Positive electrode material, preparation method, positive electrode plate and application

Abstract

The invention provides a positive electrode material and a preparation method thereof, positive electrode slurry, a positive electrode plate 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 one part of the surface of the positive electrode active material, the positive electrode active material comprises a material with the chemical formula of LiNi1-xMxO2, x is greater than or equal to 0 and less than or equal to 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 for preparing the secondary battery, the coating layer can react with lithium impurities of the positive electrode active material, so that the lithium impurity amount of the positive electrode active material of the secondary battery is reduced, and the cycle performance of the battery is improved.

Description

[0001] Related applications

[0002] This application is a divisional application of the Chinese patent application filed by the applicant on March 1, 2023, with application number 2023101863731 and titled "Positive electrode material and preparation method, positive electrode sheet and application". Technical Field

[0003] This application relates to the field of secondary battery technology, and more particularly to a positive electrode material and preparation method, a positive electrode sheet, a secondary battery and preparation method, and an electrical device. Background Technology

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

[0005] In secondary batteries, positive electrode active materials with high nickel content have higher specific capacity, but also higher levels of impure lithium, which has a certain adverse effect on battery performance. Summary of the Invention

[0006] In view of the above problems, this application provides a positive electrode material and preparation method, a positive electrode sheet, a secondary battery and preparation method, and an electrical device.

[0007] To achieve the above objectives, this application provides a positive electrode material, comprising a positive electrode active material and a coating layer located on at least a portion of the surface of the positive electrode active material, wherein 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 the coating layer includes at least one of sulfur, selenium and tellurium.

[0008] The aforementioned cathode material includes a cathode active material with a high nickel content and a coating layer located on at least a portion of the surface of the cathode active material. In this cathode material, by introducing a coating layer containing at least one of sulfur, selenium, and tellurium onto the surface of the cathode active material, when this cathode material is used to prepare a secondary battery, the coating layer can react with the impure lithium in the cathode active material, thereby reducing the amount of impure lithium in the secondary battery's cathode active material and improving the battery's cycle performance.

[0009] In some implementations, 0 ≤ x ≤ 0.1.

[0010] In some implementations, M includes Co and Mn.

[0011] In some implementations, the atomic ratios of Co and Mn are equal;

[0012] In some embodiments, the amount of impure lithium in the positive electrode active material is 0.5% to 0.7%.

[0013] In some embodiments, the amount of impure lithium in the positive electrode active material is 0.55% to 0.65%.

[0014] In some embodiments, the positive electrode active material includes primary particles and secondary particles formed by the agglomeration of primary particles.

[0015] In some embodiments, the Dv50 of the primary particles is 3μm to 10μm, and the Dv50 of the secondary particles is 5μm to 20μm.

[0016] In some embodiments, the mass ratio of the primary particles to the secondary particles is 1:9 to 4:6.

[0017] In some embodiments, the coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0018] In some embodiments, the thickness of the coating layer is 100 nm to 1000 nm.

[0019] In some embodiments, 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.

[0020] In some embodiments, the mass percentage of the coating layer is 0.1% to 1%, which is the mass percentage of the total mass of the positive electrode active material and the coating layer.

[0021] This application also provides a method for preparing a cathode material, comprising the following steps:

[0022] The positive electrode active material and the coating material are mixed to obtain a mixture, wherein the positive electrode active material includes 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 the coating material includes at least one of sulfur, selenium and tellurium.

[0023] The mixture is sintered under a protective gas atmosphere.

[0024] In some embodiments, the sintering temperature of the sintering process is 250°C to 350°C.

[0025] In some embodiments, the sintering time of the sintering treatment is 3h to 10h.

[0026] In some embodiments, the Dv50 of the coating material is ≤2μm.

[0027] In some embodiments, the process of grinding the mixture is further included before sintering the mixture.

[0028] In some embodiments, the Dv50 of the mixture after milling is 10 μm to 20 μm.

[0029] This application also provides a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, wherein the positive electrode film layer includes the above-described positive electrode material or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0030] This application also provides a secondary battery, including the above-mentioned positive electrode sheet, wherein the surface of the positive electrode active material of the positive electrode sheet has an electrolyte interface film, and the electrolyte interface film includes at least one of lithium sulfate, lithium selenate and lithium tellurate.

[0031] In some embodiments, the thickness of the electrolyte interface film is 5 nm to 20 nm.

[0032] This application also provides a method for preparing a secondary battery, comprising the following steps:

[0033] The pre-finished secondary battery equipped with the above-mentioned positive electrode sheet is subjected to a formation treatment 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.

