CN117577842A

CN117577842A - Positive electrode lithium supplementing material, preparation method thereof, positive electrode material and secondary battery

Info

Publication number: CN117577842A
Application number: CN202311491015.8A
Authority: CN
Inventors: 刘丽婷; 万远鑫; 裴现一男; 孔令涌; 王盈莹; 林律欢; 钟文
Original assignee: Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
Current assignee: Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
Priority date: 2023-11-08
Filing date: 2023-11-08
Publication date: 2024-02-20

Abstract

The positive electrode lithium supplementing material comprises a core and a coating layer, wherein the core comprises a lithium-rich material; the outer surface of the inner core is coated with the coating layer which comprises mesoporous microspheres and carbon materials. According to the invention, the mesoporous microspheres and the carbon material jointly coat the inner core of the lithium-rich material, so that the positive electrode lithium-supplementing material with electrolyte stability and gas production inhibition can be obtained.

Description

Positive electrode lithium supplementing material, preparation method thereof, positive electrode material and secondary battery

Technical Field

The invention relates to the technical field of secondary batteries, in particular to a positive electrode lithium supplementing material, a preparation method thereof, a positive electrode material and a secondary battery.

Background

In the formation process of the lithium ion battery, the negative electrode reacts with the electrolyte to form a layer of solid electrolyte interface film SEI on the electrode, the solid electrolyte interface film SEI contains various lithium salts, the SEI film inhibits the further reaction of the negative electrode and the electrolyte, the SEI film is a good conductor for lithium ions, and the SEI film is an insulator for electrons, so that the SEI film plays a great role in improving the performance of the lithium ion battery. However, the SEI film also has a disadvantageous side, and lithium ions are consumed in the formation process of the SEI film, and these lithium ions are originally stored in the positive electrode material, consuming about 10% of the lithium ions, meaning that the capacity of the positive electrode material is reduced by 10% by the SEI formation process. In order to reduce the loss of capacity, the industry has developed various lithium supplementing techniques, which are classified into positive electrode lithium supplementing and negative electrode lithium supplementing according to a large category.

The existing positive electrode lithium supplementing material has higher gas yield, and the generated gas is easy to react with electrolyte in a harmful way, so that the battery is damaged. In the prior art, in order to inhibit gas production, a coating layer is arranged on the surface of a lithium-rich material, but the inhibition of the coating layer on the gas production is still not ideal enough, and the arrangement of the coating layer can also lead to the reduction of the conductivity of the material, so that the free path of lithium ions is greatly influenced, and therefore, part of the advantages of the lithium-rich material can be sacrificed. It becomes critical how to ensure the conductivity of the positive electrode lithium-supplementing material while suppressing gas generation.

Disclosure of Invention

The invention aims to provide a positive electrode lithium supplementing material, a preparation method thereof, a positive electrode material and a secondary battery, and the problems of high gas yield and low conductivity of the positive electrode lithium supplementing material can be solved.

In order to achieve the purpose of the invention, the invention provides the following technical scheme:

in a first aspect, the invention provides a positive electrode lithium supplementing material, which comprises a core and a coating layer, wherein the core comprises a lithium-rich material; the coating layer is coated on the outer surface of the inner core, and comprises mesoporous microspheres and carbon materials.

According to the invention, the mesoporous microspheres and the carbon material jointly coat the inner core of the lithium-rich material, so that the positive electrode lithium-supplementing material with electrolyte stability and gas production inhibition can be obtained; the coating layer can isolate the contact between the electrolyte and the lithium-rich material, and the mesoporous microspheres can absorb the gas generated by the lithium-rich material in the discharge process, so that the gas is less released to cause harmful side reaction with the electrolyte, and the stability of the electrolyte of the positive electrode lithium-supplementing material is improved; the carbon material in the coating layer can improve the coated conductivity and provide a conductive channel for the derivation of lithium ions in the lithium-rich material, so that the cathode lithium-supplementing material can be ensured to have higher conductivity while gas production is reduced.

In one embodiment, the mesoporous microsphere has a pore structure therein, and at least a portion of the carbon material is filled in the pore structure.

In one embodiment, the coating layer includes a first coating layer and a second coating layer, the first coating layer is coated on the outer surface of the inner core, the second coating layer is coated on the outer surface of the first coating layer, the first coating layer includes the mesoporous microsphere, and the second coating layer includes the carbon material.

In one embodiment, the coating layer further comprises an encapsulating material, the encapsulating material is combined on the outer surface of the mesoporous microsphere and/or the carbon material, the encapsulating material comprises one or more of a fluoroamine compound, an ester compound and a nitrile compound, and the mass ratio of the encapsulating material in the positive electrode lithium supplementing material is 0.1% -2.5%.

In one embodiment, the mesoporous microspheres are plural in number, and pores are formed between adjacent mesoporous microspheres, and the encapsulating material is filled in the pores.

In one embodiment, the mesoporous microspheres are a plurality of, and pores are arranged between adjacent mesoporous microspheres, and the carbon material is filled in the pores.

In one embodiment, the carbon material and/or the encapsulation material is coated on the outer surface of the mesoporous microsphere.

In one embodiment, the positive electrode lithium supplementing material further comprises an encapsulation layer, the encapsulation layer is coated on the outer surface of the coating layer, the encapsulation layer is made of the encapsulation material, and the thickness of the encapsulation layer is 20-50 nm.

In one embodiment, the fluoroamine compound comprises one or more of 3-trifluoromethyl-aniline, N-diethyl-1, 2, 3-hexafluoropropylamine, and ibutethylamine.

In one embodiment, the mesoporous microspheres comprise one or more of ceria, titania, zirconia;

in one embodiment, the carbon material comprises one or more of graphene, carbon nanotubes, fullerenes, carbon black.

In one embodiment, the mass ratio of the core to the cladding is 100 (0.5-10).

In one embodiment, the mass ratio of the mesoporous microspheres to the carbon material is (50-1): 1-50.

In one embodiment, the mesoporous microspheres have a particle size D50 of 0.1 μm to 2. Mu.m.

In one embodiment, the positive electrode lithium-supplementing material has a particle diameter D50 of 10-80 μm.

In one embodiment, the carbon material has a diameter D50 of 0.7nm to 15nm.

In one embodiment, the specific surface area of the carbon material is 1m ² /g～300m ² /g。

In one embodiment, the total residual alkali on the surface of the positive electrode lithium-supplementing material is less than or equal to 5%.

In one embodiment, the tap density of the positive electrode lithium supplementing material is 0.5g/cm ³ ～2.5g/cm ³ 。

In one embodiment, the gram capacity of the positive electrode lithium supplementing material is greater than or equal to 300mAh/g under a 0.05C charging environment.

In a second aspect, the present invention also provides a method for preparing a positive electrode lithium supplementing material, including: uniformly mixing and drying the mesoporous microsphere precursor and the pore-forming agent, uniformly mixing with the lithium-rich material, and drying and sintering to obtain the mesoporous microsphere coated lithium-rich material; and uniformly mixing the lithium-rich material coated by the mesoporous microspheres with the carbon material, and sintering to obtain the positive electrode lithium-supplementing material, wherein the lithium-rich material forms an inner core, and the mesoporous microspheres and the carbon material form a coating layer to coat the outer surface of the inner core.

