A secondary battery and its preparation method

Abstract

This application belongs to the field of electrochemical technology, specifically relating to a secondary battery, and further disclosing its preparation method. The lithium-ion secondary battery described in this application has a positive electrode active material with good crystal structure stability and surface inertness. After 1C charge-discharge cycles, the amount of transition metals (Ni, Mn) on the negative electrode binder layer increases relatively little, effectively suppressing side reactions between the positive electrode active material and the electrolyte, and the dissolution of transition metals (Ni, Co, Mn) in the positive electrode active material. This improves the high-temperature cycling performance of the secondary battery and suppresses high-temperature gas generation, thereby improving the gas generation phenomenon and optimizing the cycle performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemistry, and particularly relates to a secondary battery, and further discloses a preparation method thereof. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, have been applied in various fields due to the advantages of high specific energy, wide application temperature range, low self-discharge rate, long cycle life, good safety performance, and no pollution.

[0003] However, positive electrode materials such as lithium iron phosphate (LiFePO4), low-nickel ternary (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) and the like are difficult to meet the demand of lithium ion battery positive electrode materials for energy density of power batteries due to the limitations of the properties of the materials themselves. Increasing the nickel content of the ternary positive electrode material and increasing the voltage of the ternary positive electrode material (the cut-off voltage is as high as 4.45V) can improve the energy density of the battery. However, with the increase of the nickel content and the increase of the voltage, the side reactions directly generated by the positive active material and the electrolyte will be significantly intensified, and the dissolution of transition metal ions will also be significantly intensified, which will affect the high-temperature gas production performance and the cycle performance of the secondary battery. At present, the main means to solve the high-temperature gas production performance by modifying the material will cause damage to the performance of the secondary battery to different degrees, such as the decrease of the energy density (the reversible capacity of the active material decreases), the deterioration of the cycle performance, and the like. Therefore, how to balance the cycle performance and the high-temperature gas production performance of the secondary battery has become an important problem affecting the development of the secondary battery. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a secondary battery which has a good cycle service life and a low gas production at high temperature without sacrificing the energy density.

[0005] To solve the above technical problems, the secondary battery provided by the present application comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode mixture layer arranged on the positive electrode current collector, the positive electrode mixture layer comprises a positive electrode active material, and the positive electrode active material comprises nickel elements and manganese elements.

[0006] The negative electrode sheet comprises a negative electrode current collector and a negative electrode mixture layer arranged on the negative electrode current collector, and the negative electrode mixture layer comprises a negative electrode active material.

[0007] The secondary battery satisfies the following relationship: (W Ni ’-W Ni ) / (30+29n-n 2 )≤7, (W Mn ’-W Mn) / (n 2 + 4n + 3) ≤ 35, n = N / 500; wherein,

[0008] W Ni is the content value of Ni element in the negative electrode mixture layer, in ppm, based on the weight of the negative electrode mixture layer, tested by ICP - OES;

[0009] W Ni ’ is the content value of Ni element in the negative electrode mixture layer, in ppm, based on the weight of the negative electrode mixture layer, after the secondary battery has undergone N cycles of 1C charge - discharge, tested by ICP - OES;

[0010] in ppm;

[0011] W Mn is the content value of Mn element in the negative electrode mixture layer, in ppm, based on the weight of the negative electrode mixture layer, tested by ICP - OES;

[0012] W Mn ’ is the content value of Mn element in the negative electrode mixture layer, in ppm, based on the weight of the negative electrode mixture layer, after the secondary battery has undergone N cycles of 1C charge - discharge, tested by ICP - OES;

[0013] N is an integer greater than 0.

[0014] Specifically, in some embodiments of the present application, the parameters of the secondary battery satisfy the following relationships: 3 < W Ni < 150, 3 < W Ni ’ < 2000, 2 < W Mn < 50, 2 < W Mn ’ < 1800.

[0015] In some embodiments of the present application, the positive electrode active material contains a chemical compound as shown in Li x Ni y Co z Mn k Me p O r A m where 0.95 ≤ x ≤ 1.07, 0.50 ≤ y ≤ 0.96, 0 ≤ z ≤ 0.2, 0 < k ≤ 0.4, 0 ≤ p ≤ 0.05, 1 ≤ r ≤ 2, 0 ≤ m ≤ 2, m + r ≤ 2; the Me element contains one or more of Al, Zr, Zn, Cu, Ba, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, B, Mo elements; the A element contains one or more of N, F, S, Cl elements.

[0016] In some embodiments of this application, in the positive electrode active material, 0.70≤y≤0.90, 0≤z≤0.15, 0 <k≤0.2,0≤p≤0.03。

[0017] In some embodiments of this application, the positive electrode active material comprises secondary particles composed of primary particles, and the Dv of the positive electrode active material... 50 5μm-18μm, Dn 10 Its diameter ranges from 0.5μm to 10μm, and its specific surface area (BET) is 0.1m². 2 / g-1.0m 2 / g. Where, Dv 50 Dn is the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material. 10 The particle size is the size corresponding to a cumulative percentage distribution of the positive electrode active material reaching 10%.

[0018] In some embodiments of this application, the positive electrode active material may include secondary particles composed of primary particles, and the Dv of the positive electrode active material... 50 The active Dn of the positive electrode is 5μm-18μm. 10 The range is 0.5μm-10μm. The Dv... 50 This typically refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for a sample; the Dn 10 The particle size is the size corresponding to a cumulative percentage distribution of the positive electrode active material reaching 10%.

[0019] In some embodiments of this application, the Dv of the positive electrode active material 50 It can also be 8-15μm.

[0020] In some embodiments of this application, the Dn of the positive electrode active material 10 It can also be 1.5-4μm.

[0021] In some embodiments of this application, the positive electrode active material described in this application may include single crystal or single crystal-like particles.

[0022] In some embodiments of this application, the surface of the positive electrode active material particles further includes a coating layer, the coating layer including coating elements; the coating elements include one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, Ce, B, and P.

[0023] In some embodiments of this application, the volume content (Mv) of the coating element in the positive electrode active material is 0.4 mg / cm³. 3 -15mg / cm 3 .

[0024] In some embodiments of this application, the volume content (Mv) of the coating element in the positive electrode active material is 0.8 mg / cm³. 3 -10mg / cm 3 .

[0025] In some embodiments of this application, the coating layer includes: an inner coating layer disposed inside the secondary particles in the positive electrode active material and at least covering a portion of the surface of the primary particles.

[0026] In some embodiments of this application, the coating layer includes an outer coating layer disposed on the surface of the positive electrode active material.

[0027] In some embodiments of this application, the coating layer described in this application may include an inner coating layer, which may be located inside the secondary particles and on the surface of at least a portion of the primary particles. The inner coating layer includes a coating element, which may include one or more combinations of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, and Ce.

[0028] In some embodiments of this application, the coating layer includes a continuous and / or discontinuous coating layer.

[0029] In some embodiments of this application, the coating layer includes a continuous first coating layer and a discontinuous second coating layer.

[0030] In some embodiments of this application, the coating layer includes at least two coating elements.

[0031] In some embodiments of this application, the positive electrode active material comprises Li2CO3 and / or LiOH, wherein, based on the weight of the positive electrode active material, the content of Li2CO3 is less than 3000 ppm and the content of LiOH is less than 5000 ppm.

