CN116504935A

CN116504935A - Lithium-intercalation phosphate composite material, preparation method thereof and secondary battery

Info

Publication number: CN116504935A
Application number: CN202310293615.7A
Authority: CN
Inventors: 薛山; 孔令涌; 万远鑫; 李意能; 陈燕玉; 王鹏; 刘厅
Original assignee: Foshan Dynanonic Technology Co ltd; Shenzhen Dynanonic Co ltd
Current assignee: Foshan Dynanonic Technology Co ltd; Shenzhen Dynanonic Co ltd
Priority date: 2023-03-17
Filing date: 2023-03-17
Publication date: 2023-07-28

Abstract

The application belongs to the technical field of battery materials, and particularly relates to a lithium-intercalation phosphate composite material, a preparation method thereof and a secondary battery. The lithium-intercalated phosphate composite material comprises an inner core of lithium-intercalated phosphate and a coating layer coated on the outer surface of the inner core; the coating layer comprises a carbon material and black phosphorus, and the black phosphorus and the carbon material form a mosaic and overlapping composite structure. The coating layer in the lithium-intercalation phosphate composite material provided by the application can not only improve the stability of the core phosphate, but also effectively improve the conductivity and the carrier transmission rate, and the lithium-intercalation phosphate composite material has the characteristics of high capacity, high rate performance, high cycle stability and the like through the synergistic effect of the core and the coating layer.

Description

Lithium-intercalation phosphate composite material, preparation method thereof and secondary battery

Technical Field

The application belongs to the technical field of battery materials, and particularly relates to a lithium-intercalation phosphate composite material, a preparation method thereof and a secondary battery.

Background

The secondary battery can reversibly convert chemical energy and electric energy, and is an ideal carrier for human use and energy storage. Since the advent of lithium ion batteries, the lithium ion batteries have been widely used due to their advantages of high energy density, good cycle performance, environmental friendliness, and the like. At present, the lithium ion battery is already applied to various fields such as 3C electronics, new energy automobiles, smart grids and the like. The cathode material is a key to influence the performance of the battery, and often determines the cycle life, energy density, power density and the like of the battery.

The main positive electrode materials commercialized at present are layered LiCoO ₂ LiMn of layered ternary material and spinel structure ₂ O ₄ And olivine structured LiFePO ₄ Etc. The positive electrode material of the lithium ion battery applied to the field of new energy automobiles mainly comprises lithium iron phosphate and a ternary material battery. Wherein, liFePO ₄ The advantage of the material is safety and cycle performance, but is poor in energy density and power density, whereas the ternary material is the opposite. With the continuous development of the new energy automobile field, higher and higher requirements are put on the energy density, the power density, the cycle and the safety performance of the lithium ion battery.

With LiFePO ₄ LiMnPO of similar structure ₄ The oxidation-reduction potential of the material is about 4.1V, and the material is more LiFePO under the same specific capacity ₄ With a higher energy density. However, liMnPO ₄ Leading to difficulties in electron and ion migration and therefore in LiFePO replacement ₄ . Solid solution lithium manganese iron phosphate formed by replacing part of Mn with Fe is combined with LiFePO ₄ And LiMnPO ₄ Is a positive electrode material with very good commercial prospect. However, the cycle stability and rate performance of the lithium iron manganese phosphate still need to be further improved. Surface coating is one of the common electrode material modification means, and factors such as chemical composition, component distribution, thickness, coverage rate and the like of the surface coating can influence the performance of the electrode material. Therefore, the current modification means has limited effect of improving electrochemical properties such as cycle stability and rate performance of the phosphate system, and the performance of the phosphate system needs to be further improved.

Disclosure of Invention

The purpose of the application is to provide a lithium-intercalation phosphate composite material, a preparation method thereof and a secondary battery, and aims to solve the problem that the cycle stability and the rate capability of the existing lithium-intercalation phosphate are to be further improved to a certain extent.

In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:

in a first aspect, the present application provides a lithium-intercalated phosphate composite material, comprising a core of lithium-intercalated phosphate and a coating layer coating the outer surface of the core; the coating layer comprises a carbon material and black phosphorus, and the black phosphorus and the carbon material form a mosaic and overlapping composite structure.

In some possible implementations, the tessellated and overlapped composite structure includes: part of the black phosphorus is embedded in the carbon material in the form of nano black phosphorus sheets to form a composite coating layer; part of the black phosphorus and the carbon material form a plurality of layers of overlapped composite coating layers which are mutually staggered and stacked.

In some possible implementations, in the coating layer, a portion of the black phosphorus replaces carbon atoms in the carbon material in the form of clusters or single atoms to form a phosphorus atom doped carbon material.

In some possible implementations, the lithium intercalation phosphate includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt phosphate, lithium vanadium phosphate.

In some possible implementations, the nano black phosphorus flakes include: a small-sized sheet having an average thickness of 1 to 5nm and an average length/width of 5 to 15nm, and a large-sized sheet having an average thickness of 5 to 15nm and an average length/width of 15 to 1000 nm.

In some possible implementations, the mass percentage of the black phosphorus in the lithium-intercalation phosphate composite material is 0.1-3 wt%.

In some possible implementations, the mass percentage of the coating layer in the lithium-intercalation phosphate composite material is 1-5 wt%.

In some possible implementations, the mass percentage of the black phosphorus in the coating layer is 10-60 wt%.

In some possible implementations, the lithium-intercalation phosphate-based composite material has a primary particle size of 30-500 nm and a secondary particle size of 0.3-10 μm.

In some possible implementations, the coating layer thickness in the lithium-intercalation phosphate-based composite material is 0.5-8 nm.