[0034] In some embodiments, the cutoff voltage of the formation process is 3.8V to 4.1V.

[0035] In some embodiments, the formation current of the formation process is 0.08C to 0.15C.

[0036] This application also provides an electrical device, including the above-described secondary battery or a secondary battery prepared by the above-described method for preparing a secondary battery. Attached Figure Description

[0037] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0038] Figure 1 This is a schematic diagram illustrating the preparation of the positive electrode material in one embodiment of this application.

[0039] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0040] Figure 3 for Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0041] Figure 4 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0042] Figure 5 This is a schematic diagram of the positive electrode slurry in Embodiment 1 of this application.

[0043] Figure 6 This is a schematic diagram of the positive electrode slurry in Comparative Example 1 of this application.

[0044] Figure 7 This is a schematic diagram of the positive electrode slurry in Comparative Example 3 of this application.

[0045] Figure 8 The viscosity change curves of the positive electrode slurry in Example 1 and Comparative Example 1 of this application are shown.

[0046] Figure 9 This is a transmission electron microscope (TEM) image of the positive electrode sheet after formation in Example 1 of this application.

[0047] Explanation of reference numerals in the attached figures:

[0048] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device.

[0049] To better describe and illustrate embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the currently described embodiments and / or examples, or the best mode of these inventions as currently understood. Detailed Implementation

[0050] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0051] 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 this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] 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 also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "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.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0054] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0055] 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.

[0056] 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.

[0057] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true or exists, and B is false or does not exist; A is false or does not exist, and B is true or exists; or both A and B are true, or both A and B exist.

[0058] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art. For example, they can be tested according to the methods given in the embodiments of this application.

[0059] One embodiment of this application provides a positive electrode material, including a positive electrode active material and a coating layer located on at least a portion of the surface of the positive electrode active material. The positive electrode active material includes a material with the chemical formula LiNi. 1-x M x The material contains O2, wherein 0 ≤ x ≤ 0.2, M includes at least one of Co, Mn, Al, Fe, Cu, and V, and the coating layer includes at least one of sulfur, selenium, and tellurium. In this cathode material, the cathode material includes a cathode active material with a high nickel content and a coating layer located on at least a portion of the surface of the cathode active material. In this cathode material, by introducing a coating layer containing at least one of sulfur, selenium, and tellurium onto the surface of the cathode active material, when this cathode material is used to prepare a secondary battery, the coating layer can react with the impure lithium in the cathode active material, thereby reducing the amount of impure lithium in the secondary battery cathode active material and improving the battery's cycle performance.

[0060] Specifically, when this cathode material is used in a secondary battery, during the preparation of the cathode slurry, the coating layer can undergo a preliminary reaction with the impure lithium in the cathode active material, reducing the amount of impure lithium. Furthermore, the intermediate products generated during the reaction between the coating layer and the impure lithium in the cathode active material can improve the fluidity of the slurry and enhance its coating performance.

[0061] Furthermore, when this cathode material is used in a secondary battery, during the formation stage, the intermediate products are electrochemically oxidized and can react further with impure lithium to form an electrolyte interphase (SEI) film. This improves the stability of the surface structure of the cathode active material, reduces side reactions between the cathode material and the electrolyte, lowers the battery's internal impedance, and further improves the battery's cycle performance. Additionally, during the formation stage, electrochemical oxidation converts impure lithium into lithium ions. These converted lithium ions can compensate for lithium ion losses caused by the formation of the SEI film, thus enabling the secondary utilization of impure lithium and increasing battery capacity.

[0062] Furthermore, when this cathode material is used in a secondary battery, the coating layer can react with the solvent in the electrolyte through reduction and oxidation to generate poly(ethylene oxide) (PEO)-like polymers and lithium alkyl oxides, which can alleviate the volume expansion of the electrode during charging and form a conductive network for rapid lithium ion transport, thereby further improving the cycle performance of the battery.

[0063] Taking sulfur in the coating layer as an example, the reaction between the coating layer and the mixed lithium of the positive electrode active material during the preparation of the positive electrode slurry can be represented by equation (1).

[0064] 4LiMO2+2S → 4MO+Li2S2O3+Li2O Equation (1).

[0065] Wherein, M includes at least one of Co, Mn, Al, Fe, Cu, and V. As can be seen from equation (1), when this cathode material is used to prepare cathode slurry, sulfur can undergo a preliminary reaction with the impure lithium in the cathode active material, reducing the amount of impure lithium. Simultaneously, when sulfur reacts with the impure lithium on the surface of the cathode active material, the resulting intermediate product, lithium thiosulfate, can improve the fluidity of the slurry and enhance its coating performance.