In a third aspect, the present invention also provides a positive electrode material, where the positive electrode material includes a positive electrode active material and the positive electrode lithium-supplementing material according to the first aspect, or the positive electrode material includes a positive electrode lithium-supplementing material obtained by the method for preparing a positive electrode lithium-supplementing material according to the second aspect.

In a fourth aspect, the present invention also provides a secondary battery, including the positive electrode material according to the third aspect, or including the positive electrode lithium-supplementing material according to any one of the embodiments of the first aspect, or including the positive electrode lithium-supplementing material obtained by the method for preparing the positive electrode lithium-supplementing material according to the second aspect.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained from them without inventive effort for a person skilled in the art.

Fig. 1 is a cross-sectional view of a positive electrode lithium-supplementing material of an embodiment;

FIG. 2 is an enlarged partial cross-sectional view of a positive electrode lithium-compensating material of an embodiment;

FIG. 2A is an enlarged cross-sectional view of a mesoporous microsphere of one embodiment and having a channel structure;

fig. 3 is a cross-sectional view of another embodiment of a positive electrode lithium-supplementing material;

fig. 4 is a cross-sectional view of a positive electrode lithium-supplementing material of yet another embodiment;

FIG. 5 is a cross-sectional view of a mesoporous microsphere coated according to one embodiment;

fig. 6 is a flowchart of the preparation of a positive electrode lithium-supplementing material according to an embodiment.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.

It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When a component is considered to be "connected" to another component, it can be directly connected to the other component or intervening components may also be present.

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

Some embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other without conflict.

The invention provides a positive electrode lithium supplementing material, referring to fig. 1 and 2, the positive electrode lithium supplementing material comprises a core 10 and a coating layer 20, wherein the core 10 comprises a lithium-rich material; the coating layer 20 is coated on the outer surface of the inner core 10, and comprises mesoporous microspheres 20A and carbon materials 20B.

Specifically, the lithium-rich material is a core of the positive electrode lithium-supplementing material that provides lithium ions, and the shape of the lithium-rich material is not particularly limited. Alternatively, the shape of the lithium-rich material may be spherical or spheroid in structure, or other irregular shapes.

Alternatively, the lithium-rich material has the formulaIncluding LiaA _b O _c Wherein A is at least one element in Ni, fe, mn, co, cr, V, mo, ti, nb, zr, cu, mg, a is more than 0 and less than or equal to 8, b is more than 0 and less than or equal to 5, and c is more than 0 and less than or equal to 8. In a particular embodiment, the lithium-rich oxide may be Li ₅ FeO ₄ 、Li ₆ MnO ₄ 、Li ₆ CoO ₄ 、Li ₆ ZnO ₄ 、Li ₂ NiO ₂ 、Li ₂ CuO ₂ 、Li ₂ CoO ₂ 、Li ₂ MnO ₂ 、Li ₂ Ni _0.5 Mn _1.5 O ₄ 、Li ₂ Ni _d Cu _(1-d) O ₂ (0 < d < 1) and the like. The lithium-rich material may also be Li ₂ C ₂ O ₄ 、Li ₂ CO ₃ Etc.

It can be understood that the lithium-rich material is added into the electrode, so that the lithium-rich material is used as a sacrificial agent in the first-cycle charging process, and all lithium ions contained in the lithium-rich material are released as soon as possible to supplement irreversible lithium ions consumed by the negative electrode forming an SEI film, thereby maintaining the abundance of lithium ions in the battery system and improving the first effect and the overall electrochemical performance of the battery.

Alternatively, the core 10 may be primary particles or secondary particles composed of a plurality of primary particles.

Further, the cladding layer 20 is coated on the outer surface layer of the core 10. Alternatively, the coating layer 20 may be directly coated on the outer surface of the inner core 10, or indirectly coated on the outer surface of the inner core 10. It can be appreciated that the cladding layer 20 directly covers the outer surface of the core 10, i.e. is in direct contact with the core 10; the coating 20 may be indirectly coated on the outer surface of the core 10 in indirect contact, i.e., other structures may be provided between the coating 20 and the core 10.

The coating 20 comprises mesoporous microspheres 20A, the mesoporous microspheres 20A including, but not limited to, one or more of ceria, titania, zirconia. It should be noted that the external shape of the mesoporous microspheres 20A may be spherical, elliptical or spheroid. As shown in fig. 2, the mesoporous microsphere 20A has a plurality of holes 20A1. The hole 20A1 may include an inner hole, a blind hole, and a through hole. Wherein, the inner hole is formed in the inner part of the mesoporous microsphere 20A and is not communicated with the external space; the blind holes are structures formed by inwards sinking from the outer surface of the mesoporous microsphere 20A; the through holes are channels penetrating through the mesoporous microspheres 20A.

The mesoporous microspheres 20A may be used to absorb gas generated when the lithium-rich material is charged and discharged, and to house the gas in the holes 20A 1. Thereby reducing the gas yield of the lithium-rich material and reducing the harmful side reaction on the outer side of the positive electrode lithium-supplementing material.

Preferably, the mesoporous microspheres 20A are ceria mesoporous spheres. The advantage of using ceria mesoporous spheres is that their conductivity is higher than that of other microspheres, resulting in a higher conductivity of the coating 20.

Also included in the coating 20 is a carbon material 20B, the carbon material 20B including, but not limited to, one or more of graphene, carbon nanotubes, fullerenes, carbon black. The carbon material 20B may be bonded to the outer surface of the mesoporous microsphere 20A and improve the conductivity of the positive electrode lithium-supplementing material.

Preferably, the carbon material 20B is graphene. The advantage of using graphene is that the graphene is a two-dimensional material, so that the graphene has a larger specific surface area and stronger conductivity, so that the conductivity of the formed coating layer 20 is also higher.

Optionally, the bonding means between the mesoporous microspheres 20A and the carbon material 20B in the coating layer 20 includes, but is not limited to: mesoporous microspheres 20A and carbon material 20B are disposed in the coating layer 20 in a homogeneously mixed manner, as shown in fig. 1; or the carbon material 20B is coated on the outer surface of the mesoporous microsphere 20A, and then the mesoporous microsphere 20A coated by the carbon material 20B is coated on the outer surface of the inner core 10, as shown in FIG. 3; or the carbon material 20B and the mesoporous microspheres 20A are separately disposed, and the coating layer 20 includes a mesoporous microsphere layer and a carbon material layer, as shown in fig. 4.

Alternatively, as shown in fig. 2, the carbon material 20B and the mesoporous microspheres 20A may be combined in such a manner that at least a portion of the carbon material 20B is contained in the pores 20A1 of the mesoporous microspheres 20A. For example, the mesoporous microsphere 20A has a through hole or a blind hole therein, the carbon material 20B is graphene or carbon nanotube, and at least a portion of the carbon material 20B extends into the hole 20A1 of the mesoporous microsphere 20A, and a portion of the space is reserved in the hole 20A1 for accommodating gas.

