Positive electrode materials and their preparation methods, positive electrode sheets, batteries and electrical devices

Abstract

This application discloses a positive electrode material and its preparation method, a positive electrode sheet, a battery, and an electrical device. The positive electrode material includes a positive electrode active material, a one-dimensional conductive material distributed on the surface of the positive electrode active material, and an additive. At least a portion of the one-dimensional conductive material is encapsulated by the additive, which contains a reducing chalcogenide element. This application introduces an additive containing a reducing chalcogenide element onto the surface of the positive electrode active material. This additive effectively removes residual lithium compounds from the surface of the positive electrode active material. Simultaneously, a one-dimensional conductive material is introduced onto the surface of the positive electrode active material, with at least a portion of the one-dimensional conductive material encapsulated by the additive. The one-dimensional conductive material acts as a carrier to anchor the additive, and it can also construct a three-dimensional conductive system, thereby improving the conductivity of the positive electrode material.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries, as secondary batteries, can reversibly convert chemical energy and electrical energy, and are ideal carriers for human energy utilization and storage. Since the advent of lithium ion batteries, they have been widely used due to their advantages such as long service life, high energy density and low maintenance cost. Currently, lithium ion batteries have been used in various fields such as portable electronic devices, new energy vehicles and energy storage systems.

[0003] As a key factor affecting the performance of lithium ion batteries, the positive electrode active material often determines the cycle life, energy density and power density of lithium ion batteries. Due to the preparation process of the positive electrode active material or the characteristics of the positive electrode active material itself, residual lithium compounds (RLCs) such as lithium hydroxide, lithium carbonate and lithium oxide are easily formed on the surface of the positive electrode active material. Generally, the residual lithium compounds have poor conductivity, which increases the positive electrode / electrolyte interface impedance, exacerbates the battery polarization, and deteriorates the discharge capacity and cycle stability, thereby negatively affecting the performance of the battery. SUMMARY

[0004] In view of the above problems, the embodiments of the present application provide a positive electrode material and a preparation method thereof, a positive electrode sheet, a battery and an electric device, which aim to alleviate the negative effects of residual lithium compounds in the positive electrode active material on the performance of the battery.

[0005] In a first aspect, the embodiments of the present application provide a positive electrode material, comprising: a positive electrode active material, and a one-dimensional conductive material and an additive distributed on the surface of the positive electrode active material, at least part of the one-dimensional conductive material being wrapped by the additive, and the additive containing a chalcogen element with reducibility.

[0006] The positive electrode material provided in the embodiments of the present application comprises a positive electrode active material, one-dimensional conductive material and additive, at least part of the one-dimensional conductive material is wrapped by the additive, the one-dimensional conductive material and the additive are distributed on the surface of the positive electrode active material, and the additive contains a chalcogen element with reducibility. By introducing the additive on the surface of the positive electrode active material, the additive contains a chalcogen element with reducibility (usually a low-valence chalcogen element), the chalcogen element with reducibility in the additive is easy to be oxidized and react with residual lithium compounds (such as LiOH, Li2O, Li2CO3, etc.) on the surface of the positive electrode active material, thereby generating an intermediate product (such as Li2S2O3, Li2Se2O3, Li2Te2O3, etc.) containing a chalcogen element with an intermediate valence on the surface of the positive electrode active material in situ, and in the subsequent formation process, the intermediate product continues to react, and the chalcogen element with reducibility is also continuously oxidized and reacts with the residual lithium compounds, and finally all generate a final product (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.) containing a chalcogen element with a high valence, and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the positive electrode active material in the formation process, thereby removing the residual lithium compounds on the surface of the positive electrode active material and improving the conductivity and electrochemical performance of the positive electrode active material. Further, the one-dimensional conductive material is introduced on the surface of the positive electrode active material, and the one-dimensional conductive material is located on the surface of the positive electrode active material and can be overlapped together to form a conductive system, thereby improving the overall conductivity of the material; at the same time, at least part of the one-dimensional conductive material is wrapped by the additive, which can increase the area of physical combination between the additive and the one-dimensional conductive material, and further increase the combination area between the additive and the one-dimensional carbon material due to the high specific surface area of the one-dimensional conductive material, thereby increasing the combination force between the additive and the one-dimensional conductive material, improving the stability of the combination of the two, and achieving the anchoring of the additive. Since the additive is wrapped on the surface of the one-dimensional conductive material, when the one-dimensional conductive material is overlapped together, the additive also wraps the joint of the overlapped one-dimensional conductive material, thereby not affecting the conductive system formed by the one-dimensional conductive material.

[0007] In summary, in the embodiments of the present application, the one-dimensional conductive material not only serves as a carrier to anchor the additive, but also is distributed on the surface of the positive electrode active material, and the conductive network formed by the one-dimensional conductive material makes the overall conductivity of the positive electrode material better; in addition, the one-dimensional conductive material has a large specific surface area, which not only promotes the anchoring of the additive but also improves the contact area between the one-dimensional conductive material and the positive electrode active material, thereby accelerating the electron / ion transmission rate and the kinetic reaction speed of the chalcogen element on the positive electrode material.

[0008] In some embodiments, the chalcogen element includes at least one of a sulfur element, a selenium element and a tellurium element.

[0009] By setting the additive to contain a chalcogen element with reducibility, the chalcogen element including at least one of a sulfur element, a selenium element and a tellurium element, the above-mentioned chalcogen element can react with residual lithium compounds, consume the residual lithium compounds while promoting the growth of the CEI film on the positive electrode, and improve the electrochemical performance of the battery; in this process, additional lithium ions are released synchronously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0010] In some embodiments, the chalcogen element includes a sulfur element, and the additive includes at least one of a sulfur element, a metal sulfide, a polysulfide, a sulfur-containing organic polymer or copolymer, and a polymerized sulfur.

[0011] The above-mentioned additive contains a sulfur element, and the valence of the sulfur element is low. The sulfur element has reducibility, which is beneficial to eliminate residual lithium compounds on the surface of the positive active material.

[0012] In some embodiments, the additive includes a chalcogen element element.

[0013] The valence of the chalcogen element element is zero, and the chalcogen element element itself has strong reducibility, so it is easy for the chalcogen element element to eliminate residual lithium compounds. At the same time, the composition of the chalcogen element element is simple, and the introduction of the chalcogen element element into the surface of the positive active material can reduce the introduction of other elements, thereby reducing the risk of side reactions.

[0014] In some embodiments, the one-dimensional conductive material includes a one-dimensional conductive carbon material.

[0015] In addition to having a large specific surface area, the one-dimensional conductive carbon material also has strong adsorption capacity, so that the one-dimensional conductive carbon material can effectively adsorb the additive attached to the surface of the one-dimensional conductive carbon material, enhance the binding capacity between the one-dimensional conductive carbon material and the additive, and improve the anchoring effect of the one-dimensional conductive carbon material on the additive.

[0016] In some embodiments, the one-dimensional conductive carbon material includes at least one of a short carbon fiber, a nanometer carbon fiber and a carbon nanotube.

[0017] The above-mentioned one-dimensional conductive carbon material has good conductivity, which is beneficial to build a more developed conductive network. At the same time, it also has a large specific surface area, which is beneficial to improve the contact area between the one-dimensional conductive carbon material and the additive, and to improve the anchoring effect on the additive.

[0018] In some embodiments, the short carbon fiber includes at least one of a PAN-based carbon fiber, a phenolic-based carbon fiber, a viscose-based carbon fiber, a pitch-based carbon fiber, a biomass-based carbon fiber and an activated carbon fiber.

[0019] The short carbon fiber filaments have good electrical conductivity, large specific surface area, and are easy to obtain and have high cost performance.

[0020] In some embodiments, the short carbon fiber filaments have a diameter of 100 nm-500 nm.

[0021] By setting the diameter of the short carbon fiber filaments to 100 nm-500 nm, the short carbon fiber filaments have a large specific surface area, which improves the anchoring effect of the additives, and the short carbon fiber filaments have good dispersibility, which improves the electrical conductivity of the positive electrode material.

[0022] In some embodiments, the short carbon fiber filaments have a length of 1 μm-5 μm.

[0023] By setting the length of the short carbon fiber filaments to 1 μm-5 μm, the short carbon fiber filaments have good contact with the surface of the positive electrode active material, and the short carbon fiber filaments can be well overlapped together and form a conductive network, which improves the electrical conductivity of the positive electrode material.

[0024] In some embodiments, the mass percentage of the chalcogen element is 0.02wt%-5wt% based on the total mass of the positive electrode material.

[0025] By setting the mass percentage of the chalcogen element in the positive electrode material to 0.02wt%-5wt%, residual lithium compounds on the surface of the positive electrode active material can be effectively removed, and the increase in battery polarization caused by excessive chalcogen elements can be prevented.

[0026] In some embodiments, the mass percentage of the one-dimensional conductive material is greater than 0 and less than or equal to 1wt% based on the total mass of the positive electrode material.

[0027] By setting the mass percentage of the one-dimensional conductive material in the positive electrode material to be greater than 0 and less than or equal to 1wt%, the positive electrode material has good electrical conductivity and processing performance.

[0028] In some embodiments, the surface of the positive electrode active material is coated with a coating layer, and the coating layer comprises a first sub-coating layer, and the first sub-coating layer comprises the one-dimensional conductive material and the additives wrapped on the one-dimensional conductive material.

[0029] By wrapping the one-dimensional conductive material wrapped with the additives on the surface of the positive electrode active material to form the first sub-coating layer, the additives can remove residual lithium compounds on the surface of the positive electrode active material, and the performance of the positive electrode active material is improved.

[0030] In some embodiments, the coating layer further comprises a second sub-coating layer, the second sub-coating layer is arranged on the side of the first sub-coating layer away from the positive active material, the second sub-coating layer comprises the conductive agent and the binder, the content of the chalcogen element in the second sub-coating layer is greater than or equal to 0 and less than the content of the chalcogen element in the first sub-coating layer.

[0031] By coating the first sub-coating layer and the second sub-coating layer on the surface of the positive active material in sequence, and the content of the chalcogen element in the first sub-coating layer is greater than the content of the chalcogen element in the first sub-coating layer, the first sub-coating layer serves as the inner layer, the high specific surface one-dimensional conductive material is used as the conductive agent in the first sub-coating layer, which is conducive to fixing the additive and inhibiting the outward diffusion of the chalcogen element, the second sub-coating layer serves as the outer layer, which can use one-dimensional conductive material as the conductive agent or other carbon materials as the conductive agent, thereby expanding the material selection range and facilitating cost control, and the content of the chalcogen element in the second sub-coating layer is less than the content of the chalcogen element in the first sub-coating layer, on the one hand, the content of the chalcogen element in the second sub-coating layer is reduced, which can reduce the outward diffusion of the chalcogen element, and on the other hand, the second sub-coating layer as the outer layer can form a barrier to the first sub-coating layer as the inner layer, thereby alleviating the outward diffusion of the chalcogen element in the first sub-coating layer, because the chalcogen element tends to flow to the negative electrode after diffusing outward, and the chalcogen element reacts with active lithium in the negative electrode, thereby causing lithium consumption and reducing the battery capacity.

[0032] In some embodiments, the content of the chalcogen element in the second sub-coating layer is greater than 0, and the coating layer further comprises a third sub-coating layer, the third sub-coating layer is coated on the surface of the second sub-coating layer, and the third sub-coating layer comprises the conductive agent and the binder.

[0033] By coating the first sub-coating layer, the second sub-coating layer and the third sub-coating layer on the surface of the positive active material in sequence, and the content of the chalcogen element in each sub-coating layer decreases from the inside to the outside, and the third sub-coating layer as the outermost layer does not contain the chalcogen element, which can provide a diffusion space for the chalcogen element and enhance the blocking effect of the chalcogen element, thereby limiting as much chalcogen element as possible inside the positive electrode material.

[0034] In some embodiments, the thickness of the coating layer is 100 nm to 1000 nm.

[0035] By setting the thickness of the coating layer to 100 nm to 1000 nm, the residual lithium compounds can be effectively removed while ensuring the theoretical specific capacity of the positive electrode material.

[0036] In some embodiments, the mass percentage of the coating layer based on the total mass of the positive electrode material is 0.01 wt% to 6 wt%; optionally, the mass percentage of the coating layer is 0.1 wt% to 1 wt%.

[0037] By setting the mass percentage of the coating layer in the positive electrode material to 0.01wt%-6wt%, the residual lithium compound is effectively removed while the theoretical specific capacity of the positive electrode material is ensured.

[0038] In some embodiments, the positive electrode active material comprises a nickel-rich active material with a chemical formula of Li a Ni m Co n M 1-m-n O2, wherein M comprises at least one of Mn and Al, wherein m≥0.6, n≤0.2, 0.9≤a≤1.2; optionally, the m≥0.9.

