Secondary battery, positive active material, preparation method of positive active material, positive pole piece and electric device

Abstract

The invention relates to a secondary battery, a positive active material, a preparation method of the positive active material, a positive pole piece and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive active layer, and the positive active layer comprises a positive active material; in a particle size distribution curve of primary particles in the positive electrode active material, the half-peak width is marked as WH, and WH is less than or equal to 2.5 microns; the average particle diameter D1 of the primary particles in the positive electrode active material satisfies 1.3 [mu] m < = D1 < = 3 [mu] m. The battery life of the secondary battery at a high voltage is significantly improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and further to secondary batteries, positive electrode active materials and preparation methods thereof, positive electrode plates and electrical devices. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] With the development of secondary battery technology, secondary batteries represented by lithium-ion secondary batteries are increasingly widely used in smart phones, tablet computers, laptops, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and are also widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations. With the increasing popularity of secondary batteries under high voltage, the requirements for the life of secondary batteries under high voltage are getting higher and higher. Summary of the invention

[0004] According to various embodiments and examples of the present application, the present application provides a secondary battery, a positive electrode active material and a preparation method thereof, a positive electrode sheet and an electric device. The battery life of the secondary battery at high voltage is significantly improved.

[0005] In a first aspect of the present application, a secondary battery is provided, which includes a positive electrode plate, wherein the positive electrode plate includes a positive electrode active material; the particle size distribution of primary particles in the positive electrode active material is narrow; and the average particle size D1 of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0006] In some embodiments, a secondary battery is provided, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material;

[0007] In the particle size distribution curve of the primary particles in the positive electrode active material, the half peak width is denoted as W H , satisfying W H ≤2.5μm;

[0008] The average particle size of primary particles in the positive electrode active material is recorded as D1, which satisfies 1.3 μm≤D1≤3 μm.

[0009] In the positive electrode active material of the secondary battery, the primary particle is a particle basic unit.

[0010] For the positive electrode active materials of traditional secondary batteries, on the one hand, the small-sized, large-surface-area non-agglomerated primary particles are prone to cause large interfacial side reactions, and such interfacial side reactions are easily aggravated under high voltage, affecting the battery life under high voltage, such as cycle and / or storage life. On the other hand, the secondary particles in traditional positive electrode active materials are usually agglomerated by smaller-sized nanoscale primary particles. Since the contact area between adjacent primary particles is relatively small, the secondary particles are prone to cracking due to stress under high voltage and forming a fresh interface, which will accelerate the consumption of electrolyte during the cycle and / or storage under high voltage, thereby deteriorating the battery life.

[0011] In the secondary battery provided in the first aspect of the present application, by controlling the half peak width (W H ) is within the aforementioned range, so that the particle size distribution of the primary particles in the positive electrode active material is relatively uniform, and the average particle size (D1) of the primary particles in the positive electrode active material is further controlled within the aforementioned range, so that the primary particles in the positive electrode active material have a relatively large micron-level size; thereby, on the one hand, the content of non-agglomerated primary particles with small size and large specific surface area can be reduced, so that the interface side reaction of the positive electrode active material under high voltage can be significantly suppressed; on the other hand, when there are secondary particles formed by the agglomeration of primary particles in the positive electrode active material, by controlling the average particle size and particle size distribution of the primary particles within the aforementioned range, the primary particles in the secondary particles can have The relatively large micron-scale size can make the primary particles in the secondary particles have a relatively large contact area, so that the primary particles in the secondary particles are more firmly combined under high voltage, reducing the risk of cracking of the positive electrode active material under high voltage, reducing the generation of fresh interfaces, and slowing down the consumption of electrolyte during circulation and / or storage under high voltage; through the aforementioned multiple effects, the interfacial side reactions under high voltage can be significantly inhibited, the risk of cracking of the positive electrode active material under high voltage can be reduced, the structural stability of the positive electrode active material can be improved, and the consumption of electrolyte during circulation and / or storage under high voltage can be slowed down, thereby significantly improving the battery life of the secondary battery under high voltage.

[0012] The effects described in any part of the present application are not intended to be limited by any theory.

[0013] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0014] (ta1)1μm≤W H ≤2.5μm;

[0015] (ta2)1.4μm≤D1≤2.5μm.

[0016] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0017] (tb1)1.2μm≤W H ≤2.5μm;

[0018] (tb2)1.5μm≤D1≤2.4μm.

[0019] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H ≤2.5μm) and 1.3μm≤D1≤3μm, by controlling the positive electrode active material to satisfy one or more of the characteristics (ta1), (ta2), (tb1) and (tb2), the distribution width and / or the average particle size of the primary particles can be further regulated within a more suitable range, thereby better improving the battery life under high voltage.

[0020] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H ≤2.5μm) and 1.3μm≤D1≤3μm, by further controlling the half peak width (W H ) is within the aforementioned optional range, which is conducive to making the particle size distribution of the primary particles in the positive electrode active material more uniform; on the one hand, it is more conducive to reducing the content of non-agglomerated primary particles with small size and large specific surface area, and reducing interfacial side reactions under high voltage; on the other hand, 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 the consumption of electrolyte during circulation and / or storage under high voltage. Based on the influence of the aforementioned multiple effects, it is conducive to better improving the battery life under high voltage.

[0021] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H ≤2.5μm) and 1.3μm≤D1≤3μm, by further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned optional range, it is beneficial to make the primary particles in the positive electrode active material have a more suitable micron-level size, and is more beneficial to reduce the content of non-agglomerated primary particles with small size and large specific surface area, better reduce interfacial side reactions under high voltage and improve the stability of the CEI film (the solid electrolyte interface film of the positive electrode can be called CEI film). At the same time, 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 the consumption of electrolyte during cycling and / or storage under high voltage. Based on the influence of the aforementioned multiple effects, it is beneficial to better improve the battery life under high voltage.

[0022] On the other hand, by inhibiting the generation of fresh interfaces under high voltage, it is also beneficial to resist the increase of impedance, inhibit the deterioration of battery dynamics, and promote the discharge capacity of the positive electrode active material and improve the battery rate performance.

[0023] 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, which may reduce the deintercalation area of ​​the active ions and thus affect the deintercalation rate. It will also cause the solid phase transmission path of the active ions to become longer and the diffusion time to increase. During high-rate discharge, the active ions may not be able to fully escape in a short time. Therefore, it 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 more suitable micron size (such as 1.3μm≤D1≤3μm, further such as 1.4μm≤D1≤2.5μm, and further such as 1.5μm≤D1≤2.4μm), it is also beneficial for the positive electrode to have good discharge capacity and rate performance.

[0024] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

[0025] 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 better improve the uniformity of the particle size distribution of the primary particles in the positive electrode active material.

[0026] 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 recorded as R1, and satisfies 1≤R1≤3.

[0027] In some embodiments, 1.5≤R1≤2.2.

[0028] By increasing the D v 50 (can be recorded as D v 50 A ) relative to the average particle size (D1) of the primary particles in the positive electrode active material (R1 = D v 50 A / D1) is controlled within the aforementioned range, which is beneficial to making the median particle size of the positive electrode active material close to the average particle size of the primary particles as the basic unit of the particles, and further helps to reduce the agglomeration ratio of the primary particles in the positive electrode active material, reduce the content of the secondary particles as the primary particle agglomerates, and accordingly increase the proportion of non-agglomerated primary particles. The non-agglomerated primary particles do not have interfaces between the primary particles in the secondary particles, which can better resist the changes in volume stress and the risk of cracking under high voltage, so that the positive electrode active material has better structural stability under high voltage, and thus is more conducive to improving the battery life under high voltage.

[0029] In some embodiments, the positive electrode active material includes non-agglomerated primary particles; the mass proportion of the non-agglomerated primary particles in the positive electrode active material is denoted as f M The non-agglomerated primary particles in the positive electrode active material are denoted as f N ;

[0030] The positive electrode active material satisfies one or more of the following characteristics:

[0031] (tc1)40%≤f M ≤100%;

[0032] (tc2)60%≤f N ≤100%.

[0033] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0034] (td1)55%≤f M ≤100%;

[0035] (td2)80%≤f N ≤100%.

[0036] The mass proportion of non-agglomerated primary particles in the positive electrode active material (f M ) and the proportion of non-agglomerated primary particles in the positive electrode active material (f N ) is controlled within the aforementioned range, the proportion of non-agglomerated primary particles can be controlled within a more appropriate range, so that the positive electrode active material can better resist volume stress changes and cracking risks under high voltage, have better structural stability, and thus be more conducive to improving the battery life under high voltage.

[0037] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0038] (te1)80%≤f M <100%;

[0039] (te2)90%≤f N <100%.

[0040] The mass proportion of non-agglomerated primary particles in the positive electrode active material (f M ) and the proportion of non-agglomerated primary particles in the positive electrode active material (f N) is controlled within the aforementioned higher range. When 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 further more conducive to improving the battery life under high voltage.

[0041] In some embodiments, the D of the positive electrode active material v 50 is 2μm~6μm.

[0042] In some embodiments, the D of the positive electrode active material v 50 is 2.8μm~4.5μm.

[0043] The half-peak width (W ) in the particle size distribution curve of primary particles in the positive electrode active material is synergistically controlled. H ) and the average particle size (D1) of the primary particles in the positive electrode active material, by further increasing the D v Controlling the value of 50 within the aforementioned range is beneficial to making the particle size in the positive electrode active material more moderate, and is beneficial to reducing the agglomeration ratio of the primary particles in the positive electrode active material, and can increase the proportion of non-agglomerated primary particles. The non-agglomerated primary particles do not have interfaces between the primary particles in the secondary particles, and 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, which can better improve the battery life under high voltage.

[0044] By v Further control of 50 can further reduce the content of non-agglomerated primary particles with small size and large specific surface area in the positive electrode active material, which is more conducive to reducing interfacial side reactions under high voltage, and further more conducive to improving battery life under high voltage.

[0045] On the other hand, by increasing the D v Controlling the value of 50 within the aforementioned range is also helpful in controlling the content of large-sized secondary particles formed by the agglomeration of primary particles to be lower. Therefore, the problem of the generation of fresh interfaces caused by the cracking of the agglomerated large-sized secondary particles under high voltage is suppressed, which is beneficial to reduce the increase in impedance caused by the generation of fresh interfaces and improve the battery kinetic performance.

[0046] 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.

[0047] In some embodiments, the SPAN value of the positive electrode active material is 0.85 to 1.35.

[0048] 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, which is beneficial to reduce the content of small-sized non-agglomerated primary particles and reduce interfacial side reactions under high voltage. It is also beneficial to reduce the content of large-sized secondary particles and reduce the negative impact of possible cracking of secondary particles under high voltage on the battery life under high voltage. Through the aforementioned multiple effects, it is beneficial to significantly improve the battery life under high voltage.

[0049] In some embodiments, the positive electrode active material includes a lithium composite metal oxide, the lithium composite metal oxide includes a lithium element, a non-lithium metal element, and an oxygen element; and the non-lithium metal element includes a transition metal element.

[0050] In some embodiments, the lithium composite metal oxide includes one or more of lithium nickel-based oxide, lithium-rich manganese-based positive electrode material, spinel lithium manganese oxide, lithium cobalt oxide and any modified form of the foregoing positive electrode active material; wherein the modified form includes one or more of a doping element and a coating element.

[0051] By introducing lithium nickel-based oxides into the positive electrode active material, it is beneficial to improve the energy density.

[0052] By introducing lithium-rich manganese-based positive electrode materials, spinel lithium manganese oxide, lithium cobalt oxide and other positive electrode active materials into the positive electrode active materials, it is beneficial to make the positive electrode active materials have better structural stability under high voltage, which is beneficial to extend the battery life under high voltage.

[0053] In some embodiments, the lithium composite metal oxide includes a lithium nickel-based oxide, the lithium nickel-based oxide includes a Li element, a non-lithium metal element and an O element, the non-lithium metal element includes a Ni element; the lithium nickel-based oxide satisfies one or more of the following characteristics:

[0054] (t1) the atomic molar ratio of the Ni element to the non-lithium metal element in the lithium nickel-based oxide is q1, wherein 0.5≤q1<1;

[0055] (t2) the lithium nickel-based oxide comprises Ni and Li elements in an atomic molar ratio of q2:x2, wherein 0.5≤q2<1, 0.6≤x2≤1.2;

[0056] (t3) The lithium nickel-based oxide contains Ni element and O element in an atomic molar ratio of q3:x3, wherein 0.5≤q3<1, 1.6≤x3≤2.1.

[0057] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics:

[0058] (i) 0.5 ≤ q1 ≤ 0.99;

[0059] (ii) 0.5 ≤ q2 ≤ 0.99;

[0060] (iii) 0.5 ≤ q3 ≤ 0.99;

[0061] (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;

[0062] (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;

[0063] (vi) The mass fraction of the lithium nickel-based oxide in the lithium composite metal oxide is 80% - 100%.

[0064] In some embodiments, the lithium composite metal oxide satisfies one or more of the following characteristics:

[0065] (ti) 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99;

[0066] (tii) 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99;

[0067] (tiii) 0.8 ≤ x2 ≤ 1.1;

[0068] (tiv) 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99;

[0069] (tv) 1.8 ≤ x3 ≤ 2.06;

[0070] (tvi) The lithium nickel-based oxide contains Co element, 0.05 ≤ q4 ≤ 0.2;

[0071] (tvii) The lithium nickel-based oxide contains Mn element, 0.02 ≤ q5 ≤ 0.38;

[0072] (tviii) The mass fraction of the lithium nickel-based oxide in the lithium composite metal oxide is 90% - 100%.

[0073] By controlling the lithium nickel-based oxide in the positive electrode active material to have the aforementioned nickel content, the positive electrode active material has better crystal structure stability under high voltage, which is more conducive to improving the battery life under high voltage.

[0074] In some embodiments, the lithium composite metal oxide includes one or more of lithium nickel cobalt manganese-based oxides and modified lithium nickel cobalt manganese-based oxides, and the modified lithium nickel cobalt manganese-based oxides include one or more of doping elements and coating elements.

[0075] In lithium nickel cobalt manganese-based oxides, the nickel element can play a role in improving the energy density, the cobalt element can play a role in reducing cation mixing and enhancing the material structure stability and rate performance, and the manganese element can play a role in stabilizing the layered structure stability of the lithium nickel cobalt manganese-based oxide material, but is not limited to the roles described above.

[0076] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0077] (tf1) the positive electrode active material includes a doping element, and the doping element includes one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb;

[0078] (tf2) The positive electrode active material includes a coating element located on the surface of the particle, and the coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0079] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0080] (tf1') the positive electrode active material includes a doping element, and the doping element includes one or both of Zr and W;

[0081] (tf2′) The positive electrode active material includes a coating element located on the surface of the particle, and the coating element includes Ti.

[0082] By introducing one or more of the doping elements and the coating elements into the positive electrode active material, the positive electrode active material can be modified by one or more of the doping modification and the coating modification. Taking the introduction of doping elements as an example, as a non-limiting example, by introducing doping elements (such as Zr, W, etc.), it can be beneficial to improve the binding force between the transition metal elements and O atoms in the positive electrode active material, thereby improving the lattice stability during the lithium insertion and extraction process and improving the stability of the positive electrode active material. Taking the introduction of the coating element Ti as an example, it is beneficial to form an oxide coating layer, which hinders the direct contact between the electrolyte and the positive electrode material, thereby reducing the interface side reactions.

[0083] In some embodiments, the secondary battery further includes a negative electrode plate, the negative electrode plate 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 a carbon-based material and a silicon-based material.

[0084] In some embodiments, the negative electrode active material includes a graphite material.

[0085] The negative electrode active material in the negative electrode sheet can be selected from the aforementioned types, but is not limited thereto.

[0086] In some embodiments, the secondary battery is a lithium ion secondary battery.

[0087] In some embodiments, the charging cut-off voltage of the secondary battery is greater than or equal to 4.2V;

[0088] Optionally, the charging cut-off voltage of the secondary battery is greater than or equal to 4.3V;

[0089] Alternatively, the charging cut-off voltage of the secondary battery is 4.2V to 4.5V, and further optionally 4.3V to 4.5V.

[0090] In the second aspect of the present application, a method for preparing a positive electrode active material is provided. The prepared positive electrode active material can be used as the positive electrode active material in the secondary battery described in the first aspect of the present application or as a partial raw material of the positive electrode active material in the secondary battery described in the first aspect of the present application.

[0091] In some embodiments, a method for preparing a positive electrode active material is provided, comprising the following steps:

[0092] Mixing a positive electrode active material solid precursor and a lithium source to obtain a primary mixture, performing a first sintering and a first crushing on the primary mixture, and then performing a second sintering and a second crushing on the primary mixture to prepare the positive electrode active material;

[0093] The temperature for performing the first sintering is higher than the temperature for performing the second sintering;

[0094] In the particle size distribution curve of the primary particles in the positive electrode active material, the half peak width is denoted as W H , satisfying W H ≤2.5μm;

[0095] The average particle size of primary particles in the positive electrode active material is recorded as D1, which satisfies 1.3 μm≤D1≤3 μm.

[0096] By sintering and crushing the primary mixture including the solid precursor of the positive electrode active material and the lithium source multiple times, the solid precursor can be lithiated by the first sintering to form the target crystal structure of the positive electrode active material, the first crushing can reduce the agglomeration between particles, and the second sintering can achieve the effects of repairing the particle morphology, reducing defects, and promoting the fusion of fine particles. The second crushing can reduce the agglomeration between particles again, thereby preparing a positive electrode active material with a moderate primary particle size and uniform particle size distribution.

[0097] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0098] (1) The positive electrode active material includes a doping element, and the primary mixture also includes a raw material containing the doping element;

[0099] (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 performed simultaneously with the second sintering, and the second coating step is achieved by a third sintering after the second crushing.