[0066] Furthermore, when this cathode material is used to prepare a secondary battery, the reaction that occurs during the formation stage can be represented by equations (2) and (3).

[0067] Li₂S₂O₃ + Li₂CO₃ → 8e⁻ - → 2 Li₂SO₄ + 5CO₂ + 8Li + Equation (2).

[0068] 2LiMO2 + S + 2Li2CO3 - 4e - →2MO + Li₂SO₄ + 2CO₂ + 4Li + Equation (3).

[0069] As can be seen from equations (2) and (3), during the formation stage, Li2S2O3 can be electrochemically oxidized to Li2SO4, while the residual lithium compounds of Li2O and Li2CO3 on the surface are removed, and the generated CO2 can be released together with other gases formed during the battery formation process.

[0070] As can be seen from equations (1), (2), and (3), sulfur reduces LiMO2 on one hand, forming a MO protective layer on the surface of the positive electrode active material particles, and on the other hand, removes residual lithium compounds (RLCs) such as Li2O and Li2CO3 from the surface of LiMO2 particles. In addition, the electrochemically stable Li2SO4CEI film exists on the surface of LiMO2 particles or alone, and the lithium ions released by the sulfur reaction can be used to compensate for the lithium ion loss caused by the formation of the SEI film.

[0071] 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 cathode active material with a high nickel content. In this case, the amount of impure lithium in the cathode active material is high. By setting the coating layer in this application, when this cathode material is applied to the battery, the amount of impure lithium in the active material can be effectively reduced, which is beneficial to improving battery performance. Optionally, 0 ≤ x ≤ 0.1. Further optionally, LiNi... 1-x M x O2 can 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 optionally, the positive electrode active material is selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, and nickel-rich layered oxides.

[0072] In some embodiments, M includes Co and Mn. Further, the atomic ratios of Co and Mn are 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.

[0073] In some embodiments, the chemical formula of the positive electrode active material is LiNi. 1-x M xO2, wherein 0 ≤ x ≤ 0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V. Optionally, 0 ≤ x ≤ 0.1. Further optionally, M includes Co and Mn. Further optionally, the atomic ratios of Co and Mn are equal.

[0074] In some embodiments, the amount of impure lithium in the positive electrode active material is 0.5% to 0.7%. For example, the amount of impure lithium in the positive electrode active material is 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, etc. When the nickel content of the positive electrode active material is high, the corresponding amount of impure lithium is relatively high. Within this range, the coating layer and the positive electrode active material can work together better, reducing the amount of impure lithium to a low level and improving battery performance. Optionally, the amount of impure lithium in the positive electrode active material is 0.55% to 0.65%.

[0075] In some embodiments, the positive electrode active material includes primary particles and secondary particles formed by the agglomeration of the primary particles. The use of primary and secondary particles allows the positive electrode sheet to achieve a high compaction density.

[0076] Optionally, the mass ratio of primary particles to secondary particles is 1:9 to 4:6. For example, the mass ratio of primary particles to secondary particles is 1:9, 2:8, 3:7, 4:6, etc.

[0077] In some embodiments, the Dv50 of primary particles is 3 μm to 10 μm, and the Dv50 of secondary particles is 5 μm to 20 μm. Further optionally, the Dv50 of primary particles is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The Dv50 of secondary particles is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc.

[0078] It is understood that in this application, Dv50 refers to the particle size at which the cumulative particle size distribution reaches 50% in the volume cumulative distribution curve. Physically, it means that 50% of the particles are smaller (or larger) than Dv50. As an example, Dv50 can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0079] In some embodiments, the coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0080] In some embodiments, the coating layer is located on the surface of the positive electrode active material particles. Furthermore, each positive electrode active material particle has a coating layer on its surface. This allows the coating layer to interact better with the positive electrode active material, further reducing the amount of impure lithium in the positive electrode active material.

[0081] In some implementations, the coating layer completely covers the positive electrode active material. In this case, the coating layer can interact more fully with the amount of impure lithium in the positive electrode active material, further reducing the amount of impure lithium.

[0082] As some optional examples of the coating layer, the thickness of the coating layer is 100nm~1000nm. More optionally, the thickness of the coating layer is 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.

