve of primary particles in the positive electrode active material," including non-agglomerated primary particles and primary particles in any secondary particles that may exist. Taking the positive electrode active material as an example where both non-agglomerated primary particles and secondary particles are present, the statistical range of "average particle size of primary particles in the positive electrode active material" includes both the particle size of non-agglomerated primary particles and the particle size of primary particles in secondary particles.

[0213] The average particle size of primary particles in the positive electrode active material can be obtained by the following method: Obtain a SEM scan image of the positive electrode active material using the method described above. Randomly select one or more regions in the sample to be tested for scanning. At a certain magnification, statistically analyze the particle size of each primary particle within the scanned region, and then calculate the average particle size of the statistically analyzed primary particles. Non-limitingly, the magnification of a single scanned region can be, for example, 1000X, but is not limited to this. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning.

[0214] In the positive electrode active material of secondary batteries, primary particles are the basic unit of particles.

[0215] For the positive electrode active materials of traditional rechargeable batteries, on the one hand, small-sized, large-specific-surface-area non-agglomerated primary particles are prone to large interfacial side reactions, which are easily amplified under high voltage, affecting battery life at high voltage, such as cycle and / or storage life. On the other hand, secondary particles in traditional positive electrode active materials are usually agglomerated from smaller nanoscale primary particles. Due to the relatively small contact area between adjacent primary particles, secondary particles are prone to cracking under stress at high voltage, forming fresh interfaces. This accelerates electrolyte consumption during high-voltage cycling and / or storage, thus deteriorating battery life.

[0216] In the secondary battery provided in the first aspect of this application, the half-width (W) of the peak value in the particle size distribution curve of the primary particles in the positive electrode active material is controlled. H Within the aforementioned range, the particle size distribution of primary particles in the positive electrode active material is made relatively uniform. Further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned range results in primary particles with relatively large micron-sized dimensions. This reduces, on the one hand, the content of small-sized, large-specific-surface-area non-agglomerated primary particles, significantly suppressing interfacial side reactions of the positive electrode active material under high voltage. On the other hand, when secondary particles formed by the agglomeration of primary particles exist in the positive electrode active material, controlling the average particle size and particle size distribution of the primary particles within the aforementioned range allows the secondary particles to have relatively large micron-sized dimensions. The relatively large micron-sized particles allow for a larger contact area between the primary particles in the secondary particles, resulting in stronger bonding between the primary particles under high voltage. This reduces the risk of cracking of the positive electrode active material under high voltage, decreases the generation of fresh interfaces, and slows down electrolyte consumption during high-voltage cycling and / or storage. Through these multiple effects, interfacial side reactions under high voltage can be significantly suppressed, reducing the risk of cracking of the positive electrode active material under high voltage, improving the structural stability of the positive electrode active material, and slowing down electrolyte consumption during high-voltage cycling and / or storage. Consequently, the battery life of the secondary battery under high voltage can be significantly improved.

[0217] The improvement described in any part of the context of this application is not intended to be limited by any theoretical constraints.

[0218] In this application, unless otherwise specified, "high voltage" means a voltage greater than or equal to 4.2V. Non-limiting examples of "high voltage" include 4.3V, 4.4V, 4.5V, etc.

[0219] In some implementations, W H ≤2.5μm, optionally, 1μm≤W H ≤2.5μm, and further optionally, 1.2μm≤W H ≤2.5μm. WH W is the half-maximum width of the particle size distribution curve of primary particles in the positive electrode active material. Non-limitingly, W H It can also be any of the following values ​​or a range consisting of any two of the following values: 1μm, 1.1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2.0μm, 2μm, 2.2μm, 2.4μm, 2.5μm, etc.

[0220] In some embodiments, 1.3 μm ≤ D1 ≤ 3 μm; optionally, 1.4 μm ≤ D1 ≤ 2.5 μm; further optionally, 1.5 μm ≤ D1 ≤ 2.5 μm; and even more optionally, 1.5 μm ≤ D1 ≤ 2.4 μm. D1 is the average particle size of the primary particles in the positive electrode active material. Non-limitingly, D1 can also be any of the following values ​​or a range selected from any two of the following values: 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0221] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0222] (ta1)W H ≤2.5μm, optionally, 1μm≤W H ≤2.5μm, and further optionally, 1.2μm≤W H ≤2.5μm;

[0223] (ta2) 1.3μm≤D1≤3μm, optionally, 1.4μm≤D1≤2.5μm, further optionally, 1.5μm≤D1≤2.5μm, and even further optionally, 1.5μm≤D1≤2.4μm.

[0224] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0225] (tb1)1.2μm≤W H ≤2.5μm;

[0226] (tb2)1.5μm≤D1≤2.5μm.

[0227] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). HBased on the condition that the positive electrode active material meets one or more of the characteristics (ta1), (ta2), (tb1) and (tb2), the distribution width and / or average particle size of the primary particles can be further controlled within a more suitable range, thereby improving the battery life under high voltage.

[0228] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). H Based on the condition that the particle size distribution curve of the primary particles in the positive electrode active material is ≤2.5μm and 1.3μm≤D1≤3μm, the half-maximum width (W) of the primary particles in the positive electrode active material can be further controlled. H Within the aforementioned optional range, it is beneficial to make the particle size distribution of primary particles in the positive electrode active material more uniform. On the one hand, it is more beneficial to reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles and reduce interfacial side reactions under high voltage. On the other hand, it is also more beneficial to improve the structural stability of secondary particles that may exist in the positive electrode active material under high voltage, which can better reduce the generation of fresh interfaces and slow down electrolyte consumption during high-voltage cycling and / or storage. Based on the aforementioned multiple effects, it is beneficial to better improve battery life under high voltage.

[0229] In controlling the positive electrode active material, primary particles have a narrow distribution (e.g., W). H Based on the condition that the average particle size (D1) of the primary particles in the positive electrode active material is ≤2.5μm and 1.3μm≤D1≤3μm, further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned selectable range is beneficial to give the primary particles in the positive electrode active material a more suitable micron-scale size. This is more conducive to reducing the content of small-sized, large-specific-surface-area non-agglomerated primary particles, better reducing interfacial side reactions under high voltage and improving the stability of the CEI film. At the same time, it is also more conducive to improving the structural stability of secondary particles that may exist in the positive electrode active material under high voltage, which can better reduce the generation of fresh interfaces and slow down electrolyte consumption during high-voltage cycling and / or storage. Based on the aforementioned multiple effects, it is beneficial to better improve the battery life under high voltage.

[0230] On the other hand, by suppressing the generation of fresh interfaces under high voltage, it is also beneficial to resist the increase in impedance, suppress the deterioration of battery dynamics, and promote the discharge capacity of positive electrode active materials and improve battery rate performance.

[0231] When the primary particle size in the positive electrode active material is relatively large, the specific surface area of ​​the positive electrode active material is relatively small. This may reduce the intercalation / deintercalation area of ​​active ions, thus affecting the intercalation / deintercalation rate. It also leads to a longer solid-phase transport path for active ions and an increased diffusion time. During high-rate discharge, active ions may not have enough time to fully deintercalate in a short period of time, which may be detrimental to the discharge capacity and rate performance of the positive electrode active material. By controlling the primary particles in the positive electrode active material to have a suitable micron-scale size (e.g., 1.3μm≤D1≤3μm, further such as 1.4μm≤D1≤2.5μm, and even further such as 1.5μm≤D1≤2.4μm), it is beneficial to achieve good discharge capacity and rate performance of the positive electrode.

[0232] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve. In this case, the half-peak width (WHM) of this single peak is the same as the half-peak width (WHM) of the main peak.

[0233] By controlling the particle size distribution curve of the primary particles in the positive electrode active material to be a single-peak curve, it is beneficial to improve the uniformity of the particle size distribution of the primary particles in the positive electrode active material.

[0234] In this application, the D of the positive electrode active material is... v The ratio of 50 to the average particle size (D1) of the primary particles in the positive electrode active material is denoted as R1.

[0235] In some implementations, 1 ≤ R1 ≤ 3.

[0236] In some implementations, 1.5 ≤ R1 ≤ 2.2.

[0237] Without limitation, R1 can also be any of the following values ​​or a range consisting of any two of the following values: 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.0, 2.1, 2.2, 2.4, 2.5, 2.6, 2.8, 3, etc.

[0238] In the context of this application, the volumetric cumulative distribution particle size D can be used. v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, referring to the particle size corresponding to the cumulative volume distribution percentage of the material reaching N%, where the particle size is less than or equal to D. v N's volume percentage is N%. D v N can be obtained from the volumetric cumulative distribution curve of the material particles. Unless otherwise specified, the volumetric cumulative distribution curve is accumulated from zero on the smaller particle size side. Let D... v 90. D v 50. D v Example 10 will be used for illustration. Unless otherwise stated in this application, D v90 refers to the particle size corresponding to a cumulative volume distribution percentage of 90% for a material. This parameter indicates that the particle size of 90% of the material's volume is less than or equal to D. v 90, and particles accounting for 10% of the material volume have a particle size greater than D. v 90. Unless otherwise stated in this application, D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. This parameter indicates that the particle size of 50% of the material's volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. Unless otherwise stated in this application, D v 10 refers to the particle size corresponding to a cumulative volume distribution percentage of 10% in the material. This parameter indicates that the particle size of 10% of the material volume is less than or equal to D. v 10, and the particle size of 90% of the material volume is greater than D. v 10. Those skilled in the art will understand D v 90. D v 50 and D v The meaning of 10 can be determined using instruments and methods known in the field. For example, particle size distribution can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd. (UK). Furthermore, for equipment models such as the Malvern 2000 laser particle size analyzer, the standard procedure GB / T19077-2016 / ISO 13320:2009 can be referenced for testing.

[0239] In some implementations, the D of the positive electrode active material can be tested using the following method. v 50. A Malvern 2000 (MasterSizer 2000) laser particle size analyzer can be used. Refer to the standard procedure: GB / T19077-2016 / ISO 13320:2009. The detailed test procedure includes: taking an appropriate amount of the sample to be tested, adding 20mL–30mL of solvent (to ensure the sample concentration in the injection cell meets the 8%–12% light-blocking requirement), and ultrasonically treating for 5 minutes (53kHz / 120W) to fully disperse the sample; adding the ultrasonically dispersed sample to the injection cell, and starting the test after the sample has stabilized for 5–10 seconds; recording the data after the test. Non-limiting examples of solvents include deionized water and pure water. To avoid agglomeration during the drying process affecting the particle size test, a washed and moistened sample can be used for dispersion testing, and anhydrous ethanol can be used for washing.

[0240] It's understandable, various Dv N is a statistical parameter representing the particle size of dispersible particles in the material. A non-agglomerated particle and a secondary particle are each counted as one dispersible particle. However, some non-agglomerated primary particles that are identifiable on SEM images may slightly agglomerate during testing; these slightly agglomerated primary particle clusters may be counted as one dispersible particle.

[0241] By using the D of the positive electrode active material v 50 (can be written as D) v 50 A The ratio of the average particle size (D1) of the primary particles in the positive electrode active material to the average particle size (R1 = D) v 50 A Controlling / D1) within the aforementioned range helps to make the median particle size of the positive electrode active material particles close to the average particle size of the primary particles, which are the basic unit of particles. This helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and reduce the content of secondary particles, which are agglomerates of primary particles. Correspondingly, it increases the proportion of non-agglomerated primary particles. Since there is no interface between primary particles in secondary particles inside the non-agglomerated primary particles, they can better resist volume stress changes and cracking risks under high voltage. This makes the positive electrode active material have better structural stability under high voltage, which is more conducive to improving battery life under high voltage.

[0242] In some embodiments, the positive electrode active material comprises non-agglomerated primary particles.

[0243] In some embodiments, the positive electrode active material may include, or may not include, secondary particles in addition to non-agglomerated primary particles.

[0244] In this application, the mass percentage of non-agglomerated primary particles in the positive electrode active material is denoted as f. M The proportion of non-agglomerated primary particles in the positive electrode active material is denoted as f. N .

[0245] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0246] (tc1)40%≤f M ≤100%, optional is 50%≤f M <100%, further optional is 55% ≤ f M <100%, or further, 60% ≤ f M <100%, or further, 80% ≤ f M <100%;

[0247] (tc2)60%≤f N <100%, can be selected as 80%≤f N <100%, further optional is 90% ≤ f N <100%.

[0248] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0249] (td1)55%≤f M ≤100%;

[0250] (td2)80%≤f N ≤100%.

[0251] In some implementations, 40% ≤ f M ≤100%, or 55%≤f M <100%, further optional is 80% ≤ f M <100%. Without limitation, f M It can also be any of the following percentages or a range selected from any two of the following percentages: 40%, 45%, 50%, 55%, 60%, 70%, 80%, 90%, 95%, 100%, etc. In some embodiments, 50% ≤ f M ≤100%, optional is 60%≤f M <100%.

[0252] In some implementations, 60% ≤ f N ≤100%, optional is 80%≤f N <100%, further optional is 90% ≤ f N <100%. Without limitation, f N It can also be any of the following percentages or a range selected from any two of the following percentages: 60%, 70%, 80%, 90%, 95%, 100%, etc.

[0253] In this application, unless otherwise stated, "the mass percentage (f) of non-agglomerated primary particles in the positive electrode active material" M ")" and "the proportion of non-agglomerated primary particles in the positive electrode active material (f)" N The numbers ")" all reflect the content of non-agglomerated primary particles in the positive electrode active material. M and f N The higher the value, the more non-agglomerated primary particles there are, and correspondingly, the fewer secondary particles.

[0254] By measuring the mass ratio (f) of non-agglomerated primary particles in the positive electrode active materialM The proportion of non-agglomerated primary particles in the positive electrode active material (f) N By controlling one or two of the above-mentioned parameters within the specified range, the proportion of non-agglomerated primary particles can be controlled within a more suitable range, enabling the positive electrode active material to better resist volume stress changes and cracking risks under high voltage, thus exhibiting better structural stability and further improving battery life under high voltage.

[0255] Non-limitingly, the "proportion of non-agglomerated primary particles in the positive electrode active material" can be obtained through statistical analysis of SEM scan images of the positive electrode active material. One or more regions are randomly selected for scanning tests. The number of non-agglomerated primary and secondary particles within the scanned region is counted, and the proportion of non-agglomerated primary particles is calculated as the test value of the "proportion of non-agglomerated primary particles in the positive electrode active material." The magnification of a single scanned region can be from 1000X to 3000X, for example, 1000X, 2000X, 3000X, etc., but is not limited to the aforementioned magnification. For example, a magnification of 1000X can be used. The number of particles in the positive electrode active material being counted can be greater than or equal to 2000, but is not limited to the aforementioned number.

