CN115832236B

CN115832236B - Lithium iron phosphate positive electrode material, preparation method thereof, positive electrode plate, lithium ion battery, battery module, battery pack and power utilization device

Info

Publication number: CN115832236B
Application number: CN202210299303.2A
Authority: CN
Inventors: 尹子伊; 凌洋芳
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-03-25
Filing date: 2022-03-25
Publication date: 2025-02-21
Anticipated expiration: 2042-03-25
Also published as: CN115832236A

Abstract

A lithium iron phosphate positive electrode material and a preparation method thereof, the lithium iron phosphate positive electrode material comprising a lithium iron phosphate matrix and a coating layer, the coating layer is selected from one of boron oxide, silicon oxide and aluminum oxide, and the mass ratio of the coating layer to the lithium iron phosphate matrix is 0.01-1.18:100, preferably 0.05-0.87:100. The present application also provides a positive electrode sheet, a lithium ion battery, a battery module, a battery pack and an electric device comprising the lithium iron phosphate positive electrode material. The lithium iron phosphate positive electrode material of the present application has an improved surface pH and an increased compaction density, the processing performance of the lithium iron phosphate positive electrode material is improved, the moisture absorption of the material is reduced, the risk of gelation is not likely to occur during slurrying, and the slurry stability and dispersibility are improved, so that the lithium ion battery prepared therefrom is improved in terms of energy density and cycle performance.

Description

Lithium iron phosphate positive electrode material, preparation method thereof, positive electrode plate, lithium ion battery, battery module, battery pack and power utilization device

Technical Field

The application relates to the field of lithium battery materials, in particular to a lithium iron phosphate positive electrode material and a preparation method thereof, and a positive electrode plate, a lithium ion battery, a battery module, a battery pack and an electric device containing the lithium iron phosphate positive electrode material.

Background

In recent years, along with the wider application range of lithium ion batteries, the lithium ion batteries are widely applied to energy storage power supply systems such as hydraulic power, firepower, wind power, solar power stations and the like, and a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, aerospace and the like. As lithium ion batteries have been greatly developed, higher demands are also being made on energy density, cycle performance, safety performance, and the like.

The lithium iron phosphate as a lithium ion battery anode material has high theoretical capacity, stable charge and discharge pressure, wide source and wide application condition. However, residual lithium sources such as LiOH, li ₂CO₃ or LiHCO ₃ in the preparation process of the lithium iron phosphate material can enable the surface of the material to be slightly alkaline (the pH value is about 9-10), so that the lithium iron phosphate has stronger moisture absorption, the water content of the prepared pole piece is not easy to control, and finally impurity water which is difficult to dry and remove can accelerate side reaction in the use process of the battery, so that the service life of the battery is greatly reduced. In addition, in the process of sizing the positive electrode, residual alkali on the surface of the lithium iron phosphate material can induce the binder to undergo elimination reaction, so that intermolecular crosslinking is further caused, and the viscosity of the positive electrode sizing agent is increased, even chemical gel is generated. Therefore, a certain strategy is needed to reduce the alkalinity of the surface of the lithium iron phosphate material, and the processing performance and the material stability of the lithium iron phosphate material are improved, so that the performance of the lithium ion battery of the lithium iron phosphate system is improved.

Disclosure of Invention

The present application has been made in view of the above problems, and an object thereof is to provide a lithium iron phosphate positive electrode material having a reduced surface pH and an increased compacted density, which is improved in energy density and battery cycle performance over conventional lithium iron phosphate positive electrode materials, a method for producing the lithium iron phosphate positive electrode material, and a positive electrode sheet, a lithium ion battery, a battery module, a battery pack, and an electric device including the lithium iron phosphate positive electrode material of the present application.

In order to achieve the above object, a first aspect of the present application provides a lithium iron phosphate positive electrode material, comprising a lithium iron phosphate matrix and a coating layer, wherein the coating layer is selected from one of boron oxide, silicon oxide and aluminum oxide, and the mass ratio of the coating layer to the lithium iron phosphate matrix is 0.01-1.18:100, preferably 0.05-0.87:100.

Therefore, the coating layer in the lithium iron phosphate positive electrode material can be combined with residual alkali on the surface of the lithium iron phosphate matrix, and the pH value of the surface of the material is reduced, so that the processing performance of the lithium iron phosphate positive electrode material is improved, the moisture absorption of the material is reduced, the slurry chemical gel risk is reduced, the slurry stability and the dispersibility are improved, and the lithium ion battery prepared from the lithium iron phosphate positive electrode material is enabled to obtain remarkably improved cycle performance.

In any embodiment, the lithium iron phosphate positive electrode material has a median particle size of 2.1 to 2.5 μm.

