Cathode material and preparation method, cathode sheet and application

Abstract

The application provides a positive electrode material and a preparation method thereof, a positive electrode slurry, a positive electrode sheet and a preparation method thereof, a secondary battery and a preparation method thereof, and an electric device. The positive electrode material comprises a positive electrode active material and a coating layer located on at least a part of the surface of the positive electrode active material, the positive electrode active material comprises a material with a chemical formula of LiNi 1‑x M x O2, wherein 0<=x<=0.2, M comprises at least one of Co, Mn, Al, Fe, Cu and V, and the coating layer comprises at least one of sulfur, selenium and tellurium. When the positive electrode material is used to prepare a secondary battery, the coating layer can react with the lithium impurities of the positive electrode active material, thereby reducing the lithium impurity content of the positive electrode active material of the secondary battery and improving the cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode material and a preparation method, a positive electrode sheet, a secondary battery and a preparation method, and an electric device. BACKGROUND

[0002] The statements herein are provided only to enhance understanding of the present application and are not necessarily intended to constitute the prior art.

[0003] In a secondary battery, a positive electrode active material with high nickel content has a high specific capacity, but also has a high lithium impurity content, which has a certain adverse effect on the performance of the battery. SUMMARY

[0004] Based on the above problems, the present application provides a positive electrode material and a preparation method, a positive electrode sheet, a secondary battery and a preparation method, and an electric device.

[0005] To achieve the above-mentioned purpose, the present application provides a positive electrode material, comprising a positive electrode active material and a coating layer located on at least a part of the surface of the positive electrode active material, the positive electrode active material comprising a material with a chemical formula of LiNi 1-x M x O2, wherein 0≤x≤0.2, M comprises at least one of Co, Mn, Al, Fe, Cu and V, and the coating layer comprises at least one of sulfur, selenium and tellurium.

[0006] The above-mentioned positive electrode material comprises a positive electrode active material with high nickel content and a coating layer located on at least a part of the surface of the positive electrode active material. In this positive electrode material, by introducing a coating layer comprising at least one of sulfur, selenium and tellurium on the surface of the positive electrode active material, when the positive electrode material is used to prepare a secondary battery, the coating layer can react with the lithium impurities of the positive electrode active material, thereby reducing the lithium impurity content of the positive electrode active material of the secondary battery and improving the cycle performance of the battery.

[0007] In some embodiments, 0≤x≤0.1.

[0008] In some embodiments, M comprises Co and Mn.

[0009] In some embodiments, the atomic ratio of Co and Mn is equal.

[0010] In some embodiments, the lithium impurity content of the positive electrode active material is 0.5% to 0.7%.

[0011] In some embodiments, the lithium impurity content of the positive electrode active material is 0.55% to 0.65%.

[0012] In some embodiments, the positive electrode active material comprises primary particles and secondary particles formed by agglomeration of the primary particles.

[0013] In some embodiments, the Dv50 of the primary particles is 3 μm to 10 μm, and the Dv50 of the secondary particles is 5 μm to 20 μm.

[0014] In some embodiments, the mass ratio of the primary particles to the secondary particles is 1:9 to 4:6.

[0015] In some embodiments, the coating layer comprises at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0016] In some embodiments, the thickness of the coating layer is 100 nm to 1000 nm.

[0017] In some embodiments, the mass percentage of the coating layer is 0.01% to 6% based on the total mass of the positive electrode active material and the coating layer.

[0018] In some embodiments, the mass percentage of the coating layer is 0.1% to 1% based on the total mass of the positive electrode active material and the coating layer.

[0019] The present application also provides a method for preparing a positive electrode material, comprising the following steps:

[0020] mixing a positive electrode active material and a coating layer material to obtain a mixture, wherein the positive electrode active material comprises a material with a chemical formula of LiNi 1-x M x O2, wherein 0≤x≤0.2, M comprises at least one of Co, Mn, Al, Fe, Cu, and V, and the coating layer material comprises at least one of elemental sulfur, elemental selenium, and elemental tellurium;

[0021] sintering the mixture under a protective gas atmosphere.

[0022] In some embodiments, the sintering temperature of the sintering process is 250°C to 350°C.

[0023] In some embodiments, the sintering time of the sintering process is 3 h to 10 h.

[0024] In some embodiments, the Dv50 of the coating layer material is ≤2 μm.

[0025] In some embodiments, the sintering process further comprises a grinding process before sintering the mixture.

[0026] In some embodiments, the Dv50 of the mixture after the grinding process is 10 μm to 20 μm.

[0027] The application also provides a positive electrode tab, comprising a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode material or the positive electrode material prepared by the preparation method of the positive electrode material.

[0028] The application also provides a secondary battery, comprising the positive electrode tab, wherein the surface of the positive electrode active material of the positive electrode tab has an electrolyte interface film, and the electrolyte interface film comprises at least one of lithium sulfate, lithium selenate and lithium tellurite.

[0029] In some embodiments, the thickness of the electrolyte interface film is 5 nm to 20 nm.

[0030] The application also provides a preparation method of a secondary battery, comprising the following steps:

[0031] The secondary battery pre-product assembled with the positive electrode tab is subjected to formation treatment to form an electrolyte interface film on the surface of the positive electrode active material of the positive electrode tab, and the electrolyte interface film comprises at least one of lithium sulfate, lithium selenate and lithium tellurite.