Alternatively, the holes 20A1 in the mesoporous microspheres 20A may be obtained by a pore former. For example, the pore-forming agent is an acid solution, such as an organic acid, and the mesoporous microspheres 20A with the holes 20A1 can be obtained by etching the precursor of the mesoporous microspheres 20A with the organic acid. Alternatively, the pore-forming agent and the precursor of the mesoporous microsphere 20A may be mixed to form a mixed precursor, the pore-forming agent is located in the mixed precursor, and then the pore-forming agent is removed by sintering, and the hole 20A1 is formed at the original position of the pore-forming agent, thereby obtaining the mesoporous microsphere 20A.

According to the invention, the mesoporous microspheres 20A and the carbon materials 20B jointly cover the inner core 10 of the lithium-rich material, so that the positive electrode lithium supplementing material with electrolyte stability and gas production inhibition can be obtained; the coating layer 20 can isolate the contact between the electrolyte and the lithium-rich material, and the mesoporous microspheres 20A can absorb the gas generated by the lithium-rich material in the discharge process, so that the gas is less released to cause harmful side reaction with the electrolyte, and the stability of the electrolyte of the positive electrode lithium-supplementing material is improved; the carbon material 20B in the coating layer 20 can improve the conductivity of the coating and provide a conductive path for the export of lithium ions in the lithium-rich material, so that the cathode lithium-supplementing material can have higher conductivity while reducing gas production.

In one embodiment, referring to fig. 2A, the mesoporous microsphere 20A has a structure of pores 20A2, and at least a portion of the carbon material is filled in the structure of the pores 20A 2. Specifically, the mesoporous microsphere 20A may have a pore channel 20A2 structure, i.e. a pore channel 20A2 with a curved extension, as shown in the figure. The cell 20A2 may communicate with the external space, and a part of the carbon material may enter and fill the cell 20 A2.

The pore canal 20A2 structure of the mesoporous microsphere 20A is beneficial to increasing the volume inside the mesoporous microsphere, thereby improving the containing amount of gas; and the structure of the pore canal 20A2 which is bent and extended increases the difficulty of gas escape, and can better capture the gas in the mesoporous microsphere 20A. On the other hand, the carbon material filled in the pore passages 20A2 can further increase the conductivity of the mesoporous microspheres 20A, thereby improving the conductivity of the entire coating layer 20.

In one embodiment, referring to fig. 3, the mesoporous microspheres 20A are plural in number, and voids are formed between adjacent mesoporous microspheres 20A, and the carbon material 20B is filled in the voids. The mesoporous microspheres 20A are granular materials, and after the mesoporous microspheres 20A form the coating layer 20, gaps exist between every two mesoporous microspheres 20A. The carbon material 20B may be filled in the gaps so that the carbon material 20 and the mesoporous microspheres 20A are combined, and the carbon material 20B in the gaps may improve the combination of the two.

In one embodiment, referring to fig. 4, the coating layer 20 includes a first coating layer 21 and a second coating layer 22, the first coating layer 21 is coated on the outer surface of the core 10, the second coating layer 22 is coated on the outer surface of the first coating layer 21, the first coating layer 21 includes mesoporous microspheres 20A, and the second coating layer 22 includes carbon material 20B.

Specifically, the cladding layer 20 includes two layers, a first cladding layer 21 and a second cladding layer 22, respectively. The first coating layer 21 includes a plurality of mesoporous microspheres 20A, and a plurality of mesoporous microspheres are connected to form a continuous layer on the outer surface of the core 10, so as to form the first coating layer 21, and the outer surface of the core 10 is coated with the first coating layer. The second cladding layer 22 is a strong conductive layer formed of the carbon material 20B, and the carbon material 20B forms the second cladding layer 22 and coats the outer surface of the first cladding layer 21.

Alternatively, the structure may be formed by preparing the mesoporous microspheres 20A in advance, coating the mesoporous microspheres 20A on the outer surface of the core 10, and then coating the first coating layer 21 having the mesoporous microspheres 20A with the carbon material 20B.

The advantages of arranging the coating layer 20 as the first coating layer 21 and the second coating layer 22 are that the mesoporous microspheres 20A in the first coating layer 21 can provide an accommodating space for gas, so that the gas generated by the lithium-rich material is primarily ensured not to be discharged; the second coating layer 22 forms a coating outside the first coating layer 21, further ensuring that the gas in the first coating layer 21 does not escape, and the second coating layer 22 is a carbon material 20B, further improving the conductivity of the coating layer 20, ensuring that lithium ions in the lithium-rich material can be exported.

In one embodiment, referring to fig. 3 and 4, the coating layer 20 further includes an encapsulating material 30A, where the encapsulating material 30A is combined with the outer surface of the mesoporous microsphere 20A and/or the carbon material 20B, and the encapsulating material 30A includes one or more of a fluoroamine compound, an ester compound, and a nitrile compound.

Specifically, the encapsulation material 30A is an electrolyte-soluble material that fills in the gaps between the mesoporous microspheres 20A and the carbon materials 20B, or in the gaps between the mesoporous microspheres 20A, or in the gaps between the carbon materials 20B. The packaging material 30A is used to further protect the core 10 from contact with moisture and carbon dioxide in the air prior to storage and assembly and packaging of the battery, and ensures stability of the lithium supplementing performance of the positive electrode lithium supplementing material. After the lithium ion battery is assembled and packaged to form a battery, the lithium ion battery can be dissolved in electrolyte, so that the effect of supplementing lithium to the positive electrode of the battery is achieved, the lithium extraction of the positive electrode lithium supplementing material is ensured not to be influenced, and the service life of the battery is prolonged.

Optionally, the fluoroamine compound comprises one or more of 3-trifluoromethyl-aniline, N-diethyl-1, 2, 3-hexafluoropropylamine and Bo-fluoroamine. The fluoroamine compound has stable properties, and is adopted, wherein the bond energy of the formed carbon-hydrogen bond and carbon-fluorine bond is higher, so that the formed compact film layer is ensured to be higher in stability and not easy to break and damage, a strong protection effect is realized on the inner core, the inner core is favorably isolated from water vapor or carbon dioxide in the air, in addition, the introduction of fluorine atoms can improve the lipophilicity of molecules, the formed coating layer 20 is favorably and rapidly dissolved in an electrolyte solution, and the inner core is subjected to lithium supplementing effect.

Optionally, the ester compound comprises at least one of tetrabutyl phosphate, glyceryl tristearate and glyceryl trioleate. The protective film formed by the ester compound is connected with each other by the ester group, carbon-oxygen bonds in the ester group are favorable for forming a compact film layer, and the ester bonds are non-covalent bonds and do not react with water, so that the inner core can be isolated from reacting with water vapor and carbon dioxide in the air; and after the battery is assembled and packaged, the ester group can be dissolved in the organic solvent and can be dissolved in the electrolyte, so that the effect of supplementing lithium to the positive electrode of the battery is achieved, and the service life of the battery is prolonged.

Optionally, the nitrile compound includes at least one of benzyl cyanide, dodecyl nitrile, tridecyl nitrile, tetradecyl nitrile, pentadecyl nitrile, hexadecyl nitrile, heptadecyl nitrile, and octadecyl nitrile. The nitrile compound is an organic compound formed by connecting carbon atoms containing hydrocarbon groups and cyano groups, and the provided benzyl cyanide, dodecanitrile and tetradecyl nitrile are organic matters containing organic groups-CN, are insoluble in water and can be dissolved in electrolyte, and the formed-CN functional groups can form a compact film layer, so that the inner core can form a protection effect, and simultaneously can promote the inner core to release lithium ions in electrolyte to supplement irreversible lithium ions consumed by forming an SEI film, thereby keeping the abundance of lithium ions in a battery system and improving the initial efficiency and the overall electrochemical performance of the battery.

