Positive electrode material and its manufacturing method, positive electrode sheet and its use

Abstract

The present application provides a cathode material and a manufacturing method thereof, a cathode slurry, a cathode sheet and a manufacturing method thereof, a secondary battery and a manufacturing method thereof, and an electric device. The cathode material includes a cathode active material and a coating layer located on at least a part of the surface of the cathode active material, and the cathode active material has the chemical formula LiNi 1-x M x O2 (where 0≦x≦0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V), and the coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium. When the positive electrode material is used in the manufacture of a secondary battery, the coating layer reacts with residual lithium in the positive electrode active material to reduce the amount of residual lithium in the positive electrode active material of the secondary battery, thereby improving the cycle performance of the battery.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority from a Chinese patent application filed on March 1, 2023, with application number 2023101863731, entitled "Positive electrode material and manufacturing method thereof, positive electrode sheet and use thereof," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode material and a manufacturing method thereof, a positive electrode sheet, a secondary battery and a manufacturing method thereof, and an electric device. [Background technology]

[0003] This discussion may not necessarily constitute prior art, but rather merely provides background information relevant to the present application.

[0004] In secondary batteries, positive electrode active materials with a high nickel content have a high specific capacity, but also a high amount of residual lithium, which has some adverse effect on the performance of the battery. Summary of the Invention

[0005] The present application relates to a positive electrode material including a positive electrode active material and a coating layer located on at least a portion of a surface of the positive electrode active material, wherein the positive electrode active material has a chemical formula of LiNi 1-x M x O2 (where 0≦x≦0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V), and the coating layer includes at least one of sulfur element, selenium element, and tellurium element.

[0006] 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. The coating layer, which contains at least one of sulfur, selenium, and tellurium, is introduced onto the surface of the cathode active material. When the cathode material is used to manufacture a secondary battery, the coating layer reacts with the remaining lithium in the cathode active material, reducing the amount of remaining lithium in the cathode 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 includes Co and Mn.

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

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

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

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

[0013] In some embodiments, 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.

[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 coating layer has a thickness of 100 nm to 1000 nm.

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

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

[0019] This application is The chemical formula is LiNi 1-x M x a step of mixing a positive electrode active material containing a material of O2 (where 0≦x≦0.2, and M contains at least one of Co, Mn, Al, Fe, Cu, and V) with a coating layer material containing at least one of elemental sulfur, elemental selenium, and elemental tellurium to obtain a mixture; sintering the mixture under a protective gas atmosphere; Further provided is a method for producing a positive electrode material, comprising:

[0020] In some embodiments, the sintering temperature of the sintering process is 250°C to 350°C.

[0021] In some embodiments, the sintering time of the sintering process is 3 hours to 10 hours.

[0022] In some embodiments, the coating layer material has a Dv50≦2 μm.

[0023] In some embodiments, the method further comprises subjecting the admixture to a grinding treatment prior to the step of subjecting the admixture to a sintering treatment.

[0024] In some embodiments, the Dv50 of the admixture after the polishing treatment is 10 μm to 20 μm.

[0025] The present application further provides a positive electrode sheet including a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the above-described positive electrode material or a positive electrode material produced by the above-described method for producing a positive electrode material.

[0026] The present application further provides a secondary battery including the above-mentioned positive electrode sheet, wherein an electrolyte interface film including at least one of lithium sulfate, lithium selenate, and lithium tellurite is provided on a surface of the positive electrode active material of the positive electrode sheet.

[0027] In some embodiments, the electrolyte interfacial film has a thickness of 5 nm to 20 nm.

[0028] This application is and performing a chemical conversion treatment on the intermediate secondary battery product to which the positive electrode sheet is attached, thereby forming an electrolyte interfacial film containing at least one of lithium sulfate, lithium selenate, and lithium tellurite on a surface of the positive electrode active material of the positive electrode sheet. A method for manufacturing a secondary battery is also provided.

[0029] In some embodiments, the cutoff voltage of the chemical conversion treatment is 3.8V to 4.1V.

[0030] In some embodiments, the chemical conversion current for the chemical conversion treatment is 0.08C to 0.15C.

[0031] The present application further provides an electric device including the above secondary battery or a secondary battery manufactured by the above method for manufacturing a secondary battery. [Brief explanation of the drawings]

[0032] In order to more clearly explain the technical solution of the present application, the drawings used in the present application are briefly described below. The drawings described below only show some embodiments of the present application, and it is obvious that those skilled in the art can conceive of other drawings based on these drawings without creative work.

[0033] [Figure 1] FIG. 1 is a schematic diagram of the preparation of a positive electrode material in one embodiment of the present application. [Figure 2] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Figure 3] FIG. 3 is an exploded view of the secondary battery shown in FIG. 2 according to the embodiment of the present application. [Figure 4] 1 is a schematic diagram of an electrical device that uses a secondary battery according to an embodiment of the present application as a power source. [Figure 5] FIG. 1 is a schematic diagram of a positive electrode slurry in Example 1 of the present application. [Figure 6] FIG. 2 is a schematic diagram of a positive electrode slurry in Comparative Example 1 of the present application. [Figure 7] FIG. 1 is a schematic diagram of a positive electrode slurry in Example 12 of the present application. [Figure 8] 1 shows viscosity change curves of positive electrode slurries in Example 1 and Comparative Example 1 of the present application. [Figure 9] 1 is a transmission electron microscope image (TEM image) of a positive electrode sheet after chemical formation in Example 1 of the present application.