[0032] In some embodiments, the cut-off voltage of the formation treatment is 3.8 V to 4.1 V.

[0033] In some embodiments, the formation current of the formation treatment is 0.08 C to 0.15 C.

[0034] The application also provides an electric device, comprising the secondary battery or the secondary battery prepared by the preparation method of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the application, the drawings used in the application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of the drawings.

[0036] Figure 1 The figure is a schematic diagram of the preparation of the positive electrode material in an embodiment of the application.

[0037] Figure 2 The figure is a schematic diagram of the secondary battery in an embodiment of the application.

[0038] Figure 3 The figure is a schematic diagram of the secondary battery in an embodiment of the application. Figure 2 The figure is an exploded view of the secondary battery in an embodiment of the application.

[0039] Figure 4 A schematic diagram of a power consuming device using the secondary battery as a power source according to an embodiment of the present application.

[0040] Figure 5 A schematic diagram of the positive electrode slurry according to Example 1 of the present application.

[0041] Figure 6 A schematic diagram of the positive electrode slurry according to Comparative Example 1 of the present application.

[0042] Figure 7 A schematic diagram of the positive electrode slurry according to Comparative Example 3 of the present application.

[0043] Figure 8 A viscosity change curve of the positive electrode slurry according to Example 1 and Comparative Example 1 of the present application.

[0044] Figure 9 A transmission electron microscope (TEM) image of the positive electrode sheet after formation according to Example 1 of the present application.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] 5. Secondary battery; 51, housing; 52, electrode assembly; 53, cover plate; 6, power consuming device.

[0047] For a better understanding of those embodiments and / or examples of the application herein disclosed, reference can be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, presently described embodiments and / or examples, and the best mode presently contemplated of these applications. DETAILED DESCRIPTION

[0048] In order to facilitate the understanding of the present application, a more complete description of the present application will be made with reference to the accompanying drawings. The preferred embodiments of the present application are illustrated in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein only for the purpose of describing the specific embodiments of the present application and is not intended to limit the present application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0055] The term "or" is inclusive in this application, unless otherwise indicated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true or present, and B is false or not present; A is false or not present, and B is true or present; or both A and B are true or both A and B are present.

[0056] Unless otherwise indicated, the terms used in this application have the meanings commonly understood by a person of ordinary skill in the art. Unless otherwise indicated, the values of the parameters mentioned in this application can be measured by various measuring methods commonly used in the art. For example, the tests can be performed according to the methods given in the examples of this application.

[0057] An embodiment of the present application provides a positive electrode material, comprising a positive electrode active material and a coating layer on at least a part of the surface of the positive electrode active material, the positive electrode active material comprising a material with a chemical formula of LiNi 1-x M x O2, wherein 0≤x≤0.2, M comprises at least one of Co, Mn, Al, Fe, Cu and V, and the coating layer comprises at least one of sulfur element, selenium element and tellurium element. In the positive electrode material, the positive electrode material comprises a positive electrode active material with a high nickel content and a coating layer on at least a part of the surface of the positive electrode active material. In the positive electrode material, when the positive electrode material is used to prepare a secondary battery, the coating layer can react with the lithium impurities of the positive electrode active material by introducing the coating layer comprising at least one of sulfur element, selenium element and tellurium element on the surface of the positive electrode active material, thereby reducing the amount of lithium impurities of the positive electrode active material of the secondary battery and improving the cycle performance of the battery.

[0058] Specifically, when the positive electrode material is used in a secondary battery, the coating layer can react with the lithium impurities of the positive electrode active material during the preparation of the positive electrode slurry, thereby reducing the amount of lithium impurities. In addition, when the coating layer reacts with the lithium impurities of the positive electrode active material, the intermediate product generated can improve the flowability of the slurry and improve the coating performance of the slurry.

[0059] Further, when the positive electrode material is used in a secondary battery, during the formation stage, the intermediate product can be electrochemically oxidized and further react with the lithium impurities to form a solid electrolyte interface film (CEI film), which can improve the stability of the surface structure of the positive electrode active material, reduce the side reaction between the positive electrode material and the electrolyte, reduce the internal resistance of the battery, and further improve the cycle performance of the battery. In addition, during the formation stage, the electrochemical oxidation can convert the lithium impurities into lithium ions, and the converted lithium ions can be used to compensate for the loss of lithium ions due to the formation of the solid electrolyte interface film (SEI film), thereby realizing the secondary use of the lithium impurities and improving the capacity of the battery.

[0060] Further, when the positive electrode material is used in a secondary battery, the coating layer can react with solvents in the electrolyte through reduction and oxidation pathways to form poly(ethylene oxide) (PEO)-like polymers and lithium alkyls, which can alleviate volume expansion during charging of the electrode and simultaneously form a conductive network that rapidly transports lithium ions, which can further improve the cycling performance of the battery.

[0061] For example, with sulfur in the coating layer, the reaction between the coating layer and the lithium impurities of the positive electrode active material can be represented by equation (1) during preparation of the positive electrode slurry.

[0062] 4LiMO2+ 2S → 4MO + Li2S2O3 + Li2O equation (1).

[0063] where M includes at least one of Co, Mn, Al, Fe, Cu, and V. As can be seen from equation (1), when the positive electrode material is used to prepare a positive electrode slurry, sulfur can react with lithium impurities of the positive electrode active material to reduce the amount of lithium impurities. At the same time, when sulfur reacts with lithium impurities on the surface of the positive electrode active material, the intermediate product lithium thiosulfate generated can improve the flowability of the slurry and improve the coating performance of the slurry.