Therefore, the lithium iron phosphate positive electrode material has larger median particle diameter, the compaction density of the lithium iron phosphate positive electrode material is improved, and the improved gram capacity is obtained, so that the energy density of a lithium ion battery prepared from the lithium iron phosphate positive electrode material is improved.

The second aspect of the present application provides a method for preparing a lithium iron phosphate positive electrode material, the method comprising the steps of:

(S1) dispersing a precursor of the coating layer in water, then adding ferric phosphate, a lithium source, a carbon source and a proper amount of water, continuously dispersing, and drying to obtain uniformly mixed powder, wherein the precursor of the coating layer is selected from one of tetramethyl ammonium silicate, boric acid and aluminum chloride, and the mass ratio of the precursor of the coating layer to the ferric phosphate is 0.02-1.2:100, preferably 0.1-0.9:100;

(S2) carrying out two-stage sintering on the uniformly mixed powder obtained in the step (S1) to obtain a lithium iron phosphate positive electrode material:

(S2-A) heating at a heating rate of 1-5 ℃ per min under the purging of inert atmosphere, and sintering for 1-5h at a temperature of 180-250 ℃;

(S2-B) sintering for 8-12h in an inert atmosphere at a temperature of 650-750 ℃.

In any embodiment, the preparation method further comprises a step (S3), wherein the step (S3) is to crush the lithium iron phosphate positive electrode material obtained in the step (S2) by adopting a jet milling method.

Therefore, the lithium iron phosphate positive electrode material obtained by the preparation method has improved surface pH and increased compaction density, the processing performance of the lithium iron phosphate positive electrode material is improved, the moisture absorption of the material is reduced, the risk of gel is not easy to occur during size mixing, and the stability and dispersibility of the size are improved, so that the energy density and the cycle performance of a lithium ion battery prepared by the lithium iron phosphate positive electrode material are improved.

In any embodiment, in the step (S2-A), the temperature rising rate is 2-4 ℃ per minute, the sintering temperature is 200-230 ℃, and the sintering time is 2-4h.

Therefore, by controlling the temperature rising rate, the sintering temperature and the sintering time in the step (S2-A), a uniform and compact coating layer can be formed on the surface of the lithium iron phosphate matrix, so that the obtained lithium iron phosphate positive electrode material has high consistency, improved surface pH and improved compaction density, and a lithium ion battery prepared from the lithium iron phosphate positive electrode material has improved energy density and/or cycle performance.

In any embodiment, in the step (S2-B), the temperature is raised at a temperature raising rate of 5 to 8 ℃ per minute. Thereby, the energy density and/or cycle performance of the lithium ion battery can be improved.

In any embodiment, the inert atmosphere is argon or nitrogen.

In any embodiment, in said step (S2-A), an inert atmosphere purge is performed at a flow rate of 1-4 mL/min. Thereby, the energy density and/or cycle performance of the lithium ion battery can be improved.

In any embodiment, in the step (S1), the precursor of the coating layer is dispersed in water in a frosted dispersion manner, and then the added iron phosphate, lithium source, carbon source and an appropriate amount of water continue to be frosted dispersed. Therefore, the precursor of the coating layer is uniformly dispersed and adhered on the surfaces of the lithium source and the iron phosphate particles through chemical adsorption or physical adsorption, so that the lithium iron phosphate positive electrode material has reduced surface pH and increased compaction density, and the processability is improved, and the lithium ion battery prepared from the lithium iron phosphate positive electrode material has improved energy density and cycle performance.

In any embodiment, in the step (S1), the drying is performed by a centrifugal spray method. Thus, the obtained lithium iron phosphate positive electrode material has high consistency.

In any embodiment, the lithium source is one or more of lithium carbonate, lithium nitrate, lithium hydroxide and lithium acetate.

In any embodiment, the carbon source is one or more of sucrose, glucose, starch and polyethylene glycol.

Thus, the performance of the lithium iron phosphate positive electrode material can be improved by selecting the lithium source and the carbon source.

A third aspect of the present application provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the lithium iron phosphate positive electrode material of the first aspect of the present application or the lithium iron phosphate positive electrode material prepared according to the method of the second aspect of the present application, and the content of the lithium iron phosphate positive electrode material in the positive electrode film layer being 10 wt% or more based on the total weight of the positive electrode film layer.

In any embodiment, the lithium iron phosphate positive electrode material is present in the positive electrode film layer in an amount of 95 to 99.5 wt%, based on the total weight of the positive electrode film layer.

