CN106816600B - Lithium iron manganese phosphate material, preparation method thereof, battery slurry, positive electrode and lithium battery - Google Patents

Abstract

The invention discloses a lithium iron manganese phosphate material, a preparation method thereof, a battery slurry, a positive electrode and a lithium battery. The lithium iron manganese phosphate material includes an active component with a LiMn _x Fe _{1‑x‑y My} PO ₄ /C structure, wherein 0≤x≤1, 0≤y≤1, and M is Co, Ni, Mg, one or more of Zn, V and Ti; and a coating layer wrapped on the surface of the active component, the coating layer containing an amorphous metal compound. The lithium iron manganese phosphate-based material coats the surface of the active component with the LiMn _x Fe _{1-x-y My} PO ₄ /C structure with a coating layer containing an amorphous metal compound with a low water absorption rate. The electrochemical performance of the lithium iron manganese phosphate material reduces the water absorption rate of the lithium iron manganese phosphate material, which is beneficial to improve the storage capacity retention rate of the corresponding lithium battery at high temperature.

Description

A kind of lithium iron manganese phosphate material and preparation method thereof, battery slurry, positive electrode and lithium battery

technical field

The present invention relates to the field of lithium battery preparation, in particular, the present invention relates to a lithium iron manganese phosphate material and a preparation method thereof, the present invention also relates to a battery slurry comprising the aforementioned lithium iron manganese phosphate material, and the present invention further relates to A positive electrode comprising the aforementioned lithium manganese iron phosphate material, and a lithium battery comprising the aforementioned positive electrode.

Background technique

Lithium-ion secondary battery is a new type of green high-energy rechargeable battery. It has many advantages such as high voltage, high energy density, good cycle performance, small self-discharge, no memory effect, and wide working range. It is widely used in mobile phones, notebook computers, Portable power tools, electronic instruments, weapons and equipment also have good application prospects in electric vehicles, and have become the focus of research and development in countries around the world. The positive electrode material is a very important part of the lithium-ion battery. During the charging and discharging process of the lithium-ion battery, it is not only necessary to provide the lithium required for reciprocating intercalation/deintercalation in the positive and negative lithium intercalation compounds, but also to provide the surface of the negative electrode material to form SEI. Therefore, research and development of high-performance cathode materials is the key to the development of lithium-ion batteries.

Among the cathode materials for lithium ion batteries, lithium manganese iron phosphate materials have the best overall performance and are considered to be ideal cathode materials for lithium ion secondary power batteries. However, the particle size of the existing lithium iron manganese phosphate materials is generally controlled at nanoscale, and its specific surface area is relatively large. Once it comes into contact with humid air, the water is easy to contact with the hydrophilic Li on the surface of the material. After the lithium iron phosphate is exposed to humid air within a few weeks, the surface lithium will also undergo a lithiation reaction with water, resulting in an increase in the moisture content of lithium manganese iron phosphate. When this kind of lithium manganese iron phosphate material with relatively high water content is used as the positive electrode material of the battery, the water in the material is difficult to remove in the subsequent battery batching process, and it will remain in the battery all the time, which makes the battery 's storage capacity retention rates are mostly underperforming. In order to improve the storage capacity retention rate of batteries, researchers have studied various schemes, such as reducing the water absorption rate of lithium manganese iron phosphate materials.

In the Chinese patent application with the application number of No. 200910053346, a method for improving the conductivity of lithium iron phosphate positive electrode material is disclosed. Without any doping activation, on the basis of synthesizing lithium ferrous phosphate materials according to conventional methods, the residues in the lithium ferrous phosphate materials are removed by introducing dehydrating gas during high temperature calcination, vacuum pumping water and phosphorus pentoxide absorbing water. moisture, which can greatly improve the electrical conductivity of the material. However, the processing process of this method is relatively complicated, and a variety of auxiliary raw materials need to be introduced to remove the moisture in the material, and the lithium iron phosphate cathode material prepared by this method cannot guarantee the water absorption of the material in subsequent contact with air.