[0100] According to the target composition of the positive electrode active material, one or more of the doping elements and the coating elements can be selectively introduced during the preparation process.

[0101] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0102] (tg1) the positive electrode active material includes a doping element, and the doping element includes one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn and Sb;

[0103] (tg2) the positive electrode active material includes a doping element, and the primary mixed material further includes a raw material containing the doping element; the raw material containing the doping element includes one or more of an oxide, a hydroxide, a carbonate and a phosphate containing the doping element;

[0104] (tg3) the positive electrode active material includes a coating element, and the coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na;

[0105] (tg4) providing a raw material for the coating element including one or more of an oxide, a hydroxide, a carbonate and a phosphate containing the coating element;

[0106] (tg5) the temperature of the first sintering is 900° C. to 980° C.;

[0107] (tg6) the first sintering time is 5h to 15h;

[0108] (tg7) the temperature of the second sintering is 700° C. to 800° C.;

[0109] (tg8) The second sintering time is 4h to 12h;

[0110] (tg9) The step of performing the second sintering is performed in the presence of a first coating agent, wherein the first coating agent 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.

[0111] By controlling one or more parameters in the preparation process within the aforementioned range, it is helpful to better regulate the particle size and particle size distribution of the primary particles in the positive electrode active material.

[0112] In some embodiments, the positive electrode active material solid precursor satisfies one or more of the following characteristics:

[0113] (tj1) the X-ray diffraction spectrum of the positive electrode active material solid precursor has a peak at a 2θ (°) diffraction angle of 15° to 25°;

[0114] (tj2) The X-ray diffraction spectrum of the positive electrode active material solid precursor has a (001) crystal plane diffraction peak, and the half-peak width of the (001) crystal plane diffraction peak is recorded as FWDH (001) , where 0.35≤FWDH (001) ≤0.70, optionally, 0.35≤FWDH (001) ≤0.64;

[0115] (tj3) D of the solid precursor of the positive electrode active material v 50: 2.5μm~4.5μm;

[0116] (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m 2 / g~35m 2 / g;

[0117] (tj5) The SPAN value of the solid precursor of the positive electrode active material is 0.4 to 1.5; wherein SPAN = (D v 90-D v 10) / D v 50.

[0118] In some embodiments, the positive electrode active material solid precursor satisfies one or more of the following characteristics:

[0119] (tk1)0.35≤FWDH (001) ≤0.64;

[0120] (tk2) D of the solid precursor of the positive electrode active material v 50: 3.0μm~4.2μm;

[0121] (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6 m 2 / g~30m 2 / g;

[0122] (tk4) The SPAN value of the solid precursor of the positive electrode active material is 0.60 to 1.30.

[0123] The position of the diffraction peak in the X-ray diffraction spectrum of the positive electrode active material solid precursor can be used to determine the formation of the (001) crystal plane. The solid precursor of the lithium nickel cobalt manganese-based oxide positive electrode active material usually has a layered structure, and the (001) crystal plane is a crystal plane in the layered structure that is perpendicular to the stacking direction of the layered structure. The "half peak width of the (001) crystal plane" (denoted as FWDH (001) ) characterizes the crystallinity of the solid precursor of the positive electrode active material, and the lower FWDH (001) Corresponding to higher crystallinity. (001) Controlling within the aforementioned range can make the solid precursor of the positive electrode active material have a more suitable crystallinity, make the particles after sintering have a more suitable hardness, and help reduce the generation of micropowder or fine particles in the crushing step; therefore, on the basis of the aforementioned multiple sintering and multiple crushing processes, the FWDH of the solid precursor of the positive electrode active material is further controlled. (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.

[0124] The positive electrode active material is prepared by using a solid precursor of the positive electrode active material with relatively high crystallinity, and then the positive electrode plate and the secondary battery are prepared. During the process of lithium insertion and extraction under high voltage, the amount of transition metal dissolution in the positive electrode active material is reduced, the transition metal deposition at the negative electrode is reduced, the thickening of the negative electrode solid electrolyte interface (SEI) film is inhibited, and the loss of active lithium is weakened, which can inhibit the deterioration of the battery life under high voltage.

[0125] By controlling the FWDH of the solid precursor of the cathode active material (001) , D of the solid precursor of the positive electrode active material vWhen one or more parameters among the specific surface area of the solid precursor of the positive electrode active material and the SPAN value of the solid precursor of the positive electrode active material are within the aforementioned ranges, it is beneficial to control the average particle size (D1) and particle size distribution (such as W H ) of the primary particles, the D v 50 and SPAN value of the positive electrode active material, R1 (the ratio of D v 50 of the positive electrode active material to the average particle size D1 of the primary particles), etc. are within more appropriate ranges, without being limited to any theory. For example, it can be more beneficial to reduce the contact area between the positive electrode active material and the electrolyte, more beneficial to reduce the side reactions at the positive electrode - electrolyte interface under high voltage, more beneficial to reduce the metal dissolution of the positive electrode, and more beneficial to improve the structural stability of the positive electrode active material under high voltage. Thus, it is more beneficial to improve the battery life under high voltage. Exemplarily, when the positive electrode active material contains manganese elements, it is also beneficial to reduce manganese dissolution.

[0126] In some embodiments, the prepared positive electrode active material satisfies one or more of the following characteristics (tm1) and (tm2):

[0127] (tm1) The prepared positive electrode active material is the positive electrode active material defined in the first aspect of the present application;

[0128] (tm2) The prepared positive electrode active material 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, 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.

[0129] In the third aspect of the present application, a positive electrode active material is provided, and the positive electrode active material includes primary particles;

[0130] In the particle size distribution curve of the primary particles in the positive electrode active material, the full width at half maximum is denoted as WH , satisfying W H ≤2.5μm;

[0131] The average particle size of primary particles in the positive electrode active material is recorded as D1, which satisfies 1.3 μm≤D1≤3 μm.

[0132] The positive electrode 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 under high voltage. Without being limited to any theory, please refer to the description in the first aspect of the present application.

[0133] 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 the present application, or is the positive electrode active material defined in the first aspect of the present application (that is, the same characteristics as the positive electrode active material in the secondary battery of the first aspect).

[0134] In a fourth aspect of the present application, a positive electrode sheet is provided, comprising a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material;

[0135] In the particle size distribution curve of the primary particles in the positive electrode active material, the half peak width is denoted as W H , satisfying W H ≤2.5μm;

[0136] The average particle size of primary particles in the positive electrode active material is recorded as D1, which satisfies 1.3 μm≤D1≤3 μm.

[0137] 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, and the battery life of the secondary battery at high voltage can be improved, including the cycle and / or storage life.

[0138] In some embodiments, the positive electrode plate satisfies one or more of the following characteristics:

[0139] (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 the present application;

[0140] (to2) the positive electrode active material is the positive electrode active material defined in the first aspect of the present application;

[0141] (to3) The positive electrode plate is the positive electrode plate defined in the first aspect of the present application.

[0142] In the fifth aspect of the present application, an electrical device is provided, which includes the secondary battery described in the first aspect of the present application, the positive electrode active material prepared by the preparation method of the positive electrode active material described in the second aspect of the present application, the positive electrode active material described in the third aspect of the present application, and at least one of the positive electrode plates described in the fourth aspect of the present application.

[0143] The details of one or more implementations or embodiments of the present application are set forth in the following drawings and description. Other features, objects and advantages of the present application will become apparent from the description, drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0144] In order to better describe and illustrate the embodiments, examples or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments, examples or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0145] Figure 1 It is a particle size distribution curve diagram of the primary particles in the positive electrode active material in one embodiment of the present application. The statistical range of the primary particles includes non-agglomerated primary particles and primary particles that may exist in secondary particles. The horizontal axis is the particle size of the primary particles, and the vertical axis is the number of primary particles of different particle sizes.

[0146] Figure 2 This is a scanning electron microscope (SEM) image of a solid precursor of a positive electrode active material in an embodiment of the present application.

[0147] Figure 3 It is an X-ray diffraction (XRD) diagram of a solid precursor for preparing a positive electrode active material in an embodiment of the present application, wherein the abscissa is 2θ (unit is ° (degree)) and the coordinate axis is intensity (Intensity (au)).

[0148] Figure 4 is a SEM image of the positive electrode active material in one embodiment of the present application.

[0149] Figure 5 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0150] Figure 6 for Figure 5 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0151] Figure 7 FIG. 1 is a schematic diagram of a battery device according to an embodiment of the present application.

[0152] Figure 8 A schematic diagram of a battery pack according to an embodiment of the present application.

[0153] Fig. 9 for Figure 8 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0154] Fig.10 A schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0155] Description of reference numerals:

[0156] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery device; 5. Battery cell; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0157] Below, some embodiments and some examples of the secondary battery, positive electrode active material and preparation method thereof, positive electrode sheet and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0158] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0159] In the present application, when it comes to "numerical value", its meaning includes the present number and its reasonable approximation. The definition of "numerical value" can be applied to discrete numerical points and the endpoints of the numerical range. If not specifically limited, when it comes to "approximation", it covers the numerical interval based on the reasonable fluctuation range of the present number, and the reasonable fluctuation range may vary depending on the type and numerical value of the present number. The reasonable fluctuation range can be reasonably confirmed according to the accuracy of the test or measurement method. Therefore, when it comes to numerical values ​​or numerical ranges, if there is no special explanation, it should be understood that the numerical value covers its reasonable approximation, and the numerical range covers the reasonable approximation of the two endpoints. Those skilled in the art can understand that the acceptable fluctuation range of the relevant approximation can be included in the definition of the numerical value or the numerical range. In the present application, if there is no other explanation, "N1" can be reasonably understood as "about N1", and "N1~N2" can be reasonably understood as "about N1 to about N2", wherein N1 and N2 are two unequal numerical values.

[0160] In this application, unless otherwise specified, "about" means within a reasonable range above and below the number, and the fluctuation range may vary depending on the type and value of the number. For example, it may be allowed to be within a range of ±10%, ±5%, ±2%, ±1%, etc. For example, taking "about 20°C" and its approximate value of ±1°C as an example, the approximate values ​​of 19°C, 19.5°C, etc. within the approximate range shown in "about 20°C" should also be included in the range indicated by "about 20°C".

[0161] In the present application, when "multiple", "multiple", "multiple", "several", etc. are involved, unless otherwise specified, it means that the number is greater than 2 or equal to 2. For example, "one or more" means one or ≥ (greater than or equal to) two. It is understood that when "any number" of items are involved, it means any suitable combination of multiple items, that is, the combination of "any number" of items is carried out in a way that does not conflict and can implement the present application.

[0162] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0163] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0164] Those skilled in the art will appreciate that in the methods of the various embodiments or embodiments of the present application, if not particularly limited, the order of writing of each step does not mean a strict execution order and constitutes any limitation to the implementation process, and the detailed execution order of each step should be determined by its function and possible internal logic. If there is no special description, all steps of the present application can be performed in sequence, or can be performed randomly, and can preferably be performed in sequence. For example, method M includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, method M may also include step (c), indicating that step (c) can be added to method M in any order, for example, method M may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0165] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, a includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "a consists of a1, a2 and a3" or "a is selected from a1, a2 and a3", and the feature or solution of "a includes not only a1, a2 and a3, but also other members".

[0166] In the present application, unless otherwise specified, M (such as m1) means that m1 is a non-limiting example of M, and it can be understood that M is not limited to m1.

[0167] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel solutions of "yes" or "no". If there are multiple "optional" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent. Unless otherwise specified, the descriptions of "optionally include", "optionally include", etc. in this application, taking "optionally include" as an example, mean "may include or not include".

[0168] In the present application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more related listed items, and also include any and all combinations of the related listed items, wherein 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" means a group consisting of M, N, and "a combination of M and N". Among them, "including M and / or N" can mean "including M, including N, and including M and N", and can also mean "including M, including N, or including M and N", which can be properly understood according to the sentence in which it is located.

[0169] As used herein, "combination thereof", "any combination thereof", "any combination thereof" etc. include all suitable combinations of any two or more of the listed items.

[0170] Herein, the word “suitable” in “suitable combination”, “suitable method”, “any suitable method”, etc., shall be based on the technical solution that can implement the present application.

[0171] Herein, "preferred", "better", "more preferred", "suitable", "better", and "preferable" are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute a limitation on the scope of protection of this application. If multiple "preferred" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "preferred" item is independent.

[0172] In the present application, “further”, “furthermore”, “particularly”, “for example”, “such as”, “example”, “for example”, etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of the present application.

[0173] In the present application, the terms "first", "second", "third", "fourth", etc. in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0174] In the description of the present application, it should be understood that the terms "length", "width", "thickness", "height", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0175] In this application, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection. For ordinary technicians in this field, the meanings of the above terms in this application can be understood according to the circumstances.

[0176] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean a relative positional relationship in terms of horizontal height, or may mean that there is an attachment relationship without limiting the relative positional relationship in terms of horizontal height.

[0177] In the present application, the term "room temperature" generally refers to 4°C to 35°C, and may refer to 20°C±5°C. In some embodiments or examples of the present application, room temperature refers to 20°C to 30°C.

[0178] In this application, when the units of a data range are mentioned, if there is a unit only after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 3-5μm or 3-5μm both mean that the units of the left endpoint "3" and the right endpoint "5" are both μm (micrometers), which have the same meaning as 3μm-5μm. In addition, similar descriptions of other parameters such as temperature and size are also understood in the same way.

[0179] 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 expressed as ">", and "less than" can be equivalently expressed as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be regarded as providing two solutions of "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be regarded as providing two solutions of "less than" and "equal to".

[0180] In the present application, exemplary descriptions such as "in some implementation modes (or examples)" and "in one implementation mode (or example)" may include but are not limited to the following meanings: these solutions may be combined with other solutions in a suitable manner to form new technical solutions.

[0181] The improved effects described in this application, unless otherwise stated, are not intended to be limited to any theory.

[0182] With the increasing popularity of secondary battery applications, in order to meet the ever-increasing demand for long battery life, the high voltage performance of secondary batteries has received increasing attention. By increasing the operating voltage of secondary batteries, energy reserves can be increased under the same battery volume or weight, thereby extending battery life. Under high voltage, the positive electrode active material is prone to detaching or embedding a large number of active ions. During cycling and / or storage at high voltage, the positive electrode active material is prone to aggravated interfacial side reactions, and the risk of cracking of the positive electrode active material increases, resulting in deterioration of the battery life under high voltage.

[0183] In order to improve the structural stability of the positive electrode active material under high voltage and thus improve the battery life under high voltage, the positive electrode active material can select non-agglomerated primary particles. Compared with the secondary particles formed by the agglomeration of primary particles, there is no interface between the primary particles in the non-agglomerated primary particles, so that the non-agglomerated primary particles can better resist the change of volume stress and the risk of cracking under high voltage. Therefore, the non-agglomerated primary particles have better structural stability under high voltage. The existence of interfaces between multiple primary particles in the secondary particles leads to a relatively large risk of cracking of the secondary particles under high voltage, and the cracking of particles will form a fresh interface; during the cycle and / or storage under high voltage, the fresh interface will further react with the electrolyte to form a new solid electrolyte interface film (the solid electrolyte interface film of the positive electrode can be called CEI film), which consumes lithium, causes an increase in impedance, and leads to a deterioration of battery life.

[0184] However, non-agglomerated primary particle positive electrode materials are prone to introduce some small-sized non-agglomerated primary particles, and these small-sized non-agglomerated primary particles will have a relatively large specific surface area, a large interface area in contact with the electrolyte, and more interface side reactions. Moreover, such interface side reactions are easily aggravated under high voltage, which will in turn deteriorate the battery life under high voltage. If you want to increase the size of non-agglomerated primary particles, you usually need to increase the sintering temperature and / or extend the sintering time in the preparation process, which will easily lead to aggravated agglomeration of primary particles and increase the secondary particle content; and those small-sized secondary particles are difficult to screen out from non-agglomerated primary particles of similar size. This makes it challenging to improve the battery life of secondary batteries at high voltages.

[0185] According to various embodiments and examples of the present application, the present application provides a secondary battery, a positive electrode active material and a preparation method thereof, a positive electrode sheet and an electric device. The battery life of the secondary battery at high voltage is significantly improved.

[0186] Normally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The secondary battery may also include a separator, which is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. A solid electrolyte membrane may also be used to conduct active ions between the positive electrode layer and the negative electrode layer, and to isolate the positive electrode from the negative electrode to prevent the positive and negative electrodes from short-circuiting.

[0187] In the present application, unless otherwise specified, the "electrode active material layer" includes at least one of the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet. Depending on the detailed circumstances, the electrode active material layer may refer to the positive electrode active material layer or the negative electrode active material layer. It can be understood that the positive electrode active material layer contains positive electrode active materials, and the negative electrode active material layer contains negative electrode active materials. In the present application, the "electrode active material layer" may also be recorded as the "active material layer", the "positive electrode active material layer" may also be recorded as the "positive electrode active layer", and the "negative electrode active material layer" may also be recorded as the "negative electrode active layer".

[0188] In this application, the terms "pole sheet" and "electrode pole sheet" have the same meaning and can be used interchangeably. The electrode pole sheet can be a positive pole sheet or a negative pole sheet, and the "active material" or "active substance" in the electrode pole sheet has the ability to reversibly embed and release active ions. When the battery cell or secondary battery is charged, the active ions are released from the positive electrode and embedded in the negative electrode through the electrolyte; when the battery cell or secondary battery is discharged, the active ions are released from the negative electrode and embedded in the positive electrode.

[0189] In the present application, the term "negative electrode sheet" includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that can reversibly insert and extract active ions.

[0190] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. "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 can be located on one side or both sides of the negative electrode current collector.