[0064] Further, when the positive electrode material is used to prepare a secondary battery, the reactions that occur during formation can be represented by equations (2) and (3).

[0065] Li2S2O3 + Li2CO3 - 8e - → 2Li2SO4 + 5CO2 + 8Li + equation (2).

[0066] 2LiMO2 + S + 2Li2CO3 - 4e - → 2MO + Li2SO4 + 2CO2 + 4Li + equation (3).

[0067] As can be seen from equations (2) and (3), during formation, Li2S2O3 can be electrochemically oxidized to Li2SO4, while surface Li2O and Li2CO3 residual lithium compounds are removed, and the CO2 generated can be released together with other gases formed during battery formation.

[0068] As can be seen from equations (1), (2), and (3), sulfur reduces LiMO2 on the surface of the positive electrode active material particles to form a MO protective layer, and at the same time removes Li2O, Li2CO3, and other residual lithium compounds (RLCs) from the surface of the LiMO2 particles. In addition, the electrochemically stable Li2SO4 CEI film exists on the surface of the LiMO2 particles or alone, and the lithium ions released by the sulfur reaction can be used to compensate for the loss of lithium ions due to the formation of the SEI film.

[0069] In some embodiments, x can be 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, etc. 0≤x≤0.2 corresponds to a positive electrode active material with a high nickel content, in which case the positive electrode active material has a high amount of lithium impurities. By providing the coating layer in the present application, the amount of lithium impurities of the active material can be effectively reduced when the positive electrode active material is applied to a battery, which is conducive to improving the performance of the battery. Alternatively, 0≤x≤0.1. Further alternatively, LiNi 1-x M x O2may be LiNi 0.8 M 0.2 O2, LiNi 0.85 M 0.15 O2, LiNi 0.9 M 0.1 O2, LiNi 0.95 M 0.05 O2, etc. Further alternatively, the positive electrode active material is selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, and a nickel-rich layered oxide.

[0070] In some embodiments, M includes Co and Mn. Further, the atomic ratio of Co and Mn is equal. In this case, the positive electrode active material can be LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0071] In some embodiments, the positive electrode active material has a chemical formula of LiNi 1-x M x O2, wherein 0≤x≤0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V. Alternatively, 0≤x≤0.1. Further alternatively, M includes Co and Mn. Further alternatively, the atomic ratio of Co and Mn is equal.

[0072] In some embodiments, the positive electrode active material has an amount of lithium impurities of 0.5% to 0.7%. For example, the positive electrode active material has an amount of lithium impurities of 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, etc. When the positive electrode active material has a high nickel content, the corresponding amount of lithium impurities is relatively high. When the amount of lithium impurities is within this range, the coating layer and the positive electrode active material can better cooperate to reduce the amount of lithium impurities to a low content, thereby improving the performance of the battery. Alternatively, the positive electrode active material has an amount of lithium impurities of 0.55% to 0.65%.

[0073] In some embodiments, the positive electrode active material comprises primary particles and secondary particles formed by agglomeration of the primary particles. The use of the primary particles and the secondary particles can enable the positive electrode sheet to obtain a higher compaction density.

[0074] Optionally, the mass ratio of the primary particles to the secondary particles is 1:9-4:6. For example, the mass ratio of the primary particles to the secondary particles is 1:9, 2:8, 3:7, 4:6, etc.

[0075] In some embodiments, the Dv50 of the primary particles is 3-10 μm, and the Dv50 of the secondary particles is 5-20 μm. Further optionally, the Dv50 of the primary particles is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The Dv50 of the secondary particles is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0076] It can be understood that, in the present application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number of 50% in the volume cumulative distribution curve, and its physical meaning is that the particles with a particle size smaller (or larger) than it account for 50%. As an example, Dv50 can be conveniently determined by using a laser particle size analyzer according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, such as a Mastersizer 2000E laser particle size analyzer of Malvern Instruments Limited, UK.

[0077] In some embodiments, the coating layer comprises at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0078] In some embodiments, the coating layer is located on the surface of the positive electrode active material particles. Further, the surface of each positive electrode active material particle has a coating layer. This can enable the coating layer to better act on the positive electrode active material, and further reduce the lithium impurity content of the positive electrode active material.

[0079] In some embodiments, the coating layer entirely coats the positive electrode active material. At this time, the coating layer can more fully act on the lithium impurity content of the positive electrode active material, and further reduce the lithium impurity content.

[0080] As some optional examples of the coating layer, the thickness of the coating layer is 100-1000 nm. Further optionally, the thickness of the coating layer is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc.

[0081] In some embodiments, the mass percentage of the coating layer is 0.01% to 6% based on the total mass of the positive electrode active material and the coating layer. If the mass percentage of the coating layer is too high, there will be more coating layer on the surface of the positive electrode active material during the preparation of the secondary battery, which can cause the impedance of the surface of the positive electrode active material to deteriorate, affecting the capacity of the active material and the cycle stability of the battery. If the mass percentage of the coating layer is too low, the residual lithium compounds (RLCs) do not react completely, and the remaining RLCs can deteriorate the impedance and increase the polarization, reducing the battery capacity. In addition, it can also strengthen the side reaction of the positive electrode and the electrolyte interface, thereby reducing the battery life and performance. Alternatively, the mass percentage of the coating layer is 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or the like based on the total mass of the positive electrode active material and the coating layer. Further alternatively, the mass percentage of the coating layer is 0.1% to 1% based on the total mass of the positive electrode active material and the coating layer.