In the Chinese patent application No. 200910044154, a surface-modified lithium ion battery cathode material lithium cobalt oxide material and a modification method thereof are disclosed. The patent firstly uses the molar mass ratio of Li:Co to be 1.038, respectively. Weigh the lithium salt and the cobalt salt; firstly add the lithium salt in the ball mill, then add the coating material calcium carbonate, then add the cobalt salt, and finally add industrial alcohol to perform ball milling; after the ball-milled material is vacuum-dried, the first firing After the sintered material is crushed and pulverized, it is washed with deionized water and sintered for a second time; the dispersion treatment is to obtain a positive electrode material coated with a layer of calcium carbonate on the surface of lithium cobalt oxide. This modification method coats the surface of lithium cobalt oxide with a layer of hydrophobic calcium carbonate, which can block the contact between the active material and water, and improve the water absorption performance of lithium cobalt oxide to a certain extent. Active constituents drop, affecting the electrochemical performance of the final material.

As can be seen from the above content, although some schemes for reducing the water absorption of lithium iron manganese phosphate materials have been proposed in the prior art, the effect is not ideal, and the high temperature storage capacity of the battery using the electrode prepared by this material is used. Retention rates also tend to be poor.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a kind of lithium iron manganese phosphate material and its preparation method as well as battery slurry, positive electrode and lithium battery, so as to provide a kind of lithium iron manganese phosphate material with low water absorption rate, and then improve the high temperature storage of the battery. capacity retention rate.

In order to achieve the above object, according to a first aspect of the present invention, a lithium iron manganese phosphate material is provided, and the lithium iron manganese phosphate material includes an active component having a LiMn _x Fe _{1-xy My PO 4} /C structure , wherein 0≤x≤1, 0≤y≤1, M is one or more of Co, Ni, Mg, Zn, V and Ti; and a coating layer wrapped on the surface of the active component, the The coating layer contains an amorphous metal compound.

According to a second aspect of the present invention, there is provided a preparation method of a lithium iron manganese phosphate material, the preparation method comprising the following steps: S1, providing an active group having a LiMn _x Fe _{1-xy My PO 4} /C structure points, wherein 0≤x≤1, 0≤y≤1, M is one or more of Co, Ni, Mg, Zn, V and Ti; S2, using the active component as the base material, in the A coating layer containing an amorphous metal compound is formed on the surface of the active component.

According to a third aspect of the present invention, a lithium iron manganese phosphate material is provided, and the lithium iron manganese phosphate material is prepared by the above preparation method.

According to a fourth aspect of the present invention, a battery slurry is provided, the battery slurry includes a lithium iron manganese phosphate material and a solvent, wherein the lithium iron manganese phosphate material is the above-mentioned lithium iron manganese phosphate of the present invention Material.

According to a fifth aspect of the present invention, there is provided a positive electrode comprising a current collector and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer comprising the lithium iron manganese phosphate material of the present invention.

According to a sixth aspect of the present invention, a lithium battery is provided, wherein the lithium battery is equipped with a positive electrode, and the positive electrode is the above-mentioned positive electrode material of the present invention.

The lithium iron manganese phosphate material and its preparation method as well as the battery slurry, the positive electrode and the lithium battery provided by the present invention, wherein the lithium iron manganese phosphate material has a LiMn _x Fe _{1-xy My PO 4} /C structure through the active The surface of the component is coated with a coating layer containing an amorphous metal compound with a low water absorption rate, which reduces the water absorption rate of the lithium manganese iron phosphate material while maintaining the electrochemical performance of the lithium iron manganese phosphate material, thereby reducing the The water content of the positive electrode prepared therefrom is improved, and the storage capacity retention rate at high temperature of the lithium battery prepared from the positive electrode material is improved.