[0256] As an example, the particle size range of primary particles and secondary particles can be obtained from the SEM scan of the positive electrode active material. The particle size and frequency of occurrence of non-agglomerated primary particles and secondary particles (which act as agglomerates) can then be statistically analyzed to obtain the "particle size distribution curve of the positive electrode active material." Alternatively, a laser particle size analyzer can be used to obtain the "particle size distribution curve of the positive electrode active material." In this application, unless otherwise specified, the horizontal axis of the "particle size distribution curve of the positive electrode active material" corresponds to the particle size of non-agglomerated primary particles or secondary particles in the positive electrode active material, and the vertical axis corresponds to the frequency of occurrence of each particle size or the proportion of the statistically analyzed particles. The particle statistical range of the "particle size distribution curve of the positive electrode active material" includes non-agglomerated primary particles and any possible secondary particles. Taking the example that the positive electrode active material includes both non-agglomerated primary and secondary particles, the statistical range of the "particle size distribution curve of the positive electrode active material" includes both the particle size of non-agglomerated primary particles and the particle size of secondary particles. Furthermore, by combining elemental analysis (such as EDS), the mass percentage (f) of non-agglomerated primary particles in the positive electrode active material can be obtained. M ).

[0257] In some embodiments, the positive electrode active material includes non-agglomerated primary particles and secondary particles.

[0258] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0259] (te1)80%≤f M <100%;

[0260] (te2)90%≤f N <100%.

[0261] Without restriction, f M It can be greater than or equal to M min And less than 100%, M min It can be any of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, etc.

[0262] Without restriction, f N It can be greater than or equal to N min And less than 100%, N min It can be any of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc.

[0263] By measuring the mass ratio (f) of non-agglomerated primary particles in the positive electrode active material M The proportion of non-agglomerated primary particles in the positive electrode active material (f) N If one or two of the above conditions are controlled within a higher range, and there are still agglomerated primary particles in the positive electrode active material, the proportion of non-agglomerated primary particles can be controlled within a higher range, which is more conducive to improving the structural stability of the positive electrode active material under high voltage, and thus more conducive to improving the battery life under high voltage.

[0264] In some embodiments, the D of the positive electrode active material v 50 is 2μm to 6μm.

[0265] In some embodiments, the D of the positive electrode active material v 50 is 2.8μm to 4.5μm.

[0266] Non-limiting, the D of the positive electrode active material v 50 can also be any of the following values ​​or a range consisting of any two of the following values: 2μm, 2.1μm, 2.2μm, 2.4μm, 2.5μm, 2.6μm, 2.8μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.2μm, 5.4μm, 5.5μm, 5.6μm, 5.8μm, 6μm, etc.

[0267] The half-width (W) of the primary particle size distribution curve in the synergistically controlled positive electrode active material H Based on the average particle size (D1) of the primary particles in the positive electrode active material, further improvements are made to the D1 of the positive electrode active material. v Controlling the 50 within the aforementioned range helps to make the particle size in the positive electrode active material more appropriate, which helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and can increase the proportion of non-agglomerated primary particles. Since there is no interface between primary particles in the secondary particles inside the non-agglomerated primary particles, it can better resist volume stress changes and cracking risks under high voltage, so that the positive electrode active material has better structural stability under high voltage and can better improve battery life under high voltage.

[0268] Through the D of the positive electrode active material v Further control of 50 can further reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles in the positive electrode active material, which is more conducive to reducing interfacial side reactions under high voltage, and thus more conducive to improving battery life under high voltage.

[0269] On the other hand, by using the D of the positive electrode active material v Controlling the content of 50 within the aforementioned range also helps to control the content of large-diameter secondary particles formed by the agglomeration of primary particles to be low. Therefore, the problem of large-diameter secondary particles in agglomeration cracking under high voltage, which leads to the formation of fresh interfaces, is suppressed. This helps to reduce the increase in impedance caused by the formation of fresh interfaces and improves the battery dynamic performance.

[0270] In some embodiments, the SPAN value of the positive electrode active material is 0.7 to 1.8; wherein, SPAN = (D v 90-D v 10) / D v 50.

[0271] In some implementations, the SPAN value of the positive electrode active material is 0.85 to 1.35.

[0272] In a non-limiting manner, the SPAN of the positive electrode active material may also be any of the following values ​​or selected from any two of the following values: 0.7, 0.75, 0.8, 0.80, 0.85, 0.90, 0.9, 0.95, 1.0, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, etc.

[0273] In this application, unless otherwise specified, the SPAN value of the positive electrode active material is calculated using the following formula: SPAN = (D v 90-D v 10) / Dv 50. SPAN indicates the degree of particle size dispersion. The higher the SPAN value, the wider the particle size distribution of the material.

[0274] By controlling the SPAN value of the positive electrode active material within the aforementioned range, it is beneficial to make the particle size in the positive electrode active material more uniform and the particle size distribution narrower. This helps to reduce the content of small-sized non-agglomerated primary particles, reduce interfacial side reactions under high voltage, and also helps to reduce the content of large-sized secondary particles. This reduces the negative impact of secondary particle cracking under high voltage on battery life. Through the aforementioned multiple effects, it is beneficial to significantly improve battery life under high voltage.

[0275] The half-width (W) of the peak in the particle size distribution curve of primary particles in the positive electrode active material. H Based on the average particle size (D1) of the primary particles in the positive electrode active material, the D of the positive electrode active material can be further controlled. v 50 (denoted as D) v 50 A ), D of positive electrode active material v One or more parameters, such as the ratio of 50 to D1 (R1) and the SPAN value of the positive electrode active material, can better control the particle size and particle size distribution of primary particles in the positive electrode active material, as well as the proportion of non-agglomerated primary particles (f). N One or more parameters, such as the agglomeration ratio of primary particles, the particle size and particle size distribution of the positive electrode active material, can better improve battery life under high voltage. However, this is not limited to the aforementioned theories. For example, it can also achieve one or more of the following: more favorable reduction of the contact area between the positive electrode active material and the electrolyte; more favorable reduction of the occurrence of positive electrode-electrolyte interface side reactions under high voltage; more favorable reduction of metal dissolution from the positive electrode; and more favorable improvement of the structural stability of the positive electrode active material under high voltage. For example, when the positive electrode active material contains manganese, it also helps to reduce manganese dissolution.

[0276] In some embodiments, the positive electrode active material includes a lithium composite metal oxide, which includes lithium, non-lithium metal elements, and oxygen; the non-lithium metal elements include transition metal elements.

[0277] In this application, unless otherwise specified, "lithium complex metal oxide" refers to a positive electrode active material comprising lithium, non-lithium metal elements, and oxygen. Typically, the non-lithium metal elements in lithium complex metal oxides include transition metal elements; therefore, lithium complex metal oxides can also be called "lithium transition metal oxides."

[0278] In this application, "non-lithium metal element" refers to a metal element that is not lithium.

[0279] In some embodiments, in the lithium composite metal oxide, the molar percentage of the transition metal element relative to the non-lithium metal element is 90% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0280] In some embodiments, the lithium composite metal oxide may include one or more of lithium nickel-based oxides, lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and modified versions of any of the aforementioned cathode active materials; wherein the modified version may include one or more of doping elements and coating elements.

[0281] It is understandable that lithium nickel-based oxides include lithium, nickel, and oxygen.

[0282] Introducing lithium nickel-based oxides into the positive electrode active material can help improve energy density.

[0283] Introducing lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and other cathode active materials into the cathode active material can improve the structural stability of the cathode active material under high voltage, thereby extending the battery life under high voltage, including cycle and / or storage life.

[0284] In this application, unless otherwise specified, "a modified positive electrode active material" includes the positive electrode active material itself and the modifying element. Furthermore, the modifying element may exist as a dopant element, a coating element, or a combination of a dopant element and a coating element. Unless otherwise specified, "a modified positive electrode active material" still falls within the scope of positive electrode active materials.

[0285] In this application, unless otherwise specified, "doping element" in positive electrode active material refers to a modifying element doped into the positive electrode active material; unless otherwise specified, "coating element" in positive electrode active material refers to a positive electrode active material comprising a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, wherein the coating element is a modifying element located in the coating layer. As a non-limiting example, in positive electrode active material, "the modifying element exists in a combination of doping element and coating element" means that the positive electrode active material comprises a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, at least a portion of the modifying element is doped into the positive electrode active particle body, and at least a portion of the modifying element is also contained in the coating layer. Both the doping modification method of introducing doping elements and the coating modification method of introducing coating elements can adopt or refer to existing modification methods in the art, including but not limited to the selection of element type, doping amount, and coating amount. In some embodiments, the positive electrode active particle body can be a positive electrode active material or a doped modified version of a positive electrode active material. In some embodiments, the doping element may include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn, and Sb; in some embodiments, the doping element may include one or both of Zr and W. In some embodiments, the coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W, and Na; in some embodiments, the coating element may include Ti.

[0286] In this application, unless otherwise specified, "lithium nickel-based oxide" refers to a lithium complex metal oxide comprising lithium, nickel, and oxygen. It is understood that a lithium nickel-based oxide is a lithium complex metal oxide in which the non-lithium metal element includes at least nickel. Non-limitingly, lithium nickel-based oxides may include one or more of lithium nickel cobalt manganese-based oxides and lithium nickel cobalt aluminum-based oxides. Unless otherwise specified, lithium nickel-based oxides have a layered structure.

[0287] In some embodiments, lithium nickel-based oxides include lithium nickel cobalt-based oxides. In this application, unless otherwise specified, "lithium nickel cobalt-based oxide" refers to a lithium composite metal oxide comprising lithium, nickel, cobalt, and oxygen, specifically a lithium nickel-based oxide containing cobalt. The non-lithium metal elements included are at least nickel and cobalt. The introduced cobalt element can reduce cation mixing, enhance material structural stability, and improve rate performance.

[0288] In some embodiments, lithium nickel-based oxides include those with the chemical formula Li x (Ni a Co b M' c M” d)O 2-e The lithium composite metal oxide, where 0.6 ≤ x ≤ 1.2, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d < 1 (optionally, 0 < d < 1), a + b + c + d = 1, -0.1 ≤ e ≤ 0.4 (optionally, -0.1 ≤ e ≤ 0.1). M' may include at least one of Mn and Al. M'' may include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, and Ta. Without limitation, the value or range of x may refer to the value or range of x2. The value of a may refer to the value or range of q1, q2, or q3. Without limitation, the value of b may refer to the value or range of q4. Without limitation, the value of c may refer to the value or range of q5. Without limitation, (2 - e) may refer to the value or range of x3. In some of these embodiments, M' is the Mn element.

[0289] In this application, unless otherwise specified, "lithium-rich manganese-based cathode material" refers to a cathode active material containing Li2MnO3, and may also optionally contain LiMO2, where M is a transition metal element. Without limitation, M may include one or more of transition metal elements such as Ni, Co, Mn, Cr, Fe, Al, Nb, Zr, Mo, Ta, etc. The layered lithium-rich manganese-based cathode material has advantages such as high specific capacity, high voltage platform, and easy synthesis. In some embodiments, the chemical formula of the layered lithium-rich manganese-based cathode material is y(Li2MnO3)·(1 - y)(LiMO2), where 0 < y ≤ 1, optionally, 0 < y < 1. In some embodiments, the lithium-rich manganese-based cathode material is a layered lithium-rich manganese-based cathode material.

[0290] In this application, unless otherwise specified, "spinel lithium manganate" refers to LiMn2O4 with a spinel structure, which has a three-dimensional tunnel structure, can provide a fast diffusion channel for lithium ions, and has advantages such as good rate performance and low cost, and can operate under some high voltage conditions. The precursor for preparing spinel lithium manganate can be a layered structure.

[0291] In some embodiments, the lithium composite metal oxide includes a lithium nickel-based oxide. The lithium nickel-based oxide contains Li element, non-lithium metal element, and O element. The non-lithium metal element includes Ni element. The lithium nickel-based oxide satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

[0292] (t1) The atomic molar ratio of Ni element to the non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1;

[0293] (t2) The lithium nickel-based oxide contains Ni and Li elements with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.6 ≤ x2 ≤ 1.2;

[0294] (t3) The lithium nickel-based oxide contains Ni and O elements with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.6 ≤ x3 ≤ 2.1.

[0295] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics (any numerical parameter in the following characteristics may also be selected from any suitable value or range in the context):

[0296] (i) 0.5 ≤ q1 ≤ 0.99;

[0297] (ii) 0.5 ≤ q2 ≤ 0.99;

[0298] (iii) 0.5 ≤ q3 ≤ 0.99;

[0299] (iv) The lithium nickel-based oxide contains Co element, and the atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3, optionally, 0.02 ≤ q4 ≤ 0.3;

[0300] (v) The lithium nickel-based oxide contains Mn element, and the atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5, optionally, 0.01 ≤ q5 ≤ 0.5;

[0301] (vi) The mass percentage of the lithium nickel-based oxide in the lithium composite metal oxide is 80% - 100%.

[0302] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics (any numerical parameter in the following characteristics may also be selected from any suitable value or range in the context):

[0303] (ti) 0.5 ≤ q1 ≤ 0.99, optionally, 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99;

[0304] (tii) 0.5 ≤ q2 ≤ 0.99, optionally, 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99;

[0305] (tiii) 0.6 ≤ x2 ≤ 1.2, optionally, 0.8 ≤ x2 ≤ 1.1;

[0306] (tiv) 0.5 ≤ q3 ≤ 0.99, optionally, 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99;

[0307] (tv) 1.6 ≤ x3 ≤ 2.1, optionally, 1.8 ≤ x3 ≤ 2.06;

[0308] (tvi) The lithium nickel-based oxide contains Co element, 0 < q4 ≤ 0.3, optionally, 0.02 ≤ q4 ≤ 0.3, further optionally, 0.05 ≤ q4 ≤ 0.2;

[0309] (tvii) The lithium nickel-based oxide contains Mn element, 0 < q5 ≤ 0.5, optionally, 0.01 ≤ q5 ≤ 0.5, further optionally, 0.02 ≤ q5 ≤ 0.38;

[0310] (tviii) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide is 90% - 100%.

[0311] Non-limitingly, q1, q2, and q3 can each independently be any one of the following values, or selected from the range formed by any two of the following values: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc.

[0312] Non-limitingly, x2 can be any one of the following values, or selected from the range formed by any two of the following values: 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, etc.

[0313] Non-limitingly, x3 can be any one of the following values, or selected from the range formed by any two of the following values: 1.6, 1.7, 1.8, 1.9, 2, 2.05, 2.06, 2.08,​​​​​Without limitation, q5 can be any one of the following values, or a range selected from any two of the following values: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.35, 0.36, 0.38, 0.4, 0.42, 0.44, 0.45, 0.46, 0.48, 0.5, etc.

[0316] In some embodiments, 0.5 ≤ q1 ≤ 0.8. In some of these embodiments, 0.5 ≤ q1 ≤ 0.7.

[0317] In some embodiments, 0.5 ≤ q2 ≤ 0.8. In some of these embodiments, 0.5 ≤ q2 ≤ 0.7.

[0318] In some embodiments, 0.5 ≤ q3 ≤ 0.8. In some of these embodiments, 0.5 ≤ q3 ≤ 0.7.