[0083] In some embodiments, the mass percentage of the coating layer, representing a percentage of the total mass of the positive electrode active material and the coating layer, is 0.01% to 6%. If the mass percentage of the coating layer is too high, a large amount of coating layer will remain on the surface of the positive electrode active material during the fabrication of the secondary battery, potentially leading to deterioration of the surface impedance of the positive electrode active material, 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 remaining lithium compounds (RLCs) will not react completely. The remaining RLCs may worsen the impedance, increase polarization, and reduce battery capacity. Furthermore, they may enhance side reactions at the interface between the positive electrode and the electrolyte, thereby reducing battery life and performance. Optionally, the mass percentage of the coating layer, based on the total mass of the positive electrode active material and 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%, etc. More preferably, the mass percentage of the coating layer, based on the total mass of the positive electrode active material and the coating layer, is 0.1% to 1%.

[0084] Another embodiment of this application provides a method for preparing a cathode material. The method for preparing the cathode material includes the following steps: mixing a cathode active material and a coating layer material to obtain a mixture, wherein the cathode active material comprises a material with the chemical formula LiNi. 1-x M xThe material is O2, wherein 0 ≤ x ≤ 0.2, M includes at least one of Co, Mn, Al, Fe, Cu, and V, and the coating material includes at least one of sulfur, selenium, and tellurium. The mixture is sintered under a protective gas atmosphere. This preparation method yields a positive electrode material comprising a positive electrode active material and a coating layer located on at least a portion of the surface of the positive electrode active material. The preparation method is simple, easy to implement, and readily applicable.

[0085] It is understood that in the preparation method of this embodiment, the sintered product is cooled to room temperature to obtain granular cathode material. Optionally, after cooling to room temperature, cathode material meeting particle size requirements can be obtained by sieving as needed. It is also understood that, unless otherwise specified, in this application, the term "room temperature" generally refers to 4℃~30℃, and optionally refers to 25±5℃.

[0086] In some embodiments, the sintering temperature for the sintering treatment is 250℃ to 350℃. Optionally, the sintering temperature for the sintering treatment is 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, etc. Sintering temperatures within this range are beneficial for the bonding of the positive electrode active material and the coating layer material, resulting in a positive electrode material with better performance.

[0087] In some embodiments, the sintering time of the sintering treatment is 3h to 10h. Optionally, the sintering time of the sintering treatment is 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0088] Optionally, the protective gas includes at least one of nitrogen, helium, neon, argon, and xenon.

[0089] Alternatively, the sintering process can be carried out in a tube furnace.

[0090] In some embodiments, the Dv50 of the coating material is ≤2μm. A particle size within this range allows the coating material to adhere well 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 good adhesion between the positive electrode active material and the coating layer. Optionally, the Dv50 of the coating 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.

[0091] In some embodiments, the coating material includes at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0092] Optionally, the mixture may be further subjected to grinding before sintering. More preferably, the grinding process is ball milling. The ball milling time is 5 to 8 hours, and the ball milling speed is 150 to 250 r / min. Even more preferably, the ball milling time is 5 hours, 6 hours, 7 hours, 8 hours, etc., and the ball milling speed is 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, 210 r / min, 220 r / min, 230 r / min, 240 r / min, 250 r / min, etc.

[0093] In some embodiments, the Dv50 of the milled mixture is 10 μm to 20 μm. For example, the Dv50 of the milled mixture is 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc. Controlling the Dv50 of the milled mixture within the range of 10 μm to 20 μm is beneficial to improving the sintering sufficiency, enhancing the sintering effect, and obtaining a cathode material with good performance.

[0094] Please see Figure 1 The diagram illustrates the preparation of the cathode material according to one embodiment of this application. In the preparation process, the cathode active material and the coating material are mixed to obtain a mixture. The mixture is then ground. Argon gas is then introduced into a tube furnace, and the mixture is sintered at 300°C for 6 hours. After sintering, the temperature is lowered to room temperature to obtain granular cathode material.

[0095] Another embodiment of this application provides a positive electrode slurry. This positive electrode slurry includes the above-described positive electrode material or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0096] Optionally, the positive electrode slurry may also include at least one of a conductive agent, a binder, and a solvent.

[0097] Another embodiment of this application provides a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, the positive electrode film layer including the above-described positive electrode material or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0098] Another embodiment of this application provides a method for preparing a positive electrode sheet. The method for preparing the positive electrode sheet includes the following steps: transferring the above-mentioned positive electrode slurry to at least one surface of a positive electrode current collector and curing it to form a positive electrode film layer on the corresponding surface of the positive electrode current collector.