Other features and advantages of the present invention will be described in detail in the detailed description that follows.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and together with the following specific embodiments, are used to explain the present invention, but do not constitute a limitation to the present invention. In the attached image:

1 shows a 5 μm scanning electron microscope (SEM) pattern of the lithium manganese iron phosphate material P1 prepared according to Preparation Example 1 of the present invention;

FIG. 2 shows a 5 μm scanning electron microscope (SEM) pattern of the lithium iron manganese phosphate material DP1 prepared according to Comparative Example 1 of the present invention.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, but not to limit the present invention.

In response to the technical problem that "the storage capacity retention rate of batteries is mostly poor in the prior art" pointed out in the background of the present invention. The inventors of the present invention have done a lot of work and research on the removal of material moisture and the like. And according to the first aspect of the present invention, there is provided a lithium manganese iron phosphate material, the lithium iron manganese phosphate material includes an active component with a LiMn _x Fe _{1-xy My PO 4} /C structure, wherein 0 ≤x≤1, 0≤y≤1, M is one or more of Co, Ni, Mg, Zn, V and Ti; and a coating layer wrapped on the surface of the active component, the coating The layer contains an amorphous metal compound.

In the present invention, "active component with LiMn _x Fe _{1-xy My} PO ₄ /C structure" refers to a carbon-coated lithium iron manganese phosphate material (LiMn _x Fe _{1-xy My PO 4} ) structure active ingredient.

The lithium iron manganese phosphate material provided by the present invention coats the surface of the active component with LiMn _x Fe _{1-xy My} PO ₄ /C structure with a coating layer containing an amorphous metal compound with a low water absorption rate , while maintaining the electrochemical performance of the lithium manganese iron phosphate material, the water absorption rate of the lithium manganese iron phosphate material is reduced, thereby reducing the water content of the positive electrode material prepared by it, thereby helping to improve the positive electrode material. High temperature storage capacity retention of the prepared lithium battery.

In the lithium iron manganese phosphate material of the present invention, there is no special requirement for the particle size of the material, and the conventional selection in the field can be referred to, for example, the particle size _D50 can be 0.5-2.0 μm. The particle size of the lithium manganese iron phosphate material to be prepared can reasonably arrange the particle size of the active component and the thickness of the coating layer in the lithium manganese iron phosphate material. In the present invention, as long as the amorphous metal compound is contained The coating layer can be coated on the surface of the active component. Preferably in the present invention, in the lithium iron manganese phosphate material, the particle size _D50 of the active component is 0.5-1.0 μm, preferably 0.5-0.8 μm, and the thickness of the amorphous metal compound coating layer is 1-5 nm . In the present invention, the particle size D ₅₀ is the volume average particle size, which is obtained by dispersing the powder to be tested in water, then ultrasonically oscillating for 30 minutes, and performing particle size testing with a laser particle size analyzer.

In the lithium iron manganese phosphate material of the present invention, there is no special requirement for the amorphous metal compound in the coating layer, as long as its water absorption rate is lower than that of the active component. In the present invention, preferably, the amorphous metal compound is selected from amorphous aluminum oxide, amorphous lithium phosphate, amorphous lithium pyrophosphate, amorphous iron pyrophosphate, amorphous lithium iron pyrophosphate , one or more mixtures of amorphous lithium manganese pyrophosphate and amorphous silver oxide. The inventors of the present invention have found that cladding layers formed from these amorphous metal compounds have lower absorption rates than cladding layers formed from conventional crystalline metal compounds. The inventor speculates that this may be because this "amorphous metal compound" usually grows regularly and disorderly, and non-polar bonds are formed on its surface, and these non-polar bonds are not easy to combine with polar water, which can It plays the role of blocking the infiltration of moisture, so it can better block the contact between active components and moisture, thereby improving the water absorption performance of lithium manganese iron phosphate materials. At the same time, the coating layer formed by this inorganic amorphous metal compound is thick It is very thin, so it will not affect the electrochemical performance of the prepared lithium iron manganese phosphate material, thereby making the prepared lithium iron manganese phosphate material have better electrochemical performance.

