CN114361458B

CN114361458B - Positive electrode material and preparation method thereof, positive electrode piece, secondary battery, battery module, battery pack and electric device

Info

Publication number: CN114361458B
Application number: CN202210232645.2A
Authority: CN
Inventors: 陈祥斌; 赵子萌; 卢晓康; 高凯; 来佑磊
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-03-10
Filing date: 2022-03-10
Publication date: 2022-07-15
Anticipated expiration: 2042-03-10
Also published as: CN114361458A

Abstract

The application provides a positive electrode material, a preparation method thereof, a positive electrode piece, a secondary battery, a battery module, a battery pack and an electric device. The positive electrode material includes secondary particles formed by aggregating a plurality of primary particles of a positive electrode active material, wherein the surfaces of the primary particles are coated with a coating layer containing a C element and a Si element. In the cathode material of this application, the surface cladding of primary particle has above-mentioned coating, and this coating does not react and has good electric conductivity with electrolyte, can avoid anodal active material and electrolyte to take place the side reaction, improve cathode material's electric conductivity to can effectively improve secondary battery's cyclicity ability, extension secondary battery's cycle life.

Description

Positive electrode material and preparation method thereof, positive electrode plate, secondary battery, battery module, battery pack and electric device

Technical Field

The application relates to the technical field of secondary batteries, in particular to a positive electrode material and a preparation method thereof, a positive electrode piece, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, with the wider application range of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, vehicles, military equipment and aerospace. As the development of secondary batteries has been greatly advanced, higher requirements are also placed on energy density, cycle performance, safety performance, and the like.

However, the conventional positive electrode active material is liable to undergo a side reaction with the electrolyte during the cycle of the secondary battery, resulting in a loss of the active material and a reduction in the cycle life of the secondary battery. Therefore, the existing positive electrode material still needs to be improved.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a positive electrode material that can achieve both high energy density and long cycle life of a secondary battery.

In order to achieve the purpose, the application provides a positive electrode material, a preparation method thereof, a positive electrode plate, a secondary battery, a battery module, a battery pack and an electric device.

A first aspect of the present application provides a positive electrode material comprising secondary particles formed by aggregating a plurality of primary particles of a positive electrode active material, wherein the primary particles are surface-coated with a coating layer containing a C element and a Si element, optionally, the coating layer contains a simple substance of carbon and SiO₂。

In the cathode material that this application provided, the primary particle surface cladding that constitutes secondary particle has the cladding that contains C element and Si element, and wherein, Si element can avoid anodal active material and electrolyte to contact and take place the side reaction, and C element can improve the electron conductivity of cladding to make cathode material have lower surface impedance. Therefore, the cathode material is applied to the secondary battery, the cycle performance of the secondary battery can be improved, and the secondary battery has a long cycle life. In addition, the cathode material carries out surface coating on primary particles, even if the secondary particles crack along the grain boundary of the primary particles in the charging and discharging process of the secondary battery, the generated new surface is still coated with a coating layer containing C elements and Si elements, the secondary battery cannot contact with electrolyte to generate side reaction, and the cycle performance of the secondary battery is ensured. Further, the coating layer contains simple substance of carbon and SiO₂When the carbon simple substance has higher electronic conductivity, the cathode material has lower surface impedance, and SiO₂The secondary battery can avoid side reaction between the transition metal in the anode active material and the electrolyte, thereby reducing the dissolution of the transition metal and avoiding the anode material from being converted into an inactive rock salt phase, thereby effectively improving the cycle performance of the secondary battery and prolonging the cycle life of the secondary battery.

In any embodiment of the first aspect of the present application, the secondary particles have a polycrystalline structure.

The cathode material comprises secondary particles with a polycrystalline structure, can have higher theoretical gram capacity, and can enable the secondary battery to have higher energy density when being applied to the secondary battery.

In any embodiment of the first aspect of the present application, the positive electrode active material is selected from at least one of a ternary positive electrode material, a quaternary positive electrode material, optionally the positive electrode active material comprises at least one of NCM, NCA, NCMA, more optionally the positive electrode active material comprises a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂ formula 1

In formula 1, x is greater than or equal to 0.5 and less than 1, y is greater than or equal to 0 and less than or equal to 0.5, z is greater than or equal to 0 and less than or equal to 0.5, and x + y + z = 1.

The positive electrode active material is selected from the above-mentioned suitable materials, enabling the secondary battery to have higher energy density, good cycle performance and long cycle life.

In any embodiment of the first aspect of the present application, the positive electrode material satisfies one or more of the following (1) to (3).

(1) In the positive electrode material, the median diameter D of the primary particles₅₀Is 0.2 μm to 1.5 μm. The primary particles have a proper median particle size, so that the positive electrode material has a proper coating structure, and the positive electrode material has lower surface impedance and higher energy density on the premise of avoiding side reaction of the positive electrode active material and the electrolyte, thereby prolonging the cycle life of the secondary battery, improving the cycle performance of the secondary battery and ensuring that the secondary battery has higher energy density.

(2) In the positive electrode material, the median diameter D of the secondary particles ₅₀4 to 12 μm. The secondary particles have a median diameter within the above-mentioned suitable range, which is not only beneficial to preventing the secondary particles from being broken or pulverized in the charging and discharging process, thereby reducing the capacity loss of the secondary battery, but also capable of shortening the diffusion path of active ions, improving the conduction rate of electrons, and being beneficial to improving the cycle performance of the secondary battery. Further, the secondary particles having a median diameter within the above-described appropriate range can also provide the positive electrode material with an appropriate valueThe coating structure can prolong the cycle life of the secondary battery, improve the cycle performance of the secondary battery and ensure that the secondary battery has higher energy density.

(3) In the primary particles, the thickness of the coating layer is 10 nm-50 nm. The thickness of the coating layer is within the range, so that the side reaction caused by the contact of the anode active material and the electrolyte can be effectively avoided on the premise of ensuring that the anode material has higher energy density, and the anode material can be ensured to have lower surface impedance. The thickness of the coating layer is controlled within the above-mentioned appropriate range, which can ensure the high energy density, good cycle performance and long cycle life of the secondary battery.

The second aspect of the present application also provides a method for preparing a positive electrode material according to any one of the embodiments of the first aspect of the present application, comprising:

uniformly mixing primary particles of the positive electrode active material with first silicone oil, second silicone oil, a hydrosilylation catalyst and an organic solvent to obtain primary particles of which the surfaces are coated with the silicone oil, wherein one of the first silicone oil and the second silicone oil is the silicone oil containing the silicon-hydrogen bond, and the other is the silicone oil containing the alkenyl group;

granulating the primary particles coated with the silicone oil at a reaction temperature to solidify the first silicone oil and the second silicone oil on the surfaces of the primary particles, thereby obtaining an organic silicon-coated secondary particle precursor of the positive electrode active material, wherein the secondary particle precursor of the positive electrode active material comprises a plurality of primary particles of the positive electrode active material coated with the organic silicon on the surfaces;

calcining the precursor of the secondary particles of the positive electrode active material in an inert atmosphere to obtain secondary particles formed by aggregating a plurality of primary particles of the positive electrode active material, wherein the surface of the primary particles is coated with a coating layer containing a C element and a Si element, and optionally, the coating layer contains a carbon simple substance and SiO₂。

Thus, according to the method of the present application, secondary particles in which a plurality of primary particles of a positive electrode active material are aggregated are prepared, and the surface and internal pore channels of each primary particle are coated with a coating layer containing a C element and a Si element. The coating toolThe conductive material has good conductivity, can be tightly combined with primary particles, is not easy to fall off even in the later cycle period, and can effectively avoid the contact of the positive active material and electrolyte, so that the positive material has lower surface impedance and higher stability, and the secondary battery has good cycle performance and long cycle life. Further, when the clad layer contains C and SiO₂The coating layer also has good mechanical properties, and can inhibit the volume expansion of the positive active material, thereby further improving the cycle performance of the secondary battery and prolonging the cycle life of the secondary battery.

In addition, according to the secondary particles prepared by the method, even if the secondary battery cracks along the grain boundary of the primary particles in the charging and discharging processes, the generated new surface is still coated with the coating layer containing the C element and the Si element, so that the side reaction caused by the contact of the positive electrode active material and the electrolyte can be avoided, and the cycle performance of the secondary battery is ensured.