[0319] By controlling the nickel content of the lithium nickel-based oxide in the positive electrode active material to be the aforementioned value, the crystal structure stability of the positive electrode active material at high voltage is better, which is more conducive to improving the battery life at high voltage.

[0320] In some embodiments, 0.7 < q1 ≤ 0.99. In some of these embodiments, 0.8 < q1 ≤ 0.99.

[0321] In some embodiments, 0.7 < q2 ≤ 0.99. In some of these embodiments, 0.8 < q2 ≤ 0.99.

[0322] In some embodiments, 0.7 < q4 ≤ 0.99. In some of these embodiments, 0.8 < q3 ≤ 0.99.

[0323] When the lithium nickel-based oxide in the positive electrode active material has the aforementioned higher nickel content, by adjusting W H and D1 within the aforementioned range, the improvement effect on the battery life at high voltage is more obvious.

[0324] In some embodiments, the lithium composite metal oxide includes one or more of lithium nickel cobalt manganese-based oxides and modified versions of lithium nickel cobalt manganese-based oxides. Non-limitingly, the modified material may include one or more of a dopant element and a coating element; both the doping modification method introducing the dopant element and the coating modification method introducing the coating element can employ or refer to existing modification methods in the art, including but not limited to the selection of element type, doping amount, and coating amount. In some embodiments, the lithium nickel cobalt manganese-based oxide may optionally include a modifying element; further, the modifying element may exist as a dopant element, as a coating element, or as a combination of a dopant element and a coating element.

[0325] In some embodiments, the lithium nickel cobalt manganese-based oxide includes a doping element, which may further include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb.

[0326] In this application, unless otherwise specified, "lithium nickel cobalt manganese-based oxide" refers to a lithium composite metal oxide comprising lithium, nickel, cobalt, manganese, and oxygen, specifically a lithium nickel-based oxide containing cobalt and manganese. The non-lithium metal elements in lithium nickel cobalt manganese-based oxides include nickel, cobalt, and manganese. In this application, unless otherwise specified, lithium nickel cobalt manganese-based oxides used as positive electrode active materials typically have a layered structure.

[0327] In lithium nickel cobalt manganese-based oxides, nickel can increase energy density, cobalt can reduce cation mixing, enhance material structural stability and rate performance, and manganese can stabilize the layered structure of lithium nickel cobalt manganese-based oxide materials, but these roles are not limited to those described above. An example of cation mixing is Li / Ni mixing.

[0328] In lithium nickel cobalt manganese-based oxides, the ratio of the atomic molar ratio of nickel to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Ni / NCM The ratio of the atomic molar ratio of cobalt to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Co / NCM The ratio of the atomic molar ratio of manganese to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Mn / NCM .

[0329] Without limitation, R Ni / NCMIt can be any of the following values, or greater than or equal to any of the following values ​​and less than 1, or selected from a range consisting of any two of the following values: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc. In some embodiments, 0.5 ≤ R Ni / NCM <1. R Ni / NCM For numerical values ​​and the range of options, please refer to q1.

[0330] Without limitation, R Co / NCM It can be any of the following values, or a range selected from any two of the following values: 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, etc. R Co / NCM For numerical values ​​and the range of options, please refer to q4.

[0331] Without limitation, R Mn / NCM It can be any of the following values, or a range selected from any two of the following values: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.35, 0.36, 0.38, 0.4, 0.42, 0.44, 0.45, 0.46, 0.48, 0.5, etc. R Mn / NCM For numerical values ​​and the range of options, please refer to q5.

[0332] By controlling one or more of the nickel, cobalt, and manganese content in the lithium nickel cobalt manganese-based oxide in the positive electrode active material within the aforementioned range, the crystal structure stability of the positive electrode active material under high voltage can be improved, which is more conducive to extending the battery life under high voltage.

[0333] In some embodiments, the positive electrode active material containing lithium composite metal oxide has a moderate primary particle size, narrow particle size distribution, high crystallinity, and low Li / Ni mixing.

[0334] In some embodiments, in lithium nickel cobalt manganese-based oxides, the ratio of the sum of the atomic molar ratios of nickel, cobalt, and manganese to the sum of the atomic molar ratios of non-lithium metal elements is denoted as R. NCM .

[0335] Without limitation, R NCMIt can be 0.9 to 1, can be selected from 0.95 to 1, or can be any of the following values ​​or a range composed of any two of the following values: 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc.

[0336] Non-limitingly, the mass percentage of lithium nickel cobalt manganese-based oxide in lithium composite metal oxide is 80% to 100%, optionally 90% to 100%, or any of the following percentages or selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0337] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed using methods known in the art, including but not limited to the following: inductively coupled plasma atomic emission spectrometry (ICP), X-ray diffraction (XRD), single-crystal X-ray diffraction (SCXRD), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the sample characteristics. ICP can be used for quantitative analysis of the component content in the positive electrode active material.

[0338] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When the positive electrode active material is applied to the positive electrode in a battery system, the Li content in the positive electrode active material at the positive electrode will usually change after charge-discharge cycles. The Li content can be measured in atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material," the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriate modification based on the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0339] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0340] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0341] (tf1) The positive electrode active material includes doping elements, and, without limitation, the doping elements may include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb;

[0342] (tf2) The positive electrode active material includes a coating element located on the particle surface. Non-limitingly, the coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0343] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0344] (tf1') The positive electrode active material includes doping elements, which include one or both of Zr and W;

[0345] (tf2') The positive electrode active material includes coating elements located on the particle surface, including Ti.

[0346] By introducing one or more doping and coating elements into the positive electrode active material, the positive electrode active material can be modified in one or more ways, either through doping or coating. Taking the introduction of doping elements as a non-limiting example, introducing doping elements (such as Zr, W, etc.) can improve the bonding force between transition metal elements and O atoms in the positive electrode active material, thereby improving lattice stability during lithium insertion / extraction and enhancing the stability of the positive electrode active material. Taking the introduction of coating element Ti as an example, it facilitates the formation of an oxide coating layer, hindering direct contact between the electrolyte and the positive electrode material, thus reducing interfacial side reactions.

[0347] In some embodiments, the mass percentage of lithium composite metal oxide in the positive electrode active layer can be 80% to 97%, and optionally 90% to 100%. Non-limitingly, the mass percentage of lithium composite metal oxide in the positive electrode active layer can be any of the following percentages or within a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, etc.

[0348] In some embodiments, the mass percentage of lithium composite metal oxide in the positive electrode active material can be 80% to 100%, and optionally 90% to 100%. Non-limitingly, the mass percentage of lithium composite metal oxide in the positive electrode active material can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0349] In some embodiments, the lithium composite metal oxide includes lithium nickel-based oxide. In some embodiments, the mass percentage of lithium nickel-based oxide in the positive electrode active material can be 80% to 100%, optionally 90% to 100%. Non-limitingly, the mass percentage of lithium nickel-based oxide in the positive electrode active material can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0350] In some embodiments, the lithium composite metal oxide includes lithium nickel cobalt manganese-based oxide. In some embodiments, the mass percentage of lithium nickel cobalt manganese-based oxide in the positive electrode active material can be 80% to 100%, optionally 90% to 100%. Non-limitingly, the mass percentage of lithium nickel cobalt manganese-based oxide in the positive electrode active material can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0351] It is understandable that a secondary battery also includes a negative electrode sheet, which includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material.

[0352] In some embodiments, the negative electrode active material includes one or more of carbon-based and silicon-based materials. In some embodiments, the negative electrode active material includes graphite material. In this application, "graphite material" refers to a negative electrode active material containing graphite, and the graphite material includes at least a graphite bulk. In this application, "graphite bulk" is composed of graphite. The graphite material may include one or more of artificial graphite and natural graphite. In some embodiments, the negative electrode active material includes graphite material, and more specifically, it may be graphite material. Non-limitingly, the mass percentage of graphite material in the negative electrode active material may be 80% to 100%, optionally 90% to 100%, more specifically 97% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 97%, 98%, 99%, 100%, etc.

[0353] In some embodiments, the negative electrode active material includes graphite, and further, the graphite may include one or more of artificial graphite and natural graphite.

[0354] The negative electrode active material in the negative electrode sheet can be one of the aforementioned types, but is not limited to these.

[0355] In some implementations, the secondary battery is a lithium-ion secondary battery.

[0356] In some implementations, the charging cutoff voltage of the secondary battery is greater than or equal to 4.2V.

[0357] In some implementations, the charging cutoff voltage of the secondary battery is greater than or equal to 4.3V.

[0358] In some embodiments, the charging cutoff voltage of the secondary battery is 4.2V to 4.5V, further optionally 4.3V to 4.5V, or any of the following voltages or a range selected from any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc.

[0359] In this application, unless otherwise specified, the "charging cut-off voltage" of a secondary battery has a well-known meaning in the art and is usually marked on battery products. Secondary battery products can operate at voltages equal to or lower than the charging cut-off voltage. Taking a lithium-ion secondary battery as an example, as charging progresses, the battery voltage continuously rises; when the charging cut-off voltage is reached, it indicates that the distribution of lithium ions in the positive and negative electrode materials and the electrochemical equilibrium inside the battery have reached a specific state. If charging continues at a high current, exceeding the charging cut-off voltage, irreversible chemical reactions can easily occur inside the battery.

[0360] In some embodiments, the secondary battery is a lithium-ion secondary battery, and the electrolyte salt may include an electrolyte lithium salt.

[0361] In some implementations, the secondary battery includes a single battery cell.

[0362] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0363] The following is a description of the positive electrode sheet.

[0364] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0365] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0366] As a non-limiting example, the positive current collector has two surfaces that are opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0367] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, 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. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0368] The positive electrode active material may be any positive electrode active material known in the art for use in batteries. These positive electrode active materials may be used alone or in combination of two or more.

[0369] In some embodiments, the positive electrode active material includes a lithium transition metal oxide. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co0.15 Al 0.05 O2.

[0370] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typically, the binder may constitute 0–10 wt% of the weight of the positive electrode active layer, more commonly 0–8 wt%, and even more commonly 1 wt%–5 wt%, based on the total weight of the positive electrode active layer.

[0371] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the weight percentage of the conductive agent in the positive electrode active layer can be 0–10 wt%, more commonly 0–8 wt%, and even more commonly 0–5 wt%, based on the total weight of the positive electrode active layer.

[0372] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, it can include N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 15 mg / cm³. 2 ~35mg / cm 2 The density is measured by the coating surface density on one side. The compacted density of the positive electrode sheet can be 3.0 g / cm³. 3 ~4.2g / cm 3 3.3g / cm³ is an option. 3 ~3.8g / cm 3 .

[0373] The term "compacted density" as used in this application has a meaning well-known in the art and is one of the reference indicators for material energy density. In this application, unless otherwise specified, the compacted density of an electrode sheet refers to the ratio of the mass of the electrode active layer to its volume. The compacted density of a positive electrode sheet refers to the ratio of the mass of the positive active layer to its volume, and the compacted density of a negative electrode sheet refers to the ratio of the mass of the negative active layer to its volume.

[0374] The following is a description of the negative electrode plate.

[0375] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0376] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0377] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0378] 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. In the negative electrode current collector, 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. In the negative electrode current collector, the composite current collector may be formed by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limitingly, in the negative electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0379] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more 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 include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials or substances, 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.

[0380] In some embodiments, the negative electrode active material includes a carbon-based material. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material can be ≥80%, optionally ≥90%, further optionally ≥95%, even more optionally ≥96%, and even more optionally 100%. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material can also be any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or selected from any two of the following percentages: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc. Non-limitingly, the carbon-based material can be one or more of graphite, soft carbon, hard carbon, etc. Graphite can include one or more of artificial graphite and natural graphite. The carbon-based material can include graphite material, and more specifically, graphite material, but is not limited thereto.

[0381] In some embodiments, the negative electrode active material includes carbon-based materials and silicon-based materials. Non-limitingly, the percentage of the total mass of carbon-based and silicon-based materials in the total mass of the negative electrode active material can be ≥80%, optionally ≥90%, further optionally ≥95%, even more optionally ≥96%, and even more optionally 100%. Non-limitingly, the percentage of the total mass of graphite and silicon-based materials in the total mass of the negative electrode active material can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0382] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, the binder may include one or more 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). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0383] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0384] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0385] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density, based on dry weight (excluding solvent), can be 75 g / m². 2 ~220g / m 2 The density is measured by the surface area density of the coating on one side. The compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm³ is an optional value. 3 ~1.8g / cm 3 .

[0386] The electrolyte is described below as an example.

[0387] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0388] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0389] In some embodiments, the electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte may include an electrolyte salt and a solvent.

[0390] The concentration of electrolyte salts in the electrolyte solution is typically 0.5 mol / L to 5 mol / L.

[0391] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Non-limitingly, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0392] In some embodiments, the solvent in the non-aqueous electrolyte may include ethylene carbonate (EC). ), propylene carbonate (PC, propylene carbonate) ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC). One or more of the following: fluoroethylene carbonate (FEC), 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.

[0393] 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.

[0394] The following is an exemplary description of the separator membrane.

[0395] In some embodiments, the secondary battery 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.

[0396] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0397] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 6 μm to 20 μm.

[0398] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0399] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0400] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0401] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0402] 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 5 shows a square battery cell 5 as an example.

[0403] In some embodiments, referring to FIG6, the outer packaging may include a housing 51 and a cover plate 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 cover plate 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. The electrode assembly 52 is immersed in an electrolyte. 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 actual needs.

[0404] In some implementations, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0405] The secondary battery can be either battery device 4 or battery pack 1.

[0406] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0407] Figure 7 shows a battery device 4 as an example. Referring to Figure 7, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0408] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0409] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0410] Figures 8 and 9 illustrate a battery pack 1 as an example. Referring to Figures 8 and 9, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0411] In a second aspect of this application, a method for preparing a positive electrode active material is provided. The obtained positive electrode active material can be used as a positive electrode active material in the secondary battery described in the first aspect of this application, or as a partial raw material for the positive electrode active material in the secondary battery described in the first aspect of this application. The obtained positive electrode active material can also be used to prepare the positive electrode sheet described in the fourth aspect of this application, and can also be used to prepare the secondary battery described in the first aspect of this application.

[0412] It should be noted that the second aspect of this application provides an exemplary method for obtaining positive electrode active materials, but does not limit the method of obtaining positive electrode active materials. It is understood that those skilled in the art can also use other methods to obtain the positive electrode active materials involved in the embodiments of this application. For example, they can be obtained by sieving non-agglomerated primary particles within a specific size range from commercially available or prepared positive electrode active materials.

[0413] In some embodiments, a method for preparing a positive electrode active material is provided, comprising sequentially performed steps S100, S200, and S300:

[0414] S100: Mix the solid precursor of the positive electrode active material and the lithium source to obtain the initial mixture;

[0415] S200: The initial mixture undergoes its first sintering and first crushing.

[0416] S300: A second sintering and a second crushing process are performed to prepare the positive electrode active material.