[0191] In the present 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 can reversibly extract and insert active ions.

[0192] In this application, unless otherwise specified, "positive electrode sheet" includes positive electrode current collector. "Positive electrode current collector" refers to the structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive electrode active layer is located on at least one side of the positive electrode current collector, and can be located on one side or both sides of the positive electrode current collector.

[0193] In the present application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0194] In a first aspect of the present application, a secondary battery is provided, which includes a positive electrode plate, the positive electrode plate includes a positive electrode active material; the particle size distribution uniformity of primary particles in the positive electrode active material is good, and the primary particles in the positive electrode active material have a moderate average particle size. The battery life of the secondary battery at high voltage is significantly improved.

[0195] In some embodiments, a secondary battery is provided, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material;

[0196] 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;

[0197] The average particle size of primary particles in the positive electrode active material is denoted as D1, which satisfies 1.3 μm ≤ D1 ≤ 3 μm.

[0198] In the present application, unless otherwise specified, the "primary particles" in the positive electrode active material are the basic units of particles in the positive electrode active material. It is understood that there are primary particles in the positive electrode active material. In the positive electrode active material, the primary particles can be in a non-agglomerated state or can be formed into aggregates by multiple primary particles. The non-agglomerated primary particles can be referred to as "non-agglomerated primary particles", and the aggregates formed by multiple primary particles can be referred to as "secondary particles".

[0199] In some embodiments of the present application, the positive electrode active material includes non-agglomerated primary particles.

[0200] The purpose of some embodiments of the present 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.

[0201] In this application, unless otherwise specified, in the “particle size distribution curve of primary particles in the positive electrode active material”, the horizontal axis corresponds to the particle size of the 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 number of primary particles counted. Unless otherwise specified, the “particle size of the primary particle” refers to the maximum diameter of the primary particle in each direction.

[0202] In this application, unless otherwise specified, the statistical range of primary particles counted in the "particle size distribution curve of primary particles in the positive electrode active material" includes both non-agglomerated and agglomerated primary particles. Taking the positive electrode active material as an example, where both non-agglomerated primary particles and secondary particles are included in the positive electrode active material, the statistical range of the "particle size distribution curve 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.

[0203] 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 further be 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 the primary particles in the positive electrode active material is a single-peak curve, the single peak is the main peak.

[0204] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

[0205] In this application, unless otherwise specified, in the “particle size distribution curve of primary particles in the positive electrode active material”, “half peak width” refers to the width between the particle size boundaries on both sides corresponding to half the peak height of the distribution curve. “Half peak width in the particle size distribution curve of primary particles in the positive electrode active material” can be recorded as “W H ". The half-peak width can reflect the concentration of the particle size distribution of the primary particles. The smaller the half-peak width is, the narrower the particle size distribution of the primary particles is, the better the particle size uniformity is, and the more concentrated the particle size distribution is. Conversely, the larger the half-peak width is, the wider the particle size distribution of the primary particles is, and the greater the particle size difference is. At this time, the more particles deviate from the average particle size, and the larger the proportion of smaller primary particles and larger primary particles is.

[0206] The particle morphology of the positive electrode active material can be used to count the particle size and distribution of the primary particles in the positive electrode active material, and the "particle size distribution curve of the primary particles in the positive electrode active material" can be obtained by drawing. The particle morphology of the positive electrode active material can be obtained by using the test results of a scanning electron microscope (such as ZEISS Sigma 300, JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope, etc.). The sample to be tested can be obtained by laying and sticking the powder sample of the positive electrode active material on a conductive glue. Without limitation, the SEM test can refer to JY / T(001)-1996. Randomly select one or more areas in the sample to be tested for scanning test, and based on the SEM image at a certain magnification, count the particle size of each primary particle in the scanned area and the frequency of occurrence of different particle sizes. Without limitation, the magnification of a single scanning area can be 1000X, but is not limited thereto. In order to improve the accuracy of the statistical results, multiple areas can be randomly selected for scanning.

[0207] Unless otherwise specified, based on the particle morphology of the positive electrode active material, the "particle size of the primary particles in the positive electrode active material" is the maximum diameter of the primary particles in each direction in the morphology. For example, the maximum diameter of the primary particles in each direction in the SEM image can be taken.

[0208] In a non-limiting manner, the particle size distribution curve of the primary particles in the positive electrode active material can be drawn and analyzed with the help of LIBMAS lithium-ion battery material microscopic intelligent analysis system.

[0209] In the present application, the sample to be tested of the "positive electrode active material" in the secondary battery can be obtained by disassembling the battery, taking out the positive electrode sheet, extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet by solvent washing, ultrasonic dispersion, centrifugal separation, graded sedimentation and other methods, and drying to obtain a powder sample. The obtained powder sample can be used for SEM testing and can also be used for other tests, such as laser particle size analyzer analysis. In addition, the powder material extracted from the positive electrode active layer can also be sintered to remove the organic components, thereby obtaining a powder sample of the positive electrode active material.

[0210] Exemplarily, the preparation of the powder sample of the positive electrode active material can be carried out by the following method: disassembling the battery, taking out the positive electrode plate, soaking and cleaning it with a solvent such as dimethyl carbonate to remove the residual electrolyte; scraping the powder material of the positive electrode active layer, using a solvent (such as N-methylpyrrolidone (NMP) etc.) to fully soak the powder material extracted from the positive electrode active layer, so that organic components such as binders are dissolved in the solvent (the dissolution can also be promoted by ultrasonic dispersion etc.), washing and filtering, collecting the solid phase, and then using the density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collecting the centrifugal precipitate to obtain the positive electrode active material to be tested.

[0211] In this application, unless otherwise specified, the statistical range of primary particles counted in the "average particle size of primary particles in the positive electrode active material (which can be recorded as D1)" is the same as the "particle size distribution curve of primary particles in the positive electrode active material", including non-agglomerated primary particles and primary particles in possible secondary particles. Taking the positive electrode active material as an example, which includes both non-agglomerated primary particles and secondary particles, the statistical range of the "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.

[0212] The following method can be used to test and obtain the average particle size of the primary particles in the positive electrode active material: the SEM scan of the positive electrode active material is obtained by the aforementioned method. One or more areas are randomly selected in the sample to be tested for scanning test, and the particle size of each primary particle in the scanned area is counted at a certain magnification, and then the average particle size of each primary particle counted is calculated. Non-limitingly, the magnification of a single scanning area can be 1000X, but is not limited to this. In order to improve the accuracy of the statistical results, multiple areas can be randomly selected for scanning.

[0213] In the positive electrode active material of the secondary battery, the primary particle is a particle basic unit.

[0214] For the positive electrode active materials of traditional secondary batteries, on the one hand, the small-sized, large-surface-area non-agglomerated primary particles are prone to cause large interfacial side reactions, and such interfacial side reactions are easily aggravated under high voltage, affecting the battery life under high voltage, such as cycle and / or storage life. On the other hand, the secondary particles in traditional positive electrode active materials are usually agglomerated by smaller-sized nanoscale primary particles. Since the contact area between adjacent primary particles is relatively small, the secondary particles are prone to cracking due to stress under high voltage and forming a fresh interface, which will accelerate the consumption of electrolyte during the cycle and / or storage under high voltage, thereby deteriorating the battery life.

[0215] In the secondary battery provided in the first aspect of the present application, by controlling the half peak width (W H ) is within the aforementioned range, so that the particle size distribution of the primary particles in the positive electrode active material is relatively uniform, and the average particle size (D1) of the primary particles in the positive electrode active material is further controlled within the aforementioned range, so that the primary particles in the positive electrode active material have a relatively large micron-level size; thereby, on the one hand, the content of non-agglomerated primary particles with small size and large specific surface area can be reduced, so that the interface side reaction of the positive electrode active material under high voltage can be significantly suppressed; on the other hand, when there are secondary particles formed by the agglomeration of primary particles in the positive electrode active material, by controlling the average particle size and particle size distribution of the primary particles within the aforementioned range, the primary particles in the secondary particles can have The relatively large micron-scale size can make the primary particles in the secondary particles have a relatively large contact area, so that the primary particles in the secondary particles are more firmly combined under high voltage, reducing the risk of cracking of the positive electrode active material under high voltage, reducing the generation of fresh interfaces, and slowing down the consumption of electrolyte during circulation and / or storage under high voltage; through the aforementioned multiple effects, the interfacial side reactions under high voltage can be significantly inhibited, the risk of cracking of the positive electrode active material under high voltage can be reduced, the structural stability of the positive electrode active material can be improved, and the consumption of electrolyte during circulation and / or storage under high voltage can be slowed down, thereby significantly improving the battery life of the secondary battery under high voltage.

[0216] The effects described in any part of this application are not intended to be limited by any theory.

[0217] In this application, unless otherwise specified, "high voltage" refers to a voltage greater than or equal to 4.2 V. Non-limiting examples of "high voltage" include 4.3 V, 4.4 V, 4.5 V, etc.

[0218] In some embodiments, W H ≤2.5μm, optionally, 1μm≤W H ≤2.5μm, further optionally, 1.2μm≤W H ≤2.5μm.WH W is the half peak width in the particle size distribution curve of the primary particles in the positive electrode active material. H It can also be any of the following values ​​or a range consisting of 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.

[0219] 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 further optionally, 1.5 μm ≤ D1 ≤ 2.4 μm. D1 is the average particle size of the primary particles in the positive electrode active material. Without limitation, 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.

[0220] In some embodiments, 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):

[0221] (ta1)W H ≤2.5μm, optionally, 1μm≤W H ≤2.5μm, further optionally, 1.2μm≤W H ≤2.5μm;

[0222] (ta2)1.3μm≤D1≤3μm, optionally, 1.4μm≤D1≤2.5μm, further optionally, 1.5μm≤D1≤2.5μm, further optionally, 1.5μm≤D1≤2.4μm.

[0223] In some embodiments, 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):

[0224] (tb1)1.2μm≤W H ≤2.5μm;

[0225] (tb2)1.5μm≤D1≤2.5μm.

[0226] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H≤2.5μm) and 1.3μm≤D1≤3μm, by controlling the positive electrode active material to satisfy one or more of the characteristics (ta1), (ta2), (tb1) and (tb2), the distribution width and / or the average particle size of the primary particles can be further regulated within a more suitable range, thereby better improving the battery life under high voltage.

[0227] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H ≤2.5μm) and 1.3μm≤D1≤3μm, by further controlling the half peak width (W H ) is within the aforementioned optional range, which is conducive to making the particle size distribution of the primary particles in the positive electrode active material more uniform; on the one hand, it is more conducive to reducing the content of non-agglomerated primary particles with small size and large specific surface area, and reducing interfacial side reactions under high voltage; on the other hand, 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 the consumption of electrolyte during circulation and / or storage under high voltage. Based on the influence of the aforementioned multiple effects, it is conducive to better improving the battery life under high voltage.

[0228] In the control of the positive electrode active material, the primary particles have a narrow distribution (e.g. W H ≤2.5μm) and 1.3μm≤D1≤3μm, by further controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned optional range, it is beneficial to make the primary particles in the positive electrode active material have a more suitable micron-level size, and is more beneficial to reduce the content of non-agglomerated primary particles with small size and large specific surface area, better reduce interfacial side reactions under high voltage and improve the stability of the CEI film. At the same time, 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 the consumption of electrolyte during cycling and / or storage under high voltage. Based on the influence of the aforementioned multiple effects, it is beneficial to better improve the battery life under high voltage.

[0229] On the other hand, by inhibiting the generation of fresh interfaces under high voltage, it is also beneficial to resist the increase of impedance, inhibit the deterioration of battery dynamics, and promote the discharge capacity of the positive electrode active material and improve the battery rate performance.

[0230] 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, which may reduce the deintercalation area of ​​the active ions and thus affect the deintercalation rate. It will also cause the solid phase transmission path of the active ions to become longer and the diffusion time to increase. During high-rate discharge, the active ions may not be able to fully escape in a short time. Therefore, it 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 more suitable micron size (such as 1.3μm≤D1≤3μm, further such as 1.4μm≤D1≤2.5μm, and further such as 1.5μm≤D1≤2.4μm), it is also beneficial for the positive electrode to have good discharge capacity and rate performance.

[0231] 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 of the single peak is the half-peak width of the main peak.

[0232] 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 better improve the uniformity of the particle size distribution of the primary particles in the positive electrode active material.

[0233] In this application, 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 recorded as R1.

[0234] In some embodiments, 1≤R1≤3.

[0235] In some embodiments, 1.5≤R1≤2.2.

[0236] 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.

[0237] In the context of this application, the volume cumulative distribution particle size D v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, which refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches N%, and the particle size is less than or equal to D v The volume percentage of N is N%. v N can be obtained from the volume cumulative distribution curve of the material particle size. If there is no other explanation, the volume cumulative distribution curve starts from zero from the small particle size side. v 90.D v 50. D v 10 is used as an example for explanation. In this application, unless otherwise specified, D v90 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 90%. This parameter indicates that the particle size of 90% of the material volume is less than or equal to D v 90, and 10% of the particles by volume are larger than D v 90. In this application, unless otherwise specified, D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%. This parameter indicates that the particle size of 50% of the material volume is less than or equal to D v 50, and 50% of the particles by volume are larger than D v 50. In this application, unless otherwise specified, D v 10 refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 10%. This parameter indicates that the particle size of 10% of the volume of the material is less than or equal to D v 10, and 90% of the particles by volume are larger than D v 10. Those skilled in the art will understand that v 90.D v 50 and D v 10, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by laser particle size analyzer with reference to GB / T 19077-2016 particle size distribution laser diffraction method, such as Mastersizer 2000E laser particle size analyzer and LS-909 laser particle size analyzer (OMEC) of Malvern Instruments Ltd., UK. Further, for equipment models such as Malvern 2000 (MasterSizer 2000) laser particle size analyzer, the standard process GB / T19077-2016 / ISO13320:2009 can be referred to for testing.

[0238] In some embodiments, the following method can be used to test the D of the positive electrode active material: v 50. Malvern 2000 (MasterSizer2000) laser particle size analyzer can be used, refer to the standard process: GB / T19077-2016 / ISO 13320:2009, the detailed test process includes: take an appropriate amount of the sample to be tested, add 20mL~30mL of solvent (so that the sample concentration in the injection pool meets 8%~12% shading), ultrasonic treatment for 5min (53KHz / 120W) to fully disperse the sample; add the ultrasonically dispersed sample to the injection pool, start the test after the sample is stable for 5s~10s, and record the data after the test. Non-limiting examples of solvents include deionized water, pure water, etc. In order to avoid the agglomeration of the drying process affecting the particle size test, take the washed wet sample for dispersion test, and wash it with anhydrous ethanol.

[0239] Understandably, various Dv N is a statistical parameter for the particle size of dispersible particles in the material. One non-agglomerated particle and one secondary particle are each counted as one dispersible particle. However, some non-agglomerated primary particles that can be identified in the SEM image may slightly agglomerate during the test. These slightly agglomerated primary particle clusters may be counted as one dispersible particle.

[0240] By increasing the D v 50 (can be recorded as D v 50 A ) relative to the average particle size (D1) of the primary particles in the positive electrode active material (R1 = D v 50 A / D1) is controlled within the aforementioned range, which is beneficial to making the median particle size of the positive electrode active material close to the average particle size of the primary particles as the basic unit of the particles, and further helps to reduce the agglomeration ratio of the primary particles in the positive electrode active material, reduce the content of the secondary particles as the primary particle agglomerates, and accordingly increase the proportion of non-agglomerated primary particles. The non-agglomerated primary particles do not have interfaces between the primary particles in the secondary particles, which can better resist the changes in volume stress and the risk of cracking under high voltage, so that the positive electrode active material has better structural stability under high voltage, and thus is more conducive to improving the battery life under high voltage.

[0241] In some embodiments, the positive electrode active material includes non-agglomerated primary particles.

[0242] In some embodiments, the positive electrode active material may or may not include secondary particles in addition to the non-agglomerated primary particles.

[0243] In this application, the mass proportion 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 recorded as f N .

[0244] In some embodiments, 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):

[0245] (tc1)40%≤f M ≤100%, optional 50%≤f M <100%, further optional 55%≤f M <100%, further optional 60%≤f M <100%, further optional 80%≤f M <100%;

[0246] (tc2)60%≤f N <100%, optional 80%≤f N <100%, further optional 90%≤f N <100%.

[0247] In some embodiments, 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):

[0248] (td1)55%≤f M ≤100%;

[0249] (td2)80%≤f N ≤100%.

[0250] In some embodiments, 40%≤f M ≤100%, optional 55%≤f M <100%, further optional 80%≤f M <100%. Without limitation, f M It can also be any of the following percentages or a range consisting of 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 60%≤f M <100%.

[0251] In some embodiments, 60%≤f N ≤100%, optional 80%≤f N <100%, further optional 90%≤f N <100%. Without limitation, f N It can also be any of the following percentages or a range consisting of any two of the following percentages: 60%, 70%, 80%, 90%, 95%, 100%, etc.

[0252] In this application, unless otherwise specified, “the mass proportion of non-agglomerated primary particles in the positive electrode active material (f M )” and “the proportion of non-agglomerated primary particles in the positive electrode active material (f N )" reflects the content of non-agglomerated primary particles in the positive electrode active material. M and f N The larger the value of , the more non-agglomerated primary particles there are, and correspondingly, the fewer secondary particles there are.

[0253] The mass proportion of non-agglomerated primary particles in the positive electrode active material (fM ) and the proportion of non-agglomerated primary particles in the positive electrode active material (f N ) is controlled within the aforementioned range, the proportion of non-agglomerated primary particles can be controlled within a more appropriate range, so that the positive electrode active material can better resist volume stress changes and cracking risks under high voltage, have better structural stability, and thus be more conducive to improving the battery life under high voltage.