In any embodiment of the second aspect of the present application, uniformly mixing primary particles of a positive electrode active material with a first silicone oil, a second silicone oil, a catalytic amount of a hydrosilylation catalyst, and an organic solvent to obtain primary particles of a positive electrode active material with a surface coated with the silicone oil, the primary particles of a positive electrode active material comprising:

mixing and grinding the secondary particles of the positive electrode active material, the first silicone oil and the organic solvent to obtain primary particles of the positive electrode active material, a mixture of the first silicone oil and the organic solvent, optionally defining a ratio of a volume of the organic solvent to a mass of the secondary particles of the positive electrode active material as a, the range of a satisfying: a = 0.5L/kg-1.5L/kg;

and uniformly mixing the mixture with second silicone oil and a hydrosilylation catalyst to obtain the primary particles of the positive electrode active material with the surface coated with the silicone oil.

Therefore, the first silicone oil and the second silicone oil can be prevented from reacting and solidifying in the mixing process, and the coating layer can be uniformly and fully covered on the surface of the primary particles in the prepared cathode material. The range of the parameter a is within the above-mentioned suitable range, and a suitable amount of silicone oil can be coated on the surface of the primary particles. Therefore, in the prepared cathode material, the coating layer on the surface of the primary particles can have a proper thickness, the volume expansion of the cathode active material can be effectively inhibited, and the capacity exertion and the cycle performance of the secondary battery are ensured.

In any embodiment of the second aspect of the present application, the positive electrode active material is selected from at least one of a ternary positive electrode material, a quaternary positive electrode material, optionally the positive electrode active material comprises at least one of NCM, NCA, NCMA, more optionally the positive electrode active material comprises a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂ formula 1

In formula 1, x is 0.5. ltoreq. x < 1, y is 0. ltoreq. y.ltoreq.0.5, z is 0. ltoreq. z.ltoreq.0.5, and x + y + z = 1.

The positive electrode active material is selected from the appropriate materials, and the prepared positive electrode material is applied to a secondary battery, so that the secondary battery has higher energy density, good cycle performance and long cycle life.

In any embodiment of the second aspect of the present application, the primary particles of the positive electrode active material have a median particle diameter D₅₀Is 0.2 μm to 1.5 μm. The median diameter D of the primary particles of the positive electrode active material obtained by grinding₅₀The prepared positive electrode material has a proper coating structure by controlling within the proper range, so that the positive electrode material has lower surface impedance and higher energy density on the premise of avoiding side reaction of the positive electrode active material and the electrolyte, the cycle life of the secondary battery can be prolonged, the cycle performance of the secondary battery is improved, and the secondary battery is ensured to have higher energy density.

In any embodiment of the second aspect of the present application, the silicon-hydrogen bond-containing silicone oil includes a silicone oil having at least two silicon-hydrogen bonds in a molecule, optionally, the silicon-hydrogen bond-containing silicone oil includes a silicone oil having two silicon-hydrogen bonds in a molecule, more optionally, the silicon-hydrogen bond-containing silicone oil includes a silicone oil represented by formula 2,

formula 2

In formula 2, m is not less than 2 and not more than 20.

The silicone oil containing the silicon-hydrogen bond meeting the requirements can react with the silicone oil containing the alkenyl group at a reaction temperature in the presence of a hydrosilylation catalyst to obtain the silicone with a larger molecular weight, so that the liquid silicone oil is cured to form the silicone.

In any embodiment of the second aspect of the present application, the alkenyl group-containing silicone oil includes a silicone oil having at least two alkenyl groups in a molecule, alternatively, the alkenyl group-containing silicone oil includes a silicone oil having two alkenyl groups in a molecule, more alternatively, the alkenyl group-containing silicone oil includes a silicone oil represented by formula 3,

formula 3

In formula 3, n is not less than 2 and not more than 20.

The silicone oil containing alkenyl groups meeting the requirements can react with the silicone oil containing the silicon-hydrogen bonds at the reaction temperature in the presence of a hydrosilylation catalyst to obtain the silicone with larger molecular weight, so that the liquid silicone oil is cured to form the silicone.

In any embodiment of the second aspect of the present application, the ratio of the amount of the material of the silicon-hydrogen bond to the alkenyl group in the first silicone oil and the second silicone oil is 1:1 to 1:4, and optionally 1:2 to 1: 4.

In the first silicone oil and the second silicone oil, the ratio of the quantity of the substance of the silicon-hydrogen bond and the alkenyl group is proper, the molecular weight of the generated solid silicone can be effectively controlled, and therefore the silicone coated on the surface of the primary particles has proper thickness.

In any embodiment of the second aspect of the present application, the hydrosilylation catalyst comprises at least one of a Karstedt catalyst, chloroplatinic acid, chlororhodic acid, chloroiridic acid, optionally the hydrosilylation catalyst comprises a Karstedt catalyst.

The hydrosilylation catalyst of the above kind enables the first silicone oil and the second silicone oil to have a suitable curing rate, thereby enabling the coating layer on the surface of the primary particle to have a suitable thickness. In addition, the hydrosilylation catalyst of the above kind has stable properties and does not affect the performance of the prepared positive electrode material.

In any embodiment of the second aspect of the present application, the median particle diameter D of the precursor of the secondary particles of the positive electrode active material₅₀Is 3 μm to 12 μm.

Median diameter D of precursor of secondary particles of positive electrode active material₅₀The control within the proper range can ensure that the median particle size of the secondary particles in the prepared cathode material is within the proper range, thereby prolonging the cycle life of the secondary battery, improving the cycle performance of the secondary battery and ensuring that the secondary battery has higher energy density.

In any embodiment of the second aspect of the present application, the calcination temperature is 300 ℃ to 600 ℃, and the calcination time is 2h to 6 h.

The calcination temperature and time of the secondary particle precursor of the positive electrode active material are controlled within the above ranges, and the prepared secondary particles can have a more stable structure. The anode material prepared in the way is applied to a secondary battery, and can ensure that the secondary battery has high energy density, good cycle performance and long cycle life.

In any embodiment of the second aspect of the present application, the coating layer has a thickness of 10nm to 50nm in the primary particle.

The thickness of the coating layer is within the range, so that the side reaction caused by the contact of the anode active material and the electrolyte can be effectively avoided on the premise of ensuring that the anode material has higher energy density, and the anode material can be ensured to have lower surface impedance. The thickness of the coating layer is controlled within the above-mentioned appropriate range, which can ensure the high energy density, good cycle performance and long cycle life of the secondary battery.

A third aspect of the present application provides a positive electrode sheet comprising the positive electrode material of the first aspect of the present application or the positive electrode material prepared according to the method of the second aspect of the present application.

A fourth aspect of the present application provides a secondary battery comprising the positive electrode sheet of the third aspect of the present application.

A fifth aspect of the present application provides a battery module including the secondary battery of the fourth aspect of the present application.

A sixth aspect of the present application provides a battery pack including the battery module of the fifth aspect of the present application.

A seventh aspect of the present application provides an electric device including at least one selected from the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application.

The positive electrode plate, the secondary battery, the battery module, the battery pack and the power utilization device comprise the positive electrode material provided by the application, so that the positive electrode plate, the secondary battery, the battery module, the battery pack and the power utilization device at least have the same advantages as the positive electrode material provided by the application.

Drawings

Fig. 1 is a schematic view of an embodiment of the secondary battery of the present application.

Fig. 2 is an exploded view of the embodiment of the secondary battery of the present application shown in fig. 1.

Fig. 3 is a schematic diagram of an embodiment of a battery module of the present application.

Fig. 4 is a schematic diagram of an embodiment of a battery pack of the present application.

Fig. 5 is an exploded view of the embodiment of the battery pack of the present application shown in fig. 4.

Fig. 6 is a schematic diagram of an electric device in which an embodiment of the secondary battery of the present application is used as a power source.

Fig. 7 is a Scanning Electron Microscope (SEM) image of the positive electrode material of example 1 in the present application.

Fig. 8 is an SEM image of the positive electrode material of comparative example 1 in the present application.

Fig. 9 is an SEM image of the cathode material of comparative example 2 in the present application.

Fig. 10 is a 45 c cycle capacity retention rate test chart of the secondary batteries of example 1, comparative example 1 and comparative example 2 in the present application.

Description of reference numerals:

1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 a cap assembly.