[0082] The application also provides a preparation method of a positive electrode material. The preparation method of the positive electrode material comprises the following steps: mixing a positive electrode active material and a coating layer material to obtain a mixture, the positive electrode active material comprises a material with a chemical formula of LiNi 1-x M x O2, wherein 0≤x≤0.2, M comprises at least one of Co, Mn, Al, Fe, Cu and V, and the coating layer material comprises at least one of sulfur, selenium and tellurium; and performing sintering treatment on the mixture in a protective gas atmosphere. The preparation method can obtain a positive electrode material comprising a positive electrode active material and a coating layer on at least part of the surface of the positive electrode active material, and the preparation method is simple and easy to implement.

[0083] It can be understood that in the preparation method of the present embodiment, the product after sintering treatment is cooled to room temperature, i.e. a granular positive electrode material can be obtained. Alternatively, after cooling to room temperature, the positive electrode material meeting the particle size requirement can be obtained by sieving as needed. It can also be understood that, unless otherwise specified, in the present application, the term "room temperature" generally refers to 4°C to 30°C, and alternatively refers to 25±5°C.

[0084] In some embodiments, the sintering temperature of the sintering process is 250-350°C. Alternatively, the sintering temperature of the sintering process is 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, etc. The sintering temperature in this range is conducive to the combination of the positive electrode active material and the coating layer material, and a positive electrode material with better performance is obtained.

[0085] In some embodiments, the sintering time of the sintering process is 3-10h. Alternatively, the sintering time of the sintering process is 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0086] Alternatively, the protective gas comprises at least one of nitrogen, helium, neon, argon, and xenon.

[0087] Further alternatively, the sintering process can be carried out in a tube furnace.

[0088] In some embodiments, the Dv50 of the coating layer material is ≤2μm. The particle size of the coating layer material in this range can be better attached to the surface of the positive electrode active material, facilitating the formation of a coating layer on the surface of the positive electrode active material, and also enabling better bonding force between the positive electrode active material and the coating layer. Alternatively, the Dv50 of the coating layer material can be, but is not limited to, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, etc.

[0089] In some embodiments, the coating layer material comprises at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0090] Alternatively, before the sintering process on the mixture, the mixture is further subjected to a grinding process. Further alternatively, the grinding process is carried out by ball milling. The ball milling time is 5-8h, and the ball milling speed is 150-250r / min. Still further alternatively, the ball milling time is 5h, 6h, 7h, 8h, etc. The ball milling speed is 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min, 210r / min, 220r / min, 230r / min, 240r / min, 250r / min, etc.

[0091] In some embodiments, the Dv50 of the mixture after the grinding treatment is 10-20 μm. For example, the Dv50 of the mixture after the grinding treatment is 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc. Controlling the Dv50 of the mixture after the grinding treatment in the range of 10-20 μm is conducive to improving the sintering completeness, improving the sintering effect, and obtaining a positive electrode material with good performance.

[0092] Referring to Figure 1 A preparation schematic of a positive electrode material in an embodiment of the present application is shown in FIG. 1. In the preparation process, the positive electrode active material and the coating layer material are mixed to obtain a mixture. The mixture is subjected to a grinding treatment. Then, argon is introduced into a tube furnace, and sintering is performed at a temperature of 300 °C for 6 h. After sintering, the temperature is lowered to room temperature, and a granular positive electrode material is obtained.

[0093] In another embodiment of the present application, a positive electrode slurry is provided. The positive electrode slurry includes the positive electrode material described above or the positive electrode material prepared by the preparation method of the positive electrode material described above.

[0094] Optionally, the positive electrode slurry can further include at least one of a conductive agent, a binder, and a solvent.

[0095] In another embodiment of the present application, a positive electrode tab is provided. The positive electrode tab includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode material described above or the positive electrode material prepared by the preparation method of the positive electrode material described above.

[0096] In another embodiment of the present application, a preparation method of a positive electrode tab is provided. The preparation method of the positive electrode tab includes the following steps: transferring the positive electrode slurry described above to at least one surface of the positive electrode current collector and solidifying to form a positive electrode film layer on the corresponding surface of the positive electrode current collector.

[0097] In another embodiment of the present application, a secondary battery is provided. The secondary battery includes the positive electrode tab described above or the positive electrode tab prepared by the preparation method of the positive electrode tab described above, and the surface of the positive electrode active material of the positive electrode tab has an electrolyte interface film (CEI film) including at least one of lithium sulfate, lithium selenate, and lithium tellurite. The presence of the electrolyte interface film is conducive to improving the stability of the surface structure of the positive electrode active material, reducing the side reaction of the positive electrode tab with the electrolyte, and improving the cycle performance of the battery.

[0098] In some embodiments, the thickness of the electrolyte interface film is 5-20 nm. Optionally, the thickness of the electrolyte interface film is 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, etc.

[0099] Optionally, as the negative electrode of the secondary battery, the negative electrode active material comprises at least one of graphite and silicon-based material. Further optionally, when the negative electrode material comprises graphite and silicon-based material, the mass percentage of the silicon-based material in the negative electrode active material is ≤50%.