[0254] Without limitation, the "ratio of the number of non-agglomerated primary particles in the positive electrode active material" can be obtained by statistical analysis based on the SEM scan of the positive electrode active material. Randomly select one or more areas for scanning test, count the number of non-agglomerated primary particles and secondary particles in the scanned area, calculate the ratio of the number of non-agglomerated primary particles, and use it as the test value of "the ratio of the number of non-agglomerated primary particles in the positive electrode active material". The magnification of a single scanning area can be 1000X to 3000X, such as 1000X, 2000X, 3000X, etc., but is not limited to the aforementioned magnification. Exemplarily, a magnification of 1000X can be used. The number of particles of the positive electrode active material counted may be greater than or equal to 2000, but is not limited to the aforementioned number.

[0255] As an example, the particle size range of primary particles and the particle size range of secondary particles can be obtained according to the SEM scan of the positive electrode active material, and the particle size and frequency of occurrence of non-agglomerated primary particles and secondary particles as agglomerates can be counted to obtain the "particle size distribution curve of positive electrode active material". A laser particle size analyzer can also be used to test and obtain the "particle size distribution curve of positive electrode active material". In this application, unless otherwise specified, the "particle size distribution curve of positive electrode active material" has a horizontal axis corresponding to the particle size of non-agglomerated primary particles or secondary particles in the positive electrode active material, and a vertical axis corresponding to the frequency of occurrence of each particle size or the proportion of the number of particles in the counted particles. The particle statistical range of the "particle size distribution curve of positive electrode active material" includes non-agglomerated primary particles and possible secondary particles. Taking the positive electrode active material as an example in which both non-agglomerated primary particles and secondary particles are included, the statistical range of the "particle size distribution curve of positive electrode active material" includes both the particle size of non-agglomerated primary particles and the particle size of secondary particles. Furthermore, combined with elemental analysis (such as EDS, etc.), the mass proportion of non-agglomerated primary particles in the positive electrode active material (f M ).

[0256] In some embodiments, the positive electrode active material includes non-agglomerated primary particles and also includes secondary particles.

[0257] In some embodiments, 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):

[0258] (te1)80%≤f M <100%;

[0259] (te2)90%≤f N <100%.

[0260] Without limitation, f M 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.

[0261] Without limitation, f N 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.

[0262] The mass proportion of non-agglomerated primary particles in the positive electrode active material (f M ) and the proportion of non-agglomerated primary particles in the positive electrode active material (f N ) is controlled within the aforementioned higher range. When 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 further more conducive to improving the battery life under high voltage.

[0263] In some embodiments, the D of the positive electrode active material v 50 is 2μm~6μm.

[0264] In some embodiments, the D of the positive electrode active material v 50 is 2.8μm~4.5μm.

[0265] Without limitation, 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.

[0266] The half-peak width (W ) in the particle size distribution curve of primary particles in the positive electrode active material is synergistically controlled. H ) and the average particle size (D1) of the primary particles in the positive electrode active material, by further increasing the D v Controlling the value of 50 within the aforementioned range is beneficial to making the particle size in the positive electrode active material more moderate, and is beneficial to reducing the agglomeration ratio of the primary particles in the positive electrode active material, and can increase the proportion of non-agglomerated primary particles. The non-agglomerated primary particles do not have interfaces between the primary particles in the secondary particles, and 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, which can better improve the battery life under high voltage.

[0267] By v Further control of 50 can further reduce the content of non-agglomerated primary particles with small size and large specific surface area in the positive electrode active material, which is more conducive to reducing interfacial side reactions under high voltage, and further more conducive to improving battery life under high voltage.

[0268] On the other hand, by increasing the D v Controlling the value of 50 within the aforementioned range is also helpful in controlling the content of large-sized secondary particles formed by the agglomeration of primary particles to be lower. Therefore, the problem of the generation of fresh interfaces caused by the cracking of the agglomerated large-sized secondary particles under high voltage is suppressed, which is beneficial to reduce the increase in impedance caused by the generation of fresh interfaces and improve the battery kinetic performance.

[0269] 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.

[0270] In some embodiments, the positive electrode active material has a SPAN value of 0.85 to 1.35.

[0271] Without limitation, the SPAN of the positive electrode active material can also be any of the following values ​​or a range consisting of 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.

[0272] In this application, unless otherwise specified, the SPAN value of the positive electrode active material is calculated according to the following formula: SPAN = (D v 90-D v 10) / Dv 50. SPAN can indicate the dispersion of particle size. The larger the SPAN value, the wider the particle size distribution of the material.

[0273] 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, which is beneficial to reduce the content of small-sized non-agglomerated primary particles and reduce interfacial side reactions under high voltage. It is also beneficial to reduce the content of large-sized secondary particles and reduce the negative impact of possible cracking of secondary particles under high voltage on the battery life under high voltage. Through the aforementioned multiple effects, it is beneficial to significantly improve the battery life under high voltage.

[0274] The half peak width (W ) in the particle size distribution curve of the primary particles in the positive electrode active material is controlled. H ) and the average particle size (D1) of the primary particles in the positive electrode active material, the D 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), the SPAN value of the positive electrode active material, etc. can better control the particle size and particle size distribution of the primary particles in the positive electrode active material, the number ratio of non-agglomerated primary particles (f N ) or 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, etc., can better improve the battery life under high voltage. However, it is not limited to the aforementioned theory. For example, it can be more conducive to reducing the contact surface between the positive electrode active material and the electrolyte, it can be more conducive to reducing the occurrence of positive electrode-electrolyte interface side reactions under high voltage, it can be more conducive to reducing the metal dissolution of the positive electrode, and it can be more conducive to improving the structural stability of the positive electrode active material under high voltage. One or more of the above. Exemplarily, when the positive electrode active material contains manganese, it is also beneficial to reduce manganese dissolution.

[0275] In some embodiments, the positive electrode active material includes a lithium composite metal oxide, the lithium composite metal oxide includes a lithium element, a non-lithium metal element, and an oxygen element; the non-lithium metal element includes a transition metal element.

[0276] In this application, unless otherwise specified, "lithium composite metal oxide" refers to a positive electrode active material including lithium, non-lithium metal elements and oxygen. Generally, the non-lithium metal elements in the lithium composite metal oxide include transition metal elements, so the lithium composite metal oxide can also be called "lithium transition metal oxide".

[0277] In the present application, “non-lithium metal element” refers to a metal element other than lithium.

[0278] 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 can also be any of the following percentages or a range consisting of any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0279] In some embodiments, the lithium composite metal oxide may include one or more of lithium nickel-based oxides, lithium-rich manganese-based positive electrode materials, spinel lithium manganese oxide, lithium cobalt oxide, and modifications of any of the foregoing positive electrode active materials; wherein the modifier may include one or more of doping elements and coating elements.

[0280] It can be understood that the lithium nickel-based oxide includes lithium elements, nickel elements and oxygen elements.

[0281] By introducing lithium nickel-based oxides into the positive electrode active material, it is beneficial to improve the energy density.

[0282] By introducing lithium-rich manganese-based positive electrode materials, spinel lithium manganese oxide, lithium cobalt oxide and other positive electrode active materials into the positive electrode active materials, it is beneficial to make the positive electrode active materials have better structural stability under high voltage, which is beneficial to extend the battery life under high voltage, which may include cycle and / or storage life.

[0283] In this application, unless otherwise specified, "a modified substance of a positive electrode active material" includes the positive electrode active material itself and the modified element. Furthermore, the modified element may exist in the form of a doping element, a coating element, or a combination of a doping element and a coating element. Unless otherwise specified, "a modified substance of a positive electrode active material" still falls within the scope of positive electrode active material.

[0284] In the present application, unless otherwise specified, the "doping element" involved in the positive electrode active material refers to the modified element doped in the positive electrode active material; unless otherwise specified, the "coating element" involved in the positive electrode active material refers to the positive electrode active material including the positive electrode active particle body and the coating layer located at least a part of the surface of the positive electrode active particle body, wherein the coating element is the modified element located in the coating layer. As a non-limiting example, in the positive electrode active material, "the modified element exists in a combination of a doping element and a coating element" means that the positive electrode active material includes the positive electrode active particle body and the coating layer located at least a part of the surface of the positive electrode active particle body, at least a part of the modified element is doped in the positive electrode active particle body, and at least a part of the modified element is also contained in the coating layer. The doping modification method of introducing the doping element and the coating modification method of introducing the coating element can adopt or refer to the 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 product 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, etc.; 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, etc.; in some embodiments, the coating element may include Ti.

[0285] In the present application, unless otherwise specified, "lithium nickel-based oxide" refers to a lithium composite metal oxide comprising lithium, nickel and oxygen. It is understood that the lithium nickel-based oxide is a lithium composite metal oxide in which the non-lithium metal element at least comprises nickel. Without limitation, the lithium nickel-based oxide may include one or more of a lithium nickel cobalt manganese-based oxide and a lithium nickel cobalt aluminum-based oxide. Unless otherwise specified, the lithium nickel-based oxide has a layered structure.

[0286] In some embodiments, the lithium nickel-based oxide includes a lithium nickel cobalt-based oxide. In the present application, unless otherwise specified, "lithium nickel cobalt-based oxide" refers to a lithium composite metal oxide including lithium, nickel, cobalt and oxygen elements, and is a lithium nickel-based oxide containing cobalt elements. The non-lithium metal elements include at least nickel and cobalt. The introduced cobalt element can reduce cation mixing, enhance the structural stability of the material and the rate performance.

[0287] In some embodiments, the lithium nickel-based oxide comprises a chemical formula of Li x (Ni a Co b M' c M” d)O 2-e a lithium composite metal oxide, wherein 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 embodiments, M' is the Mn element.

[0288] 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.

[0289] 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.

[0290] 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, and 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):

[0291] (t1) The atomic molar ratio of Ni element to non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1;

[0292] (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;

[0293] (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.

[0294] In some embodiments, the lithium composite metal 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):

[0295] (i) 0.5 ≤ q1 ≤ 0.99;

[0296] (ii) 0.5 ≤ q2 ≤ 0.99;

[0297] (iii) 0.5 ≤ q3 ≤ 0.99;

[0298] (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;

[0299] (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;

[0300] (vi) The mass percentage of the lithium nickel-based oxide in the lithium composite metal oxide is 80% - 100%.

[0301] In some embodiments, the lithium composite metal 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):

[0302] (ti) 0.5 ≤ q1 ≤ 0.99, optionally, 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99;

[0303] (tii) 0.5 ≤ q2 ≤ 0.99, optionally, 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99;

[0304] (tiii) 0.6 ≤ x2 ≤ 1.2, optionally, 0.8 ≤ x2 ≤ 1.1;

[0305] (tiv) 0.5 ≤ q3 ≤ 0.99, optionally, 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99;

[0306] (tv) 1.6 ≤ x3 ≤ 2.1, optionally, 1.8 ≤ x3 ≤ 2.06;

[0307] (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;

[0308] (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;

[0309] (tviii) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide is 90% - 100%.

[0310] Non-limitingly, q1, q2 and q3 can each independently be any one of the following values, or be selected from the ranges 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.

[0311] Non-limitingly, x2 can be any one of the following values, or be selected from the ranges 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.

[0312] Non-limitingly, x3 can be any one of the following values, or be selected from the ranges formed by any two of the following values: 1.6, 1.7, 1.8, 1.9, 2, 2.05, 2.06, 2.08, 2.1, etc.

[0313] Non-limitingly, q4 can be any one of the following values, or be selected from the ranges formed by 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.

[0314] Non-limitingly, 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.

[0315] In some embodiments, 0.5 ≤ q1 ≤ 0.8. In some of these embodiments, 0.5 ≤ q1 ≤ 0.7.

[0316] In some embodiments, 0.5 ≤ q2 ≤ 0.8. In some of these embodiments, 0.5 ≤ q2 ≤ 0.7.

[0317] In some embodiments, 0.5 ≤ q3 ≤ 0.8. In some of these embodiments, 0.5 ≤ q3 ≤ 0.7.

[0318] 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.

[0319] In some embodiments, 0.7 < q1 ≤ 0.99. In some of these embodiments, 0.8 < q1 ≤ 0.99.

[0320] In some embodiments, 0.7 < q2 ≤ 0.99. In some of these embodiments, 0.8 < q2 ≤ 0.99.

[0321] In some embodiments, 0.7 < q4 ≤ 0.99. In some of these embodiments, 0.8 < q3 ≤ 0.99.

[0322] 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.

[0323] In some embodiments, the lithium composite metal oxide includes one or more of lithium nickel cobalt manganese-based oxides and modified products of lithium nickel cobalt manganese-based oxides. Without limitation, the modified product may include one or more of a doping element and a coating element; both the doping modification method for introducing a doping element and the coating modification method for introducing a coating element may 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 lithium nickel cobalt manganese-based oxide may optionally include a modifying element, and further, the modifying element may exist in the form of a doping element, in the form of a coating element, or in the form of a combination of a doping element and a coating element.

[0324] In some embodiments, the lithium nickel cobalt manganese-based oxide includes doping elements, and further, 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.

[0325] In the present application, unless otherwise specified, "lithium nickel cobalt manganese-based oxide" refers to a lithium composite metal oxide including lithium, nickel, cobalt, manganese and oxygen, and is a lithium nickel-based oxide containing cobalt and manganese. The non-lithium metal elements in the lithium nickel cobalt manganese-based oxide include nickel, cobalt and manganese. In the present application, unless otherwise specified, the lithium nickel cobalt manganese-based oxide used as a positive electrode active material generally has a layered structure.

[0326] In lithium nickel cobalt manganese-based oxides, nickel can play a role in improving energy density, cobalt can play a role in reducing cation mixing, enhancing material structural stability and rate performance, and manganese can play a role in stabilizing the layered structure stability of lithium nickel cobalt manganese-based oxide materials, but is not limited to the above-described roles. An example of cation mixing is Li / Ni mixing.

[0327] In lithium nickel cobalt manganese-based oxides, the ratio of the atomic molar ratio of nickel element to the sum of the atomic molar ratios of nickel element, cobalt element and manganese element is denoted as R Ni / NCM The ratio of the atomic molar ratio of the cobalt element to the sum of the atomic molar ratios of the nickel element, the cobalt element and the manganese element 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 .

[0328] 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 the 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 values ​​and optional ranges, please refer to q1.

[0329] Without limitation, R Co / NCM It can be any of the following values, or a range consisting of 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. Co / NCM For values ​​and optional ranges, please refer to q4.

[0330] Without limitation, R Mn / NCM It can be any of the following values, or a range consisting of 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 values ​​and optional ranges, please refer to q5.

[0331] By controlling one or more of the nickel content, cobalt content and manganese content of 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 at high voltage can be improved, which is more conducive to extending the battery life at high voltage.

[0332] In some embodiments, the positive electrode active material containing the lithium composite metal oxide has a moderate primary particle size, a narrow particle size distribution, a high crystallinity, and little Li / Ni mixing.

[0333] In some embodiments, in the lithium nickel cobalt manganese-based oxide, the ratio of the sum of the atomic molar ratios of the nickel element, the cobalt element, and the manganese element to the sum of the atomic molar ratios of the non-lithium metal elements is denoted as R NCM .

[0334] Without limitation, R NCMIt can be 0.9 to 1, optionally 0.95 to 1, and can also be any of the following values ​​or a range consisting 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.

[0335] Without limitation, the mass proportion of lithium nickel cobalt manganese-based oxide in the lithium composite metal oxide is 80% to 100%, optionally 90% to 100%, and can also be any of the following percentages or selected from the range consisting of any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0336] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed by methods known in the art, including but not limited to the following methods: inductively coupled plasma spectroscopy (ICP), X-ray diffraction (XRD), single crystal X-ray diffraction (SCXRD), energy dispersive spectrometer (EDS), etc. The sample preparation methods and test methods of these test methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the characteristics of the sample. The ICP method can be used to perform quantitative test analysis of the content of the components in the positive electrode active material.

[0337] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode sheet is different when the battery is discharged to different states. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the content of Li can be the initial state of the material or the non-initial state after the charge and discharge cycle. The positive electrode active material is applied to the positive electrode in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material at the positive electrode usually changes. Among them, the content of Li can be measured by atomic molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before being made into a positive electrode active layer. It is understandable that new materials or new substances obtained by appropriate modification on the basis of the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, non-limiting examples such as coating modification and doping modification. One or more.

[0338] In the exemplary description of the positive electrode active material in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the atomic molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by atomic molar content, but is not limited to this.

[0339] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0340] (tf1) The positive electrode active material includes a doping element, and without limitation, 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;

[0341] (tf2) The positive electrode active material includes a coating element located on the surface of the particle. Without limitation, the coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

[0342] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0343] (tf1') the positive electrode active material includes a doping element, and the doping element includes one or both of Zr and W;

[0344] (tf2′) The positive electrode active material includes a coating element located on the surface of the particle, and the coating element includes Ti.

[0345] By introducing one or more of the doping elements and the coating elements into the positive electrode active material, the positive electrode active material can be modified by one or more of the doping modification and the coating modification. Taking the introduction of doping elements as a non-limiting example, by introducing doping elements (such as Zr, W, etc.), it can be beneficial to improve the binding force between the transition metal elements and O atoms in the positive electrode active material, thereby improving the lattice stability during the lithium insertion and extraction process and improving the stability of the positive electrode active material. Taking the introduction of the coating element Ti as an example, it is beneficial to form an oxide coating layer, which hinders the direct contact between the electrolyte and the positive electrode material, thereby reducing the interface side reactions.

[0346] In some embodiments, the mass proportion of the lithium composite metal oxide in the positive electrode active layer can be 80% to 97%, optionally 90% to 100%. Non-limitingly, the mass proportion of the lithium composite metal oxide in the positive electrode active layer can be any of the following percentages or selected from the range consisting of any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, etc.