Detailed Description

Hereinafter, embodiments of the positive electrode material, the method for producing the positive electrode material, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electric device according to the present application are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually the same structures may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is simply an abbreviated representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not specifically mentioned.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, any one of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

With the gradual decrease of traditional energy resources, the development of new energy storage devices is more and more emphasized. Among them, the secondary battery is receiving attention because of its high energy density, high theoretical capacity, good cycle stability and environmental protection characteristics.

The energy density and stability of the positive electrode material are important factors affecting the energy density and cycle performance of the secondary battery. At present, low cost, high theoretical capacity polycrystalline positive electrode materials, such as layered Li (Ni)_xCo_yMn_1-x-y）O₂（0 <x <1,0 <y <1，0 <1-x-y <1) And the like, are widely used.

However, during the charge and discharge of the secondary battery, the high-valence metal ions in the positive electrode active material are liable to undergo a side reaction with the electrolyte, thereby causing deactivation of the positive electrode active material, and further causing problems such as reduction in energy density and cycle life of the secondary battery. With Li (Ni)_xCo_yMn_1-x-y）O₂（0 <x <1,0 <y <1，0 <1-x-y <1) As an example of the positive electrode active material, during charge and discharge of the secondary battery, the valence state of Ni changes between +2, +3, +4, and nickel having a valence of +4 has a strong oxidizing property and is liable to undergo a side reaction with an electrolyte to generate nickel having a valence of +2, resulting in Li (Ni)_xCo_yMn_1-x-y）O₂Transition from the hexagonal phase to the halite phase results in loss of active species. In addition, since the electrolyte contains HF, it is likely to react with the positive electrode active material, thereby dissolving out transition metal ions, precipitating on the surface of the negative electrode, and destroying the SEI film, resulting in loss of active lithium. Therefore, it is important to suppress the reaction of the positive electrode active material with the electrolyte to improve the cycle life of the secondary battery.

At present, the method for inhibiting the reaction of the positive electrode active material with the electrolyte is mainly to coat the surface of the positive electrode active material with an inert oxide, for example, Al₂O₃、TiO₂、ZrO₂、SiO₂And coating the surface of the positive electrode active material to avoid the positive electrode active material from contacting with the electrolyte, so that the side reaction between the positive electrode active material and the electrolyte is reduced.

However, the inventors have found through research that coating the positive electrode active material with the inert oxide increases the surface impedance of the positive electrode active material, which affects the electrochemical performance of the secondary battery, and that the positive electrode active material is prone to crack and generate a new surface due to volume expansion and contraction during charge and discharge, and the positive electrode active material inevitably contacts with the electrolyte, thereby causing pulverization and deactivation of the positive electrode active material particles. In particular, in the case of a polycrystalline positive electrode active material, intergranular cracks are easily generated due to the anisotropy of primary particles during the occurrence of volume expansion and contraction, resulting in secondary particle cracks to generate new surfaces. The positive electrode active material exposed on the new surface is eroded by the electrolyte, eventually resulting in pulverization deactivation of the positive electrode active material particles. At present, the problem of surface impedance increase of the positive electrode material caused by coating is mostly relieved by composite coating of fast ion conductor carbon. However, the effect of composite-coated fast ion conductor carbon on the reduction of surface resistance still cannot meet the current demand for use, and the problem of pulverization deactivation of particles of the positive electrode active material cannot be solved.

In view of the above, the inventors of the present invention have made extensive consideration and provide a positive electrode material, a method for preparing the same, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device.

Positive electrode material

A first aspect of the present application provides a positive electrode material including secondary particles aggregated from a plurality of primary particles of a positive electrode active material. Wherein the surface of the primary particles is coated with a coating layer containing C element and Si element, optionally, the coating layer contains simple substance of carbon and SiO₂。

Although the mechanism is not clear, the applicant has surprisingly found that: this application has the coating that contains C element and Si element through the cladding in positive pole active material's primary particle surface, can effectively improve the stability of positive pole material at secondary battery charge-discharge in-process to improve secondary battery's cyclicity ability.

Specifically, without intending to be bound by any theory or explanation, the inventors found that, compared to the prior art of composite coating of inert oxide and fast ion conductor carbon on the positive electrode active material, the coating layer on the surface of the primary particles in the present application is a single layer, which has more uniform properties on one hand and better conductivity on the other hand, and can make the positive electrode material have lower surface impedance under the condition of avoiding the positive electrode active material contacting with the electrolyte, thereby improving the cycle performance of the secondary battery and making the secondary battery have longer cycle life.

Further, the positive electrode material coats the surface of the primary particles, so that even if the secondary particles crack along the grain boundary of the primary particles in the charging and discharging processes of the secondary battery, the generated new surface is still coated with the coating layer containing the C element and the Si element, the secondary battery cannot contact with electrolyte to generate side reaction, and the cycle performance of the secondary battery is ensured.

Furthermore, the coating layer contains carbon simple substance and SiO₂Wherein the carbon simple substance can improve the conductivity of the anode material, and SiO₂Can react with HF in the electrolyte, thereby consuming HF impurities in the electrolyte and reducing the dissolution of transition metals in the anode material by HF, so as to avoid the conversion of the anode active material into an inactive rock salt phase and reduce the loss of the anode active material. In addition, the coating layer contains carbon simple substance and SiO₂And the coating layer has good mechanical property, and the volume expansion of the positive electrode active material is inhibited. The coating layer contains carbon simple substance and SiO₂The cycle performance of the secondary battery can be effectively improved, and the cycle life of the secondary battery can be prolonged.

In some embodiments, the secondary particles may have a polycrystalline structure.

The secondary particles have a polycrystalline structure, which may mean: the secondary particles are spherical secondary particles formed by agglomerating a plurality of single crystal particles (primary particles).

The cathode material comprises secondary particles with a polycrystalline structure, can have higher theoretical gram capacity, and can enable the secondary battery to have higher energy density when being applied to the secondary battery. The secondary particles with the polycrystalline structure are formed by gathering primary particles of a plurality of anode active materials, and the surfaces of the primary particles are coated with coatings containing C elements and Si elements, so that the secondary particles have higher stability and lower impedance, the capacity of the anode materials can be ensured to be exerted, and the secondary battery is ensured to have high energy density, good cycle performance and long cycle life.

In some embodiments, the positive active material may be selected from at least one of a ternary positive material, a quaternary positive material. Optionally, the positive electrode active material comprises at least one of NCM, NCA, NCMA. More alternatively, the positive active material includes a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂formula 1

Without intending to be bound by any theory or explanation, the inventors found that, in the cathode material of the present application, the cathode active material is selected from the above-mentioned suitable materials, enabling a secondary battery to have higher energy density, good cycle performance, and long cycle life.

In some embodiments, the positive electrode material may satisfy one or more of the following (1) to (3).

(1) In the positive electrode material, the median diameter D of the primary particles₅₀Is 0.2 μm to 1.5 μm. Optionally, 0.2 μm to 0.3 μm, 0.2 μm to 0.4 μm, 0.2 μm to 0.5 μm, 0.2 μm to 0.8 μm, 0.2 μm to 1 μm, 0.2 μm to 1.2 μm, 0.2 μm to 1.4 μm, 0.3 μm to 0.4 μm, 0.3 μm to 0.5 μm, 0.3 μm to 0.8 μm, 0.3 μm to 1 μm, 0.3 μm to 1.2 μm, 0.3 μm to 1.4 μm, 0.4 μm to 0.5 μm, 0.4 μm to 0.6 μm, 0.4 μm to 0.8 μm, 0.4 μm to 1 μm, 0.4 μm to 1.2 μm, 0.4 μm to 0.5 μm, 0.4 μm to 0.6 μm, 0.4 μm to 0.8 μm, 0.4 μm to 0.6 μm to 0.7 μm, 0.6 μm to 0.7 μm to 0.6 μm, 0.7 μm to 0.6 μm, 0.6 μm to 0.7 μm to 0.6 μm to 1.7 μm to 0.6 μm to 0.7 μm, 0.6 μm to 0.7 μm to 0.6 μm to 1.7 μm to 0.7 μm to 0.6 μm, 0.7 μm to 0.6 μm, 0.7 μm to 0.6 μm to 1.6 μm to 0.6 μm to 0.7 μm, 0.7 μm to 0.6 μm to 0.7 μm, 0.6 μm to 0.7 μm to 0.6 μm to 0.7 μm to 0.6 μm, 0.7 μm to 1.3 μm, 0.8 μm to 0.9 μm, 0.8 μm to 1 μm, or 0.8 μm to 1.3 μm.