In a preferred embodiment of the present invention, the above-mentioned lithium manganese iron phosphate material further includes a conductive carbon layer coated on the surface of the coating layer, and a conductive carbon layer is further provided on the surface of the coating layer containing the amorphous metal compound. The carbon layer is beneficial to further optimize the electrical conductivity of the material. More preferably, the thickness of the conductive carbon layer is 2-10 nm.

In the lithium iron manganese phosphate material of the present invention, there is no special requirement for the element ratio in the active component having the LiMn _x Fe _{1-xy My} PO ₄ /C structure, which can refer to conventional elements in the art The mixing ratio may be as long as it can form the aforementioned structure. Preferably, the molar ratio of Li to the sum of Mn, Fe and M is 0.98-1.02:1. Meanwhile, preferably, the content of element C in the active component is 0.5-3.5 wt % of the total weight of the active component.

In the present invention, there is no special requirement for the magnetic induction intensity of the lithium iron manganese phosphate material, which can be selected with reference to the routine in the field. However, in order to optimize the electrochemical performance of the prepared lithium iron manganese phosphate material, preferably the magnetic induction intensity of the lithium iron manganese phosphate material is 750-1100 ppm. Among them, the magnetic induction intensity of lithium iron manganese phosphate materials is tested with a magnetic analyzer MA1040 of Mack Instruments. The test method is to put the lithium iron manganese phosphate material powder into a sample cup (the height of the sample is 12 cm), and measure the magnetic intensities in 5 different directions to take the average value.

According to the second aspect of the present invention, the present invention also provides a preparation method of lithium iron manganese phosphate material. The above-mentioned lithium iron manganese phosphate materials of the present invention can be prepared with reference to conventional methods in the art, or can be prepared by the preferred preparation method provided by the present invention. The preparation method provided by the present invention includes the following steps: S1, preparing an active component with a LiMn _x Fe _{1-xy My PO 4} /C structure, wherein 0≤x≤1, 0≤y≤1, and M is One or more of Co, Ni, Mg, Zn, V and Ti; S2. Using the active component as a base material, a coating layer containing an amorphous metal compound is formed on the surface of the active component .

The preparation method of the iron manganese lithium phosphate material provided by the present invention forms the active component and the coating layer covering the surface of the active component in different steps, which is beneficial to ensure the iron phosphate. At the same time of the electrochemical performance of manganese-lithium materials, the coating layer is more uniform and complete to coat the surface with active components, so as to block the contact between the active components and water, thereby improving the water absorption performance of lithium iron manganese phosphate.

In the above preparation method, in the step of S1 providing an active component having a structure of LiMn _x Fe _{1-xy My PO 4} /C, the active component having a structure of LiMn _x Fe _{1-xy My PO 4} /C may be Commercially available products can also be prepared with reference to conventional methods in the art. In the present invention, it is preferably prepared by using a high temperature solid phase method, which includes the following steps: S11, adding a lithium source, an optional iron source, an optional manganese source, an optional M source, a phosphorus source and a first carbon source Mix according to the proportion, and obtain the first dry mixture after drying; S12, sintering the first dry mixture at a constant temperature of 600-800° C. for 5-30 hours to form the active component.

In S11 of the above preparation method, each raw material can be mixed in proportion by a grinding method, and the grinding methods that can be used include but are not limited to ball milling, sand milling or stirring mill. For the grinding process conditions, reference can be made to the process conditions commonly used in the art, for example, grinding at a speed of 1000-2000 rpm for 1-6 hours. The step of grinding and mixing also includes the step of adding grinding liquid, the grinding liquid including but not limited to one or more of deionized water and C ₁ -C ₅ alcohol. The C ₁ -C ₅ alcohol is preferably a C ₁ -C ₅ monohydric alcohol, including but not limited to methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, 2-methyl-1 -Propanol, 2-methyl-2-propanol, n-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3- One or more of methyl-2-butanol and 2,2-dimethyl-1-propanol, preferably ethanol.