[0100] Optionally, as the electrolyte of the secondary battery, the electrolyte comprises lithium salt. Optionally, the lithium salt can be selected from LiTFSI, LiFSI, LiN(C a F 2a+1 SO2)(C b F 2b+1 SO2), LiPF6, LiBF4, LiBOB, LiAsF6, LiCF3SO3, and LiClO4, wherein a and b are natural numbers.

[0101] Optionally, the electrolyte comprises non-aqueous organic solvent, and the non-aqueous organic solvent can be selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0102] The application also has an embodiment to provide a preparation method of a secondary battery. The preparation method of the secondary battery comprises the following steps: performing formation treatment on a secondary battery pre-product assembled with the above-mentioned positive electrode sheet or the positive electrode sheet prepared by the above-mentioned preparation method of a positive electrode sheet, so as to form an electrolyte interface film on the surface of the positive electrode active material of the positive electrode sheet, and the electrolyte interface film comprises at least one of lithium sulfate, lithium selenate, and lithium tellurite.

[0103] It can be understood that the secondary battery pre-product represents the battery product before formation.

[0104] Optionally, the cutoff voltage of the formation treatment is 3.8V-4.1V. Further optionally, the cutoff voltage of the formation treatment is 3.8V, 3.9V, 4.0V, 4.1V, etc. The use of a higher formation cutoff voltage is more conducive to the formation of the CEI film, improves the conversion rate of lithium impurities, and further improves the cycle performance of the battery.

[0105] Optionally, the formation current of the formation treatment is 0.08C-0.15C. Further optionally, the formation current of the formation treatment is 0.08C, 0.09C, 0.1C, 0.12C, 0.13C, 0.14C, 0.15C, etc.

[0106] The application also has an embodiment to provide an electric device. The electric device comprises the above-mentioned secondary battery or the secondary battery prepared by the above-mentioned preparation method of a secondary battery.

[0107] The secondary battery and the electric device of the application are described below with reference to the accompanying drawings.

[0108] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and functions to prevent short circuiting between the positive and negative electrodes while allowing ions to pass through.

[0109] The positive electrode sheet

[0110] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0111] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0112] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on a polymer material base. Optionally, the metal material can include, but is not limited to, one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. Optionally, the polymer material base can include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0113] As an example, the positive electrode active material can include a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, at least one 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 a modified compound thereof. Optionally, the lithium cobalt oxide includes LiCoO2. The lithium nickel oxide includes LiNiO2. The lithium manganese oxide includes at least one of LiMnO2and LiMn2O4. The lithium nickel cobalt manganese oxide includes LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2(NCM333 LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 ) and LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 At least one of the following. Lithium nickel cobalt aluminum oxides include LiNi 0.85 Co 0.15 Al 0.05 O2. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Optionally, lithium iron phosphate includes LiFePO4 (LFP). Lithium manganese phosphate includes LiMnPO4. The positive electrode active material accounts for 80-100% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0114] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0–20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0115] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0–20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0116] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent to form a positive electrode slurry. Optionally, the solvent comprises N-methyl pyrrolidone. The positive electrode slurry has a solid content of 40-80 wt%, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is coated on the surface of the positive electrode current collector, dried and then cold-pressed by a cold rolling machine to form the positive electrode sheet. The unit area density of the positive electrode powder coating is 150-350 mg / m 2 , and the compaction density of the positive electrode sheet is 3.0-3.6 g / cm 3 , optionally 3.4-3.6 g / cm 3 . The compaction density is calculated by the formula: compaction density = coating area density / (thickness of the electrode sheet after extrusion - thickness of the current collector).

[0117] It can be understood that the positive electrode sheet in the embodiments of the present application can be prepared by taking the above-mentioned positive electrode sheet as the main body of the positive electrode sheet and forming a solid electrolyte interface film on the surface of the main body of the positive electrode sheet.

[0118] The negative electrode sheet

[0119] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises a negative electrode active material.

[0120] For example, the negative electrode current collector has two opposite surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0121] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on the polymer material base layer. Optionally, the metal material comprises at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The polymer material comprises at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0122] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more. The weight ratio of the negative active material in the negative electrode film layer is 70 to 100% by weight, based on the total weight of the negative electrode film layer.

[0123] In some embodiments, the negative electrode film layer can also optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

[0124] In some embodiments, the negative electrode film layer can also optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight, based on the total weight of the negative electrode film layer.

[0125] In some embodiments, the negative electrode film layer can also optionally include other auxiliary agents, such as thickening agents, etc. The weight ratio of the other auxiliary agents in the negative electrode film layer is 0 to 15% by weight, based on the total weight of the negative electrode film layer. Optionally, the thickening agent includes sodium carboxymethyl cellulose (CMC-Na).

[0126] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent to form a negative electrode slurry. Optionally, the solvent includes deionized water. The negative electrode slurry has a solid content of 30 to 70 wt% and a viscosity of 2000 to 10000 mPa·s at room temperature. The obtained negative electrode slurry is coated on a negative electrode current collector, and subjected to a drying process, cold pressing, such as roll-to-roll, to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 75 to 220 mg / m 2 , and the negative electrode sheet compaction density is 1.2 to 2.0 g / m 3 .

[0127] It can be understood that the negative electrode tab in the embodiments of the present application can be made by taking the above-mentioned negative electrode tab as a negative electrode tab body and forming a solid electrolyte interface film on the surface of the negative electrode tab body.