[0032] In some embodiments of this application, the electrolyte contains a lithium salt additive, which comprises one or more of lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium dioxalate borate, lithium bis(trifluoromethanesulfonyl)imide, or lithium bis(fluorosulfonyl)imide, and the content of the lithium salt additive is 0.01%-4% based on the weight of the electrolyte.

[0033] In some embodiments of this application, the secondary battery includes a lithium-ion battery or a sodium-ion battery.

[0034] The secondary battery described in this application features an optimized positive electrode active material with good crystal structure stability and surface inertness. After 1C charge-discharge cycles, the deposition amount of transition metals (Ni, Mn) on the negative electrode is within an appropriate range, effectively suppressing side reactions between the positive electrode active material and the electrolyte, thereby improving gas generation and optimizing cycle performance. Furthermore, by optimizing the electrolyte additives, the positive electrode active material and electrolyte are better matched, further suppressing side reactions between them and further improving the performance of the secondary battery. Detailed Implementation

[0035] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Process equipment or apparatus not specifically specified in the following embodiments are all conventional equipment or apparatus in the art.

[0036] The secondary battery described in this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive electrode flux layer contains a positive electrode active material, which contains nickel and manganese. The negative electrode includes a negative current collector and a negative electrode flux layer disposed on the negative current collector. The negative electrode flux layer contains a negative electrode active material.

[0037] The secondary battery satisfies the following relationship: (W Ni '-W Ni ) / (30+29n-n 2 )≤7,(W Mn '-W Mn ) / (n 2 +4n+3)≤35, n=N / 500; where,

[0038] W Ni For ICP-OES testing, the value of Ni element content in the negative electrode mixture layer is based on the weight of the negative electrode mixture layer, in ppm;

[0039] W Ni After the secondary battery has undergone N 1C charge-discharge cycles, it is tested using ICP-OES to determine the Ni content in the negative electrode mixture layer based on its weight, in ppm.

[0040] W Mn For ICP-OES testing, the content of Mn element in the negative electrode mixture layer is the value in ppm based on the weight of the negative electrode mixture layer.

[0041] W MnAfter the secondary battery has undergone N 1C charge-discharge cycles, ICP-OES testing is performed to determine the content of Mn element in the negative electrode mixture layer based on the weight of the negative electrode mixture layer, in ppm.

[0042] N is an integer greater than 0.

[0043] It should be noted here that, in the following embodiments of the present invention, the W... Ni W Ni '、W Mn and W Mn 'When measuring the numerical value, the test is performed directly on the negative electrode plate. However, when calculating the content value, the weight of the current collector is automatically deducted.'

[0044] In some embodiments of this application, the secondary battery satisfies: (W Ni '-W Ni ) /

[0045] (30+29n-n 2 )≤7,(W Mn '-W Mn ) / (n 2 +4n+3)≤35. The increase in Ni content (W) on the negative electrode plate of the secondary battery described in this application after N cycles of 1C charge-discharge cycle is... Ni '-W Ni The value of ) exceeds 7×(30+29n-n) 2 ) and / or the increase in Mn element quantity (W Mn '-W Mn The value of ) exceeds 35×(n) 2 When the concentration is +4n+3), it indicates that nickel and / or manganese elements in the positive electrode active material particles of the secondary battery are more easily dissolved. At this time, the surface of the positive electrode active material of the secondary battery is prone to side reactions with the electrolyte, resulting in excessive gas production and poor cycle performance. The lower the increase in the amount of transition metals (e.g., Ni, Mn) on the negative electrode after 1C charge-discharge cycles, the stronger the stability of the crystal structure, especially the surface crystal structure, of the positive electrode active material of the secondary battery, and the fewer side reactions between the secondary battery and the electrolyte.

[0046] In some embodiments of this application, (W Ni '-W Ni ) / (30+29n-n 2 )≤6.1. When (W Ni '-W Ni ) / (30+29n-n 2 When the value of ) meets the above range, the crystal structure of the positive electrode active material of the secondary battery, especially the surface crystal structure, is more stable, and there are fewer side reactions between the secondary battery and the electrolyte.

[0047] In some embodiments of this application, (W Ni '-W Ni ) / (30+29n-n 2 )≤5.8. When (W Ni '-W Ni ) / (30+29n-n 2 When the value of ) meets the above range, the crystal structure of the positive electrode active material of the secondary battery is more stable, and the overall performance of the secondary battery is better.

[0048] In some embodiments of this application, (W Mn '-W Mn ) / (n 2 +4n+3)≤30. When (W Ni '-W Ni ) / (30+29n-n 2 When the value of ) meets the above range, the crystal structure of the positive electrode active material of the secondary battery is more stable, and the overall performance of the secondary battery is better.

[0049] In some embodiments of this application, (W Mn '-W Mn ) / (n 2 +4n+3)≤28. When (W Mn '-W Mn ) / (n 2 When the value of (+4n+3) meets the above range, the crystal structure of the positive electrode active material of the secondary battery, especially the surface crystal structure, is more stable, there are fewer side reactions between the positive electrode active material and the electrolyte, and the performance of the secondary battery is better.

[0050] In some embodiments of this application, 3 <W Ni <150. When W Ni Within this range, the structure of the positive electrode active material is more stable.

[0051] In some embodiments of this application, 3 <W Ni <2000. When W Ni Within this range, the positive electrode active material has a more stable crystal structure and fewer side reactions with the electrolyte.

[0052] In some embodiments of this application, 2 <W Mn <50. When W Mn Within this range, the structure of the positive electrode active material is more stable.

[0053] In some embodiments of this application, 2 <W Mn <1800. When W MnWithin this range, the positive electrode active material has a more stable crystal structure, less Mn dissolution, and fewer side reactions with the electrolyte.

[0054] In this application, the Ni and Mn element content (W) in the negative electrode mixture layer of the secondary battery is... Ni W Mn The method for determining the content of Ni and Mn elements in the negative electrode mixture layer of the secondary battery typically includes testing the content of Ni and Mn elements in the negative electrode mixture layer of the secondary battery using inductively coupled plasma-optical emission spectrometers (ICP-OES). In a specific embodiment of this application, the content of Ni and Mn elements in the negative electrode mixture layer of the secondary battery (W) is... Ni W Mn The method for determining the negative electrode layer may specifically include the following steps: discharging the secondary battery at 1C to 2.8V, then disassembling and removing the negative electrode sheet, washing to remove the electrolyte, cutting it into a certain area, dissolving the negative electrode sheet, and testing the amount of transition metals Ni and Mn deposited on the negative electrode layer using an inductively coupled plasma-optical emission spectrometer (ICP-OES).