Without intending to be bound by any theory or explanation, the inventors find that the primary particles have a suitable median diameter, so that the cathode material has a suitable coating structure, and thus the cathode material has a lower surface impedance and a higher energy density on the premise of avoiding a side reaction between the cathode active material and the electrolyte, and further the cycle life of the secondary battery can be prolonged, the cycle performance of the secondary battery can be improved, and the secondary battery can be ensured to have a higher energy density.

(2) In the positive electrode material, the median diameter D of the secondary particles₅₀Is 4 μm to 12 μm. Optionally, the particle size is 4 μm to 10 μm, 4.5 μm to 10 μm, 4.7 μm to 10 μm, 4.8 μm to 10 μm, 5 μm to 10 μm, 4 μm to 8 μm, 4.5 μm to 8 μm, 4.7 μm to 8 μm, 4.8 μm to 8 μm, 5 μm to 8 μm, 4 μm to 5 μm5 μm, 4.5 μm to 5.5 μm, 4.7 μm to 5.5 μm, 4.8 μm to 5.5 μm, 5 μm to 5.5 μm, 4 μm to 5.2 μm, 4.5 μm to 5.2 μm, 4.8 μm to 5.2 μm, or 5 μm to 5.2 μm.

Without intending to be bound by any theory or explanation, the median diameter of the secondary particles within the above-mentioned suitable range is not only advantageous for preventing the secondary particles from being crushed or pulverized during the charge and discharge processes, thereby reducing the capacity loss of the secondary battery, but also advantageous for shortening the diffusion path of active ions, increasing the conduction rate of electrons, and improving the cycle performance of the secondary battery. In addition, the median diameter of the secondary particles is in the appropriate range, and the anode material can be enabled to have an appropriate coating structure, so that the anode material has lower surface impedance and higher energy density on the premise of avoiding side reaction between the anode active material and the electrolyte, and further the cycle life of the secondary battery can be prolonged, the cycle performance of the secondary battery can be improved, and the secondary battery can be ensured to have higher energy density.

(3) In the primary particles, the thickness of the coating layer is 10 nm-50 nm. Optionally, 15nm to 45nm, 15nm to 40nm, 15nm to 35nm, 15nm to 30nm, 15nm to 25nm, 15nm to 23nm, 15nm to 20nm, 20nm to 45nm, 20nm to 40nm, 20nm to 35nm, 20nm to 30nm, 20nm to 25nm, 20nm to 23nm, 25nm to 45nm, 25nm to 40nm, 25nm to 35nm, 25nm to 30nm, 30nm to 45nm, 30nm to 40nm, 30nm to 35nm, 35nm to 45nm or 40nm to 45 nm.

Without intending to be bound by any theory or explanation, the thickness of the coating layer within the above range can effectively avoid side reactions caused by the contact of the cathode active material and the electrolyte on the premise of ensuring that the cathode material has higher energy density, and can ensure that the cathode material has lower surface impedance. The thickness of the coating layer is controlled within the above-mentioned appropriate range, and it is possible to ensure a secondary battery having high energy density, good cycle performance and a long cycle life.

Method for preparing positive electrode material

A second aspect of the present application provides a method for preparing a positive electrode material according to any embodiment of the first aspect of the present application, including step S10 of uniformly mixing primary particles of a positive electrode active material with a first silicone oil, a second silicone oil, a hydrosilylation catalyst, and an organic solvent to obtain primary particles of a surface-coated silicone oil, wherein one of the first silicone oil and the second silicone oil is a silicone oil containing a silicon-hydrogen bond, and the other is a silicone oil containing an alkenyl group.

In step S10, the first silicone oil and the second silicone oil are both polysiloxanes that can be kept in a liquid state at room temperature. The silicone oil containing a silicon-hydrogen bond may include a polysiloxane having a silicon-hydrogen bond in a terminal group and/or a silicon-hydrogen bond in a segment. The silicone oil containing alkenyl groups may include polysiloxane containing alkenyl groups at the end groups and/or in the chain segments, wherein the alkenyl groups may include groups containing carbon-carbon double bonds such as vinyl groups, propenyl groups, allyl groups, and the like, and are not limited herein. The hydrosilylation catalyst may be a catalyst for catalyzing a hydrosilylation reaction, and the type and amount of the specific hydrosilylation catalyst may be selected according to the actual circumstances, as long as the hydrosilylation reaction between the first silicone oil and the second silicone oil is promoted, and is not limited herein. The type of the organic solvent is not limited in the present application as long as the first silicone oil and the second silicone oil can be uniformly dispersed, and the performance of the positive electrode material is not affected, and specifically, the organic solvent may include at least one of dichloromethane, chloroform, toluene, xylene, and dichlorotoluene.

In the step S10, the liquid first silicone oil and the liquid second silicone oil, the hydrosilylation catalyst, the organic solvent, and the primary particles of the positive electrode active material are uniformly mixed, and the liquid silicone oil has good fluidity, so that the surface and the inner pore channels of the primary particles can be sufficiently coated, thereby uniformly coating the surface of the primary particles.

The method further includes step S20, granulating the primary particles with the surface coated with the silicone oil at a reaction temperature, so as to cure the first silicone oil and the second silicone oil on the surface of the primary particles, thereby obtaining a precursor of the secondary particles of the positive electrode active material coated with the silicone, where the precursor of the secondary particles of the positive electrode active material includes a plurality of primary particles of the positive electrode active material coated with the silicone.

In step S20, the reaction temperature may be a temperature that facilitates the hydrosilylation reaction, and is not limited herein. As an example, the reaction temperature may be 100 ℃ to 220 ℃, for example, may be 200 ℃. The granulation may be performed by a method known in the art, and is not limited thereto, and may be performed by spray granulation using a spray drier, as an example. The first and second silicone oils are cured on the surface of the primary particle, and may include a hydrosilation reaction of the first and second silicone oils on the surface of the primary particle to produce a solid silicone. The positive electrode active material secondary particle precursor may include a plurality of positive electrode active material primary particles surface-coated with solid silicone.

And step S20, granulating the primary particles with the surfaces uniformly coated with the liquid silicone oil at the reaction temperature, so as to solidify the liquid silicone oil, thereby obtaining the organic silicon-coated secondary particle precursor of the cathode active material. In the obtained precursor of the secondary particles of the positive electrode active material, the surface and the inner pore channels of each primary particle are uniformly coated with the solid organic silicon. And, since the liquid silicone oil is directly cured on the surface of the primary particles, the formed solid silicone can be tightly bonded to the primary particles.

The method of the present application further includes a step S30 of calcining the positive electrode active material secondary particle precursor under an inert atmosphere to obtain secondary particles in which a plurality of primary particles of the positive electrode active material are aggregated. Wherein the surface of the primary particles is coated with a coating layer containing a C element and a Si element. Optionally, the cladding comprises elemental carbon and SiO₂。

In step S30, the inert atmosphere may include at least one of a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, and a xenon atmosphere.

According to the method, the first and second liquid silicone oils, the hydrosilylation catalyst, the organic solvent and the primary particles of the positive active material are uniformly mixed, and the liquid silicone oil has good fluidity and can fully coat the surfaces and the inner pore channels of the primary particles, so that the surfaces of the primary particles are uniformly coated. And granulating the primary particles uniformly coated with the liquid silicone oil on the surface at a reaction temperature to solidify the liquid silicone oil so as to obtain the organic silicon-coated secondary particle precursor of the cathode active material. In the obtained precursor of the secondary particles of the positive electrode active material, the surface and the internal pore canal of each primary particle are uniformly coated with the solid organosilicon. The anode material according to the first aspect of the present application can be obtained by calcining the secondary particle precursor of the anode active material.

According to the method of the present application, secondary particles in which a plurality of primary particles of a positive electrode active material are aggregated are prepared, and the surface and internal pore channels of each primary particle are coated with a coating layer containing a C element and a Si element. The coating layer has good conductivity, can be tightly combined with primary particles, is not easy to fall off in a cycle later period, and can effectively avoid the contact of the positive active material and electrolyte, so that the positive material has lower surface impedance and higher stability, and the secondary battery has good cycle performance and long cycle life. Further, when the coating layer contains carbon simple substance and SiO₂In this case, the coating layer also has good mechanical properties, and can suppress volume expansion of the positive electrode active material, thereby further improving the cycle performance of the secondary battery and prolonging the cycle life of the secondary battery.