The encapsulating material 30A combined on the mesoporous microsphere 20A or the carbon material 20B can further fill the pores in the coating layer 20, so that the coating layer 20 becomes a denser layer, and the invasion of external water vapor can be effectively prevented; and the materials are adopted as the packaging material 30A, so that after the positive electrode lithium supplementing material is assembled and packaged to form a battery, the packaging material 30A can be dissolved in electrolyte, the lithium extraction of the positive electrode lithium supplementing material is not influenced, and the service life of the battery is prolonged.

In one embodiment, referring to fig. 3 and 4, the mesoporous microspheres 20A are plural in number, and voids are provided between adjacent mesoporous microspheres 20A, and the voids are filled with the carbon material 20B and/or the encapsulation material 30A.

Specifically, the coating layer 20 has a plurality of mesoporous microspheres 20A, and pores are formed between the mesoporous microspheres 20A due to the spheroid structure of the mesoporous microspheres 20A. The carbon material 20B and the encapsulation material 30A may be filled in the pores.

Filling the voids with the carbon material 20B and/or the encapsulating material 30A may further reduce the voids between the mesoporous microspheres 20A, improve the stability of the gaps in the coating layer 20, and thereby ensure the sealability of the coating layer 20.

In one embodiment, the carbon material 20B and/or the encapsulating material 30A is coated on the outer surface of the mesoporous microspheres 20A. Specifically, the carbon material 20B and/or the encapsulation material 30A may also coat the outer surface of the mesoporous microspheres 20A, thereby forming a single coated unit. And then a plurality of cladding units are coated on the outer surface of the inner core.

Alternatively, the carbon material 20B and the encapsulating material 30A may be mixed into a homogeneous material and jointly coated on the outer surface of the mesoporous microspheres 20A, as shown in fig. 5 a). The carbon material 20B and the encapsulation material 30A are mixed and then mixed with the mesoporous microspheres 20A, so that the carbon material 20B and the encapsulation material 30A are coated on the surfaces of the mesoporous microspheres 20A.

Optionally, the carbon material 20B and the encapsulating material 30A form different levels on the surface of the mesoporous microsphere 20A, respectively. The carbon material 20B is coated on the outer surface of the mesoporous microsphere 20A, and the encapsulation material 30A is coated on the outer surface of the carbon material 20B, as shown in B) of fig. 5; or, the encapsulation material 30A is coated on the outer surface of the mesoporous microsphere 20A, and the carbon material 20B is coated on the outer surface of the encapsulation material 30A, as shown in fig. 5 c).

In one embodiment, the positive electrode lithium supplementing material further includes an encapsulation layer 30, the encapsulation layer 30 is wrapped on the outer surface of the wrapping layer 20, and the encapsulation layer 30 includes an encapsulation material 30A. Specifically, when the amount of the encapsulating material 30A is large, a part of the encapsulating material 30A may form the encapsulating layer 30 on the outer surface of the cladding 20, and the encapsulating layer 30 is wrapped on the outer surface of the cladding 20. That is, it can be understood that a portion of encapsulation material 30A is located in encapsulation layer 20 and a portion of encapsulation material 30A is located on the outer surface of encapsulation layer 20 to form encapsulation layer 30.

The encapsulation material 30A can improve the stability of the gap outside the core 10 that is not covered by the covering layer 20. In addition, the packaging layer 30 can be digested after the positive electrode lithium supplementing material is assembled and packaged to form a battery, so that the lithium supplementing performance of the positive electrode lithium supplementing material is not affected.

In one embodiment, the mass ratio of the core to the cladding is 100 (0.5-10). Specifically, the mass ratio of the core and the cladding may be, but is not limited to, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10. Optionally, the mass ratio of the inner core to the coating layer can be 100 (1-10), 100 (3-10), 100 (4-10), 100 (0.5-8), 100 (0.5-6), 100 (0.5-4), 100 (2-8) and 100 (1-6).

The mass ratio of the inner core to the coating layer is controlled within the range, so that the capacity of the anode lithium supplementing material can be ensured, the pre-lithiation effect is ensured, and the resource waste caused by excessive use of non-lithiation materials can be avoided.

When the mass ratio of the coating layer is larger than the above range, the gram capacity of the positive electrode lithium supplementing material is reduced, and the positive electrode lithium supplementing material cannot provide enough lithium ions in the first charging process, so that the coulomb efficiency is reduced, and the cycle life and the energy density of the lithium battery are directly influenced. When the mass ratio of the coating layer is smaller than the above range, the gas generated in the core cannot be effectively absorbed in the mesoporous microspheres, resulting in an increase in gas production and side reactions.

In one embodiment, the mass ratio of the mesoporous microsphere to the carbon material is (50-1): 1-50. Specifically, the mass ratio of mesoporous microspheres to carbon material may be, but is not limited to, 1:50, 10:40, 20:30, 30:20, 40:10, 50:1. Optionally, the mass ratio of the mesoporous microspheres to the carbon material can be (50-20): (1-30), (50-30): (1-20), (20-1): (30-50), (30-1): (20-50), (40-10): (10-40).

It can be appreciated that the coating layer is composed of mesoporous microspheres and a carbon material, and the mesoporous microspheres are used for accommodating gas, and the carbon material is used for enhancing conductivity. Therefore, the mass ratio of the mesoporous microspheres to the carbon material is controlled within the above range, so that the coating layer can be ensured to have high gas containing capacity and conductivity.

When the mass ratio of the mesoporous microspheres is larger than the above range, the carbon material in the coating layer is less, so that the capability of the coating layer for guiding out lithium ions is reduced, and the holes of the mesoporous microspheres cannot be shielded by the carbon material, so that the water absorption rate of the positive electrode lithium supplementing material is increased. When the mass ratio of the mesoporous microspheres is smaller than the above range, holes for accommodating gas in the coating layer are fewer, so that gas production cannot be effectively controlled.

In one embodiment, the mass ratio of the packaging material in the positive electrode lithium supplementing material is 0.1% -2.5%. Specifically, the mass ratio of the encapsulating material in the positive electrode lithium supplementing material may be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%. Optionally, the mass ratio of the packaging material in the positive electrode lithium supplementing material can be 0.3% -2.5%, 0.5% -2.5%, 1% -2.5%, 0.1% -2%, 0.1% -1.5%, 0.5% -2% and 0.8% -2.3%.

It should be explained that the mass ratio of the packaging material in the positive electrode lithium supplementing material is the ratio of the packaging material to the sum of the core and the coating layer; for example, the mass ratio of the encapsulating material is 0.5%, so the mass ratio of the core and the cladding is 99.5%. The mass ratio of the packaging material is related to the filling rate of holes in the positive electrode lithium supplementing material, so that the stability of the positive electrode lithium supplementing material before assembly can be ensured.

When the mass ratio of the encapsulating material is greater than the above range, the encapsulating material is relatively high, resulting in less lithium-rich material at the same mass when the battery is assembled, resulting in poor lithium supplementing effect. When the mass ratio of the packaging material is smaller than the above range, the packaging material is less, and the filling effect of pores and holes in the coating layer is poor, so that the anode lithium supplementing material is easy to absorb water, and the stability is poor.

