CN115832219A

CN115832219A - Composite material, positive pole piece and secondary battery

Info

Publication number: CN115832219A
Application number: CN202210009170.0A
Authority: CN
Inventors: 陈祥斌; 高凯; 来佑磊; 黄玉平; 史松君
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-01-05
Filing date: 2022-01-05
Publication date: 2023-03-21

Abstract

The application provides a combined material, positive pole piece and secondary battery, in particular to a combined material, it is the spherical particle who has the nucleocapsid structure, the core of spherical particle contains lithium iron silicate, the shell layer of spherical particle contains lithium iron phosphate contain carbon between core and the shell layer.

Description

Composite material, positive pole piece and secondary battery

Technical Field

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

Background

Depletion of energy resources has led to significant development of new energy storage devices. Secondary batteries have attracted attention because of their high energy density, high capacity, good cycle stability, and environmental protection characteristics. The lithium iron phosphate anode material has the advantages of relatively low price, environmental friendliness, high safety and the like, and thus becomes the mainstream anode material at present. The structure Of the lithium iron phosphate positive electrode material determines that two-phase transition from lithium iron phosphate to iron phosphate occurs in the charging and discharging process, so that the discharging curve Of the lithium iron phosphate positive electrode material has a long platform, the voltage Of the battery and the residual capacity (SOC) are in a nonlinear relation, the residual capacity is difficult to estimate through the voltage, and the difficulty is brought to a battery management system for accurately measuring and calculating the SOC Of the battery.

Disclosure of Invention

At present, the mainstream method for improving the SOC precision of the lithium iron phosphate battery is to blend other anode materials to shorten a voltage platform, the difference between the selected anode material and the voltage interval of the lithium iron phosphate is not large, and the voltage and the SOC are preferably in a linear relation. The lithium iron silicate has the advantages of rich raw material resources, low price, no hygroscopicity, no toxicity, environmental friendliness, good thermal stability and the like, and is also a research and development hotspot of the anode material of the secondary battery. The working voltage interval of the lithium iron silicate material is 2.0V-3.7V, the lithium iron silicate material is matched with lithium iron phosphate, the slope degree of a charging and discharging curve is very high, the voltage platform is about 2.8V, the electric voltage platform of the lithium iron phosphate material is about 3.2V, the two are mixed to form a double platform, and the SOC estimation precision of the BMS of the lithium iron phosphate is improved.

The current methods for mixing lithium iron phosphate with lithium iron silicate mainly comprise two methods: physically mixing and building a composite structure. The physical mixing is to mix two anode materials according to a certain proportion when preparing anode slurry, but the difference of the electronic conductivity of the two anode materials is too large, and the lithium iron phosphate is 10 ^-9 S/cm, lithium iron silicate is 10 ^-14 S/cm, which causes large electrochemical polarization and concentration polarization caused by overlarge difference of electron transport capacity in the charging and discharging processes. The composite structure compounds the nanoparticles of the two into large particles, but the process has the problem of inconsistent volume change in the charging and discharging process besides the problem of overlarge polarization. In the charging and discharging process, the volume change of the lithium iron phosphate is small, the volume change of the lithium iron silicate exceeds 2 percent, and the composite particles are cracked due to inconsistent volume expansion and contractionAnd further, a fresh interface is exposed to generate side reaction with the electrolyte, and finally particle pulverization failure is caused.

In order to solve the technical problems, the application provides a composite material, which takes lithium iron silicate as a core and lithium iron phosphate as a shell layer, and a carbon layer is arranged between the lithium iron silicate and the shell layer. The composite material can be used as a positive active material of a secondary battery, a charging and discharging curve of the composite material has double platforms, and the problems that a lithium iron phosphate voltage platform is too long and the SOC estimation precision of a BMS is low can be solved. Particularly, the composite material takes the lithium iron phosphate with high electronic conductivity as a shell to increase interface electron transmission, and a carbon layer is arranged between the shell layer and the core, so that the electron conduction between the lithium iron silicate and the lithium iron phosphate is improved, and a buffer space is provided for the volume expansion and contraction of the lithium iron silicate, thereby solving the problem of cracking of composite particles caused by the inconsistent volume expansion and contraction of the lithium iron silicate and the lithium iron phosphate.

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

A first aspect of the present application provides a composite material which is a spherical particle having a core-shell structure, a core of the spherical particle contains lithium iron silicate, a shell layer of the spherical particle contains lithium iron phosphate, and a carbon layer is contained between the core and the shell layer.

In some embodiments, the spherical particles have a particle size, expressed as D50, of from 3 μm to 15 μm.

In some embodiments, the lithium iron silicate and lithium iron phosphate are each particles having a single crystal structure.

In some embodiments, the lithium iron silicate has a particle size, expressed as D50, of from 2 μm to 6 μm.

In some embodiments, the lithium iron phosphate has a particle size, expressed as D50, of 0.1 μm to 0.5 μm.

In some embodiments, the molar ratio of the lithium iron phosphate to the lithium iron silicate is 1.1 to 1:1.