In addition, according to the secondary particles prepared by the method, even if the secondary particles crack along the grain boundary of the primary particles in the charging and discharging processes of the secondary battery, the generated new surface is still coated with the coating layer containing the C element and the Si element, so that the side reaction caused by the contact of the positive electrode active material and the electrolyte can be avoided, and the cycle performance of the secondary battery is ensured.

The method provided by the application has the advantages of simple raw materials, low operation difficulty and low cost, and the prepared cathode material is applied to the secondary battery, so that the cycle performance of the secondary battery can be effectively improved, the cycle life of the secondary battery can be prolonged, and the capacity exertion of the secondary battery can be ensured.

In some embodiments, the uniformly mixing the primary particles of the positive electrode active material with the first silicone oil, the second silicone oil, the hydrosilylation catalyst, and the organic solvent to obtain the primary particles of the positive electrode active material with the surface coated with the silicone oil may specifically include:

the secondary particles of the positive electrode active material, the first silicone oil, and the organic solvent are mixed and ground to obtain a mixture of the primary particles of the positive electrode active material, the first silicone oil, and the organic solvent. Alternatively, the ratio of the volume of the organic solvent to the mass of the secondary particles of the positive electrode active material is defined as a, and the range of a may satisfy: a = 0.5L/kg-1.5L/kg, 0.6L/kg-1.3L/kg, 0.8L/kg-1.2L/kg.

The secondary particle size in the above-mentioned grinding step is not limited in the present application. As an example, the median particle diameter D of the secondary particles in the grinding step₅₀Can be 5-15 μm. The above-mentioned grinding can be carried out by a method known in the art, for example, grinding with a sand mill, a ball mill or the like.

The secondary particles of the positive active material, the first silicone oil and the organic solvent are mixed and ground, and then are mixed with the second silicone oil and the hydrosilylation catalyst, so that the first silicone oil and the second silicone oil can be prevented from reacting and solidifying in the mixing process, the primary particles of the positive active material, the first silicone oil, the second silicone oil, the hydrosilylation catalyst and the organic solvent can be uniformly mixed together, and the coating layer can be uniformly and fully covered on the surface of the primary particles in the prepared positive material.

The range of the parameter a within the above-mentioned suitable range enables a mixture of the organic solvent, the first silicone oil, and the second silicone oil to have a suitable viscosity so that the surface of the primary particle is coated with a suitable amount of the silicone oil. Therefore, in the prepared cathode material, the coating layer on the surface of the primary particles can have a proper thickness, the volume expansion of the cathode active material can be effectively inhibited, and the capacity exertion and the cycle performance of the secondary battery are ensured.

In some embodiments, the positive active material may be selected from at least one of a ternary positive material, a quaternary positive material. Specifically, the positive electrode active material may include at least one of NCM, NCA, and NCMA. More specifically, the positive active material may include a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂formula 1

Without intending to be bound by any theory or explanation, the inventors have found that the cathode active material is selected from the above-mentioned suitable materials, and the prepared cathode material is applied to a secondary battery, enabling the secondary battery to have higher energy density, good cycle performance and long cycle life.

In some embodiments, the median particle diameter D of the primary particles of the positive electrode active material₅₀Can be 0.2 μm to 1.5 μm. As an example, the median particle diameter D of the primary particles of the positive electrode active material₅₀Further, the particles may be 0.2 to 0.3 μm, 0.2 to 0.4 μm, 0.2 to 0.5 μm, 0.2 to 0.8 μm, 0.2 to 1 μm, 0.2 to 1.2 μm, 0.2 to 1.4 μm, 0.3 to 0.4 μm, 0.3 to 0.5 μm, 0.3 to 0.8 μm, 0.3 to 1 μm, 0.3 to 1.2 μm, 0.3 to 1.4 μm, 0.4 to 0.5 μm, 0.4 to 0.6 μm, 0.4 to 0.8 μm, 0.4 to 1 μm, 0.4 to 0.7 to 0.6 μm, 0.4 to 0.8 μm, 0.4 to 1 μm, 0.4 to 1.2 μm, 0.4 to 0.5 μm, 0.4 to 0.6 μm, 0.7 to 0.6 to 0.7 to 0.6 μm, 0.6 to 1.7 to 0.6 μm, 0.7 to 0.6 μm, 0.5 to 0.5 μm to 0.6 μm, 0.5 μm, 0.7 to 0.6 μm, 0.6 μm to 1.6 μm, 0.7 μm to 1.3 μm, 0.8 μm to 0.9 μm, 0.8 μm to 1 μm, or 0.8 μm to 1.3 μm.

The median diameter D of the primary particles of the positive electrode active material obtained by grinding₅₀The prepared positive electrode material has a proper coating structure by controlling within the proper range, so that the positive electrode material has lower surface impedance and higher energy density on the premise of avoiding side reaction of the positive electrode active material and the electrolyte, the cycle life of the secondary battery can be prolonged, the cycle performance of the secondary battery is improved, and the secondary battery is ensured to have higher energy density.

In some embodiments, the silicone oil containing silicon hydrogen bonds may include a silicone oil containing at least two silicon hydrogen bonds in the molecule. Specifically, the silicone oil containing a silicon hydrogen bond may include a silicone oil containing two silicon hydrogen bonds in the molecule. More specifically, the silicon oil having a silicon-hydrogen bond may include a silicon oil represented by formula 2,

formula 2

In formula 2, m is more than or equal to 2 and less than or equal to 20.

The silicone oil containing the silicon-hydrogen bond meeting the requirements can react with the silicone oil containing the alkenyl group at the reaction temperature in the presence of a hydrosilylation catalyst to obtain the silicone with larger molecular weight, so that the liquid silicone oil is cured to form the silicone.

In some embodiments, the silicone oil containing an alkenyl group may include a silicone oil containing at least two alkenyl groups in a molecule. Specifically, the silicone oil containing an alkenyl group may include a silicone oil containing two alkenyl groups in the molecule. More specifically, the silicone oil containing an alkenyl group may include a silicone oil represented by formula 3,

formula 3

In formula 3, n is not less than 2 and not more than 20.

The silicone oil containing alkenyl groups meeting the requirements can react with the silicone oil containing silicon hydrogen bonds at a reaction temperature in the presence of a hydrosilylation catalyst to obtain the silicone with a larger molecular weight, so that the liquid silicone oil is cured to form the silicone.

In some embodiments, the ratio of the amount of the material of the silicon-hydrogen bond to the alkenyl group in the first silicone oil and the second silicone oil may be 1:1 to 1:4, 1:1 to 1:3, 1:1 to 1:2, 1:2 to 1:4, 1:2 to 1:3, 1:3 to 1: 4.

In the first silicone oil and the second silicone oil, the ratio of the quantity of the substance of the silicon-hydrogen bond and the alkenyl group is proper, the molecular weight of the generated solid silicone can be effectively controlled, and therefore the silicone coated on the surface of the primary particles has proper thickness. The organic silicon coated on the surface of the primary particles has proper thickness, and the coating layer on the surface of the primary particles in the prepared cathode material can have proper thickness, so that the secondary battery is ensured to have high energy density, good cycle performance and long cycle life.

In some embodiments, the hydrosilylation catalyst may include at least one of Karstedt's catalyst, chloroplatinic acid, chlororhodic acid, chloroiridic acid. Specifically, the hydrosilylation catalyst may include a Karstedt catalyst.

In some embodiments, the median particle diameter D of the precursor of the secondary particles of the positive electrode active material₅₀Can be 3 to 12 μm, 3 to 10 μm, 3.5 to 10 μm, 4 to 10 μm, 4.5 to 10 μm, 4.8 to 10 μm, 3 to 8 μm, 3.5 to 8 μm, 4.5 to 8 μm, 4.8 to 8 μm, 3 to 5.5 μm, 3.5 to 5.5 μm, 4 to 5.5 μm, 4.5 to 5.5 μm, 4.8 to 5.5 μm, 3 to 5.2 μm, 3.5 to 5.2 μm, 4 to 5.2 μm, 4.5 to 5.2 μm, or 4.8 to 5.2 μm.