In a second aspect, the present application provides a method for preparing a phosphate-based composite material, comprising the steps of:

according to the stoichiometric ratio of elements in the lithium-intercalated phosphate, after each raw material component is obtained, mixing and grinding the raw material component, red phosphorus and an organic grinding aid in inert atmosphere to obtain a mixed precursor;

and sintering the mixed precursor in an inert atmosphere to obtain the lithium-intercalation phosphate composite material with the core-shell structure, wherein the core is lithium-intercalation phosphate, and the coating layer comprises carbon materials and black phosphorus which form an inlaid and overlapped composite structure.

In some possible implementations, the step of sintering process includes: performing first sintering treatment on the mixed precursor, and performing second sintering treatment after cooling; wherein the temperature of the first sintering process is lower than the temperature of the second sintering process.

In some possible implementations, the conditions of the hybrid milling process include: ball milling for 6-24 h in inert atmosphere with ball material ratio of (15-50): 1 and rotation speed of 500-1200 rpm.

In some possible implementations, the conditions of the first sintering process include: heating to 200-500 ℃ at a speed of 1-5 ℃/min under inert atmosphere, and then preserving heat for 3-15 h.

In some possible implementations, the conditions of the second sintering process include: under inert atmosphere, the temperature is raised to 500-800 ℃ at the speed of 1-5 ℃/min, and then the temperature is kept for 3-15 h.

In some possible implementations, the means of the mixed milling process includes planetary ball milling or shimmy ball milling.

In some possible implementations, the mass percent of the red phosphorus in the mixed precursor is 0.1-3 wt%.

In some possible implementations, the mass percent of the organic grinding aid in the mixed precursor is 0.5-6 wt%.

In some possible implementations, the organic grinding aid includes at least one of urea, starch, glucose, sucrose, fructose, citric acid.

In a third aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode comprises the lithium-intercalation phosphate composite material or the lithium-intercalation phosphate composite material prepared by the method.

The lithium-intercalated phosphate composite material provided in the first aspect of the application comprises a core of lithium-intercalated phosphate and a coating layer coated on the outer surface of the core. The lithium phosphate intercalation in the core combines the stability of the olivine crystal structure. The coating layer comprises a carbon material and black phosphorus which form an embedded and overlapped composite structure, wherein the black phosphorus is the lowest in reactivity in allotropes of phosphorus, a crystal lattice of the black phosphorus consists of linked six-membered rings, the black phosphorus has three crystal structures of three directions, cubes and orthogonality, and the black phosphorus has a lamellar structure similar to graphite, and has excellent conductivity and high ion/electron transmission rate. The black phosphorus in the coating layer and the carbon material form physical doping of an inlaid and overlapped composite structure, and the black phosphorus existing in atomic clusters or single atoms can also form chemical doping with the carbon material, so that the stability of a core phosphate system can be improved, the conductivity and the carrier transmission rate of the coating layer can be effectively improved, and the rate capability and the cycle stability of the phosphate composite material are improved.

According to the preparation method of the lithium-intercalation phosphate composite material, provided by the second aspect, after the lithium-intercalation phosphate raw material components are obtained, the lithium-intercalation phosphate raw material components, red phosphorus and an organic grinding aid are mixed and ground in an inert atmosphere, the raw material components can be fully and uniformly mixed through the process of mixed and ground, the red phosphorus is primarily converted into black phosphorus by utilizing local high temperature and high pressure in the mixed and ground process, and the black phosphorus is stripped to generate two-dimensional black phosphorus nano sheets or atomic clusters under the assistance of the organic grinding aid. Wherein, the inert atmosphere is used for avoiding the unstable oxidation of red phosphorus in the process of mixing and grinding. And sintering the mixed precursor in an inert atmosphere, thoroughly converting the rest red phosphorus in the partial ball milling process into black phosphorus in the sintering process, converting the organic grinding aid into a carbon material in the sintering process, forming an inlaid and overlapped composite structure with the black phosphorus, and coating the carbon material on the surface of the phosphate particles to obtain the lithium-intercalated phosphate composite material with the core-shell structure. The prepared composite material has higher capacity, conductivity, rate performance and other electrochemical characteristics. The preparation process is simple, low in cost and small in environmental impact, and provides an optional method for industrially preparing the phosphate electrode material with high rate performance.

In the secondary battery provided in the third aspect of the application, the positive electrode comprises the lithium-intercalation phosphate composite material, the lithium-intercalation phosphate composite material is of a core-shell structure, the core is of a lithium-intercalation phosphate system, and the coating layer comprises a carbon material and black phosphorus which form an inlaid and overlapped composite structure, and has the characteristics of high capacity, high rate performance, high cycle stability and the like. Thus, the energy density, the cycle stability, and the rate capability of the secondary battery can be improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following description will briefly introduce the drawings that are needed in the embodiments or the description of the prior art, it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic flow chart of a preparation method of a lithium-intercalation phosphate composite material according to an embodiment of the present application;

FIG. 2 is an X-ray diffraction pattern of a black phosphorus and carbon co-coated lithium iron manganese phosphate composite material provided in example 1 of the present application;

FIG. 3 is an SEM image of a black phosphorus and carbon co-coated lithium iron manganese phosphate composite material provided in example 1 of the present application;

FIG. 4 is a graph of capacity versus voltage at 0.1C for a button cell made from the black phosphorus and carbon co-coated lithium iron manganese phosphate composite provided in example 1 of the present application and the carbon coated lithium iron manganese phosphate composite made in comparative example 1;

fig. 5 is a graph showing specific capacity test at different rates of button cells made of lithium iron manganese phosphate composites prepared in example 1 and comparative examples 1 and 2 of the present application.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application. In the specific embodiment, lithium iron manganese phosphate is taken as an example to implement.