[0417] In some implementations, the temperature at which the first sintering is performed is higher than the temperature at which the second sintering is performed.

[0418] Unless otherwise specified, step S300 is performed after step S200.

[0419] In some embodiments, for the prepared positive electrode active material, the half-maximum width (W) of the primary particles in the particle size distribution curve of the positive electrode active material is... H Satisfying W H ≤2.5μm; the average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0420] The solid precursor of the positive electrode active material can be prepared using conventional methods in the art, based on the elemental composition of the positive electrode active material, by adjusting the preparation parameters to obtain the solid precursor of the positive electrode active material with the properties required in this application. As an example, for those skilled in the art, adjusting the preparation parameters to adjust the D of the solid precursor of the positive electrode active material... v 50. Obtaining the desired target values ​​for parameters such as specific surface area and SPAN value is achievable. Methods including, but not limited to, co-precipitation can be used.

[0421] By subjecting the initial mixture, including a solid precursor of positive electrode active material and a lithium source, to multiple sintering and crushing processes, the solid precursor can be lithiated in the first sintering to form the target crystal structure of the positive electrode active material. The first crushing can reduce particle agglomeration. The second sintering can achieve particle morphology repair, reduce defects, and promote the fusion of fine particles. The second crushing can further reduce particle agglomeration. Thus, a positive electrode active material with moderate particle size and uniform particle size distribution can be prepared.

[0422] It is generally known to those skilled in the art that sintering and crushing are both conventional processes for preparing positive electrode active materials. Typically, sintering is used to transform the precursor into the target crystal, and sintering can be carried out using a muffle furnace. Commonly used crushing equipment includes, but is not limited to, jaw crushers, roll crushers, and air jet mills; among them, jaw crushers and roll crushers can be used for pre-crushing or coarse crushing, while air jet mills can be used for fine crushing. An air jet mill is a physical crushing device that utilizes the energy of a high-speed airflow to cause collisions and friction between material particles to achieve fine crushing. This equipment integrates crushing and classification functions and is commonly used in the preparation of positive electrode active materials. The operation of an air jet mill typically follows a "crushing-classification-collection" process. The main mechanism is as follows: (1) High-pressure gas generates supersonic airflow through nozzles, causing the material to collide at high speed in the crushing chamber and be crushed. This process can break large particles into smaller particles and de-agglomerate agglomerated particles. (2) Then, a high-speed rotating classifying wheel is used to finely classify materials of different sizes. During this process, under the action of centrifugal force and airflow drag, coarse particles are thrown back into the crushing chamber by the classifying wheel and participate in the crushing again until the target fineness is reached. Fine particles that have reached the target fineness enter the subsequent collection system through the gap between the blades of the classifying wheel. (3) In the collection system, the centrifugal force of the cyclone separator is used to initially collect particles of the target fineness. Then, a bag filter is used to intercept any ultrafine powder that may be present for secondary collection, thereby collecting materials that meet the target particle size and have good particle size distribution. Commonly used air jet mills include structural components such as crushing chamber, classifying wheel, and cyclone separator. Models include Shenfei QLM-4.5, etc.

[0423] In some embodiments, the positive electrode active material includes lithium composite metal oxide.

[0424] In some embodiments, the method for preparing the positive electrode active material provided in the second aspect of this application is used to prepare lithium composite metal oxides.

[0425] In some embodiments, the method for preparing lithium composite metal oxides includes sequentially performed steps S100, S200, and S300:

[0426] S100: Mix the solid precursor of the positive electrode active material and the lithium source to obtain the initial mixture;

[0427] S200: The initial mixture undergoes its first sintering and first crushing.

[0428] S300: A second sintering and a second crushing process are performed to prepare the positive electrode active material.

[0429] In this application, the temperature for the first sintering in the method for preparing the positive electrode active material can be denoted as T1, and the temperature for the second sintering can be denoted as T2.

[0430] In some implementations, the temperature (T1) for the first sintering is different from the temperature (T2) for the second sintering.

[0431] In some implementations, the temperature at which the first sintering is performed (T1) is higher than the temperature at which the second sintering is performed (T2).

[0432] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0433] (1) Positive electrode active material includes doped elements, and initial mixture also includes raw materials containing doped elements;

[0434] (2) The positive electrode active material includes coating elements, and the preparation method of the positive electrode active material includes at least one of the first coating step and the second coating step. The first coating step is carried out simultaneously with the second sintering, and the second coating step is achieved by the third sintering after the second crushing.

[0435] Depending on the target composition of the positive electrode active material, one or more of doping elements and coating elements can be selectively introduced during the preparation process. When the positive electrode active material includes doping elements, the initial mixture also includes raw materials containing doping elements; when the positive electrode active material includes coating elements, the preparation method of the positive electrode active material includes at least one of a first coating step and a second coating step.

[0436] In this application, unless otherwise stated, the first coating step is performed simultaneously with the second sintering, and the second coating step is achieved through a third sintering after the second crushing.

[0437] Non-limitingly, the doping element may include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn, and Sb. The raw material containing the doping element may include one or more of oxides, hydroxides, carbonates, and phosphates containing the doping element. The coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W, and Na. The raw material providing the coating element may include one or more of oxides, hydroxides, carbonates, and phosphates containing the coating element.

[0438] In some embodiments, in step S200, the temperature for the first sintering is 900°C to 980°C.

[0439] In some embodiments, in step S300, the temperature for the second sintering is 700°C to 800°C.

[0440] In some embodiments, a method for preparing a positive electrode active material is provided, which includes the following steps: mixing a solid precursor of the positive electrode active material and a lithium source to obtain a preliminary mixture; subjecting the preliminary mixture to a first sintering and a first crushing, and then subjecting it to a second sintering and a second crushing to prepare the positive electrode active material; wherein the temperature (T1) for the first sintering is different from the temperature (T2) for the second sintering.

[0441] In the particle size distribution curve of primary particles in the positive electrode active material, the half-maximum width (W) is... H Satisfying W H ≤2.5μm; the average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0442] The lithium source can be any lithium source known in the art that can be used to prepare lithium-ion active materials. Suitable lithium sources may include, but are not limited to, lithium salts, lithium hydroxide, and their hydrates. Examples of lithium salts may include lithium carbonate.

[0443] In some embodiments, the temperature (T1) for the first sintering can be 900°C to 980°C. Without limitation, T1 can also be any of the following temperatures or a range selected from any two of the following temperatures: 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, etc.

[0444] In some embodiments, the time (t1) for the first sintering can be 5h to 15h. Non-limitingly, t1 can also be any of the following durations or a range selected from any two of the following durations: 5h, 6h, 7h, 8h, 10h, 12h, 14h, 15h, etc.

[0445] In some embodiments, the temperature (T2) for the second sintering can be 700°C to 800°C. Without limitation, T2 can also be any of the following temperatures or a range selected from any two of the following temperatures: 700°C, 720°C, 740°C, 750°C, 760°C, 780°C, 800°C, etc.

[0446] In some embodiments, the time (t2) for the second sintering can be 4h to 12h. Non-limitingly, t2 can also be any of the following durations or a range selected from any two of the following durations: 4h, 5h, 6h, 7h, 8h, 10h, 12h, etc.

[0447] In some embodiments, the second sintering step is performed in the presence of the first coating agent.

[0448] In some embodiments, the preparation method of the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0449] (tg5) The temperature (T1) for the first sintering is 900 °C to 980 °C;

[0450] (tg6) The time (t1) for the first sintering is 5 h to 15 h;

[0451] (tg7) The temperature (T2) for the second sintering is 700 °C to 800 °C;

[0452] (tg8) The time (t2) for the second sintering is 4 h to 12 h;

[0453] (tg9) The step of the second sintering is carried out under the condition of the presence of the first coating agent; non - restrictively, the first coating agent may include one or more of oxides, hydroxides, carbonates and phosphates of the first coating element, and the first coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0454] By controlling one or more parameters in the preparation process within the foregoing ranges, it is beneficial to better regulate the particle size and particle size distribution of the primary particles in the positive electrode active material.

[0455] In some embodiments, after the second crushing, the preparation method of the positive electrode active material further includes the following step S400: performing a third sintering. The temperature for the third sintering can be denoted as T3. The time for the third sintering can be denoted as t3.

[0456] In some embodiments, T3 < T2, that is, the temperature for the third sintering is lower than the temperature for the second sintering. Non - restrictively, T3 can be 300 °C to 600 °C, and can also be any one of the following temperatures or a range composed of any two of the following temperatures: 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, etc.

[0457] In some embodiments, T1 > T2 > T3, that is, the temperatures for the first sintering, the second sintering and the third sintering decrease in sequence.

[0458] In some embodiments, the time (t3) for the third sintering can be 3 h to 10 h. Non - restrictively, t'3 can also be any one of the following durations or a range composed of any two of the following durations: 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 10 h, etc.

[0459] In some embodiments, the preparation method of the positive electrode active material includes a second coating step, which is achieved by a third sintering after the second crushing, and the temperature of the third sintering (T3) is lower than the temperature of the second sintering (T2).

[0460] In some implementations, the third sintering step satisfies one or more of the following conditions:

[0461] The third sintering time for (tg10-i) is 3h to 10h;

[0462] (tg10-ii) The third sintering step is carried out in the presence of the second coating agent; without limitation, the second coating agent may include one or more of the oxides, hydroxides, carbonates and phosphates of the second coating element, and the second coating element may include one or more of Ti, Al, Zr, W and Na.

[0463] By introducing a third sintering process after the second sintering, the cathode active material with moderate particle size and uniform particle size distribution can be further modified as needed. For example, further coating with Ti element facilitates the formation of an oxide coating layer, hindering direct contact between the electrolyte and the cathode material, thereby reducing interfacial side reactions.

[0464] In this application, the product of the first sintering and first crushing in step S200 can be referred to as "the first sintered product".

[0465] In this application, the product of the second sintering and second crushing in step S300 can be referred to as "second-sintered product".

[0466] In some embodiments, in step S300, a sintered product is subjected to a second sintering and a second crushing to prepare a positive electrode active material.

[0467] In some embodiments, the first sintering, the second sintering, and the third sintering can be carried out under oxygen-containing conditions, such as in an oxygen atmosphere or an air atmosphere.

[0468] In some embodiments, in step S300, a calcined product is mixed with a first coating agent, and then subjected to a second sintering and a second crushing to prepare a positive electrode active material.

[0469] In this application, unless otherwise specified, "first coating agent" refers to a coating agent that can be used during the second sintering process, and may also be referred to as "high temperature coating agent".

[0470] In some embodiments, after the second sintering and the second crushing, the sintered product obtained from the second sintering and the second crushing can be mixed with a low-temperature coating agent and then sintered at a low temperature to prepare a positive electrode active material.

[0471] In this application, unless otherwise specified, "low-temperature coating agent" may also be referred to as "second coating agent". In this application, unless otherwise specified, the terms "first" and "second" in "first coating agent" and "second coating agent" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0472] In this application, unless otherwise specified, "low-temperature coating agent" refers to a coating agent that can be used for sintering under low-temperature conditions. Unless otherwise specified, the temperature for low-temperature sintering is lower than the temperature for the second sintering (T2). As a non-limiting example, the temperature for low-temperature sintering can be 300°C to 600°C, optionally 450°C to 550°C, such as 300°C, 350°C, 400°C, 450°C, 460°C, 480°C, 500°C, 520°C, 540°C, 550°C, 600°C, etc., or can be selected from any range of two of the aforementioned temperatures. In some embodiments, the low-temperature coating agent may include a second coating agent.

[0473] In some implementations, by controlling the FWDH of the positive electrode active material solid precursor... (001) D of solid precursors for positive electrode active materials v 50. One or more parameters, such as the specific surface area (BET) of the solid precursor of the positive electrode active material, the SPAN value of the solid precursor of the positive electrode active material, the temperature and time of the first sintering, and the temperature and time of the second sintering, can be used to control the average particle size and particle size distribution characteristics of the primary particles in the positive electrode active material.

[0474] The position of the diffraction peaks in the X-ray diffraction pattern of the solid precursor of the cathode active material can be used to determine the formation of the (001) crystal plane. The solid precursor of lithium nickel cobalt manganese-based oxide cathode active materials typically has a layered structure, and the (001) crystal plane is the crystal plane perpendicular to the stacking direction of the layered structure. In the X-ray diffraction pattern of the solid precursor of the cathode active material, the full width at half maximum (FWHM) of the (001) crystal plane diffraction peak can be denoted as FWDH. (001) FWDH can be used. (001) Characterizing the crystallinity of the solid precursor of the positive electrode active material, a lower FWDH (001) This corresponds to a higher degree of crystallinity. By using FWDH... (001)By controlling the process within the aforementioned range, the solid precursor of the positive electrode active material can achieve a more suitable crystallinity, resulting in more suitable hardness of the sintered particles. This is beneficial for reducing the generation of micro-powder or fine particles during the crushing process. Therefore, based on the aforementioned multiple sintering and multiple crushing processes, further combined control of the FWDH of the solid precursor of the positive electrode active material is necessary. (001) Within the aforementioned range, it is beneficial to better control the particle size and particle size distribution of the primary particles in the prepared positive electrode active material, so that the size of the primary particles in the positive electrode active material is more moderate and the particle size concentration is higher.

[0475] By using a relatively highly crystalline solid precursor for positive electrode active materials to prepare positive electrode active materials, positive electrode sheets and secondary batteries can be obtained. During the lithium insertion / extraction process at high voltage, the amount of transition metal dissolved in the positive electrode active material is reduced, the deposition of transition metal in the negative electrode is reduced, the thickening of the solid electrolyte interphase (SEI) film of the negative electrode is suppressed, and the loss of active lithium is weakened, which can suppress the degradation of battery life under high voltage.

[0476] In some embodiments, the X-ray diffraction pattern of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 15° to 25°. See Figure 3. In some other embodiments, the X-ray diffraction pattern of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 17° to 23°.

[0477] In some embodiments, the X-ray diffraction pattern of the solid precursor of the positive electrode active material shows (001) crystal plane diffraction peaks.

[0478] In some implementations, 0.35 ≤ FWDH (001) ≤0.70. In some embodiments, 0.35≤FWDH (001) ≤0.64. In some embodiments, the half-width at half maximum (FWHM) of the (001) crystal plane diffraction peak corresponds to the half-width at half maximum (FWHM) of the 2θ (°) diffraction peak in the range of 15° to 25°.

[0479] Without limitation, FWDH (001) It can be any of the following values ​​or a range selected from any two of the following values: 0.35, 0.36, 0.38, 0.40, 0.42, 0.44, 0.45, 0.46, 0.48, 0.50, 0.52, 0.54, 0.55, 0.56, 0.58, 0.60, 0.62, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, etc. FWDH (001) It can also be selected from any of the following ranges: 0.36 to 0.69, 0.36 to 0.62, etc.