A second aspect of the present application provides a method of making a composite material comprising the steps of:

step 1: mixing lithium iron silicate particles, silicone oil A and an organic solvent to obtain a mixture a, wherein the silicone oil A is polysiloxane containing at least two silicon-hydrogen bonds;

and 2, step: adding silicone oil B and a hydrosilylation catalyst into the mixture a obtained in the step 1, and mixing to obtain a mixture B, wherein the silicone oil B is polysiloxane containing at least two alkenyl groups;

and step 3: spray-drying the mixture b obtained in the step 2 to form lithium iron silicate particles with the surfaces coated with the organic silicon layers;

and 4, step 4: mixing lithium iron phosphate particles, a carbon source, water and the lithium iron silicate particles coated with the organic silicon layer on the surface, which are obtained in the step (3), wherein the carbon source is an organic matter containing oxygen and/or nitrogen; then, forming secondary particles through spray granulation, wherein the secondary particles have a composite structure with lithium iron silicate with the surface coated with an organic silicon layer as a core and lithium iron phosphate coated with the carbon source as a shell layer;

and 5: and (4) calcining the secondary particles obtained in the step (4) in an inert atmosphere to obtain the composite material.

In some embodiments, the lithium iron silicate particles in step 1 have a single crystal structure.

In some embodiments, the lithium iron silicate particles have a particle size, expressed as D50, of from 2 μm to 6 μm.

In some embodiments, the silicone oil a is methyl hydrogen silicone oil.

In some embodiments, the organic solvent is selected from one or more of dichloromethane, chloroform, toluene, xylene, dichlorotoluene.

In some embodiments, the ratio of the volume of the organic solvent to the mass of the lithium iron silicate is 0.5L/kg to 5L/kg.

In some embodiments, the molar ratio of the lithium iron silicate particles to the silicone oil a is 1.

In some embodiments, the silicone oil B is a vinyl silicone oil.

In some embodiments, the molar ratio of silicone oil a to silicone oil B is 1:1 to 1:4.

In some embodiments, the hydrosilylation catalyst of step 2 is selected from one or more of Karstedt's catalyst, chloroplatinic acid, chlororhodic acid, chloroiridic acid, and more preferably Karstedt's catalyst.

In some embodiments, the mass of the hydrosilylation catalyst is 0.001% to 0.05% of the total mass of the silicone oil a and the silicone oil B.

In some embodiments, step 3 is performed using a spray dryer having a drying temperature of 50 ℃ to 200 ℃.

In some embodiments, the particles obtained in step 3 have a particle size, expressed as D50, of from 2 μm to 6 μm.

In some embodiments, the lithium iron phosphate particles in step 4 are single crystal structures.

In some embodiments, the lithium iron phosphate particles have a particle size, expressed as D50, of 0.1 μm to 0.5 μm.

In some embodiments, the carbon source of step 4 is selected from the group consisting of carbohydrates, polyethylene glycol, polyacrylic acid.

In some embodiments, the molar ratio of the lithium iron phosphate particles of step 4 to the lithium iron silicate of step 1 is 1.1 to 1:1.

In some embodiments, the molar ratio of the lithium iron phosphate to the carbon source of step 4 is 1.

In some embodiments, step 4 is performed using a spray dryer having a drying temperature of 50 ℃ to 200 ℃.

In some embodiments, the secondary particles obtained in step 4 have a particle size, expressed as D50, of from 3 μm to 15 μm.

In some embodiments, the inert atmosphere in step 5 is selected from nitrogen, argon, helium, xenon.

In some embodiments, the calcination temperature is from 300 ℃ to 800 ℃.

In some embodiments, the calcination time is from 2h to 10h.

In some embodiments, the composite material made by the method provided by the second aspect of the present application is a composite material provided by the first aspect of the present application.

A third aspect of the present application provides a positive electrode plate, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the positive electrode film layer comprises the composite material of the first aspect of the present application, or comprises a composite material prepared by the method of the second aspect of the present application. Optionally, the positive electrode film layer further comprises a conductive agent and a binder.

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

A fifth aspect of the present application provides a battery module comprising the composite material of the first aspect of the present application, the positive electrode sheet of the third aspect of the present application, or the secondary battery of the fourth aspect of the present application.

A sixth aspect of the present application provides a battery pack comprising the composite material of the first aspect of the present application, the positive electrode sheet of the third aspect of the present application, or the secondary battery of the fourth aspect of the present application, or the battery module of the fifth aspect of the present application.

A seventh aspect of the present application provides an electric device comprising the composite material of the first aspect of the present application, the positive electrode sheet of the third aspect of the present application, or the secondary battery of the fourth aspect of the present application, or the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application.

The application provides a combined material is as secondary battery's anodal active material, can solve the low problem of BMS estimation SOC precision, and further, has still solved lithium iron silicate and the inconsistent problem that leads to the compound granule fracture of lithium iron phosphate volume expansion shrinkage.

Drawings

Fig. 1 is an SEM photograph of a composite material according to an embodiment of the present application.

Fig. 2 is an enlarged view of fig. 1.

Fig. 3 is a cross-sectional view of fig. 2.

Fig. 4 is a schematic view of a secondary battery having a square structure according to an embodiment of the present application.

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

Fig. 6 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 7 is a schematic view of a battery pack according to an embodiment of the present application.

Fig. 8 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 7.

The reference numerals appearing in fig. 4-8 illustrate: 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.

Fig. 9 is a schematic view of a secondary battery of a cylindrical structure according to an embodiment of the present application.