[0347] In some embodiments, the mass proportion of lithium composite metal oxide in the positive electrode active material can be 80% to 100%, optionally 90% to 100%. Non-limitingly, the mass proportion of lithium composite metal oxide in the positive electrode active material can be any of the following percentages or selected from the range consisting of any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

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

[0350] It can be understood that the secondary battery further includes a negative electrode plate, the negative electrode plate includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material.

[0351] In some embodiments, the negative electrode active material includes one or more of a carbon-based material and a silicon-based material. In some of these embodiments, the negative electrode active material includes a graphite material. In the present application, "graphite material" refers to a negative electrode active material containing graphite, and the graphite material includes at least a graphite body. In the present application, the "graphite body" 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 a graphite material, and may further be a graphite material. Non-limitingly, the mass proportion of graphite material in the negative electrode active material may be 80% to 100%, optionally 90% to 100%, further optionally 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.

[0352] 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.

[0353] The negative electrode active material in the negative electrode sheet can be selected from the aforementioned types, but is not limited thereto.

[0354] In some embodiments, the secondary battery is a lithium ion secondary battery.

[0355] In some embodiments, the charge cut-off voltage of the secondary battery is greater than or equal to 4.2V.

[0356] In some embodiments, the charge cut-off voltage of the secondary battery is greater than or equal to 4.3V.

[0357] In some embodiments, the charging cut-off voltage of the secondary battery is 4.2V to 4.5V, and can further be 4.3V to 4.5V, or any one of the following voltages or a range consisting of any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc.

[0358] In this application, unless otherwise specified, the "charge cut-off voltage" of a secondary battery has a well-known meaning in the art and is usually marked on the battery product. Secondary battery products can operate under voltage conditions equal to or lower than the charge cut-off voltage. Taking lithium-ion secondary batteries as an example, as charging proceeds, the battery voltage continues to rise; when the charge cut-off voltage is reached, it indicates that the distribution of lithium ions in the positive and negative electrode materials and the electrochemical balance inside the battery have reached a specific state. If you continue to charge at a high current and exceed the charge cut-off voltage, it is easy for some irreversible chemical reactions to occur inside the battery.

[0359] In some embodiments, the secondary battery is a lithium ion secondary battery, and the electrolyte salt may include an electrolyte lithium salt.

[0360] In some embodiments, a secondary battery includes a battery cell.

[0361] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0362] The following is some description about the positive electrode.

[0363] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material.

[0364] 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 further may be greater than or equal to 90 wt %.

[0365] As a non-limiting example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode active layer is disposed on any one or both of the two surfaces of the positive electrode current collector that are opposite to each other.

[0366] 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 base layer and a metal layer formed on at least one surface of the polymer material base layer. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In a non-limiting manner, 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), polyethylene (PE), etc.

[0367] The positive electrode active material may be a positive electrode active material for a battery known in the art. These positive electrode active materials may be used alone or in combination of two or more.

[0368] In some embodiments, the positive electrode active material includes a lithium transition metal oxide. Examples of lithium transition metal oxides may 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 modified compounds thereof. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.80 Co0.15 Al 0.05 O2.

[0369] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. Generally, the weight percentage of the binder in the positive electrode active layer can be 0 to 10wt%, further can be 0 to 8wt%, and further can be 1wt% to 5wt%, based on the total weight of the positive electrode active layer.

[0370] 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 may be 0 to 10 wt%, further 0 to 8 wt%, and further 0 to 5 wt%, based on the total weight of the positive electrode active layer.

[0371] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. Cold pressing can be performed by a cold rolling mill. The type of solvent in the positive electrode slurry can include but is not limited to any of the aforementioned embodiments, for example, it can include N-methylpyrrolidone (NMP), and further can be NMP. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode 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 5000mPa·s to 25000mPa·s. When the positive electrode slurry is coated, the coating unit surface density on a dry weight basis (excluding the solvent) can be 15mg / cm 2 ~35mg / cm 2 , measured by the coating surface density on one side. The compacted density of the positive electrode sheet can be 3.0g / cm 3 ~4.2g / cm 3 , optional 3.3g / cm 3 ~3.8g / cm 3 .

[0372] The "compacted density" used in this application has a well-known meaning in the art and is one of the reference indicators of material energy density. In this application, unless otherwise specified, the compacted density of an electrode plate refers to the ratio of the mass of the electrode active layer to its volume. The compacted density of a positive electrode plate refers to the ratio of the mass of the positive electrode active layer to its volume, and the compacted density of a negative electrode plate refers to the ratio of the mass of the negative electrode active layer to its volume.

[0373] The following is some description about the negative electrode.

[0374] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material.

[0375] 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 further may be greater than or equal to 90 wt %.

[0376] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active layer is disposed on any one or both of the two surfaces facing each other of the negative electrode current collector.

[0377] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as a metal foil, a copper foil may be used. In the negative electrode current collector, the composite current collector may include a polymer material base layer 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 a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In a non-limiting manner, 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), polyethylene (PE), etc.

[0378] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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, 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, the present application is not limited to these materials or substances, and other traditional 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.

[0379] 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%, further optionally ≥96%, etc., further optionally 100%, etc. 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 the range of 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 may include but is not limited to one or more of graphite, soft carbon, hard carbon, etc. Graphite may include one or more of artificial graphite and natural graphite. The carbon-based material may include a graphite material, and may further be a graphite material, but is not limited thereto.

[0380] In some embodiments, the negative electrode active material includes a carbon-based material and a silicon-based material. Without limitation, the sum of the mass of the carbon-based material and the silicon-based material in the total mass of the negative electrode active material can be ≥80%, optionally ≥90%, further optionally ≥95%, further optionally ≥96%, etc., further optionally 100%, etc. Without limitation, the sum of the mass of the graphite material and the silicon-based material 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.

[0381] In some embodiments, the negative electrode active layer may optionally include a binder. In a non-limiting manner, 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). In a non-limiting manner, the weight percentage of the binder in the negative electrode active layer may be 0wt% to 20wt%, further 0wt% to 10wt%, further 0 to 5wt%, further 1wt% to 5wt%, and further 1wt% to 3wt%.

[0382] In some embodiments, the negative electrode active layer may optionally include a conductive agent. In a non-limiting manner, 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. In a non-limiting manner, the weight percentage of the conductive agent in the negative electrode active layer may be 0wt% to 15wt%, further optionally 0wt% to 10wt%, and further optionally 0wt% to 5wt%.

[0383] In some embodiments, the negative electrode active layer may optionally include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na), etc. In a non-limiting manner, the weight percentage of other additives in the negative electrode active layer may be 0wt% to 15wt%, further optionally 0wt% to 10wt%, further optionally 0wt% to 5wt%, further optionally 0wt% to 3wt%, further optionally 0wt% to 2wt%.

[0384] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, and can be optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s, and can be optionally 3000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 75g / m 2 ~220g / m 2 , measured by the coating surface density on one side. The compacted density of the negative electrode sheet can be 1.0g / cm 3 ~2.0g / cm 3 , optional 1.0g / cm 3 ~1.8g / cm 3 .

[0385] The electrolyte is exemplarily described below.

[0386] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0387] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0388] In some embodiments, the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte may include an electrolyte salt and a solvent.

[0389] The concentration of the electrolyte salt in the electrolyte solution may generally be 0.5 mol / L to 5 mol / L.

[0390] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Without limitation, the electrolyte lithium salt may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP) One or more.

[0391] In some embodiments, the solvent in the non-aqueous electrolyte may include ethylene carbonate (EC, ), propylene carbonate (PC, ), 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 fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0392] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0393] The separator is exemplarily described below.

[0394] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0395] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0396] In some embodiments, the thickness of the isolation film is 6 μm to 40 μm, and optionally 6 μm to 20 μm.

[0397] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0398] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0399] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0400] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0401] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 5 The battery cell 5 is a square structure as an example.

[0402] In some embodiments, reference Figure 6 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0403] In some embodiments, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0404] The secondary battery may be a battery device 4 or a battery pack 1 .

[0405] The battery device includes at least one battery cell. The number of battery cells contained in the battery device can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery device.

[0406] Figure 7 4 is an example of a battery device. Figure 7 In the battery device 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery device 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0407] Optionally, the battery device 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0408] In some embodiments, the battery devices described above may also be assembled into a battery pack. The number of battery devices contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0409] Figure 8 and Fig. 9 1 is a battery pack 1 as an example. Figure 8 and Fig. 9 The battery pack 1 may include a battery box and a plurality of battery devices 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery devices 4. The plurality of battery devices 4 can be arranged in the battery box in any manner.

[0410] In the second aspect of the present application, a method for preparing a positive electrode active material is provided. The prepared positive electrode active material can be used as a positive electrode active material in a secondary battery described in the first aspect of the present application or as a partial raw material of a positive electrode active material in a secondary battery described in the first aspect of the present application. The prepared positive electrode active material can also be used to prepare the positive electrode sheet described in the fourth aspect of the present application, and can also be used to prepare the secondary battery described in the first aspect of the present application.

[0411] In some embodiments, a method for preparing a positive electrode active material is provided, which comprises steps S100, S200 and S300 performed sequentially:

[0412] S100: mixing a positive electrode active material solid precursor and a lithium source to obtain a primary mixed material;

[0413] S200: sintering and crushing the primary mixed material for the first time;

[0414] S300: performing a second sintering and a second crushing to prepare a positive electrode active material.

[0415] In some embodiments, the first sintering is performed at a temperature higher than the temperature at which the second sintering is performed.

[0416] If not otherwise specified, step S300 is performed after step S200.

[0417] In some embodiments, for the prepared positive electrode active material, in the particle size distribution curve of primary particles in the positive electrode active material, the half peak width (W H ) satisfies W H ≤2.5μm; the average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0418] The solid precursor of the positive electrode active material can be prepared by adjusting the preparation parameters according to the conventional method in the art based on the element composition of the positive electrode active material to obtain the solid precursor of the positive electrode active material with the desired properties of the present 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. It is possible to adjust the parameters such as specific surface area and SPAN value and obtain the desired target values. Methods including but not limited to co-precipitation method can be used.

[0419] By sintering and crushing the primary mixture including the solid precursor of the positive electrode active material and the lithium source multiple times, the solid precursor can be lithiated by the first sintering to form the target crystal structure of the positive electrode active material, the first crushing can reduce the agglomeration between particles, and the second sintering can achieve the effects of repairing the particle morphology, reducing defects, and promoting the fusion of fine particles. The second crushing can reduce the agglomeration between particles again, thereby preparing a positive electrode active material with a moderate primary particle size and uniform particle size distribution.

[0420] In some embodiments, the positive electrode active material includes a lithium composite metal oxide.

[0421] In some embodiments, the method for preparing the positive electrode active material provided in the second aspect of the present application is used to prepare lithium composite metal oxide.

[0422] In some embodiments, the method for preparing a lithium composite metal oxide comprises steps S100, S200 and S300 performed sequentially:

[0423] S100: mixing a positive electrode active material solid precursor and a lithium source to obtain a primary mixed material;

[0424] S200: sintering and crushing the primary mixed material for the first time;

[0425] S300: performing a second sintering and a second crushing to prepare a positive electrode active material.

[0426] In the present application, in the method for preparing a positive electrode active material, the temperature for the first sintering may be recorded as T1, and the temperature for the second sintering may be recorded as T2.

[0427] In some embodiments, the temperature at which the first sintering is performed (T1) is different from the temperature at which the second sintering is performed (T2).

[0428] In some embodiments, the temperature (T1) at which the first sintering is performed is higher than the temperature (T2) at which the second sintering is performed.

[0429] In some embodiments, the method for preparing the positive electrode active material satisfies one or more of the following characteristics:

[0430] (1) The positive electrode active material includes a doping element, and the primary mixed material also includes a raw material containing the doping element;

[0431] (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 performed simultaneously with the second sintering, and the second coating step is achieved by a third sintering after the second crushing.

[0432] According to the target composition of the positive electrode active material, one or more of the doping element and the coating element can be selectively introduced during the preparation process. When the positive electrode active material includes the doping element, the primary mixture also includes a raw material containing the doping element; when the positive electrode active material includes the coating element, the preparation method of the positive electrode active material includes at least one of a first coating step and a second coating step.

[0433] In the present application, unless otherwise specified, the first coating step is performed simultaneously with the second sintering, and the second coating step is achieved by the third sintering after the second crushing.

[0434] Without limitation, 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 the oxide, hydroxide, carbonate and phosphate 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 the oxide, hydroxide, carbonate and phosphate containing the coating element.

[0435] In some embodiments, in step S200, the temperature for the first sintering is 900°C to 980°C.

[0436] In some embodiments, in step S300, the temperature of the second sintering is 700°C to 800°C.

[0437] In some embodiments, a method for preparing a positive electrode active material is provided, comprising the following steps: mixing a positive electrode active material solid precursor and a lithium source to obtain a primary mixture; performing a first sintering and a first crushing on the primary mixture, and then performing a second sintering and a second crushing on the primary mixture to prepare a positive electrode active material; wherein the temperature (T1) for performing the first sintering is different from the temperature (T2) for performing the second sintering;

[0438] In the particle size distribution curve of primary particles in the positive electrode active material, the half peak width (W H ) satisfies W H ≤2.5μm; the average particle size (D1) of the primary particles in the positive electrode active material satisfies 1.3μm≤D1≤3μm.

[0439] In some embodiments, the temperature (T1) for the first sintering may be 900° C. to 980° C. Without limitation, T1 may also be any of the following temperatures or a range consisting of 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.

[0440] In some embodiments, the time (t1) for the first sintering may be 5 to 15 hours. Without limitation, t1 may also be any of the following time periods or a range consisting of any two of the following time periods: 5 hours, 6 hours, 7 hours, 8 hours, 10 hours, 12 hours, 14 hours, 15 hours, etc.

[0441] In some embodiments, the temperature (T2) for the second sintering may be 700° C. to 800° C. Without limitation, T2 may also be any of the following temperatures or a range consisting of any two of the following temperatures: 700° C., 720° C., 740° C., 750° C., 760° C., 780° C., 800° C., etc.

[0442] In some embodiments, the second sintering time (t2) may be 4 to 12 hours. Without limitation, t2 may also be any of the following time periods or a range consisting of any two of the following time periods: 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 10 hours, 12 hours, etc.

[0443] In some embodiments, the second sintering step is performed in the presence of the first coating agent.

[0444] In some embodiments, the method for preparing 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):

[0445] (tg5) The temperature (T1) for the first sintering is 900°C to 980°C;

[0446] (tg6) The time (t1) for the first sintering is 5 h to 15 h;

[0447] (tg7) The temperature (T2) for the second sintering is 700°C to 800°C;

[0448] (tg8) The time (t2) for the second sintering is 4 h to 12 h;

[0449] (tg9) The step of performing the second sintering is carried out in the presence of a first coating agent; non - restrictively, the first coating agent may include one or more of oxides, hydroxides, carbonates, and phosphates of a first coating element, and the first coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W, and Na.

[0450] 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 primary particles in the cathode active material.

[0451] In some embodiments, after the second crushing, the method for preparing the cathode 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.

[0452] 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.

[0453] In some embodiments, T1 > T2 > T3, that is, the temperatures for the first sintering, the second sintering, and the third sintering decrease in sequence.

[0454] In some embodiments, the time (t3) for the third sintering can be 3 h to 10 h. Non - restrictively, t3 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.

[0455] In some embodiments, the method for preparing the cathode active material includes a second coating step, which is achieved by the third sintering after the second crushing, and the temperature (T3) for the third sintering is lower than the temperature (T2) for the second sintering.

[0456] In some embodiments, the step of performing the third sintering satisfies one or more of the following conditions:

[0457] (tg10-i) The time for the third sintering is 3h to 10h;

[0458] (tg10-ii) The step of performing the third sintering is performed in the presence of a second coating agent; without limitation, the second coating agent may include one or more of 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.

[0459] By introducing a third sintering after the second sintering, the positive electrode active material with a moderate primary particle size and uniform particle size distribution can be further modified as needed. For example, by further coating the Ti element, it is beneficial to form an oxide coating layer, which hinders direct contact between the electrolyte and the positive electrode material, thereby reducing the interface side reaction.

[0460] In the present application, the product of the first sintering and the first crushing in step S200 may be referred to as a “first sintered product”.

[0461] In the present application, the product of the second sintering and second crushing in step S300 may be referred to as a “second sintering product”.

[0462] 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.

[0463] In some embodiments, the first sintering, the second sintering, and the third sintering may be performed under oxygen-containing conditions, for example, may be performed in an oxygen atmosphere or an air atmosphere.

[0464] In some embodiments, in step S300, a sintered product is mixed with a first coating agent, and a second sintering and a second crushing are performed to prepare a positive electrode active material.

[0465] In the present application, unless otherwise specified, the "first coating agent" refers to a coating agent that can be used in the second sintering, and may also be referred to as a "high-temperature coating agent".

[0466] In some embodiments, after the second sintering and the second crushing, the second sintered product obtained by the second sintering and the second crushing can be mixed with a low-temperature coating agent and subjected to low-temperature sintering to prepare a positive electrode active material.

[0467] In this application, unless otherwise specified, "low-temperature coating agent" may also be recorded as "second coating agent". In this application, unless otherwise specified, "first" and "second" in "first coating agent" and "second coating agent" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0468] In the present 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 (T2) for the second sintering. As a non-limiting example, the temperature for low temperature sintering can be 300°C to 600°C, and can be 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., and can also be selected from the range of any two of the aforementioned temperatures. In some embodiments, the low temperature coating agent may include a second coating agent.