In this application, the term "and/or" describes an association relationship of an association object, which means that there may be three relationships, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.

In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c" may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

It should be understood that, in various embodiments of the present application, the sequence number of each process does not mean that the sequence of execution is sequential, and some or all of the steps may be executed in parallel or sequentially, where the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application in the examples and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weights of the relevant components mentioned in the examples of the present application may refer not only to specific contents of the respective components but also to the proportional relationship between the weights of the respective components, and thus, it is within the scope of the disclosure of the examples of the present application as long as the contents of the relevant components are scaled up or down according to the examples of the present application. Specifically, the mass in the examples of the present application may be a mass unit known in the chemical industry such as μ g, mg, g, kg.

The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.

A first aspect of the embodiments of the present application provides a lithium-intercalated phosphate composite material, which is characterized by comprising a core intercalated with lithium phosphate and a coating layer coating the outer surface of the core; the coating layer comprises a carbon material and black phosphorus, and the black phosphorus and the carbon material form a mosaic and overlapping composite structure.

The lithium-intercalated phosphate composite material provided in the first aspect of the embodiment of the application comprises a core of lithium manganese iron phosphate and a coating layer coated on the outer surface of the core. The lithium phosphate intercalation in the core combines the stability of the olivine crystal structure. The coating layer comprises a carbon material and black phosphorus which form a mosaic and overlapped composite structure, wherein the black phosphorus is the lowest in reactivity in allotropes of phosphorus, a crystal lattice of the black phosphorus consists of linked six-membered rings, and the black phosphorus has three crystal structures of three directions, cubes and orthogonality, has a lamellar structure similar to graphite, and has excellent conductivity and high ion/electron transmission rate. The black phosphorus and the carbon material in the coating layer form physical doping, such as mutual insertion and embedding to form a composite material coating layer together; and the black phosphorus existing in atomic clusters or single atoms can form chemical doping with a carbon material, so that the stability of the core lithium manganese iron phosphate can be improved, the conductivity and the carrier transmission rate of the coating layer can be effectively improved, and the rate capability and the cycle stability of the lithium-intercalated phosphate composite material are improved. Therefore, the lithium-intercalation phosphate composite material provided by the embodiment of the application has the characteristics of high capacity, high rate performance, high cycle stability and the like through the synergistic effect of the core and the coating layer.

In some possible implementations, the tessellated and overlapped composite structure includes: part of the black phosphorus is embedded in the carbon material in the form of nano black phosphorus sheets to form a composite coating layer. The black phosphorus sheets are embedded in the carbon material to form a composite coating layer, and in this case, the black phosphorus sheets have smaller sheet diameters, such as the sheet diameter is smaller than 10nm, and the like, and the black phosphorus sheets with small sheet diameters can be embedded in the carbon material in a mosaic mode to form a composite material to be coated on the surface of the lithium ferromanganese phosphate core, so that the cycle stability, the multiplying power performance, the capacity and other characteristics of the composite material are improved. In addition, part of the black phosphorus forms a multi-layer overlapped composite coating layer which is mutually staggered and stacked with the carbon material in a sheet form. In this case, the black phosphorus flakes have a larger flake diameter, for example, the flake size is greater than 10nm, and the black phosphorus flakes with a larger flake diameter can be individually coated on the surface of the core lithium iron manganese phosphate particles and jointly coated with the carbon material to form a multi-layer coating or mixed coating layer. Specifically, the number of layers of the composite coating layer may be 1 to 10 layers or the like. The carbon material and the black phosphorus in the coating layer form the physical doping of the embedded and overlapped composite structure, so that the high conductivity and the high ion/electron transmission efficiency of the carbon material and the black phosphorus are integrated; and through the doping of the carbon material and the black phosphorus, the influence of volume expansion of the black phosphorus is reduced, the ion diffusion path is shortened, and the conductivity and the carrier transmission efficiency of the coating layer are better improved. Thereby improving the cycle stability and the multiplying power performance of the composite material.

In some possible implementations, the nano black flakes include: a small-sized sheet having an average thickness of 1 to 5nm and an average length/width of 5 to 15nm, and a large-sized sheet having an average thickness of 5 to 15nm and an average length/width of 15 to 500 nm. Wherein, the black phosphorus of the small-sized sheet is favorable for forming an embedded structure with the carbon material; while the black flakes of the large-sized sheet material facilitate the formation of a multi-layered overlapping structure with the carbon material. In addition, the black phosphorus is of a nano lamellar structure, the nano size shortens an ion diffusion path, improves ion migration efficiency, reduces the influence of volume expansion of the black phosphorus, and improves the conductivity of the black phosphorus.

In some possible implementations, in the cladding layer, a portion of the black phosphorus replaces a portion of the carbon atoms in the carbon material in clusters or monoatoms to form a phosphorus atom doped carbon material, forming a chemical doping. In this case, the black phosphorus forms a chemical doping with the carbon material, and the phosphorus atoms replace part of the carbon atoms, causing defects in the carbon material, providing more lithium ion and electron transport active sites. Meanwhile, the phosphorus atoms are compounded to enable the carbon film material to be in an electron-rich state, electron cloud coupling occurs when the electron cloud deviates from the bulk material, and the electron conductivity of the coating layer material is increased. Therefore, the carbon material and the black phosphorus in the coating layer form chemical doping, and the electronic conductivity and the ion migration efficiency of the coating layer are better improved, so that the rate capability and the cycle stability of the composite material can be better improved.