Fig. 10 is an exploded view of the secondary battery according to one embodiment of the present application shown in fig. 9, and reference numerals illustrate: (1) a positive electrode top cover, (2) a positive electrode tab glue, (3) a battery JR; (4) blue glue; (5) an aluminum shell; (6) gluing a negative pole tab; (7) and a negative electrode top cover.

Fig. 11 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Fig. 12 is a particle size distribution curve of the positive electrode material obtained in example 1.

Fig. 13 is a charge and discharge graph of example 1 and comparative example 1.

Fig. 14 is a graph of the battery capacity retention rate versus the number of cycles for the positive electrode materials of example 1 and comparative examples 1-2.

Fig. 15 is a graph of battery rate performance for example 1 and the positive electrode materials of comparative examples 1-2.

Detailed Description

Hereinafter, embodiments of the composite material and the method for producing the same, and 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 detailed description thereof will be omitted unnecessarily. 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 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Further, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3,4 and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 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 only a shorthand 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 otherwise specified.

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, if not 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).

[ composite Material and production method ]

One embodiment of the present application provides a composite material which is a spherical particle having a core-shell structure, a core of the spherical particle containing lithium iron silicate, a shell of the spherical particle containing lithium iron phosphate, and carbon between the core and the shell. The composite material provided by the application takes lithium iron silicate as a core and lithium iron phosphate as a shell layer, and a carbon layer is arranged between the lithium iron silicate and the shell layer. The working voltage interval of the lithium iron silicate and the lithium iron phosphate is close to each other and is 2.0V-3.7V, the voltage platform of the lithium iron silicate is about 2.8V, and the voltage platform of the lithium iron phosphate is about 3.2V.

Further, the composite material provided by the application is lithium iron phosphate (10) with high electronic conductivity ^-9 S/cm) as shell, low electron conductivity lithium iron silicate (10) ^-14 S/cm) can increase interfacial electron transport. Meanwhile, a carbon layer is arranged between the core and the shell layer, so that the electron conduction between the lithium iron silicate and the lithium iron phosphate can be improved, and the volume expansion of the lithium iron silicate is realizedThe constriction provides a buffer space.

The inventors have found that when the spherical particles have a particle diameter, as represented by D50, of from 3 μm to 15 μm, the composite material can be made to have a suitable compacted density and specific surface area, and the particles are not easily cracked, avoiding deterioration of the power performance of the battery in use. Thus, in some embodiments, the spherical particles have a particle size, expressed as D50, of from 3 μm to 15 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

In some embodiments, the lithium iron silicate and lithium iron phosphate are each particles having a single crystal structure. The lithium iron silicate particles with larger particle size can be selected so as to form a core-shell structure. In some embodiments, the lithium iron silicate particles have a particle size, expressed as D50, of from 2 μm to 6 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm. In some embodiments, the lithium iron phosphate has a particle size, expressed as D50, of 0.1 μm to 0.5 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm. The shell layer may include a plurality of lithium iron phosphate particles. Lithium iron phosphate particles with the particle size of 0.1-0.5 mu m can be uniformly coated on the surface of the lithium iron silicate, so that a coating layer is better formed.

The composite structure of the present invention contains carbon, which may be continuously or discontinuously distributed on the surface of lithium iron silicate as a core to form a continuous or discontinuous carbon layer. In some embodiments, the carbon layer between the core and the shell layer is formed by coating lithium iron silicate with organic silicon. Therefore, the core and shell layers may contain silicon dioxide generated during the formation of the carbon layer in addition to carbon.

The appropriate carbon layer content can be selected according to actual needs, so that the function of the carbon layer for improving electron conduction can be exerted, and the energy density of the anode material cannot be influenced due to the excessively high carbon layer content. In some embodiments, the mass ratio of lithium iron silicate to the carbon layer is from 100 to 100, for example 100.

Further, the lithium iron phosphate constituting the shell layer may also be coated with carbon. These lithium iron phosphate-coated carbons can also function to improve electron conduction and buffer volume changes of the lithium iron silicate. The gram capacity of the lithium iron silicate in the working voltage interval of the lithium iron phosphate is low, so that the addition amount is not too large, and the function of regulating a voltage platform is achieved. In some embodiments, the molar ratio of the lithium iron phosphate to the lithium iron silicate is from 1. Fig. 1-3 schematically show the morphology of the composite material provided herein. As can be seen from the figure, the composite material provided by the present application is a secondary particle, which has a high sphericity, and an enlarged view of the particle (fig. 2) shows that the surface of the secondary particle is uniformly distributed with primary lithium iron phosphate particles, and it can be seen from a cross-sectional view (fig. 3) that the inner core of the secondary particle is a large lithium iron silicate single crystal, the middle is a punctate coated carbon layer, and the outer layer is a lithium iron phosphate layer.