A fourth aspect of the application provides a lithium ion battery comprising a lithium iron phosphate positive electrode material according to the first aspect of the application or a lithium iron phosphate positive electrode material prepared according to the method of the second aspect of the application or a positive electrode sheet according to the third aspect of the application. Thus, the lithium ion battery of the present application achieves significantly improved energy density and cycle performance.

A fifth aspect of the application provides a battery module comprising the lithium ion battery of the fourth aspect of the application.

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

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

The battery module, the battery pack and the power utilization device comprise the lithium ion battery provided by the application, and therefore have at least the same advantages as the lithium ion battery.

Drawings

Fig. 1 is a scanning electron microscope picture of a lithium iron phosphate positive electrode material of example 1 of the present application.

Fig. 2 is a scanning electron microscope picture of the lithium iron phosphate cathode material of comparative example 1.

Fig. 3 is a schematic view of a lithium ion battery according to an embodiment of the present application.

Fig. 4 is an exploded view of the lithium ion battery of the embodiment of the present application shown in fig. 1.

Fig. 5 is a schematic view of a battery module according to an embodiment of the present application.

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

Fig. 7 is an exploded view of the battery pack of the embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic diagram of an electric device using a lithium ion battery as a power source according to an embodiment of the present application.

Reference numerals illustrate:

1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 lithium ion battery, 51 case, 52 electrode assembly, 53 top cover assembly

Detailed Description

Hereinafter, embodiments of the lithium iron phosphate positive electrode material, the method for preparing the same, the positive electrode sheet, the lithium ion battery, the battery module, the battery pack and the electrical device of the present application are specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.

The "range" disclosed herein is defined in terms of lower and upper limits, with the given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values 1 and 2 are listed, and if maximum range values 3,4, and 5 are listed, then the following ranges are all contemplated as 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise indicated, 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, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed 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 of the application and alternative embodiments may be combined with each other to form new solutions, unless otherwise specified.

All technical features and optional technical features of the application may be combined with each other to form new technical solutions, unless specified otherwise.

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

The term "or" is inclusive in this application, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either condition satisfies the condition "A or B" that A is true (or present) and B is false (or absent), that A is false (or absent) and B is true (or present), or that both A and B are true (or present).

In the preparation process of lithium iron phosphate, residual lithium sources such as LiOH, li ₂CO₃ or LiHCO ₃ on the surface can make the surface of the material alkaline, which can make the powder material have stronger moisture absorption, worsen side reactions caused by trace water impurities in the battery and accelerate battery aging, and on the other hand, the alkaline surface can easily cause crosslinking fracture of a binder such as polyvinylidene fluoride (PVDF) to cause chemical gelation of the slurry, so that the coating uniformity and consistency are poor, and the adhesion of active substances on the surface of a current collector is reduced, thereby affecting the battery performance. The current method for reducing the pH of the lithium ion battery anode material is mainly a water washing method, namely, a large amount of aqueous solution is used for washing the anode material, and residual alkali on the surface of the material is dissolved into water, so that the effect of reducing the residual alkali on the surface of the material and further reducing the pH is achieved. However, the general water washing method has poor effect of removing residual alkali on the surface and is not environment-friendly.

Through repeated researches, the inventor of the application obtains the lithium iron phosphate positive electrode material with improved surface pH and improved compaction density through adopting wet coating (the modified additive is fully dissolved and dispersed in a solvent, and the additive is subjected to chemical reaction and precipitation on the surface of the matrix to form the coating in the processes of stirring, evaporating/drying or filter pressing and the like after the modified additive is added into the matrix) and two-stage sintering, so that the energy density and the cycle performance of the lithium iron phosphate positive electrode material are improved compared with those of the lithium iron phosphate positive electrode material obtained by the existing method. On one hand, the precursor of the coating layer is added in the early stage of wet mixing and grinding of powder, so that the precursor of the coating layer is uniformly dispersed on the surfaces of lithium sources and iron phosphate particles, the coating layer obtained after two-stage sintering has higher compactness and consistency, the coating layer is Lewis acid oxide and can be combined with residual alkali on the surface of the iron phosphate lithium, the pH value of the surface of the iron phosphate lithium material is reduced, the moisture absorption of the material is reduced, the chemical gel risk during size mixing is reduced, the dispersibility and stability of the sizing agent are improved, and on the other hand, the precursor of the coating layer can be used as a fluxing agent in the preparation process, the growth of the iron phosphate lithium crystal is promoted, the average particle size of the iron phosphate lithium positive electrode material is increased, and the compaction density is improved. Therefore, the lithium iron phosphate positive electrode material has improved energy density and cycle performance.