[0039] The present application introduces an additive on the surface of the nickel-rich active material, the additive contains a chalcogen element with reducibility, the Ni, Co, Mn in the nickel-rich active material exist in the form of Ni 3+ / Ni 2+ , Co 3+ and Mn 4+ ions, the chalcogen element with reducibility in the additive is easily oxidized by the nickel-rich active material and reacts with the residual lithium compound on the surface of the nickel-rich active material to generate an intermediate product containing a chalcogen element with an intermediate valence in situ on the surface of the nickel-rich active material, and in the subsequent formation process, the intermediate product continues to react, and the chalcogen element with reducibility is also continuously oxidized and reacts with the residual lithium compound, and finally all generate a final product containing a chalcogen element with a high valence (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), while the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the nickel-rich active material during the formation process, thereby removing the residual lithium compound on the surface of the nickel-rich active material and improving the electrical conductivity and electrochemical performance of the nickel-rich active material; in this process, additional lithium ions are also released simultaneously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0040] In some embodiments, the DV50 particle size of the positive electrode active material is 5μm-15μm.

[0041] By setting the DV50 particle size of the positive electrode active material to 5μm-15μm, the positive electrode material can have better processing performance and electrochemical performance.

[0042] In a second aspect, the embodiments of the present application provide a preparation method of a positive electrode material, comprising:

[0043] Mixing the one-dimensional conductive material and the additive to obtain a mixture, the additive containing a chalcogen element with reducibility;

[0044] sintering the mixture to melt the additive, and at least part of the one-dimensional conductive material is wrapped by the additive, thereby obtaining a sintered material;

[0045] stirring the sintered material with the positive electrode active material, thereby obtaining the positive electrode material.

[0046] The preparation method of the positive electrode material provided in the embodiments of the present application melts the additive by sintering the mixture of the one-dimensional conductive material and the additive, and at least part of the one-dimensional conductive material is wrapped by the additive, which increases the physical contact area of the additive and the one-dimensional conductive material, and in combination with the large specific surface area of the one-dimensional conductive material itself, the combination ability of the additive and the one-dimensional conductive material is enhanced, and the additive containing the chalcogen element is effectively fixed. Further, the sintered material obtained after sintering is stirred and mixed with the positive electrode active material, so that the one-dimensional conductive material wrapped with the additive is distributed on the surface of the positive electrode active material, thereby forming the positive electrode material. Since the one-dimensional conductive material itself has good conductivity, the one-dimensional conductive material is used to form a conductive network, and even after being wrapped with the additive, the conductive network can also be well connected, thereby ensuring the overall conductivity of the positive electrode material. In addition, the additive wrapped on the surface of the one-dimensional conductive material will contact the positive electrode active material, and in this process, the chalcogen element with reducing property in the additive will undergo an oxidation-reduction reaction with the metal cations in the positive electrode active material and consume the residual lithium compound on the surface of the positive electrode active material to generate an intermediate product containing the chalcogen element with an intermediate valence (such as Li2S2O3, Li2Se2O3, Li2Te2O3, etc.) in situ on the surface of the positive electrode active material, and in the subsequent formation process, the intermediate product continues to react, and the chalcogen element with reducing property is also continuously oxidized and reacts with the residual lithium compound, and finally generates a final product containing the chalcogen element with a high valence (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the positive electrode active material during the formation process, thereby removing the residual lithium compound on the surface of the positive electrode active material and improving the conductivity and electrochemical performance of the positive electrode active material. In the process of converting the chalcogen element with reducing property into the CEI film, additional lithium ions are also released synchronously to compensate for the loss of lithium ions caused by the formation of the SEI film, thereby ensuring the capacity of the battery. In addition, the preparation method of the positive electrode material provided in the embodiments of the present application is simple, easy to operate, and conducive to industrialization.

[0047] In some embodiments, the chalcogen element includes at least one of a sulfur element, a selenium element, and a tellurium element.

[0048] By setting the additive to contain a chalcogen element with reducibility, the chalcogen element including at least one of a sulfur element, a selenium element and a tellurium element, the above chalcogen element can react with residual lithium compounds, consume the residual lithium compounds while promoting the growth of the CEI film on the positive electrode, and improve the electrochemical performance of the battery; in this process, additional lithium ions are released synchronously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0049] In some embodiments, the additive includes a chalcogen element simple substance.

[0050] The valence of the chalcogen element simple substance is zero, and the chalcogen element simple substance itself has strong reducibility, so that the chalcogen element simple substance is easy to eliminate residual lithium compounds, and the composition of the chalcogen element simple substance is single, so that the introduction of the chalcogen element simple substance to the surface of the positive active material can reduce the introduction of other elements, thereby reducing the risk of side reactions.

[0051] In some embodiments, the one-dimensional conductive material includes a one-dimensional conductive carbon material.

[0052] In addition to having a large specific surface area, the one-dimensional conductive carbon material also has strong adsorption capacity, so that the one-dimensional conductive carbon material can effectively adsorb the additive attached to the surface of the one-dimensional conductive carbon material, enhance the binding capacity between the one-dimensional conductive carbon material and the additive, and improve the anchoring effect of the one-dimensional conductive carbon material on the additive.

[0053] In some embodiments, the additive includes a sulfur simple substance, the temperature of the sintering treatment is 180°C-220°C, and / or the sintering time is 5h-7h.

[0054] By using a sulfur simple substance as the additive, compared with other additives, the chemical properties of the sulfur simple substance are more active, the effect of eliminating residual lithium compounds is better, and the raw material of the sulfur simple substance is easy to obtain and has low cost. Using the sulfur simple substance as the additive has high cost performance. Further, by setting the temperature of the sintering treatment to 180°C-220°C, the sulfur simple substance can exist in a molten liquid state stably in this temperature range, and then be coated on the surface of the one-dimensional conductive material. In addition, by setting the sintering time to 5h-7h, the content of the sulfur simple substance in the positive electrode material can be effectively controlled, so that the sulfur simple substance can effectively eliminate residual lithium compounds without causing an increase in battery polarization.

[0055] In some embodiments, the DV50 particle size of the additive is greater than 0 and less than or equal to 1μm; optionally, the DV50 particle size of the additive is 100nm-500nm.

[0056] By setting the DV50 particle size of the additive to be greater than 0 and less than or equal to 1 μm, within this range, the dispersion effect of the additive is good, and the combination of the additive and the one-dimensional conductive material is better when the additive is pre-loaded with the one-dimensional conductive material.

[0057] In some embodiments, the mixing treatment includes a ball milling treatment.

[0058] By designing a ball milling treatment in the mixing treatment, on the one hand, the limitation on the particle size of the additive before the mixing treatment can be reduced, and on the other hand, the particle size of the additive can be reduced through the ball milling treatment, thereby improving the combination stability of the additive and the one-dimensional conductive material.

[0059] In some embodiments, the rotation speed of the stirring treatment is 400 r / s ~ 1000 r / s.

[0060] By setting the rotation speed of the stirring treatment to be 400 r / s ~ 1000 r / s, the sintered material and the positive active material can be effectively mixed together.

[0061] In some embodiments, the positive active material includes a nickel-rich active material with a chemical formula of Li a Ni m Co n M 1-m-n O2, wherein M includes at least one of Mn and Al, m ≥ 0.6, n ≤ 0.2, 0.9 ≤ a ≤ 1.2; optionally, m ≥ 0.9.

[0062] The present application introduces an additive on the surface of the nickel-rich active material, the additive contains a chalcogen element with reducing property, and the Ni, Co, Mn in the nickel-rich active material are reduced to Ni 3+ / Ni 2+ , Co 3+ , and Mn 4+The ion exists in the form of ions, and the sulfur element with reducing property in the additive is easily oxidized by the nickel-rich active material and reacts with the residual lithium compound on the surface of the nickel-rich active material to generate an intermediate product containing an intermediate valence state of the sulfur element in situ on the surface of the nickel-rich active material, and in the subsequent formation process, the intermediate product continues to react, and the sulfur element with reducing property is also continuously oxidized and reacts with the residual lithium compound, and finally all generate a final product containing a high valence state of the sulfur element (for example, Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the nickel-rich active material during the formation process, thereby removing the residual lithium compound on the surface of the nickel-rich active material and improving the conductivity and electrochemical performance of the nickel-rich active material; in this process, additional lithium ions are also released to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0063] In a third aspect, the embodiments of the present application provide a positive electrode tab, comprising a positive electrode current collector and a positive electrode material layer combined on the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material provided in the first aspect of the embodiments of the present application or the positive electrode material prepared by the preparation method provided in the second aspect of the embodiments of the present application.

[0064] The positive electrode tab provided in the embodiments of the present application comprises a positive electrode current collector and a positive electrode material layer, and the positive electrode material layer comprises the positive electrode material described above, so that the content of residual lithium compound in the positive electrode tab is low, the overall conductivity of the positive electrode tab is improved, and the cycle performance is improved.

[0065] In a fourth aspect, the embodiments of the present application provide a battery comprising the positive electrode tab provided in the third aspect of the embodiments of the present application.

[0066] The battery provided in the embodiments of the present application comprises the positive electrode tab described above, and the cycle performance of the battery is stable and the rate performance is good.

[0067] In a fifth aspect, the embodiments of the present application provide an electric device comprising the battery provided in the fourth aspect of the embodiments of the present application.

[0068] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0069] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the illustrative embodiments. The accompanying drawings are included to provide a description of the illustrative embodiments and are not intended to limit the scope of the application. Moreover, the drawings are not necessarily drawn to scale. In the drawings:

[0070] Figure 1 Structure diagram of a vehicle for some embodiments of the application;

[0071] Figure 2 Structure diagram of an explosion of a battery for some embodiments of the application;

[0072] Figure 3 Structure diagram of an explosion of a battery cell for some embodiments of the application;

[0073] Figure 4 Structure diagram of an electrode assembly for some embodiments of the application;

[0074] Figure 5 Structure diagram of a positive electrode material provided by some embodiments of the application.

[0075] Reference signs in the detailed description of the embodiments are as follows:

[0076] 20, electrode assembly; 101, negative electrode tab; 102, positive electrode tab; 201, negative electrode lug; 202, positive electrode lug; 203, separator;

[0077] 30, battery cell; 301, shell; 302, end cover; 303, negative electrode adapter plate; 304, positive electrode adapter plate; 305, insulating member;

[0078] 40, battery; 401, box body; 4011, box body; 4012, box cover;

[0079] 50, electric device; 501, controller; 502, motor;

[0080] 6, positive electrode active material particle;

[0081] 71, first sub-coating layer; 72, second sub-coating layer; 73, third sub-coating layer. DETAILED DESCRIPTION

[0082] The embodiments of the technical solutions of the application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, and therefore only serve as examples, and cannot limit the protection scope of the application.

[0083] 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 this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. Unless otherwise required by context, singular terms shall include pluralities and vice versa. Unless otherwise required by context, the use herein of the singular is also to be construed as a reference to the plural and vice versa.

[0084] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise explicitly and specifically limited.

[0085] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification is not necessarily all referring to the same embodiment, or to a particular embodiment, or to a particular set of embodiments. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0086] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0087] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), and similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0088] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0089] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "linking", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0090] Lithium ion batteries, as secondary batteries, can reversibly convert chemical energy and electrical energy, and are ideal carriers for humans to utilize and store energy. Since the advent of lithium ion batteries, they have been widely used due to their advantages such as long service life, high energy density, and low maintenance cost. Currently, lithium ion batteries have been used in various fields such as portable electronic devices, new energy vehicles, and energy storage systems.

[0091] The positive active material is a key factor affecting the performance of lithium ion batteries, and often determines the cycle life, energy density, and power density of lithium ion batteries. Due to the preparation process of the positive active material or the characteristics of the positive active material itself, residual lithium compounds (RLCs) such as lithium hydroxide, lithium carbonate, and lithium oxide are easily formed on the surface of the positive active material. Generally, residual lithium compounds have poor electrical conductivity, which increases the positive electrode / electrolyte interface impedance, exacerbates battery polarization, and deteriorates the discharge capacity and cycle stability, which negatively affects the performance of the battery.

[0092] To reduce the content of residual lithium compounds on the surface of the positive active material, the related art introduces an additive containing low-valence chalcogen elements on the surface of the positive active material, and utilizes the low-valence chalcogen elements in the additive to be oxidized and reduced to high-valence chalcogen elements during formation and to react with residual lithium compounds to remove the residual lithium compounds. However, the introduction of the additive containing low-valence chalcogen elements not only affects the electrical conductivity of the positive active material, but also has the problem of insufficient anchoring of the additive itself, which causes the additive to easily separate from the positive active material, resulting in insufficient reaction and incomplete removal of residual lithium compounds.