[0480] In this application, the following method can be used to perform X-ray diffraction (XRD) testing on the solid precursor of the positive electrode active material. Testing instrument: Bruker-D8 advance. A Cu target Kα1 ray is used with a wavelength λ of 0.15406 nm. The X-ray tube is controlled at 40 kV and 40 mA. The 2θ (°) scanning range is 10°–80°, and the 2θ (°) scanning speed is 0.02° / second.

[0481] In some embodiments, the solid precursor of the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0482] (tj1) The X-ray diffraction pattern of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 15° to 25°;

[0483] (tj2) The X-ray diffraction pattern of the solid precursor of the positive electrode active material shows (001) crystal plane diffraction peaks; in some embodiments, the full width at half maximum (FWDH) of the (001) crystal plane diffraction peaks is... (001) ) satisfies 0.35≤FWDH (001) ≤0.70, optionally, 0.35≤FWDH (001) ≤0.64; where the half-width of the (001) crystal plane diffraction peak corresponds to the half-width of the 2θ(°) diffraction peak in the range of 15°~25°, and can further correspond to the half-width of the 2θ(°) diffraction peak in the range of 17°~23°;

[0484] (tj3) D of solid precursor of positive electrode active material v 50 has a thickness of 2.5μm to 4.5μm, and can be selected from 3.0μm to 4.2μm;

[0485] (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m². 2 / g~35m 2 / g, optional 6m 2 / g~30m 2 / g;

[0486] (tj5) The SPAN value of the solid precursor of the positive electrode active material is 0.4–1.5, and can be selected as 0.60–1.30; where SPAN = (D v 90-D v 10) / D v 50.

[0487] D of solid precursor of positive electrode active material v 50. For the SPAN value test and analysis method of the solid precursor of the positive electrode active material, please refer to the aforementioned test and analysis method of the positive electrode active material.

[0488] In this application, unless otherwise specified, "specific surface area" has the common meaning in the art. It can be tested using nitrogen adsorption specific surface area analysis and calculated using the BET (Brunauer Emmett Teller) method. Nitrogen adsorption specific surface area analysis can be performed using a Tri Star II specific surface area and porosity analyzer from Micromeritics, USA. The test procedures can refer to GB / T 19587-2004. Detailed steps are as follows: Using nitrogen as the adsorbent gas, calculate the specific surface area of ​​the material using the BET method; add the sample to be tested into a BET test tube until it reaches 2 / 3 of the bottom bulb, degas the sample, and heat it; after cooling to room temperature, refill with nitrogen to remove the vacuum, and plug the sample tube opening with a stopper, recording the sample weight; remove the stopper, add a filling rod, install the sample tube onto the instrument analysis station, input the sample weight, and begin the test.

[0489] Non-limiting, the D of the solid precursor of the positive electrode active material v 50 has a thickness of 2.5μm to 4.5μm, and can be selected as 3.0μm to 4.2μm. The D of the solid precursor for the positive electrode active material... v 50 can also be any of the following values ​​or a range selected from any two of the following values: 2.5μm, 2.6μm, 2.8μm, 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4.0μm, 4μm, etc.

[0490] Without limitation, the specific surface area (BET) of the solid precursor of the positive electrode active material can be 5 m². 2 / g~35m 2 / g, optional 6m 2 / g~30m 2 / g. The specific surface area (BET) of the solid precursor of the positive electrode active material can also be any of the following values ​​or a range selected from any two of the following values: 6m 2 / g、8m 2 / g, 10m 2 / g、12m 2 / g, 15m 2 / g, 16m 2 / g、18m 2 / g、20m 2 / g、22m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、28m 2 / g、30m 2 / g、32m2 / g、34m 2 / g、35m 2 / g etc.

[0491] Non-limitingly, the SPAN value of the solid precursor of the positive electrode active material can be 0.4 to 1.5, and optionally 0.60 to 1.30. The SPAN value of the solid precursor of the positive electrode active material can also be any of the following values ​​or a range selected from any two of the following values: 0.4, 0.45, 0.5, 0.55, 0.6, 0.60, 0.7, 0.8, 0.85, 0.90, 0.9, 0.95, 1, 1.0, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.30, 1.3, 1.35, 1.4, 1.5, etc. The SPAN value of the solid precursor of the positive electrode active material can also be selected from any of the following ranges: 0.6 to 1.3.

[0492] In some embodiments, the solid precursor of the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0493] (tk1)0.35≤FWDH (001) ≤0.64;

[0494] (tk2) D of the solid precursor of the positive electrode active material v 50 is 3.0μm~4.2μm;

[0495] (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6m². 2 / g~30m 2 / g;

[0496] (tk4) The SPAN value of the solid precursor of the positive electrode active material is 0.60 to 1.30.

[0497] In some embodiments, the XRD pattern of the solid precursor of the positive electrode active material shows that 0.35 ≤ FWDH (001) ≤0.70, can be selected as 0.35≤FWDH (001) ≤0.64; the temperature for the first sintering is 900℃~980℃, T1>T2.

[0498] In some embodiments, the D of the positive electrode active material solid precursor v 50 is 2.5μm to 4.5μm, and can be selected as 3.0μm to 4.2μm; the temperature for the first sintering is 900℃ to 980℃, T1>T2.

[0499] In some embodiments, the specific surface area of ​​the bulk precursor of the positive electrode active material is 5 m².2 / g~35m 2 / g, optional 6m 2 / g~30m 2 / g; The temperature for the first sintering is 900℃~980℃, T1>T2.

[0500] In some embodiments, according to steps S100, S200, S300 and optional step S400, a positive electrode active material with highly non-agglomerated primary particles (which may be referred to as material A) can be prepared.

[0501] In some embodiments, the preparation method of the positive electrode active material further includes step S500: mixing material A with secondary particulate material to prepare the positive electrode active material, wherein the secondary particulate material is a material comprising secondary particles.

[0502] In step S500, the secondary particulate material can be denoted as material B.

[0503] In step S500, the average particle size and half-maximum width of the particle size distribution of the primary particles in the secondary particulate material (material B) can be adjusted to be close to those of material A, so that the average particle size (D1) and half-maximum width of the particle size distribution curve of the primary particles in the prepared positive electrode active material are similar. H It is basically consistent with material A.

[0504] In this application, the average particle size of the primary particles in the secondary particulate material can be denoted as D2, and the half-maximum width of the particle size distribution of the primary particles in the secondary particulate material can be denoted as (W2).

[0505] In some embodiments, 1.3 μm ≤ D2 ≤ 3 μm; optionally, 1.4 μm ≤ D2 ≤ 2.5 μm; further optionally, 1.5 μm ≤ D2 ≤ 2.5 μm; and even more optionally, 1.5 μm ≤ D2 ≤ 2.4 μm. Non-limitingly, D2 may also be any of the following values ​​or a range selected from any two of the following values: 1 μm, 1.1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0506] In some embodiments, W2 ≤ 2.5 μm; optionally, 1 μm ≤ W2 ≤ 2.5 μm; and further optionally, 1.2 μm ≤ W2 ≤ 2.5 μm. Non-limitingly, W2 may also be any of the following values ​​or a range selected from any two of the following values: 1 μm, 1.1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, etc.

[0507] By controlling the FWDH of the solid precursor of the positive electrode active material (001) D of solid precursors for positive electrode active materials v 50. Having one or more parameters, such as the specific surface area of ​​the positive electrode active material solid precursor and the SPAN value of the positive electrode active material solid precursor, within the aforementioned range is beneficial for controlling the average particle size (D1) and particle size distribution (e.g., W) of the primary particles. H ), D of positive electrode active material v 50 and SPAN value, R1 (D of positive electrode active material) v One or more parameters, such as the ratio of 50 to the average particle size D1 of the primary particles, are within a more suitable range and are not limited to any theory. For example, this can be more beneficial in reducing the contact area between the positive electrode active material and the electrolyte, more beneficial in reducing the occurrence of side reactions at the positive electrode-electrolyte interface under high voltage, more beneficial in reducing metal dissolution of the positive electrode, and more beneficial in improving the structural stability of the positive electrode active material under high voltage, thereby improving battery life under high voltage. For example, when the positive electrode active material contains manganese, it is also beneficial in reducing manganese dissolution.

[0508] In some embodiments, a positive electrode active material with moderate primary particle size, narrow particle size distribution, high crystallinity, and low Li / Ni mixing was prepared based on a solid precursor of a positive electrode active material containing lithium composite metal oxide.

[0509] In some embodiments, a co-precipitation method is used to prepare the solid precursor of the positive electrode active material. Taking the preparation of lithium nickel cobalt manganese-based oxide as an example, the solid precursor is the corresponding hydroxide, and a method including the following steps can be adopted:

[0510] S10: Add pure water to the reactor, and under nitrogen protection, start stirring (e.g., 200 rpm to 250 rpm, or even 220 rpm) and heating (reaction temperature, e.g., 60℃ to 70℃, or even 65℃). Add ammonia water to adjust the pH value to a suitable alkaline condition (e.g., pH 11 to 12, or even pH 11.2 to 11.8). Then, continuously add metal salt solution to carry out a co-precipitation reaction, allowing the particles to grow continuously. During the reaction, use alkaline solution to adjust the pH value of the reaction system. The metal salt solution includes nickel salt, cobalt salt, and manganese salt.

[0511] S20: Continue adding metal salt solution until the particles grow to a suitable size, collect the reaction precipitate, and obtain the solid precursor of the positive electrode active material.

[0512] In a non-limiting manner, during the step of starting the stirring under nitrogen protection, the stirring speed may be, but is not limited to, 200 rpm to 250 rpm, or any of the following values ​​or a range consisting of any two of the following values: 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, etc.

[0513] Non-limitingly, in the step of starting stirring and heating under nitrogen protection, the heating temperature can be, but is not limited to, 42℃~75℃, can be selected from 60℃~70℃, or can be any of the following temperatures or a range selected from any two of the following temperatures: 42℃, 44℃, 45℃, 46℃, 48℃, 50℃, 52℃, 53℃, 54℃, 55℃, 56℃, 58℃, 60℃, 62℃, 64℃, 65℃, 66℃, 68℃, 70℃, 72℃, 73℃, 74℃, 75℃, etc.

[0514] It is understood that nickel salts, cobalt salts, and manganese salts are respectively soluble salts, with sulfates being a non-limiting example.

[0515] Unless otherwise specified, the solvent for metal salt solutions may be water.

[0516] The ratio of metal cations in the metal salt solution can be controlled according to the target elemental composition in the positive electrode active material. Taking the preparation of lithium nickel cobalt manganese-based oxide with an atomic number ratio (or atomic molar ratio) of 0.7:0.1:0.2 of nickel, cobalt, and manganese as an example, the metal cations in the metal salt solution include nickel ions, cobalt ions, and manganese ions. Furthermore, the molar ratio of nickel ions, cobalt ions, and manganese ions in the metal salt solution can be controlled to be 0.65:0.10:0.25.

[0517] Non-limiting, the total molar concentration of metal cations in the metal salt solution can be from 1.4 mol / L to 1.8 mol / L, but is not limited thereto. The total molar concentration of metal cations in the metal salt solution can also be any of the following values ​​or a range selected from any two of the following values: 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, etc.

[0518] For example, the concentration of ammonia water can be from 3.5 g / L to 9.5 g / L, but is not limited to this. For example, the concentration of ammonia water can also be any of the following values ​​or a range selected from any two of the following values: 3.5 g / L, 3.6 g / L, 3.8 g / L, 3.9 g / L, 4.0 g / L, 4 g / L, 4.4 g / L, 4.5 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L, etc.

[0519] For example, the concentration of ammonia water can also be 5 g / L to 7 g / L, but is not limited thereto.

[0520] In the step of adding ammonia to adjust the pH value to a suitable alkaline condition, the pH value of the alkaline condition can be, but is not limited to, 11–12, or 11.2–11.8. The pH value of the alkaline condition can also be any of the following values ​​or a range selected from any two of the following values: 11, 11.2, 11.4, 11.5, 11.6, 11.8, 12, etc.

[0521] Without limitation, the alkaline solution can be an aqueous solution of sodium hydroxide, but is not limited thereto.

[0522] To maintain a constant internal environment in the reactor during the feeding of metal salt solution, a microporous filtration device can be used to filter out the clear liquid inside the reactor, thus keeping the liquid level in the reactor constant.

[0523] As the metal salt solution is continuously added, the material inside the reactor becomes increasingly concentrated, and the particles continue to grow. By controlling the timing of stopping the feeding, the reaction time can be controlled, and thus the particle size can be managed.

[0524] Taking the preparation of solid precursors for positive electrode active materials by co-precipitation as an example, the FWDH of the solid precursors for positive electrode active materials can be adjusted by regulating parameters such as reaction temperature. (001) However, this is not the only possibility. See Preparation Examples 9-11 below.

[0525] Taking the preparation of solid precursors for positive electrode active materials by co-precipitation as an example, the D of the solid precursors for positive electrode active materials can be adjusted by controlling parameters such as the timing of stopping the feeding. v 50, but not limited to this. See preparation examples 4-5 below.

[0526] Taking the preparation of solid precursors for positive electrode active materials by co-precipitation as an example, the specific surface area of ​​the solid precursors can be adjusted by controlling parameters such as ammonia concentration, but this is not the only possible method. See Preparation Examples 6-8 below.

[0527] Taking the preparation of solid precursors for positive electrode active materials by coprecipitation as an example, the SPAN value of the solid precursors can be adjusted by controlling parameters such as reaction temperature and reaction time, but it is not limited to this. See Preparation Examples 2-3 below.

[0528] In some embodiments, the prepared positive electrode active material is the positive electrode active material defined in the first aspect of this application.

[0529] In some embodiments, the prepared positive electrode active material satisfies one or more of the following characteristics (tm1) and (tm2):

[0530] (tm1) The positive electrode active material prepared is the positive electrode active material defined in the first aspect of the present application;

[0531] (tm2) The positive electrode active material prepared includes a lithium nickel-based oxide, the lithium nickel-based oxide contains Li element, non-lithium metal elements and O element, the non-lithium metal elements include Ni element, and the lithium nickel-based oxide satisfies one or more of the following characteristics (tn1), (tn2), (tn3), (tn4) and (tn5):

[0532] (tn1) The atomic molar ratio of Ni element to non-lithium metal elements in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1, and the value or range of q1 in the first aspect of the present application can also be referred to;

[0533] (tn2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.98 ≤ x2 ≤ 1.02, and the value or range of q2 in the first aspect of the present application can also be referred to;

[0534] (tn3) The lithium nickel-based oxide contains Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.96 ≤ x3 ≤ 2.04, and the value or range of q3 in the first aspect of the present application can also be referred to;

[0535] (tn4) The atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3, and the value or range of q4 in the first aspect of the present application can also be referred to;

[0536] (tn5) The atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5, and the value or range of q5 in the first aspect of the present application can also be referred to.

[0537] In the third aspect of the present application, a positive electrode active material is provided, and the positive electrode active material includes primary particles, and the particle size of the primary particles is moderate and the particle size distribution is relatively narrow.