Specifically, the first aspect of the application provides a lithium iron phosphate positive electrode material, which comprises a lithium iron phosphate matrix and a coating layer, wherein the coating layer is selected from one of boron oxide, silicon oxide and aluminum oxide, and the mass ratio of the coating layer to the lithium iron phosphate matrix is 0.01-1.18:100, preferably 0.05-0.87:100.

According to the application, the coating layer (Lewis acid oxide) in the lithium iron phosphate positive electrode material can be combined with residual alkali on the surface of the lithium iron phosphate matrix, so that the pH value of the surface of the material is reduced, the processing performance of the lithium iron phosphate positive electrode material is improved, the moisture absorption of the material is reduced, the slurry chemical gel risk is reduced, and the slurry stability and dispersibility are improved, so that the lithium ion battery prepared from the lithium iron phosphate positive electrode material has obviously improved ring performance.

In some embodiments, the lithium iron phosphate positive electrode material has a median particle size of 2.1 to 2.5 μm.

According to the application, the precursor of the coating layer is used as a fluxing agent to promote the growth of lithium iron phosphate crystals, so that the average particle size of the lithium iron phosphate anode material is increased, the compaction density is increased, and the improved gram capacity is obtained, thereby improving the energy density of the lithium ion battery prepared from the lithium iron phosphate anode material.

In some embodiments, the preparation method further comprises a step (S3), wherein the step (S3) is to crush the lithium iron phosphate positive electrode material obtained in the step (S2) by adopting a jet milling method.

According to the application, the precursor of the coating layer is uniformly dispersed on the surfaces of the lithium source and the iron phosphate particles through wet coating, and then two-stage sintering is carried out, wherein the precursor of the coating layer can be used as a fluxing agent to promote the melting of the iron phosphate particles in the sintering stage, so that the coating layer with high compactness and consistency can be obtained, and the oxide-coated lithium iron phosphate positive electrode material has larger particle size and lower surface pH value, so that the energy density and the cycle performance of a lithium ion battery prepared from the coating layer are improved.

In some embodiments, in the step (S2-A), the temperature increase rate is 2-4 ℃ per minute, the sintering temperature is 200-230 ℃, and the sintering time is 2-4 hours. By controlling the rate of temperature rise and/or sintering temperature and/or sintering time in step (S2-a), a uniform and dense coating layer can be formed on the surface of the lithium iron phosphate substrate, so that the obtained lithium iron phosphate positive electrode material has high consistency, improved surface pH and increased compaction density, and a lithium ion battery prepared from the lithium iron phosphate positive electrode material has improved energy density and/or cycle performance.

In some embodiments, in the step (S2-B), the temperature is raised at a temperature raising rate of 5-8 ℃ per minute. By controlling the rate of temperature increase in step (S2-B), the energy density and/or cycle performance of the lithium ion battery can be improved.

In some embodiments, the inert atmosphere is argon or nitrogen.

In some embodiments, in the step (S2-A), an inert atmosphere purge is used at a flow rate of 1-4 mL/min. By controlling the flow rate of the inert atmosphere purging in the step (S2-A), a more uniform and compact coating layer can be formed on the surface of the lithium iron phosphate matrix, so that the processing performance of the lithium iron phosphate positive electrode material is improved.

In some embodiments, in the step (S1), the precursor of the coating layer is dispersed in water in a frosted dispersion manner, and then the added iron phosphate, lithium source, carbon source, and an appropriate amount of water continue to be frosted dispersed. Thus, in step (S1), the powder is dispersed in a frosted dispersion manner, and the precursor of the coating layer is uniformly dispersed and attached to the surfaces of the lithium source and the iron phosphate particles by chemical adsorption or physical adsorption. The precursor of the uniformly distributed coating layer enables the coating layer obtained after sintering to have higher compactness and consistency on one hand, and can be used as a fluxing agent to promote the melting of the iron phosphate particles in the sintering stage, so that the lithium iron phosphate particles with larger particle size are obtained, and the lithium iron phosphate positive electrode material with reduced surface pH and improved compaction density is finally obtained.

In some embodiments, in the step (S1), drying is performed using a centrifugal spray method. The temperature and time of spray drying may be those conventional in the art for spray drying. The precursor of the coating layer is uniformly dispersed and adhered on the surfaces of the iron phosphate and the lithium carbonate particles through chemical adsorption or physical adsorption, so that on one hand, the obtained coating layer after sintering has higher compactness and consistency, the pH value of the surface of the lithium iron phosphate anode material is reduced, and on the other hand, the uniformly distributed precursor of the coating layer can be used as a fluxing agent to promote the melting of the iron phosphate particles in the sintering stage, so that the lithium iron phosphate particles with larger granularity and higher compaction density are obtained.