In some possible implementations, the mass percent of black phosphorus in the lithium-intercalated phosphate-based composite material is 0.1-3 wt%. In this case, the content of black phosphorus in the lithium-intercalated phosphate composite material sufficiently ensures improvement of the conductivity and carrier transport efficiency of the clad layer, thereby contributing to improvement of the rate performance and cycle stability of the composite material. In some embodiments, the mass percent of black phosphorus in the lithium-intercalated phosphate composite material may be 0.1-0.5 wt%, 0.5-1 wt%, 1-1.5 wt%, 1.5-2 wt%, 2-2.5 wt%, 2.5-3 wt%, etc.

In some possible implementations, the mass percentage of the coating layer in the lithium-intercalated phosphate composite material is 1-5 wt%; in this case, the coating layer of the mass percentage content sufficiently ensures the improvement of the cycling stability and the rate capability of the core lithium iron manganese phosphate by the coating layer.

In some possible implementations, the percentage by mass of black phosphorus in the coating layer is 10-60 wt%; under the condition, the doping mass content of the black phosphorus in the coating layer is beneficial to improving the characteristics of the composite material such as the circulation stability, the multiplying power performance and the capacity, and the volume expansion influence caused by excessive doping amount of the black phosphorus is avoided.

In some possible implementations, the lithium-intercalated phosphate-based composite material has a primary particle size of 30 to 300nm and a secondary particle size of 0.3 to 10 μm. The primary particle size refers to the particle size of single particles of the lithium-embedded phosphate composite material under microscopic test conditions, namely the particle size of single microscopic particles. The primary particle size is nano-scale, the particle size is small, the active specific surface area is large, and the nano-scale active material is applied to the electrode material of the secondary battery, so that the ion intercalation and deintercalation efficiency is improved, and the rate performance and the cycle performance of the secondary battery are improved. The secondary particle size refers to the bulk particle size formed after stacking single particles of the lithium-intercalation phosphate composite material, i.e. the macroparticle particle size formed after stacking a plurality of primary particles. The secondary macroscopic particle diameter of the lithium-intercalation phosphate composite material is small, the uniformity is high, the compaction density of the lithium-intercalation phosphate composite material is improved, and the application of the lithium-intercalation phosphate composite material to the electrode material of the secondary battery is beneficial to improving the energy density.

In some possible implementations, the coating layer thickness in the lithium-intercalated phosphate-based composite material is 0.5-8 nm; under the condition, the coating layer with the thickness can not only effectively improve the characteristics of the core lithium manganese iron phosphate such as structural stability, circulation stability, electric conductivity and the like, but also shorten the ion diffusion path and improve the ion migration efficiency. Thereby improving the cycle stability, the multiplying power performance, the capacity and other characteristics of the lithium-intercalation phosphate composite material. In some embodiments, the coating layer thickness in the lithium-intercalation phosphate-based composite material may be 0.5-1 nm, 1-2 nm, 2-3 nm, 3-5 nm, 5-6 nm, 6-7 nm, 7-8 nm, etc.

In some possible implementations, the lithium intercalation phosphate is lithium manganese iron phosphate of the formula LiMn in the core _x Fe _1-x PO ₄ The value range of x is 0.2-0.8. In this case, the lithium iron manganese phosphate has better safety performance, cycle performance, oxidation-reduction potential, energy density and other characteristics.

The lithium intercalation phosphate composite material provided by the embodiment of the present application can be prepared by the following example method.

As shown in fig. 1, a second aspect of the embodiment of the present application provides a method for preparing a lithium-intercalated phosphate composite material, including the following steps:

s10, according to the stoichiometric ratio of elements in the lithium-intercalated phosphate, after each raw material component is obtained, mixing and grinding the raw material component, red phosphorus and an organic grinding aid in inert atmosphere to obtain a mixed precursor;

s20, sintering the mixed precursor in an inert atmosphere to obtain the lithium-intercalated phosphate composite material with the core-shell structure, wherein the core is lithium-intercalated phosphate, and the coating layer comprises carbon materials and black phosphorus which form an inlaid and overlapped composite structure.

According to the preparation method of the lithium-intercalation phosphate composite material, provided by the second aspect of the embodiment, after the lithium-intercalation phosphate raw material components are obtained, the raw material components, red phosphorus and an organic grinding aid are mixed and ground in an inert atmosphere, the raw material components can be fully and uniformly mixed through the process of mixed and ground, the red phosphorus is primarily converted into black phosphorus by utilizing local high temperature and high pressure in the mixed and ground process, and the black phosphorus is stripped to generate two-dimensional black phosphorus nano sheets or atomic clusters under the assistance of the organic grinding aid. Wherein, the inert atmosphere is used for avoiding the unstable oxidation of red phosphorus in the process of mixing and grinding. And (3) sintering the mixed precursor in an inert atmosphere, thoroughly converting the red phosphorus remained in the partial ball milling process into black phosphorus in the sintering process, converting the organic grinding aid into a carbon material in the sintering process, and coating the carbon material and the black phosphorus on the surface of the phosphate particles to obtain the lithium-intercalated phosphate composite material with the core-shell structure. The prepared composite material has higher capacity, conductivity, rate performance and other electrochemical characteristics. The preparation process is simple, low in cost and small in environmental impact, and provides an optional method for industrially preparing the phosphate electrode material with high rate performance.