[0055] In this application, after the secondary battery undergoes N 1C charge-discharge cycles, the Ni and Mn element content (W) in the negative electrode mixture layer is as follows: Ni '、W Mn The method for determining the content of Ni and Mn elements in the negative electrode layer typically includes: after the secondary battery has undergone N 1C charge-discharge cycles, the content of Ni and Mn elements in the negative electrode layer is measured using an inductively coupled plasma-optical emission spectrometer (ICP-OES). In a specific embodiment of this application, the content of Ni and Mn elements in the negative electrode layer after the secondary battery has undergone N 1C charge-discharge cycles is (W... Ni '、W MnThe determination method for the negative electrode layer may specifically include the following steps: The secondary battery is charged at 1C to 4.2-4.45V at 2.8-(4.2-4.45)V, then charged at a constant voltage at 4.2-4.45V until the current is ≤0.05C, left to stand for 10 minutes, then discharged at 1C to 2.8V, left to stand for 10 minutes, and then cycled according to the above charge and discharge regime. After N cycles, the secondary battery is discharged at 1C to 2.8V, then disassembled to remove the negative electrode sheet, washed to remove the electrolyte, cut into a certain area, and the negative electrode sheet is dissolved. The amount of transition metal Ni and Mn deposited on the negative electrode layer is tested by inductively coupled plasma-optical emission spectrometers (ICP-OES). The secondary battery used for testing the Ni and Mn content in the negative electrode mixture layer of the secondary battery, and the secondary battery used for testing the Ni and Mn content in the negative electrode mixture layer after the secondary battery has undergone N 1C charge-discharge cycles, can be obtained by testing different batteries in the same battery module.

[0056] In some embodiments of this application, N ≤ 2000. For example, it can be 100, 200, 400, 500, 700, 900, 1000, 1300, 1500, 1900, or 2000.

[0057] In some embodiments of this application, after the secondary battery undergoes 500 1C charge-discharge cycles, the Ni content in the negative electrode mixture layer is W. Ni1 After the secondary battery undergoes 1000 1C charge-discharge cycles, the Ni content in the negative electrode mixture layer is W. Ni2 ', satisfy W Ni2 '-W Ni1 '≤190. When W Ni2 '-W Ni1 Within the above range, the positive electrode active material has better crystal structure stability and fewer side reactions with the electrolyte, resulting in better overall performance.

[0058] In some embodiments of this application, after the secondary battery undergoes 500 1C charge-discharge cycles, the Mn element content W in the negative electrode mixture layer is... Mn1 After the secondary battery undergoes 1000 1C charge-discharge cycles, the Mn element content W in the negative electrode mixture layer is... Mn2 ', satisfy W Mn2 '-W Mn1 '≤190. When W Mn2 '-W Mn1Within the above range, the crystal structure of the positive electrode active material is relatively stable, with less Mn dissolution and fewer side reactions with the electrolyte, and it has better comprehensive performance.

[0059] Specifically, the positive electrode active material includes a compound as shown in Li x Ni y Co z Mn k Me p O r A m where 0.95 ≤ x ≤ 1.07, 0.50 ≤ y ≤ 0.96, 0 ≤ z ≤ 0.2, 0 < k ≤ 0.4, 0 ≤ p ≤ 0.05, 1 ≤ r ≤ 2, 0 ≤ m ≤ 2, and m + r ≤ 2; Me includes one or more of the elements Al, Zr, Zn, Cu, Ba, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, B, and Mo; A includes one or more of the elements N, F, S, and Cl.

[0060] In some embodiments of the present application, in the positive electrode active material, 0.70 ≤ y ≤ 0.90, 0 ≤ z ≤ 0.15, 0 ≤ k ≤ 0.2, and 0 ≤ p ≤ 0.03.

[0061] When the relative content of nickel element in the ternary material is high and the cut-off voltage of the ternary material is increased, the specific capacity per gram is usually larger, which is beneficial to improving the energy density of the secondary battery. However, it will also bring problems to the overall performance of the secondary battery, such as the collapse of the layered structure of the ternary material, making the insertion and extraction of Li + in the ternary material more and more difficult; the phenomenon of dissolution of transition metals (Ni, Co, Mn) occurs during the cycling process. After the transition metal elements dissolve into the electrolyte, they will migrate to the surface of the negative electrode and damage the SEI film. In particular, the Mn element will seriously damage the SEI film of the negative electrode. In addition, the dissolution of transition metals will also damage the layered structure of the ternary positive electrode material; when the electrolyte contacts the ternary material, the electrolyte will react with the ternary material more, and in order to maintain charge balance, the ternary material will release oxygen, which will damage the crystal structure of the ternary material and exacerbate the gas evolution of the secondary battery. Through a large number of studies in the present application, it is found that by controlling the positive electrode active material, such as changing the morphology of the positive electrode active material, the particle size of the positive electrode active material, the type of doping elements, the content of doping elements, the doping process, the coating method, the coating elements, the coating process, etc., the composition of the positive electrode active material of the secondary battery can be controlled, the performance of the secondary battery can be improved, and the deposition amount of transition metals (Ni, Mn) on the negative electrode mixture layer after the secondary battery is cycled can be within an appropriate range, which can, to a certain extent, isolate the contact between the electrolyte and the positive electrode active material, and then optimize the cycling performance of the secondary battery and improve its gas evolution phenomenon.

[0062] In some embodiments of this application, the positive electrode active material may include secondary particles composed of primary particles, wherein the Dv of the secondary particles is... 50 The secondary particles have a Dn value of 5μm-18μm. 10 The range is 0.5μm-10μm. The Dv... 50 This typically refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for a sample; the Dn 10 The particle size is the size corresponding to a cumulative percentage distribution of the positive electrode active material reaching 10%.

[0063] In some embodiments of this application, Dv 50 The size is 8μm-15μm.

[0064] In some embodiments of this application, Dn 10 The range is 1.5μm-4μm.

[0065] In some embodiments of this application, the particle size of the primary particles ranges from 0.1 μm to 2.0 μm. The particle size of the primary particles can be measured using a scanning electron microscope. For ternary materials with high nickel content, the relative number of small-diameter cathode active material particles significantly affects the residual lithium content and gas generation of the cathode active material. Therefore, controlling the morphology of high-nickel ternary secondary particles and improving the Dv of the ternary material is crucial. 50 、Dn 10 Within a certain range, it is an effective means to improve the gas generation problem of secondary batteries.

[0066] When the positive electrode active material comprises secondary particles composed of primary particles, the specific surface area (BET) of the positive electrode active material is 0.1 m². 2 / g-1.0m 2 / g. In some embodiments of this application, when the positive electrode active material comprises secondary particles composed of primary particles, the specific surface area (BET) of the positive electrode active material is 0.3m². 2 / g-0.7m 2 / g. A suitable specific surface area of ​​the positive electrode active material can, on the one hand, reduce the contact area between the electrolyte and the positive electrode active material, which helps to suppress side reactions and avoid electrolyte corrosion and damage to the crystal structure of the positive electrode active material, thus aggravating the problem of gas expansion in the secondary battery. On the other hand, it can also help to use less auxiliary materials when mixing to form the positive electrode slurry. The positive electrode active material has relatively strong adsorption performance with binders and conductive agents, which is beneficial to improving the energy density of the secondary battery.