In some embodiments, the lithium source is one or more of lithium carbonate, lithium nitrate, lithium hydroxide, and lithium acetate.

In some embodiments, the carbon source is one or more of sucrose, glucose, starch, polyethylene glycol.

In some embodiments, the lithium iron phosphate positive electrode material is present in the positive electrode film layer in an amount of 95-99.5 wt%, based on the total weight of the positive electrode film layer.

A fourth aspect of the application provides a lithium ion battery comprising a lithium iron phosphate positive electrode material according to the first aspect of the application or a lithium iron phosphate positive electrode material prepared according to the method of the second aspect of the application or a positive electrode sheet according to the third aspect of the application.

Typically, a lithium ion battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film. In the present application, the battery group margin is 90-93%.

The lithium ion battery, the battery module, the battery pack, and the power consumption device according to the present application will be described below with reference to the drawings.

[ Positive electrode sheet ]

The positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of the application.

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

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

In some embodiments, the positive electrode active material may employ a positive electrode active material for a battery well known in the art, in addition to the positive electrode active material of the first aspect of the present application. As an example, the positive electrode active material may include at least one of an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Wherein, examples of lithium transition metal oxides 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、LiMn₂O₄), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi _1/ ₃Co_1/3Mn_1/3O₂ (which may also be abbreviated as NCM ₃₃₃)、LiNi_0.5Co_0.2Mn_0.3O₂ (which may also be abbreviated as NCM ₅₂₃)、LiNi_0.5Co_0.25Mn_0.25O₂ (which may also be abbreviated as NCM ₂₁₁)、LiNi_0.6Co_0.2Mn_0.2O₂ (which may also be abbreviated as NCM ₆₂₂)、LiNi_0.8Co_0.1Mn_0.1O₂ (which may also be abbreviated as NCM ₈₁₁)), lithium nickel manganese oxide (which may also be abbreviated as NCM ₃₃₃)、LiNi_0.5Co_0.2Mn_0.3O₂ (which may also be abbreviated as NCM 42 examples of the olivine structured lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (which may also be abbreviated as LFP)), a composite of lithium iron phosphate and carbon, a composite of lithium manganese phosphate (such as LiMnPO ₄), a composite of lithium manganese phosphate and carbon, a composite of lithium manganese phosphate, lithium iron phosphate, and a composite of lithium manganese phosphate and carbon.

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

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

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

[ Negative electrode sheet ]

The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode 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 may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material 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 polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the anode active material may employ an anode active material for a battery, which is well known in the art. As an example, the anode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like. The silicon-based material may be at least one selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery anode active material may be used. These negative electrode active materials may be used alone or in combination of two or more. The anode active material may have an average particle diameter (D ₁₀) of 1 μm to 15 μm, preferably 4 μm to 9 μm, an average particle diameter (D ₅₀) of 12 μm to 22 μm, preferably 14 μm to 17 μm, and an average particle diameter (D ₉₀) of 26 μm to 40 μm, preferably 30 μm to 37 μm.

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

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent is at least one selected from 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 optionally further include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

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

[ Electrolyte ]

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The application is not particularly limited in the kind of electrolyte, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.

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

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium difluorodioxaato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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 sulfone, and diethyl sulfone.

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

[ Isolation Membrane ]

In some embodiments, a separator is also included in the lithium ion battery. The type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability can be used.

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

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

In some embodiments, the lithium ion battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

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

The shape of the lithium ion battery is not particularly limited, and may be cylindrical, square, or any other shape. For example, fig. 3 is a lithium ion battery 5 of a square structure as an example.

In some embodiments, referring to fig. 4, the outer package may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation 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. The electrode assembly 52 is enclosed in the accommodating chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the lithium-ion battery 5 may be one or more, and those skilled in the art may choose according to specific practical requirements.

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

Fig. 5 is a battery module 4 as an example. Referring to fig. 5, in the battery module 4, a plurality of lithium ion batteries 5 may be sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of lithium ion batteries 5 may be further fixed by fasteners.

Alternatively, the battery module 4 may further include a housing having an accommodating space in which the plurality of lithium ion batteries 5 are accommodated.

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

Fig. 6 and 7 are battery packs 1 as an example. Referring to fig. 6 and 7, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 1. The battery box includes an upper box body 2 and a lower box body 3, and 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. The plurality of battery modules 4 may be arranged in the battery box in any manner.

In addition, the application also provides an electric device which comprises at least one of the lithium ion battery, the battery module or the battery pack. The lithium ion battery, battery module, or battery pack may be used as a power source of the power device, and may also be used as an energy storage unit of the power device. The power utilization device may include mobile devices (e.g., cell phones, notebook computers, etc.), electric vehicles (e.g., electric-only vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

As the electricity utilization device, a lithium ion battery, a battery module, or a battery pack may be selected according to the use requirements thereof.