In some possible implementations, in step S10, the conditions of the hybrid grinding process include: ball milling for 6-24 h in inert atmosphere with ball material ratio of (15-50) 1 and rotating speed of 500-1200 rpm; under the mixed grinding condition, the uniform mixing of all raw material components can be fully ensured, meanwhile, the organic grinding aid and the red phosphorus are continuously collided and rubbed in the mixed grinding process, the generated local high temperature and high pressure enable the red phosphorus to be primarily converted into the black phosphorus, the size of the black phosphorus is reduced, a nano sheet layer is formed, the nano size is reduced, the ion diffusion path is shortened, the influence of volume expansion of the black phosphorus is reduced, and the conductivity of the black phosphorus is improved. In some embodiments, the inert atmosphere includes, but is not limited to, nitrogen, argon, helium, and the like.

In some possible implementations, the means of the hybrid milling process includes planetary ball milling or shimmy ball milling.

In some possible implementations, the mass percent of red phosphorus in the mixed precursor is 0.1-3 wt%; in this case, the addition amount of red phosphorus sufficiently ensures improvement of the rate performance and cycle stability performance of the lithium-intercalation phosphate composite material by the black phosphorus to be formed later, and if the addition amount is too low, improvement of the performance of the composite material is not significant. In some embodiments, the mass percent of red phosphorus in the mixed precursor may be 0.1-0.5 wt%, 0.5-1 wt%, 1-1.5 wt%, 1.5-2 wt%, 2-2.5 wt%, 2.5-3 wt%, etc.

In some possible implementations, the mass percent of the organic grinding aid in the mixed precursor is 0.5-6 wt%. Under the condition, the addition amount of the organic grinding aid not only ensures that red phosphorus can be converted into black phosphorus with a nano sheet diameter in the mixing and grinding process, but also ensures that a carbon material formed by converting the organic grinding aid after subsequent sintering is enough to form a composite coating layer of the carbon material and the black phosphorus on the surface of the lithium iron manganese phosphate, and the capacity, the circulation stability and the multiplying power performance of the composite material are improved. In some embodiments, the mass percent of the organic grinding aid in the mixed precursor may be 0.5-1 wt%, 1-2 wt%, 2-3 wt%, 3-4 wt%, 4-5 wt%, 5-6 wt%, etc.

In some possible implementations, the organic grinding aid includes at least one of urea, starch, glucose, sucrose, fructose and citric acid, and the organic grinding aid not only can convert red phosphorus into black phosphorus with a nano-sheet diameter in the mixed grinding process, but also can be converted into a carbon material after sintering, and the carbon material and the black phosphorus form an inlaid and overlapped composite structure to be coated on the surface of lithium manganese iron phosphate particles together.

In some possible implementations, the lithium intercalation phosphate specifically includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt phosphate, lithium vanadium phosphate. In some embodiments, the lithium iron manganese phosphateThe chemical formula is LiMn _x Fe _1-x PO ₄ The value range of x is 0.2-0.8. In this case, the lithium iron manganese phosphate has better safety performance, cycle performance, oxidation-reduction potential, energy density and other characteristics.

In some possible implementations, the feedstock components obtained as lithium intercalation phosphates include lithium sources, manganese sources, iron sources, cobalt sources, vanadium sources, phosphates, and the like. Wherein the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium oxalate. The phosphate comprises at least one of phosphoric acid, monoammonium phosphate and ammonium phosphate. The manganese source comprises at least one of manganese monoxide, manganous oxide, manganese acetate, manganese sulfate, manganese nitrate and manganese chloride. The cobalt source comprises at least one of cobalt sulfate, cobalt carbonate, cobalt nitrate, cobalt chloride and cobalt acetate. The vanadium source comprises at least one of vanadyl acetylacetonate, vanadium dichloride, vanadium acetylacetonate, bismuth vanadate, magnesium vanadate, sodium metavanadate, ammonium metavanadate, potassium metavanadate, silver metavanadate and sodium orthovanadate. The iron source comprises at least one of ferrous sulfate, ferrous nitrate, ferrous acetate and ferrous oxalate. The raw material components such as the lithium source, the manganese source, the iron source, the vanadium source, the cobalt source, the phosphate and the like selected in the embodiment of the application are easy to obtain, and the lithium iron manganese phosphate material can be generated through mixed grinding treatment and sintering treatment.

In some possible implementations, in step S20, the step of sintering includes: performing first sintering treatment on the mixed precursor, and performing second sintering treatment after cooling; wherein the temperature of the first sintering process is lower than the temperature of the second sintering process. In this case, first sintering treatment is performed at a relatively low temperature, so that raw material components such as a lithium source, a manganese source, an iron source, phosphate and the like in the precursor are sintered and primarily converted into lithium iron manganese phosphate crystals. Meanwhile, the sintering process further converts the red phosphorus which is not completely converted into black phosphorus. The organic grinding aid is converted into a carbon material, and the carbon material and black phosphorus form a composite structure embedded and overlapped to be coated on the surface of the lithium iron manganese phosphate particles. Then, the second sintering treatment is carried out under the condition of higher temperature, so that the crystallinity of the lithium iron manganese phosphate material is further improved, and the graphitization degree of the carbon material in the coating layer is improved. Further optimizing the crystallinity, shape and size, impurity phase, surface coating and the like of the particles of the composite material. According to the embodiment of the application, the primary sintering is performed at a relatively low temperature, the secondary sintering is performed at a relatively high temperature after cooling, and the sintering treatment stages at two different temperatures are beneficial to improving the crystallinity of the composite material particles and preventing the particle size from being oversized and agglomerated. Meanwhile, part of phosphorus atoms in the black phosphorus volatilize in the sintering process to replace part of carbon atoms in the carbon material, so that part of phosphorus atom doped carbon material is formed, the carbon material is defective, and more lithium ions and electron transport active sites are provided. And the phosphorus atoms are compounded to enable the carbon material to be in an electron-rich state, and electron cloud coupling occurs when the electron cloud is deviated from the bulk material, so that the electron conductivity of the material is increased.