[0034] To better describe and explain the embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more drawings, in which additional detail or illustrations for the purposes of illustrating the drawings should not be considered as limiting the scope of any one of the disclosed inventions, the presently described embodiments and / or examples, and the best modes of these inventions as currently understood. DETAILED DESCRIPTION OF THE INVENTION

[0035] In order to facilitate the understanding of the present application, the present application will now be described more fully hereinafter with reference to the associated drawings, in which preferred embodiments of the present application are shown. However, the present application is not limited to the embodiments set forth herein, but may be embodied in many different forms. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. As used herein, the terms used in the specification of this application are only for the purpose of describing specific examples and are not intended to limit the scope of this application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0037] The "ranges" disclosed herein are defined by lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of that particular range. Such defined ranges may or may not include endpoints and may be arbitrarily combined; that is, any lower limit and any upper limit may be combined to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, the ranges of 60 to 110 and 80 to 120 are also understood to be predictable. Furthermore, if the minimum range values ​​are 1 and 2 and the maximum range values ​​are 3, 4, and 5, the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all predictable. In this application, unless otherwise specified, a numerical range of "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely shorthand for combinations of these numbers. Note that describing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is an integer, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and alternative embodiments in this application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all technical features and alternative technical features in this application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all steps in this application may be performed in sequence or randomly, and in some embodiments, are performed in sequence. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated above that the method may further include step (c), it means that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

[0041] Unless otherwise specified, the terms "comprise" and "comprises" in this application are open-ended but may also be closed-ended. For example, the terms "comprise" and "comprises" may further include or include other components not listed, or may include or include only the listed components.

[0042] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true or present and B is false or absent; A is false or absent and B is true or present; or A and B are both true or present.

[0043] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter described in this application can be measured by various measurement methods commonly used in this field. For example, they can be measured according to the methods shown in the examples of this application.

[0044] One embodiment of the present application is a positive electrode material including a positive electrode active material and a coating layer located on at least a portion of a surface of the positive electrode active material, wherein the positive electrode active material has a chemical formula of LiNi 1-x M x O2 (where 0≦x≦0.2 and M includes at least one of Co, Mn, Al, Fe, Cu, and V), and the coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium. The positive electrode material includes a positive electrode active material with a high nickel content and a coating layer located on at least a portion of the surface of the positive electrode active material. In the positive electrode material, a coating layer including at least one of elemental sulfur, elemental selenium, and elemental tellurium is introduced onto the surface of the positive electrode active material, so that when the positive electrode material is used to manufacture a secondary battery, the coating layer reacts with residual lithium in the positive electrode active material, reducing the amount of residual lithium in the positive electrode active material of the secondary battery and improving the cycle performance of the battery.

[0045] Specifically, when the positive electrode material is used in a secondary battery, the coating layer can initially react with the residual lithium in the positive electrode active material during the preparation of the positive electrode slurry, thereby reducing the amount of residual lithium, and the intermediate product generated during the reaction between the coating layer and the residual lithium in the positive electrode active material can improve the fluidity of the slurry and enhance the coating performance of the slurry.

[0046] Furthermore, when the positive electrode material is used in a secondary battery, the intermediate product can be electrochemically oxidized during the formation step to further react with residual lithium to form an electrolyte interfacial film (CEI film), thereby increasing the stability of the surface structure of the positive electrode active material, reducing side reactions between the positive electrode material and the electrolyte, lowering the impedance inside the battery, and further improving the cycle performance of the battery.In addition, during the formation step, the residual lithium can be converted into lithium ions through electrochemical oxidation, and the converted lithium ions are used to compensate for the lithium ion loss due to the formation of the solid electrolyte interfacial film (SEI film), thereby realizing the reuse of residual lithium and improving the battery capacity.

[0047] Furthermore, when the positive electrode material is used in a secondary battery, the coating layer can react with the solvent in the electrolyte through reduction and oxidation to produce a poly(ethylene oxide) (PEO)-based polymer and a lithium alkylate, which can form a conductive network that rapidly conducts lithium ions while mitigating the volume expansion of the electrode during charging, thus further improving the cycle performance of the battery.

[0048] Taking sulfur in the coating layer as an example, the reaction between the coating layer and the residual lithium in the positive electrode active material when preparing the positive electrode slurry may be represented by formula (1).

[0049] 4LiMO2+2S→4MO+Li2S2O3+Li2O Formula (1)

[0050] where M includes at least one of Co, Mn, Al, Fe, Cu, and V. As can be seen from formula (1), when this positive electrode material is used to prepare a positive electrode slurry, sulfur initially reacts with residual lithium in the positive electrode active material, thereby reducing the amount of residual lithium. Furthermore, the intermediate product lithium thiosulfate produced during the reaction between sulfur and residual lithium on the surface of the positive electrode active material can improve the fluidity of the slurry and enhance the coating performance of the slurry.

[0051] Furthermore, when the positive electrode material is used in the manufacture of a secondary battery, the reactions occurring in the formation step may be represented by equations (2) and (3).

[0052] Li2S2O3+Li2CO3-8e - →2Li2SO4+5CO2+8Li + Formula (2) 2LiMO2+S+2Li2CO3-4e - →2MO+Li2SO4+2CO2+4Li + Formula (3)

[0053] As can be seen from equations (2) and (3), during the formation step, Li2S2O3 is electrochemically oxidized to Li2SO4, while the remaining lithium compounds Li2O and Li2CO3 on the surface are removed, and the generated CO2 can be released along with other gases formed during the formation of the battery.

[0054] As can be seen from equations (1), (2), and (3), sulfur reduces LiMO2 and forms an MO protective layer on the surface of the positive electrode active material particles, while removing residual lithium compounds (RLCs) such as Li2O and Li2CO3 from the surface of the LiMO2 particles. Note that an electrochemically stable Li2SO4CEI film exists on the surface of the LiMO2 particles or exists independently, and the lithium ions released by the sulfur reaction are used to compensate for the loss of lithium ions due to the formation of the SEI film.