Median diameter D of precursor of secondary particles of positive electrode active material₅₀By controlling the average particle size of the secondary particles in the positive electrode material to be obtained, the average particle size of the secondary particles can be ensured to be within the appropriate range. Therefore, the secondary particles are prevented from being broken or pulverized in the charging and discharging process, so that the capacity loss of the secondary battery is reduced, the diffusion path of active ions can be shortened, the conduction rate of electrons is improved, and the cycle performance of the secondary battery is improved. In addition, the median diameter of the precursor of the secondary particles of the positive electrode active material is in the proper range, and the prepared positive electrode material can have a proper coating structure, so that the positive electrode material has lower surface impedance and higher energy density on the premise of avoiding side reaction of the positive electrode active material and electrolyte, the cycle life of the secondary battery can be prolonged, and the secondary power can be improvedThe cycle performance of the cell ensures that the secondary battery has higher energy density.

In some embodiments, the temperature of calcination can be from 300 ℃ to 600 ℃, from 350 ℃ to 550 ℃, and from 400 ℃ to 500 ℃. The calcination time can be 2h to 6h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6 h.

Without intending to be bound by any theory or explanation, the calcination temperature and time of the secondary particle precursor of the cathode active material are controlled within the above ranges, and the resulting secondary particle may have a more stable structure. In addition, the calcination temperature and time of the secondary particle precursor of the positive electrode active material are controlled within the above ranges, and a suitable coating structure can also be formed. The anode material prepared in the way is applied to a secondary battery, and the secondary battery can be ensured to have high energy density, good cycle performance and long cycle life.

In some embodiments, the thickness of the coating layer in the primary particle may be 10nm to 50nm, 15nm to 40nm, 15nm to 35nm, 15nm to 30nm, 15nm to 25nm, 15nm to 23nm, 15nm to 20nm, 20nm to 45nm, 20nm to 40nm, 20nm to 35nm, 20nm to 30nm, 20nm to 25nm, 20nm to 23nm, 25nm to 45nm, 25nm to 40nm, 25nm to 35nm, 25nm to 30nm, 30nm to 45nm, 30nm to 40nm, 30nm to 35nm, 35nm to 45nm, or 40nm to 45 nm.

In the present application, the median diameter D of the primary particles₅₀Median diameter D of secondary particles₅₀Have the meaning known in the art and can be determined using methods and apparatus known in the art. For example, it can be determined by a laser particle size analyzer (e.g. Marvin Mastersizer 2000E, England) with reference to GB/T19077-。

In the present application, the thickness of the coating layer has a meaning known in the art and can be determined by methods and apparatuses known in the art. For example, the positive electrode material of the present invention may be dispersed in an ethanol solvent, dropped on a micro-grid support film, and the thickness of the coating layer may be measured by a high-resolution transmission electron microscope.

Positive pole piece

In a third aspect, the present application provides a positive electrode sheet, including a positive electrode material according to any one of the embodiments of the first aspect of the present application, or a positive electrode material prepared by the method according to any one of the embodiments of the second aspect of the present application.

The positive pole piece comprises a positive pole current collector and a positive pole film layer arranged on at least one surface of the positive pole current collector, wherein the positive pole film layer comprises the positive pole material of the first aspect of the application or the positive pole material prepared by the method of the second aspect of the application.

As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.

In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), Polystyrene (PS), Polyethylene (PE), etc.).

In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode plate, such as the positive electrode material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

[ Positive electrode sheet ]

The positive electrode plate is selected from the positive electrode plates according to the third aspect of the present application.

[ negative electrode sheet ]

The negative pole piece includes the negative current collector and sets up the negative pole rete on the negative current collector at least one surface, the negative pole rete includes negative active material.

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

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), Polystyrene (PS), Polyethylene (PE), etc.).

In some embodiments, the negative active material may employ a negative active material for a battery known in the art. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate and the like. The silicon-based material can be at least one selected from the group consisting of elemental silicon, a silicon oxy compound, a silicon carbon compound, a silicon nitrogen compound and a silicon alloy. The tin-based material may be selected from at least one of elemental tin, tin-oxygen compounds, and tin alloys. The present application is not limited to these materials, however, and other conventional materials that can be used as a battery negative active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the anode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), Polyacrylamide (PAM), polyvinyl alcohol (PVA), Sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode film layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the negative electrode sheet can be prepared by: dispersing the above components for preparing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and performing the procedures of drying, cold pressing and the like to obtain the negative electrode piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

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

In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethylsulfone, methylethylsulfone, and diethylsulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film forming additive, a positive electrode film forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

[ isolation film ]

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

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

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and the electrolyte.

In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 1 is a secondary battery 5 of a square structure as one example.

In some embodiments, referring to fig. 2, the overpack may include a housing 51 and a cap assembly 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and the top cover assembly 53 can cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of the electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to specific practical needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries included in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

Fig. 3 is a battery module 4 as an example. Referring to fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and capacity of the battery pack.

Fig. 4 and 5 are a battery pack 1 as an example. Referring to fig. 4 and 5, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides a power consumption device, power consumption device includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include, but is not limited to, a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, and a satellite, an energy storage system, etc.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

Fig. 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the powered device may be a mobile phone, a tablet computer, a notebook computer, or the like. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples do not specify particular techniques or conditions, and are performed according to techniques or conditions described in literature in the art or according to the product specification. The reagents or instruments used are conventional products which are commercially available, and are not indicated by manufacturers.

Example 1

Preparation of cathode material

Mixing and grinding 10mol of secondary particles of the positive electrode active material, 0.015mol of first silicone oil and 1L of dichloromethane to obtain primary particles of the positive electrode active material, a mixture of the first silicone oil and the dichloromethane, wherein D of the primary particles₅₀Is 1 μm;

uniformly mixing the mixture with 0.015mol of second silicone oil and a catalytic amount of Karstedt catalyst to obtain primary particles of the positive active material with the surface coated with the silicone oil;

coating the primary particles of the positive electrode active material with the silicone oil on the surface at a reaction temperature T by a spray dryer₁Granulating to obtain an organic silicon coated anode active material secondary particle precursor;

calcining the secondary particle precursor of the positive electrode active material in an inert atmosphere to obtain a positive electrode material, wherein the calcining temperature is T₂The calcination time is t;

wherein the first silicone oil is a silicone oil represented by formula 2 (m = 10), and the second silicone oil is a silicone oil represented by formula 3 (n = 10).

Formula 2

Formula 3

Examples 2 to 23

Based on the preparation process of the cathode material of example 1, the kind of the cathode active material, D of the primary particles were adjusted as shown in table 1₅₀The dosage of the first silicone oil and the second silicone oil, the value of m in the first silicone oil, the value of n in the second silicone oil, and T₁、T₂And t, preparing the cathode materials of examples 2-23.

In examples 1 to 23, the median particle diameter D of the secondary particle precursor of the positive electrode active material in examples 1 to 20 was controlled by a spray dryer ₅₀4 to 5 μm so that the median diameter D of the secondary particles prepared in examples 1 to 20₅₀The particle size of the precursor of the secondary particles of the positive electrode active material in examples 21 to 23 is controlled to be 4 to 6 μm₅₀11 to 12 μm, 9 to 10 μm, and 7 to 8 μm, respectively, so that the median particle diameter D of the secondary particles prepared in examples 21 to 23 is₅₀12 μm, 10 μm, and 8 μm, respectively.

Comparative example 1

Uniformly mixing 10mol of secondary particles of the positive electrode active material, 0.015mol of first silicone oil, 1L of dichloromethane, 0.015mol of second silicone oil and a catalytic amount of Karstedt catalyst to obtain secondary particles of the positive electrode active material with the surface coated with the silicone oil;

coating the secondary particles of the positive electrode active material with the silicone oil on the surface at a reaction temperature T by a spray dryer₁The mixture is granulated at the lower part of the granulator,obtaining an organic silicon coated secondary particle precursor of the positive active material;

the first silicone oil is a silicone oil represented by formula 2 (m = 10), and the second silicone oil is a silicone oil represented by formula 3 (n = 10).

Comparative example 2

By direct use of median particle diameter D₅₀LiNi of 5.2 μm_0.8Co_0.1Mn_0.1The secondary particles serve as a positive electrode material.

Comparative examples 3 to 4

The preparation process of the cathode material was the same as that of example 1 except that:

comparative example 3 no second silicone oil was added; comparative example 4 no first silicone oil was added.