Fig. 8 is an electrical 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. To meet the high power and high energy density requirements of the power device for lithium ion batteries, a battery pack or battery module may be employed.

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a lithium ion battery can be used as a power supply.

Examples

Hereinafter, embodiments of the present application are described. The following examples are illustrative only and are not to be construed as limiting the application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Example 1

1) Preparation of lithium iron phosphate positive electrode material

(S1) respectively weighing ferric phosphate, lithium carbonate, glucose and boric acid according to the mass ratio of 100:25:11:0.4, firstly adding boric acid into water, using 0.3mm pick beads, sanding for 1h at the rotating speed of 2000r/min, then adding ferric phosphate, lithium carbonate, glucose and a proper amount of water (the solid content of slurry is 42%), continuing sanding for 16h at the rotating speed of 2000r/min, and then drying by adopting a centrifugal spray drying method to obtain uniformly mixed pale yellow powder (the water content is 1.5 percent);

(S2) carrying out two-stage sintering on the uniformly mixed powder obtained in the step (S1) by adopting a tube furnace, (S2-A) firstly heating to 250 ℃ at a heating rate of 2mL/min under nitrogen purging at a flow rate of 2 ℃, sintering for 3 hours at the temperature of 250 ℃, then stopping purging, (S2-B) maintaining a nitrogen atmosphere, heating to 700 ℃ at a heating rate of 5 ℃ per min, and sintering for 10 hours at the temperature to obtain the lithium iron phosphate anode material;

And (S3) crushing the obtained lithium iron phosphate positive electrode material by adopting a jet milling method.

Analysis was performed using a scanning electron microscope of Sigma300 of zeiss and an X-ray spectrometer of oxford instrument X-max-50mm ² to obtain the mass ratio of coating layer to lithium iron phosphate matrix in the lithium iron phosphate positive electrode material. The test results are shown in tables 1-2.

2) Preparation of button cell

The lithium iron phosphate positive electrode material, polyvinylidene fluoride (PVDF) and Super-P prepared above are added into N-methyl pyrrolidone solvent (NMP) in a weight ratio of 90:5:5, and stirred in a drying room to prepare slurry. Coating the slurry on an aluminum foil, drying and cold pressing to obtain the positive electrode plate. The coating amount was 0.3g/cm ² and the compacted density was 2.5g/cm ³.

The lithium sheet is used as a negative electrode, a solution of LiPF ₆ with the volume ratio of EC+DEC+DMC of 1:1:1 is used as electrolyte, and the electrolyte and the prepared positive electrode sheet are assembled into a CR3032 type button cell (hereinafter also called as button cell) in a button cell box. Diameter of button cell = thickness of 30.0mm x 3.2mm.

3) Preparation of full cell

And uniformly mixing the prepared lithium iron phosphate anode material, a conductive agent Super-P and a binder PVDF in a weight ratio of 92:2.5:5.5 in NMP, coating the mixture on an aluminum foil on two sides, drying and cold pressing to obtain the anode sheet. The single-sided coating amount was 0.4g/cm ² and the compacted density was 2.5g/cm ³.

Uniformly mixing negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder Styrene Butadiene Rubber (SBR) and thickener sodium carboxymethylcellulose (CMC) in deionized water according to the weight ratio of 90:5:2:2:1, and then coating the mixture on a copper foil on two sides, drying and cold pressing to obtain a negative electrode plate. The single-sided coating amount was such that the capacity ratio of the negative electrode to the positive electrode was kept at 1.1.

And (3) taking the PE porous polymeric film as an isolating film, sequentially stacking the positive electrode plate, the isolating film and the negative electrode plate, enabling the isolating film to be positioned in the middle of the positive electrode and the negative electrode to play a role of isolation, and winding to obtain the bare cell. The bare cell was placed in an external package, and the same electrolyte as that in the above-described preparation of the snap-down was injected and packaged to obtain a full battery (hereinafter also referred to as "full power"). Length x width x height of the full cell = 148mm x 28.5mm x 97.5mm, group margin of the cell is 91.0%.

Example 2

The procedure of example 1 was repeated except that boric acid was changed to tetramethylammonium silicate in "1) preparation of lithium iron phosphate cathode material".

Example 3

The procedure of example 1 was repeated except that in "1) preparation of lithium iron phosphate positive electrode material", boric acid was changed to aluminum chloride.

Examples 4 to 9

The procedure of example 1 was repeated except that the mass ratio of boric acid as a precursor of the coating layer was changed to 0.02, 0.1, 0.5, 0.7, 0.9, and 1.2, respectively, in the "preparation of 1) lithium iron phosphate cathode material".