One embodiment of the present application provides a method of making a composite material comprising the steps of:

step 2: adding silicone oil B and a hydrosilylation catalyst into the mixture a obtained in the step 1, and mixing to obtain a mixture B, wherein the silicone oil B is polysiloxane containing at least two alkenyl groups;

and 4, step 4: mixing lithium iron phosphate particles, a carbon source, water and the lithium iron silicate particles coated with the organic silicon layer on the surface, which are obtained in the step (3), wherein the carbon source is an organic matter containing oxygen and/or nitrogen; then forming secondary particles through spray granulation, wherein the secondary particles have a composite structure with lithium iron silicate coated with an organic silicon layer on the surface as a core and lithium iron phosphate coated with the carbon source as a shell layer;

In the method for preparing the composite material, the organic silicon-coated lithium iron silicate is used as a core, the carbon source-coated lithium iron phosphate is used as a secondary particle of a shell layer, and the secondary particle is calcined to obtain the spherical particle composite material with the core-shell structure. The composite material takes the lithium iron phosphate with high electronic conductivity as a shell, and increases interface electron transmission. A carbon layer is arranged between the shell layer and the core, so that the electronic conduction between the lithium iron silicate and the lithium iron phosphate is improved, and a buffer space is provided for the volume expansion and contraction of the lithium iron silicate. The silicon dioxide and carbon obtained by calcining the organic silicon in the inert atmosphere can reduce the capacity of the anode material by a small amount, but can greatly improve the electronic conductivity and the cycle performance.

The method of the present invention includes a step of coating lithium iron silicate particles with organosilicon. Coating polysiloxane (silicone oil A) containing at least two silicon-hydrogen bonds and polysiloxane (silicone oil B) containing at least two alkenyl groups on the surface of lithium iron silicate particles, curing under the conditions of heating and catalysis, and then calcining to form a compact carbon layer which is not easy to fall off.

In some embodiments, step 1 may use lithium iron silicate particles having a single crystal structure as a raw material. In some embodiments, the lithium iron silicate particles have a particle size, expressed as D50, of from 2 μm to 6 μm (e.g., 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm). The large-particle lithium iron silicate is selected to facilitate the surface to be coated with the lithium iron phosphate to form a lithium iron phosphate coating layer, so that the phenomenon that a mixed structure is easy to form instead of a core-shell structure due to the fact that the particles are too small is avoided. Silicone oil a can be selected from polysiloxanes containing at least two (e.g., 2, 3,4 or more) silicon hydrogen bonds, such as methyl hydrogen silicone oil, which is often used in hydrosilylation reactions.

In step 1, an organic solvent that can dissolve polysiloxane and does not react with lithium iron silicate and lithium iron phosphate may be selected. The proper organic solvent can improve the dispersion degree of the catalyst in the polysiloxane and can also play a role in improving the flowability of the lithium iron silicate and the lithium iron phosphate. Organic solvents that may be used include, but are not limited to, one or more of dichloromethane, chloroform, toluene, xylene, dichlorotoluene.

In some embodiments, the ratio of the volume of the organic solvent to the mass of the lithium iron silicate is from 0.5L/kg to 5L/kg (e.g., from 0.5L/kg to 1L/kg, from 1L/kg to 2L/kg, from 2L/kg to 3L/kg, from 3L/kg to 4L/kg, or from 4L/kg to 5L/kg). Within the range, the lithium iron silicate and the lithium iron phosphate can be ensured to have better fluidity, and the phenomenon that the subsequent drying is difficult due to excessive solvents can be avoided. In some embodiments, silicone oil B is a vinyl silicone oil.

The proportion of the silicone oil A and the silicone oil B can be adjusted according to actual needs so as to achieve a proper curing degree. In some embodiments, the molar ratio of silicone oil a to silicone oil B is 1:1 to 1:4 (e.g., 1:1, 1:2, 1:3, or 1:4).

Commonly used hydrosilylation catalysts may be used, such as one or more of Karstedt's catalyst, chloroplatinic acid, chlororhodic acid, chloroiridic acid, preferably Karstedt's catalyst, which is relatively common and has a relatively high activity. The catalyst is active platinum, the concentration of the platinum is about 10ppm, the curing effect can be achieved, the curing time is faster as the concentration is higher, but the platinum can be deposited to form platinum black when the concentration is too high. Therefore, the amount of the catalyst to be used can be appropriately selected according to actual needs. In some embodiments, the mass of the hydrosilylation catalyst is 0.001% to 0.05% of the total mass of the silicone oil a and the silicone oil B, such as 0.001% to 0.005%, 0.005% to 0.01%, or 0.01% to 0.05%.

The proportion of the lithium iron silicate and the silicone oil can be adjusted according to actual needs to form a carbon layer with proper content, so that the function of the carbon layer for improving electron conduction can be exerted, and the energy density of the anode material cannot be influenced due to overhigh content of the carbon layer. In some embodiments, the molar ratio of the lithium iron silicate particles to the silicone oil a is 1.

In some embodiments, step 2 comprises: adding lithium iron silicate, an organic solvent and silicone oil A into a stirrer, uniformly mixing to obtain a mixture A, mixing silicone oil B with a catalyst to obtain a mixture B, and uniformly mixing the mixture A with the mixture B. In some embodiments, mixture B can be added to mixture a while stirring, and mixture C is obtained after uniform mixing.