[0055] In some embodiments, x may be 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, etc. When 0≦x≦0.2, the positive electrode active material has a high nickel content, and the amount of residual lithium in the positive electrode active material is high. By providing a coating layer in the present application, when the positive electrode material is applied to a battery, the amount of residual lithium in the active material can be effectively reduced, which is beneficial to improving battery performance. Optionally, 0≦x≦0.1. More optionally, LiNi 1-x M x O2 is LiNi 0.8 M 0.2 O2, LiNi0.85 M 0.15 O2, LiNi 0.9 M 0.1 O2, LiNi 0.95 M 0.05 O2, etc. More preferably, 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 oxide.

[0056] In some embodiments, M includes Co and Mn. Furthermore, the atomic ratio of Co to Mn is equal. At this time, the positive electrode active material is LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 It may also be O2.

[0057] In some embodiments, the formula of the positive electrode active material is LiNi 1-x M x O2, with the proviso that 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 ratio of Co to Mn is equal.

[0058] In some embodiments, the residual lithium content of the positive electrode active material is 0.5% to 0.7%. For example, the residual lithium content of 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 residual lithium content is relatively high. When the residual lithium content is within this range, the coating layer and the positive electrode active material interact better, reducing the residual lithium content to a low content and improving battery performance. Optionally, the residual lithium content of the positive electrode active material is 0.55% to 0.65%.

[0059] In some embodiments, the positive electrode active material includes primary particles and secondary particles formed by agglomeration of the primary particles. The use of the primary particles and the secondary particles allows the positive electrode sheet to achieve a high degree of compaction.

[0060] Optionally, the mass ratio of the primary particles to the secondary particles is 1:9 to 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.

[0061] In some embodiments, the Dv50 of the primary particles is between 3 μm (micrometers) and 10 μm, and the Dv50 of the secondary particles is between 5 μm and 20 μm. More preferably, the Dv50 of the primary particles is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. 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.

[0062] In the present application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number of particles at 50% in a cumulative volume distribution curve, and is understood to mean that particles having a particle size smaller (or larger) than this particle size account for 50% of the total. For example, Dv50 can be easily measured using a laser particle size analyzer, such as a Mastersizer 2000E laser particle size analyzer manufactured by Malvern Instruments Ltd. in the UK, in accordance with GB / T 19077-2016 Laser Diffraction Method for Particle Size Analysis.

[0063] In some embodiments, the coating layer comprises at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0064] In some embodiments, the coating layer is located on the surface of the positive electrode active material particle. Furthermore, each positive electrode active material particle has a coating layer on its surface. In this way, the coating layer and the positive electrode active material interact better, thereby further reducing the amount of residual lithium in the positive electrode active material.

[0065] In some embodiments, the coating layer covers the entire positive electrode active material, whereby the coating layer can more effectively interact with the remaining lithium in the positive electrode active material and further reduce the amount of remaining lithium.

[0066] In some preferred examples of the coating layer, the thickness of the coating layer is 100 nm (nanometers) to 1000 nm, and more preferably, 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.

[0067] In some embodiments, the mass percentage of the coating layer relative to the total mass of the positive electrode active material and coating layer is 0.01% to 6%. If the mass percentage of the coating layer is too high, the presence of a large amount of coating layer on the surface of the positive electrode active material during secondary battery production may deteriorate 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) may react incompletely, causing the remaining RLCs to deteriorate the impedance, increase polarization, and reduce the battery capacity. Furthermore, it may also enhance side reactions at the interface between the positive electrode and the electrolyte, further reducing the battery's life and performance. Alternatively, the mass percentage of the coating layer relative to 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. Also, optionally, the mass percentage of the coating layer relative to the total mass of the positive electrode active material and the coating layer is 0.1% to 1%.

[0068] Another embodiment of the present application further provides a method for producing a cathode material, the method comprising: 1-x M xThe method includes the steps of: mixing a positive electrode active material containing O2 (where 0≦x≦0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V) with a coating layer material containing at least one of sulfur, selenium, and tellurium to obtain a mixture; and sintering the mixture in a protective gas atmosphere. This manufacturing method makes it possible to obtain a positive electrode material containing 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 manufacturing method is simple and easy to carry out, making it suitable for wide application.

[0069] In the manufacturing method of this embodiment, it is understood that a particulate positive electrode material can be obtained by cooling the sintered product to room temperature. Optionally, after cooling to room temperature, the product can be passed through a sieve as needed to obtain a positive electrode material that meets particle size requirements. Unless otherwise specified, it is further understood that in this application, the term "room temperature" generally refers to 4°C (Celsius) to 30°C, and optionally refers to 25±5°C.

[0070] In some embodiments, the sintering temperature is 250° C. to 350° C. Optionally, the sintering temperature is 250° C., 260° C., 270° C., 280° C., 290° C., 300° C., 310° C., 320° C., 330° C., 340° C., 350° C., etc. A sintering temperature within this range is advantageous for bonding between the positive electrode active material and the coating layer material, resulting in a positive electrode material with better performance.

[0071] In some embodiments, the sintering time of the sintering process is 3 hours to 10 hours. Optionally, the sintering time of the sintering process is 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0072] Optionally, the protective gas includes at least one of nitrogen gas, helium gas, neon gas, argon gas, and xenon gas.

[0073] Further alternatively, the sintering process may be carried out in a tube furnace.