In one embodiment, the mesoporous microspheres have a particle size D50 of 0.1 μm to 2. Mu.m. Specifically, the particle diameter D50 of the mesoporous microspheres may be, but is not limited to, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm. Alternatively, the mesoporous microspheres may have a particle size D50 of 0.5 μm to 2 μm, 0.7 μm to 2 μm, 1 μm to 2 μm, 0.1 μm to 1.7 μm, 0.1 μm to 1.5 μm, 0.5 μm to 1.5 μm.

The particle size of the mesoporous microsphere is controlled within the range, so that the pore occupation in the coating layer can be controlled to be small, and the mesoporous microsphere is kept to have higher porosity. It can be understood that when the particle diameter of the mesoporous microspheres is larger than the above range, the mesoporous microspheres are larger, the specific surface area of the mesoporous microspheres is reduced, resulting in a smaller amount of pores that can be formed, and the pores between the mesoporous microspheres having a large particle diameter are larger, resulting in easier permeation of external moisture. When the particle diameter of the mesoporous microspheres is smaller than the above range, the difficulty of preparing the mesoporous microspheres increases, and the particles form relatively serious agglomeration.

In one embodiment, the positive electrode lithium-supplementing material has a particle diameter D50 of 10 μm to 80. Mu.m. Specifically, the particle diameter D50 of the positive electrode lithium-supplementing material may be, but is not limited to, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm. Alternatively, the particle diameter D50 of the positive electrode lithium-supplementing material may be 20 μm to 80 μm, 30 μm to 80 μm, 50 μm to 80 μm, 10 μm to 70 μm, 10 μm to 60 μm, 10 μm to 50 μm, 20 μm to 60 μm.

When the particle size of the positive electrode lithium supplementing material is larger than the range, the overall specific surface area of the positive electrode lithium supplementing material is reduced, so that the energy density and the deintercalation efficiency of lithium ions are not improved; when the particle diameter of the positive electrode lithium supplementing material is smaller than the above range, the preparation difficulty increases, and the particles form relatively serious agglomeration.

In one embodiment, the carbon material has a diameter D50 of 0.7nm to 15nm. In particular, the diameter D50 of the carbon material may be, but is not limited to, 0.7nm, 1nm, 2nm, 3nm, 6nm, 8nm, 10nm, 12nm, 13nm, 14nm, 15nm. Alternatively, the diameter D50 of the carbon material may be 1nm to 15nm, 5nm to 15nm, 7nm to 15nm, 0.7nm to 13nm, 0.7nm to 11nm, 4nm to 12nm, 2nm to 11nm.

It should be explained that the diameter of the carbon material may be a median diameter, such as the diameter of a carbon nanotube, or the largest dimension of a graphene sheet. The diameter of the carbon material is controlled within the above range, and the filling amount and the coating thickness of the carbon material can be effectively controlled. When the diameter of the carbon material is larger than the above range, it is difficult for the carbon material to fill in the pores between the mesoporous microspheres, and also the second coating layer may be excessively thick. When the diameter of the carbon material is smaller than the above range, the carbon material is difficult to disperse, and the second coating layer may be too thin, resulting in poor conductive effect of the second coating layer.

In one embodiment, the specific surface area of the carbon material is 1m ² /g～300m ² And/g. Specifically, the specific surface area of the carbon material may be, but is not limited to, 1m ² /g、5m ² /g、10m ² /g、20m ² /g、40m ² /g、60m ² /g、80m ² /g、100m ² /g、200m ² /g、300m ² And/g. Alternatively, the specific surface area of the carbon material may be 30m ² /g～300m ² /g、50m ² /g～300m ² /g、100m ² /g～300m ² /g、1m ² /g～250m ² /g、1m ² /g～150m ² /g、1m ² /g～100m ² /g、50m ² /g～200m ² /g。

In one embodiment, the encapsulation layer has a thickness of 20nm to 50nm. Specifically, the thickness of the encapsulation layer may be, but is not limited to, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm. Alternatively, the thickness of the encapsulation layer may be 25nm to 50nm, 30nm to 50nm, 20nm to 45nm, 20nm to 40nm, 25nm to 45nm, 22nm to 48nm.

In one embodiment, the thickness of the first coating layer is 0.1 μm to 2 μm. Specifically, the thickness of the first cladding layer may be, but is not limited to, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm. Alternatively, the thickness of the first coating layer may be 0.5 μm to 2 μm, 0.7 μm to 2 μm, 1 μm to 2 μm, 0.1 μm to 1.7 μm, 0.1 μm to 1.5 μm, 0.5 μm to 1.5 μm.

Wherein, the first coating thickness is too thin, so that the lattice volume expansion of the positive electrode lithium supplementing material is difficult to be restrained; too thick a first coating layer can affect the lithium ion transport rate.

In one embodiment, the second cladding layer has a thickness of 0.7nm to 15nm. Specifically, the thickness of the second cladding layer may be, but is not limited to, 0.7nm, 1nm, 2nm, 3nm, 6nm, 8nm, 10nm, 12nm, 13nm, 14nm, 15nm. Alternatively, the thickness of the second coating layer may be 1nm to 15nm, 5nm to 15nm, 7nm to 15nm, 0.7nm to 13nm, 0.7nm to 11nm, 4nm to 12nm, 2nm to 11nm.

Wherein, the second coating thickness is too thin, so that the lattice volume expansion of the positive electrode lithium supplementing material is difficult to be restrained; too thick a second coating layer may affect the lithium ion transmission rate.

In one embodiment, the total residual alkali on the surface of the positive electrode lithium-supplementing material is 5% or less.

In one embodiment, the tap density of the positive electrode lithium supplementing material is 0.5g/cm ³ ～2.5g/cm ³ . The tap density is within the above range, and the overall energy density assembled in the positive electrode material can be improved. Specifically, as the cerium dioxide mesoporous spheres have rich pores and the Shen Duowei particles have certain gaps when combined and coated on the inner core, the space utilization rate is smaller, and a plurality of combining modes exist in the scheme to effectively utilize the gap space and achieve corresponding effects, so that the reaction has larger interval difference in tap density, the true density in the material is reduced due to excessive micropores, and meanwhile, the tap density of the pole piece is lower, and the processability of the pole piece and the volume energy density of the battery cell are influenced; thus being capable of matching corresponding practical schemes for different tap density requirements.

In an embodiment, the present invention further provides a method for preparing a positive electrode lithium-supplementing material, please refer to fig. 6, which is specifically used for preparing the positive electrode lithium-supplementing material in the above embodiment. The preparation method comprises the following steps:

and S10, uniformly mixing and drying the mesoporous microsphere precursor and the pore-forming agent, uniformly mixing with the lithium-rich material, and drying and sintering to obtain the mesoporous microsphere coated lithium-rich material.

And S20, uniformly mixing the lithium-rich material and the carbon material coated by the mesoporous microspheres, and sintering to obtain the positive electrode lithium-supplementing material, wherein the lithium-rich material forms a core, and the mesoporous microspheres and the carbon material form a coating layer to coat the outer surface of the core.