[0093] Based on this, the application introduces an additive on the surface of the positive electrode active material, the additive contains a sulfur element with reducing property (usually a low-valence sulfur element), the sulfur element with reducing property in the additive is easily oxidized and reacts with residual lithium compounds (such as LiOH, Li2O, Li2CO3, etc.) on the surface of the positive electrode active material to generate an intermediate product containing a sulfur element with an intermediate valence (such as Li2S2O3, Li2Se2O3, Li2Te2O3, etc.) in situ on the surface of the positive electrode active material, and in the subsequent formation process, the intermediate product continues to react, and the sulfur element with reducing property is also continuously oxidized and reacts with the residual lithium compounds, and finally all generate a final product containing a sulfur element with a high valence (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the positive electrode active material during the formation process, thereby removing the residual lithium compounds on the surface of the positive electrode active material and improving the conductivity and electrochemical performance of the positive electrode active material. Further, one-dimensional conductive materials are introduced on the surface of the positive electrode active material, and the one-dimensional conductive materials are located on the surface of the positive electrode active material and can be connected together to form a conductive system, thereby improving the overall conductivity of the material; at the same time, at least part of the one-dimensional conductive materials are wrapped by the additive, which can increase the physical bonding area between the additive and the one-dimensional conductive materials, and due to the high specific surface area of the one-dimensional conductive materials, the bonding area between the additive and the one-dimensional conductive materials is further increased, the bonding force between the additive and the one-dimensional conductive materials is increased, thereby improving the stability of the combination of the two and anchoring the additive. Since the additive is wrapped on the surface of the one-dimensional conductive material, when the one-dimensional conductive materials are connected together, the additive also wraps the junction of the connected one-dimensional conductive materials, so as not to affect the conductive system formed by the one-dimensional conductive materials.

[0094] Some embodiments of the application disclose a battery which can be used in, but is not limited to, an electric device such as a vehicle, a ship or an aircraft. A power supply system of the electric device can be composed of the battery disclosed in the application.

[0095] Some embodiments of the present application provide a power consuming device using a battery as a power source. The power consuming device can be, but is not limited to, a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be, but is not limited to, a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be, but is not limited to, a pure electric vehicle, a hybrid electric vehicle, or a range extended electric vehicle. The spacecraft includes an airplane, a rocket, a space shuttle, a spacecraft, and the like. The electric toy includes a stationary or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy, an electric airplane toy, and the like. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, an electric planer, and the like.

[0096] The following embodiments are described by taking a vehicle as an example for convenience of description.

[0097] Please refer to Figure 1 , Figure 1 A structural schematic diagram of a vehicle is provided for some embodiments of the present application. The vehicle is internally provided with a battery 40. The battery 40 can be arranged at the bottom, the head, or the tail of the vehicle. The battery 40 can be used for power supply of the vehicle, for example, the battery 40 can be used as an operating power source of the vehicle. The vehicle can further include a controller 501 and a motor 502. The controller 501 is used to control the battery 40 to supply power to the motor 502, for example, to meet the power demand of the vehicle during starting, navigation, and driving.

[0098] In some embodiments of the present application, the battery 40 can not only be used as an operating power source of the vehicle, but also be used as a driving power source of the vehicle, to replace or partially replace fuel or natural gas to provide driving power for the vehicle.

[0099] In some embodiments of the present application, the battery 40 is a secondary battery. The secondary battery has various forms, including but not limited to a battery monomer, a battery module, a battery pack, and the like. Here, the secondary battery refers to a battery that can be activated by charging after discharging.

[0100] Please refer to Figure 2 , Figure 2 An exploded view of the battery 40 is provided for some embodiments of the present application. The battery 40 includes a box body 401 and a battery monomer 30. The battery monomer 30 is accommodated in the box body 401. The box body 401 is used to provide an accommodation space for the battery monomer 30. The box body 401 can have various structures.

[0101] In some embodiments, the box 401 can include a box body 4011 and a box cover 4012, which are coupled to each other and together define a receiving space for receiving the battery cell 30. Optionally, the box body 4011 can be a hollow structure with one end open, and the box cover 4012 can be a plate-shaped structure, which is coupled to the open end of the box body 4011.

[0102] In the battery 40, the battery cell 30 can be multiple, and the multiple battery cells 30 can be connected in series, in parallel, or in a mixed manner. The mixed connection means that there are both series and parallel connections among the multiple battery cells 30. The multiple battery cells 30 can be directly connected in series, in parallel, or in a mixed manner, and then the multiple battery cells 30 are received in the box 401; of course, the battery 40 can also be that the multiple battery cells 30 are first connected in series, in parallel, or in a mixed manner to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a mixed manner to form a whole, which is received in the box 401. The battery 40 can also include other structures, such as a busbar component (not shown in the figure), for realizing the electrical connection among the multiple battery cells 30. Among them, the battery cell 30 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes.

[0103] Please refer to Figure 3 , Figure 3 is an exploded view of the battery cell 30 in some embodiments of the present application. The battery cell 30 refers to a basic unit for realizing the mutual conversion between chemical energy and electrical energy, and is also the smallest unit for constituting a battery. As Figure 3 , the battery cell 30 includes a shell 301, an end cover 302, an electrode assembly 20, and other functional components.

[0104] The shell 301 is a hollow structure with one end open, and the shell 301 is used to cooperate with the end cover 302 to form an internal environment for receiving the electrode assembly 20, the electrolyte, and other functional components. The shell 301 can be in various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 301 can be determined according to the specific shape and size of the electrode assembly 20. The material of the shell 301 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited herein.

[0105] The end cover 302 refers to a component that covers the opening of the housing 301 to isolate the internal environment of the battery cell 30 from the external environment. Optionally, the shape of the end cover 302 can be adapted to the shape of the housing 301 to fit the housing 301. Optionally, the end cover 302 can be made of a material with certain hardness and strength, such as aluminum alloy, so that the end cover 302 is less likely to deform when subjected to extrusion collision, allowing the battery cell 30 to have higher structural strength and improved safety performance. The material of the end cover 302 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited herein.

[0106] In some embodiments, the battery cell 30 further includes functional components such as a negative tab 303 and a positive tab 304, where the negative tab 303 is used to electrically connect with the negative tab on the electrode assembly 20, and the positive tab 304 is used to electrically connect with the positive tab on the electrode assembly 20 for outputting or inputting the electrical energy of the battery cell 30. It can be understood that the negative tab 303 is made of conductive material, and the material of the negative tab 303 can be, but is not limited to, copper, iron, aluminum, etc. The positive tab 304 is made of conductive material, and the material of the positive tab 304 can be, but is not limited to, copper, iron, aluminum, etc.

[0107] In some embodiments, the battery cell 30 further includes an insulating member 305 located inside the housing 301 for isolating the housing 301 from the electrode assembly 20 to reduce the risk of short circuit. For example, the insulating member 305 can be plastic, rubber, etc.

[0108] The housing 301 can contain one or more electrode assemblies 20.

[0109] Please refer to Figure 4 , Figure 4 is a structural schematic diagram of the electrode assembly 20 in some embodiments of the present application. The electrode assembly 20 is a component in which electrochemical reactions occur in the battery cell 30. The electrode assembly 20 is mainly formed by winding or stacking the electrode sheet structure in which the negative electrode sheet 101 and the positive electrode sheet 102 are integrated, and an insulating film 203 is usually provided between adjacent negative electrode sheets 101 and positive electrode sheets 102.

[0110] The negative electrode sheet 101 includes a negative current collector and a negative material layer coated on the surface of the negative current collector. Taking a lithium ion battery as an example, the material of the negative current collector can include copper, and the negative material layer includes a negative material, which can include a silicon-based material, etc.

[0111] The positive electrode tab 102 includes a positive current collector and a positive material layer coated on the surface of the positive current collector. Taking a lithium ion battery as an example, the material of the positive current collector can include aluminum, and the positive material layer includes a positive material, which can include lithium cobaltate, lithium iron phosphate, ternary lithium, or lithium manganate, etc.

[0112] The isolation film 203 is a porous plastic film that allows lithium ions in the electrolyte to pass freely, but separates the negative electrode tab 101 and the positive electrode tab 102, so that the electrons inside the battery cannot pass freely.

[0113] The negative current collector and the positive current collector also have parts that are not coated with an active material layer, and these parts without the active material layer are provided with connecting tabs. Specifically, the negative current collector is connected with a negative tab 201, and the positive current collector is connected with a positive tab 202. During the charging and discharging process of the battery, the positive material layer and the negative material layer react with the electrolyte, and the tab 201 is connected with a negative adapter tab 303 and the positive tab 202 is connected with a positive adapter tab 304 to form a current loop. Of course, in some embodiments, the part of the negative current collector and the positive current collector that is not coated with an active material layer each constitutes a tab.

[0114] Some embodiments of the present application provide a positive material, a positive active material, and a one-dimensional conductive material and an additive distributed on the surface of the positive active material, at least part of the one-dimensional conductive material is wrapped by the additive, and the additive contains a sulfur element with reducing property.

[0115] The positive material includes a positive active material, which refers to a compound with three-dimensional lithium ion channels, which is used on the positive electrode for reversible insertion and extraction of lithium ions. Optionally, the positive active material includes at least one of lithium nickel cobaltate, lithium nickel manganate, and lithium nickel cobalt manganate. Lithium nickel cobaltate (LiNi 1-x Co x O2, referred to as NC binary material) has a layered structure and good electrochemical performance and thermal stability. Lithium nickel manganate (LiNi x Mn 2-xO4, referred to as NM binary material) is a material with spinel structure prepared based on improvement of original spinel lithium manganate, and has higher cycle stability and voltage platform compared with lithium manganate. Nickel cobalt lithium manganate (referred to as NCM ternary material) contains Ni, Co and Mn three transition metal elements, which effectively overcomes the respective shortcomings of LiNiO2, LiCoO2 and LiMnO2, and in the electrochemical performance and thermal stability tests, the three transition metals in the material can exhibit their respective characteristics, and have high development potential. Optionally, the positive active material can be doped and modified. Optionally, the doping elements include, but are not limited to, at least one of Zr, Zn, Cu, V, Ti, Sr, Sb, Y, W, Nb, B, Ba, Ce, Si, Ga, Sn, Mo, P, Al, Fe, Mg, Cr, F, N, S, Cl.

[0116] The one-dimensional conductive material refers to a fiber-like or tubular material in which electrons are free to move in only one non-nanoscale direction. The one-dimensional conductive material includes, but is not limited to, metal nanowires, one-dimensional conductive carbon materials. The metal nanowires include, but are not limited to, silver nanowires, copper nanowires, and the like. The one-dimensional conductive carbon material can be one-dimensional nanocarbon material or one-dimensional micrometer carbon material. Optionally, the one-dimensional conductive carbon material includes at least one of carbon fiber, nanocarbon fiber and carbon nanotube.

[0117] The additive contains a chalcogen element with reducing property, where the chalcogen element refers to a sulfur element and an element with similar chemical properties to the sulfur element. Optionally, the chalcogen element includes an element in the oxygen family except oxygen. Optionally, the chalcogen element includes at least one of a sulfur (S) element, a selenium (Se) element and a tellurium (Te) element. The additive contains the chalcogen element, where the additive can be a compound, and the chalcogen element is one of the constituent elements of the compound, or the additive can be a single substance, for example, the chalcogen element single substance itself is used as the additive. The chalcogen element has reducing property, that is, the chalcogen element can be oxidized to a high-valence chalcogen element through an oxidation-reduction reaction. Optionally, the chalcogen element has a valence less than or equal to zero, that is, a low-valence chalcogen element, at this time, the chalcogen element is easy to be oxidized to a high-valence chalcogen element. As an example, the chalcogen element includes sulfur, the low-valence sulfur has a valence of -2 or zero, and the high-valence sulfur has a valence of +6 or +4.

[0118] The one-dimensional conductive material and the additive are distributed on the surface of the positive active material, which can be loose distribution of the one-dimensional conductive material and the additive on the surface of the positive active material, or the one-dimensional conductive material and the additive form a coating layer to wrap the surface of the positive active material.

[0119] The at least partial one-dimensional conductive material being wrapped by the additive means that the surface of the at least partial one-dimensional conductive material is covered by the additive. The additive can be attached to the surface of the one-dimensional conductive material in the form of a film layer, so that the additive and the one-dimensional conductive material form a skin-core structure, in which the one-dimensional conductive material is the core layer and the additive is the skin layer; or the additive can be formed into a substrate layer, and the one-dimensional conductive material is at least partially embedded in the substrate layer and forms a conductive network structure. As an example, the additive can be melted and then solidified on the surface of the one-dimensional conductive material, so as to realize that the additive is wrapped and covered on the surface of the one-dimensional conductive material. As an example, the additive can be sublimated into a gaseous state and then solidified on the surface of the one-dimensional conductive material, so as to realize that the additive is wrapped on the surface of the one-dimensional conductive material. Here, the additive is wrapped on the surface of the one-dimensional conductive material, and for a single one-dimensional conductive material, the surface of the one-dimensional conductive material can be completely wrapped by the additive, or part of the surface of the one-dimensional conductive material can be wrapped by the additive, for example, when the content of the additive is relatively low, most of the surface of the one-dimensional conductive material can be wrapped by the additive, and a small part of the surface of the one-dimensional conductive material is exposed, or the content of the additive is relatively high but affected by the process, and a small part of the surface of the one-dimensional conductive material is not wrapped by the additive and is exposed. The at least partial one-dimensional conductive material being wrapped by the additive means that for all one-dimensional conductive materials, a part of the one-dimensional conductive materials can be wrapped by the additive, or all one-dimensional conductive materials (i.e. each one-dimensional conductive material) can be wrapped by the additive.