[0128] Electrolyte

[0129] The electrolyte plays a role of conducting ions between the positive electrode tab and the negative electrode tab. The type of the electrolyte is not specifically limited in the present application and can be selected according to requirements. For example, the electrolyte can be in a liquid state, a gel state or a full solid state.

[0130] In some embodiments, the electrolyte adopts an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluorophosphate di-oxalate (LiDFOP) and lithium tetrafluorophosphate oxalate (LiTFOP). The concentration of the electrolyte salt is usually 0.5-5 mol / L.

[0132] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), 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), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0133] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, etc.

[0134] Separator film

[0135] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0136] In some embodiments, the separator can be made of at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0137] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly by a winding process or a stacking process.

[0138] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte.

[0139] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed. The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure of the secondary battery 5 as an example.

[0140] In some embodiments, referring to Figure 3 , the outer package can comprise a shell 51 and a cover plate 53. The shell 51 can comprise a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person in the art can select according to the specific actual needs.

[0141] In addition, the application further provides a power utilization device comprising the secondary battery provided by the application. The secondary battery can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0142] As the power utilization device, the secondary battery can be selected according to the use requirement thereof.

[0143] Figure 4 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of the power utilization device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0144] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power supply.

[0145] Embodiments

[0146] In order to make the technical problems, technical solutions and beneficial effects solved by the application clearer, the application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the application, but not all the embodiments. The description of the at least one exemplary embodiment below is actually only illustrative, but not as any limitation on the application and its application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0147] Unless specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product instructions are used. Unless the manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase in the market.

[0148] Embodiment 1

[0149] In this embodiment, the positive active material is LiNi 0.9 Co 0.05 Mn 0.05O2, the initial impurity lithium content of the positive electrode active material is 0.55%, the coating layer material is sulfur element, and the mass percentage of the sulfur element in the total mass of the positive electrode active material and the coating layer is 0.5%. The Dv50 of the sulfur element is 1 μm. The positive electrode active material is primary particles and secondary particles, wherein the Dv50 of the primary particles is 5 μm, the Dv50 of the secondary particles is 15 μm, and the mass ratio of the primary particles to the secondary particles is 2:8.

[0150] (1) Preparation method of the positive electrode material in the embodiment:

[0151] The positive electrode active material and the coating layer material are mixed and ball milled at a rotation speed of 200 r / min. The Dv50 of the mixed material after ball milling is 17.9 μm. Then the mixed material after ball milling is sintered in a tube furnace with argon as the protective atmosphere, the sintering temperature is 300 ℃, and the sintering time is 5 h. After sintering, the temperature is lowered to room temperature to obtain the positive electrode material.

[0152] (2) Preparation method of the positive electrode slurry in the embodiment:

[0153] The positive electrode material, the conductive agent carbon black, the binder polyvinylidene fluoride (PVDF), and the carbon nanotube (CNT) are dry mixed and stirred uniformly according to the weight ratio of 77.3:10:8.7:2.7:1.3. The stirring and mixing are performed under the condition that the rotation speed is 400-1000 r / s. Then the wetting, kneading, and dispersion treatment are performed to obtain the positive electrode slurry. The positive electrode slurry in the embodiment is as shown in Table 1. Figure 5

[0154] (3) Preparation method of the positive electrode tab in the embodiment:

[0155] The positive electrode slurry is coated on the aluminum foil, and after drying, cold pressing, and slitting, the positive electrode tab is obtained.

[0156] (4) Preparation method of the negative electrode tab in the embodiment:

[0157] The negative electrode active material artificial graphite, the conductive agent carbon black, the binder styrene butadiene rubber (SBR), and the thickening agent sodium hydroxymethyl cellulose (CMC) are dry mixed uniformly according to the weight ratio of 96.85:1.15:0.8:1.2. Then deionized water is added and mixed uniformly to prepare the negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode tab is obtained.

[0158] (5) Preparation method of the electrolyte in the embodiment:

[0159] ​In an argon atmosphere glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), organic solvent ethylene carbonate and methyl ethyl carbonate were mixed uniformly in a volume ratio of 4:6, 12.5% LiPF6 lithium salt dissolved in organic solvent was added, and stirred uniformly to obtain an electrolyte.

[0160] (6) In this embodiment, a polyethylene film is used as the separator film.

[0161] (7) The preparation method of the battery in this embodiment is as follows:

[0162] The positive electrode sheet, the separator film and the negative electrode sheet were stacked in order with the separator film between the positive and negative electrode sheets, and the bare battery cell was obtained by winding. The bare battery cell was placed in the battery outer package, and then the electrolyte was injected, packaged, rested, formed, shaped, and capacity tested to complete the preparation of the lithium ion battery. The thickness of the lithium ion battery was 4.2 mm, the width was 32 mm, and the length was 82 mm. The formation was carried out in a formation machine, the cutoff voltage of the formation was 4 V, and the formation current was 0.1 C.

[0163] The TEM image of the positive electrode sheet after formation in this embodiment is shown in Figure 9 From Figure 9 it can be seen that an electrolyte interface film with a thickness of 15 nm is generated on the surface of the active material of the positive electrode sheet.

[0164] Examples 2 to 11

[0165] Compared with Example 1, the differences of Examples 2 to 11 are that the coating layer material and / or the positive active material and / or the mass percentage of the coating layer and / or the formation cutoff voltage are as shown in Table 1.