[0469] In some embodiments, by controlling the FWDH of the solid precursor of the positive electrode active material (001) , D of the solid precursor of the positive electrode active material v 50. The average particle size and particle size distribution characteristics of the primary particles in the positive electrode active material can be regulated by 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.

[0470] The position of the diffraction peak in the X-ray diffraction spectrum 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 the lithium nickel cobalt manganese-based oxide positive electrode active material usually has a layered structure, and the (001) crystal plane is a crystal plane in the layered structure that is perpendicular to the stacking direction of the layered structure. In the X-ray diffraction spectrum of the solid precursor of the positive electrode active material, the half-peak width of the (001) crystal plane diffraction peak can be recorded as FWDH (001) You can use FWDH (001) Characterize the crystallinity of the solid precursor of the positive electrode active material, lower FWDH (001) Corresponding to higher crystallinity. (001) Controlling within the aforementioned range can make the solid precursor of the positive electrode active material have a more suitable crystallinity, make the particles after sintering have a more suitable hardness, and help reduce the generation of micropowder or fine particles in the crushing step; therefore, on the basis of the aforementioned multiple sintering and multiple crushing processes, the FWDH of the solid precursor of the positive electrode active material is further controlled. (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.

[0471] The positive electrode active material is prepared by using a solid precursor of the positive electrode active material with relatively high crystallinity, and then the positive electrode plate and the secondary battery are prepared. During the process of lithium insertion and extraction under high voltage, the amount of transition metal dissolution in the positive electrode active material is reduced, the transition metal deposition at the negative electrode is reduced, the thickening of the negative electrode solid electrolyte interface (SEI) film is inhibited, and the loss of active lithium is weakened, which can inhibit the deterioration of the battery life at high voltage.

[0472] In some embodiments, the X-ray diffraction spectrum of the positive electrode active material solid precursor has a peak at a 2θ (°) diffraction angle of 15° to 25°. Figure 3 In some embodiments, the X-ray diffraction spectrum of the positive electrode active material solid precursor has a peak at a 2θ (°) diffraction angle of 17° to 23°.

[0473] In some embodiments, the X-ray diffraction spectrum of the positive electrode active material solid precursor has a (001) crystal plane diffraction peak.

[0474] In some embodiments, 0.35≤FWDH (001) ≤0.70. In some embodiments, 0.35≤FWDH (001) In some embodiments, the half-peak width of the (001) crystal plane diffraction peak corresponds to the half-peak width of the 2θ (°) diffraction peak in the range of 15° to 25°.

[0475] Without limitation, FWDH (001) It can be any of the following values ​​or a range consisting of 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.

[0476] In the present application, the following method can be used to perform X-ray diffraction (XRD) test on the positive electrode active material solid precursor. Test instrument: Bruker-D8advance. Cu target Kα1 ray is used, the wavelength λ is 0.15406nm, the X-ray tube is controlled at 40kV and 40mA, the 2θ(°) scanning range is 10°~80°, and the 2θ(°) scanning speed is 0.02° / sec.

[0477] In some embodiments, the positive electrode active material solid precursor 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):

[0478] (tj1) The X-ray diffraction spectrum of the solid precursor of the positive electrode active material has a peak at a 2θ (°) diffraction angle of 15° to 25°;

[0479] (tj2) The X-ray diffraction spectrum of the solid precursor of the positive electrode active material has a (001) crystal plane diffraction peak; in some embodiments, the half-peak width (FWDH) of the (001) crystal plane diffraction peak is (001) ) satisfies 0.35≤FWDH (001) ≤0.70, optionally, 0.35≤FWDH (001) ≤0.64; wherein the half-peak width of the (001) crystal plane diffraction peak corresponds to the half-peak width of the 2θ(°) diffraction peak in the range of 15° to 25°, and further corresponds to the half-peak width of the 2θ(°) diffraction peak in the range of 17° to 23°;

[0480] (tj3) D of the solid precursor of the positive electrode active material v 50 is 2.5μm~4.5μm, and can be 3.0μm~4.2μm;

[0481] (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m 2 / g~35m 2 / g, optional 6m 2 / g~30m 2 / g;

[0482] (tj5) The SPAN value of the solid precursor of the positive electrode active material is 0.4 to 1.5, and can be optionally 0.60 to 1.30; wherein SPAN = (D v 90-D v 10) / D v 50.

[0483] D of the solid precursor of the 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 test and analysis method of the aforementioned positive electrode active material.

[0484] In this application, unless otherwise specified, "specific surface area" has a well-known meaning in the art. It can be tested by nitrogen adsorption specific surface area analysis test method and calculated by BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by Tri Star II specific surface area and pore analyzer of Micromeritics, USA, and the test steps can refer to GB / T 19587-2004. The detailed steps are as follows: using nitrogen as adsorption gas, the specific surface area of ​​the material is calculated by BET method; taking the sample to be tested and adding it into the BET test tube to meet the bottom bulb 2 / 3, the sample is degassed and heated; after cooling to room temperature, backfill with nitrogen to remove vacuum and plug the sample tube mouth with a bottle stopper, and record the sample weight; remove the bottle stopper, add the filling rod, install the sample tube to the instrument analysis station, enter the sample weight and start the test.

[0485] In a non-limiting manner, the D of the solid precursor of the positive electrode active material is v 50 is 2.5 μm to 4.5 μm, and can be 3.0 μm to 4.2 μm. D of the solid precursor 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: 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.

[0486] Without limitation, the specific surface area (BET) of the positive electrode active material solid precursor may be 5 m 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 consisting of 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.

[0487] Without limitation, the SPAN value of the solid precursor of the positive electrode active material can be 0.4 to 1.5, and can be 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 consisting of 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.

[0488] In some embodiments, the positive electrode active material solid precursor 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):

[0489] (tk1)0.35≤FWDH (001) ≤0.64;

[0490] (tk2) D of the solid precursor of the positive electrode active material v 50: 3.0μm~4.2μm;

[0491] (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6m 2 / g~30m 2 / g;

[0492] (tk4) The SPAN value of the solid precursor of the positive electrode active material is 0.60~1.30.

[0493] In some embodiments, in the XRD spectrum of the solid precursor of the positive electrode active material, 0.35≤FWDH (001) ≤0.70, optional 0.35≤FWDH (001) ≤0.64; the temperature for the first sintering is 900℃~980℃, T1>T2.

[0494] In some embodiments, the D of the positive electrode active material solid precursor v 50 is 2.5μm~4.5μm, and can be optionally 3.0μm~4.2μm; the temperature for the first sintering is 900℃~980℃, T1>T2.

[0495] In some embodiments, the specific surface area of ​​the bulk precursor of the positive electrode active material is 5 m2 / g~35m 2 / g, optional 6m 2 / g~30m 2 / g; the temperature for the first sintering is 900℃~980℃, T1>T2.

[0496] In some embodiments, according to steps S100, S200, S300 and the optional step S400, a positive electrode active material with highly non-agglomerated primary particles (referred to as material A) may be prepared.

[0497] In some embodiments, the method for preparing a positive electrode active material further includes step S500: mixing material A with a secondary particle material to prepare a positive electrode active material, wherein the secondary particle material is a material including secondary particles.

[0498] In step S500 , the secondary particle material may be referred to as material B.

[0499] In step S500, the average particle size and the half-peak width of the particle size distribution of the primary particles in the secondary particle material (material B) can be adjusted to be close to those of material A, so that the average particle size (D1) of the primary particles in the prepared positive electrode active material and the half-peak width (W1) of the particle size distribution curve of the primary particles are close to those of material A. H ) is basically the same as that in Material A.

[0500] In the present application, the average particle size of the primary particles in the secondary granular material may be recorded as D2, and the half-peak width of the particle size distribution of the primary particles in the secondary granular material may be recorded as (W2).

[0501] 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 further optionally, 1.5 μm ≤ D2 ≤ 2.4 μm. Without limitation, D2 can 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.

[0502] In some embodiments, W2≤2.5μm, optionally, 1μm≤W2≤2.5μm, further optionally, 1.2μm≤W2≤2.5μm. Without limitation, W2 can also be any of the following values ​​or a range selected from 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.

[0503] By controlling the FWDH of the solid precursor of the cathode active material (001) , D of the solid precursor of the positive electrode active material v 50. When one or more of the specific surface area of ​​the solid precursor of the positive electrode active material and the SPAN value of the solid precursor of the positive electrode active material are within the above range, it is beneficial to control the average particle size (D1) and particle size distribution (such as W H ), D of positive electrode active material v 50 and SPAN value, R1 (D v 50 relative to the average particle size D1 of the primary particles) and the like are within a more suitable range, not limited to any theory. For example, it can be more conducive to reducing the contact surface between the positive electrode active material and the electrolyte, more conducive to reducing the occurrence of side reactions at the positive electrode-electrolyte interface under high voltage, more conducive to reducing the metal dissolution of the positive electrode, 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. Exemplarily, when the positive electrode active material contains manganese, it is also conducive to reducing manganese dissolution.

[0504] In some embodiments, based on a solid precursor of a positive electrode active material containing a lithium composite metal oxide, a positive electrode active material with a moderate primary particle size, a narrow particle size distribution, a high crystallinity, and little Li / Ni mixing is prepared.

[0505] In some embodiments, a coprecipitation method is used to prepare a solid precursor of a positive electrode active material. Taking the preparation of lithium nickel cobalt manganese-based oxide as an example, the solid precursor is a corresponding hydroxide, and a method including the following steps can be used:

[0506] Add pure water into the reactor, start stirring (such as 200rpm-250rpm, further such as 220rpm) and heating (reaction temperature such as 60°C-70°C, further such as 65°C) under nitrogen protection, add ammonia water, and adjust the pH value to a suitable alkaline condition (such as pH 11.2-11.8); then continue to add a metal salt solution to perform a coprecipitation reaction to allow the particles to continue to grow, and use an alkali solution to adjust the pH value of the reaction system during the reaction; wherein the metal salt solution includes nickel salt, cobalt salt and manganese salt;

[0507] When the particles grow to a suitable particle size, the addition of the metal salt solution is stopped, and the reaction precipitate is collected to obtain a solid precursor of the positive electrode active material.

[0508] It is understood that the nickel salt, the cobalt salt and the manganese salt are corresponding soluble salts, such as sulfates for non-limiting example.

[0509] Unless otherwise specified, the solvent for the metal salt solution is water.

[0510] The amount ratio of metal cations in the metal salt solution can be controlled according to the target element 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, at this time, the metal cations in the metal salt solution include nickel ions, cobalt ions and manganese ions, and the molar ratio of nickel ions, cobalt ions and manganese ions in the metal salt solution can be further controlled to be 0.65:0.10:0.25.

[0511] Without limitation, in the metal salt solution, the total molar concentration of metal cations may be 1.4 mol / L to 1.8 mol / L, but is not limited thereto.

[0512] The concentration of the ammonia water may be 5 g / L to 7 g / L, but is not limited thereto.

[0513] Without limitation, the alkali solution may be a sodium hydroxide aqueous solution, but is not limited thereto.

[0514] During the feeding process of the metal salt solution, the environment in the reactor is kept constant, and the clear liquid in the kettle can be filtered out by a microporous filtration device to keep the liquid level in the kettle constant.

[0515] As the metal salt solution is continuously added, the material in the reactor is continuously concentrated and the particles continue to grow. By controlling the timing of stopping the addition of materials to control the reaction time, the size of the particles can be controlled.

[0516] Taking the coprecipitation method to prepare the solid precursor of the positive electrode active material as an example, the FWDH of the solid precursor of the positive electrode active material can be adjusted by adjusting parameters such as the reaction temperature. (001) , but not limited thereto. See the following Preparation Examples 9-11.

[0517] Taking the coprecipitation method to prepare the solid precursor of the positive electrode active material as an example, the D of the solid precursor of the positive electrode active material can be adjusted by controlling the timing of stopping the addition of materials. v 50, but not limited thereto. See the following Preparation Examples 4-5.

[0518] Taking the preparation of the positive electrode active material solid precursor by coprecipitation as an example, the specific surface area of ​​the positive electrode active material solid precursor can be adjusted by controlling parameters such as the concentration of ammonia water, but it is not limited thereto. Please refer to the following preparation examples 6-8.

[0519] Taking the preparation of the positive electrode active material solid precursor by coprecipitation as an example, the SPAN value of the positive electrode active material solid precursor can be adjusted by controlling the reaction temperature, reaction time and other parameters, but it is not limited thereto. Please refer to the following preparation examples 2-3.

[0520] In some embodiments, the prepared cathode active material is the cathode active material defined in the first aspect of the present application.

[0521] In some embodiments, the prepared cathode active material satisfies one or more of the following characteristics (tm1) and (tm2):

[0522] (tm1) The prepared cathode active material is the cathode active material defined in the first aspect of the present application;

[0523] (tm2) The prepared cathode active material 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, and the lithium nickel-based oxide satisfies one or more of the following characteristics (tn1), (tn2), (tn3), (tn4) and (tn5):

[0524] (tn1) The atomic molar ratio of Ni element to non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1. For the value or range of q1, reference can also be made to the value or range of q1 in the first aspect of the present application;

[0525] (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. For the value or range of q2, reference can also be made to the value or range of q2 in the first aspect of the present application;

[0526] (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. For the value or range of q3, reference can also be made to the value or range of q3 in the first aspect of the present application;

[0527] (tn4) The atomic molar ratio of Co element to non-lithium metal element in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.3. For the value or range of q4, reference can also be made to the value or range of q4 in the first aspect of the present application;

[0528] (tn5) The atomic molar ratio of Mn element to non-lithium metal element in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.5. For the value or range of q5, reference can also be made to the value or range of q5 in the first aspect of the present application.

[0529] In the third aspect of the present application, a cathode active material is provided. The cathode active material includes primary particles, and the particle size of the primary particles is moderate and the particle size distribution is relatively narrow.

[0530] In some embodiments, in the particle size distribution curve of the primary particles in the cathode active material, the full width at half maximum (W H ) and the average particle size (D1) of the primary particles in the cathode active material are controlled within a better range. W HThe definitions of and D1 can be found in the first aspect of the present application.

[0531] The positive electrode active material can be used to prepare the secondary battery of the first aspect of the present application, which can significantly improve the battery life of the secondary battery at high voltage, including cycle and / or storage life. Without being limited to any theory, please refer to the description in the first aspect of the present application.

[0532] In some embodiments, a positive electrode active material is provided, the positive electrode active material comprising primary particles, W H ≤2.5μm, 1.3μm≤D1≤3μm.

[0533] The third aspect of the present application may provide a positive electrode active material having the same characteristics as the positive electrode active material defined in the first aspect of the present application. It is understood that the positive electrode active material provided in the third aspect of the present application may be an independent raw material, or may be present in an independent positive electrode sheet, or may be present in the positive electrode sheet of the battery.

[0534] 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 the present application.

[0535] In some embodiments, the positive electrode active material includes non-agglomerated primary particles and secondary particles.

[0536] In some embodiments, the positive electrode active material is the positive electrode active material defined in the first aspect of the present application (ie, has the same characteristics 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.

[0537] In a fourth aspect of the present application, a positive electrode plate is provided, which includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material.

[0538] In some embodiments, the positive electrode active layer includes the positive electrode active material described in the third aspect of the present application.

[0539] In some embodiments, a positive electrode sheet is provided, which includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material;

[0540] In the particle size distribution curve of primary particles in the positive electrode active material, the half peak width (W H ) satisfies W H ≤2.5μm;

[0541] The average particle size (D1) of primary particles in the positive electrode active material satisfies 1.3 μm ≤ D1 ≤ 3 μm.

[0542] 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, and the battery life of the secondary battery at high voltage can be improved, including the cycle and / or storage life.

[0543] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0544] (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 the present application;

[0545] (to2) the positive electrode active material is the positive electrode active material defined in the first aspect of the present application;

[0546] (to3) The positive electrode sheet is the positive electrode sheet defined in the first aspect of the present application.

[0547] The fourth aspect of the present application may provide a positive electrode sheet having the same characteristics as the positive electrode sheet defined in the first aspect of the present application. It can be understood that the positive electrode sheet provided in the fourth aspect of the present application may be an independent film material or may exist in a battery.

[0548] In some embodiments, the positive electrode sheet is the positive electrode sheet defined in the first aspect of the present application. The positive electrode sheet described in the first aspect is present in a secondary battery.

[0549] In another aspect of the present 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 the present application. The positive electrode sheet can be used to prepare the secondary battery described in the first aspect of the present application.

[0550] In some embodiments, a method for preparing a positive electrode sheet is provided, comprising the following steps: applying a positive electrode slurry on at least one side of a positive electrode current collector, drying, and cold pressing to prepare a positive electrode sheet; wherein the positive electrode slurry comprises a positive electrode active material. The definition of the positive electrode active material can refer to the first aspect, the second aspect, and the third aspect of the present application.

[0551] 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, the binder and the conductive agent in the positive electrode slurry can refer to any suitable embodiment or example in the context of the present application.

[0552] In yet another aspect of the present 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 the present application.

[0553] In some embodiments, a method for preparing a secondary battery is provided, comprising the following steps: placing an electrode assembly in a shell, injecting an electrolyte, allowing the electrolyte to stand and soak, and forming the electrolyte to prepare a secondary battery; wherein the electrode assembly comprises a positive electrode plate, the positive electrode plate comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material.

[0554] The definition of the positive electrode active material can refer to the first aspect, the second aspect and the third aspect of the present application.

[0555] The definition of the positive electrode plate can refer to the first aspect and the fourth aspect of the present application.

[0556] In some embodiments, the electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material.

[0557] In the fifth aspect of the present application, an electrical device is provided, which includes the secondary battery described in the first aspect of the present application, the positive electrode active material prepared by the preparation method of the positive electrode active material described in the second aspect of the present application, the positive electrode active material described in the third aspect of the present application, and at least one of the positive electrode plates described in the fourth aspect of the present application.