[0120] The positive electrode material provided in the embodiments of the present application comprises a positive electrode active material, one-dimensional conductive material and additive, at least part of the one-dimensional conductive material is wrapped by the additive, the one-dimensional conductive material and the additive are distributed on the surface of the positive electrode active material, and the additive contains a chalcogen element with reducibility. By introducing the additive on the surface of the positive electrode active material, the additive contains a chalcogen element with reducibility (usually a low-valence chalcogen element), the chalcogen element with reducibility in the additive is easy to be oxidized and react with residual lithium compounds (such as LiOH, Li2O, Li2CO3, etc.) on the surface of the positive electrode active material, thereby generating an intermediate product (such as Li2S2O3, Li2Se2O3, Li2Te2O3, etc.) containing a chalcogen element with an intermediate valence on the surface of the positive electrode active material in situ, and in the subsequent formation process, the intermediate product continues to react, and the chalcogen element with reducibility is also continuously oxidized and reacts with the residual lithium compounds, and finally generates a final product (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.) containing a chalcogen element with a high valence, while in the formation process, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the positive electrode active material, thereby removing the residual lithium compounds on the surface of the positive electrode active material, and improving the conductivity and electrochemical performance of the positive electrode active material. Further, the one-dimensional conductive material is introduced on the surface of the positive electrode active material, and the one-dimensional conductive material is located on the surface of the positive electrode active material and can be overlapped together to form a conductive system, thereby improving the overall conductivity of the material; at the same time, at least part of the one-dimensional conductive material is wrapped in the additive, which can increase the area of physical combination between the additive and the one-dimensional conductive material, and at the same time, due to the high specific surface area of the one-dimensional conductive material itself, the combination area between the additive and the one-dimensional conductive material is further increased, the binding force between the additive and the one-dimensional conductive material is increased, thereby improving the stability of the combination of the additive and the one-dimensional conductive material, and achieving the anchoring of the additive. Since the additive is wrapped on the surface of the one-dimensional conductive material, when the one-dimensional conductive material is overlapped together, the additive also wraps the joint of the overlapped one-dimensional conductive material, thereby not affecting the conductive system formed by the one-dimensional conductive material.

[0121] In summary, in the embodiments of the present application, the one-dimensional conductive material not only serves as a carrier to anchor the additive, but also is distributed on the surface of the positive electrode active material, and the conductive network formed by the one-dimensional conductive material makes the overall conductivity of the positive electrode material better; in addition, the one-dimensional conductive material has a large specific surface area, which not only promotes the anchoring of the additive, but also improves the contact area between the one-dimensional conductive material and the positive electrode active material, thereby accelerating the electron / ion transmission rate and the kinetic reaction speed of the chalcogen element on the positive electrode material.

[0122] In some embodiments, the chalcogen element includes at least one of a sulfur element, a selenium element and a tellurium element.

[0123] Optionally, the chalcogen element includes a sulfur element, i.e., the additive contains a sulfur element with reducing property. As an example, the additive is a sulfur element, and a positive electrode material is obtained by introducing the sulfur element S and a one-dimensional conductive material onto the surface of a positive electrode active material (e.g., a nickel-rich active material), in which part of the sulfur element S is oxidized and reduced with metal cations in the positive electrode active material, and the residual lithium compound (e.g., LiOH, Li2O, Li2CO3, etc.) on the surface of the positive electrode active material also participates in the reaction, in which the sulfur element S is oxidized and combined with the residual lithium compound to form Li2S2O3. Further, the positive electrode material is prepared into a positive electrode sheet and applied to a battery, in which Li2S2O3 is further oxidized and converted into Li2SO3 and / or Li2SO4 during formation of the battery, and the sulfur element S in the positive electrode material also continues to react with the residual lithium compound to generate Li2SO3 and / or Li2SO4. During formation, the battery is subjected to charging and discharging, and a CEI film is formed on the positive electrode of the battery, and Li2SO3 and / or Li2SO4 can participate in the growth of the CEI film, thereby converting the residual lithium compound that negatively affects the performance of the battery into a CEI film, improving the electrochemical performance of the battery. In addition, additional lithium ions are usually released when the sulfur element S reacts with the residual lithium compound to generate Li2SO3 and / or Li2SO4, which can be used to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0124] Optionally, the chalcogen element includes a tellurium element, i.e., the additive contains a tellurium element with reducing property. As an example, the additive is a tellurium element, and a positive electrode material is obtained by introducing the tellurium element Te and a one-dimensional conductive material onto the surface of a positive electrode active material (e.g., a nickel-rich active material), in which part of the tellurium element Te is combined with the residual lithium compound to form Li2Te2O3, and Li2Te2O3 and the tellurium element Te are further converted into Li2TeO3 and / or Li2TeO4 and participate in the growth of the CEI film during formation of the battery, thereby improving the electrochemical performance of the battery. In this process, additional lithium ions are simultaneously released to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0125] Optionally, the chalcogen element includes selenium element, i.e., the additive contains selenium element with reducing property. As an example, the additive is selenium element, and the positive electrode material is obtained by introducing selenium element Se and one-dimensional conductive material onto the surface of the positive electrode active material (e.g., nickel-rich active material). Similar to the sulfur element S, part of the selenium element Se in the positive electrode material is combined with residual lithium compounds to form Li2Se2O3, and in the subsequent formation process of the battery, Li2Se2O3 and selenium element Se are further converted into Li2SeO3 and / or Li2SeO4 and participate in the growth of the CEI film, thereby improving the electrochemical performance of the battery. In this process, additional lithium ions are released synchronously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0126] Optionally, the chalcogen element includes selenium element and sulfur element. Optionally, the chalcogen element includes sulfur element and tellurium element. Optionally, the chalcogen element includes selenium element and tellurium element. Optionally, the chalcogen element includes sulfur element, selenium element and tellurium element.

[0127] By setting the additive to contain chalcogen element with reducing property, the chalcogen element includes at least one of sulfur element, selenium element and tellurium element, and the above-mentioned chalcogen element can react with residual lithium compounds, consume the residual lithium compounds while promoting the growth of the CEI film on the positive electrode, thereby improving the electrochemical performance of the battery. In this process, additional lithium ions are released synchronously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0128] In some embodiments, the chalcogen element includes sulfur element, and the additive includes at least one of elemental sulfur, metal sulfide, polysulfide, sulfur-containing organic polymer or copolymer, and polymerized sulfur.

[0129] The chalcogen element includes sulfur element, i.e., the additive contains sulfur element, and the additive can be elemental sulfur or sulfur-containing compound. Optionally, the sulfur-containing compound includes metal sulfide. Optionally, the metal sulfide includes transition metal sulfide, and the basic chemical formula of the transition metal sulfide (TMDs) is MS2, where M represents a transition metal element, including Ti, V, Ta, Mo, W, Re, etc. Optionally, the sulfur-containing compound includes polysulfide, and the polysulfide is a compound containing polysulfide ion. Optionally, the polysulfide is an alkali metal or alkaline earth metal polysulfide. Optionally, the polysulfide includes lithium polysulfide (Li2S n where n = 2-8). Optionally, the sulfur-containing compound includes sulfur-containing organic polymer or copolymer. Optionally, the sulfur-containing compound includes polymerized sulfur, which is a product obtained by polymerization of elemental sulfur and organic matter at high temperature.

[0130] The additive contains sulfur element, and the valence of the sulfur element is low. The sulfur element has reducing property, and is beneficial to eliminate residual lithium compounds on the surface of the positive active material.

[0131] In some embodiments, the additive includes a chalcogen element.

[0132] The additive includes a chalcogen element, and optionally, the chalcogen element includes at least one of a sulfur element, a selenium element, and a tellurium element. The additive includes at least one of a sulfur element, a selenium element, and a tellurium element.

[0133] The valence of the chalcogen element is zero, and the chalcogen element itself has strong reducing property. Thus, the chalcogen element is easy to eliminate residual lithium compounds. Meanwhile, the composition of the chalcogen element is single. When the chalcogen element is introduced to the surface of the positive active material, the introduction of other elements can be reduced, thereby reducing the risk of side reactions.

[0134] In some embodiments, the one-dimensional conductive material includes a one-dimensional conductive carbon material.

[0135] The one-dimensional conductive carbon material refers to a fibrous or tubular carbon material in which electrons are free to move in only one non-nanoscale direction.

[0136] In addition to having a large specific surface area, the one-dimensional conductive carbon material also has strong adsorption capacity, so that the one-dimensional conductive carbon material can effectively adsorb the additive attached to the surface of the one-dimensional conductive carbon material, enhance the binding capacity between the one-dimensional conductive carbon material and the additive, and improve the anchoring effect of the one-dimensional conductive carbon material on the additive.

[0137] In some embodiments, the one-dimensional conductive carbon material includes at least one of a short carbon fiber, a nanometer carbon fiber, and a carbon nanotube.

[0138] The short carbon fiber refers to a carbon fiber with a relatively short length and a relatively small diameter. Optionally, the length of the short carbon fiber is less than 10 microns. Optionally, the diameter of the short carbon fiber is less than 1 micron.

[0139] The nanometer carbon fiber, also known as carbon nanofiber (CNF for short), has a diameter of generally 50 nm to 500 nm and a length of 50 microns to 100 microns, and is a one-dimensional conductive carbon material between carbon nanotubes and ordinary carbon fibers.

[0140] The carbon nanotube (CNT for short) is a tubular nanoscale graphite crystal, which is a seamless nanoscale tube formed by a single-layer or multi-layer graphite sheet curled around a central axis at a certain spiral angle. The diameter of the carbon nanotube is generally less than 50 nm.

[0141] The one-dimensional conductive carbon material has good conductivity, is beneficial to the construction of a more developed conductive network, and has a large specific surface area, which is beneficial to improving the contact area of the one-dimensional conductive carbon material and the additive and improving the anchoring effect on the additive.

[0142] In some embodiments, the short carbon fiber filaments include at least one of PAN-based carbon fibers, phenolic-based carbon fibers, viscose-based carbon fibers, pitch-based carbon fibers, biomass-based carbon fibers, and activated carbon fibers.

[0143] The PAN-based carbon fibers are made of urethane (PA) and nylon (N) through high-temperature thermal solidification liquid polymerization.

[0144] The phenolic-based carbon fibers are amorphous carbon fibers made of phenolic filaments.

[0145] The viscose-based carbon fibers refer to carbon fibers prepared by pre-oxidation and carbonization of viscose fibers.

[0146] The pitch-based carbon fibers refer to a type of carbon fibers prepared by polymerization, spinning, infusibilization, and carbonization of pitch and other substances rich in condensed aromatic hydrocarbons.

[0147] The biomass-based carbon fibers are made of cellulose and lignin from trees.

[0148] The activated carbon fibers are carbon-containing fibers activated. Specifically, a certain carbon-containing fiber (such as a phenolic-based fiber, a PAN-based fiber, a viscose-based fiber, a pitch-based fiber, etc.) is activated at a high temperature (different activation methods have different activation temperatures), so that nanoscale pores are generated on the surface of the fiber, and the specific surface area is increased.

[0149] The short carbon fiber filaments have good conductivity, a large specific surface area, and are easy to obtain and cost-effective.

[0150] In some embodiments, the diameter of the short carbon fiber filaments is 100 nm-500 nm.

[0151] Generally, the diameter of the short carbon fiber filaments affects the specific surface area of the short carbon fiber filaments. The smaller the diameter of the short carbon fiber filaments, the larger the specific surface area of the short carbon fiber filaments. However, too small a diameter of the short carbon fiber filaments may cause the short carbon fiber filaments to aggregate, which is not conducive to the dispersion of the short carbon fiber filaments, and may affect the construction of the conductive system and thus the conductivity of the positive electrode material.

[0152] Optionally, the diameter of the short carbon fiber filaments is any one value or a range value between any two values of 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm.

[0153] By setting the diameter of the short carbon fiber filaments to 100 nm - 500 nm, it is beneficial to ensure that the short carbon fiber filaments have a large specific surface area, improving the anchoring effect of the additives, while the short carbon fiber filaments have good dispersibility, which is beneficial to improve the conductivity of the positive electrode material.

[0154] In some embodiments, the length of the short carbon fiber filaments is 1 μm - 5 μm.