A spray dryer can be used to form lithium iron silicate particles coated with an organosilicon layer on the surface, and in the process, the silicone oil A and the silicone oil B are subjected to hydrosilylation under the action of a catalyst. The hydrosilylation reaction, also known as thermal curing, occurs rapidly under heating conditions and does not occur at all at ambient temperatures. Through the hydrosilylation reaction, a compact carbon layer which is not easy to fall off can be formed on the surface of the lithium iron silicate. The hydrosilylation reaction can be initiated at about 50 ℃, the organic silicon is cured quickly, the upper limit of the curing temperature generally does not exceed 200 ℃, so that the brittleness of the organic silicon is prevented from being increased due to overhigh temperature, and the energy consumption is prevented from being overhigh. Thus, in some embodiments, the drying temperature of the spray dryer is 50 to 200 ℃, e.g., 50 ℃ to 70 ℃, 70 ℃ to 100 ℃, 100 ℃ to 130 ℃, 130 ℃ to 150 ℃, 150 ℃ to 170 ℃, or 170 ℃ to 200 ℃. In some embodiments, the lithium iron silicate particles having a surface coated with a silicone layer obtained in step 3 have a particle size, represented by D50, of 2 μm to 6 μm (e.g., 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm).

And (4) adding the organosilicon-coated lithium iron silicate particles obtained in the step (3), lithium iron phosphate particles, a carbon source and water into a stirrer, uniformly mixing, and transferring to a spray dryer for spray granulation.

In some embodiments, the lithium iron phosphate particles are single crystal structures. Lithium iron phosphate particles with smaller particle size can be selected to facilitate the uniform coating of lithium iron phosphate on the surface of lithium iron silicate, so that a coating layer is easier to form. In some embodiments, the lithium iron phosphate particles have a particle size, expressed as D50, of 0.1 μm to 0.5 μm (e.g., 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm).

Suitable nitrogen-containing and/or oxygen-containing small molecule or macromolecule organic matters can be selected as the carbon source for coating the lithium iron phosphate particles, and can be naturally occurring or artificially synthesized, including but not limited to carbohydrates, polyethylene glycol, polyacrylic acid and the like. The carbohydrate may be a monosaccharide, oligosaccharide or polysaccharide, such as glucose, sucrose or starch. Glucose, starch and sucrose are preferred carbon sources because they are raw materials for synthesizing lithium iron phosphate.

An appropriate amount of water can be added according to actual needs to dissolve the carbon source and improve the fluidity of the material. Deionized water may be used to minimize the introduction of impurities. In some embodiments, the amount of water added is 0.5L/kg to 5L/kg (e.g., 0.5L/kg to 1L/kg, 1L/kg to 2L/kg, 2L/kg to 3L/kg, 3L/kg to 4L/kg, or 4L/kg to 5L/kg) based on the total mass of the lithium iron silicate and the lithium iron phosphate.

In some embodiments, the molar ratio of the lithium iron phosphate particles added in step 4 to the lithium iron silicate in step 1 is 1. The gram capacity of the lithium iron silicate in the working voltage interval of the lithium iron phosphate is low, so that the addition amount is not too large, and the function of regulating a voltage platform is achieved.

The proportion of the lithium iron phosphate to the carbon source can be adjusted according to actual needs to form a carbon coating layer with proper content, so that the function of the carbon layer for improving electron conduction can be exerted, and the energy density of the anode material cannot be influenced due to overhigh carbon content. In some embodiments, the molar ratio of the lithium iron phosphate added in step 4 to the carbon source is 1.

And (3) carrying out spray granulation on the lithium iron silicate particles coated with the organic silicon, the lithium iron phosphate particles and a carbon source to form secondary particles. Spray granulation may be performed using a spray dryer, and the accessories used may be different from those used for spray drying. In some embodiments, the spray dryer drying temperature is 50 ℃ to 200 ℃, such as 50 ℃ to 70 ℃, 70 ℃ to 100 ℃, 100 ℃ to 130 ℃, 130 ℃ to 150 ℃, 150 ℃ to 170 ℃ or 170 ℃ to 200 ℃. In this temperature range, the silicone is further cured, and at the same time, the solvent can be sufficiently volatilized.

In the present invention, the lithium iron silicate particles and the lithium iron phosphate particles are referred to as primary particles, particles formed by spray granulation are referred to as secondary particles, and the secondary particles are formed by combining a plurality of primary particles. In some embodiments, the secondary particles obtained in step 4 have a particle size, expressed as D50, of from 3 μm to 15 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

Since the coating layer formed by spray granulation is not firmly bonded, the coating layer is not dropped off by increasing intermolecular force by calcination. And (3) calcining the secondary particles obtained in the step (4) in an inert atmosphere, wherein the inert atmosphere can be selected from nitrogen, argon, helium and xenon. The upper limit of the calcination temperature can be set near the synthesis temperature of lithium iron phosphate to avoid the possibility that too high a temperature may melt the material into large single crystals, resulting in deteriorated kinetic performance. Thus, in some embodiments, the calcination temperature is from 300 ℃ to 800 ℃ (e.g., 300 ℃ to 400 ℃, 400 ℃ to 500 ℃, 500 ℃ to 600 ℃, 600 ℃ to 700 ℃, or 700 ℃ to 800 ℃). In some embodiments, the calcination time is from 2h to 10h (e.g., from 2h to 4h, from 4h to 6h, from 6h to 8h, or from 8h to 10 h).