[0538] In some embodiments, in the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W H ) and the average particle size (D1) of the primary particles in the positive electrode active material are controlled within a better range. The definitions of W H and D1 can be referred to the first aspect of the present application.

[0539] This positive electrode active material can be used to prepare the secondary battery of the first aspect of this application, which can significantly improve the battery life of the secondary battery at high voltage, including cycle and / or storage life. It is not limited to any theory; see the description in the first aspect of this application.

[0540] In some embodiments, a positive electrode active material is provided, comprising primary particles, W H ≤2.5μm, 1.3μm≤D1≤3μm.

[0541] The third aspect of this application provides a positive electrode active material having the same characteristics as the positive electrode active material defined in the first aspect of this application. It is understood that the positive electrode active material provided in the third aspect of this application can be a separate raw material, or it can exist in a separate positive electrode sheet, or it can exist in the positive electrode sheet of a battery.

[0542] In some embodiments, the positive electrode active material includes the positive electrode active material prepared by the method for preparing the positive electrode active material described in the second aspect of this application.

[0543] In some embodiments, the positive electrode active material includes non-agglomerated primary particles and secondary particles.

[0544] In some embodiments, the positive electrode active material is the positive electrode active material defined in the first aspect of this application (i.e., the same as the positive electrode active material in the secondary battery of the first aspect). The positive electrode active material described in the first aspect is present in the positive electrode sheet of the secondary battery.

[0545] In a fourth aspect of this application, a positive electrode sheet is provided, which includes a positive active layer comprising a positive active material.

[0546] In some embodiments, the positive electrode active layer includes the positive electrode active material described in the third aspect of this application.

[0547] In some embodiments, a positive electrode sheet is provided, which includes a positive active layer, the positive active layer including a positive active material;

[0548] In the particle size distribution curve of primary particles in the positive electrode active material, the half-maximum width (W) is... H Satisfying W H ≤2.5μm;

[0549] The average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0550] By introducing the aforementioned positive electrode active material into the positive electrode active layer of the positive electrode sheet, the advantages of the aforementioned positive electrode active material can be realized, improving the battery life of the secondary battery under high voltage, including cycle and / or storage life.

[0551] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics:

[0552] (to1) The positive electrode active material includes the positive electrode active material prepared by the method described in the second aspect of this application;

[0553] (to2) The positive electrode active material is the positive electrode active material as defined in the first aspect of this application;

[0554] (to3) The positive electrode is the positive electrode as defined in the first aspect of this application.

[0555] The fourth aspect of this application provides a positive electrode sheet having the same characteristics as the positive electrode sheet defined in the first aspect of this application. It is understood that the positive electrode sheet provided in the fourth aspect of this application can be a standalone film material or can be present within a battery.

[0556] In some embodiments, the positive electrode is the positive electrode as defined in the first aspect of this application. The positive electrode described in the first aspect is present in a secondary battery.

[0557] In another aspect of this application, a method for preparing a positive electrode sheet is provided, which can be used to prepare the positive electrode sheet described in the fourth aspect of this application. This positive electrode sheet can be used to prepare the secondary battery described in the first aspect of this application.

[0558] In some embodiments, a method for preparing a positive electrode sheet is provided, comprising the following steps: coating a positive electrode slurry onto at least one side of a positive electrode current collector, drying, and cold pressing to obtain a positive electrode sheet; wherein the positive electrode slurry comprises a positive electrode active material. The definition of the positive electrode active material can be found in the first, second, and third aspects of this application.

[0559] In some embodiments, the positive electrode slurry includes a positive electrode active material, a binder, and a conductive agent. The types and amounts of the positive electrode active material, binder, and conductive agent in the positive electrode slurry can be found in any suitable embodiment or example within the context of this application.

[0560] In another aspect of this application, a method for preparing a secondary battery is provided, which can be used to prepare the secondary battery described in the first aspect of this application.

[0561] In some embodiments, a method for preparing a secondary battery is provided, which includes the following steps: placing an electrode assembly in a housing, injecting an electrolyte, allowing it to stand and wet, forming, and preparing a secondary battery; wherein, the electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material.

[0562] For a definition of positive electrode active material, please refer to the first, second and third aspects of this application.

[0563] For the definition of the positive electrode sheet, please refer to the first and fourth aspects of this application.

[0564] In some embodiments, the electrode assembly includes a positive electrode, a separator, and a negative electrode, with the separator disposed between the positive and negative electrode; the positive electrode includes a positive active layer, which includes a positive active material.

[0565] In a fifth aspect of this application, an electrical device is provided, comprising at least one of the secondary battery described in the first aspect of this application, a positive electrode active material prepared by the method for preparing the positive electrode active material described in the second aspect of this application, a positive electrode active material described in the third aspect of this application, and a positive electrode sheet described in the fourth aspect of this application.

[0566] In some embodiments, the electrical device includes a secondary battery as provided in any of the embodiments of this application.

[0567] Secondary batteries can be used as a power source for electrical devices or as an energy storage unit for those devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, power tools, etc., but are not limited to these. This type of electrical device can also be applied to military equipment, aerospace, and other fields, as well as to energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0568] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0569] Figure 10 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery device or battery pack can be used.

[0570] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0571] In a sixth aspect of this application, the application of the secondary battery described in the first aspect of this application, the positive electrode active material prepared by the method described in the second aspect of this application, the positive electrode active material described in the third aspect of this application, and the positive electrode sheet described in the fourth aspect of this application in supplying and / or storing electrical energy is provided.

[0572] In some implementations, the application includes at least one process of charging and discharging at a voltage of 4.2V or higher.

[0573] In some embodiments, the charging process includes a phase of charging at at least one voltage condition from 4.2V to 4.5V.

[0574] In some embodiments, the discharge process includes a phase in which the discharge is performed at at least one voltage condition between 4.5V and 4.2V.

[0575] Non-limiting, the voltage condition can be any of the following voltages or a range selected from any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc., for example 4.3V to 4.5V.

[0576] In some embodiments, the application includes performing charge-discharge cycles, the steps of which include at least one process of charging at voltage V1 and discharging at voltage V1. In some embodiments, voltage V1 ≥ 4.2V. Non-limiting examples of voltage V1 include 4.3V, 4.4V, 4.5V, etc., and it can also be within the range of any of the aforementioned voltages.

[0577] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0578] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0579] In the following examples, room temperature refers to 20°C to 30°C.

[0580] The secondary batteries in the following examples are lithium-ion secondary batteries.

[0581] I. Preparation of Positive Electrode Active Materials

[0582] (I) Preparation

[0583] Preparation Example 1.

[0584] The target positive electrode active material is a lithium nickel cobalt manganese-based oxide, with the target chemical formula LiNi. 0.63 Co 0.13 Mn 0.24 O2.

[0585] The preparation method of the solid precursor of the positive electrode active material is as follows:

[0586] Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 1.6 mol / L metal salt solution with a metal cation molar ratio of 0.65:0.10:0.25. The solvent was water, and the sum of the molar volume concentrations of nickel ions, cobalt ions, and manganese ions was 1.6 mol / L.

[0587] Add pure water to the reactor, introduce nitrogen gas, start stirring and heating at 220 rpm and 65℃ (i.e., control the reaction temperature inside the reactor at 65℃), and ammonia concentration of 7.0 g / L. Introduce alkali solution (sodium hydroxide aqueous solution) to adjust the pH inside the reactor to 11.6, and then simultaneously introduce alkali solution and metal salt solution to carry out precipitation reaction. Keep the environment inside the reactor constant during the feeding process. Filter the clear liquid inside the reactor through a microporous filter to keep the liquid level inside the reactor constant. Continue feeding, and the material inside the reactor will be continuously concentrated and the particles will continue to grow until the particle size grows to 3.5 μm. After feeding is completed, the precursor preparation is complete.

[0588] A solid precursor for the positive electrode active material, lithium hydroxide monohydrate (lithium source), and additives (tungsten oxide and zirconium oxide) were thoroughly mixed at a mass ratio of 948.9:433.6:2.3:4.1. The mixture was then sintered at 940℃ for 12 hours, followed by a first crushing to obtain a first-burned product. The first-burned product was then thoroughly mixed with a high-temperature coating agent (first coating agent), and sintered at 750℃ for 6 hours, followed by a second crushing to obtain a second-burned product. The second-burned product was then thoroughly mixed with a low-temperature coating agent (second coating agent), and sintered at 500℃ for 5 hours to prepare the positive electrode active material, which can be labeled as the "finished product".

[0589] In this example, the first sintering step was simultaneously doped with W and Zr, and the raw material containing the doping elements was a combination of tungsten oxide and zirconium oxide.

[0590] In this example, the first, second, and third sintering processes were carried out in an oxygen atmosphere.

[0591] The first coating agent consists of cobalt hydroxide and aluminum hydroxide; the amount of the first coating agent used is 28.4g of cobalt hydroxide and 2.9g of aluminum hydroxide.

[0592] The second coating agent consists of titanium dioxide; the amount of the second coating agent used is 3.3g.

[0593] The parameters for the first crushing are: air pressure of 0.4 MPa and feeding frequency of 20 Hz; the parameters for the second crushing are: air pressure of 0.3 MPa and feeding frequency of 20 Hz.

[0594] Preparation Examples 2-3 used the same method as Preparation Example 1 to prepare positive electrode active materials, the difference being that the pH inside the reactor was different during the reaction process.

[0595] Preparation Example 2: During the preparation of the solid precursor of the positive electrode active material, the pH in the reactor was controlled to be 11.

[0596] Preparation Example 3: During the preparation of the solid precursor of the positive electrode active material, the pH in the reactor was controlled to be 12.

[0597] Preparation Examples 4-5 used the same method as Preparation Example 1 to prepare positive electrode active materials, the difference being that the timing of stopping the addition of the metal salt solution was different, that is, the timing of stopping the addition was different.

[0598] In Preparation Example 4, during the preparation of the solid precursor of the positive electrode active material, feeding was stopped when the particle size grew to 3.1 μm.

[0599] Preparation Example 5: During the preparation of the solid precursor of the positive electrode active material, feeding was stopped when the particle size grew to 4 μm.

[0600] Preparation Examples 6-8 used the same method as Preparation Example 1 to prepare positive electrode active materials, the difference being the different concentrations of ammonia.

[0601] In Preparation Example 6, during the preparation of the solid precursor of the positive electrode active material, the concentration of ammonia water was 9 g / L.

[0602] In Preparation Example 7, during the preparation of the solid precursor of the positive electrode active material, the concentration of ammonia water was 5 g / L.

[0603] In Preparation Example 8, during the preparation of the solid precursor of the positive electrode active material, the concentration of ammonia water was 3.9 g / L.

[0604] Preparation Examples 9-11 used the same method as Preparation Example 1 to prepare positive electrode active materials, the difference being that the reaction temperatures were different.

[0605] Preparation Example 9: During the preparation of the solid precursor of the positive electrode active material, the reaction temperature inside the reactor was 73°C.

[0606] Preparation Example 10: During the preparation of the solid precursor of the positive electrode active material, the reaction temperature inside the reactor was 54°C.

[0607] Preparation Example 11: During the preparation of the solid precursor of the positive electrode active material, the reaction temperature inside the reactor was 44°C.

[0608] Preparation Examples 12-15 used the same method as Preparation Example 1 to prepare positive electrode active materials, and used the same solid precursor. The difference was that Preparation Examples 12-13 changed the temperature (T1) of the first sintering, and Preparation Examples 14-15 changed the time (t1) of the first sintering.

[0609] In Preparation Example 12, the temperature T1 for the first sintering was 980°C.

[0610] In Preparation Example 13, the temperature T1 for the first sintering was 900°C.

[0611] In Preparation Example 14, the first sintering time t1 was 15 h.

[0612] In Preparation Example 15, the first sintering time t1 was 8 hours.

[0613] Preparation Example 16. The positive electrode active material was prepared using a method that was basically the same as that used in Preparation Example 1, except that the temperature (T1) and the time (t1) of the first sintering were changed.

[0614] In Preparation Example 16, the temperature T1 for the first sintering was 900°C, and the time t1 for the first sintering was 5 hours.

[0615] Preparation Example 17. The positive electrode active material does not have a coating layer. Based on Preparation Example 1, the high-temperature coating agent (first coating agent) and the low-temperature coating agent (second coating agent) are omitted.

[0616] The solid precursor of the positive electrode active material (same as in Preparation Example 1), lithium hydroxide monohydrate (lithium source) and additives are thoroughly mixed and sintered at 940°C for 12 hours. After the first crushing, a first-burned product is obtained. The first-burned product is sintered at 750°C for 6 hours and then crushed for the second time to obtain a second-burned product. The second-burned product is used as the positive electrode active material and can be labeled as the "finished product".

[0617] Preparation Example 18. A positive electrode active material was prepared using essentially the same method as in Preparation Example 1, except that the molar ratio of nickel ions, cobalt ions, and manganese ions was adjusted during the synthesis of the solid precursor to obtain the positive electrode active material NCM. 523 (LiNi 0.5 Co0.2 Mn 0.3 O2); at the same time, the high-temperature coating agent (first coating agent) and the low-temperature coating agent (second coating agent) are omitted.

[0618] Comparative Example 1 was prepared using a method that was basically the same as that used in Example 1 to prepare the positive electrode active material. The difference was that the pH inside the reactor was different during the reaction process.

[0619] In the preparation of Comparative Example 1, the pH inside the reactor was controlled at 12.5 during the preparation of the solid precursor of the positive electrode active material.

[0620] Preparation of Comparative Example 2: The positive electrode active material was prepared using a method that was basically the same as that used in Preparation Example 1, except that the concentration of ammonia was different.

[0621] In the preparation of Comparative Example 2, the concentration of ammonia water was 11.5 g / L during the preparation of the solid precursor of the positive electrode active material.

[0622] Comparative Examples 3-4: The positive electrode active material was prepared using a method that was basically the same as that used in Example 1, except that the temperature (T1) and time (t1) of the first sintering were changed.

[0623] Comparative Example 3 was prepared, with the first sintering temperature T1 being 1050℃ and the first sintering time t1 being 15h.

[0624] Comparative Example 4 was prepared, with the first sintering temperature T1 being 850℃ and the first sintering time t1 being 8h.

[0625] Comparative Example 5: The positive electrode active material was prepared using a method that was basically the same as that used in Example 17 (the positive electrode active material was not coated). The difference was that the reaction temperature inside the reactor was 40°C during the preparation of the solid precursor of the positive electrode active material.

[0626] It should be noted that in the above preparation examples and comparative examples, in the process of using a solid precursor of positive electrode active material for multiple sintering and multiple crushing, the crushing parameters can be adjusted according to the agglomeration of the material in order to control the particle size and distribution and the agglomeration of primary particles in the material as much as possible.

[0627] (II) Material Characterization

[0628] Samples to be tested: solid precursors of positive electrode active materials and finished positive electrode active materials in each example.