[0067] In some embodiments of this application, the positive electrode active material may include single-crystal or single-crystal-like particles. When the positive electrode active material contains single-crystal or single-crystal-like particles, the particle size Dv of the positive electrode active material is... 50The particle size can be 1μm-6μm; the particle size Dn of the positive electrode active material 10 It can be 0.4μm-3μm. In some embodiments, Dv 50 It can be 3μm-5μm, Dn 10 The particle size can range from 0.5 μm to 2 μm. The single-crystal or near-single-crystal particles typically refer to positive electrode active materials composed of a single, complete particle or an agglomeration of fewer than ten particles. When the positive electrode active material comprises single-crystal or near-single-crystal particles, the surface area (BET) of the positive electrode active material can be 0.5 m². 2 / g-2.0m 2 / g. In this application, when the positive electrode active material includes single-crystal or near-single-crystal structures with the above-mentioned particle size and BET within the above-mentioned range, the surface and internal crystal structure of the positive electrode active material is more complete, and the contact area with the electrolyte is smaller, which is beneficial to improving the problem of dissolution of transition metals nickel, cobalt, and manganese on the particle surface.

[0068] In some embodiments of this application, the positive electrode active material further includes a coating layer containing coating elements; the coating elements include one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, Ce, B, and P.

[0069] In some embodiments of this application, the volume content (Mv) of the coating element in the positive electrode active material is 0.4 mg / cm³. 3 -15mg / cm 3 In some embodiments of this application, the volume content (Mv) of the coating element in the positive electrode active material is 0.8 mg / cm³. 3 -10mg / cm 3 The appropriate content of coating elements can usually ensure that the surface modification and polarization of the positive electrode active material are compatible in systems with different volume particle size distributions, effectively improving the gas generation problem of high-capacity lithium-ion batteries and optimizing cycle and rate performance.

[0070] In the coating layer, the coating element is usually present in the form of an oxide. For example, the coating layer may include one or more of the oxides of the above-mentioned coating elements, or lithium-containing oxides including the above-mentioned coating elements and lithium. Specifically, it may include, but is not limited to, aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide, boron oxide, cerium oxide, and one or more of lithium aluminum oxide, lithium zirconium oxide, lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, lithium boron oxide, or lithium cerium oxide.

[0071] In some embodiments of this application, the coating layer includes an outer coating layer disposed on the surface of the positive electrode active material.

[0072] In the secondary battery provided in this application, the positive electrode active material comprises secondary particles, and the coating layer may include an inner coating layer. The inner coating layer may be located inside the positive electrode active material particles and may be located on the surface of at least a portion of the primary particles. The inner coating layer includes a coating element, which may include one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, and Ce. Since the positive electrode active material comprises secondary particles composed of primary particles, at least a portion of the coating layer may be located between the primary particles within the secondary particles, that is, on the surface of at least a portion of the primary particles within the secondary particles. This portion of the coating layer can be considered the inner coating layer. The inner coating layer may include oxides of the coating elements; that is, at least a portion of the coating elements in the inner coating layer may exist in the form of their oxides or in the form of lithium-containing oxides. Specifically, it may include, but is not limited to, one or more combinations of aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide, boron oxide, or cerium oxide, as well as lithium aluminum oxide, lithium zirconium oxide, lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, lithium boron oxide, or lithium cerium oxide. Since secondary particles are formed by the close packing of several primary particles, during cycling, the secondary particles undergo volume expansion and contraction, leading to an increase in the spacing between the primary particles within the secondary particles and exposing a large amount of uncoated fresh surface. Therefore, there is a risk of side reactions with the electrolyte. In this application, while a coating layer is provided on the surface of the secondary particles, at least a portion of the primary particles inside are further coated on the surface or at the grain boundaries between adjacent primary particles. This can enhance the internal density of the secondary particles, increase the interaction force between the internal primary particles, and further optimize the gas generation problem during the lithium-ion battery cycle.

[0073] In the lithium-ion secondary battery provided in this application, the coating layer may include an outer coating layer, which is typically located on the surface of the secondary particles. The outer coating layer includes coating elements, which may include one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, and Ce. In the secondary battery, the positive electrode active material comprises secondary particles composed of primary particles, and at least a portion of the coating layer may be located on the surface of the secondary particles. The coating elements in the oxide coating layer may be distributed on the surface of the secondary particles. The outer coating layer may include oxides of coating elements, meaning that at least a portion of the coating elements in the outer coating layer may exist in their oxide form or in the form of lithium-containing oxides. Specifically, it may include, but is not limited to, one or more combinations of aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide, boron oxide, cerium oxide, and lithium aluminum oxide, lithium zirconium oxide, lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, lithium boron oxide, or lithium cerium oxide. In the lithium-ion secondary battery, the outer coating layer mainly reduces the contact area between the substrate and the electrolyte. The presence of the outer coating layer can effectively modify the surface of the high-nickel cathode material, reduce the side reactions between the cathode material and the electrolyte, and thus effectively suppress the gas generation phenomenon of the battery. In the secondary battery provided in this application, the coating layer may contain at least two or more of the aforementioned coating elements, and more specifically, may contain oxides formed by at least two or more of the aforementioned coating elements, thereby improving the stability of the coating layer's adhesion to the substrate surface, enabling the coating layer to possess both ion-conducting and electronic-conducting properties, and reducing the impact of the coating layer on the polarization problem of the positive electrode material.

[0074] Specifically, the coating layer includes continuous and / or discontinuous coating layers.

[0075] In some embodiments of this application, the coating layer includes a continuous first coating layer and a discontinuous second coating layer.

[0076] In some embodiments of this application, the coating layer contains element B.

[0077] In some embodiments of this application, the inner covering layer and the outer covering layer comprise different covering elements.

[0078] In the lithium-ion secondary battery provided in this application, the outer coating layer may include a continuous and / or discontinuous coating layer. A continuous coating layer can form a more complete protection for the substrate surface, which is beneficial for stabilizing the surface structure of the positive electrode active material, suppressing the dissolution of transition metals nickel, cobalt, and manganese in the positive electrode material, and suppressing side reactions in the electrolyte; however, a continuous coating layer needs to have good electronic and ion conductivity to avoid increasing the impedance of the electrode and affecting the kinetic performance of the secondary battery. The advantage of a discontinuous coating layer is that it reduces the proportion of the coating layer on the substrate surface and retains more ion transport channels, but the improvement effect on the structural stability of the substrate surface is slightly worse than that of a continuous coating layer.

[0079] In a preferred embodiment of this application, the outer coating layer may include a continuous first coating layer and a discontinuous second coating layer, which may be a composite of the two forms. The second coating layer may be located on the surface of the first coating layer or between the first coating layer and the substrate. In a preferred embodiment of this application, the area of ​​the discontinuous second coating layer in a single unit is typically smaller than the area of ​​the first coating layer in a single unit. In another preferred embodiment of this application, the second coating layer and the first coating layer may include different coating elements, such that the coating material of the discontinuous coating layer is at least partially different from the coating material of the continuous coating layer.

[0080] In the coating scheme described in this invention, elements with low melting points, such as boron oxide, have relatively low viscosity and can be uniformly coated on the material surface even in small amounts, forming a continuous coating structure. Other oxide coatings, due to their properties, can form point-to-point coatings, thus forming a discontinuous coating layer.