Optionally, in step S10, the mesoporous microsphere precursor may be a metal salt, such as a soluble cerium salt, a titanium salt, and the like. The soluble cerium salt includes one or more of cerium nitrate hexahydrate, cerium chloride, cerium sulfate, or cerium bromide.

Alternatively, in step S10, the pore-forming agent may be an organic acid including one or more of malic acid, oxalic acid, citric acid, or lactic acid.

Optionally, in step S10, the mesoporous microsphere precursor is dissolved in ethanol to obtain a mesoporous microsphere precursor solution, then the pore-forming agent is added into the solution for reaction, and then the lithium-rich material is added into the solution, stirred until the solution is completely evaporated, and then dried.

Optionally, in step S10, the reaction time between the mesoporous microsphere precursor and the pore-forming agent is 1min to 10min. The concentration of the solution of the mesoporous microsphere precursor and the pore-forming agent is 0.05 mol/L-3 mol/L.

Optionally, in step S10, the mass ratio of the lithium-rich material to the mesoporous microsphere precursor is 1: (0.01-0.5), the mass ratio of the mesoporous microsphere precursor to the pore-forming agent is (1-1.5): (0.1-1).

Optionally, in step S10, the stirring temperature may be 0 ℃ to 80 ℃, and the drying temperature may be 80 ℃ to 150 ℃. The drying time can be 5-15 h.

Alternatively, in step S10, the sintering temperature may be 400 to 600 ℃. The sintering time may be 2 to 8 hours and is performed under an inert atmosphere.

Optionally, in step S20, the lithium-rich material coated with mesoporous microspheres is added to an ethanol solution of the carbon material, stirred to a viscous substance, and sintered.

Alternatively, in step S20, the sintering temperature may be 300 ℃ to 600 ℃. The sintering time may be 0.5 to 3 hours and is performed under an inert atmosphere.

Optionally, the inert atmosphere comprises at least one of nitrogen, argon, neon, helium.

According to the positive electrode lithium supplementing material with the mesoporous microsphere and the carbon material coating, the holes of the mesoporous microsphere are regulated by the pore-forming agent, so that the holes in the mesoporous microsphere can be used for accommodating gas generated by the lithium-rich material, the stability of electrolyte of the positive electrode lithium supplementing material is improved, and the carbon material can improve the conductivity of the positive electrode lithium supplementing material coated by the mesoporous microsphere.

In one embodiment, the invention also provides a positive electrode material, which comprises a positive electrode active material and a positive electrode lithium supplementing material. The positive electrode lithium supplementing material is provided in the above embodiment. Alternatively, the positive electrode active material may be a phosphate positive electrode active material or a ternary positive electrode active material, and in a specific embodiment, the positive electrode active material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium vanadium fluorophosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.

In one embodiment, the content of the positive electrode lithium supplementing material in the positive electrode material can be controlled to be 1-6% of the mass of the positive electrode active material. The ratio can exactly compensate the loss of active lithium in the first charging process of the battery. If the addition amount of the positive electrode lithium supplementing material in the positive electrode material is too low, the lost active lithium in the positive electrode active material cannot be fully supplemented, which is unfavorable for improving the energy density, capacity retention rate and the like of the battery. If the addition amount of the positive electrode lithium supplementing material in the positive electrode active material is too high, the original reversible capacity is occupied, and the cost is increased. In some embodiments, the mass percentage of the positive electrode lithium supplementing material in the positive electrode material may be 1%, 2%, 4%, 6%, etc.

In one embodiment, the invention also provides a positive electrode sheet, which comprises a current collector and an active material layer arranged on the current collector, wherein the active material layer comprises the positive electrode lithium supplementing material in any one of the embodiments. Or the active material layer comprises the positive electrode lithium supplementing material obtained by the preparation method of the positive electrode lithium supplementing material in the embodiment.

In one embodiment, the positive electrode plate comprises a positive electrode current collector, a positive electrode active layer is arranged on the positive electrode current collector, the positive electrode active layer comprises positive electrode active materials, positive electrode lithium supplementing materials, conductive agents, binders and the like, the materials are not particularly limited, and proper materials can be selected according to actual application requirements. The positive electrode current collector includes, but is not limited to, any one of copper foil and aluminum foil. The conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nano tube, and the content of the conductive agent in the positive electrode active layer is 3-5 wt%. The binder comprises one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive electrode active layer is 2-4wt%.

In one embodiment, the invention also provides a secondary battery, which comprises a negative electrode plate, a diaphragm and the positive electrode plate. The positive electrode plate comprises the positive electrode material.

The technical scheme of the invention is described in detail by specific examples.

Example 1

The embodiment provides a positive electrode lithium supplementing material and a preparation method thereof, wherein the positive electrode lithium supplementing material comprises an inner core Li of a lithium-rich material ₅ FeO ₄ The coating layer consists of cerium oxide mesoporous spheres and graphene, and the packaging layer of 3-trifluoromethyl-aniline. Wherein the mass ratio of the coating layer is 1.0%, the mass ratio of the cerium oxide mesoporous spheres to the graphene is 1:2, the mass ratio of the 3-trifluoromethyl-aniline is 0.5%, the thickness of the coating layer is 0.63 mu m, the particle size of the cerium oxide mesoporous spheres is 0.32 mu m-0.62 mu m, the D50 of the graphene is 2nm, and the specific surface area of the graphene is 3.4m ² /g。

The preparation method of the positive electrode lithium supplementing material comprises the following steps:

(1) Cerium chloride and citric acid are used as raw materials, and the mass ratio of the cerium chloride to the citric acid is 1:0.1 preparing ethanol solution with concentration of 0.5mol/L, stirring at 60 ℃ until the solution is completely evaporated, drying at 120 ℃ for 10h, and then adding 15g of Li ₅ FeO ₄ And (3) uniformly mixing by using a deaeration machine, and then placing the mixture in a tube furnace at 600 ℃ for calcination for 5 hours in an argon atmosphere to obtain the cerium dioxide mesoporous sphere-wrapped lithium-rich material.

(2) And adding the material into an ethanol solution of graphene, wherein the graphene D50=2 nm, the specific surface area is 3.4m2/g, stirring to be a viscous substance, and calcining for 1h in an air atmosphere at 400 ℃ to obtain the cerium oxide mesoporous sphere and graphene double-coated positive electrode lithium supplementing material.

(3) In argon atmosphere, the coated positive electrode lithium supplementing material and 3-trifluoromethyl-aniline are prepared according to the following ratio of 1: mixing 0.005 proportion and a certain amount of N-methyl pyrrolidone in a deaeration machine for 10 minutes, drying, crushing, and sieving with a 200-mesh sieve to obtain the final positive electrode lithium supplementing material.

Example 2

The embodiment provides a positive electrode lithium supplementing material and a preparation method thereof, wherein the positive electrode lithium supplementing material comprises a high content ofInner core Li of lithium material ₅ FeO ₄ The coating layer consists of cerium oxide mesoporous spheres and graphene. Wherein, the mass ratio of the coating layer is 1.0 percent, the mass ratio of the cerium oxide mesoporous spheres to the graphene is 1:2, the thickness of the coating layer is 0.68 mu m, the particle size of the cerium oxide mesoporous spheres is 0.32 mu m-0.62 mu m, the D50 of the graphene is 2nm, and the specific surface area of the graphene is 3.4m ² /g。

Compared with the embodiment 1, the preparation method of the positive electrode lithium supplementing material is different in that: there is no step (3).