[0558] In some embodiments, an electric device includes the secondary battery of any embodiment provided in the present application.

[0559] Secondary batteries can be used as power sources for electrical devices, or as energy storage units for electrical devices. Electrical devices may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, mobile devices may be, for example, mobile phones, laptop computers, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, electric tools, etc., but are not limited thereto. The electrical device may also be used in the fields of military equipment, aerospace, etc., and may also be used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations.

[0560] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0561] Fig.10 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery device or a battery pack can be used.

[0562] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0563] In the sixth aspect of the present application, there is provided the use of the secondary battery described in the first aspect of the present application, the positive electrode active material prepared by the preparation method of the positive electrode active material described in the second aspect of the present application, the positive electrode active material described in the third aspect of the present application, and the positive electrode plate described in the fourth aspect of the present application in supplying electric energy and / or storing electric energy.

[0564] In some embodiments, the use includes performing at least one of charging and discharging at a voltage greater than or equal to 4.2V.

[0565] In some embodiments, the charging process includes a charging stage under at least one voltage condition of 4.2V to 4.5V.

[0566] In some embodiments, the discharging process includes a stage of discharging under at least one voltage condition of 4.5V to 4.2V.

[0567] Without limitation, the voltage condition may be any one of the following voltages or a range consisting of any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc., for example, 4.3V to 4.5V.

[0568] In some embodiments, the application includes performing a charge-discharge cycle, and the step of performing the charge-discharge cycle includes at least one of charging at a voltage V1 and discharging at a voltage V1. In some embodiments, the voltage V1 ≥ 4.2 V. Non-limiting examples of the voltage V1 include 4.3 V, 4.4 V, 4.5 V, etc., and may also be within a range of any two of the aforementioned voltages.

[0569] Below, some embodiments of the present application are described. The described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limitations on the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0570] If the techniques or conditions are not specified in the examples, the above description, or the techniques or conditions described in the literature in the field, or the product instructions are used. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially, or can be synthesized in a conventional manner from commercially available products.

[0571] In the following examples, room temperature refers to 20°C to 30°C.

[0572] The secondary battery in the following examples takes a lithium ion secondary battery as an example.

[0573] 1. Preparation of positive electrode active materials

[0574] (I) Preparation

[0575] Preparation Example 1.

[0576] The target positive electrode active material is lithium nickel cobalt manganese-based oxide, and the target chemical formula is LiNi 0.63 Co 0.13 Mn 0.24 O2.

[0577] The preparation method of the positive electrode active material solid precursor is as follows:

[0578] Nickel sulfate, cobalt sulfate and manganese sulfate are prepared into a 1.6 mol / L metal salt solution according to the molar ratio of metal cations of 0.65:0.10:0.25 for use, the solvent is water, and the sum of the molar volume concentrations of nickel ions, cobalt ions and manganese ions is 1.6 mol / L.

[0579] Add pure water to the reactor, introduce nitrogen, start stirring and heating, the speed is 220 rpm, the temperature is 65°C (that is, the reaction temperature in the reactor is controlled to be 65°C), the ammonia concentration is 7.0 g / L, and alkali solution (alkali solution is sodium hydroxide aqueous solution) is introduced to adjust the pH in the reactor to 11.6, and then alkali solution and metal salt solution are introduced at the same time for precipitation reaction. During the feeding process, the environment in the reactor is kept constant, and the clear liquid in the reactor is filtered out through a microporous filtration device to keep the liquid level in the reactor constant. Continuously feed, the material in the reactor is continuously concentrated, and the particles continue to grow until the particle size grows to 3.5 μm. After the feeding is completed, the precursor preparation is completed.

[0580] The solid precursor of the positive electrode active material, lithium salt (lithium hydroxide monohydrate), and additives (tungsten oxide and zirconium oxide) are fully mixed in a mass ratio of 948.9:433.6:2.3:4.1, and the first sintering is performed at 940°C for 12 hours, and the first crushing is performed to obtain a first sintered product; the first sintered product is fully mixed with a high-temperature coating agent (first coating agent), and the second sintering is performed at 750°C for 6 hours, and the second crushing is performed to obtain a second sintered product. The second sintered product is fully mixed with a low-temperature coating agent (second coating agent), and low-temperature sintering is performed at 500°C for 5 hours to prepare a positive electrode active material, which can be marked as a "finished product".

[0581] In this example, doping is performed simultaneously with the first sintering step, the doping elements are W and Zr, and the raw material containing the doping elements is a combination of tungsten oxide and zirconium oxide.

[0582] In this example, the first sintering, the second sintering and the third sintering are performed in an oxygen atmosphere.

[0583] The first coating agent is composed of cobaltous hydroxide and aluminum hydroxide; the amount of the first coating agent is 28.4g of cobaltous hydroxide and 2.9g of aluminum hydroxide;

[0584] The composition of the second coating agent is: titanium dioxide; the amount of the second coating agent is 3.3g;

[0585] The parameters for the first crushing include: air intake pressure of 0.4 MPa, feeding frequency of 20 Hz; the parameters for the second crushing include: air intake pressure of 0.3 MPa, feeding frequency of 20 Hz.

[0586] Preparation Example 2-3 uses a method substantially the same as Preparation Example 1 to prepare the positive electrode active material, except that the pH in the reactor during the reaction process is different.

[0587] 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.

[0588] 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.

[0589] Preparation Example 4-5 uses a method substantially the same as Preparation Example 1 to prepare the positive electrode active material, except that the timing of stopping the addition of the metal salt solution is different, that is, the timing of stopping the feeding is different.

[0590] Preparation Example 4: During the preparation of the solid precursor of the positive electrode active material, the addition of material was stopped until the particle size grew to 3.1 μm.

[0591] Preparation Example 5: During the preparation of the solid precursor of the positive electrode active material, the addition of material was stopped until the particle size grew to 4 μm.

[0592] Preparation Examples 6-8 use a method substantially the same as that of Preparation Example 1 to prepare positive electrode active materials, except that the concentration of ammonia water is different.

[0593] 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.

[0594] 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.

[0595] 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.

[0596] Preparation Examples 9-11 use a method substantially the same as that of Preparation Example 1 to prepare positive electrode active materials, except that the reaction temperatures are different.

[0597] In Preparation Example 9, during the preparation of the solid precursor of the positive electrode active material, the reaction temperature in the kettle was 73°C.

[0598] In Preparation Example 10, during the preparation of the solid precursor of the positive electrode active material, the reaction temperature in the kettle was 54°C.

[0599] In Preparation Example 11, during the preparation of the solid precursor of the positive electrode active material, the reaction temperature in the kettle was 44°C.

[0600] Preparation Examples 12-15 use a method basically the same as Preparation Example 1 to prepare positive electrode active materials and use the same solid precursor. The difference is that Preparation Examples 12-13 change the temperature (T1) for the first sintering, and Preparation Examples 14-15 change the time (t1) for the first sintering.

[0601] In Preparation Example 12, the temperature T1 for the first sintering is 980°C.

[0602] In Preparation Example 13, the temperature T1 for the first sintering is 900°C.

[0603] In Preparation Example 14, the first sintering time t1 is 15 h.

[0604] In Preparation Example 15, the time t1 for the first sintering is 8 h.

[0605] Preparation Example 16. A positive electrode active material was prepared by a method substantially the same as that of Preparation Example 1, except that the temperature (T1) and the time (t1) of the first sintering were changed.

[0606] In Preparation Example 16, the temperature T1 for the first sintering is 900° C., and the time t1 for the first sintering is 5 h.

[0607] Preparation Example 17. The positive electrode active material is not provided with 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.

[0608] The solid precursor of the positive electrode active material (the same as that in Preparation Example 1), lithium salt and additives are fully mixed, and the first sintering is performed at 940°C for 12 hours, and the first crushing is performed to obtain a first sintered product; the first sintered product is sintered for a second time at 750°C for 6 hours, and the second sintering product is obtained after the second crushing. The second sintered product is used as the positive electrode active material and can be marked as a "finished product".

[0609] Preparation Example 18. The positive electrode active material was prepared by the same method as in Preparation Example 1, except that the molar ratio of nickel ions, cobalt ions and manganese ions in the solid precursor synthesis process was adjusted to prepare 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 (the first coating agent) and the low temperature coating agent (the second coating agent) are also omitted.

[0610] Preparation Comparative Example 1 The positive electrode active material was prepared by a method substantially the same as that of Preparation Example 1, except that the pH in the reactor during the reaction was different.

[0611] In the preparation of Comparative Example 1, during the preparation of the solid precursor of the positive electrode active material, the pH in the reactor was controlled to be 12.5.

[0612] Preparation Comparative Example 2: The positive electrode active material was prepared by a method substantially the same as that of Preparation Example 1, except that the concentration of ammonia water was different.

[0613] In the preparation of Comparative Example 2, during the preparation of the solid precursor of the positive electrode active material, the concentration of ammonia water was 11.5 g / L.

[0614] Preparation Comparative Example 3-4. The positive electrode active material was prepared by the same method as Preparation Example 1, except that the temperature (T1) and the time (t1) of the first sintering were changed.

[0615] Comparative Example 3 was prepared, and the temperature T1 for the first sintering was 1050° C., and the time t1 for the first sintering was 15 h.

[0616] In the preparation of comparative example 4, the temperature T1 for the first sintering was 850° C., and the time t1 for the first sintering was 8 h.

[0617] Preparation Comparative Example 5. The positive electrode active material was prepared by a method basically the same as that of Preparation Example 17 (the positive electrode active material was not provided with a coating layer), except that, during the preparation of the solid precursor of the positive electrode active material, the reaction temperature in the kettle was 40°C.

[0618] It should be noted that in the above preparation examples and comparative examples, in the steps of multiple sintering and multiple crushing of the solid precursor of the positive electrode active material, the crushing parameters can be adjusted according to the agglomeration of the material to control the particle size and distribution in the material and the agglomeration of the primary particles as much as possible.

[0619] (II) Material Characterization

[0620] Samples to be tested: the positive electrode active material solid precursor and the positive electrode active material (finished product) in each example.

[0621] 1. D v 50. D v 90.D v 10 and SPAN value, where SPAN = (D v 90-Dv 10) / D v 50.

[0622] Malvern MasterSizer 2000 laser particle size analyzer was used.

[0623] Reference standard process: GB / T19077-2016 / ISO 13320:2009, the detailed test process includes: take an appropriate amount of the sample to be tested, add 20mL of solvent deionized water (the sample concentration can be controlled at 8% to 12% shading), ultrasonically treat for 5 minutes (53KHz / 120W) to fully disperse the sample, and then measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard. Add the ultrasonically dispersed sample to the injection pool, and start the test after the sample stabilizes for 5s to 10s. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light. The volume cumulative distribution diagram of the particle size is drawn according to the test data, and D is obtained from the distribution diagram. v 50. D v 90.D v 10, the SPAN value can be calculated. In order to avoid the influence of agglomeration in the drying process on the particle size test, the sample was washed with anhydrous ethanol and then wetted for dispersion test.

[0624] 2. Specific surface area BET

[0625] Test instrument: Tri Star II surface area and pore analyzer from Micromeritics, USA.

[0626] The test steps can refer to GB / T 19587-2004. Use nitrogen as the adsorption gas and calculate the specific surface area of ​​the material by the BET method; take the sample to be tested and add it into the BET test tube until it meets 2 / 3 of the bottom bulb, and degas and heat the sample; after cooling to room temperature, backfill with nitrogen to remove the vacuum and plug the sample tube with a bottle stopper, and record the sample weight; remove the bottle stopper, add the filling rod, install the sample tube to the instrument analysis station, enter the sample weight and start the test.

[0627] 3. The half-peak width of the (001) crystal plane diffraction peak in the X-ray diffraction spectrum of the solid precursor of the positive electrode active material is denoted as FWDH (001) .

[0628] Test instrument: Bruker-D8advance.

[0629] Test method: Cu target Kα1 ray is used, the wavelength λ is 0.15406nm, the X-ray tube is controlled at 40kV and 40mA, the 2θ(°) scanning range is 10°~80°, and the 2θ(°) scanning speed is 0.02° / sec.

[0630] The half-peak width of the (001) crystal plane diffraction peak corresponds to the half-peak width of the 2θ (°) diffraction peak in the range of 15° to 25°.

[0631] 4. Analysis based on scanning electron microscope (SEM) images

[0632] Characterization parameters: morphology observation of positive electrode active materials; particle size distribution and average particle size of primary particles in the finished positive electrode active materials, and the proportion of non-agglomerated primary particles in the positive electrode active materials.

[0633] Equipment: JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope and ZEISS Sigma 300 scanning electron microscope.

[0634] For SEM test, please refer to JY / T(001)-1996.

[0635] Test method: Lay the positive electrode active material and stick it on the conductive glue, place the sample on the scanning electron microscope workbench, image the sample under the bombardment of the electron beam generated by the electron gun, and obtain the SEM microscopic morphology of the sample.

[0636] Analysis equipment: LIBMAS lithium-ion battery material microscopic intelligent analysis system.

[0637] (1) Half-peak width of the particle size distribution curve of primary particles in the positive electrode active material.

[0638] The maximum diameter of the primary particles in each direction in the SEM morphology image was recorded as the "particle size of the primary particles in the positive electrode active material".

[0639] The statistical scope of “primary particles in the positive electrode active material” includes non-agglomerated primary particles and primary particles in secondary particles in the SEM morphology image.

[0640] Analysis method: The horizontal axis of the curve corresponds to the particle size of the 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 number of primary particles counted. Randomly select one area in the sample to be tested for scanning test, and count the particle size of each primary particle and the frequency of occurrence of different particle sizes at 1000X magnification. The number of primary particles counted is ≥2000. The particle size distribution curve of the primary particles is obtained by the following method: Draw a histogram of the particle size data of the primary particles using Minitab and fit the curve.

[0641] The “half peak width” of the “particle size distribution curve of primary particles in the positive electrode active material” refers to the width between the particle size boundaries on both sides corresponding to half the peak height of the distribution curve.

[0642] (2) The average particle size of the primary particles in the positive electrode active material.

[0643] The statistical scope of “primary particles in the positive electrode active material” includes non-agglomerated primary particles and primary particles in secondary particles in the SEM morphology image.

[0644] Analysis method: Randomly select an area in the sample to be tested for scanning test, and count the particle size of each primary particle at a magnification of 1000X, and then calculate the average value of the particle size of each primary particle counted.

[0645] (3) The percentage of non-agglomerated primary particles in the positive electrode active material.

[0646] Analysis method: Randomly select an area 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.

[0647] (III) Test results

[0648] Preparation Examples 1-18 all prepared positive electrode active materials with moderate primary particle size and narrow particle size distribution.

[0649] For example, the particle size distribution curve of the primary particles in the positive electrode active material prepared in Preparation Example 1 can be found in Figure 2 The SEM micromorphology of the prepared positive electrode active material can be found in Figure 4 For example, the particle size distribution curve of the primary particles in the positive electrode active material prepared in Preparation Example 1 can be found in Figure 1 .

[0650] The positive electrode active materials prepared in Preparation Examples 1-18 all meet the following two characteristics:

[0651] The half-peak width (W) of the particle size distribution curve of the primary particles in the positive electrode active material H )≤2.5μm; and

[0652] The average particle size (D1) of primary particles in the positive electrode active material satisfies 1.3 μm ≤ D1 ≤ 3 μm.

[0653] For example, the X-ray diffraction spectrum of the solid precursor of the positive electrode active material in Preparation Example 1 can be found at Figure 3Among them, the X-ray diffraction spectrum of the positive electrode active material solid precursor has a peak at a 2θ (°) diffraction angle of 15° to 25°. The X-ray diffraction spectra of the positive electrode active material solid precursors prepared in the other preparation examples also have peaks at a 2θ diffraction angle of 15° to 25°.

[0654] According to the X-ray diffraction spectrum of the positive electrode active material solid precursor, it can be confirmed that the X-ray diffraction spectrum of the positive electrode active material solid precursor has a (001) crystal plane diffraction peak, and accordingly, the positive electrode active material solid precursor has a (001) crystal plane. Figure 3 .

[0655] The test characterization results of the positive electrode active material solid precursor and the positive electrode active material (finished product) in each preparation example and preparation comparative example can be found in Table 1.

[0656] Table 1.

[0657]

[0658] In Table 1, “precursor SPAN” represents the SPAN value of the solid precursor of the positive electrode active material, and “precursor D v 50" represents the D of the solid precursor of the positive electrode active material v 50, “BET of precursor” refers to the specific surface area of ​​the solid precursor of the positive electrode active material, and “XRD FWHM of precursor” refers to the specific surface area of ​​the solid precursor of the positive electrode active material. (001) " indicates that the X-ray diffraction spectrum of the solid precursor of the positive electrode active material has a half-peak width of the (001) crystal plane diffraction peak.

[0659] In Table 1, “Finished Product D v 50" represents the D of the prepared positive electrode active material v 50 value, “finished product SPAN” represents the SPAN value of the prepared positive electrode active material, “the average particle size D1 of the finished product primary particles” represents the average particle size of the primary particles in the positive electrode active material, and “the half peak width W of the particle size distribution curve of the finished product primary particles” represents the average particle size of the primary particles in the 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.

[0660] 2. Preparation of secondary batteries

[0661] Examples 1-18 and Comparative Examples 1-5 respectively used the positive electrode active materials prepared in Preparation Examples 1-18 and Comparative Examples 1-5.

[0662] In the following examples, lithium-ion secondary batteries are used as examples to prepare secondary batteries.

[0663] Example 1.