Examples 10 to 13

The procedure of example 1 was repeated except that in "1) preparation of lithium iron phosphate positive electrode material", the step (S2-a) was first sintered at temperatures of 180 ℃, 200 ℃, 210 ℃ and 230 ℃ for 3 hours, respectively.

Examples 14 to 17

The procedure of example 1 was repeated except that in "1) preparation of lithium iron phosphate positive electrode material", the step (S2-A) was first sintered at 250℃for 1h, 2h, 4h, and 5h, respectively.

Examples 18 to 21

The procedure of example 1 was repeated except that in "1) preparation of lithium iron phosphate positive electrode material", the temperature was first raised to 250℃at the respective temperature raising rates of 1℃and 3℃and 4℃and 5℃in step (S2).

Comparative example 1

Respectively weighing iron phosphate, lithium carbonate and glucose according to the mass ratio of 1:0.25:0.11, adding the iron phosphate, the lithium carbonate and the glucose into water, using 0.3mm pick beads, sanding for 16 hours at the rotating speed of 2000r/min (the solid content of slurry is 42%), then drying by adopting a centrifugal spray drying method to obtain pale yellow powder (the water content is 1.5%), sintering the obtained powder by adopting a tube furnace, heating to 700 ℃ at the heating rate of 5 ℃ per min under nitrogen atmosphere, sintering for 10 hours at the temperature to obtain the lithium iron phosphate anode material, and crushing the lithium iron phosphate anode material by adopting an air current crushing method.

2. Testing of relevant parameters

(1) Compaction density test

A certain amount of powder is placed in a compaction special mould, which is then placed on a compaction density instrument. The thickness of the powder under pressure (thickness after pressure relief) was read on the apparatus by applying a pressure of 5T, and the compaction density was calculated by ρ=m/v.

The test results are shown in tables 1-2.

(2) Surface pH test

Preparing a solution of the lithium iron phosphate anode active material and pure water according to a fixed ratio of 1:9, sealing, and stirring for 30min on a magnetic stirrer. After stirring, the conical flask was placed in a water bath thermostat at 25℃and allowed to stand for 1.5h. The pH composite electrode is inserted into the solution to form an electrochemical cell, the electromotive force of which is related to the pH of the solution by measuring the electromotive force of the cell and directly expressed as pH.

The test results are shown in tables 1-2.

(3) Median particle size D50 test

Taking a clean beaker, adding a proper amount of lithium iron phosphate anode active material, dripping a proper amount of pure water after adding a surfactant, and carrying out ultrasonic treatment for 120W/5min to ensure that the material powder is completely dispersed in the water. Pouring the solution into a sample tower of a laser particle size analyzer (Markov company, model: mastersizer 3000), circulating the solution to a test light path system, and obtaining particle size distribution characteristics (shading degree: 8-12%) of the particles by receiving and measuring energy distribution of scattered light under irradiation of laser beams

The test results are shown in tables 1-2.

3. Test of cell Performance

(1) Capacity test for power button

The charge was charged to 3.65V at 0.1C under 2.5-3.65V, then charged to 0.05C at constant voltage at 3.65V, left standing for 5min, and then discharged to 2.5V at 0.1C, at which time the ratio of discharge capacity to mass of positive electrode active material was material gram capacity (mAh/g).

The test results are shown in tables 1-2.

(2) Full-electric cycle performance test

The lithium metal battery is charged to 3.65V at 25 ℃ with a constant current of 0.5 ℃, then is charged to 0.05C with a constant voltage of 3.65V, and is discharged to 2.5V with a constant current of 1C, so as to obtain the first-week discharge capacity (C _d1), and the charging and discharging are repeated until 400 weeks, so that the discharge capacity of the lithium battery after 400 weeks of cycle is recorded as C _d400. Capacity retention = discharge capacity after 400 weeks of cycling (C _d400)/first week discharge capacity (C _d1).

The test results are shown in tables 1-2.

From the above results, it can be seen that the lithium iron phosphate cathode material of the present application has a larger median particle diameter, an increased compacted density, and an effective decrease in pH of the material surface, compared to the lithium iron phosphate cathode material (comparative example 1) without the coating layer. Although the internal resistance of the lithium iron phosphate cathode material of the present application was increased (the internal resistance increase ratio was not more than 6% relative to comparative example 1), it falls within the acceptable range of the battery. Therefore, the lithium ion battery prepared from the lithium iron phosphate cathode material of the present application has a larger gram capacity and improved capacity retention.