The preparation parameters of the positive electrode materials of examples 1 to 23 and comparative examples 1 to 4 are shown in table 1 below.

In comparative examples 1 and 3 to 4, the median diameter D of the precursor of the secondary particles of the positive electrode active material in comparative examples 1 and 3 to 4 was controlled by a spray dryer ₅₀4 to 5 μm so that the median diameter D of the secondary particles prepared in comparative examples 1, 3 to 4₅₀Is in the range of 5.2 μm,

table 1: preparation parameters of examples 1 to 23 and comparative examples 1 to 4

The following tests were performed on the positive electrode materials of examples 1 to 23 and comparative examples 1 to 4, and the test results are shown in table 2 below.

(1) Median diameter D of the secondary particles₅₀Testing

The equipment model is as follows: malvern 2000 (MasterSizer 2000) laser particle sizer

Taking a proper amount of sample to be tested (the sample concentration can ensure 8-12% shading degree), adding 20ml deionized water, and simultaneously performing ultra-5 min (53 KHz/120W) to ensure that the sample isCompletely dispersed, and then D of the sample is subjected to GB/T19077-2016/ISO 13320:2009 standard₅₀And (4) carrying out measurement.

(2) Coating thickness test

The equipment model is as follows: transmission Electron microscope of JEM-2010(HR) manufactured by Japan Electron Ltd

And dispersing the anode material in an ethanol solvent, dripping the ethanol solvent on the micro-grid support film, and measuring the thickness of the coating layer by using a high-resolution transmission electron microscope.

(3) Morphology test of positive electrode material

The equipment model is as follows: ZEISS sigma 300 scanning electron microscope

And testing according to a standard JY/T010-1996, and observing the appearance of the sample.

Fig. 7, 8, and 9 show Scanning Electron Microscope (SEM) images of the positive electrode materials of example 1 and comparative examples 1 and 2, respectively.

Table 2: test parameters of the positive electrode materials of examples 1 to 23 and comparative examples 1 to 4

As can be seen from fig. 7, according to the method of the present application, surface coating of the primary particles constituting the secondary particles can be achieved.

In addition, secondary batteries were prepared from the positive electrode materials obtained in examples 1 to 23 and comparative examples 1 to 4, respectively, as follows, and performance tests were performed. The test results are shown in table 3 below.

(1) Preparation of secondary battery

Preparation of positive pole piece

The prepared positive electrode material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), solvent N-methyl pyrrolidone (NMP) are 67.34: 2.7: 1.1: 28.86 stirring and mixing evenly to obtain anode slurry; and then uniformly coating the positive electrode slurry on a positive electrode current collector, and then drying, cold pressing and cutting to obtain the positive electrode piece of the comparative example.

Preparation of negative pole piece

Preparing active substance artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR), thickener carboxymethylcellulose sodium (CMC-Na) according to the weight ratio of 96.2: 0.8: 0.8: 1.2 dissolving in solvent deionized water, and uniformly mixing to prepare cathode slurry; and uniformly coating the negative electrode slurry on the copper foil of the negative current collector for one time or multiple times, and drying, cold pressing and slitting to obtain the negative electrode pole piece.

Preparation of the electrolyte

In an argon atmosphere glove box (H)₂O<0.1ppm，O₂<0.1 ppm), uniformly mixing an organic solvent Ethylene Carbonate (EC)/Ethyl Methyl Carbonate (EMC) according to the volume ratio of 3/7, adding 12.5 percent LiPF6 lithium salt, dissolving in the organic solvent, and uniformly stirring to obtain the catalyst.

Isolation film

Polypropylene film was used as the separator.

Preparation of secondary battery

And sequentially stacking the positive pole piece, the isolating film and the negative pole piece to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, then winding to obtain an electrode assembly, welding a tab of the electrode assembly, putting the electrode assembly into an aluminum shell, baking at 100 ℃ to remove water, immediately injecting electrolyte and sealing to obtain the uncharged battery. And the uncharged battery sequentially undergoes the working procedures of standing, hot and cold pressing, formation, shaping, capacity testing and the like to obtain the secondary battery.

(2) Test of retention ratio of cycle capacity of secondary battery

45 ℃ cyclic Capacity test

Charging the secondary battery at 45 deg.C with 1/3C constant current to 4.3V, charging at 4.3V constant voltage to current of 0.05C, standing for 5min, discharging at 1/3C to 2.8V, and recording the obtained capacity as initial capacity C₀. Repeating the steps on the same battery, and simultaneously recording the discharge capacity Cn of the battery after the nth cycle, so that the capacity retention rate P of the battery after each cycle_n=C_n/C ₀100%. With P₁、P₂……P₂₀₀The 200 point values are used as ordinate and the corresponding cycle times are used as abscissa, so as to obtain a 45 ℃ cycle capacity retention rate test chart.

Fig. 10 shows the 45 ℃ cycle capacity retention rate test charts of the secondary batteries of example 1 and comparative examples 1 and 2.

Retention ratio of 200 cycles

Charging the secondary battery at 25 deg.C with 1/3C constant current to 4.3V, charging at 4.3V constant voltage to current of 0.05C, standing for 5min, discharging at 1/3C to 2.8V, and recording the obtained capacity as initial capacity C₀. Repeating the above steps for the same cell, and simultaneously recording the discharge capacity C of the cell after the nth cycle_nThe battery capacity retention ratio P after each cycle_n=C_n/C₀*100%。

200-cycle capacity retention ratio P of secondary battery₂₀₀=C₂₀₀/C₀*100%。

(3) 50% SOC discharge DC resistance DCR test

At 25 ℃, the secondary battery is subjected to constant current charging to 4.2V at the rate of 1/3C, then is subjected to constant voltage charging to 0.05C at the rate of 4.2V, and is left for 5 min. And then discharging at the rate of 1/3C for 90min, adjusting the electrode assembly to be 50% SOC, standing for 60min, then discharging at the rate of 3C for 30S, and obtaining 50% SOC discharge DCR according to test data.

Table 3: performance test results of examples 1 to 23 and comparative examples 1 to 4

As is clear from the above results and FIG. 10, the examples 1 to 23 all exhibited excellent effects. For different positive active materials, the positive material prepared by the method can be applied to the secondary battery, and can reduce the resistance of the secondary battery and improve the cycle capacity retention rate of the secondary battery.

Specifically, as can be seen from tables 1 and 2,the dosage of the first silicone oil and the second silicone oil, the ratio of the quantity of the substance of the silicon-hydrogen bond and the alkenyl group, the molecular weight of the first silicone oil and the second silicone oil, and the median diameter D of the primary particles₅₀The reaction temperature, the temperature of calcination and the time of calcination all have an effect on the thickness of the coating layer. Specifically, it is understood from examples 1 to 4 and 9 that, in both the first silicone oil and the second silicone oil, primary particles having a suitable coating thickness can be obtained when the ratio of the amount of the substance having a silicon-hydrogen bond to the alkenyl group is 1:1 to 1:4, and the coating thickness increases as the amount of the first silicone oil and the second silicone oil increases. As can be seen from examples 1 and 5 to 8, the first silicone oil and the second silicone oil have relatively large molecular weights, and the coating layer on the surface of the primary particle in the prepared cathode material has a relatively large thickness. From examples 1 and 10 to 11, it is clear that the median diameter D of the primary particles₅₀The smaller the thickness of the clad layer. As can be seen from the reaction temperatures of examples 1 and 14 to 16, the thickness of the coating layer increases with the increase of the reaction temperature. On the other hand, referring to examples 1 and 17 to 20, it can be seen that the higher the temperature and the longer the time for calcining the secondary particle precursor of the positive electrode active material, the smaller the thickness of the coating layer.

As can be seen from table 3, for the same positive electrode active material, the median particle diameter D of the primary particles was set to be equal to₅₀When the reaction temperature, the firing temperature, and the firing time are the same, the surface resistance of the positive electrode material is lower and the cycle retention rate of the secondary battery is higher as the thickness of the coating layer of the obtained positive electrode material is larger. Therefore, in the cathode material, the coating layer has good electronic conductivity, and the surface impedance of the cathode material can be effectively reduced. In addition, the coating layer is coated on the surface of the primary particles, so that the deactivation caused by side reaction of the primary particles and the electrolyte can be effectively avoided, the cycle performance of the secondary battery can be improved, and the cycle life of the secondary battery can be prolonged. Therefore, the amounts of the first silicone oil and the second silicone oil, the ratio of the amount of the material of the silicon-hydrogen bond to the alkenyl group, and the molecular weights of the first silicone oil and the second silicone oil need to be controlled within appropriate ranges.