[0664] (1) Positive electrode

[0665] The positive electrode active material (prepared in Preparation Example 1), the conductive agent Super-P, the conductive agent carbon nanotube (CNT) and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:1.5:0.5:3, and fully dispersed in a solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry was coated on both sides of the positive electrode current collector Al foil with a thickness of 13μm, and the total coating surface density on both sides was 0.5g / 1540.25mm 2 After vacuum drying at 120°C and cold pressing, the positive electrode sheet was obtained. The compaction density of the positive electrode sheet was 3.4 g / cm 3 .

[0666] (2) Negative electrode

[0667] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent at a mass ratio of 95:2:2:1 to prepare a negative electrode slurry. The negative electrode slurry was coated on both sides of the negative electrode current collector Cu foil, and the total coating surface density on both sides was 0.34g / 1540.25mm 2 , drying and cold pressing to obtain the negative electrode sheet, the compaction density of the negative electrode sheet is 1.6g / cm 3 .

[0668] (3) Isolation film

[0669] A polyethylene (PE) separator with a thickness of 7 μm is used.

[0670] (4) Electrolyte

[0671] In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65, lithium salt lithium hexafluorophosphate (LiPF6) and additives are added and mixed evenly to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte is 1 mol / L. The mass concentration of the additives in the electrolyte is 2.5wt% of vinylene carbonate (VC), 1wt% of fluoroethylene carbonate (FEC), and 0.5wt% of diethylene sulfate (DTD).

[0672] (5) Preparation of secondary battery (further lithium ion secondary battery)

[0673] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with a prepared electrolyte, and packaged, injected, formed, and vented to obtain a lithium-ion secondary battery.

[0674] Examples 2-18 and Comparative Examples 1-5 respectively use the same method as Example 1 to prepare secondary batteries, except that the positive electrode active materials are different. Examples 2-18 and Comparative Examples 1-5 respectively use the positive electrode active materials prepared in Preparation Examples 2-18 and Comparative Examples 1-5.

[0675] 3. Testing and Analysis

[0676] (I) Testing and analysis methods

[0677] 1. Material and pole piece characterization

[0678] (1) Mn dissolution test of positive electrode active material:

[0679] Samples to be tested: positive electrode active materials prepared in Preparation Examples 1-18 and Comparative Preparation Examples 1-5.

[0680] Weigh 5±0.005g of EDTA-disodium powder with weighing paper, pour it into a 500mL beaker and stir ultrasonically for 3min~5min until it is completely dissolved; use aluminum foil paper with a fold of about 5cm×5cm and fold the four sides slightly to weigh the powder; use the folded aluminum foil to weigh 30±0.01g of sample and record the sample mass; clean the soaked small magnetic beads and put them into the beaker; use a measuring cylinder to measure 100mL of the prepared EDTA-disodium mixed solution and add it to the beaker; set the speed of the magnetic stirrer to 720 rpm; place the beaker on a magnetic stirrer and add the weighed powder sample (powder sample of the positive electrode active material, record the mass M0) while stirring, stir for 30 min and let stand for 1 min; use a 1mL or 3mL syringe to draw the solution, use two 0.22μm filters to filter 3mL of the solution into a test tube, prepare a 50mL glass volumetric flask, add 1mL to 2mL of nitric acid to the volumetric flask, use a 1ml pipette, draw 1mL of the filtrate into a 50mL volumetric flask to make up the volume; use ICP-OES to test the concentration of Mn element C Mn , input solution volume V0 / sample mass M0, record the experimental result Mn (ppm) = C Mn ×V0 / M0.

[0681] Wherein EDTA represents ethylenediaminetetraacetic acid.

[0682] In the present application, percentages can be converted to ppm (parts per million), 1% = 10000 ppm, for example, 0.2% = 2000 ppm, 0.1% = 1000 ppm, 0.01% = 100 ppm, 0.005% = 50 ppm, etc.

[0683] Some test results can be found in Table 2.

[0684] 2. Positive electrode and battery performance test

[0685] (1) Test of gram capacity of positive electrode

[0686] The positive electrode plate and the lithium plate are assembled into a button battery. After the assembled button battery is left to stand for 120 minutes, it is charged to 4.3V at a constant current of 0.1C in a constant temperature environment of 25°C, then charged at a constant voltage of 4.3V until the current drops to 0.05C, and then discharged to 2.8V at a constant current of 0.33C to obtain the first cycle discharge capacity in grams.

[0687] The record is "4.4V 0.1C, discharge capacity in grams", please refer to Table 3.

[0688] (2) 60℃ storage performance test (charged to 4.4V)

[0689] The lithium-ion battery was charged to 4.4V at a constant current of 0.33C at a constant temperature of 25°C, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged to 2.8V at a constant current of 0.33C to obtain the first cycle discharge capacity. The battery was charged to 4.4V at a constant current of 0.33C, and then charged to a cut-off current of 0.05C at a constant voltage of 4.4V, and then placed in a 60°C constant temperature oven for 30 days. After being taken out, it was cooled for 5 hours, and then discharged to 2.8V at a constant current of 0.33C at a constant temperature of 25°C, and then charged to 4.4V at a constant current of 0.33C, and then charged to a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged to 2.8V at a constant current of 0.33C to obtain the reversible capacity after 30 days of storage at 60°C.

[0690] Reversible capacity retention rate after storage at 60°C for 30 days (charged to 4.4 V) = reversible capacity after storage at 60°C for 30 days / first cycle discharge capacity × 100%.

[0691] It is recorded as “60°C storage 30D capacity retention rate (charged to 4.4V)”, and can be found in Table 2.

[0692] (3) 45℃ cycle performance test (charged to 4.4V)

[0693] At 45°C, charge the lithium-ion secondary battery to 4.4V at 1C constant current, then charge it to a cut-off current of 0.05C at 4.4V constant voltage, leave it for 10 minutes, then discharge it to 2.8V at 1C constant current, leave it for 5 minutes. This is a charge-discharge cycle. Record the discharge capacity at this time as C0. Repeat this charge-discharge cycle process for the same lithium-ion secondary battery, and record the discharge capacity C of the first, second, and nth cycles. n .

[0694] The cycle capacity retention rate P100 (charged to 4.4 V) of the battery after 100 cycles = C100 / C0×100% was recorded.

[0695] It 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.

[0696] (4) 60℃ storage performance test (charged to 4.5V)

[0697] The lithium-ion battery was charged to 4.5V at a constant current of 0.33C at a constant temperature of 25°C, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged to 2.8V at a constant current of 0.33C to obtain the first cycle discharge capacity. The battery was charged to 4.4V at a constant current of 0.33C, and then charged to a cut-off current of 0.05C at a constant voltage of 4.4V, and then placed in a 60°C constant temperature oven for 30 days. After being taken out, it was cooled for 5 hours, and then discharged to 2.8V at a constant current of 0.33C at a constant temperature of 25°C, and then charged to 4.5V at a constant current of 0.33C, and then charged to a current of 0.05C at a constant voltage of 4.5V, and then discharged to 2.8V at a constant current of 0.33C to obtain the reversible capacity after 30 days of storage at 60°C.

[0698] Reversible capacity retention rate after storage at 60° C. for 30 days (charged to 4.5 V)=reversible capacity after storage at 60° C. for 30 days / first cycle discharge capacity×100%.

[0699] It is recorded as “60°C storage 30D capacity retention rate (charged to 4.5V)”. Some test results can be found in Table 4.

[0700] (5) 45℃ cycle performance test (charged to 4.5V)

[0701] At 45°C, charge the lithium-ion secondary battery to 4.5V at 1C constant current, then charge it to a cut-off current of 0.05C at 4.5V constant voltage, leave it for 10 minutes, then discharge it to 2.8V at 1C constant current, leave it for 5 minutes. This is a charge-discharge cycle. Record the discharge capacity at this time as C0. Repeat this charge-discharge cycle process for the same lithium-ion secondary battery, and record the discharge capacity C of the first, second, and nth cycles. n .

[0702] The cycle capacity retention rate P100 (charged to 4.5 V) of the battery after 100 cycles = C100 / C0×100% was recorded.

[0703] It is recorded as “45°C cycle capacity 100-cycle retention rate (charged to 4.5V)”. Some test results can be found in Table 4.

[0704] (II) Test results analysis

[0705] The half peak width (W) of the particle size distribution curve of the primary particles in the positive electrode active material prepared in Preparation Example 1-18 is H) 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.

[0706] Each embodiment 1-18 uses the positive electrode active material prepared in the preparation examples 1-18 to prepare the secondary battery. The prepared secondary batteries can be charged and discharged at a voltage higher than or equal to 4.2V (for example, 4.4V, 4.5V), and the battery life at high voltage is significantly improved, including the cycle life and storage life at high voltage are significantly improved, and the capacity retention rate of the cycle performance test and the storage performance test at high voltage is significantly improved. Exemplarily, in Example 1 relative to Comparative Examples 1-2, 4, and in Example 17 relative to Comparative Example 5, the "60°C storage 30D capacity retention rate" of the secondary battery at high voltage is significantly improved. Exemplarily, in Example 1 relative to Comparative Examples 1-2, 4, and in Example 17 relative to Comparative Example 5, the cycle capacity retention rate of the secondary battery at high voltage (45°C cycle 100 week capacity retention rate (charged to 4.4V) and 45°C cycle capacity 100 week retention rate (charged to 4.5V)) are significantly improved. Exemplarily, the relevant data of the secondary battery prepared in Example 1 can be found in Table 4.

[0707] The metal dissolution in the positive electrode active materials prepared in Preparation Examples 1-18 is low. Some results are listed in Table 3.

[0708] The positive electrode sheets prepared using the positive electrode active materials of Preparation Examples 1-18 also have good discharge capacity in grams, as shown in Table 3. The average particle size D1 of the primary particles in the positive electrode active material of Comparative Example 3 is relatively large, resulting in a significant decrease in discharge capacity in grams.

[0709] Table 2.

[0710]

[0711]

[0712] Table 3.

[0713] serial number Transition metal dissolution, Mn / ppm 4.4V 0.1C, discharge capacity in grams Example 1 80 198 Example 2 98 199 Example 3 110 199.5 Example 4 87 200.5 Example 5 91 195 Example 6 120 200 Example 7 60 194 Example 8 56 193.5 Example 9 130 201 Example 10 96 195 Embodiment 11 168 191 Example 12 83 194 Embodiment 13 86 203 Embodiment 14 66 193 Embodiment 15 140 201 Example 16 55 191 Comparative Example 1 180 198.5 Comparative Example 2 185 200.5 Comparative Example 3 40 177 Comparative Example 4 230 204

[0714] Table 4.

[0715]

[0716] The description of each embodiment and example above tends to emphasize the differences between each embodiment and example, and the same or similar parts can be referenced to each other. For the sake of brevity, this article will not repeat them. The technical features of the above-described embodiments and examples can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0717] It should be noted that the present application is not limited to the above-mentioned embodiments and examples. The above-mentioned embodiments and examples are only examples. Within the scope of the technical solution of the present application, the embodiments and examples that have the same structure as the technical idea and play the same effect are all included in the technical scope of the present application. The above-described embodiments and examples only express several embodiments and examples of the present application, and the description is relatively detailed, but it cannot be understood as a limitation on the scope of the patent. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be thought of by a person skilled in the art to the embodiments or examples, and other methods of combining some of the constituent elements in the embodiments or examples are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: It 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; In the particle size distribution curve of the primary particles in the positive electrode active material, the half peak width 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, characterized in that: 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, characterized in that: 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, characterized in that 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, characterized in that: 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 recorded as R1, and satisfies 1≤R1≤3.

6. The secondary battery according to claim 5, characterized in that: 1.5≤R1≤2.2。 7. The secondary battery according to any one of claims 1 to 6, characterized in that: The positive electrode active material includes non-agglomerated primary particles; the mass proportion 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 recorded 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, characterized in that: 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, characterized in that: 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, characterized in that: The positive electrode active material D v 50 is 2μm~6μm.

11. The secondary battery according to claim 10, characterized in that: The positive electrode active material D v 50 is 2.8μm~4.5μm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: 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.

13. The secondary battery according to claim 12, characterized in that: The SPAN value of the positive electrode active material is 0.85 - 1.

35.

14. The secondary battery according to any one of claims 1 to 13, characterized in that: 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, characterized in that: 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, characterized in that: 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, wherein, 0.5 ≤ q1 < 1; (t2) The lithium nickel-based oxide contains Ni element and Li element with an atomic molar ratio of q2:x2, wherein, 0.5 ≤ q2 < 1, 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, wherein, 0.5 ≤ q3 < 1, 1.6 ≤ x3 ≤ 2.

1.

17. The secondary battery according to claim 16, characterized in that: 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, wherein, 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, wherein, 0 < q5 ≤ 0.5, optionally, 0.01 ≤ q5 ≤ 0.5; (vi) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide is 80% - 100%.

18. The secondary battery according to claim 17, characterized in that: 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 element, 0.05≤q4≤0.2; (tvii) the lithium nickel-based oxide contains Mn element, 0.02≤q5≤0.38; (tviii) The mass proportion of the lithium nickel-based oxide in the lithium composite metal oxide is 90% to 100%.

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

20. The secondary battery according to any one of claims 1 to 19, characterized in that: The positive electrode active material satisfies one or more of the following characteristics: (tf1) the positive electrode active material includes a doping element, and the doping element includes 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 a coating element located on the surface of the particle, and the coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na.

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

22. The secondary battery according to any one of claims 1 to 21, characterized in that: The secondary battery further comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active layer, the negative electrode active layer comprises the negative electrode active material, and the negative electrode active material comprises one or more of a carbon-based material and a silicon-based material.

23. The secondary battery according to claim 22, characterized in that: The negative electrode active material includes a graphite material.

24. The secondary battery according to any one of claims 1 to 23, characterized in that: The secondary battery is a lithium ion secondary battery.

25. The secondary battery according to any one of claims 1 to 24, characterized in that: The charging cut-off 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 cut-off voltage of the secondary battery is 4.2V to 4.5V, and further optionally 4.3V to 4.5V.

26. A method for preparing a positive electrode active material, characterized in that: The steps include: Mixing a positive electrode active material solid precursor and a lithium source to obtain a primary mixture, performing a first sintering and a first crushing on the primary mixture, and then performing a second sintering and a second crushing on the primary mixture to prepare the positive electrode active material; The temperature for performing the first sintering is higher than the temperature for performing the second sintering; In the particle size distribution curve of the primary particles in the positive electrode active material, the half peak width is denoted as W H , satisfying W H ≤2.5μm; The average particle size of primary particles in the positive electrode active material is recorded as D1, which satisfies 1.3 μm≤D1≤3 μm.

27. The method for preparing the positive electrode active material according to claim 26, characterized in that: Meet one or more of the following characteristics: (1) The positive electrode active material includes a doping element, and the primary mixture also includes a raw material containing the doping element; (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 performed 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 a positive electrode active material according to claim 26 or 27, characterized in that: Meet one or more of the following characteristics: (tg1) the positive electrode active material includes a doping element, and the doping element includes 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 primary mixed material further includes a raw material containing the doping element; the raw material containing the doping element includes one or more of an oxide, a hydroxide, a carbonate and a phosphate containing the doping element; (tg3) the positive electrode active material includes a coating element, and the coating element includes one or more of Al, Ti, Mg, Zr, Y, Li, W and Na; (tg4) providing a raw material for the coating element including one or more of an oxide, a hydroxide, a carbonate and a phosphate containing the coating element; (tg5) the temperature of the first sintering is 900° C. to 980° C.; (tg6) the first sintering time is 5h to 15h; (tg7) the temperature of the second sintering is 700° C. to 800° C.; (tg8) The second sintering time is 4h to 12h; (tg9) The step of performing the second sintering is performed in the presence of a first coating agent, wherein the first coating agent 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 a positive electrode active material according to any one of claims 26 to 28, characterized in that: The positive electrode active material solid precursor meets one or more of the following characteristics: (tj1) the X-ray diffraction spectrum of the positive electrode active material solid precursor has a peak at a 2θ (°) diffraction angle of 15° to 25°; (tj2) The X-ray diffraction spectrum of the positive electrode active material solid precursor has a (001) crystal plane diffraction peak, and the half-peak width of the (001) crystal plane diffraction peak is recorded as FWDH (001) , where 0.35≤FWDH (001) ≤0.70; (tj3) D of the solid precursor of the positive electrode active material v 50: 2.5μm~4.5μm; (tj4) The specific surface area of ​​the solid precursor of the positive electrode active material is 5m 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; wherein SPAN = (D v 90-D v 10) / D v 50.

30. The method for preparing the positive electrode active material according to claim 29, characterized in that: The positive electrode active material solid precursor meets one or more of the following characteristics: (tk1)0.35≤FWDH (001) ≤0.64; (tk2) D of the solid precursor of the positive electrode active material v 50: 3.0μm~4.2μm; (tk3) The specific surface area of ​​the solid precursor of the positive electrode active material is 6 m 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 a positive electrode active material according to any one of claims 26 to 30, characterized in that: The prepared positive electrode active material satisfies one or more of the following characteristics (tm1) and (tm2): (tm1) the prepared positive electrode active material is the positive electrode active material defined in any one of claims 1 to 16 and 19 to 21; (tm2) The prepared positive electrode active material 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): (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, 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, 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, characterized in that 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 half peak width 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, characterized in that The positive electrode active material includes the positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 26 to 31, or is the positive electrode active material defined in any one of claims 2 to 21.

34. A positive electrode plate, characterized in that: It 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 half peak width 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, characterized in that: It 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 according to any one of claims 26 to 31; (to2) The positive electrode active material is the positive electrode active material defined 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, characterized in that: It includes at least one of the secondary battery according to any one of claims 1 to 25, the positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 26 to 31, the positive electrode active material according to claim 32 or 33, and the positive electrode sheet according to claim 34 or 35.

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