In some possible implementations, the conditions of the first sintering process include: heating to 200-500 ℃ at a speed of 1-5 ℃/min under inert atmosphere, and then preserving heat for 3-15 h. Under the condition, raw material components such as a lithium source, a manganese source, an iron source, phosphate and the like in the precursor can be sintered and primarily converted into lithium iron manganese phosphate crystals. Meanwhile, the red phosphorus which is not completely converted is further converted into black phosphorus in the sintering process. The organic grinding aid is converted into a carbon material, and the carbon material and black phosphorus form an inlaid and overlapped composite structure to be coated on the surface of lithium iron manganese phosphate particles.

In some possible implementations, the conditions of the second sintering process include: under inert atmosphere, the temperature is raised to 500-800 ℃ at the speed of 1-5 ℃/min, and then the temperature is kept for 3-15 h. Under such conditions, the crystallinity of the lithium iron manganese phosphate material can be sufficiently improved, and the graphitization degree of the carbon material in the coating layer can be improved. And further optimize the crystallinity, morphology size, impurity phase, surface coating and the like of the particles of the composite material.

In some embodiments, the inert atmosphere includes, but is not limited to, nitrogen, argon, helium, and the like.

In some possible implementations, the mass percent of black phosphorus in the lithium-intercalated phosphate-based composite material is 0.1-3 wt%.

In some possible implementations, the mass percentage of the coating layer in the lithium-intercalated phosphate composite material is 1-5 wt%.

In some possible implementations, the percentage by mass of black phosphorus in the coating layer is 10-60 wt%.

In some possible implementations, the lithium-intercalated phosphate-based composite material has a primary particle size of 30 to 300nm and a secondary particle size of 0.3 to 10 μm.

In some possible implementations, the coating layer thickness in the lithium-intercalated phosphate-based composite is 0.5-8 nm.

In some possible implementations, in the cladding layer, a portion of the black phosphorus replaces a portion of the carbon atoms in the carbon material in clusters or monoatoms to form a phosphorus atom doped carbon material.

In some possible implementations, the tessellated and overlapped composite structure includes: part of black phosphorus is embedded in the carbon material in the form of nano black phosphorus sheets to form a composite coating layer; the partially black phosphorus forms a multi-layer overlapping composite coating layer which is mutually staggered and stacked with the carbon material in a sheet form.

In some possible implementations, in the coating layer of the lithium-intercalated phosphate-based composite material, the nano black flakes include: a small-sized sheet having an average thickness of 1 to 5nm and an average length/width of 5 to 15nm, and a large-sized sheet having an average thickness of 5 to 15nm and an average length/width of 15 to 1000 nm.

The beneficial effects of the embodiments of the lithium-intercalation phosphate composite material are discussed in detail above, and are not described in detail herein.

A third aspect of embodiments of the present application provides a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode contains the lithium-intercalation phosphate composite material or the lithium-intercalation phosphate composite material prepared by the method.

In the secondary battery provided by the third aspect of the embodiment of the application, the positive electrode comprises the lithium-intercalation phosphate composite material, the lithium-intercalation phosphate composite material is of a core-shell structure, the inner core is of lithium iron manganese phosphate, and the coating layer comprises a carbon material and black phosphorus which form an inlaid and overlapped composite structure, and has the characteristics of high capacity, high rate performance, high cycle stability and the like. Thus, the energy density, the cycle stability, and the rate capability of the secondary battery can be improved.

In some possible implementations, the negative electrode of the secondary battery includes, but is not limited to, graphite, soft carbon (e.g., coke, etc.), hard carbon, etc., carbon materials, or nitrides, tin-based oxides, tin alloys, and nano-negative electrode materials, etc.

In some possible implementations, the separator includes at least one material of polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly (ethylene terephthalate), polyethylene terephthalate, polyamide fibers, poly (paraphenylene terephthalamide).

In some possible implementations, the electrolyte is an organic solution containing a soluble lithium salt.

In order that the details and operations of the foregoing implementation of the present application may be clearly understood by those skilled in the art, and that the lithium-intercalation phosphate composite material, the preparation method thereof and the secondary battery according to the embodiments of the present application may be significantly embodied, the foregoing technical solutions are exemplified by a plurality of examples.

Example 1

A black phosphorus and carbon co-coated lithium iron manganese phosphate composite material is prepared by the following steps:

(1) 3.69g (0.05 mol) of lithium carbonate, 11.50g (0.1 mol) of monoammonium phosphate, 5.34g (0.0233 mol) of trimanganese tetraoxide, 5.38g (0.003 mol) of ferrous oxalate dihydrate are weighed into a ball milling tank, then 0.259g (0.1 wt%) of red phosphorus, 0.259g of urea and 0.13g of glucose are weighed into the ball milling tank, 380g of ball milling beads with different sizes are added, and ball milling is carried out for 8 hours under the nitrogen protection atmosphere at the rotating speed of 700rmp, so that the mixed precursor is obtained.

(2) And calcining the mixed precursor obtained by ball milling for 8 hours at 350 ℃ in a nitrogen atmosphere by using a tube furnace, setting the heating rate to be 2 ℃/min, and naturally cooling to obtain a primary sintering product.