As can be seen from examples 1 and 10 to 11, the median diameter D of the primary particles₅₀Enlarge, i.e. coatThe thickness is increased and the surface resistance of the positive electrode material is also increased. Therefore, for positive electrode materials having different primary particle sizes, it is necessary to adjust the production conditions so that the thickness of the coating layer on the surface of the primary particle is appropriate to obtain a positive electrode material having a lower surface resistance.

In examples 1, 14 to 20, the correspondence between the surface resistance of the positive electrode material and the thickness of the coating layer is different from that in other examples, for example, in examples 17 and 19, the coating layer thickness is larger, and the surface resistance of the positive electrode material is higher than that in example 1. Although the mechanism is not clear, it is presumed that the reaction temperature, the calcination temperature and the calcination time have an important influence on the properties of the coating layers obtained by converting the first silicone oil and the second silicone oil. Therefore, the reaction temperature, the calcination temperature and the calcination time need to be reasonably controlled.

Furthermore, as can be seen from examples 21 to 23, the median diameter D of the secondary particles is dependent on the particle size of the secondary particles₅₀The cycle retention rate can be effectively improved when the cathode material is applied to the secondary battery, but the improvement effect is weaker than that of example 1. Therefore, it is also necessary to control the particle size of the secondary particles in the prepared cathode material within a suitable range.

On the contrary, in comparative example 1, the secondary particles of the positive electrode active material are surface-coated, in comparative example 2, the positive electrode material is not surface-coated, and in comparative examples 3 to 4, the primary particles of the positive electrode active material are coated by using only one of the first silicone oil and the second silicone oil, so that the deactivation caused by the side reaction between the cracked positive electrode active material and the electrolyte cannot be avoided. Thus, comparative examples 1 to 4 are not effective in reducing the resistance of the secondary battery and improving the cycle capacity retention rate of the secondary battery.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. Various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, which are configured by combining some of the constituent elements in the embodiments without departing from the scope of the present application.

Claims

1. A positive electrode material is characterized by comprising secondary particles formed by aggregating a plurality of primary particles of a positive electrode active material, wherein the surfaces of the primary particles are coated with coating layers containing C elements and Si elements, and the coating layers contain simple carbon and SiO₂The coating layer is a single layer.

2. The positive electrode material according to claim 1, wherein the secondary particles have a polycrystalline structure.

3. The positive electrode material according to claim 1, wherein the positive electrode active material is at least one selected from a ternary positive electrode material and a quaternary positive electrode material.

4. The positive electrode material according to claim 1, wherein the positive electrode active material comprises at least one of NCM, NCA, and NCMA.

5. The positive electrode material according to claim 1, wherein the positive electrode active material comprises a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂formula 1

6. The positive electrode material according to claim 1, wherein the positive electrode material satisfies one or more of the following (1) to (3):

(1) in the positive electrode material, the median diameter D of the primary particles₅₀0.2 to 1.5 μm;

(2) in the positive electrode material, the secondary particles have a median diameter D₅₀4-12 μm;

(3) in the primary particles, the thickness of the coating layer is 10 nm-50 nm.

7. A method for preparing the positive electrode material according to any one of claims 1 to 6, comprising:

uniformly mixing the primary particles of the positive electrode active material with first silicone oil, second silicone oil, a hydrosilylation catalyst and an organic solvent to obtain primary particles of the positive electrode active material with the surface coated with the silicone oil, wherein one of the first silicone oil and the second silicone oil is the silicone oil containing a silicon-hydrogen bond, and the other is the silicone oil containing an alkenyl group;

granulating the positive electrode active material primary particles with the surface coated with the silicone oil at a reaction temperature so as to enable the first silicone oil and the second silicone oil to be solidified on the surface of the positive electrode active material primary particles, thereby obtaining an organic silicon coated positive electrode active material secondary particle precursor, wherein the positive electrode active material secondary particle precursor comprises a plurality of positive electrode active material primary particles with the surface coated with the organic silicon;

calcining the precursor of the secondary particles of the positive electrode active material in an inert atmosphere to obtain secondary particles formed by aggregating a plurality of primary particles of the positive electrode active material, wherein the surface of the primary particles is coated with a coating layer containing a C element and a Si element, and the coating layer contains a carbon simple substance and SiO₂And the coating layer is a single layer.

8. The method according to claim 7, wherein the step of uniformly mixing the primary particles of the positive electrode active material with the first silicone oil, the second silicone oil, the hydrosilylation catalyst, and the organic solvent to obtain the primary particles of the positive electrode active material with the surface coated with the silicone oil comprises the steps of:

mixing and grinding the secondary particles of the positive electrode active material, the first silicone oil, and the organic solvent to obtain a mixture of the primary particles of the positive electrode active material, the first silicone oil, and the organic solvent;

and uniformly mixing the mixture with the second silicone oil and the hydrosilylation catalyst to obtain the primary particles of the positive electrode active material with the surface coated with the silicone oil.

9. The method according to claim 8, wherein a ratio of the volume of the organic solvent to the mass of the secondary particles of the positive electrode active material is defined as a, and a is in a range satisfying: a = 0.5L/kg-1.5L/kg.

10. The method of claim 7, wherein the positive active material is selected from at least one of a ternary positive material and a quaternary positive material.

11. The method of claim 7, wherein the positive electrode active material comprises at least one of NCM, NCA, NCMA.

12. The method according to claim 7, wherein the positive electrode active material comprises a compound represented by formula 1,

Li(Ni_xCo_yMn_z)O₂formula 1

13. The method according to claim 7, wherein the median particle diameter D of the primary particles of the positive electrode active material₅₀Is 0.2 μm to 1.5 μm.

14. The method according to claim 7, wherein the silicone oil containing silicon hydrogen bonds comprises a silicone oil containing at least two silicon hydrogen bonds in a molecule.

15. The method according to claim 7, wherein the silicone oil containing silicon hydrogen bonds comprises a silicone oil containing two silicon hydrogen bonds in a molecule.

16. The method according to claim 7, wherein the silicone oil containing a silicon-hydrogen bond comprises a silicone oil represented by formula 2,

formula 2

In formula 2, m is more than or equal to 2 and less than or equal to 20.

17. The method according to claim 7, wherein the silicone oil having an alkenyl group comprises a silicone oil having at least two alkenyl groups in a molecule.

18. The method according to claim 7, wherein the silicone oil having an alkenyl group comprises a silicone oil having two alkenyl groups in a molecule.

19. The method according to claim 7, wherein the silicone oil having an alkenyl group comprises a silicone oil represented by formula 3,

formula 3

In formula 3, n is not less than 2 and not more than 20.

20. The method according to claim 7, characterized in that the ratio of the amount of the substance of the silicon-hydrogen bond and the alkenyl group in the first silicone oil and the second silicone oil is 1:1 to 1: 4.

21. The method according to claim 7, wherein the ratio of the amount of the substance of the silicon-hydrogen bond to the alkenyl group in the first silicone oil and the second silicone oil is 1:2 to 1: 4.

22. The method of claim 7, wherein the hydrosilylation catalyst comprises at least one of a Karstedt catalyst, chloroplatinic acid, chlororhodic acid, and chloroiridic acid.

23. The method of claim 7, wherein the hydrosilylation catalyst comprises Karstedt's catalyst.

24. The method according to claim 7, wherein the positive electrode active material secondary particle precursor has a median particle diameter D₅₀Is 3 μm to 12 μm.

25. The method of claim 7, wherein the temperature of the calcination is 300 ℃ to 600 ℃, and the time of the calcination is 2h to 6 h.

26. The method according to claim 7, wherein the thickness of the coating layer in the primary particles is 10nm to 50 nm.

27. A positive electrode plate, characterized by comprising the positive electrode material according to any one of claims 1 to 6 or the positive electrode material prepared by the method according to any one of claims 7 to 26.

28. A secondary battery comprising the positive electrode sheet as claimed in claim 27.

29. A battery module characterized by comprising the secondary battery according to claim 28.

30. A battery pack comprising the battery module according to claim 29.

31. An electric device comprising at least one selected from the secondary battery according to claim 28, the battery module according to claim 29, and the battery pack according to claim 30.