Example 3

The embodiment provides a positive electrode lithium supplementing material and a preparation method thereof, wherein the positive electrode lithium supplementing material comprises an inner core Li of a lithium-rich material ₅ FeO ₄ The coating layer consists of cerium oxide mesoporous spheres and graphene, and the packaging layer of 3-trifluoromethyl-aniline. Wherein, the mass ratio of the coating layer is 10.0 percent, the mass ratio of the cerium oxide mesoporous sphere to the graphene is 1:2, the mass ratio of the 3-trifluoromethyl-aniline is 0.5 percent, the thickness of the coating layer is 1.23 mu m, the particle size of the cerium oxide mesoporous sphere is 0.32 mu m-0.62 mu m, the D50 of the graphene is 2nm, and the specific surface area of the graphene is 3.4m ² /g。

Compared with the embodiment 1, the preparation method of the positive electrode lithium supplementing material is different in that: in the step (1), cerium chloride and citric acid are used as raw materials, and the mass ratio of the cerium chloride to the citric acid is 1:0.1 preparing ethanol solution with concentration of 0.5mol/L, stirring at 60 ℃ until the solution is completely evaporated, drying at 120 ℃ for 10h, and then adding 15g of Li ₅ FeO ₄ And (3) uniformly mixing by using a deaeration machine, and then placing the mixture in a tube furnace at 600 ℃ for calcination for 5 hours in an argon atmosphere to obtain the cerium dioxide mesoporous sphere-wrapped lithium-rich material.

Example 4

The embodiment provides a positive electrode lithium supplementing material and a preparation method thereof, wherein the positive electrode lithium supplementing material comprises an inner core Li of a lithium-rich material ₅ FeO ₄ The coating layer consists of cerium oxide mesoporous spheres and graphene, and the packaging layer of 3-trifluoromethyl-aniline. Wherein the mass ratio of the coating layer is 1.0%, the mass ratio of the cerium oxide mesoporous spheres to the graphene is 2:1, the mass ratio of the 3-trifluoromethyl-aniline is 0.5%, the thickness of the coating layer is 0.62 mu m, The particle diameter of the cerium dioxide mesoporous sphere is 0.32-0.62 mu m, the D50 of the graphene is 2nm, and the specific surface area of the graphene is 3.4m ² /g。

Compared with the embodiment 1, the preparation method of the positive electrode lithium supplementing material is different in that: the mass ratio of the cerium oxide mesoporous spheres to the graphene is 2:1.

Example 5

The embodiment provides a positive electrode lithium supplementing material and a preparation method thereof, wherein the positive electrode lithium supplementing material comprises an inner core Li of a lithium-rich material ₅ FeO ₄ The coating layer consists of cerium oxide mesoporous spheres and graphene, and the packaging layer of 3-trifluoromethyl-aniline. Wherein, the mass ratio of the coating layer is 1.5 percent, the mass ratio of the cerium oxide mesoporous sphere to the graphene is 1:2, the mass ratio of the 3-trifluoromethyl-aniline is 0.5 percent, the thickness of the coating layer is 1.13 mu m, the particle size of the cerium oxide mesoporous sphere is 0.54 mu m-1.12 mu m, the D50 of the graphene is 2nm, and the specific surface area of the graphene is 3.4m ² /g。

Compared with the embodiment 1, the preparation method of the positive electrode lithium supplementing material is different in that: in the step (1), cerium chloride and citric acid are used as raw materials, and the mass ratio of the cerium chloride to the citric acid is 1:0.5 to prepare an ethanol solution with a concentration of 0.1mol/L, stirring at 60 ℃ until the solution is completely evaporated, drying at 150 ℃ for 8 hours, and then adding 15g of Li ₅ FeO ₄ And (3) uniformly mixing by using a deaeration machine, and then placing the mixture in a tube furnace at 600 ℃ for calcination for 5 hours in an argon atmosphere to obtain the cerium dioxide mesoporous sphere-wrapped lithium-rich material.

Comparative example 1

The embodiment provides a positive electrode lithium supplementing material comprising a lithium-rich material Li ₅ FeO ₄ And graphene coated on the surface of the lithium-rich material.

Comparative example 2

The present embodiment provides a positive electrode lithium supplementing material including a core Li of a lithium-rich material ₅ FeO ₄ And a coating layer of cerium oxide mesoporous spheres. Wherein, the mass ratio of the coating layer is 1.0 percent, the thickness of the coating layer is 0.62 mu m, and the grain diameter of the cerium oxide mesoporous sphere is 0.32-0.62 mu m.

Comparative example 3

The embodiment provides a positive electrode lithium supplementing material, which comprises a lithium-rich material Li mixed by simple ball milling ₅ FeO ₄ Cerium oxide mesoporous spheres and graphene.

The positive electrode lithium-supplementing materials provided in examples 1 to 5 and the positive electrode lithium-supplementing materials provided in comparative examples 1 to 3 were assembled into a positive electrode sheet and a lithium ion battery, respectively, according to the following methods:

gas production test

The first-circle gas production test is to assemble a lithium ion battery by using a die battery, then charge the lithium ion battery under constant current and constant voltage, wherein the first-circle charge and discharge voltage is 2.5-4.3V, the current is 0.1C, and the cut-off current is 0.01C. The gas in the die cell was introduced into a differential electrochemical mass spectrometer for testing.

Tap density

And loading the weighed powder into a measuring cylinder of a compaction device, and fixing the measuring cylinder on a support. The cam is rotated, and the orientation rod drives the support to slide up and down and impact on the anvil. Shaking 250.+ -.15 times per minute for 12 minutes. And measuring the volume of the powder in the measuring cylinder, wherein the ratio of the mass of the powder to the volume is the tap density of the powder.

Positive pole piece: positive electrode lithium supplementing material, SP and PVDF according to 90:4: mixing the homogenized positive electrode slurry according to the mass ratio of 6, coating the positive electrode slurry on the surface of an aluminum foil, vacuum drying overnight at 110 ℃, and rolling to obtain a positive electrode plate;

negative pole piece: a lithium sheet;

electrolyte solution: mixing ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and adding LiPF ₆ Electrolyte is formed, liPF ₆ The concentration of (2) is 1mol/L;

a diaphragm: a polypropylene microporous separator;

and (3) assembling a lithium ion battery: and assembling the button type lithium ion full battery in an inert atmosphere glove box according to the assembling sequence of the negative electrode plate, the diaphragm, the electrolyte and the positive electrode plate.

Each lithium ion battery assembled in the above lithium ion battery example was subjected to electrochemical performance test under the following conditions:

charging at 0.1C with a cut-off voltage of 4.3V; constant voltage charging was performed at 4.3V. After the charging process was completed, the mixture was allowed to stand for 10 minutes to discharge at a rate of 0.1C, and the cut-off voltage was 2.5V.