[0155] The longer the length of the short carbon fiber filaments, the more easily the short carbon fiber filaments are wound and overlapped together to form a three-dimensional conductive network. However, the positive electrode active material is usually in a granular form, and the short carbon fiber filaments are distributed on the surface of the positive electrode active material. If the length of the short carbon fiber filaments is too long, it will be difficult for the short carbon fiber filaments to contact the positive electrode active material, affecting the transmission of electric current between different materials. If the length of the short carbon fiber filaments is too short, it will affect the overlapping effect between the short carbon fiber filaments, especially after the short carbon fiber filaments are wrapped with additives, the short carbon fiber filaments are easily wrapped with additives to form a conductive dead angle, thereby reducing the conductivity of the positive electrode material.

[0156] Alternatively, the length of the short carbon fiber filaments is any one value or a range value between any two values selected from 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm and 5 μm.

[0157] By setting the length of the short carbon fiber filaments to 1 μm - 5 μm, it is beneficial to ensure the contact effect of the short carbon fiber filaments with the surface of the positive electrode active material, while the short carbon fiber filaments can be well overlapped together to form a conductive network, improving the conductivity of the positive electrode material.

[0158] In some embodiments, the mass percentage of the chalcogen element is 0.02wt% ~ 5wt% based on the total mass of the positive electrode material.

[0159] The content of the chalcogen element in the positive electrode material affects the removal effect of the residual lithium compound. If the content of the chalcogen element in the positive electrode material is too low, especially when the mass percentage of the chalcogen element in the positive electrode material is less than 0.02wt%, the residual lithium compound on the surface of the positive electrode active material is difficult to be eliminated, and the existence of the residual lithium compound will affect the conductivity of the positive electrode material, and also cause the occurrence of side reactions, thereby causing the cycle stability of the battery to be poor. Generally, the greater the amount of the chalcogen element loaded in the positive electrode material, the more beneficial it is for the chalcogen element to be dispersed on the surface of the positive electrode active material and to react with the residual lithium compound to eliminate the residual lithium compound. However, when the mass percentage of the chalcogen element in the positive electrode material is greater than 5wt%, it is easy to cause the additives to remain, which reduces the conductivity of the positive electrode material, increases the battery polarization, increases the battery internal resistance (DRC), and continuously consumes the active lithium inside the battery during storage, which deteriorates the performance of the battery.

[0160] Optionally, the mass percentage of the chalcogen element is any one value or a range between any two values selected from 0.02wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% and 5wt% based on the total mass of the positive electrode material.

[0161] By setting the mass percentage of the chalcogen element in the positive electrode material to 0.02wt%-5wt%, residual lithium compounds on the surface of the positive electrode active material can be effectively removed, while preventing excessive chalcogen elements from increasing the polarization of the battery.

[0162] In some embodiments, the mass percentage of the one-dimensional conductive material is greater than 0 and less than or equal to 1wt% based on the total mass of the positive electrode material.

[0163] The one-dimensional conductive material is mainly used to improve the conductivity of the positive electrode material. The higher the content of the one-dimensional conductive material in the positive electrode material, the better the conductivity of the positive electrode material. However, the one-dimensional conductive material itself is prone to agglomeration, and a too high content of the one-dimensional conductive material in the positive electrode material, especially when the content of the one-dimensional conductive material in the positive electrode material is greater than 1wt%, can easily increase the surface energy of the positive electrode material particles and cause physical gelation, thereby degrading the processability of the positive electrode material.

[0164] Optionally, the mass percentage of the one-dimensional conductive material is any one value or a range between any two values selected from 0.001wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% and 1wt% based on the total mass of the positive electrode material.

[0165] By setting the mass percentage of the one-dimensional conductive material in the positive electrode material to be greater than 0 and less than or equal to 1wt%, the positive electrode material has both good conductivity and processability.

[0166] Please refer to Figure 5 In some embodiments, the surface of the positive electrode active material is coated with a coating layer, and the coating layer includes a first sub-coating layer 71 containing a one-dimensional conductive material and an additive wrapped around the one-dimensional conductive material.

[0167] Specifically, the positive electrode active material includes positive electrode active material particles 6, and the one-dimensional conductive material and the additive are distributed on the surface of the positive electrode active material, so that the one-dimensional conductive material and the additive are wrapped on the surface of the positive electrode active material particles 6 and form a coating layer. In order to facilitate the distinction, the coating layer containing the one-dimensional conductive material and the additive wrapped on the one-dimensional conductive material is defined as a first sub-coating layer 71. The coating layer includes the first sub-coating layer 71, and in some embodiments, the coating layer can only include the first sub-coating layer 71, and in some other embodiments, the coating layer can further include other sub-coating layers.

[0168] By wrapping the one-dimensional conductive material wrapped with the additive on the surface of the positive electrode active material and forming the first sub-coating layer 71, the additive is conducive to eliminating the residual lithium compounds on the surface of the positive electrode active material, and improving the performance of the positive electrode active material.

[0169] Please refer to Figure 5 In some embodiments, the coating layer further includes a second sub-coating layer 72, the second sub-coating layer 72 is arranged on the side of the first sub-coating layer 71 away from the positive electrode active material, the second sub-coating layer 72 contains the conductive agent, the binder and the additive, and the content of the chalcogen element in the second sub-coating layer 72 is greater than or equal to 0 and less than the content of the chalcogen element in the first sub-coating layer 71.

[0170] Specifically, the coating layer includes at least two sub-coating layers, i.e., a first sub-coating layer 71 and a second sub-coating layer 72, wherein the first sub-coating layer 71 directly coats the surface of the positive active material particles 6, and the second sub-coating layer 72 is arranged outside the first sub-coating layer 71, i.e., the first sub-coating layer 71 is arranged between the positive active material particles 6 and the second sub-coating layer 72. Here, the first sub-coating layer 71 and the second sub-coating layer 72 can be in direct contact or can be arranged with a spacing. Further, the second sub-coating layer 72 contains a conductive agent, a binder, and an additive. The conductive agent in the second sub-coating layer 72 includes, but is not limited to, at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers. That is, the conductive agent in the second sub-coating layer 72 can be selected from the above-mentioned one-dimensional conductive material, or other conductive materials can also be used, thus increasing the material selection range of the second sub-coating layer 72 and facilitating the control of the cost of the positive material. The binder in the second sub-coating layer 72 is used to bond the conductive agent and the additive together and further bond with the first sub-coating layer 71. The binder includes, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, butadiene-styrene rubber, polyurethane, fluorinated rubber, and polyvinyl alcohol. The content of the chalcogen element in the second sub-coating layer 72 is greater than or equal to 0 and less than the content of the chalcogen element in the first sub-coating layer 71. It can be understood that the second sub-coating layer 72 can contain an additive (i.e., the content of the chalcogen element is greater than 0) or can not contain an additive (i.e., the content of the chalcogen element is equal to 0). When the second sub-coating layer 72 contains an additive, the content of the chalcogen element in the second sub-coating layer 72 is less than the content of the chalcogen element in the first sub-coating layer 71.

[0171] By sequentially coating the first sub-coating layer 71 and the second sub-coating layer 72 on the surface of the positive active material, and the content of the chalcogen element in the first sub-coating layer 71 being greater than the content of the chalcogen element in the first sub-coating layer 71, the first sub-coating layer 71 as an inner layer, the high specific surface one-dimensional conductive material in the first sub-coating layer 71 as a conductive substance, facilitates the fixation of the additive and inhibits the outward diffusion of the chalcogen element, the second sub-coating layer 72 as an outer layer, which can use one-dimensional conductive material as a conductive agent or other carbon material as a conductive agent, thus expanding the material selection range and facilitating the control of the cost, and the content of the chalcogen element in the second sub-coating layer 72 being less than the content of the chalcogen element in the first sub-coating layer 71, on the one hand, the content of the chalcogen element in the second sub-coating layer 72 is reduced, which can reduce the outward diffusion of the chalcogen element, and at the same time, the outer layer of the second sub-coating layer 72 can form a barrier to the inner layer of the first sub-coating layer 71, relieving the outward diffusion of the chalcogen element in the first sub-coating layer 71, because the chalcogen element diffuses outwardly and easily flows to the negative electrode, and the chalcogen element reacts with active lithium in the negative electrode, causing lithium consumption and reducing the battery capacity.

[0172] See Figure 5 In some embodiments, the content of the chalcogen element in the second sub-coating layer 72 is greater than 0, and the coating layer further comprises a third sub-coating layer 73, which is coated on the surface of the second sub-coating layer 72, and the third sub-coating layer 73 comprises a conductive agent and a binder.

[0173] Specifically, the coating layer comprises at least three sub-coating layers, namely the first sub-coating layer 71, the second sub-coating layer 72 and the third sub-coating layer 73, wherein the second sub-coating layer 72 contains an additive, and the third sub-coating layer 73 does not contain an additive. The third sub-coating layer 73 comprises a conductive agent and a binder.

[0174] By coating the first sub-coating layer 71, the second sub-coating layer 72 and the third sub-coating layer 73 on the surface of the positive electrode active material in turn, and the content of the chalcogen element in each sub-coating layer decreases from inside to outside, and the third sub-coating layer 73 as the outermost layer does not contain the chalcogen element, which can provide a diffusion space for the chalcogen element, enhance the blocking effect of the chalcogen element, and limit the chalcogen element as much as possible inside the positive electrode material.

[0175] In some embodiments, the thickness of the coating layer is 100 nm to 1000 nm.

[0176] The thickness of the coating layer refers to the total thickness of the coating layer. When the coating layer comprises a plurality of sub-coating layers, the thickness of the coating layer is the sum of the thicknesses of the respective sub-coating layers. As an example, when the coating layer only comprises the first sub-coating layer 71, the thickness of the coating layer is the thickness of the first sub-coating layer 71. As an example, when the coating layer comprises the first sub-coating layer 71, the second sub-coating layer 72 and the third sub-coating layer 73, the thickness of the coating layer is the sum of the thicknesses of the above three layers.

[0177] The coating layer mainly contains conductive materials and additives, which almost do not contribute to the capacity of the battery. If the thickness of the coating layer is too large, it will reduce the theoretical specific capacity of the positive electrode material. If the thickness of the coating layer is too small, it will lead to uneven coating, thereby affecting the removal effect of the residual lithium compound. Alternatively, the thickness of the coating layer is 100 nm to 1000 nm. Specifically, the thickness of the coating layer can be any one value or a range value between any two values selected from 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm and 1000 nm.

[0178] By setting the thickness of the coating layer to 100 nm to 1000 nm, the residual lithium compound can be effectively removed while ensuring the theoretical specific capacity of the positive electrode material.

[0179] In some embodiments, the mass percentage of the coating layer based on the total mass of the positive electrode material is 0.01 wt% to 6 wt%.

[0180] As described above, the coating layer contributes little to the battery capacity, and too large mass percentage of the coating layer in the positive electrode material reduces the theoretical specific capacity of the positive electrode material, and too small mass percentage of the coating layer affects the removal effect of residual lithium compounds. Optionally, the mass percentage of the coating layer in the positive electrode material is 0.01wt%~6wt%, specifically, the mass percentage of the coating layer is any one value or a range value between any two values of 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt% and 6wt%.

[0181] Optionally, the mass percentage of the coating layer is 0.1wt%~1wt%. In this range, the removal effect of residual lithium compounds in the positive electrode material and the theoretical specific capacity of the positive electrode material reach the best balance.

[0182] By setting the mass percentage of the coating layer in the positive electrode material to 0.01wt%~6wt%, the residual lithium compounds are effectively removed while ensuring the theoretical specific capacity of the positive electrode material.

[0183] In some embodiments, the positive electrode active material includes a nickel-rich active material having a chemical formula of Li a Ni m Co n M 1-m-n O2, where M includes at least one of Mn and Al, where m≥0.6, n≤0.2, and 0.9≤a≤1.2.

[0184] The nickel-rich active material has a chemical formula of Li a Ni m Co n M 1-m-n O2, where M includes at least one of Mn and Al. As an example, M includes Mn, and the nickel-rich active material has a chemical formula of Li a Ni m Co n Mn 1-m-n O2. As an example, M includes Al, and the nickel-rich active material has a chemical formula of Li a Ni m Co n Al 1-m-nO2. Specifically, m > 0.6, by increasing the value of m, the content of nickel element in the nickel-rich active material is increased, and thus the reversible lithium intercalation capacity of the positive electrode material is improved. Optionally, m is any one of 0.6, 0.7, 0.8, 0.9, 0.95, and 0.99 or a range value between any two of them. Optionally, m > 0.9, in this range, the reversible lithium intercalation capacity of the positive electrode material is larger. Specifically, n < 0.2, the nickel-rich active material is usually a layered structure, Co can stabilize the layered structure, but due to the high cost of Co, it will increase the cost of the nickel-rich active material, by controlling n < 0.2, the cost of the nickel-rich active material can be controlled. Optionally, n is any one of 0.05, 0.1, 0.15, and 0.2 or a range value between any two of them. 0.9 < a < 1.2, that is, the content of lithium in the nickel-rich active material can be greater than 1, can be equal to 1, or can be less than 1. When a is greater than 1, the nickel-rich active material is a lithium-rich positive electrode material. As an example, the content of Li can be greater than 1 for the nickel-rich active material obtained by pre-lithiation. Optionally, a is any one of 0.9, 0.95, 1, 1.05, 1.1, 1.15, and 1.2 or a range value between any two of them.