[0166] In Example 5, the mass ratio of the coating layer materials sulfur and selenium is 1:1. In Example 6, the mass ratio of the coating layer materials sulfur and tellurium is 1:1. In Example 7, the mass ratio of the coating layer materials selenium and tellurium is 1:1. In Example 7, the mass ratio of the coating layer materials sulfur, selenium and tellurium is 1:1:1.

[0167] Example 12

[0168] Compared with Example 1, the difference of Example 12 is that the mass percentage of the coating layer is 0.1%. The positive electrode slurry in Example 12 is as shown in Figure 7 .

[0169] Example 13

[0170] Compared with Example 1, the difference of Example 13 is that the cutoff voltage of the formation treatment is 3.7 V.

[0171] Example 14

[0172] Example 14 differs from Example 1 in that the particle size of the coating layer material is 2 pm.

[0173] Example 15

[0174] Example 15 differs from Example 1 in that the particle size of the coating layer material is 3 pm.

[0175] Example 16

[0176] Example 16 differs from Example 1 in that the Dv50 of the mixed material after ball milling is 25 pm.

[0177] Example 17

[0178] Example 17 differs from Example 1 in that the Dv50 of the mixed material after ball milling is 5 pm.

[0179] Comparative Example 1

[0180] Comparative Example 1 differs from Example 1 in that no coating layer material is added. The positive electrode slurry in Comparative Example 1 is prepared as shown in Table 1. Figure 6

[0181] Comparative Example 2

[0182] Comparative Example 2 differs from Example 1 in that no coating layer material is added to the positive electrode material. Moreover, the preparation method of the negative electrode sheet is as follows:

[0183] After the negative electrode active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium hydroxymethyl cellulose (CMC) are dry mixed uniformly at a weight ratio of 96.85:1.15:0.8:1.2, 0.5% by mass of elemental sulfur is added, and deionized water is mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on a negative electrode current collector copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0184] Comparative Example 3

[0185] Comparative Example 3 differs from Comparative Example 2 in that the negative electrode active material is graphite and SiO x , wherein 0 < x < 2, and the mass percentage of SiO x is 10%.

[0186] Comparative Example 4

[0187] Comparative Example 4 differs from Comparative Example 2 in that the positive electrode active material is different.

[0188] Comparative Example 5

[0189] ​The difference between Comparative Example 5 and Example 1 is that:

[0190] A method for preparing the positive electrode slurry:

[0191] The positive electrode material, sulfur element, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotube (CNT) are dry mixed and stirred to mix uniformly. The stirring and mixing is performed at a rotation speed of 400-1000 r / s. Then, wetting, kneading, and dispersion treatment are performed to obtain the positive electrode slurry.

[0192] Comparative Example 6

[0193] The difference between Comparative Example 6 and Example 1 is that: the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, and the initial impurity lithium amount of the positive electrode active material is 0.06%.

[0194] Table 1

[0195]

[0196]

[0197]

[0198]

[0199] In Table 1, the test methods are as follows:

[0200] (1) The test method for the impurity lithium amount is:

[0201] Pre-treatment: The active layer of the cathode electrode piece after formation is scraped and ground into powder. 30 g of powder of any particle size is weighed, stirred in 100 ml of pure water for 30 min, and then filtered. A certain amount of filtrate is removed after standing for 10 min.

[0202] Test: 0.05 mol / L hydrochloric acid standard solution is selected. The gas bubbles in the burette are discharged. The potential titrator 905 is selected to start automatic detection. The corresponding results are read, and the subsequent repeated tests are performed.

[0203] It can be understood that the initial impurity lithium amount of the positive electrode active material can be tested according to the above method by grinding the positive electrode active material into powder.

[0204] (2) The test method of the direct current internal resistance is as follows: at 25 DEG C, the lithium ion battery is charged at 0.33C to 4.25V, then charged at 4.25V to a current less than 0.05C, and then discharged at 0.33C for 30 min, that is, the capacity of the cell is adjusted to 50% SOC. Then the positive and negative pens of the TH2523A alternating current internal resistance tester are respectively contacted with the positive and negative electrodes of the battery, and the internal resistance value of the battery is read by the internal resistance tester.

[0205] (3) The test method of the 0.33C capacity retention rate is as follows:

[0206] At 25 DEG C, the lithium ion battery is charged at 0.33C to 4.25V, then charged at 4.25V to a current less than 0.05C, and then discharged at 0.33C to 2.8V, which is one charge and discharge process. The charging and discharging are repeatedly performed, and the capacity retention rate of the lithium ion battery after 500 cycles is calculated.

[0207] The capacity retention rate (%) of the lithium ion battery after 500 cycles at 25 DEG C = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) x 100%.

[0208] (4) The test method of the 60 DEG C storage capacity retention rate is as follows:

[0209] Before storage, the battery is charged at 1 / 3C to 4.25V, then charged at 4.25V to 0.05C, and then discharged at 1 / 3C to 2.8V at 25 DEG C, and the obtained capacity is recorded as the initial capacity C0. After 100 days of storage at 60 DEG C, the battery temperature is cooled to room temperature, the above steps are repeated, and the measured capacity is recorded as Cr, and then the battery capacity recovery rate H after 100 days of storage = Cr / C0*100%.