[0074] In some embodiments, the coating layer material has a Dv50 of 2 μm or less. When the particle size of the coating layer material is within this range, it can adhere well to the surface of the positive electrode active material, facilitating the formation of the coating layer on the surface of the positive electrode active material while improving the bonding strength between the positive electrode active material and the coating layer. Optionally, the Dv50 of the coating layer material may be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, etc.

[0075] In some embodiments, the material of the coating layer includes at least one of elemental sulfur, elemental selenium, and elemental tellurium.

[0076] Optionally, the method further includes polishing the mixed material before sintering the mixed material. More preferably, the polishing is performed using a ball mill. The ball milling time is 5 to 8 hours, and the ball mill rotation speed is 150 to 250 r / min. Even more preferably, the ball milling time is 5, 6, 7, 8, etc. The ball mill rotation speed is 150 r / min (revolutions per minute), 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.

[0077] In some embodiments, the Dv50 of the mixed material after the polishing treatment is 10 μm to 20 μm. For example, the Dv50 of the mixed material after the polishing treatment is 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc. Controlling the Dv50 of the mixed material after the polishing treatment within the range of 10 μm to 20 μm is advantageous for more thorough sintering, improving the sintering effect, and obtaining a positive electrode material with good performance.

[0078] Please refer to FIG. 1, which shows a schematic diagram of the manufacturing process of a cathode material in one embodiment of the present application. In the manufacturing process, the cathode active material and the coating layer material are mixed to obtain a mixture. The mixture is then polished. Argon gas is passed through a tubular furnace and sintered at 300°C for 6 hours. After sintering, the mixture is cooled to room temperature to obtain particulate cathode material.

[0079] Another embodiment of the present application provides a positive electrode slurry, which includes the above-described positive electrode material or a positive electrode material produced by the above-described method for producing a positive electrode material.

[0080] Optionally, the positive electrode slurry may further include at least one of a conductive agent, a binder, and a solvent.

[0081] Another embodiment of the present application provides a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode material described above or a positive electrode material produced by the method for producing the positive electrode material described above.

[0082] Another embodiment of the present application provides a method for manufacturing a positive electrode sheet, comprising the steps of transferring the above-described positive electrode slurry onto at least one surface of a positive electrode current collector and curing the slurry to form a positive electrode film layer on the corresponding surface of the positive electrode current collector.

[0083] Another embodiment of the present application provides a secondary battery. The secondary battery includes the above-described positive electrode sheet or a positive electrode sheet manufactured by the above-described method for manufacturing a positive electrode sheet. The surface of the positive electrode active material of the positive electrode sheet is provided with an electrolyte interfacial film (CEI film) containing at least one of lithium sulfate, lithium selenate, and lithium tellurite. The presence of the electrolyte interfacial film improves the stability of the surface structure of the positive electrode active material and helps reduce side reactions between the positive electrode sheet and the electrolyte, which is advantageous for improving the cycle performance of the battery.

[0084] In some embodiments, the thickness of the electrolyte interfacial film is between 5 nm and 20 nm. Optionally, the thickness of the electrolyte interfacial film is 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, etc.

[0085] Optionally, as a negative electrode of a secondary battery, the negative electrode active material includes at least one of graphite and a silicon-based material. Further optionally, when the negative electrode active material includes graphite and a silicon-based material, the mass percentage of the silicon-based material in the negative electrode active material is ≦50%.

[0086] Optionally, the electrolyte of the secondary battery includes a lithium salt. Optionally, the lithium salt is LiTFSI, LiFSI, LiN(C a F 2a+1 SO2)(C b F 2b+1 SO2), LiPF6, LiBF4, LiBOB, LiAsF6, LiCF3SO3, and LiClO4, where a and b are natural numbers.

[0087] Optionally, the electrolyte solution includes a non-aqueous organic solvent, and the non-aqueous organic solvent may be one or more selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0088] Yet another embodiment of the present application provides a method for manufacturing a secondary battery, the method including the step of performing a chemical conversion treatment on the above-described positive electrode sheet or a secondary battery intermediate product equipped with the positive electrode sheet manufactured by the above-described method for manufacturing a positive electrode sheet, thereby forming an electrolyte interfacial film containing at least one of lithium sulfate, lithium selenate, and lithium tellurite on a surface of a positive electrode active material of the positive electrode sheet.

[0089] It is understood that the secondary battery intermediate product represents a battery product before chemical formation.

[0090] Alternatively, the cutoff voltage of the chemical conversion treatment is 3.8 V (volts) to 4.1 V. More preferably, the cutoff voltage of the chemical conversion treatment is 3.8 V, 3.9 V, 4.0 V, 4.1 V, etc. A higher cutoff voltage of the chemical conversion treatment makes it easier to form a CEI film, increasing the conversion rate of the remaining lithium and further improving the cycle performance of the battery.

[0091] Alternatively, the chemical conversion current for the chemical conversion treatment is 0.08 C to 0.15 C. More preferably, the chemical conversion current for the chemical conversion treatment is 0.08 C, 0.09 C, 0.1 C, 0.12 C, 0.13 C, 0.14 C, 0.15 C, etc.

[0092] Yet another embodiment of the present application provides an electric device, which includes the above-described secondary battery or a secondary battery manufactured by the above-described method for manufacturing a secondary battery.

[0093] The secondary battery and the electric device of the present application will be described below with appropriate reference to the drawings.

[0094] A secondary battery typically includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging, active ions are repeatedly inserted and removed between the positive and negative electrode sheets. The electrolyte serves to conduct ions between the positive and negative electrode sheets. The separator, located between the positive and negative electrode sheets, primarily serves to prevent short-circuiting between the positive and negative electrodes while allowing ions to pass through.