[0185] However, the nickel element in the nickel-rich active material is alkaline, as the content of nickel element increases, the nickel-rich active material is easy to absorb moisture and carbon dioxide when exposed to air, and residual lithium compounds (RLCs) such as lithium hydroxide (LiOH), lithium carbonate (Li2CO3), etc. are generated on the surface of the nickel-rich active material, further increasing the PH of the nickel-rich active material, seriously affecting the electrochemical performance and storage performance of the nickel-rich active material.

[0186] Based on this, the present application introduces an additive on the surface of the nickel-rich active material, the additive contains a chalcogen element with reducing property, and the Ni, Co, Mn in the nickel-rich active material is reduced to Ni 3+ / Ni 2+ , Co 3+ , and Mn 4+The ion exists in the form of ions, and the sulfur element with reducing property in the additive is easily oxidized by the nickel-rich active material and reacts with the residual lithium compound on the surface of the nickel-rich active material to generate an intermediate product containing an intermediate valence state of the sulfur element in situ on the surface of the nickel-rich active material, and in the subsequent formation process, the intermediate product continues to react, and the sulfur element with reducing property is also continuously oxidized and reacts with the residual lithium compound, and finally generates a final product containing a high valence state of the sulfur element (for example, Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the nickel-rich active material during the formation process, thereby removing the residual lithium compound on the surface of the nickel-rich active material and improving the conductivity and electrochemical performance of the nickel-rich active material; in this process, additional lithium ions are also released synchronously to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0187] In some embodiments, the DV50 particle size of the positive electrode active material is 5 μm to 15 μm.

[0188] The average particle size is generally represented by DV50, which means that 50% of the powder particles are greater than and less than the particle size. Generally, the positive electrode active material is in a particulate form, and the particle size of the positive electrode active material affects the processing performance and electrochemical performance of the positive electrode material. Generally, the larger the particle size of the positive electrode active material, the longer the migration path of lithium ions in the positive electrode active material, which affects the rate performance of the battery. However, the smaller the particle size of the positive electrode active material, the more unstable the viscosity of the slurry during the slurry preparation process, which affects the subsequent slurry coating effect.

[0189] Alternatively, the DV50 particle size of the positive electrode active material is any one of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm, or a range value between any two thereof.

[0190] By setting the DV50 particle size of the positive electrode active material to 5 μm to 15 μm, the positive electrode material can have better processing performance and electrochemical performance.

[0191] Some embodiments of the present application also provide a preparation method of a positive electrode material, comprising:

[0192] mixing the one-dimensional conductive material and the additive to obtain a mixture, the additive containing a sulfur element with reducing property;

[0193] sintering the mixture to melt the additive, and at least part of the one-dimensional conductive material is wrapped by the additive, thereby obtaining a sintered material;

[0194] The sintering material is stirred with the positive electrode active material to obtain a positive electrode material.

[0195] As described above, the one-dimensional conductive material refers to a fiber-like or tube-like material in which electrons are free to move in only one non-nanoscale direction. The one-dimensional conductive material includes, but is not limited to, metal nanowires, one-dimensional conductive carbon materials. The metal nanowires include, but are not limited to, silver nanowires, copper nanowires, and the like. The one-dimensional conductive carbon material can be a one-dimensional nanocarbon material or a one-dimensional micrometer carbon material. Alternatively, the one-dimensional conductive carbon material includes at least one of carbon fibers, nanocarbon fibers, and carbon nanotubes.

[0196] The additive contains a chalcogen element having a reducing property, where the chalcogen element refers to a sulfur element and an element having similar chemical properties to the sulfur element. Alternatively, the chalcogen element includes an element other than oxygen in the oxygen family. Alternatively, the chalcogen element includes at least one of a sulfur (S) element, a selenium (Se) element, and a tellurium (Te) element. The additive contains the chalcogen element, where the additive can be a compound in which the chalcogen element is one of the constituent elements of the compound, or the additive can be an element itself, such as a chalcogen element element used as the additive. The chalcogen element has a reducing property, that is, the chalcogen element can be oxidized to a high-valence chalcogen element through a redox reaction. Alternatively, the chalcogen element has a valence of less than or equal to zero, that is, a low-valence chalcogen element, which is easily oxidized to a high-valence chalcogen element. As an example, the chalcogen element includes sulfur, which has a valence of -2 or zero as a low-valence sulfur, and a valence of +6 or +4 as a high-valence sulfur.

[0197] Mixing the one-dimensional conductive material and the additive refers to mixing the additive and the one-dimensional conductive material together so that the additive is attached to the one-dimensional conductive material in advance.

[0198] The sintering process refers to heat treatment of the mixture at an appropriate temperature to melt the additive, but the additive only changes in physical form without a chemical reaction. The additive melts into a liquid state with stronger fluidity during the sintering process, and the liquid additive spreads and disperses on the surface of the one-dimensional conductive material. After the temperature decreases, the liquid additive solidifies into a solid additive and remains in a spread state, and the additive wraps the one-dimensional conductive material in the form of a film and / or a block. At this time, the one-dimensional conductive material and the additive are physically combined, but the large contact area increases the stability of the combination of the additive. Alternatively, the mixture is sintered under a protective atmosphere to prevent high-temperature oxidation of the mixture by isolating oxygen using the protective atmosphere. The protective atmosphere can be an inert gas or nitrogen. Understandably, there are many chalcogen elements, so there are more additives, and the sintering temperature is different for different additives, as long as the sintering temperature is controlled to melt the additive.

[0199] The preparation method of the positive electrode material provided in the embodiments of the present application realizes effective fixation of the additive containing a chalcogen element by mixing the one-dimensional conductive material and the additive, and then performing sintering treatment to melt the additive and wrap at least part of the one-dimensional conductive material with the additive, thereby increasing the physical contact area of the additive with the one-dimensional conductive material, combining the large specific surface area of the one-dimensional conductive material itself, and enhancing the combination ability of the additive with the one-dimensional conductive material. Further, the sintered material obtained after the sintering treatment is mixed with the positive electrode active material by stirring, so that the one-dimensional conductive material wrapped with the additive is distributed on the surface of the positive electrode active material, thereby forming the positive electrode material. Since the one-dimensional conductive material itself has good conductivity, the one-dimensional conductive material is used to form a conductive network, and even after being wrapped with the additive, the conductive network can still be well connected, thereby ensuring the overall conductivity of the positive electrode material. In addition, the additive wrapped on the surface of the one-dimensional conductive material will be in contact with the positive electrode active material. In this process, the chalcogen element with reducing property in the additive will undergo an oxidation-reduction reaction with metal cations in the positive electrode active material and consume residual lithium compounds on the surface of the positive electrode active material to generate an intermediate product containing an intermediate valence chalcogen element (such as Li2S2O3, Li2Se2O3, Li2Te2O3, etc.) in situ on the surface of the positive electrode active material. In the subsequent formation process, the intermediate product continues to react, and the chalcogen element with reducing property is also continuously oxidized and reacts with residual lithium compounds, and finally generates a final product containing a high valence chalcogen element (such as Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.). At the same time, in the formation process, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the positive electrode active material, thereby removing the residual lithium compounds on the surface of the positive electrode active material and improving the conductivity and electrochemical performance of the positive electrode active material. In the process of converting the chalcogen element with reducing property into the CEI film, additional lithium ions are also released synchronously to compensate for the loss of lithium ions caused by the formation of the SEI film, thereby ensuring the capacity of the battery. In addition, the preparation method of the positive electrode material provided in the embodiments of the present application is simple, easy to operate, and conducive to industrialization.

[0200] In some embodiments, the chalcogen element includes at least one of a sulfur element, a selenium element, and a tellurium element.

[0201] As described above, by setting the additive to contain a chalcogen element with reducing property, the chalcogen element includes at least one of a sulfur element, a selenium element, and a tellurium element. The above-mentioned chalcogen element can react with residual lithium compounds, consume the residual lithium compounds, promote the growth of the CEI film on the positive electrode, and improve the electrochemical performance of the battery. In this process, additional lithium ions are also released synchronously to compensate for the loss of lithium ions caused by the formation of the SEI film, thereby ensuring the capacity of the battery.

[0202] In some embodiments, the additive comprises a chalcogen elemental substance.

[0203] The additive comprises a chalcogen elemental substance, and optionally, the chalcogen comprises at least one of a sulfur element, a selenium element, and a tellurium element, and the additive comprises at least one of a sulfur elemental substance, a selenium elemental substance, and a tellurium elemental substance.

[0204] The chalcogen elemental substance has a valence of zero, and the chalcogen elemental substance itself has strong reducing property, so that the chalcogen elemental substance is easy to eliminate residual lithium compounds, and meanwhile, the composition of the chalcogen elemental substance is single, and the introduction of the chalcogen elemental substance to the surface of the positive electrode active material can reduce the introduction of other elements, thereby reducing the risk of side reactions.

[0205] In some embodiments, the one-dimensional conductive material comprises a one-dimensional conductive carbon material.

[0206] The one-dimensional conductive carbon material refers to a fibrous or tubular carbon material in which electrons are free to move in only one non-nanoscale direction.

[0207] In addition to having a large specific surface area, the one-dimensional conductive carbon material also has strong adsorption capacity, so that the one-dimensional conductive carbon material can effectively adsorb the additive attached to the surface of the one-dimensional conductive carbon material, enhance the binding capacity between the one-dimensional conductive carbon material and the additive, and improve the anchoring effect of the one-dimensional conductive carbon material on the additive.

[0208] In some embodiments, the additive comprises a sulfur elemental substance, the temperature of the sintering treatment is 180°C to 220°C, and / or the sintering time is 5h to 7h.

[0209] Generally, the temperature of the sintering treatment will affect the melting effect of the sulfur elemental substance, and if the temperature is too low, the sulfur elemental substance cannot be melted, and if the temperature is too high, the sulfur elemental substance will undergo a chemical reaction.

[0210] Optionally, the temperature of the sintering treatment is any one of 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, and 220°C, or a range value between any two of them.

[0211] The sintering time will affect the amount of sulfur elemental substance coated on the surface of the one-dimensional conductive material, and if the sintering time is too short, the content of the sulfur elemental substance in the positive electrode material will be too low, and the effect of eliminating residual lithium compounds will be poor, and if the sintering time is too long, the content of the sulfur elemental substance in the positive electrode material will be too high, which will cause sulfur residue, and ultimately affect the internal resistance of the battery and increase the polarization of the battery.

[0212] Optionally, the sintering time is any one of 5h, 5.5h, 6h, 6.5h, and 7h, or a range value between any two of them.

[0213] Compared with other additives, elemental sulfur has more active chemical properties, and can better remove residual lithium compounds. In addition, elemental sulfur is easy to obtain and has low cost, and the cost performance is high when used as an additive. Further, by setting the sintering temperature to 180-220 DEG C, the elemental sulfur can exist in a molten liquid state in this temperature range, and then be coated on the surface of the one-dimensional conductive material. In addition, by setting the sintering time to 5-7 h, the content of elemental sulfur in the positive electrode material can be effectively controlled, so that the elemental sulfur can effectively remove residual lithium compounds without increasing the battery polarization.

[0214] In some embodiments, the DV50 particle size of the additive is greater than 0 and less than or equal to 1 pm.

[0215] Generally, in the preparation of the positive electrode material, the additive and the one-dimensional conductive material need to be mixed and treated first, so that the additive is pre-loaded on the one-dimensional conductive material. In this process, the binding force between the additive and the one-dimensional conductive material is weak. If the particle size of the additive is too large, it is not conducive to the pre-loading of the additive. However, if the particle size of the additive is too small, the additive may agglomerate and cannot be well dispersed on the one-dimensional conductive material, which will also affect the pre-loading effect.

[0216] Optionally, the DV50 particle size of the additive is any one or any range value between any two of 10 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm and 1 pm.

[0217] Optionally, the DV50 particle size of the additive is 100-500 nm. In this particle size range, the dispersibility of the additive and the binding property with the one-dimensional conductive material are in the best balance.

[0218] By setting the DV50 particle size of the additive to be greater than 0 and less than or equal to 1 pm, the dispersion effect of the additive is good in this range, and the binding property of the additive and the one-dimensional conductive material is good when pre-loaded.

[0219] In some embodiments, the mixing process includes ball milling.

[0220] In order to prevent the additive from agglomerating, the particle size of the commonly selected additive is large. However, the large particle size of the additive will make the binding property of the additive and the one-dimensional conductive material poor when pre-loaded. Therefore, ball milling is designed in the mixing process, so that the particle size of the additive is large and well dispersed during the initial mixing of the additive and the one-dimensional conductive material. Then, the particle size of the additive is reduced through ball milling, and the binding stability of the additive and the one-dimensional conductive material is improved.