In S11 of the above preparation method, the drying process includes but is not limited to vacuum drying, inert gas protection heating drying, spray drying, freeze drying or flash drying, among which spray drying is preferred. The process conditions that are conventionally selected in the field, for example, the inlet air temperature is 200-300°C, and the outlet air temperature is 80-200°C.

In S12 of the above preparation method, the step of sintering the first dry mixture may refer to a conventional operation method in the art, as long as the constant temperature sintering is performed at 600-800° C. for 5-30 hours. In the present invention, the first dry mixture is preferably heated to 600-800° C. at a rate of 0.1-2° C./min, and treated at a constant temperature for 5-30 hours. By adjusting the heating rate of the first dry mixture, it is beneficial to form a well-developed crystalline lithium iron manganese phosphate bulk material, so as to ensure that the material has relatively high electrochemical activity.

In S11 of the above preparation method, in the step of preparing the active component with LiMn _x Fe _{1-xy My PO 4} /C structure, there is no special requirement for the amount of each raw material, according to the expected formation of LiMn _x Fe _{1- xy My PO 4} /C structure, the amount of the corresponding raw materials can be reasonably selected. In the present invention, it is preferred that when preparing the raw materials, the molar ratio of the lithium source in terms of Li to the optional iron source, optional manganese source, and optional M source in terms of the total amount of Fe+Mn+M is 0.98-1.02:1 . The molar ratio of the lithium source in terms of Li and the phosphorus source in terms of phosphorus is 0.98-1.02:1. In the present invention, there is no special requirement for the selection of each raw material, and reference may be made to conventional materials used in the preparation of lithium iron manganese phosphate materials in the art. in:

Lithium sources that may be used include, but are not limited to, one or more of lithium hydroxide, lithium peroxide, lithium oxide, lithium carbonate, and lithium phosphate.

Phosphorus sources that can be used include, but are not limited to, one or more of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, lithium phosphate, and lithium pyrophosphate.

Fe sources that can be used include, but are not limited to, one or more of ferrous oxide, ferric oxide, ferric oxide, ferric nitrate, ferrous nitrate, ferrous acetate, and ferrous formate.

The Mn sources that can be used include but are not limited to one or more of manganese dioxide, manganese oxide, manganese tetroxide, manganese carbonate, manganese nitrate, manganese nitrate, manganese acetate, and manganese formate.

The optional M source is a compound containing one or more of Co, Ni, Mg, Zn, V, and Ti. Wherein, the Co-containing compounds that can be used include but are not limited to one or more of cobalt tetroxide, cobalt nitrate, cobaltous oxide, cobalt hydroxide, cobalt acetate and cobalt phosphate; Ni-containing compounds that can be used include but are not limited to cobaltous oxide One or more of nickel, nickel oxide, nickel nitrate, nickel hydroxide, nickel acetate and nickel phosphate; Mg-containing compounds that can be used include but are not limited to one or more of magnesium oxide, magnesium nitrate, magnesium hydroxide and magnesium acetate One or more; Zn-containing compounds that can be used include but are not limited to one or more of zinc oxide, zinc nitrate, zinc hydroxide and zinc acetate; V-containing compounds that can be used include but are not limited to vanadium oxide, One or more of vanadium oxide, vanadium trioxide, vanadium nitrate, vanadium hydroxide and vanadium acetate; Ti-containing compounds that can be used include but are not limited to titanium dioxide, titanium hydroxide, titanium acetate and tetrabutyl titanate one or more of.