[0081] In some embodiments of this application, the content of the coating element in the outer coating layer can account for more than 60 wt%, 70 wt%, 80 wt%, or 90 wt% of the total coating element mass in the positive electrode active material. In some embodiments of this application, the content of the coating element in the outer coating layer can account for 80 wt%-98 wt% of the total coating element mass in the positive electrode active material. Since the surface of secondary particles preferentially contacts the electrolyte and has a larger relative area, the coating element is mainly distributed on the surface of the secondary particles. When the mass distributed on the surface of the secondary particles accounts for a certain proportion or more of the total coating element mass in the positive electrode active material, the surface modification of the high-nickel positive electrode active material is more significant, and the gas generation suppression effect of the lithium-ion battery is also better.

[0082] In some embodiments of this application, specifically, in the lithium-ion secondary battery, the content of Li2CO3 on the surface of the positive electrode active material is less than 3000ppm, and the content of LiOH is less than 5000ppm.

[0083] In the lithium-ion secondary battery provided in this application, the method for measuring the residual lithium on the surface of the positive electrode active material can refer to GB / T 9736-2008 General Rules for Potentiometric Titration of Chemical Reagents. The content of Li2CO3 in the residual lithium on the surface of the positive electrode active material (i.e., the mass of Li2CO3 in the residual lithium on the surface of the positive electrode active material relative to the total mass of the positive electrode active material) is less than 3000 ppm. In some embodiments of this application, the content of Li2CO3 in the residual lithium on the surface of the positive electrode active material is less than 2000 ppm. The content of LiOH in the residual lithium on the surface of the positive electrode active material (i.e., the mass of LiOH in the residual lithium on the surface of the positive electrode active material relative to the total mass of the positive electrode active material) is less than 5000 ppm. In some embodiments of this application, the content of LiOH in the residual lithium on the surface of the positive electrode active material is less than 4000 ppm. In the actual production process of ternary materials, the lithium salt used as raw material may be impure or have a low melting point, which may lead to melting, decomposition, and volatilization losses at lower temperatures. Therefore, excess lithium salt is added during the preparation of ternary materials to compensate for lithium losses caused during sintering. Active oxygen anions exist on the surface of ternary materials, which react with CO2 and H2O in the air to form carbonate ions. Simultaneously, lithium ions migrate from the bulk to the surface and form Li2CO3 on the ternary material surface. This process is accompanied by deoxidation of the ternary material surface, forming a surface oxide layer with a distorted structure. Furthermore, excess lithium salt reacts with CO2 and H2O in the air again after high-temperature calcination to generate LiOH and Li2CO3, which remain on the ternary material surface, resulting in a higher pH value. During charge and discharge, the Li2CO3 remaining on the ternary material surface decomposes to produce CO2, causing the lithium-ion battery to swell and affecting the storage performance of the secondary battery. Applying a coating layer to the surface of the positive electrode active material can reduce the content of residual lithium (e.g., LiOH, Li₂CO₃) on the surface of the positive electrode active material to a certain extent, thereby improving the storage performance of lithium-ion batteries. Furthermore, applying a coating layer to the surface of the positive electrode active material can reduce the probability of side reactions occurring due to direct contact between the positive electrode active material and the electrolyte, thus reducing the amount of oxygen released by the positive electrode active material during charging and discharging to balance the charge and the resulting risk of crystal structure collapse. On the surface of the positive electrode active material, residual lithium (LiOH, Li₂O) readily reacts with moisture and CO₂ in the air, producing products such as Li₂CO₃.

[0084] This application also provides a method for preparing the positive electrode active material of the secondary battery.

[0085] The method for preparing the positive electrode active material provided in this application may include: mixing and sintering the raw materials for the positive electrode active material. Those skilled in the art can select appropriate raw materials and ratios based on the elemental composition of the positive electrode active material. For example, the raw materials may include a ternary material precursor of nickel, cobalt, manganese, and / or aluminum, a lithium source, a M source, a Me source, an A source, etc., and the ratio between each raw material is usually determined with reference to the ratio of each element in the positive electrode active material. More specifically, the ternary material precursor may be, but is not limited to, Ni. 1 / 3 Co 1 / 3 Mn 1 / 3 (OH)2, Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.5 Co 0.25 Mn 0.25 (OH)2, Ni 0.55 Co 0.15 Mn 0.3 (OH)2, Ni 0.55 Co 0.1 Mn 0.35 (OH)2, Ni 0.55 Co 0.05 Mn 0.4 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.65 Co 0.15 Mn 0.2 (OH)2, Ni 0.65 Co 0.12 Mn 0.23 (OH)2, Ni 0.65 Co 0.1 Mn 0.25 (OH)2, Ni 0.65 Co 0.05 Mn 0.3 (OH)2, Ni 0.75 Co 0.1 Mn 0.15 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.88 Co 0.05 Mn 0.07 (OH)2, 0.9Ni 0.8 Mn 0.2 (OH)₂·0.1Al₂(OH)₃、0.9Ni 0.9 Mn 0.1(OH)2·0.1Al2(OH)3、

[0086] 0.9Ni 0.9 Co 0.05 Mn 0.05 The lithium source in the (OH)2·0.1Al2(OH)3 solution can be a lithium-containing compound, which may include, but is not limited to, LiOH·H2O, LiOH, Li2CO3, and Li2O. The Me source is typically a compound containing the element Me, which may be one or more oxides, nitrates, or carbonates containing at least one of the elements Al, Zr, Zn, Cu, Ba, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, B, and Mo. The A source can be a compound containing the element A, which may be a salt containing the element A, specifically including, but not limited to, LiF, NaCl, and NaBr. For example, the sintering conditions may be 600℃-950℃ and an oxygen concentration ≥20%. The particle morphology of the positive electrode active material can be adjusted by selecting different ternary material precursors and modifying the synthesis process. For example, the particle size can be controlled during the preparation of the ternary material precursor by controlling the reaction time, pH value during co-precipitation, and ammonia concentration.

[0087] The method for preparing the positive electrode active material provided in this application includes forming a coating layer on the surface of the positive electrode active material. This method may involve sintering the positive electrode active material particles in the presence of a compound containing a coating element to form a coating layer on the surface of the positive electrode active material particles. Those skilled in the art can select appropriate types and ratios of the compounds containing coating elements and adjust the composition of the coating layer to ensure that the increase in the amount of transition metals (Ni, Mn) in the negative electrode sheet of the lithium-ion secondary battery is within a suitable range after 1C charge-discharge cycles. For example, the compound containing the coating element may be an oxide of these coating elements, specifically including but not limited to one or more combinations of Al2O3, ZrO2, Ba(NO3)2, ZnO, SnO2, SiO2, TiO2, Co2O3, WO3, Y2O3, H3BO3, P2O5, CeO2, etc. The amount of the coating element used may be 0.01wt%-0.5wt% of the mass of the positive electrode active material. The sintering conditions may be high-temperature sintering at 200℃-900℃.

[0088] In the secondary battery provided in this application, the negative electrode sheet includes a negative current collector and a negative electrode mixture layer disposed on the negative current collector, wherein the negative electrode mixture layer contains a negative electrode active material; the negative electrode active material includes one or a mixture of several of graphite, soft carbon, hard carbon, silicon-based materials or tin-based materials.

[0089] In the secondary battery provided in this application, the preparation process of the negative electrode active material is a conventional operation in the field, and can be selected and processed according to the traditional battery solutions in the field.