[0095] Positive electrode sheet The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0096] For example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode active material layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0097] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric substrate layer and a metal layer formed on at least one surface of the polymeric substrate layer. The composite current collector may be formed by forming a metal material on a polymeric substrate. Optionally, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Optionally, the polymeric 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).

[0098] For example, the positive electrode active material may include a positive electrode active material known in the art for use in batteries. For example, the positive electrode active material may include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials usable as positive electrode active materials in batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, 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 modified compounds thereof. Optionally, the lithium cobalt oxide may include LiCoO2. The lithium nickel oxide may include LiNiO2. The lithium manganese oxide may include at least one of LiMnO2 and LiMn2O4. Lithium nickel cobalt manganese oxide is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 ), LiNi0.5 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 ) Lithium nickel cobalt aluminum oxide contains at least one of LiNi 0.85 Co 0.15 Al 0.05 The positive electrode active material may include, but is not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. Optionally, the lithium iron phosphate includes LiFePO4 (LFP). The lithium manganese phosphate includes LiMnPO4. The weight ratio of the positive electrode active material in the positive electrode film layer is 80 wt% to 100 wt% based on the total weight of the positive electrode film layer.

[0099] In some embodiments, the positive electrode membrane layer optionally further includes a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode membrane layer is 0 wt % to 20 wt % based on the total weight of the positive electrode membrane layer.

[0100] In some embodiments, the positive electrode film layer optionally further includes a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 wt % to 20 wt % based on the total weight of the positive electrode film layer.

[0101] In some embodiments, the positive electrode sheet can be manufactured as follows. The components for manufacturing the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent to form a positive electrode slurry. Optionally, the solvent includes N-methylpyrrolidone. The solid content of the positive electrode slurry is adjusted to 40 wt% to 80 wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s (milliPascal·second) to 25000 mPa·s. The positive electrode slurry is applied to the surface of a positive electrode current collector, baked, and then cold-pressed using a cold rolling mill to form a positive electrode sheet. The unit application area density of the positive electrode powder is 150 mg / m 2 (milligrams / square meter) ~ 350mg / m 2 The compaction ratio of the positive electrode sheet is 3.0 g / cm 3 (grams / cubic centimeter) ~ 3.6g / cm 3 and selectively 3.4 g / cm 3 ~3.6g / cm 3 The formula for calculating the degree of compaction is: degree of compaction = coating surface density / (thickness of electrode sheet after rolling - thickness of current collector).

[0102] It is understood that the positive electrode sheet in the examples of the present application may be produced by using the above-described positive electrode sheet as a positive electrode sheet body and forming a solid electrolyte interface film on the surface of the positive electrode sheet body.

[0103] Negative electrode sheet The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0104] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two facing surfaces of the negative electrode current collector.

[0105] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, a copper foil may be used as the metal foil. The composite current collector may include a polymeric substrate layer and a metal layer formed on at least one surface of the polymeric substrate layer. The composite current collector may be formed by forming a metal material on a polymeric substrate. Optionally, the metal material includes at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The polymeric substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0106] In some embodiments, the negative electrode active material may be a known negative electrode active material used in batteries in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one selected from silicon elemental, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from tin elemental, tin-oxygen compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials usable as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight ratio of the negative electrode active material in the negative electrode film layer is 70 wt % to 100 wt % based on the total weight of the negative electrode film layer.

[0107] In some embodiments, the negative electrode membrane layer optionally further includes a binder. The binder may be at least one selected from 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 membrane layer is 0 to 30 wt % based on the total weight of the negative electrode membrane layer.

[0108] In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 wt % to 20 wt % based on the total weight of the negative electrode film layer.

[0109] In some embodiments, the negative electrode membrane layer optionally further includes other additives, such as a thickener. The weight ratio of the other additives in the negative electrode membrane layer is 0 wt % to 15 wt % based on the total weight of the negative electrode membrane layer. Optionally, the thickener includes sodium carboxymethyl cellulose (CMC-Na).

[0110] In some embodiments, the negative electrode sheet can be manufactured as follows. The components for manufacturing the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent to form a negative electrode slurry. Optionally, the solvent includes deionized water. The solid content of the negative electrode slurry is adjusted to 30 wt% to 70 wt%, and the viscosity at room temperature is adjusted to 2000 mPa·s to 10000 mPa·s. The resulting negative electrode slurry is applied to a negative electrode current collector, followed by a drying process and cold pressing, such as a roll press, to obtain a negative electrode sheet. The unit application area density of the negative electrode powder is 75 mg / m. 2 ~220mg / m 2 The compaction rate of the negative electrode sheet is 1.2 g / m 3~2.0g / m 3 is.

[0111] It is understood that the negative electrode sheet in the examples of the present application may be produced by using the above-mentioned negative electrode sheet as a negative electrode sheet body and forming a solid electrolyte interface film on the surface of the negative electrode sheet body.

[0112] electrolyte The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. In the present application, the type of electrolyte is not specifically limited and can be selected as needed. For example, the electrolyte may be liquid, gel, or all solid.

[0113] In some embodiments, the electrolyte uses an electrolytic solution, which includes an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt may be one or more selected from lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5 mol / L to 5 mol / L.

[0115] In some embodiments, the solvent may be one or more selected from 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0116] In some embodiments, the electrolyte solution optionally further includes an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve some battery performance, such as an additive that can improve the overcharge performance of the battery or an additive that can improve the high-temperature or low-temperature performance of the battery.

[0117] Separator In some embodiments, the secondary battery further includes a separator. In the present application, the type of separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0118] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the layers may be the same or different, and are not particularly limited.

[0119] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be fabricated into an electrode assembly by a winding process or a lamination process.