[0099] Another embodiment of this application provides a secondary battery. The secondary battery includes the above-described positive electrode sheet or a positive electrode sheet prepared by the above-described method. The surface of the positive electrode active material of the positive electrode sheet has an electrolyte interface film (CEI film), which includes at least one of lithium sulfate, lithium selenate, and lithium tellurate. The presence of the electrolyte interface film is beneficial for improving the stability of the surface structure of the positive electrode active material, reducing side reactions between the positive electrode sheet and the electrolyte, and improving the cycle performance of the battery.

[0100] In some embodiments, the thickness of the electrolyte interface film is 5 nm to 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.

[0101] Optionally, the negative electrode active material of the secondary battery includes at least one of graphite and silicon-based materials. More preferably, when the negative electrode material includes both graphite and silicon-based materials, the silicon-based material accounts for ≤50% of the mass percentage of the negative electrode active material.

[0102] Optionally, the electrolyte for the secondary battery includes a lithium salt. Optionally, the lithium salt can be selected from LiTFSI, LiFSI, or LiN(C)2. a F 2a+1 SO2)(C b F 2b+1 One or more of the following: SO2), LiPF6, LiBF4, LiBOB, LiAsF6, LiCF3SO3, and LiClO4, where a and b are natural numbers.

[0103] Optionally, the electrolyte includes a non-aqueous organic solvent, which may be selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0104] Another embodiment of this application provides a method for preparing a secondary battery. The method includes the following steps: performing a formation treatment on a pre-finished secondary battery assembly having the above-described positive electrode sheet or a positive electrode sheet prepared by the above-described method, 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.

[0105] Understandably, a pre-finished secondary battery refers to a battery product produced before it is fully formed.

[0106] Optionally, the cutoff voltage of the formation treatment is 3.8V~4.1V. More preferably, the cutoff voltage of the formation treatment is 3.8V, 3.9V, 4.0V, 4.1V, etc. Using a higher formation cutoff voltage is more conducive to the formation of the CEI film, improves the conversion rate of impure lithium, and further improves the cycle performance of the battery.

[0107] Optionally, the formation current of the formation process is 0.08C to 0.15C. More optionally, the formation current of the formation process is 0.08C, 0.09C, 0.1C, 0.12C, 0.13C, 0.14C, 0.15C, etc.

[0108] Another embodiment of this application provides an electrical device. This electrical device includes the aforementioned secondary battery or a secondary battery prepared by the aforementioned method for preparing a secondary battery.

[0109] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0110] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0111] Positive electrode sheet

[0112] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0113] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material on the polymer substrate. Optionally, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Optionally, the polymer substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0115] As an example, the positive electrode active material may comprise positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 their modified compounds. Optionally, lithium cobalt oxide includes LiCoO2. Lithium nickel oxide includes LiNiO2. Lithium manganese oxide includes at least one of LiMnO2 and LiMn2O4. Lithium nickel cobalt manganese oxide includes LiNi... 1 / 3 Co 1 / 3Mn 1 / 3 O2 (NCM) 333 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 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 manganese iron phosphate, and lithium manganese iron 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.

[0116] 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 accounts for 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0117] 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.

[0118] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Optionally, the solvent includes N-methylpyrrolidone. The positive electrode slurry has a solid content of 40-80 wt%, and its viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is coated onto the surface of the positive current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 150-350 mg / m³. 2 The compacted density of the positive electrode sheet is 3.0-3.6 g / cm³. 3 The selectable value is 3.4-3.6 g / cm³. 3 The formula for calculating the compaction density is: Compaction density = Coating surface density / (Electrode thickness after extrusion - Current collector thickness).

[0119] It is understood that, in the embodiments of this application, the positive electrode sheet may be made by using 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.

[0120] Negative electrode sheet

[0121] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0122] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. Optionally, the metal material includes at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0124] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0125] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0126] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0 to 20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0127] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners. The other additives constitute 0-15% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer. Optionally, the thickener includes sodium carboxymethyl cellulose (CMC-Na).

[0128] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent to form a negative electrode slurry. Optionally, the solvent includes deionized water. The negative electrode slurry has a solid content of 30-70 wt% and its viscosity at room temperature is adjusted to 2000-10000 mPa·s. The obtained negative electrode slurry is coated onto a negative electrode current collector, dried, and then cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coating is 75-220 mg / m². 2 The compaction density of the negative electrode sheet is 1.2~2.0 g / m³. 3 .