[0090] The inventors of this application discovered that the positive electrode active material of the lithium-ion secondary battery prepared using the scheme described in this application has good crystal structure stability and surface inertness. After 1C charge-discharge cycles, the amount of transition metals (Ni, Mn) on the negative electrode sheet of the secondary battery increases relatively little, effectively suppressing the side reactions between the positive electrode active material and the electrolyte and the dissolution of transition metals (Ni, Co, Mn) in the positive electrode active material, thereby improving the high-temperature cycling performance of the lithium-ion battery and suppressing the high-temperature gas generation performance of the secondary battery.

[0091] In the secondary battery provided in this application, the positive electrode active material layer further includes a binder and conductive carbon. The types of conductive carbon, the binder, and the positive electrode current collector are not specifically limited and can be selected according to actual needs. For example, the current collector can be aluminum foil, carbon-coated aluminum foil, nickel mesh, etc. The negative electrode binder layer further includes a binder, a dispersant, and conductive carbon. The types of conductive carbon, the binder, the dispersant, and the negative electrode current collector are not specifically limited and can be selected according to actual needs. The type of separator is not specifically limited and can be selected according to actual needs. For example, the separator can be polyethylene film, polypropylene film, polyvinylidene fluoride film, non-woven fabric, etc.; simultaneously, the separator can have different coating layers. For example, alumina coating, boehmite coating, PVDF coating, etc.

[0092] In some embodiments of this application, the electrolyte comprises a lithium salt and a solvent. The lithium salt comprises LiPF6. The concentration of the lithium salt can be between 0.8 mol / L and 1.5 mol / L.

[0093] In some embodiments of this application, the solvent includes, but is not limited to, ethylene carbonate, propylene carbonate, butene carbonate, pentene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, etc., or one or more combinations of their halogenated derivatives.

[0094] In some embodiments of this application, the electrolyte includes a lithium salt additive, which comprises one or more of lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium bis(fluorosulfonyl)imide (LiFSI). The content of the lithium salt additive is 0.01%-4% based on the weight of the electrolyte. The secondary battery of this application uses the above-mentioned positive electrode active material, and simultaneously matches it with an appropriate content of lithium salt additive. The synergistic effect of the two further reduces the contact between the electrolyte and the positive electrode active material, improves the cycle performance of the secondary battery, and mitigates its gas generation phenomenon.

[0095] In some embodiments of this application, the secondary battery has a casing, the material of which includes, but is not limited to, aluminum-plastic film, aluminum plate, and tin plate.

[0096] The secondary battery of this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0097] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, drones, robotic vacuum cleaners, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric trains, energy storage systems, etc.

[0098] Example 1

[0099] The specific preparation process of the positive electrode active material described in this embodiment includes the following steps.

[0100] Preparation of precursors

[0101] Nickel sulfate, manganese sulfate, and cobalt sulfate were prepared into a 1 mol / L solution with a Ni:Co:Mn molar ratio of 8:1:1. A precursor of lithium-nickel transition metal oxide A with a relatively large particle size, Ni, was then prepared using a hydroxide co-precipitation technique. 0.8 Co 0.1 Mn 0.1 (OH)2. During the preparation of the precursor, the reaction time is 75-125 h, the pH value during coprecipitation is 7.5-8.5, and the ammonia concentration is 1 mol / L.

[0102] Method for preparing a positive electrode active material

[0103] The above ternary material precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)₂ and LiOH·H₂O are mixed in a mixing device, then sintered in an atmosphere furnace at 800℃. After cooling, the mixture is mechanically ground to obtain the matrix of the positive electrode active material. The positive electrode active material matrix is ​​then mixed with alumina additive at a coating element content of 3.5 mg / cm³. 3 The materials are mixed in a mixing equipment and then sintered in an atmosphere furnace at 450°C to form a coating layer, which is the finished positive electrode active material.

[0104] The prepared positive electrode active material was further used to prepare a battery, as described above. The prepared battery was subjected to performance testing, and the specific parameters are shown in Table 1, while the test results are shown in Table 2.

[0105] Preparation of a positive electrode sheet

[0106] The above-mentioned high-nickel positive electrode active material, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed at a mass ratio of 96:3:1, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry; the positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 16 μm.

[0107] The coated electrode sheets are dried in an oven at 100℃-130℃, cold-pressed, and slit to obtain the positive electrode sheets.

[0108] Preparation of a negative electrode sheet

[0109] Graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black were mixed in a mass ratio of 95.7:0.8:2.5:1, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil with a thickness of 8 μm. The coated electrode was dried in an oven at 70℃-100℃, cold-pressed, and slit to obtain the negative electrode sheet.

[0110] Preparation of an electrolyte

[0111] The electrolyte organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and the lithium salt is LiPF6.

[0112] Preparation of a separator

[0113] A 12μm thick polypropylene separator membrane was selected and coated with a 4μm coating layer.

[0114] Method for preparing a lithium ion battery

[0115] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 85°C to remove water, injected with the appropriate non-aqueous electrolyte, and sealed. After processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, a lithium-ion battery is obtained.

[0116] Example 2

[0117] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is zirconium oxide, and the content of the coating element is controlled at 4.6 mg / cm³. 3 .

[0118] Example 3

[0119] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is titanium oxide, and the content of the coating element is 4.3 mg / cm³. 3 .

[0120] Example 4

[0121] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, the only difference being that the coating additive is tungsten oxide, and the content of the coating element is 5.1 mg / cm³. 3 .

[0122] Example 5

[0123] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and boron oxide, and the content of the coating elements is 4.0 mg / cm³. 3 The aluminum coating content was 2.9 mg / cm³. 3 The boron coating amount was 1.1 mg / cm³. 3 .

[0124] In this embodiment, boron oxide has a low melting point (450°C) and good wettability of molten B2O3 to active materials, and has relatively low viscosity. Even a small amount can be uniformly coated on the material surface to form a continuous coating layer structure, while aluminum oxide forms a discontinuous coating layer.

[0125] Example 6

[0126] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are titanium oxide and boron oxide, and the content of the coating elements is 3.8 mg / cm³. 3 The titanium coating content is 2.7 mg / cm³. 3 The boron coating amount was 1.1 mg / cm³. 3 .

[0127] In this embodiment, boron oxide has a low melting point (450°C) and good wettability of molten B2O3 to the active material, and has relatively low viscosity. Even a small amount can be uniformly coated on the material surface to form a continuous coating layer structure, while titanium oxide forms a discontinuous coating layer.

[0128] Example 7

[0129] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and titanium oxide, and the content of the coating elements is 3.9 mg / cm³. 3 The aluminum coating content was 2.0 mg / cm³. 3 The titanium coating amount is 1.9 mg / cm³. 3 .

[0130] In this embodiment, both titanium dioxide and aluminum oxide coatings can form point-to-point coatings due to their properties, thereby forming a discontinuous coating layer.

[0131] Example 8

[0132] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and tungsten oxide, and the content of the coating elements is 4.3 mg / cm³. 3 The aluminum coating content was 1.7 mg / cm³. 3 The tungsten coating content is 2.6 mg / cm³. 3 .

[0133] In this embodiment, alumina and tungsten oxide form a discontinuous coating layer.

[0134] Example 9

[0135] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is boron oxide, and the content of the coating element is 0.4 mg / cm³. 3 .