[0120] In some embodiments, the secondary battery may include an exterior body that can be used to encapsulate the electrode assembly and electrolyte.

[0121] In some embodiments, the exterior of the secondary battery may be a hard can such as a hard plastic can, an aluminum can, or a steel can. The exterior of the secondary battery may be a soft pack such as a pouch-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate. In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. For example, FIG. 2 shows a secondary battery 5 having a rectangular structure as an example.

[0122] In some embodiments, referring to FIG. 3 , the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates are surrounded to form a receiving cavity. The case 51 may have an opening communicating with the receiving cavity, and the cover plate 53 may be provided to cover the opening and seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed in the receiving cavity. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and this can be selected by those skilled in the art according to specific actual needs.

[0123] The present application further provides an electric device including the secondary battery provided herein. The secondary battery may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric 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.), trains, ships, satellites, energy storage systems, etc.

[0124] The electrical device may be a secondary battery selected depending on the requirements of its use.

[0125] 4 shows an example of an electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, which may employ a battery pack or a battery module to meet the demands of the electric device for high power and high energy density from secondary batteries.

[0126] Other examples of the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such devices usually need to be thin, and therefore may use a secondary battery as a power source.

[0127] In order to clarify the technical problems, technical solutions, and beneficial effects of the present application, the present application will be described in more detail below with reference to examples and drawings. Of course, the described examples are only a portion of the examples of the present application, and not all of the examples. The following description of at least one exemplary embodiment is merely illustrative in nature and does not constitute any limitation on the present application and its applications. Based on the examples in the present application, other embodiments that can be obtained by those skilled in the art without any creative work are all within the scope of protection of the present application.

[0128] Unless specific techniques or conditions are specified in the examples, they are performed in accordance with techniques or conditions described in the literature in the field or in accordance with product specifications. Reagents or equipment used are conventional, commercially available products unless the manufacturer is specified.

[0129] Example 1 In this example, the positive electrode active material is LiNi 0.9 Co 0.05 Mn 0.05 The cathode active material was O2, the initial residual lithium content was 0.55%, the coating layer material was elemental sulfur, and the mass percentage of elemental sulfur in the total mass of the cathode active material and coating layer was 0.5%. The Dv50 of elemental sulfur was 1 μm. The cathode active material consisted of primary particles and secondary particles, where the Dv50 of the primary particles was 5 μm, the Dv50 of the secondary particles was 15 μm, and the mass ratio of the primary particles to the secondary particles was 2:8.

[0130] (1) Manufacturing Method of the Positive Electrode Material in this Example The positive electrode active material and coating layer material were mixed and ball milled at 200 r / min, resulting in a Dv50 of 17.9 μm. The ball milled mixture was then sintered in a tubular furnace using argon gas as a protective atmosphere at a sintering temperature of 300°C for 5 hours. After sintering was complete, the mixture was cooled to room temperature to obtain the positive electrode material.

[0131] (2) Preparation method of positive electrode slurry in this example The positive electrode material, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and carbon nanotubes (CNT) were uniformly dry mixed and stirred in a weight ratio of 77.3:10:8.7:2.7:1.3, and the mixture was stirred and mixed at a rotation speed of 400 r / s (revolutions per second) to 1000 r / s, followed by wetting, kneading, and dispersion treatment to obtain a positive electrode slurry. The positive electrode slurry in this example is as shown in Figure 5.

[0132] (3) Manufacturing Method of Positive Electrode Sheet in this Example The positive electrode slurry was applied onto an aluminum foil, and the aluminum foil was baked, cold pressed, and slit to obtain a positive electrode sheet.

[0133] (4) Manufacturing Method of Negative Electrode Sheet in this Example The negative electrode active material, artificial graphite, the conductive agent, carbon black, the binder, styrene butadiene rubber (SBR), and the thickener, sodium carboxymethyl cellulose (CMC-Na), were uniformly dry-mixed in a weight ratio of 96.85:1.15:0.8:1.2, and then deionized water was added and mixed uniformly to prepare a negative electrode slurry. The negative electrode slurry was then uniformly applied to the copper foil of the negative electrode current collector, and after baking, cold pressing, and slitting, a negative electrode sheet was obtained.

[0134] (5) Method for preparing the electrolyte solution in this example In an argon atmosphere glove box (H2O<0.01 ppm (parts per million), O2<0.01 ppm), the organic solvents ethylene carbonate and ethyl methyl carbonate were mixed uniformly at a volume ratio of 4:6, and 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent. The mixture was stirred uniformly to obtain an electrolyte solution.

[0135] (6) In this example, a polyethylene film is used as the separator.

[0136] (7) Battery Manufacturing Method in the Present Example The positive electrode sheet, separator, and negative electrode sheet were stacked in this order, and the separator was interposed between the positive electrode sheet and the negative electrode sheet, and the resulting structure was rolled up to obtain a bare cell. The bare cell was placed in a battery housing, and then the electrolyte was injected and sealed. The battery was then left to stand, chemically formed, molded, and its capacity measured to complete the production of a lithium-ion battery. The lithium-ion battery had a thickness of 4.2 mm (millimeters), a width of 32 mm, and a length of 82 mm. Chemical formation was performed in a chemical forming machine, with a chemical formation cutoff voltage of 4 V and a chemical formation current of 0.1 C.

[0137] A TEM image of the positive electrode sheet after the anodization in this example is shown in Figure 9. As can be seen from Figure 9, an electrolyte interfacial film with a thickness of 15 nm was formed on the surface of the active material of the positive electrode sheet.