[0221] By designing the ball milling treatment in the mixing process, on one hand, the limitation on the particle size of the additive before the mixing process can be reduced, and on the other hand, the particle size of the additive can be reduced by the ball milling treatment, so as to improve the combination stability of the additive and the one-dimensional conductive material.

[0222] In some embodiments, the stirring treatment has a rotation speed of 400 r / s ~ 1000 r / s.

[0223] Optionally, the stirring treatment has a rotation speed of any one of 400 r / s, 500 r / s, 600 r / s, 700 r / s, 800 r / s, 900 r / s and 1000 r / s, or a range value between any two thereof.

[0224] By setting the rotation speed of the stirring treatment to 400 r / s ~ 1000 r / s, the sintering material and the positive active material can be effectively mixed together.

[0225] In some embodiments, the positive active material includes a nickel-rich active material with a chemical formula of Li a Ni m Co n M 1-m-n O2, wherein M includes at least one of Mn and Al, m≥0.6, n≤0.2, and 0.9≤a≤1.2.

[0226] The nickel-rich active material has a chemical formula of Li a Ni m Co n M 1-m-n O2, wherein M includes at least one of Mn and Al. As an example, M includes Mn, and the nickel-rich active material has a chemical formula of Li a Ni m Co n Mn 1-m-n O2. As an example, M includes Al, and the nickel-rich active material has a chemical formula of Li a Ni m Co n Al 1-m-nO2. Specifically, m≥0.6, by increasing the value of m, the content of nickel element in the nickel-rich active material is increased, and the reversible lithium intercalation capacity of the positive electrode material is improved. Optionally, m is any one of 0.6, 0.7, 0.8, 0.9, 0.95 and 0.99 or a range value between any two of them. Optionally, m≥0.9, in this range, the reversible lithium intercalation capacity of the positive electrode material is larger. Specifically, n≤0.2, the nickel-rich active material is usually a layered structure, Co can stabilize the layered structure, but due to the high price of Co, it will increase the cost of the nickel-rich active material, by controlling n≤0.2, the cost of the nickel-rich active material can be controlled. Optionally, n is any one of 0.05, 0.1, 0.15 and 0.2 or a range value between any two of them. 0.9≤a≤1.2, that is, the content of lithium in the nickel-rich active material can be greater than 1, can be equal to 1, or can be less than 1. When a is greater than 1, the nickel-rich active material is a lithium-rich positive electrode material. As an example, the content of Li can be greater than 1 for the nickel-rich active material obtained by pre-lithiation. Optionally, a is any one of 0.9, 0.95, 1, 1.05, 1.1, 1.15 and 1.2 or a range value between any two of them.

[0227] However, the nickel element in the nickel-rich active material is alkaline, as the content of nickel element increases, the nickel-rich active material is easy to absorb moisture and carbon dioxide when exposed to air, and residual lithium compounds (RLCs) such as lithium hydroxide (LiOH), lithium carbonate (Li2CO3) and the like are generated on the surface of the nickel-rich active material, further increasing the PH of the nickel-rich active material, seriously affecting the electrochemical performance and storage performance of the nickel-rich active material.

[0228] Based on this, the present application introduces an additive on the surface of the nickel-rich active material, the additive contains a chalcogen element with reducing property, and the Ni, Co, Mn in the nickel-rich active material is reduced to Ni 3+ / Ni 2+ , Co 3+ and Mn 4+The ion exists in the form of ions, and the sulfur element with reducing property in the additive is easily oxidized by the nickel-rich active material and reacts with the residual lithium compound on the surface of the nickel-rich active material to generate an intermediate product containing the sulfur element in an intermediate valence state in situ on the surface of the nickel-rich active material, and in the subsequent formation process, the intermediate product continues to react, and the sulfur element with reducing property is also continuously oxidized and reacts with the residual lithium compound, and finally generates a final product containing the sulfur element in a high valence state (for example, Li2SO3, Li2SO4, Li2SeO3, Li2SeO4, Li2TeO3, Li2TeO4, etc.), and at the same time, the final product further forms a positive electrode-electrolyte interface (CEI) film on the surface of the nickel-rich active material during the formation process, thereby removing the residual lithium compound on the surface of the nickel-rich active material and improving the conductivity and electrochemical performance of the nickel-rich active material; in this process, additional lithium ions are also released to compensate for the loss of lithium ions due to the formation of the SEI film, thereby ensuring the capacity of the battery.

[0229] Referring to Figure 4 Some embodiments of the present application also provide a positive electrode tab 102, comprising a positive current collector and a positive electrode material layer combined on the positive current collector, wherein the positive electrode material layer comprises the above-mentioned positive electrode material or the positive electrode material prepared according to the preparation method of the above-mentioned positive electrode material.

[0230] The current collector is a structure or part for collecting current in the battery. The current collector is usually a metal foil. The positive current collector refers to a structure or part for collecting current in the battery. The positive current collector includes but is not limited to an aluminum foil.

[0231] The positive electrode material layer refers to a film layer disposed on the positive current collector and containing a positive active material. The positive electrode material layer can be disposed on one side surface of the positive current collector, or the positive electrode material layer can be disposed on both side surfaces of the positive current collector. Optionally, the positive electrode material layer comprises a conductive agent and a binder.

[0232] The positive electrode tab 102 provided by the embodiments of the present application comprises a positive current collector and a positive electrode material layer, and the positive electrode material layer comprises the above-mentioned positive electrode material, so that the content of residual lithium compound in the positive electrode tab 102 is low, the overall conductivity of the positive electrode tab 102 is improved, and the cycle performance is improved.

[0233] Referring to Figure 2 Some embodiments of the present application also provide a battery 40, which comprises the above-mentioned positive electrode tab 102.

[0234] Optionally, the battery 40 is a secondary battery, and the secondary battery has various different forms, including but not limited to a battery monomer, a battery module, a battery pack, etc.

[0235] The battery 40 provided by the embodiment of the present application comprises the positive electrode sheet 102, and the battery 40 has stable cycle performance and good rate performance.

[0236] Please refer to Figure 1 Some embodiments of the present application also provide a power utilization device 50 comprising the battery 40.

[0237] As described above, the power utilization device 50 can be, but is not limited to, a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, and the like.

[0238] The specific embodiments will be described below.

[0239] Embodiment 1

[0240] S1. Preparation of the positive electrode material: sulfur, polypropylene-based carbon fiber filaments are uniformly mixed by ball milling, and then sintering treatment is performed in an inert atmosphere, wherein the sintering temperature is 200°C, the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM (LiNi 0.9 Co 0.05 Mn 0.05 ) to obtain a modified positive electrode material, wherein the mass ratio of sulfur, polypropylene-based carbon fiber filaments, and the positive electrode active material NCM is 0.02:0.5:99.48.

[0241] S2. Preparation of the positive electrode sheet: the positive electrode material prepared in S1, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methyl pyrrolidone (NMP) at a weight ratio of 96.5:1.5:2, and are uniformly mixed by stirring to obtain a positive electrode slurry; then the positive electrode slurry is uniformly coated on the positive electrode current collector with a primer, and then is subjected to drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0242] S3. Preparation of the negative electrode sheet: the negative electrode active material graphite, silicon, the conductive agent acetylene black, butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) are uniformly mixed in deionized water at a weight ratio of 90:5:2:2:1 to prepare a negative electrode slurry, the slurry is coated on a copper foil, and after drying, the negative electrode sheet is obtained by cold pressing and slitting.

[0243] S4. Preparation of the secondary battery: stack the positive electrode sheet, the separator, and the negative electrode sheet in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator, then roll to obtain a bare battery cell, weld the tabs to the bare battery cell, and place the bare battery cell in an aluminum shell, and bake at 80°C to remove water, then inject electrolyte and seal to obtain a battery without electricity. The battery without electricity is then subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like, to obtain a secondary battery product. The separator described above is a PE separator, the surface of which is coated with PVDF and an aluminum oxide coating to improve adhesion and heat resistance. The preparation process of the electrolyte described above is to mix ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, then uniformly dissolve LiPF6: LiFSI (2:8) in the above solution to obtain the electrolyte. In the electrolyte, the concentration of lithium salt is 1 mol / L.

[0244] Example 2

[0245] The same as Example 1, except that S1: the elemental sulfur and polypropylene-based carbon fiber filaments are ball-mixed uniformly, then sintered in an inert atmosphere, wherein the sintering temperature is 200°C, and the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM, and the stirring mixing is carried out under the condition that the rotation speed is 600r / s, to obtain a modified positive electrode material. In the positive electrode material, the mass ratio of elemental sulfur: polypropylene-based carbon fiber filaments: positive electrode active material NCM is 1:0.5:98.5.

[0246] Example 3

[0247] The same as Example 1, except that S1: the elemental sulfur and polypropylene-based carbon fiber filaments are ball-mixed uniformly, then sintered in an inert atmosphere, wherein the sintering temperature is 200°C, and the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM, and the stirring mixing is carried out under the condition that the rotation speed is 600r / s, to obtain a modified positive electrode material. In the positive electrode material, the mass ratio of elemental sulfur: polypropylene-based carbon fiber filaments: positive electrode active material NCM is 3:0.5:96.5.

[0248] Example 4

[0249] The same as Example 1, except that S1: the elemental sulfur and polypropylene-based carbon fiber filaments are ball-mixed uniformly, then sintered in an inert atmosphere, wherein the sintering temperature is 200°C, and the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM, and the stirring mixing is carried out under the condition that the rotation speed is 600r / s, to obtain a modified positive electrode material. In the positive electrode material, the mass ratio of elemental sulfur: polypropylene-based carbon fiber filaments: positive electrode active material NCM is 5:0.5:94.5.

[0250] Example 5

[0251] The same as example 1, the difference is that S1: the elemental sulfur, polypropylene-based carbon fiber yarn is uniformly mixed by ball milling, and then sintering treatment is carried out in an inert atmosphere, wherein the sintering temperature is 200°C, the sintering time is 6h, finally the obtained sintered material is mixed with the positive electrode active material NCM, and stirring mixing is carried out under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, according to the mass ratio, the elemental sulfur: polypropylene-based carbon fiber yarn: positive electrode active material NCM in the positive electrode material is 6:0.5:93.5.

[0252] Example 6

[0253] The same as example 1, the difference is that S1: the elemental sulfur, polypropylene-based carbon fiber yarn is uniformly mixed by ball milling, and then sintering treatment is carried out in an inert atmosphere, wherein the sintering temperature is 200°C, the sintering time is 6h, finally the obtained sintered material is mixed with the positive electrode active material NCM, and stirring mixing is carried out under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, according to the mass ratio, the elemental sulfur: polypropylene-based carbon fiber yarn: positive electrode active material NCM in the positive electrode material is 6:1.5:92.5.

[0254] Example 7

[0255] The same as example 1, the difference is that S1: the elemental sulfur, polypropylene-based carbon fiber yarn is uniformly mixed by ball milling, and then sintering treatment is carried out in an inert atmosphere, wherein the sintering temperature is 200°C, the sintering time is 6h, finally the obtained sintered material is mixed with the positive electrode active material NCM, and stirring mixing is carried out under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, according to the mass ratio, the elemental sulfur: polypropylene-based carbon fiber yarn: positive electrode active material NCM in the positive electrode material is 3:0.02:96.98.

[0256] Example 8

[0257] The same as example 1, the difference is that S1: the elemental sulfur, polypropylene-based carbon fiber yarn is uniformly mixed by ball milling, and then sintering treatment is carried out in an inert atmosphere, wherein the sintering temperature is 200°C, the sintering time is 6h, finally the obtained sintered material is mixed with the positive electrode active material NCM, and stirring mixing is carried out under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, according to the mass ratio, the elemental sulfur: polypropylene-based carbon fiber yarn: positive electrode active material NCM in the positive electrode material is 3:1:96.

[0258] Example 9

[0259] The same as Example 1, except that S1: the elemental sulfur and the polypropylene-based carbon fiber are uniformly mixed by ball milling, and then sintered in an inert atmosphere, wherein the sintering temperature is 200°C, and the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM, and the mixing is performed under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, and the elemental sulfur, the polypropylene-based carbon fiber and the positive electrode active material NCM in the positive electrode material are in a mass ratio of 3:1.5:95.5.

[0260] Example 10

[0261] The same as Example 3, except that S1: the elemental sulfur and the polypropylene-based carbon fiber are uniformly mixed by ball milling, and then sintered in an inert atmosphere, wherein the sintering temperature is 200°C, and the sintering time is 6h, and finally the obtained sintered material is mixed with the positive electrode active material NCM, and the mixing is performed under the condition that the rotating speed is 600r / s, to obtain the positive electrode material containing the first coating layer on the surface, and the elemental sulfur, the polypropylene-based carbon fiber and the positive electrode active material NCM in the positive electrode material are in a mass ratio of 2.5:0.5:96.5; the obtained positive electrode material is mixed with the elemental sulfur, the conductive carbon black and the PVDF in a mass ratio of 100:2:2:1, to obtain the positive electrode material containing the double-layer coating on the surface; and the positive electrode material is mixed with the conductive carbon black and the PVDF in a mass ratio of 95:3:2, to obtain the positive electrode material containing the three-layer coating.