[0136] Example 10

[0137] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, the only difference being that the coating additive is boron oxide, and the content of the coating element is 15 mg / cm³. 3 .

[0138] Example 11

[0139] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is boron oxide, and the content of the coating element is 0.35 mg / cm³. 3 .

[0140] Example 12

[0141] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is boron oxide, and the content of the coating element is 15.3 mg / cm³. 3 .

[0142] Example 13

[0143] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 9. The preparation method of the positive electrode active material and the lithium-ion battery is the same, the only difference being that the content of the coating element is 4.7 mg / cm³. 3 .

[0144] Example 14

[0145] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the sintering temperature of the precursor and LiOH is 900℃, and the resulting positive electrode material is a single crystal particle; the coating additives are aluminum oxide and boron oxide, and the content of the coating elements is 4.2 mg / cm³. 3 The aluminum coating amount was 3 mg / cm³. 3 The boron coating amount was 1.2 mg / cm³. 3 .

[0146] In this embodiment, boron oxide forms a continuous coating layer structure, while aluminum oxide forms a discontinuous coating layer.

[0147] Example 15

[0148] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 1. The positive electrode active material and the preparation method of the lithium-ion battery are the same, the only difference being that the precursor Ni... 0.7 Co 0.1 Mn 0.3The precursor (OH)₂ was sintered with LiOH at 900℃ to obtain a single-crystal cathode material; the coating additive was alumina, with a coating element content of 3.5 mg / cm³. 3 .

[0149] Example 16

[0150] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 15. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additive is titanium oxide, and the content of the coating element is 4.3 mg / cm³. 3 .

[0151] Example 17

[0152] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 15. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and titanium oxide, and the content of the coating elements is 3.8 mg / cm³. 3 The aluminum coating content was 1.9 mg / cm³. 3 The titanium coating amount is 1.9 mg / cm³. 3 .

[0153] In this embodiment, both titanium dioxide and aluminum oxide coatings can form point-to-point coatings due to their properties, thereby forming a discontinuous coating layer.

[0154] Example 18

[0155] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 15. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and tungsten oxide, and the content of the coating elements is 4.3 mg / cm³. 3 The aluminum coating content was 1.7 mg / cm³. 3 The tungsten coating content is 2.6 mg / cm³. 3 .

[0156] In this embodiment, both alumina and tungsten oxide coatings can form point-to-point coatings due to their properties, thus creating a discontinuous coating layer.

[0157] Example 19

[0158] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 15. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are aluminum oxide and boron oxide, and the content of the coating elements is 4.0 mg / cm³. 3 The aluminum coating content was 2.9 mg / cm³. 3 The boron coating amount was 1.1 mg / cm³. 3 .

[0159] In this embodiment, boron oxide forms a continuous coating layer structure, while aluminum oxide forms a discontinuous coating layer.

[0160] Example 20

[0161] The lithium-ion battery solution described in this embodiment is the same as that in Embodiment 15. The preparation method of the positive electrode active material and the lithium-ion battery is the same, except that the coating additives are titanium oxide and boron oxide, and the content of the coating elements is 3.8 mg / cm³. 3 The titanium coating content is 2.7 mg / cm³. 3 The boron coating amount was 1.1 mg / cm³. 3 .

[0162] In this embodiment, boron oxide forms a continuous coating layer structure, while titanium oxide forms a discontinuous coating layer.

[0163] Examples 21-25

[0164] The lithium-ion battery solution described in this embodiment is the same as that in embodiment 7, except that the electrolyte contains lithium salt additives. The types and contents of lithium salt additives are shown in Table 3, and the test results are shown in Table 3.

[0165] Comparative Example 1

[0166] The lithium-ion battery scheme described in this comparative example is the same as that in Example 1. The positive electrode active material and the preparation method of the lithium-ion battery are the same, except that no corresponding coating treatment is performed.

[0167] Comparative Example 2

[0168] The lithium-ion battery scheme described in this comparative example is the same as that in Example 13. The positive electrode active material and the preparation method of the lithium-ion battery are the same, except that no corresponding coating treatment is performed.

[0169] Experimental Example

[0170] 1. Lithium-ion battery parameter testing

[0171] The performance of the lithium-ion batteries in the above embodiments and comparative schemes was tested respectively (the characteristics of each parameter are shown in Tables 1 and 3), and the results are recorded in Tables 2-3 below.

[0172] (1) Test method of Ni, Mn element content (W Ni , W Mn ) on lithium ion battery negative electrode sheet

[0173] The lithium-ion battery was discharged to 2.8V at 1C, and then the negative electrode was removed. After washing to remove the electrolyte, it was cut into small circular pieces with a radius of 0.6mm. The negative electrode was then decomposed, and the amount of Ni and Mn transition metals deposited on the negative electrode was tested by inductively coupled plasma-optical emission spectrometers (ICP-OES).

[0174] (2) The content of Ni and Mn elements (W%) on the negative electrode sheet of the lithium ion battery after 1C charge-discharge cycle Ni ’、W Mn ) measurement Test method

[0175] The lithium-ion battery was charged at 1C to 4.2V or 4.4V at 2.8-4.2V (Examples 1-14, Examples 21-25, Comparative Example 1) or 2.8-4.4V (Examples 15-20, Comparative Example 2), then charged at constant voltage at 4.2V or 4.4V until the current ≤0.05C, left to stand for 10 minutes, then discharged at 1C to a voltage of 2.8V, left to stand for 10 minutes, and then charged and discharged again according to the above charge and discharge cycle.

[0176] After a certain number of cycles, the lithium-ion battery was discharged to 2.8V at 1C. Then, the negative electrode was disassembled and the electrolyte was removed. The electrode was then washed to remove the electrolyte and cut into small circular pieces with a radius of 0.6mm. The negative electrode was then decomposed, and the amount of Ni and Mn transition metals deposited on the negative electrode was measured using inductively coupled plasma-optical emission spectrometers (ICP-OES).

[0177] (3) 25 °c cycle performance test of lithium ion battery

[0178] Under a constant temperature environment of 25℃, at 2.8-4.2V (Examples 1-14, Examples 21-25, Comparative Example 1) or 2.8-4.4V (Examples 15-20, Comparative Examples 3-4), the battery was charged at 1C to 4.2V or 4.4V, then charged at a constant voltage of 4.2V or 4.4V until the current ≤0.05C, allowed to stand for 10 minutes, and then discharged at 1C to a voltage of 2.8V, allowed to stand for 10 minutes. The capacity was recorded as Dn (n=0, 1, 2…). The above process was repeated until the capacity decayed to 80% of the initial capacity, and the number of cycles of the lithium-ion battery was recorded. The test results of each example and each comparative example are shown in Table 2.

[0179] (4) Discharge capacity test of lithium ion battery

[0180] Under a constant temperature environment of 25℃, the lithium-ion battery was charged at 1 / 3C to 4.2V or 4.4V at 2.8-4.2V (Examples 1-14, Examples 21-25, Comparative Example 1) or 2.8-4.4V (Examples 15-20, Comparative Example 2). Then, it was charged at a constant voltage of 4.2V or 4.4V until the current was ≤0.05C. After standing for 5 minutes, it was discharged at 1 / 3C to 2.8V. The specific results of the capacity of the lithium-ion battery are shown in Table 2.