[0138] Examples 2 to 11 Examples 2 to 11 differ from Example 1 in that the materials of the coating layer and / or the positive electrode active material and / or the mass percentages of the coating layer and / or the cutoff voltages of the chemical conversion were as shown in Table 1.

[0139] Here, in Example 5, the mass ratio of sulfur to selenium in the coating layer material was 1:1. In Example 6, the mass ratio of sulfur to tellurium in the coating layer material was 1:1. In Example 7, the mass ratio of selenium to tellurium in the coating layer material was 1:1. In Example 7, the mass ratio of sulfur, selenium, and tellurium in the coating layer material was 1:1:1.

[0140] Example 12 Example 12 differs from Example 1 in that the mass percentage of the coating layer is 0.1%. The positive electrode slurry in Example 12 is as shown in FIG.

[0141] Example 13 Example 13 differs from Example 1 in that the cutoff voltage of the chemical conversion treatment is 3.7V.

[0142] Example 14 Example 14 differs from Example 1 in that the particle size of the material of the coating layer is 2 μm.

[0143] Example 15 Example 15 differs from Example 1 in that the particle size of the material of the coating layer is 3 μm.

[0144] Example 16 Example 16 differs from Example 1 in that the Dv50 of the mixed material after ball milling was set to 25 μm.

[0145] Example 17 Example 17 differs from Example 1 in that the Dv50 of the mixed material after ball milling was set to 5 μm.

[0146] Comparative Example 1 Comparative Example 1 differs from Example 1 in that no material for the coating layer was added. The positive electrode slurry in Comparative Example 1 is as shown in FIG.

[0147] Comparative Example 2 Comparative Example 2 differs from Example 1 in the following respects: No coating layer material was added to the positive electrode material. The negative electrode sheet was manufactured by the following method: The negative electrode active material artificial graphite, the conductive agent carbon black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were uniformly dry mixed in a weight ratio of 96.85:1.15:0.8:1.2, and then 0.5% by mass of elemental sulfur was added, and deionized water was added and mixed uniformly to prepare a negative electrode slurry. The negative electrode slurry was then uniformly applied to the copper foil of the negative electrode current collector, and after baking, cold pressing, and slitting, a negative electrode sheet was obtained.

[0148] Comparative Example 3 In Comparative Example 3, the negative electrode active material was graphite and SiO x (However, 0 <x<2であり、SiO x The difference from Comparative Example 2 is that the mass percentage of the

[0149] Comparative Example 4 Comparative Example 4 differs from Comparative Example 2 in the positive electrode active material.

[0150] Comparative Example 5 Comparative Example 5 differs from Example 1 in the following respects.

[0151] The positive electrode slurry can be prepared by the following method: The positive electrode material, elemental sulfur, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and carbon nanotubes (CNTs) were uniformly dry mixed and stirred at a rotation speed of 400 r / s to 1000 r / s, and then wetted, kneaded, and dispersed to obtain a positive electrode slurry.

[0152] Comparative Example 6 In Comparative Example 6, the positive electrode active material was LiNi 0.6 Co 0.2 Mn 0.2O2 differs from Example 1 in that the initial residual lithium amount in the positive electrode active material is 0.06%.

[0153] [Table 1] JPEG2025534166000003.jpg252170 JPEG2025534166000004.jpg77170In Table 1, the measurement methods are as follows.

[0154] (1) The method for measuring the amount of remaining lithium is as follows.

[0155] Pretreatment: The powder from the active layer of the chemically formed positive electrode sheet was scraped off and ground into a powder. 30 g (grams) of powder of a given particle size was weighed out, 100 ml (milliliters) of pure water was added, and the mixture was stirred for 30 minutes. After leaving it to stand for 10 minutes, the mixture was suction filtered and a certain amount of the filtrate was collected.

[0156] Measurement: Select a 0.05 mol / L (mole / liter) hydrochloric acid standard solution, drain the burette to remove any air bubbles, select the potentiometric titrator 905 to start automatic measurement, read the corresponding result, and then repeat the measurement.

[0157] It is understood that the initial amount of remaining lithium in the positive electrode active material can also be measured by grinding the positive electrode active material into powder and then measuring it according to the above-mentioned method.

[0158] (2) The DC internal resistance is measured as follows: At 25°C, a lithium-ion battery is charged to 4.25V at a constant current of 0.33C, then charged at a constant voltage of 4.25V until the current drops below 0.05C, and then discharged at 0.33C for 30 minutes, adjusting the cell's electrical charge to 50% SOC. Then, the positive and negative test leads of the TH2523A AC internal resistance meter are connected to the positive and negative terminals of the battery, respectively, and the battery's internal resistance is read using the internal resistance meter.

[0159] (3) The 0.33C capacity retention rate was measured as follows.

[0160] At 25°C, a lithium-ion battery is charged to 4.25 V at a constant current of 0.33 C, then charged at a constant voltage of 4.25 V until the current falls below 0.05 C, and then discharged to 2.8 V at a constant current of 0.33 C. This charge-discharge process is repeated to calculate the capacity retention rate of the lithium-ion battery after 500 cycles.

[0161] Capacity retention rate (%) of a lithium-ion battery after 500 cycles at 25°C = (discharge capacity at 500th cycle / discharge capacity at 1st cycle) x 100%

[0162] (4) The method for measuring the storage capacity retention rate at 60°C is as follows.

[0163] Before storage, the battery is charged to 4.25V at 25°C with a constant current of 1 / 3C, then charged at a constant voltage of 4.25V at 0.05C, allowed to stand for 30 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity is designated as the initial capacity C0. After storing at 60°C for 100 days, the battery is cooled to room temperature, and the above steps are repeated to measure the capacity. If the capacity is designated as Cr, the battery capacity recovery rate after 100 days of storage, H, is equal to Cr / C0 * 100%.