(2) Continuously using the primary sintered product in a tube furnace under the nitrogen atmosphere of 600 percentCalcining at the temperature of 8 hours, setting the heating rate to be 2 ℃/min, naturally cooling to obtain a black phosphorus and carbon co-coated lithium iron manganese phosphate composite material, and marking as LiMn _0.7 Fe _0.3 PO ₄ @BP@C-1。

Example 2

(1) 2.39g (0.1 mol) of lithium hydroxide (LiOH) and ammonium dihydrogen phosphate (NH) were weighed ₄ H ₂ PO ₄ ) 11.50g (0.1 mol) of manganese acetate ((CH) ₃ COO) ₂ Mn) 12.11g (0.07 mol), ferrous sulfate heptahydrate (FeSO) ₄ ·7H ₂ O) 8.34g (0.03 mol) of red phosphorus is placed in a ball milling tank, 2.59g (1 wt%) of glucose 0.15g and 0.15g of starch are weighed into the ball milling tank, then 500g of ball milling beads with different sizes are added, and ball milling is carried out for 15 hours at a rotating speed of 800rmp under the atmosphere of nitrogen protection, so as to obtain a mixed precursor.

(2) And calcining the mixed precursor obtained by ball milling for 12 hours at 400 ℃ in a nitrogen atmosphere by using a tube furnace, setting the heating rate to be 2 ℃/min, and naturally cooling to obtain a primary sintering product.

(2) Continuously using a tube furnace to calcine the primary sintered product at 650 ℃ for 8 hours in a nitrogen atmosphere, setting the heating rate to 5 ℃/min, and naturally cooling to obtain a black phosphorus and carbon co-coated lithium iron manganese phosphate composite material, namely LiMn _0.7 Fe _0.3 PO ₄ @BP@C-2。

Example 3

(1) weighing lithium acetate (CH) ₃ COOLi) 6.599g (0.1 mol), ammonium phosphate ((NH 4) ₃ PO ₄ ) 14.91g (0.1 mol), manganese monoxide (MnO) 4.96g (0.07 mol), ferrous nitrate (Fe (NO) ₃ ) ₂ ) 5.396g (0.03 mol) of the mixed precursor is placed in a ball milling tank, 0.6373g (2 wt%) of red phosphorus, 0.3187g of sucrose and 0.3g of citric acid are weighed into the ball milling tank, 600g of ball milling beads with different sizes are added, and ball milling is carried out for 18 hours at a rotating speed of 1000rmp under the atmosphere of nitrogen protection, so that the mixed precursor is obtained.

(2) Calcining the mixed precursor obtained by ball milling for 6 hours at 500 ℃ in a nitrogen atmosphere by using a tube furnace, setting the heating rate to be 5 ℃/min, and naturally cooling to obtain a primary sintering product.

(2) Continuously using a tube furnace to calcine the primary sintered product at 750 ℃ for 8 hours in a nitrogen atmosphere, setting the heating rate to 5 ℃/min, and naturally cooling to obtain a black phosphorus and carbon co-coated lithium iron manganese phosphate composite material, which is marked as LiMn _0.7 Fe _0.3 PO ₄ @BP@C-3。

Comparative example 1

The preparation steps of the carbon-coated lithium iron manganese phosphate composite material are different from those of the embodiment 1: in the step (1), red phosphorus is not added, and finally the carbon-coated lithium iron manganese phosphate composite material LiMn is prepared _0.7 Fe _0.3 PO ₄ @C。

Comparative example 2

The preparation steps of the black phosphorus and carbon co-coated lithium iron manganese phosphate composite material are different from those of the embodiment 1: urea and glucose are not added in the step (1). Finally preparing the black phosphorus and carbon co-coated lithium iron manganese phosphate composite material LiMn with very little carbon content _0.7 Fe _0.3 PO ₄ @BP@C。

Comparative example 3

The preparation steps of the black phosphorus coated lithium iron manganese phosphate composite material are different from those of the embodiment 1: the ball-milling beads used in step (1) weighed 150g and a rotational speed of 300rmp. Finally preparing the black phosphorus and carbon co-coated lithium iron manganese phosphate composite material LiMn containing red phosphorus impurities and not stripped into nano sheets _0.7 Fe _0.3 PO ₄ @BP@C。

Further, to verify the advancement of the examples of the present application, the following performance tests were performed on the examples and comparative examples, respectively:

1. lithium iron manganese phosphate composite material (LiMn) co-coated with black phosphorus and carbon prepared in example 1 _0.7 Fe _0.3 PO ₄ @ BP @ C-1) was subjected to an X-ray powder diffraction test, the test results of which are shown in FIG. 2. As can be seen from the accompanying drawing, the X-ray diffraction pattern of the black phosphorus and carbon co-coated lithium iron manganese phosphate composite material prepared in the example 1 and a standard card PDF- #13-0336Substantially identical.

2. Lithium iron manganese phosphate composite material (LiMn) co-coated with black phosphorus and carbon prepared in example 1 _0.7 Fe _0.3 PO ₄ The morphology observation is carried out at the temperature of BP@C-1), an SEM scanning electron microscope image is shown in a figure 3, the particles of the composite material are uniform, and the particle size is high at one degree.

3. Cell performance test: the lithium iron manganese phosphate composite materials provided in the above examples and comparative examples were used to assemble batteries as follows:

(1) preparation of a positive plate: mixing the lithium iron manganese phosphate composite materials prepared in each example and comparative example with SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methyl pyrrolidone) according to the mass ratio of 93.5:2.5:4:100 for 2 hours by a ball mill mixer to obtain anode slurry; and (3) adding the prepared positive electrode slurry on an aluminum foil, uniformly scraping the positive electrode slurry by a scraper, drying the positive electrode slurry at 130 ℃, and rolling the positive electrode slurry to obtain the positive electrode plate.