[0629] 1. D v 50. D v 90. D v 10 and SPAN value, where SPAN = (D v 90-Dv 10) / D v 50.

[0630] The Malvern 2000 (MasterSizer 2000) laser particle size analyzer was used.

[0631] The reference standard procedure is GB / T19077-2016 / ISO 13320:2009. The detailed test procedure includes: taking an appropriate amount of the sample to be tested, adding 20 mL of deionized water (sample concentration controlled at 8%–12% opacity), and sonicating for 5 min (53 kHz / 120 W) to fully disperse the sample. Then, the sample is measured according to GB / T19077-2016 / ISO 13320:2009. The ultrasonically dispersed sample is added to the injection cell, and testing begins after the sample has stabilized for 5–10 s. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light. Based on the test data, a volumetric cumulative distribution map of the particle size is plotted, and D is obtained from the distribution map. v 50. D v 90. D v 10, the SPAN value can be calculated. To avoid agglomeration during the drying process affecting particle size testing, a wetted sample washed with anhydrous ethanol was used for dispersion testing.

[0632] 2. Specific surface area (BET)

[0633] Testing instrument: Tri Star II specific surface area and porosity analyzer from Micromeritics, USA.

[0634] The test procedure can be referred to GB / T 19587-2004. Nitrogen is used as the adsorbent gas, and the specific surface area of ​​the material is calculated by the BET method. The sample to be tested is added into the BET test tube until it reaches 2 / 3 of the bottom bulb, and the sample is degassed and heated. After cooling to room temperature, nitrogen is backfilled to remove the vacuum, and the sample tube opening is plugged with a stopper. The sample weight is recorded. The stopper is removed, a filling rod is added, the sample tube is installed on the instrument analysis station, the sample weight is entered, and the test begins.

[0635] 3. The full width at half maximum (FWHM) of the (001) crystal plane diffraction peak in the X-ray diffraction pattern of the solid precursor of the positive electrode active material is denoted as FWDH. (001) .

[0636] Test instrument: Bruker-D8 advance.

[0637] Test method: Cu target Kα1 rays were used with a wavelength λ of 0.15406 nm. The X-ray tube was controlled at 40 kV and 40 mA. The 2θ (°) scanning range was 10° to 80° and the 2θ (°) scanning speed was 0.02° / second.

[0638] Among them, the half-width of the (001) crystal plane diffraction peak corresponds to the half-width of the 2θ(°) diffraction peak in the range of 15° to 25°.

[0639] 4. Analysis based on scanning electron microscope (SEM) images

[0640] Characterization parameters: morphological observation of the positive electrode active material; particle size distribution and average particle size of primary particles in the finished positive electrode active material, and the proportion of non-agglomerated primary particles in the positive electrode active material.

[0641] Equipment: JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope and ZEISS Sigma 300 scanning electron microscope.

[0642] For SEM testing, please refer to JY / T(001)-1996.

[0643] Test method: The positive electrode active material is laid and adhered to the conductive adhesive. The sample is placed on the stage of a scanning electron microscope. The sample is imaged under the bombardment of the electron beam generated by the electron gun to obtain the SEM microstructure of the sample.

[0644] Analysis equipment: LIBMAS intelligent microscopic analysis system for lithium-ion battery materials.

[0645] (1) Half-peak width of the particle size distribution curve of primary particles in positive electrode active material.

[0646] The maximum diameter of the primary particles in each direction in the SEM morphology image is denoted as the "particle size of the primary particles in the positive electrode active material".

[0647] The statistical scope of "primary particles in positive electrode active materials" includes primary particles in non-agglomerated state and primary particles in secondary particles as shown in SEM morphology images.

[0648] Analysis Method: The horizontal axis of the curve corresponds to the particle size of primary particles in the positive electrode active material, and the vertical axis corresponds to the frequency of occurrence of each particle size or the proportion of the counted primary particles. A region is randomly selected from the sample to be tested for scanning, and the particle size of each primary particle and the frequency of occurrence of different particle sizes are counted at 1000X magnification. The number of primary particles counted is ≥2000. The particle size distribution curve of the primary particles is obtained using the following method: the particle size data of the primary particles are plotted as a histogram using Minitab, and a curve is fitted.

[0649] The "half-peak width" of the "particle size distribution curve of primary particles in positive electrode active materials" refers to the width between the two particle size boundaries corresponding to half the peak height of the distribution curve.

[0650] (2) Average particle size of primary particles in positive electrode active material.

[0651] The statistical scope of "primary particles in positive electrode active materials" includes primary particles in non-agglomerated state and primary particles in secondary particles as shown in SEM morphology images.

[0652] Analysis method: A region is randomly selected from the sample to be tested for scanning, and the particle size of each primary particle is counted at 1000X magnification. The average particle size of each primary particle is then calculated.

[0653] (3) The proportion of non-agglomerated primary particles in the positive electrode active material.

[0654] Analysis method: Randomly select one region for scanning test, with a magnification of 1000X, count the number of non-agglomerated primary particles and secondary particles, and calculate the proportion of non-agglomerated primary particles.

[0655] (III) Test Results

[0656] Preparation Examples 1-18 all yielded positive electrode active materials with moderate primary particle size and narrow particle size distribution.

[0657] For example, the particle size distribution curve of the primary particles in the positive electrode active material prepared in Preparation Example 1 can be referred to Figure 2, and the SEM microstructure image of the obtained positive electrode active material can be referred to Figure 4. For example, the particle size distribution curve of the primary particles in the positive electrode active material obtained in Preparation Example 1 can be referred to Figure 1.

[0658] The positive electrode active materials prepared in Examples 1-18 all satisfy the following two characteristics:

[0659] The half-maximum width (W) of the particle size distribution curve of primary particles in positive electrode active materials H ≤2.5μm; and

[0660] The average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0661] For example, the X-ray diffraction pattern of the solid precursor of the positive electrode active material in Preparation Example 1 can be seen in Figure 3. The X-ray diffraction pattern of the solid precursor of the positive electrode active material shows a peak at a 2θ (°) diffraction angle of 15°–25°. The X-ray diffraction patterns of the solid precursors of the positive electrode active materials prepared in the other preparation examples also show peaks at a 2θ diffraction angle of 15°–25°.

[0662] Based on the X-ray diffraction pattern of the solid precursor of the positive electrode active material, it can be confirmed that the X-ray diffraction pattern of the solid precursor of the positive electrode active material contains (001) crystal plane diffraction peaks, and correspondingly, the solid precursor of the positive electrode active material contains (001) crystal planes. See Figure 3.

[0663] The test and characterization results of the solid precursors and finished positive electrode active materials in each preparation example and preparation comparative example can be found in Table 1.

[0664] Table 1.

[0665] In Table 1, "Precursor SPAN" represents the SPAN value of the solid precursor of the positive electrode active material, and "Precursor D" represents the SPAN value of the precursor. v 50” indicates the D of the solid precursor of the positive electrode active material. v 50, “BET” indicates the specific surface area of ​​the solid precursor of the positive electrode active material, and “FWHM” indicates the XRD value of the precursor. (001) "" indicates that the X-ray diffraction pattern of the solid precursor of the positive electrode active material has the full width at half maximum (FWHM) of the (001) crystal plane diffraction peak.

[0666] In Table 1, “Finished Product D” v 50” indicates the D of the prepared positive electrode active material. v The value is 50. "Finished Product SPAN" represents the SPAN value of the prepared positive electrode active material. "Average Particle Size of Primary Particles D1" represents the average particle size of the primary particles in the positive electrode active material. "Front-Half Width of the Particle Size Distribution Curve of the Finished Primary Particles W" represents the average particle size of the primary particles in the prepared positive electrode active material. H "" represents the half-peak width of the particle size distribution curve of primary particles in the positive electrode active material.

[0667] II. Preparation of Secondary Batteries

[0668] Examples 1-18 and Comparative Examples 1-5 used the positive electrode active materials prepared in Preparation Examples 1-18 and Comparative Examples 1-5, respectively.

[0669] The following examples demonstrate the preparation of secondary batteries using lithium-ion secondary batteries.

[0670] Example 1.

[0671] (1) Positive electrode plate

[0672] A positive electrode active material (prepared in Example 1), conductive agent Super-P, conductive agent carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:1.5:0.5:3 and thoroughly dispersed in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was coated on both sides of a 13 μm thick Al foil positive electrode current collector, with a total coating areal density of 0.5 g / 1540.25 mm. 2 The positive electrode sheet was obtained by vacuum drying and cold pressing at 120℃, with a compaction density of 3.4 g / cm³. 3 .

[0673] (2) Negative electrode plate

[0674] A negative electrode slurry was prepared by thoroughly mixing artificial graphite (anode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) in a deionized water solvent at a mass ratio of 95:2:2:1. The negative electrode slurry was then coated onto both sides of a Cu foil (anode current collector), with a total coating density of 0.34 g / 1540.25 mm². 2 The material is dried and cold-pressed to obtain a negative electrode sheet with a compacted density of 1.6 g / cm³. 3 .

[0675] (3) Separating membrane

[0676] A polyethylene (PE) separator film with a thickness of 7μm is used.

[0677] (4) Electrolyte

[0678] In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 35:65, lithium hexafluorophosphate (LiPF6) and additives were added and mixed thoroughly to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte was 1 mol / L. The additives in the electrolyte consisted of 2.5 wt% vinylene carbonate (VC), 1 wt% fluoroethylene carbonate (FEC), and 0.5 wt% ethylene sulfate (DTD).

[0679] (5) Preparation of secondary batteries (more specifically, lithium-ion secondary batteries)

[0680] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the anode and cathode for isolation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with prepared electrolyte, and undergoes processes such as encapsulation, electrolyte injection, formation, and venting to obtain a lithium-ion secondary battery.

[0681] Examples 2-18 and Comparative Examples 1-5 were prepared using essentially the same method as in Example 1, the difference being the different positive electrode active materials. Examples 2-18 and Comparative Examples 1-5 used the positive electrode active materials prepared in Examples 2-18 and Comparative Examples 1-5, respectively.

[0682] III. Testing and Analysis

[0683] (I) Testing and Analysis Methods

[0684] 1. Material and electrode characterization

[0685] (1) Mn dissolution test of positive electrode active material:

[0686] Test samples: Positive electrode active materials prepared in each of Preparation Examples 1-18 and Preparation Comparative Examples 1-5.

[0687] Weigh 5 ± 0.005 g of EDTA-disodium powder using weighing paper, pour it into a 500 mL beaker, and sonicate for 3-5 minutes until completely dissolved. Use approximately 5 cm × 5 cm pieces of aluminum foil, folding the four sides slightly, to weigh the powder. Weigh 30 ± 0.01 g of the sample using the folded foil and record the sample mass. Clean the soaked, segmented magnetic stir bar and place it in the beaker. Measure 100 mL of the prepared EDTA-disodium mixed solution using a graduated cylinder and add it to the beaker. Set the magnetic stirrer speed to 720. Rotate at rpm; Place the beaker on a magnetic stirrer and add the weighed powder sample (powder sample of positive electrode active material, record the mass M0) while stirring. Stir for 30 min and let stand for 1 min; Use a 1 mL or 3 mL syringe to draw up the solution, filter 3 mL of the solution through two stacked 0.22 μm filters into a test tube, prepare a 50 mL glass volumetric flask, add 1 mL to 2 mL of nitric acid to the volumetric flask, and use a 1 mL pipette to draw up 1 mL of the filtrate into the 50 mL volumetric flask and dilute to volume; Use ICP-OES to determine the concentration C of Mn element. Mn Input the solution volume V0 / sample mass M0, and record the experimental result Mn (ppm) = C Mn ×V0 / M0.

[0688] EDTA stands for ethylenediaminetetraacetic acid.

[0689] In this application, percentages and ppm (parts per million) can be converted, with 1% = 10,000 ppm. For example, 0.2% = 2,000 ppm, 0.1% = 1,000 ppm, 0.01% = 100 ppm, 0.005% = 50 ppm, etc.

[0690] Some test results can be found in Table 2.

[0691] 2. Positive electrode sheet and battery performance testing

[0692] (1) Testing the specific capacity of the positive electrode sheet

[0693] The positive electrode and lithium sheet are combined to form a coin cell. After the assembled coin cell is left to stand for 120 minutes, it is charged at a constant current of 0.1C to 4.3V at a constant temperature of 25℃, then charged at a constant voltage of 4.3V until the current drops to 0.05C, and finally discharged at a constant current of 0.33C to 2.8V to obtain the first discharge capacity. The unit is mAh / g.

[0694] The record is "4.4V 0.1C, coin discharge capacity", see Table 3 for reference.

[0695] (2) Storage performance test at 60℃ (charged to 4.4V)

[0696] The lithium-ion battery was charged at a constant current of 0.33C to 4.4V under a constant temperature environment of 25℃, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged at a constant current of 0.33C to 2.8V to obtain the first discharge capacity. The battery was then charged at a constant current of 0.33C to 4.4V, then charged at a constant voltage of 4.4V to the cutoff current of 0.05C. The battery was then placed in a constant temperature oven at 60℃ for 30 days. After removal and cooling for 5 hours, it was discharged at a constant current of 0.33C to 2.8V under a constant temperature environment of 25℃, then charged at a constant current of 0.33C to 4.4V, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged at a constant current of 0.33C to 2.8V to obtain the reversible capacity after 30 days of storage at 60℃.

[0697] Reversible capacity retention rate after 30 days of storage at 60℃ (charged to 4.4V) = Reversible capacity after 30 days of storage at 60℃ / First discharge capacity × 100%.

[0698] The record is "30D capacity retention rate at 60℃ (charged to 4.4V)", see Table 2 for details.

[0699] (3) 45℃ Cyclic Performance Test (Charged to 4.4V)

[0700] At 45℃, a lithium-ion secondary battery is charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to a cutoff current of 0.05C, left to rest for 10 minutes, and then discharged at a constant current of 1C to 2.8V, left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same lithium-ion secondary battery, and the discharge capacity C of the first, second, ..., nth cycle is recorded. n .

[0701] Record the battery's cycle capacity retention rate P100 (charged to 4.4V) after 100 cycles = C100 / C0 × 100%.

[0702] The result is recorded as “Capacity retention rate after 100 cycles at 45°C (charged to 4.4V)”. Some test results can be found in Table 4.

[0703] (4) Storage performance test at 60℃ (charged to 4.5V)

[0704] The lithium-ion battery was charged at a constant current of 0.33C to 4.5V under a constant temperature environment of 25℃, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged at a constant current of 0.33C to 2.8V to obtain the first discharge capacity. The battery was then charged at a constant current of 0.33C to 4.4V, and then charged at a constant voltage of 4.4V until the cutoff current was 0.05C. The battery was then placed in a constant temperature oven at 60℃ for 30 days. After removal and cooling for 5 hours, it was discharged at a constant current of 0.33C to 2.8V under a constant temperature environment of 25℃, then charged at a constant current of 0.33C to 4.5V, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged at a constant current of 0.33C to 2.8V to obtain the reversible capacity after 30 days of storage at 60℃.