[0181] (5) High temperature gas production test of lithium ion battery

[0182] The batteries were charged at 1C to 4.2V (Examples 1-14, Examples 21-25, Comparative Example 1) or 4.4V (Examples 15-20, Comparative Example 2), and then charged at a constant voltage of 4.2V or 4.4V until the current ≤0.05C. They were then placed in an 80℃ constant temperature chamber for 10 days. The initial volume and the volume after 10 days of standing were measured by the water displacement method to obtain the volume expansion rate of the lithium-ion battery. The volume expansion rate (%) of the lithium-ion battery = (volume after 10 days of standing / initial volume - 1) × 100%.

[0183] Table 1. Parameters of lithium-ion batteries for each scheme

[0184]

[0185]

[0186] Table 2. Test results of lithium-ion batteries in Examples 1-20 and Comparative Examples 1-2

[0187]

[0188]

[0189] Table 3. Parameters and test results of lithium-ion batteries in Examples 21-25

[0190]

[0191] Combining the data in Tables 1 and 2, it can be seen that in Comparative Examples 1-2, the high-nickel ternary cathode active material, due to the lack of coating material, results in the following increase in the amount of transition metal on the negative electrode after 1C charge-discharge cycles in lithium-ion batteries using this high-nickel ternary cathode active material: (W Ni '-W Ni )>7×(30+29n-n 2 ) and / or (W Mn '-W Mn )>35×(n 2+4n+3) indicates that Ni and / or Mn elements in the positive electrode active material powder particles are more easily dissolved, and the surface of the powder particles is prone to side reactions with the electrolyte, resulting in excessive gas production in lithium-ion batteries, rapid capacity decay during cycling, and reduced cycle calendar life.

[0192] In Examples 1-20, by adjusting the combined effects of factors such as the coating material of the positive electrode active material, the relative content of the coating layer, and the surface morphology of the particles, the increase in the amount of transition metals (Ni, Mn) on the negative electrode sheet after a 1C charge-discharge cycle of the lithium-ion battery is controlled to satisfy: (W Ni '-W Ni ) / )

[0193] 30+29n-n 2 )≤7, and (W Mn '-W Mn ) / (n 2 +4n+3)≤35. Because the increase in the amount of transition metals (Ni, Mn) on the negative electrode sheet of a lithium-ion battery is relatively low after a 1C charge-discharge cycle, the crystal structure, especially the surface crystal structure, of the positive electrode active material of the lithium-ion battery is more stable. Therefore, the specific capacity of the positive electrode active material measured by discharge is higher, and the cycle and high-temperature volume expansion rate is effectively suppressed. When the coating layer contains at least two or more of the above-mentioned coating elements, the stability of the coating layer on the substrate surface can be improved, so that the coating layer has both ion conduction and electronic conduction properties, reducing the influence of the coating layer on the polarization problem of the positive electrode active material. When the outer coating layer is discontinuous during the coating process of the positive electrode active material, the proportion of the coating layer on the substrate surface can be reduced, and more ion transport channels can be retained. However, the improvement effect on the structural stability of the substrate surface is slightly worse than that of the continuous coating layer. If a double-layer coating is used, high ion conduction performance can be achieved while effectively coating, avoiding excessive dissolution of nickel and manganese elements in the positive electrode active material during long-term cycling, which would deteriorate the performance of the lithium-ion battery.

[0194] As can be seen from Table 3, further optimization of the electrolyte composition in secondary batteries can improve the compatibility between the positive electrode active material and the electrolyte, thereby further enhancing the overall performance of lithium-ion batteries.

[0195] In summary, this application effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0196] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, characterized by, The positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer including a positive electrode active material, the positive electrode active material including a nickel element and a manganese element; The negative electrode sheet includes a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector, the negative electrode mixture layer including a negative electrode active material; The secondary battery satisfies the following relationships: (W Ni ’-W Ni ) / (30+29n-n 2 )≤7, (W Mn ’-W Mn ) / (n 2 +4n+3)≤35, n=N / 500; wherein, W Ni For the ICP-OES test, the content value of the Ni element in the negative electrode active material layer, in ppm, based on the weight of the negative electrode active material layer; W Ni N is the number of cycles of 1C charge-discharge cycles; and Ni is the content of Ni element in the negative electrode active material layer after the secondary battery has undergone 1C charge-discharge cycles N cycles, tested by ICP-OES, based on the weight of the negative electrode active material layer, in units of ppm. W Mn For the ICP-OES test, the content value of the Mn element in the negative electrode active material layer is in ppm based on the weight of the negative electrode active material layer. W Mn Mn is the content value of the Mn element in the negative electrode mixture layer after the secondary battery has undergone 1C charge-discharge cycling for N cycles, tested by ICP-OES, based on the weight of the negative electrode mixture layer, in ppm; N is an integer greater than 0; The parameters of the secondary battery satisfy the following relationships: 3 < W Ni <150, 3 < W Ni <2000, 2 < W Mn <50, 2 < W Mn <1800.

2. The secondary battery according to claim 1, wherein The positive electrode active material comprises Li x Ni y Co z Mn k Me p O r A m The compound represented by the formula (1), wherein 0.95≤x≤1.07, 0.50≤y≤0.96, 0≤z≤0.2, 0 The Me element includes one or more of Al, Zr, Zn, Cu, Ba, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, B, Mo elements; The A element includes one or more of N, F, S, Cl.

3. The secondary battery according to claim 1, characterized by The positive electrode active material includes secondary particles composed of primary particles, the Dv 50 is 5 μm to 18 μm, the Dn 10 is 0.5 μm to 10 μm, the specific surface area BET is 0.1 m 2 / g to 1.0 m 2 / g.

4. The secondary battery according to claim 1, wherein The particle surface of the positive electrode active material includes a coating layer, the coating layer including a coating element; The coating element includes one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, Ce, B, P elements.

5. The secondary battery according to claim 4, wherein The positive electrode active material has a unit volume content Mv of the coating element of 0.4 mg / cm 3 - 15 mg / cm 3 .

6. The secondary battery according to claim 5, characterized by The positive electrode active material has a unit volume content Mv of the coating element of 0.8 mg / cm 3 - 10 mg / cm 3 .

7. The secondary battery according to claim 4, wherein The coating layer includes an inner coating layer provided inside the positive electrode active material and coating at least part of the surface of the primary particle; and / or, an outer coating layer provided on the surface of the positive electrode active material.

8. The secondary battery according to claim 4, wherein The coating layer includes at least two coating elements.

9. The secondary battery according to claim 1, wherein The positive electrode active material includes Li2CO3 and / or LiOH, the content of the Li2CO3 is less than 3000 ppm, and the content of the LiOH is less than 5000 ppm, based on the weight of the positive electrode active material.

10. The secondary battery according to any one of claims 1 to 9, wherein The electrolyte includes a lithium salt additive; The lithium salt additive includes one or more of lithium difluorophosphate, lithium tetrafluoroborate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium bis(trifluoromethanesulfonyl)imide or lithium bisfluorosulfonylimide salt; The content of the lithium salt additive is 0.01%-4%, based on the weight of the electrolyte.

Images