(2) The battery assembling process comprises the following steps: the prepared positive electrode is adhered to a positive electrode metal shell by using conductive adhesive, a metal lithium sheet is used as a negative electrode, a Celgard 2400 microporous membrane is used as a diaphragm, and 1.0mol/L LiPF is used ₆ The solution is used as electrolyte, and the solvent of the electrolyte is a mixed solution of Ethylene Carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1, and the mixed solution is assembled into the button cell in a glove box.

And using a LAND electrochemical tester, testing the 0.1C discharge capacity, the 1C discharge capacity, the 5C discharge capacity and the 10C discharge capacity of the button cell under the conditions of a charge termination voltage of 4.2V and a discharge cutoff voltage of 2.0V, and testing the capacity retention rate, the resistivity and other performances after 1C 200 cycles of charge and discharge. The test results are shown in table 1 below:

TABLE 1

Wherein, the black phosphorus and carbon co-coated lithium iron manganese phosphate composite material (LiMn) prepared in example 1 _0.7 Fe _0.3 PO ₄ Carbon co-coated lithium manganese iron phosphate complex prepared in comparative example 1 and @ BP @ C-1)Composite material (LiMn) _0.7 Fe _0.3 PO ₄ The capacity-voltage curve of the coin cell prepared at 0.1C rate is shown in fig. 4. Specific capacities of button cells fabricated from the lithium iron manganese phosphate composites prepared in example 1 and comparative examples 1 and 2 at different rates are shown in fig. 5.

From the above test results, it is understood that the present examples 1 to 3 have better conductivity properties and better rate performance and cycle stability performance after the secondary battery is fabricated by stripping red phosphorus into black phosphorus and carbon material to form physically and chemically doped black phosphorus and carbon co-coated lithium iron manganese phosphate composite, compared to the carbon coated lithium iron manganese phosphate composite of comparative example 1, the black phosphorus and carbon coated lithium iron manganese phosphate composite of comparative example 2 having very little carbon content, and the black phosphorus and carbon coated lithium iron manganese phosphate composite of comparative example 3 having red phosphorus impurities and not stripped into nano-sheets.

The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.

Claims

1. The lithium-intercalated phosphate composite material is characterized by comprising a lithium-intercalated phosphate inner core and a coating layer coated on the outer surface of the inner core; the coating layer comprises a carbon material and black phosphorus, and the black phosphorus and the carbon material form a mosaic and overlapping composite structure.

2. The lithium-intercalated phosphate based composite material of claim 1 wherein the mosaic and overlapping composite structure comprises: part of the black phosphorus is embedded in the carbon material in the form of nano black phosphorus sheets to form a composite coating layer; part of the black phosphorus and the carbon material form a plurality of layers of overlapped composite coating layers which are mutually staggered and stacked in a flaky form;

and/or, in the coating layer, partial black phosphorus replaces partial carbon atoms in the carbon material in the form of atom clusters or single atoms to form a phosphorus atom doped carbon material;

and/or the lithium intercalation phosphate comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt phosphate and lithium vanadium phosphate.

3. The lithium-intercalated phosphate composite material according to claim 2, wherein the mass percentage of the black phosphorus in the lithium-intercalated phosphate composite material is 0.1 to 3wt%;

and/or, in the lithium-intercalation phosphate composite material, the mass percentage of the coating layer is 1-5wt%;

and/or, in the coating layer, the mass percentage of the black phosphorus is 10-60 wt%;

and/or, the nano black phosphorus sheet comprises: a small-sized sheet having an average thickness of 1 to 5nm and an average length/width of 5 to 15nm, and a large-sized sheet having an average thickness of 5 to 15nm and an average length/width of 15 to 1000 nm.

4. A lithium-intercalated phosphate composite material according to any one of claims 1 to 3, wherein the primary particle diameter of the lithium-intercalated phosphate composite material is 30 to 500nm and the secondary particle diameter is 0.3 to 10 μm;

and/or the thickness of the coating layer in the lithium-intercalation phosphate composite material is 0.5-8 nm.

5. The preparation method of the lithium-intercalated phosphate composite material is characterized by comprising the following steps of:

6. The method for producing a lithium-intercalated phosphate composite material according to claim 5, wherein the step of sintering comprises: performing first sintering treatment on the mixed precursor, and performing second sintering treatment after cooling; wherein the temperature of the first sintering process is lower than the temperature of the second sintering process;

and/or, the conditions of the mixed grinding treatment include: ball milling for 6-24 h in inert atmosphere with ball material ratio of (15-50): 1 and rotation speed of 500-1200 rpm.

7. The method for producing a lithium-intercalated phosphate composite material according to claim 6, wherein the conditions of the first sintering treatment include: heating to 200-500 ℃ at a speed of 1-5 ℃/min under inert atmosphere, and then preserving heat for 3-15 h;

and/or, the conditions of the second sintering treatment include: heating to 500-800 ℃ at a speed of 1-5 ℃/min under inert atmosphere, and then preserving heat for 3-15 h;

and/or the mode of the mixed grinding treatment comprises planetary ball milling or shimmy ball milling.

8. The method for producing a lithium-intercalated phosphate composite material according to any one of claims 5 to 7, wherein the mass percentage of the red phosphorus in the mixed precursor is 0.1 to 3wt%;

and/or, in the mixed precursor, the mass percentage of the organic grinding aid is 0.5-6wt%.

9. The method for producing a lithium-intercalated phosphate composite material according to claim 8, wherein the organic grinding aid comprises at least one of urea, starch, glucose, sucrose, fructose, and citric acid.

10. A secondary battery, characterized in that the secondary battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode comprises the lithium-intercalation phosphate composite material according to any one of claims 1 to 4 or the lithium-intercalation phosphate composite material prepared by the method according to any one of claims 5 to 9.