Fig. 1 shows a scanning electron microscope picture of a lithium iron phosphate positive electrode material prepared in example 1 of the present application, and fig. 2 shows a scanning electron microscope picture of a lithium iron phosphate positive electrode material prepared in comparative example 1. It can be seen that the lithium iron phosphate positive electrode material has larger particle size and wider particle size distribution.

The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims

1. The lithium iron phosphate positive electrode material is characterized by comprising a lithium iron phosphate matrix and a coating layer, wherein the coating layer is selected from one of boron oxide, silicon oxide and aluminum oxide, the mass ratio of the coating layer to the lithium iron phosphate matrix is 0.01-1.18:100, and the median particle size of the lithium iron phosphate positive electrode material is 2.1-2.5 mu m.

2. The lithium iron phosphate positive electrode material according to claim 1, wherein the mass ratio of the coating layer to the lithium iron phosphate matrix is 0.05-0.87:100.

3. The lithium iron phosphate positive electrode material according to claim 1, wherein the surface pH value of the lithium iron phosphate positive electrode material is 8.16 to 8.45.

4. The lithium iron phosphate positive electrode material according to claim 1, characterized in that the gram capacity of the lithium iron phosphate positive electrode material is 149-154mAh/g.

5. The lithium iron phosphate positive electrode material according to claim 1, characterized in that the compacted density of the lithium iron phosphate positive electrode material at 5T is 2.592-2.684g/cm ³.

6. A method for preparing the lithium iron phosphate positive electrode material according to any one of claims 1 to 5, characterized in that the method comprises the steps of:

Dispersing a precursor of the coating layer in water, then adding ferric phosphate, a lithium source, a carbon source and a proper amount of water, continuously dispersing, and drying to obtain uniformly mixed powder, wherein the precursor of the coating layer is selected from one of tetramethyl ammonium silicate, boric acid and aluminum chloride, and the mass ratio of the precursor of the coating layer to the ferric phosphate is 0.02-1.2:100;

And (S2) carrying out two-stage sintering on the uniformly mixed powder obtained in the step (S1) to obtain the lithium iron phosphate positive electrode material:

(S2-B) sintering for 8-12h at 650-750 ℃ in inert atmosphere.

7. The method of claim 6, wherein the mass ratio of precursor to iron phosphate of the coating is 0.1-0.9:100.

8. The method according to claim 6, further comprising a step (S3), wherein the step (S3) is to crush the lithium iron phosphate positive electrode material obtained in the step (S2) by using a jet milling method.

9. The method according to any one of claims 6 to 8, wherein in the step (S2-a), the temperature increase rate is 2 to 4 ℃ per minute, the sintering temperature is 200 to 230 ℃ and the sintering time is 2 to 4 hours.

10. The method according to any one of claims 6 to 8, wherein in the step (S2-B), the temperature is raised at a temperature raising rate of 5 to 8 ℃ per minute.

11. The method according to any one of claims 6-8, wherein the inert atmosphere is argon or nitrogen.

12. The method according to any one of claims 6 to 8, wherein in step (S2-a) an inert atmosphere purge is performed at a flow rate of 1-4 mL/min.

13. The method according to any one of claims 6 to 8, wherein in step (S1), the precursor of the coating layer is dispersed in water in a frosted dispersion manner, and then the frosted dispersion is continued by adding iron phosphate, lithium source, carbon source and an appropriate amount of water.

14. The method according to any one of claims 6 to 8, wherein in step (S1), drying is performed using a centrifugal spray method.

15. The method according to any one of claims 6 to 8, wherein the lithium source is one or more of lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate.

16. The method according to any one of claims 6 to 8, wherein the carbon source is one or more of sucrose, glucose, starch, polyethylene glycol.

17. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the lithium iron phosphate positive electrode material according to any one of claims 1 to 5 or the lithium iron phosphate positive electrode material produced by the method according to any one of claims 6 to 16, and the content of the lithium iron phosphate positive electrode material in the positive electrode film layer being 10% by weight or more based on the total weight of the positive electrode film layer.

18. The positive electrode sheet according to claim 17, wherein the content of the lithium iron phosphate positive electrode material in the positive electrode film layer is 95 to 99.5% by weight based on the total weight of the positive electrode film layer.

19. A lithium ion battery comprising the lithium iron phosphate positive electrode material according to any one of claims 1 to 5 or prepared by the method according to any one of claims 6 to 16 or the positive electrode sheet according to claim 17 or 18.

20. A battery module comprising the lithium ion battery of claim 19.

21. A battery pack comprising the battery module of claim 20.

22. An electrical device comprising at least one member selected from the group consisting of the lithium-ion battery of claim 19, the battery module of claim 20, and the battery pack of claim 21.