In the method, the spray drying temperature and the calcining temperature are both lower than or close to the synthesis temperature of the lithium iron phosphate and the lithium iron silicate, so that the single crystal structure and the particle size of the lithium iron phosphate and the lithium iron silicate are not affected basically. In addition, the lithium iron phosphate and the lithium iron silicate are not lost basically in the treatment process, so the molar ratio of the lithium iron phosphate to the lithium iron silicate in the composite material is not changed basically relative to the molar ratio of the raw materials. In some embodiments, the composite material obtained by the method provided by the second aspect of the present application is the composite material provided by the first aspect of the present application.

[ Positive electrode sheet and production method ]

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 the positive electrode film layer, the composite material of the first aspect of the present application, or the composite material produced by the method of the second aspect of the present application, is used as a positive electrode active material.

In some embodiments, the positive electrode film layer may further include other conventional materials that may be used as a positive electrode active material of a battery. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g., liNiO) ₂ ) Lithium manganese oxide (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (may also be used)To be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO) ₄ ) One or more of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer further optionally includes a binder. By way of example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and fluoroacrylate resins. In some embodiments, the binder is PVDF.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the conductive agent is carbon black (e.g., conductive carbon black SP).

In some embodiments, the positive electrode film layer comprises a composite material of the first aspect of the present application, or a composite material prepared by the method of the second aspect of the present application; the positive electrode film layer further comprises a conductive agent and a binder.

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

[ Secondary Battery ]

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.

[ negative electrode sheet ]

The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, the negative pole rete includes negative pole 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 one or more 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 one or more selected from elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, 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 one or more 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 can be selected from one or more 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 cold pressing, slitting and other processes to obtain the negative electrode plate.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of 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 electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from one or more 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 one or more 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, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

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 selected from one or more of 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 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. 4 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to fig. 5, the overwrap may include a housing 51 and a cover plate 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 a cover plate 53 can be provided to 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 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 the actual needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained 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. 6 is a battery module 4 as an example. Referring to fig. 6, 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 the capacity of the battery pack.

Fig. 7 and 8 are a battery pack 1 as an example. Referring to fig. 7 and 8, 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.

Fig. 9 is a secondary battery of a cylindrical structure as an example. In some embodiments, referring to fig. 10, the secondary battery of a cylindrical structure includes: (1) a positive electrode top cover, (2) a positive electrode tab glue, (3) a battery JR; (4) blue glue; (5) an aluminum shell; (6) gluing a negative pole tab; (7) and a negative electrode top cover.

In addition, the application also provides an electric device, and the electric device comprises one or more of the secondary battery, the battery module or the battery pack provided by the application. 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 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, a satellite, an energy storage system, etc., but is not limited thereto.

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. 11 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 or 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 device may be a cell phone, tablet, laptop, etc. 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, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

[ PREPARATION OF POSITIVE ELECTRODE MATERIAL ]

EXAMPLE 1 preparation of composite Material

1. Adding 10mol of lithium iron silicate, 1L of dichloromethane and 0.015mol of methyl hydrogen-containing silicone oil into a stirrer, and uniformly mixing to obtain a mixture A.

2. 0.015mol of vinyl silicone oil and Karstedt catalyst are mixed uniformly, wherein the amount of the catalyst is 0.005 percent of the total mass of the methyl hydrogen silicone oil and the vinyl silicone oil, and a mixture B is obtained.

3. And adding the mixture B into the mixture A while stirring, uniformly mixing to obtain a mixture C, transferring the mixture C into a spray dryer, and spray-drying at 100 ℃ to obtain dried lithium iron silicate secondary particles coated with the organic silicon, wherein the particle size D50 is 4 microns.

4. And (4) uniformly stirring the organic silicon-coated lithium iron silicate secondary particles obtained in the step (3) with 30mol of lithium iron phosphate particles, 1.5mol of glucose and 10L of deionized water to obtain a mixture D, transferring the mixture D into a spray dryer, and performing spray granulation at 100 ℃ to obtain dried lithium iron phosphate-coated lithium iron silicate cathode material secondary particles with the particle size D50 of 10 mu m.

5. And (5) calcining the composite cathode material obtained in the step (4) at 400 ℃ for 4 hours in a nitrogen atmosphere to obtain a composite structure with lithium iron silicate as a core and lithium iron phosphate as a shell layer and a carbon layer between the core and the shell layer.

Example 2

The other steps of example 2 were the same as example 1 except that the amount of methyl hydrogen silicone oil was changed to 0.0075 mol.

Example 3

The other steps of example 3 were the same as example 1 except that the amount of vinyl silicone oil was changed to 0.03 mol.

Example 4

The procedure of example 4 was the same as example 1 except that the calcination temperature was changed to 600 ℃.

Example 5

The procedure of example 5 was the same as example 1 except that the calcination time was changed to 2 hours.

Example 6

The procedure of example 6 was the same as example 1 except that the amount of lithium iron phosphate was changed to 20 mol.

Example 7

The other steps of example 7 were the same as example 1 except that the amount of glucose was changed to 0.6 mol.

Comparative example 1

Lithium iron phosphate was used as the positive electrode material.

Comparative example 2

1. Uniformly stirring 10mol of lithium iron silicate particles, 30mol of lithium iron phosphate particles, 1.5mol of glucose and 10L of deionized water, transferring the obtained mixture into a spray dryer, and performing spray granulation at 100 ℃ to obtain dried lithium iron phosphate and lithium iron silicate mixed secondary particles with the particle size D50 of 2 mu m.