[0705] Reversible capacity retention rate after 30 days of storage at 60℃ (charged to 4.5V) = Reversible capacity after 30 days of storage at 60℃ / First discharge capacity × 100%.

[0706] The record is "30D capacity retention rate at 60℃ (charged to 4.5V)". Some test results can be found in Table 4.

[0707] (5) 45℃ Cyclic Performance Test (Charged to 4.5V)

[0708] At 45℃, a lithium-ion secondary battery is charged at a constant current of 1C to 4.5V, then charged at a constant voltage of 4.5V to a cutoff current of 0.05C, left to rest for 10 minutes, and then discharged at a constant current of 1C to 2.8V, left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same lithium-ion secondary battery, and the discharge capacity C of the first, second, ..., nth cycle is recorded. n .

[0709] Record the battery's cycle capacity retention rate P100 (charged to 4.5V) after 100 cycles = C100 / C0 × 100%.

[0710] The record is "45℃ Cycle Capacity 100-Cycle Retention Rate (Charged to 4.5V)", and some test results can be found in Table 4.

[0711] (II) Test Result Analysis

[0712] Preparation Examples 1-18 show the full width at half maximum (WHM) of the particle size distribution curves of primary particles in the positive electrode active material. H The particle size is controlled within ≤2.5μm, and the average particle size of the primary particles in the positive electrode active material is within the range of 1.3μm≤D1≤3μm.

[0713] Examples 1-18 respectively used the positive electrode active materials prepared in Examples 1-18 to prepare secondary batteries. All prepared secondary batteries could be charged and discharged at voltages higher than or equal to 4.2V (e.g., 4.4V, 4.5V). Battery life under high voltage was significantly improved, including significantly improved cycle life and storage life at high voltage. Capacity retention rates in both cycle performance tests and storage performance tests at high voltage were significantly improved. For example, Example 1 showed a significant improvement in "60°C storage capacity retention rate for 30 days" at high voltage compared to Comparative Examples 1-2 and 4, and Example 17 showed a significant improvement in cycle capacity retention rates (capacity retention rate after 100 cycles at 45°C (charged to 4.4V) and 45°C cycle capacity retention rate after 100 cycles (charged to 4.5V)) at high voltage compared to Comparative Examples 1-2 and 4, and Example 17 showed a significant improvement in cycle capacity retention rates (capacity retention rate after 100 cycles at 45°C (charged to 4.4V) and 45°C cycle capacity retention rate after 100 cycles at 45°C (charged to 4.5V)) compared to Comparative Example 5. For example, relevant data for the secondary battery prepared in Example 1 can be found in Table 4.

[0714] The positive electrode active materials prepared in Examples 1-18 showed low metal dissolution. Some results are listed in Table 3.

[0715] The positive electrode sheets prepared using the positive electrode active materials of Examples 1-18 all also exhibit good discharge specific capacity. See Table 3. In Comparative Example 3, the average particle size D1 of the primary particles in the positive electrode active material is relatively large, resulting in a significant decrease in discharge specific capacity.

[0716] Table 2.

[0717] Table 3.

[0718] Table 4.

[0719] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0720] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A secondary battery, which includes a positive electrode plate, the positive electrode plate includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm; The average particle size of the primary particles in the positive electrode active material is denoted as D1, satisfying 1.3 μm ≤ D1 ≤ 3 μm.

2. The secondary battery according to claim 1, wherein, The positive electrode active material satisfies one or more of the following characteristics: (ta1)1μm≤W H ≤2.5μm; (ta2) 1.4 μm ≤ D1 ≤ 2.5 μm.

3. The secondary battery according to claim 2, wherein, The positive electrode active material satisfies one or more of the following characteristics: (tb1)1.2μm≤W H ≤2.5μm; (tb2) 1.5 μm ≤ D1 ≤ 2.4 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein, The particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

5. The secondary battery according to any one of claims 1 to 4, wherein, The positive electrode active material D v The ratio of 50 to the average particle size of the primary particles in the positive electrode active material is denoted as R1, which satisfies 1≤R1≤3.

6. The secondary battery according to claim 5, wherein, 1.5≤R1≤2.2。 7. The secondary battery according to any one of claims 1 to 6, wherein, The positive electrode active material includes non-agglomerated primary particles; the mass percentage of the non-agglomerated primary particles in the positive electrode active material is denoted as f. M The proportion of the non-agglomerated primary particles in the positive electrode active material is denoted as f. N ; The positive electrode active material satisfies one or more of the following characteristics: (tc1)40%≤f M ≤100%; (tc2)60%≤f N ≤100%。 8. The secondary battery according to claim 7, wherein, The positive electrode active material satisfies one or more of the following characteristics: (td1)55%≤f M ≤100%; (td2)80%≤f N ≤100%。 9. The secondary battery according to claim 7, wherein, The positive electrode active material satisfies one or more of the following characteristics: (te1)80%≤f M <100%; (te2)90%≤f N <100%。 10. The secondary battery according to any one of claims 1 to 9, wherein, The positive electrode active material D v 50 is 2μm to 6μm.

11. The secondary battery according to claim 10, wherein, The positive electrode active material D v 50 is 2.8μm to 4.5μm.

12. The secondary battery according to any one of claims 1 to 11, wherein, The SPAN value of the positive electrode active material is 0.7–1.8; where SPAN = (D v 90-D v 10) / D v 50.

13. The secondary battery according to claim 12, wherein, The SPAN value of the positive electrode active material is 0.85 to 1.

35.

14. The secondary battery according to any one of claims 1 to 13, wherein, The positive electrode active material includes a lithium composite metal oxide, and the lithium composite metal oxide includes lithium element, non-lithium metal element and oxygen element; the non-lithium metal element includes a transition metal element.

15. The secondary battery according to claim 14, wherein, The lithium composite metal oxide includes one or more of a lithium nickel-based oxide, a lithium-rich manganese-based positive electrode material, spinel lithium manganate, lithium cobaltate, and a modified product of any one of the foregoing positive electrode active substances; wherein, the modified product includes one or more of a doping element and a coating element.

16. The secondary battery according to claim 15, wherein, The lithium composite metal oxide includes a lithium nickel-based oxide, the lithium nickel-based oxide contains Li element, non-lithium metal element and O element, and the non-lithium metal element includes Ni element; the lithium nickel-based oxide satisfies one or more of the following characteristics: (t1) The atomic molar ratio of Ni element to the non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1; (t2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.6 ≤ x2 ≤ 1.2; (t3) The lithium nickel-based oxide contains Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.6 ≤ x3 ≤ 2.

1.

17. The secondary battery according to claim 16, wherein, The lithium composite metal oxide satisfies one or more of the following characteristics: (i) 0.5 ≤ q1 ≤ 0.99; (ii) 0.5 ≤ q2 ≤ 0.99; (iii) 0.5 ≤ q3 ≤ 0.99; (iv) The lithium nickel-based oxide contains Co element, and the atomic molar ratio of Co element to the non-lithium metal element in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3, optionally, 0.02 ≤ q4 ≤ 0.3; (v) The lithium nickel-based oxide contains Mn element, and the atomic molar ratio of Mn element to the non-lithium metal element in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5, optionally, 0.01 ≤ q5 ≤ 0.5; 18. The secondary battery according to claim 17, wherein, (vi) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide is 80% to 100%. The lithium composite metal oxide satisfies one or more of the following characteristics: (ti) 0.5 ≤ q1 ≤ 0.8 or 0.8 <q1≤0.99; (tii) 0.5 ≤ q2 ≤ 0.8 or 0.8 <q2≤0.99; (tiii) 0.8 ≤ x² ≤ 1.1; (tiv) 0.5 ≤ q3 ≤ 0.8 or 0.8 <q3≤0.99; (tv)1.8≤x3≤2.06; (tvi) The lithium nickel-based oxide contains Co, where 0.05 ≤ q4 ≤ 0.2; (tvii) The lithium nickel-based oxide contains Mn element, 0.02≤q5≤0.38; (tviii) The lithium nickel-based oxide accounts for 90% to 100% of the mass of the lithium composite metal oxide.

19. The secondary battery according to any one of claims 15 to 18, wherein, The lithium composite metal oxide includes one or more lithium nickel cobalt manganese-based oxides and modified lithium nickel cobalt manganese-based oxides, wherein the modified oxides include one or more doping elements and coating elements.

20. The secondary battery according to any one of claims 1 to 19, wherein, The positive electrode active material satisfies one or more of the following characteristics: (tf1) The positive electrode active material includes doping elements, which include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb; (tf2) The positive electrode active material includes coating elements located on the particle surface, and the coating elements include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

21. The secondary battery according to claim 20, wherein, The positive electrode active material satisfies one or more of the following characteristics: (tf1') The positive electrode active material includes doping elements, and the doping elements include one or both of Zr and W; (tf2') The positive electrode active material includes a coating element located on the particle surface, and the coating element includes Ti.

22. The secondary battery according to any one of claims 1 to 21, wherein, The secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes the negative electrode active material, and the negative electrode active material includes one or more of carbon-based materials and silicon-based materials.

23. The secondary battery according to claim 22, wherein, The negative electrode active material includes graphite.

24. The secondary battery according to any one of claims 1 to 23, wherein, The secondary battery is a lithium-ion secondary battery.

25. The secondary battery according to any one of claims 1 to 24, wherein, The charging cutoff voltage of the secondary battery is greater than or equal to 4.2V; Optionally, the charging cut-off voltage of the secondary battery is greater than or equal to 4.3V; Alternatively, the charging cutoff voltage of the secondary battery is 4.2V to 4.5V, and more preferably 4.3V to 4.5V.

26. A method for preparing a positive electrode active material, comprising the following steps: The positive electrode active material solid precursor and lithium source are mixed to obtain a preliminary mixture. The preliminary mixture is subjected to a first sintering and a first crushing, and then subjected to a second sintering and a second crushing to prepare the positive electrode active material. The temperature at which the first sintering is performed is higher than the temperature at which the second sintering is performed. In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm; The average particle size of the primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3μm≤D1≤3μm.

27. The method for preparing the positive electrode active material according to claim 26, wherein it satisfies one or more of the following characteristics: (1) The positive electrode active material includes doping elements, and the initial mixture also includes raw materials containing the doping elements; (2) The positive electrode active material includes a coating element, and the preparation method of the positive electrode active material includes at least one of a first coating step and a second coating step. The first coating step is carried out simultaneously with the second sintering, and the second coating step is achieved by a third sintering after the second crushing.

28. The method for preparing the positive electrode active material according to claim 26 or 27, wherein it satisfies one or more of the following characteristics: (tg1) The positive electrode active material includes doping elements, which include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb; (tg2) The positive electrode active material includes a doping element, and the initial mixture also includes a raw material containing the doping element; the raw material containing the doping element includes one or more of the following: oxides, hydroxides, carbonates and phosphates containing the doping element; (tg3) The positive electrode active material includes coating elements, which include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na; (tg4) The raw materials providing the coating element include one or more of oxides, hydroxides, carbonates and phosphates containing the coating element; (tg5) The temperature for the first sintering is 900℃~980℃; (tg6) The first sintering time is 5h to 15h; (tg7) The temperature for the second sintering is 700℃~800℃; (tg8) The second sintering time is 4h to 12h; (tg9) The second sintering step is carried out in the presence of a first coating agent, which includes one or more of oxides, hydroxides, carbonates and phosphates of a first coating element, and the first coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

29. The method for preparing the positive electrode active material according to any one of claims 26 to 28, wherein, The solid precursor of the positive electrode active material satisfies one or more of the following characteristics: (tj1) The X-ray diffraction pattern of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 15° to 25°; (tj2) The X-ray diffraction pattern of the solid precursor of the positive electrode active material shows (001) crystal plane diffraction peaks, and the full width at half maximum (FWH) of the (001) crystal plane diffraction peaks is denoted as FWDH. (001) Where 0.35≤FWDH (001) ≤0.70; (tj3) The D of the solid precursor of the positive electrode active material v 50 is 2.5μm~4.5μm; (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m². 2 / g~35m 2 / g; (tj5) The SPAN value of the solid precursor of the positive electrode active material is 0.4 to 1.5; where SPAN = (D v 90-D v 10) / D v 50.

30. The method for preparing the positive electrode active material according to claim 29, wherein, The solid precursor of the positive electrode active material satisfies one or more of the following characteristics: (tk1)0.35≤FWDH (001) ≤0.64; (tk2) The D of the solid precursor of the positive electrode active material v 50 is 3.0μm~4.2μm; (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6m². 2 / g~30m 2 / g; (tk4) The SPAN value of the solid precursor of the positive electrode active material is 0.60 to 1.

30.

31. The method for preparing the positive electrode active material according to any one of claims 26 to 30, wherein, The prepared positive electrode active material satisfies one or more of the following characteristics (tm1) and (tm2): (tm1) The positive electrode active material prepared is the positive electrode active material as defined in any one of claims 1 to 16, 19-21; (tm2) The prepared positive electrode active material includes a lithium nickel-based oxide, which contains Li element, non-lithium metal elements and O element. The non-lithium metal elements include Ni element. The lithium nickel-based oxide satisfies one or more of the following characteristics (tn1), (tn2), (tn3), (tn4) and (tn5): (tn1) The atomic molar ratio of Ni element to non-lithium metal elements in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1; (tn2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.98 ≤ x2 ≤ 1.02; (tn3) The lithium nickel-based oxide contains Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.96 ≤ x3 ≤ 2.04; (tn4) The atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3; (tn5) The atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.

5.

32. A positive electrode active material, wherein, The positive electrode active material includes primary particles; In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm; The average particle size of the primary particles in the positive electrode active material is denoted as D1, and 1.3 μm ≤ D1 ≤ 3 μm.

33. The positive electrode active material according to claim 32, wherein, The positive electrode active material includes the positive electrode active material prepared by the preparation method of the positive electrode active material described in any one of claims 26 to 31, or is the positive electrode active material defined in the secondary battery described in any one of claims 2 to 21.

34. A positive electrode sheet, which includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum (W) is denoted as W. H Satisfying W H ≤2.5μm; The average particle size of the primary particles in the positive electrode active material is denoted as D1, and 1.3 μm ≤ D1 ≤ 3 μm.

35. The positive electrode sheet according to claim 34 satisfies one or more of the following characteristics: (to1) The positive electrode active material includes the positive electrode active material prepared by the preparation method of the positive electrode active material described in any one of claims 26 to 31; (to2) The positive electrode active material is the positive electrode active material defined in the secondary battery described in any one of claims 2 to 21; (to3) The positive electrode sheet is the positive electrode sheet defined in any one of claims 2 to 21.

36. An electrical device includes at least one of the secondary battery described in any one of claims 1 to 25, the positive electrode active material prepared by the preparation method of the positive electrode active material described in any one of claims 26 to 31, the positive electrode active material described in claim 32 or 33, and the positive electrode sheet described in claim 34 or 35.

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