The test results are shown in table 1 below:

TABLE 1

As can be seen from the test results of examples 1-5 and comparative example 1 in Table 1, the batteries provided in examples 1-5 all have a first charge capacity exceeding 700mAh/g, and the tap density of the positive electrode lithium supplementing material reaches 1.9g/cm ³ And above, and the gas yield is lower than 15.5mL/g, the electrochemical performance of the positive electrode lithium supplementing material provided in examples 1-5 is far superior to that of comparative example 1. The positive electrode lithium supplementing material provided by the application can release more lithium ions under the same voltage so as to have higher capacity, and the gas yield is far lower than that of a lithium-rich material which is not coated by cerium oxide mesoporous spheres.

As can be seen from the test results of examples 1 to 5 and comparative example 2 in table 1, the use of both the ceria mesoporous spheres and the carbon material coating not only allows the positive electrode lithium supplementing material to provide a higher capacity, but also further reduces the gas production rate of the material, compared to the use of only the ceria mesoporous spheres coating the positive electrode lithium supplementing material. The carbon material provides a better conductive environment for the lithium-rich material, so that the ionic conductivity is higher; and the carbon material is filled in the middle of the pores among the cerium oxide mesoporous spheres, and can further realize compact packaging on the lithium-rich material, so that the gas production of the material is reduced.

From the test results of examples 1 to 5 and comparative example 3 in table 1, it can be seen that the mixture obtained by simply ball-milling and mixing the lithium-rich material, the cerium oxide mesoporous spheres and the graphene has a higher charge gram capacity but a higher gas yield. Because the lithium-rich material is not coated after simple mixing, the outer surface of the lithium-rich material is exposed, so that the generated gas is easy to escape and is difficult to capture by the cerium oxide mesoporous spheres, and finally the gas yield of the material is increased.

Further, as can be seen from the test results of example 1 and example 2 in table 1, on the basis of adopting the carbon material and the mesoporous sphere coating, the packaging material is utilized to form the packaging layer on the material, so that the mortality of the outer surface layer of the positive electrode lithium supplementing material can be further improved, and the gas yield of the material can be reduced.

As can be seen from the test results of example 1 and example 3 in table 1, when the mass ratio of the coating layer is increased, the charge gram capacity of the positive electrode lithium-compensating material is reduced and the effect of improving the strong gas amount is weak, so the mass ratio of the coating layer to the core needs to be controlled within a proper range.

From the test results of example 1 and example 4 in table 1, it can be seen that the gas yield of the positive electrode lithium supplementing material increases in the case of a carbon material having a mass ratio of Yu Jiekong balls. Because the number of mesoporous spheres in the cladding layer for accommodating gas is reduced, gas evolution is increased and charge gram capacity of the material is affected to decrease.

From the test results of example 1 and example 5 in table 1, it can be seen that when the mesoporous pellets used were increased in size, not only was the tap density of the material adversely increased, but also the gas production rate of the material was increased. Therefore, in order to ensure that the positive electrode lithium supplementing material has higher tap density and lower gas yield, the particle size of the mesoporous spheres also needs to be considered.

In the description of the embodiments of the present invention, it should be noted that, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like refer to the orientation or positional relationship described based on the drawings, which are merely for convenience of description and simplification of the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.

The above disclosure is only a preferred embodiment of the present invention, and it should be understood that the scope of the invention is not limited thereto, but all or part of the procedures for implementing the above embodiments can be modified by one skilled in the art according to the scope of the appended claims.

Claims

1. A positive electrode lithium supplementing material, characterized by comprising:

a core comprising a lithium-rich material;

the coating layer is coated on the outer surface of the inner core and comprises mesoporous microspheres and carbon materials.

2. The positive electrode lithium supplementing material according to claim 1, wherein the mesoporous microsphere has a pore structure therein, and at least a part of the carbon material is filled in the pore structure.

3. The positive electrode lithium supplementing material according to claim 1, wherein the coating layer comprises a first coating layer and a second coating layer, the first coating layer is coated on the outer surface of the inner core, the second coating layer is coated on the outer surface of the first coating layer, the first coating layer comprises the mesoporous microspheres, and the second coating layer comprises the carbon material.

4. The positive electrode lithium supplementing material according to claim 1, wherein the number of the mesoporous microspheres is plural, and pores are provided between adjacent mesoporous microspheres, and the carbon material is filled in the pores.

5. The positive electrode lithium supplementing material according to claim 1, wherein the coating layer further comprises an encapsulating material, the encapsulating material is combined on the outer surface of the mesoporous microsphere and/or the carbon material, the encapsulating material comprises one or more of a fluoroamine compound, an ester compound and a nitrile compound, and the mass ratio of the encapsulating material in the positive electrode lithium supplementing material is 0.1% -2.5%.

6. The positive electrode lithium supplementing material according to claim 5, wherein the number of the mesoporous microspheres is plural, and pores are provided between adjacent mesoporous microspheres, and the encapsulating material is filled in the pores.

7. The positive electrode lithium supplementing material according to claim 5, wherein the carbon material and/or the encapsulation material is/are coated on the outer surface of the mesoporous microsphere.

8. The positive electrode lithium supplementing material according to claim 5, further comprising an encapsulation layer, wherein the encapsulation layer is coated on the outer surface of the coating layer, the encapsulation layer is made of the encapsulation material, and the thickness of the encapsulation layer is 20 nm-50 nm.

9. The positive electrode lithium-supplementing material according to claim 5, wherein the fluoroamine compound comprises one or more of 3-trifluoromethyl-aniline, N-diethyl-1, 2, 3-hexafluoropropylamine, and ibutethylamine.

10. The positive electrode lithium-supplementing material according to claim 3, wherein,

the mesoporous microsphere comprises one or more of cerium dioxide, titanium dioxide and zirconium dioxide;

and/or the carbon material comprises one or more of graphene, carbon nanotubes, fullerenes, carbon black.

And/or the mass ratio of the inner core to the coating layer is 100 (0.5-10);

and/or the mass ratio of the mesoporous microspheres to the carbon material is (50-1): 1-50;

and/or the particle diameter D50 of the mesoporous microsphere is 0.1-2 mu m;

And/or the particle diameter D50 of the positive electrode lithium supplementing material is 10-80 mu m;

and/or the tap density of the positive electrode lithium supplementing material is 0.5g/cm ³ ～2.5g/cm ³ 。

11. The preparation method of the positive electrode lithium supplementing material is characterized by comprising the following steps of:

uniformly mixing and drying the mesoporous microsphere precursor and the pore-forming agent, uniformly mixing with the lithium-rich material, and drying and sintering to obtain the mesoporous microsphere coated lithium-rich material;

and uniformly mixing the lithium-rich material coated by the mesoporous microspheres with the carbon material, and sintering to obtain the positive electrode lithium-supplementing material, wherein the lithium-rich material forms an inner core, and the mesoporous microspheres and the carbon material form a coating layer to coat the outer surface of the inner core.

12. A positive electrode material, characterized in that the positive electrode material comprises a positive electrode active material and the positive electrode lithium-supplementing material according to any one of claims 1 to 10, or the positive electrode material comprises a positive electrode lithium-supplementing material obtained by the method for producing a positive electrode lithium-supplementing material according to claim 11.

13. A secondary battery comprising the positive electrode material according to claim 12, or the secondary battery comprising the positive electrode lithium-supplementing material according to any one of claims 1 to 10, or the secondary battery comprising the positive electrode lithium-supplementing material obtained by the method for producing the positive electrode lithium-supplementing material according to claim 11.