2. And calcining the secondary particles obtained in the second step at 400 ℃ for 4 hours in a nitrogen atmosphere to obtain the carbon/lithium iron phosphate/lithium iron silicate composite structure.

[ PREPARATION OF POSITIVE ELECTRODE PIECE ]

The cathode material, the conductive agent carbon black, the binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP) obtained in the examples or the comparative examples were mixed in a weight ratio of 67.34:30:28.86:2.7:1.1, fully stirring and uniformly mixing 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.

[ PREPARATION OF NEGATIVE ELECTRODE PIECE ]

The active substance artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR), and thickening agent sodium carboxymethylcellulose (CMC) are mixed 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 electrolyte ]

In an argon atmosphere glove box (H) ₂ O<0.1ppm，O ₂ <0.1 ppm), mixing organic solvent Ethylene Carbonate (EC)/Ethyl Methyl Carbonate (EMC) uniformly according to the volume ratio of 3/7, adding 12.5% LiPF ₆ And dissolving the lithium salt in the organic solvent, and uniformly stirring to obtain the electrolyte.

[ isolating film ]

Polypropylene film was used as the separator.

[ preparation of Secondary Battery ]

And stacking the positive pole piece, the isolating film and the negative pole piece in sequence 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 a naked electric core, welding a tab for the naked electric core, packaging the naked electric core 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 cold pressing, formation, shaping, capacity testing and the like to obtain the lithium ion battery product.

[ Positive electrode active Material-related parameter test ]

1. Volume average particle diameter D50 test

The equipment model is as follows: malvern 2000 (MasterSizer 2000) laser granulometer, reference standard procedure: GB/T19077-2016/ISO 13320, concrete test flow: taking a proper amount of a sample to be detected (the concentration of the sample can ensure 8-12% of light shading degree), adding 20ml of deionized water, simultaneously performing external super-5 min (53 kHz/120W) to ensure that the sample is completely dispersed, and then determining the sample according to GB/T19077-2016/ISO 13320.

Fig. 12 is a particle size distribution curve of the cathode material obtained in example 1, and it can be seen from the graph that the cathode material has a D50 of 10 μm and a uniform particle size.

2. Topography testing

The morphology of the samples was observed using a ZEISS Sigma 300 scanning electron microscope, with reference to the standard JY/T010-1996.

Fig. 1 to 3 are SEM photographs of the cathode material secondary particles prepared in example 1, and it can be seen from fig. 1 that the secondary particles have high sphericity, and an enlarged view of the particles (fig. 2) shows that the lithium iron phosphate primary particles are uniformly distributed on the surface of the secondary particles, and it can be seen from a cross-sectional view (fig. 3) that the secondary particles have an inner core of a large lithium iron silicate single crystal, a middle of a carbon layer coated in a dot shape, and an outer layer of a lithium iron phosphate layer.

[ Battery Performance test ]

1. Battery charge and discharge test

Taking example 1 as an example, the battery charge and discharge test process is as follows: at 25 ℃, the battery corresponding to the embodiment 1 is charged to 3.7V by a constant current of 1/3C, then charged to 0.05C by a constant voltage of 3.7V, stood for 5min, and then discharged to 2.0V by 1/3C, so as to obtain a charging and discharging curve chart.

Fig. 13 is a charge and discharge graph of example 1 and comparative example 1, and it can be seen from the graph that the composite material prepared in example 1 has dual plateaus compared to the long plateaus of lithium iron phosphate, which facilitates to improve the accuracy of the BMS in estimating the remaining capacity by recognizing the voltage.

2. Battery capacity retention rate test

Taking example 1 as an example, the battery capacity retention rate test procedure is as follows: the cell corresponding to example 1 was charged at a constant current of 1/3C to 3.7V at 25 ℃, further charged at a constant voltage of 3.7V to a current of 0.05C, left for 5min, and further discharged at 1/3C to 2.0V, and the resulting capacity was designated 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, wherein the battery capacity retention rate Pn = Cn/C0 × 100% after each cycle is obtained, a graph of the battery capacity retention rate and the cycle number is obtained by taking 200 point values of P1 and P2 … … P200 as ordinate and the corresponding cycle number as abscissa.

Fig. 14 is a graph of the battery capacity retention rate versus the number of cycles for the positive electrode materials of example 1 and comparative examples 1-2. As can be seen from the figure, the battery corresponding to the positive electrode material of example 1 has a similar cycle capacity as compared to the battery using lithium iron phosphate as the positive electrode material 1, while the positive electrode material of comparative example 2 has a deteriorated performance as compared to the batteries of example 1 and comparative example 1 due to the large polarization between lithium iron phosphate and lithium iron silicate.

3. Battery rate capability test

Taking example 1 as an example, the battery rate performance test procedure is as follows: at 25 ℃, the battery corresponding to the embodiment 1 is charged to 3.7V by a constant current of 1/3C, then charged to 0.05C by a constant voltage of 3.7V, stood for 5min, and then discharged to 2.0V by 0.2C, and the charging and discharging are repeated for 5 times, and the obtained capacity is marked as C1-C5. And then discharging at 0.5C, 1C, 2C, 3C and 0.2C multiplying powers respectively to obtain the capacity C6-C30, taking the 30 point values of C1-C30 as a vertical coordinate, and taking the corresponding cycle times as a horizontal coordinate to obtain a battery multiplying power performance graph.