[0129] It is understood that, in the embodiments of this application, the negative electrode sheet may be made by using the above-mentioned negative electrode sheet as the main body of the negative electrode sheet and forming a solid electrolyte interface film on the surface of the main body of the negative electrode sheet.

[0130] electrolytes

[0131] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0132] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0133] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5~5 mol / L.

[0134] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl 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).

[0135] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0136] Separating membrane

[0137] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0138] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0139] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0140] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0141] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0142] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0143] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0144] As for the aforementioned electrical device, a secondary battery can be selected according to its usage requirements.

[0145] Figure 4 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0146] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0147] Example

[0148] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0149] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0150] Example 1

[0151] In this embodiment, the positive electrode active material is LiNi. 0.9 Co 0.05 Mn 0.05 The initial lithium content of the positive electrode active material is 0.55% (O2). The coating material is elemental sulfur, which accounts for 0.5% of the total mass of the positive electrode active material and the coating. The Dv50 of the elemental sulfur is 1 μm. The positive electrode active material consists of primary and secondary particles, with the primary particles having a Dv50 of 5 μm and the secondary particles having a Dv50 of 15 μm. The mass ratio of primary to secondary particles is 2:8.

[0152] (1) Preparation method of the positive electrode material in this embodiment:

[0153] The positive electrode active material and the coating material were mixed and ball-milled at 200 rpm. The Dv50 of the ball-milled mixture was 17.9 μm. The ball-milled mixture was then sintered in a tube furnace under an argon protective atmosphere at 300℃ for 5 hours. After sintering, the mixture was cooled to room temperature to obtain the positive electrode material.

[0154] (2) Preparation method of positive electrode slurry in this embodiment:

[0155] The positive electrode material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNTs) were dry-mixed in a weight ratio of 77.3:10:8.7:2.7:1.3 until homogeneous. The mixture was stirred at a speed of 400-1000 r / s, followed by wetting, kneading, and dispersion treatments to obtain the positive electrode slurry. In this embodiment, the positive electrode slurry is as follows... Figure 5 As shown.

[0156] (3) The preparation method of the positive electrode sheet in this embodiment:

[0157] The positive electrode slurry is coated onto aluminum foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0158] (4) Preparation method of negative electrode sheet in this embodiment:

[0159] The negative electrode active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dry-mixed evenly in a weight ratio of 96.85:1.15:0.8:1.2, and then deionized water is added and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0160] (5) The preparation method of the electrolyte in this embodiment:

[0161] In an argon atmosphere glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), ethylene carbonate and ethyl methyl carbonate were mixed evenly in a volume ratio of 4:6. 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte.

[0162] (6) In this embodiment, polyethylene film is used as the isolation film.

[0163] (7) The battery preparation method in this embodiment:

[0164] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and then wound to obtain a bare cell. The bare cell is placed in the battery packaging, followed by electrolyte injection, encapsulation, settling, formation, shaping, and capacity testing to complete the preparation of the lithium-ion battery. The lithium-ion battery has a thickness of 4.2 mm, a width of 32 mm, and a length of 82 mm. Formation is performed in a formation machine with a cutoff voltage of 4V and a formation current of 0.1C.

[0165] The TEM image of the positive electrode sheet after formation in this embodiment is as follows: Figure 9 As shown, by Figure 9 It can be seen that an electrolyte interface film with a thickness of 15 nm was formed on the surface of the active material of the positive electrode.

[0166] Examples 2 to 11

[0167] Compared with Example 1, the difference between Examples 2 to 11 is that the mass percentage of the coating material and / or the positive electrode active material and / or the coating layer and / or the formation cutoff voltage are as shown in Table 1.

[0168] In Example 5, the mass ratio of sulfur to selenium in the coating material was 1:1. In Example 6, the mass ratio of sulfur to tellurium in the coating material was 1:1. In Example 7, the mass ratio of selenium to tellurium in the coating material was 1:1. In Example 7, the mass ratio of sulfur, selenium, and tellurium in the coating material was 1:1:1.

[0169] Example 12

[0170] The difference between Example 1 and Example 12 is that the mass percentage of the coating layer is 0.1%. The positive electrode slurry in Example 12 is as follows: Figure 7 As shown.

[0171] Example 13

[0172] The difference between Example 1 and Example 13 is that the cutoff voltage of the formation process is 3.7V.

[0173] Example 14

[0174] The difference between Example 1 and Example 14 is that the particle size of the coating material is 2 μm.

[0175] Example 15

[0176] The difference between Example 1 and Example 15 is that the particle size of the coating material is 3 μm.