[0262] Comparative Example 1

[0263] The same as Example 1, except that S1: no elemental sulfur and polypropylene-based carbon fiber are added.

[0264] Comparative Example 2

[0265] The same as Example 1, except that S1: the elemental sulfur is mixed with the positive electrode active material NCM under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, and the elemental sulfur and the positive electrode active material NCM in the positive electrode material are in a mass ratio of 0.02:99.98.

[0266] Comparative Example 3

[0267] The same as Example 1, except that S1: the polypropylene-based carbon fiber is mixed with the positive electrode active material NCM under the condition that the rotating speed is 600r / s, to obtain the modified positive electrode material, and the polypropylene-based carbon fiber and the positive electrode active material NCM in the positive electrode material are in a mass ratio of 0.5:99.5.

[0268] In order to verify the progressiveness of the embodiments of the present application, the secondary batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3 are subjected to the following tests:

[0269] 1. Secondary battery discharge DCR test:

[0270] The prepared secondary battery was placed at 25°C for 30 min, charged at 1 / 3C rate to 4.25V, and constant voltage to 0.05C to end. It was placed for 10 min, discharged at 1 / 3C rate to 50% of the full charge capacity of the battery, which was called 50% SOC; it was placed for 60 min, discharged at 4C rate for 10 s, and the DCR value of the battery was recorded.

[0271] 2. Storage test:

[0272] The prepared secondary battery was stored at 60°C and 97% SOC. The initial reversible capacity and actual reversible capacity of the battery were taken as C0 and Cn before and during storage, and the battery was taken out for testing every 15 days. The test process was as follows: the secondary battery was placed at 25°C for 30 min, charged at 1 / 3C rate to 4.25V, and constant voltage to 0.05C to end, placed for 30 min, discharged at 1 / 3C rate to 2.8V, and the initial reversible capacity C0 was recorded. The battery was tested every 15 days, and Cn (n = 1, 2, 3, 4, 5…) was recorded; when Cn / C0≤80%, n was recorded; EOL storage days = 15*n.

[0273] 3. Cycle test:

[0274] The temperature was adjusted to 45°C and kept for 2 h. It was placed for 5 min, charged at 1 / 3C to 4.25V, and constant voltage charged at 4.25V to 0.05C to end. It was placed for 5 min, discharged at 0.5C to 2.8V. It was placed for 5 min, and the above process was repeated until the capacity decayed to 80%.

[0275] The test results are shown in Table 1.

[0276] Table 1

[0277]

[0278] As can be seen from the comparison of Example 1 and Comparative Example 1 in Table 1, compared with not adding elemental sulfur and carbon fibers, the battery has improved capacity retention rate after storage or after cycling by simultaneously adding elemental sulfur and carbon fibers in the positive electrode active material NCM, because the carbon fibers can construct a conductive network on the surface of the positive electrode active material NCM to improve the conductivity of the positive electrode material and reduce the polarization loss of the battery, and the carbon fibers can anchor the elemental sulfur to introduce the elemental sulfur on the surface of the positive electrode active material NCM, promote the full reaction of the elemental sulfur and the residual lithium compound on the surface of the positive electrode active material NCM, and generate an artificial CEI film on the surface of the positive electrode active material NCM to effectively reduce the amount of residual lithium compound, thereby reducing the occurrence of side reactions in the battery, improving the stability of the positive electrode material structure and the interface stability on the positive electrode, and being beneficial to maintaining the capacity of the battery. In the process of the reaction of the elemental sulfur and the residual lithium compound, additional lithium ions are also released to compensate for the loss of lithium ions due to the formation of the SEI film, ensure the inventory of active lithium, and further ensure the capacity of the battery.

[0279] As can be seen from the comparison of Example 1 and Comparative Example 2 in Table 1, compared with only adding elemental sulfur, the battery has improved capacity retention rate after storage or after cycling by simultaneously adding elemental sulfur and carbon fibers in the positive electrode active material NCM, because the elemental sulfur itself has poor conductivity, and only adding elemental sulfur will make the conductivity of the positive electrode material poor, increase the polarization of the battery, and the elemental sulfur is not sufficiently anchored on the positive electrode active material NCM, which is easy to separate from the positive electrode active material NCM, so that the elemental sulfur and the residual lithium compound cannot fully react, and the capacity of the battery cannot be effectively maintained.

[0280] As can be seen from the comparison of Example 1 and Comparative Example 3 in Table 1, compared with only adding carbon fibers, the battery has improved capacity retention rate after storage or after cycling by simultaneously adding elemental sulfur and carbon fibers in the positive electrode active material NCM, because only adding carbon fibers improves the conductivity of the positive electrode material, but the residual lithium compound on the surface of the positive electrode active material NCM cannot be eliminated, and the existence of the residual lithium compound will affect the conductivity of the positive electrode active material NCM and promote the occurrence of side reactions, thereby affecting the capacity of the battery.

[0281] As can be seen from Example 1 to Example 5 in Table 1, when the content of carbon fibers is fixed, the capacity retention rate after storage or after cycling of the battery increases with the increase of the content of elemental sulfur, but when the content of elemental sulfur is greater than 5wt%, the capacity retention rate after storage or after cycling decreases, because too much elemental sulfur causes sulfur residue, reduces the conductivity of the positive electrode material, increases the polarization of the battery, and continuously consumes the active lithium inside the battery during storage, which deteriorates the performance of the battery.

[0282] As can be seen from Table 1, Example 7, Example 3, Example 8 and Example 9, when the content of elemental sulfur is fixed, increasing the content of carbon fibers can reduce the DCR of the battery, and the storage capacity retention rate and the cycle capacity retention rate of the battery are both relatively high.

[0283] As can be seen from Table 1, Example 6 and Example 9, although increasing the content of carbon fibers can reduce the DCR of the battery, when the content of carbon fibers is greater than 1 wt%, for example, 1.4 wt% or 1.5 wt%, the positive electrode material is prone to physical gelation during slurry preparation, and the processability of the positive electrode material is poor.

[0284] In addition, as can be seen from the comparison of Example 3 and Example 10 in Table 1, when a plurality of coating layers are arranged on the surface of the positive electrode active material NCM, and the content of elemental sulfur in each coating layer decreases from the inside to the outside, the storage capacity retention rate of the battery is significantly improved, because the outer coating layer with low content of elemental sulfur can block the inner coating layer with high content of elemental sulfur, as much as possible to limit the elemental sulfur inside the positive electrode material, inhibit the elemental sulfur from flowing to the negative electrode to react with active lithium to cause lithium consumption, thereby improving the capacity retention rate of the battery.

[0285] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode material applied to a lithium ion battery, characterized in that, The positive electrode active material and one-dimensional conductive material and additive distributed on the surface of the positive electrode active material, at least part of the one-dimensional conductive material is wrapped by the additive, the additive contains a sulfur element with reducibility. The sulfur element includes at least one of sulfur element, selenium element and tellurium element.

2. The positive electrode material of claim 1, wherein, The sulfur element includes sulfur element, and the additive includes at least one of sulfur single substance, metal sulfide, polysulfide, sulfur-containing organic polymer or copolymer and polymerized sulfur.

3. The cathode material of claim 1, wherein, The additive includes sulfur element single substance.

4. The positive electrode material of claim 2, wherein, The one-dimensional conductive material includes one-dimensional conductive carbon material.

5. The cathode material of claim 1, wherein, The one-dimensional conductive carbon material includes at least one of short carbon fiber, nanometer carbon fiber and carbon nanotube.

6. The positive electrode material of claim 5, wherein, The short carbon fiber includes at least one of PAN-based carbon fiber, phenolic-based carbon fiber, viscose-based carbon fiber, pitch-based carbon fiber, biomass-based carbon fiber and activated carbon fiber.

7. The positive electrode material according to claim 6, characterized in that, The diameter of the short carbon fiber is 100nm-500nm; and / or, the length of the short carbon fiber is 1μm-5μm.

8. The positive electrode material of claim 7, wherein, The mass percentage of the sulfur element is 0.02wt%-5wt% based on the total mass of the positive electrode material.

9. The cathode material of claim 1, wherein, The mass percentage of the one-dimensional conductive material is greater than 0 and less than or equal to 1wt% based on the total mass of the positive electrode material.

10. The cathode material of claim 1, wherein, The surface of the positive electrode active material is coated with a coating layer, the coating layer includes a first sub-coating layer, the first sub-coating layer contains the one-dimensional conductive material and the additive wrapped on the one-dimensional conductive material.

11. The cathode material of any one of claims 1 to 10, wherein, The coating layer further includes a second sub-coating layer, the second sub-coating layer is arranged on the side of the first sub-coating layer away from the positive electrode active material, the second sub-coating layer contains a conductive agent and a binder, the content of the sulfur element in the second sub-coating layer is greater than or equal to 0 and less than the content of the sulfur element in the first sub-coating layer.

12. The positive electrode material of claim 11, wherein, The content of the sulfur element in the second sub-coating layer is greater than 0, and the coating layer further includes a third sub-coating layer, the third sub-coating layer is coated on the surface of the second sub-coating layer, the third sub-coating layer contains the conductive agent and the binder.

13. The positive electrode material of claim 12, wherein, The thickness of the coating layer is 100nm-1000nm.

14. The cathode material of claim 11, wherein, The mass percentage of the coating layer is 0.01wt%-6wt% based on the total mass of the positive electrode material.

15. The cathode material of claim 11, wherein, The mass percentage of the coating layer is 0.1wt%-1wt% based on the total mass of the positive electrode material.

16. The cathode material of claim 15, wherein, The DV50 particle size of the positive electrode active material is 5μm-15μm.

17. The cathode material of any one of claims 1 to 10, wherein, The positive electrode active material includes a chemical formula Li a Ni m Co n M 1-m-n A nickel-rich active material of the chemical formula Li Ni Co M O2, where M includes at least one of Mn and Al, where m≥0.6, n≤0.2, 0.9≤a≤1.

2.

18. The cathode material of claim 17, wherein, The positive electrode active material includes a chemical formula Li a Ni m Co n M 1-m-n A nickel-rich active material of the chemical formula Li nMnaCo bO2, where M includes at least one of Mn and Al, where m≥0.9, n≤0.2, and 0.9≤a≤1.

2.

19. The cathode material of any one of claims 1 to 10, wherein, The one-dimensional conductive material and additive are mixed to obtain a mixture, the additive contains a sulfur element with reducibility; 20. A method of producing a positive electrode material, characterized by, The mixture is sintered to melt the additive, and at least part of the one-dimensional conductive material is wrapped by the additive, thereby obtaining a sintered material; The sintered material is stirred with a positive electrode active material to obtain a positive electrode material, the positive electrode material is applied to a lithium ion battery. The sulfur element includes at least one of sulfur element, selenium element and tellurium element. ​ 21. The method of claim 20, wherein the method further comprises: ​ 22. The method of claim 21, wherein the method further comprises: The additive comprises a chalcogen element simple substance; and / or the one-dimensional conductive material comprises a one-dimensional conductive carbon material.

23. The method of claim 22, wherein the method further comprises: The additive comprises a sulfur simple substance, the sintering treatment temperature is 180-220℃, and / or the sintering time is 5-7h.

24. The method of producing a cathode material according to any one of claims 20 to 23, wherein, The DV50 particle size of the additive is greater than 0 and less than or equal to 1μm.

25. The method of claim 24, wherein the method further comprises: The DV50 particle size of the additive is 100-500nm.

26. The method of claim 20 to 23, wherein the method is characterized by, The mixing treatment comprises a ball milling treatment; and / or the stirring treatment rotation speed is 400-1000r / s.

27. The method of claim 20 to 23, wherein the method is characterized by, The positive electrode active material includes a chemical formula Li a Ni m Co n M 1-m-n a nickel-rich active material of the chemical formula Li 0.9≤a≤1.

2.

28. The method of claim 27, wherein the method further comprises: The positive electrode active material includes a chemical formula Li a Ni m Co n M 1-m-n A nickel-rich active material of the chemical formula Li Ni Co Mn O2, wherein M includes at least one of Mn and Al; wherein m≥0.9, n≤0.2, 0.9≤a≤1.

2.

29. A positive electrode sheet characterized by comprising: The positive electrode plate comprises a positive electrode current collector and a positive electrode material layer combined on the positive electrode current collector, and the positive electrode material layer comprises the positive electrode material according to any one of claims 1-19 or the positive electrode material prepared by the method according to any one of claims 20-28.

30. A battery, comprising: The positive electrode plate according to claim 29.

31. An electrical device, comprising: The battery according to claim 30.

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