[0210] As can be seen from Table 1, the introduction of the coating layer in the positive electrode material is beneficial to reduce the amount of lithium impurities on the surface of the positive electrode active material, and improve the cycle performance of the battery. And, as can be seen from Table 1, Figures 5 to 8 It can be seen that the introduction of the coating layer and the control of the addition amount are beneficial to improve the flowability and viscosity stability of the positive electrode slurry.

[0211] As can be seen from Comparative Example 6 and Example 1, the LiNi 0.6 Co 0.2 Mn 0.2 O2 positive electrode active material has a battery with a better capacity retention rate, and the possible reason is that the LiNi 0.9 Co 0.05 Mn 0.05 O2 positive electrode active material has a battery with a better capacity retention rate, and the possible reason is that the LiNi 0.6 Co 0.2 Mn 0.2The capacity retention rate of the O2 positive electrode active material itself is slightly better than that of LiNi 0.9 Co 0.05 Mn 0.05 O2 positive electrode active material.

[0212] In addition, as can be seen from Comparative Example 6 and Comparative Example 4, Example 1 and Comparative Example 1, the capacity retention rate of the battery of Comparative Example 6 relative to Comparative Example 4 is less improved than the results of Example 1 and Comparative Example 1, and the reason can be that the initial impurity lithium amount of the LiNi 0.6 Co 0.2 Mn 0.2 O2 positive electrode active material is lower than that of LiNi 0.9 Co 0.05 Mn 0.05 O2 positive electrode active material, by introducing a coating layer material, the initial impurity lithium amount of the LiNi 0.6 Co 0.2 Mn 0.2 O2 positive electrode active material is relatively small.

[0213] Each of the technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description simple, not all possible combinations of each technical feature in the above-described embodiments are described, however, as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0214] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A secondary battery, characterized in that, The positive electrode includes a positive electrode sheet, wherein the surface of the positive electrode active material of the positive electrode sheet has an electrolyte interface film, the electrolyte interface film comprising at least one of lithium sulfate, lithium selenate, and lithium tellurate; the positive electrode active material comprises a material with the chemical formula LiNi. 1-x M x The material of O2, wherein 0≤x≤0.2, M includes at least one of Co, Mn, Al, Fe, Cu and V, and at least a portion of the surface of the positive electrode active material has a coating layer, the coating layer including at least one of sulfur, selenium and tellurium.

2. The secondary battery according to claim 1, characterized in that, The thickness of the electrolyte interface film is 5nm~20nm.

3. The secondary battery according to claim 1 or 2, characterized in that, The positive electrode active material satisfies at least one of the following characteristics: （1）0≤x≤0.1； (2) M includes Co and Mn; (3) The amount of impure lithium in the positive electrode active material is 0.5%~0.7%; (4) The positive electrode active material includes primary particles and secondary particles formed by the agglomeration of primary particles.

4. The secondary battery according to claim 3, characterized in that, The atomic ratios of Co and Mn are equal.

5. The secondary battery according to claim 3, characterized in that, The amount of impure lithium in the positive electrode active material is 0.55%~0.65%.

6. The secondary battery according to claim 3, characterized in that, The primary particles have a Dv50 of 3 μm to 10 μm, and the secondary particles have a Dv50 of 5 μm to 20 μm.

7. The secondary battery according to claim 3, characterized in that, The mass ratio of the primary particles to the secondary particles is 1:9 to 4:

6.

8. The secondary battery according to claim 1 or 2, characterized in that, The covering layer satisfies at least one of the following characteristics: (1) The coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium; (2) The thickness of the coating layer is 100nm~1000nm; (3) The mass percentage of the coating layer is 0.01% to 6% of the total mass of the positive electrode active material and the coating layer.

9. The secondary battery according to claim 8, characterized in that, The mass percentage of the coating layer is 0.1% to 1%, based on the total mass of the positive electrode active material and the coating layer.

10. A positive electrode plate, characterized in that, The surface of the positive electrode active material of the positive electrode sheet has an electrolyte interface film, which includes at least one of lithium sulfate, lithium selenate, and lithium tellurate; the positive electrode active material includes materials with the chemical formula LiNi. 1-x M x The material of O2, wherein 0≤x≤0.2, M includes at least one of Co, Mn, Al, Fe, Cu and V, and at least a portion of the surface of the positive electrode active material has a coating layer, the coating layer including at least one of sulfur, selenium and tellurium.

11. A method for preparing a secondary battery, characterized in that, Includes the following steps: A pre-finished secondary battery assembly with a positive electrode sheet is subjected to a formation process to form an electrolyte interface film on the surface of the positive electrode active material of the positive electrode sheet. The electrolyte interface film includes at least one of lithium sulfate, lithium selenate, and lithium tellurate. The positive electrode active material includes LiNi 1-x M x The material of O2, wherein 0≤x≤0.2, M includes at least one of Co, Mn, Al, Fe, Cu and V, and at least a portion of the surface of the positive electrode active material has a coating layer, the coating layer including at least one of sulfur, selenium and tellurium.

12. The method for preparing a secondary battery according to claim 11, characterized in that, The formation process satisfies at least one of the following characteristics: (1) The cutoff voltage of the formation process is 3.8V~4.1V; (2) The formation current of the formation process is 0.08C~0.15C.

13. An electrical appliance, characterized in that, The secondary battery includes the secondary battery according to any one of claims 1 to 9 or the secondary battery prepared by the method according to any one of claims 11 to 12.

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