[0177] Example 16

[0178] The difference between Example 1 and Example 16 is that the Dv50 of the ball-milled mixture is 25 μm.

[0179] Example 17

[0180] The difference between Example 1 and Example 17 is that the Dv50 of the ball-milled mixture is 5 μm.

[0181] Comparative Example 1

[0182] The difference between Comparative Example 1 and Example 1 is that no coating material is added. The positive electrode slurry in Comparative Example 1 is as follows: Figure 6 As shown.

[0183] Comparative Example 2

[0184] Compared to Example 1, Comparative Example 2 differs in that no coating material is added to the positive electrode material. Furthermore, the method for preparing the negative electrode sheet is as follows:

[0185] The negative electrode active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dry-mixed evenly in a weight ratio of 96.85:1.15:0.8:1.2. Then, 0.5% sulfur by mass is added, followed by deionized water and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is evenly coated onto the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0186] Comparative Example 3

[0187] The difference between Comparative Example 3 and Comparative Example 2 is that the negative electrode active material is graphite and SiO2. x Where 0 < x < 2, SiO x The mass percentage is 10%.

[0188] Comparative Example 4

[0189] The difference between Comparative Example 4 and Comparative Example 2 is that the positive electrode active material is different.

[0190] Comparative Example 5

[0191] The difference between Comparative Example 5 and Example 1 is that:

[0192] Preparation method of positive electrode slurry:

[0193] The cathode material, elemental sulfur, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNT) are dry-mixed and stirred evenly at a speed of 400~1000 r / s. Then, the mixture is wetted, kneaded, and dispersed to obtain the cathode slurry.

[0194] Comparative Example 6

[0195] 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, initial lithium content of the positive electrode active material is 0.06%.

[0196] Table 1

[0197]

[0198]

[0199] The testing methods are as follows in Table 1:

[0200] (1) The method for testing the amount of impure lithium is as follows:

[0201] Pretreatment: The active layer of the formed cathode electrode is scraped and ground into powder. 30g of powder of any particle size is weighed, 100ml of pure water is added and stirred for 30min. After standing for 10min, the mixture is filtered and a certain amount of filtrate is transferred.

[0202] Test: Use 0.05 mol / L hydrochloric acid standard solution, drain the solution to remove air bubbles from the burette, select potentiometric titrator 905 to start automatic detection, and read the corresponding results. Repeat the test in subsequent tests.

[0203] It is understandable that the initial amount of impure lithium in the positive electrode active material can be determined by grinding the positive electrode active material into powder and testing it according to the above method.

[0204] (2) The test method for DC internal resistance is as follows: At 25℃, the lithium-ion battery is charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current is less than 0.05C, and then discharged at 0.33C for 30 minutes, that is, the charge of the cell is adjusted to 50% SOC. Then, the positive and negative probes of the TH2523A AC internal resistance tester are connected to the positive and negative terminals of the battery respectively, and the internal resistance value of the battery is read through the internal resistance tester.

[0205] (3) The test method for capacity retention at 0.33C is as follows:

[0206] At 25°C, the lithium-ion battery was charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current was less than 0.05C, and then discharged at a constant current of 0.33C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process was repeated, and the capacity retention rate of the lithium-ion battery after 500 cycles was calculated.

[0207] The capacity retention rate (%) of a lithium-ion battery after 500 cycles at 25°C is calculated as follows: (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0208] (4) The test method for the storage capacity retention rate at 60℃ is as follows:

[0209] Before storage, at 25℃, the battery was charged to 4.25V with a constant current of 1 / 3C, then charged to 0.05C with a constant voltage of 4.25V, left to rest for 30 minutes, and then discharged to 2.8V with a constant current of 1 / 3C. The resulting capacity was recorded as the initial capacity C0. After storage at 60℃ for 100 days, the battery temperature was cooled to room temperature, and the above steps were repeated. The measured capacity was recorded as Cr. The battery capacity recovery rate after 100 days of storage is then calculated as H = Cr / C0 * 100%.

[0210] As shown in Table 1, introducing a coating layer into the cathode material helps reduce the amount of impurities on the surface of the cathode active material and improves the battery's cycle performance. Furthermore, from... Figures 5-8 It can be seen that introducing a coating layer and controlling its addition amount is beneficial to improving the fluidity and viscosity stability of the cathode slurry.