Fig. 15 is a graph of battery rate performance for example 1 and the positive electrode materials of comparative examples 1-2. As can be seen from the figure, the battery corresponding to the positive electrode material of example 1 has similar rate performance compared to the battery using lithium iron phosphate as the positive electrode material, while the positive electrode material prepared in comparative example 2 has worse performance than those of examples 1 and comparative example 1 due to the large polarization between lithium iron phosphate and lithium iron silicate.

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. In addition, 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, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

1. A composite material which is a spherical particle having a core-shell structure, the core of the spherical particle comprising lithium iron silicate, the shell layer of the spherical particle comprising lithium iron phosphate, and a carbon layer between the core and the shell layer.

2. The composite material according to claim 1, wherein the spherical particles have a particle diameter, expressed as D50, of 3 to 15 μm;

the lithium iron silicate and the lithium iron phosphate are respectively particles with single crystal structures;

preferably, the particle diameter of the lithium iron silicate expressed as D50 is 2 to 6 μm;

preferably, the particle diameter of the lithium iron phosphate expressed as D50 is 0.1 to 0.5 μm;

preferably, the molar ratio of the lithium iron phosphate to the lithium iron silicate is 1.1 to 1:1.

3. A method of making a composite material comprising the steps of:

and 3, step 3: spray-drying the mixture b obtained in the step 2 to form lithium iron silicate particles with the surfaces coated with the organic silicon layers;

4. The method according to claim 3, wherein in step 1, the lithium iron silicate particles have a single crystal structure; preferably, the particle diameter of the lithium iron silicate particles expressed by D50 is 2 to 6 μm;

preferably, the silicone oil A is methyl hydrogen-containing silicone oil;

preferably, the organic solvent is selected from one or more of dichloromethane, trichloromethane, toluene, xylene and dichlorotoluene;

preferably, the ratio of the volume of the organic solvent to the mass of the lithium iron silicate is 0.5L/kg-5L/kg;

preferably, the molar ratio of the lithium iron silicate particles to the silicone oil a is 1.

5. The method according to claim 3 or 4, the silicone oil B being a vinyl silicone oil;

preferably, the molar ratio of the silicone oil A to the silicone oil B is 1:1-1:4;

preferably, the hydrosilylation catalyst of step 2 is selected from one or more of Karstedt's catalyst, chloroplatinic acid, chlororhodic acid, chloroiridic acid, more preferably Karstedt's catalyst;

preferably, the mass of the hydrosilylation catalyst is 0.001 to 0.05 percent of the total mass of the silicone oil A and the silicone oil B.

6. The method according to any one of claims 3 to 5, wherein step 3 is carried out using a spray dryer having a drying temperature of 50 ℃ to 200 ℃;

preferably, the particles obtained in step 3 have a particle size, expressed as D50, of from 2 μm to 6 μm.

7. The method according to any one of claims 3 to 6, wherein in step 4, the lithium iron phosphate particles have a single crystal structure; preferably, the lithium iron phosphate particles have a particle diameter, expressed as D50, of 0.1 to 0.5 μm;

preferably, the carbon source of step 4 is selected from carbohydrates, polyethylene glycol, polyacrylic acid;

preferably, the molar ratio of the lithium iron phosphate particles in the step 4 to the lithium iron silicate in the step 1 is 1;

preferably, the molar ratio of the lithium iron phosphate to the carbon source in the step 4 is 1;

preferably, step 4 is performed using a spray dryer, the drying temperature of which is 50 ℃ to 200 ℃;

preferably, the secondary particles obtained in step 4 have a particle diameter, expressed as D50, of 3 to 15 μm.

8. The method according to any one of claims 3 to 7, wherein in step 5, the inert atmosphere is selected from nitrogen, argon, helium, xenon;

preferably, the calcining temperature is 300-800 ℃;

preferably, the calcination time is 2 to 10 hours.

9. The method according to any one of claims 3-8, the composite material being a composite material according to claim 1 or 2.

10. A 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; the positive electrode film layer comprises a composite material according to claim 1 or 2, or comprises a composite material prepared according to the method of any one of claims 3-8; optionally, the positive electrode film layer further comprises a conductive agent and a binder.

11. A secondary battery comprising the composite material according to claim 1 or 2, the composite material produced by the method according to any one of claims 3 to 8, or the positive electrode sheet according to claim 10.

12. A battery module comprising the composite material of claim 1 or 2, the composite material made by the method of any one of claims 3-8, the positive electrode sheet of claim 10, or the secondary battery of claim 11.

13. A battery pack comprising the composite material of claim 1 or 2, the composite material made by the method of any one of claims 3-8, the positive electrode sheet of claim 10, the secondary battery of claim 11, or the battery module of claim 12.

14. An electrical device comprising the composite material of claim 1 or 2, the composite material made by the method of any one of claims 3-8, the positive electrode sheet of claim 10, the secondary battery of claim 11, the battery module of claim 12, or the battery pack of claim 13.