[0164] As can be seen from Table 1, introducing a coating layer into a positive electrode material is advantageous in reducing the amount of residual lithium on the surface of the positive electrode active material and improving the cycle performance of the battery. Furthermore, as can be seen from Figures 5 to 8, introducing a coating layer and controlling its amount is advantageous in improving the fluidity and viscosity stability of the positive electrode slurry.

[0165] As can be seen from Comparative Example 6 and Example 1, the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 The battery compatible with O2 has a positive electrode active material of LiNi 0.9 Co 0.05 Mn 0.05The capacity retention rate is better than that of batteries that support O2. This is because the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 The capacity retention rate corresponding to O2 itself is 0.9 Co 0.05 Mn 0.05 This may be due to it being slightly better than O2.

[0166] As can be seen from Comparative Examples 6 and 4, and Example 1 and Comparative Example 1, the increase in the capacity retention rate of the battery of Comparative Example 6 relative to Comparative Example 4 is smaller than the results of Example 1 and Comparative Example 1. This is because the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 The initial residual lithium content of O2 is the positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 Because it is lower than O2, the introduction of the coating layer material 0.6 Co 0.2 Mn 0.2 This may be due to the relatively small improvement in the cycling performance of the battery in response to O2.

[0167] The technical features of the above-described embodiments can be combined in any manner, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, but combinations of these technical features should be considered to be within the scope described in this specification, unless they are inconsistent.

[0168] The above examples only represent some embodiments of the present application, and the description is specific and detailed, but should not be understood as limiting the patent scope of the invention. It should be noted that various modifications and improvements that a person skilled in the art can make without departing from the concept of the present application are all within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims. [Explanation of symbols]

[0169] 5 Secondary battery 6. Electrical Equipment 51 cases 52 Electrode assembly 53 Lid plate

Claims

1. 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 has a chemical formula of LiNi １－ｘ M ｘ O ２ (where 0≦x≦0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V), and the coating layer includes at least one of sulfur element, selenium element, and tellurium element.

2. The positive electrode active material is (1) 0≦x≦0.1; (2) M contains Co and Mn; optionally, the atomic ratio of Co to Mn is equal; (3) the amount of residual lithium in the positive electrode active material is 0.5% to 0.7%; Alternatively, the amount of residual lithium in the positive electrode active material is 0.55% to 0.65%; (4) The positive electrode active material includes primary particles and secondary particles formed by aggregation of the primary particles, Alternatively, 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; optionally, the mass ratio of the primary particles to the secondary particles is 1:9 to 4:6; The positive electrode material according to claim 1 , which satisfies at least one of the following characteristics:

3. The coating layer is (1) The coating layer contains at least one of elemental sulfur, elemental selenium, and elemental tellurium; (2) The thickness of the coating layer is 100 nm to 1000 nm; (3) the mass percentage of the coating layer relative to the total mass of the positive electrode active material and the coating layer is 0.01% to 6%; optionally, a mass percentage of the coating layer relative to the total mass of the positive electrode active material and the coating layer is 0.1% to 1%; The positive electrode material according to claim 1 or 2, which satisfies at least one of the following characteristics:

4. The chemical formula is LiNi １－ｘ M ｘ O ２ (where 0≦x≦0.2, and M includes at least one of Co, Mn, Al, Fe, Cu, and V) with a coating layer material including at least one of elemental sulfur, elemental selenium, and elemental tellurium to obtain a mixture; sintering the mixture under a protective gas atmosphere; A method for producing a positive electrode material, comprising:

5. The sintering process is (1) The sintering temperature of the sintering treatment is 250°C to 350°C; (2) The sintering time of the sintering treatment is 3 hours to 10 hours; The method for producing a positive electrode material according to claim 4 , wherein the method satisfies at least one of the following characteristics:

6. The method for producing a positive electrode material according to claim 4 or 5, wherein the material of the coating layer has a Dv50≦2 μm.

7. before the step of sintering the admixture, Further comprising subjecting the mixture to a polishing treatment; Optionally, the Dv50 of the admixture after the polishing treatment is 10 μm to 20 μm; A method for producing the positive electrode material according to any one of claims 4 to 6.

8. 8. A positive electrode sheet comprising: a positive electrode current collector; and a positive electrode film layer located on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode material according to any one of claims 1 to 3 or a positive electrode material produced by the method for producing a positive electrode material according to any one of claims 4 to 7.

9. 9. A secondary battery including the positive electrode sheet according to claim 8, wherein a surface of the positive electrode active material of the positive electrode sheet is provided with an electrolyte interface film including at least one of lithium sulfate, lithium selenate, and lithium tellurite.

10. 10. The secondary battery according to claim 9, wherein the electrolyte interfacial film has a thickness of 5 nm to 20 nm.

11. 9. A method for manufacturing a secondary battery, comprising: performing a chemical conversion treatment on a secondary battery intermediate product having the positive electrode sheet according to claim 8 attached thereto, thereby forming an electrolyte interface film containing at least one of lithium sulfate, lithium selenate, and lithium tellurite on a surface of a positive electrode active material of the positive electrode sheet.

12. The chemical conversion treatment is (1) The cut-off voltage of the chemical conversion treatment is 3.8 V to 4.1 V; (2) The chemical conversion current of the chemical conversion treatment is 0.08 C to 0.15 C; The method for manufacturing a secondary battery according to claim 11, wherein at least one of the following characteristics is satisfied:

13. An electric device comprising the secondary battery according to any one of claims 9 and 10, or a secondary battery manufactured by the method for manufacturing a secondary battery according to any one of claims 11 and 12.

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