[0211] As can be seen from Comparative Example 6 and Example 1, LiNi 0.6 Co 0.2 Mn 0.2 The battery corresponding to O2 positive electrode active material is LiNi 0.9 Co 0.05 Mn 0.05 Batteries using O2 as the positive electrode active material exhibit better capacity retention, possibly because LiNi... 0.6 Co0.2 Mn 0.2 O2 cathode active material has a slightly better capacity retention rate than LiNi. 0.9 Co 0.05 Mn 0.05 O2 positive electrode active material.

[0212] Furthermore, as can be seen from Comparative Examples 6 and 4, and Examples 1 and 1, the capacity retention rate of the battery in Comparative Example 6 is only slightly improved compared to that in Comparative Example 4, relative to the results of Examples 1 and 1. This may be because the LiNi... 0.6 Co 0.2 Mn 0.2 The initial lithium content of the O2 cathode active material is lower than that of LiNi. 0.9 Co 0.05 Mn 0.05 The initial amount of impure lithium in the O2 cathode active material is controlled by the introduction of the coating material, affecting the LiNi content. 0.6 Co 0.2 Mn 0.2 The improvement in cycle performance of batteries using O2 positive electrode active materials is relatively small.

[0213] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0214] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode material, characterized in that, It includes a positive electrode active material and a coating layer located on at least a portion of the surface of the positive electrode active material, wherein 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, the coating layer includes at least one of sulfur, selenium and tellurium, and the positive electrode active material includes primary particles and secondary particles formed by the agglomeration of primary particles.

2. The cathode material according to claim 1, characterized in that, The mass ratio of the primary particles to the secondary particles is 1:9 to 4:6; Optionally, the mass ratio of the primary particles to the secondary particles is 2:8 to 3:

7.

3. The cathode material according to any one of claims 1 to 2, characterized in that, The Dv50 of the primary particles is 3 μm to 10 μm; and / or, The Dv50 of the secondary particles is 5μm~20μm.

4. The cathode material according to any one of claims 1 to 3, 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, Optionally, the atomic ratios of Co and Mn are equal; (3) The amount of impure lithium in the positive electrode active material is 0.5%~0.7%. Optionally, the amount of impure lithium in the positive electrode active material is 0.55% to 0.65%.

5. The cathode material according to any one of claims 1 to 4, 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, calculated as a percentage of the total mass of the positive electrode active material and the coating layer, is 0.01% to 6%. Optionally, the mass percentage of the coating layer is 0.1% to 1%, based on the mass percentage of the total mass of the positive electrode active material and the coating layer.

6. A method for preparing a positive electrode material, characterized in that, Includes the following steps: The positive electrode active material and the coating material are mixed to obtain a mixture, wherein the positive electrode active material includes 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, the coating material includes at least one of sulfur, selenium and tellurium, and the positive electrode active material includes primary particles and secondary particles formed by the agglomeration of primary particles; The mixture is sintered under a protective gas atmosphere.

7. The method for preparing the cathode material according to claim 6, characterized in that, The sintering process satisfies at least one of the following characteristics: (1) The sintering temperature of the sintering treatment is 250℃~350℃; (2) The sintering time of the sintering treatment is 3h~10h.

8. The method for preparing the cathode material according to any one of claims 6 to 7, characterized in that, The coating material has a Dv50 ≤ 2 μm.

9. The method for preparing the cathode material according to any one of claims 6 to 8, characterized in that, The process before sintering the mixture also includes: The mixture is then ground. Optionally, the Dv50 of the mixture after grinding is 10μm~20μm.

10. A positive electrode plate, characterized in that, It includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, wherein the positive electrode film layer comprises a positive electrode material prepared by any one of claims 1 to 5 or a positive electrode material prepared by any one of claims 6 to 9.

11. A secondary battery, characterized in that, The positive electrode sheet according to claim 10 is provided, wherein the surface of the positive active material of the positive electrode sheet has an electrolyte interface film, and the electrolyte interface film includes at least one of lithium sulfate, lithium selenate and lithium tellurate.

12. The secondary battery according to claim 11, characterized in that, The thickness of the electrolyte interface film is 5nm~20nm.

13. A method for preparing a secondary battery, characterized in that, Includes the following steps: A pre-finished secondary battery assembly equipped with the positive electrode sheet of claim 10 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 comprising at least one of lithium sulfate, lithium selenate, and lithium tellurate.

14. The method for preparing a secondary battery according to claim 13, 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.

15. An electrical appliance, characterized in that, The secondary battery includes the secondary battery according to any one of claims 11-12 or the secondary battery prepared by the method according to any one of claims 13-14.

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