The carbon sources that can be used include, but are not limited to, glucose, sucrose, lactose, phenolic resin, graphene, carbon nanotubes, graphite, etc. that have been carbonized or can be carbonized at high temperature, such as organic carbon sources or inorganic carbon sources. In the present invention, the purpose of adding a carbon source in the step of preparing the active component having the LiMn _x Fe _{1-xy My} PO ₄ /C structure is to improve the electronic conductivity of the material, and is the same as the conventional method in the art, in the present invention The carbon source added in the sintering process will be enriched on the surface of the lithium manganese iron phosphate material, thus forming a phosphoric acid with a LiMn _x Fe _{1-xy My PO 4} /C structure, that is, a carbon-coated structure. Manganese iron lithium materials. The amount of carbon source added in the present invention can refer to the conventional amount in the field, for example, the amount of C source is such that the content of element C in the active component is 0.5-3.5wt% of the total weight of the active component.

In S2 of the above preparation method, in the step of preparing the amorphous metal compound coating layer, the method for forming the coating layer containing the amorphous metal compound is not particularly limited, as long as the substances in the formed coating layer are It can exist in an amorphous form. Preferably, the S2 includes the following steps: S21, mixing the active component with a material source (in a solvent, such as water) for forming a metal compound, and drying to obtain a second dry mixture; S22, drying the second The temperature of the mixture is raised to 300-500° C. without heat preservation, and the temperature is directly lowered, so as to form the amorphous metal compound coating layer on the surface of the active component.

In S21 of the above preparation method, there is no special requirement for the mixing method of the active component and the material source for forming the metal compound, as long as the two are relatively uniformly dispersed in the solvent, for example, it can be made by stirring. The mixing of the two is relatively uniform, and the stirring time is 15-50min.

In S21 of the above preparation method, the drying process may include, but is not limited to, vacuum drying, heating drying under inert gas protection, spray drying, freeze drying or flash drying, etc., among which spray drying is preferred. For the conditions of spray drying, refer to The process conditions conventionally selected in the art will not be repeated here.

In S22 of the above preparation method, there is no special requirement for the method of heat treatment, as long as the temperature of the second dry mixture is raised to 300-500° C. without heat preservation, and the temperature is directly lowered to form the surface of the active component. A coating layer containing an amorphous metal compound may be sufficient. In the present invention, the second dry mixture is preferably heated to 300-500°C at a rate of 30-80°C/min. The temperature of the second dry mixture to 300-500° C. at a rate of 30-80° C./min is beneficial to better form a coating layer containing an amorphous metal compound on the surface of the material.

In S2 of the above preparation method, a coating layer containing an amorphous metal compound is mainly formed on the surface of the active component to reduce the water absorption rate and water content of the lithium manganese iron phosphate material. In order to further reduce the water absorption and moisture content of the prepared lithium iron manganese phosphate material, preferably the amorphous metal compound contained in the coating layer is selected from amorphous aluminum oxide, amorphous lithium phosphate, One or several mixtures of amorphous lithium pyrophosphate, amorphous iron pyrophosphate, amorphous lithium iron pyrophosphate, amorphous lithium manganese pyrophosphate and amorphous silver oxide.

Preferably, sources of materials that can form aluminum oxide include, but are not limited to, aluminum oxide, aluminum acetate, aluminum nitrate, or aluminum hydroxide. Sources of materials that can form lithium phosphate include lithium sources and phosphorus sources or lithium phosphorus sources, where lithium sources include but are not limited to lithium hydroxide or lithium carbonate, phosphorus sources include but are not limited to phosphoric acid, and phosphorus sources include but are not limited to dihydrogen phosphate Lithium or Lithium Phosphate. Sources of materials that can form lithium pyrophosphate include lithium sources and phosphorus sources or lithium phosphorus sources, where lithium sources include but are not limited to lithium hydroxide or lithium carbonate, phosphorus sources include but are not limited to phosphoric acid, and phosphorus sources include but are not limited to diphosphate diphosphate Lithium hydrogen or lithium phosphate or lithium pyrophosphate. Sources of materials from which iron pyrophosphate can be formed include iron sources and phosphorus sources, or ferrophosphorus sources. The iron source includes but not limited to ferric oxide or ferric acetate, the phosphorus source includes but is not limited to phosphoric acid, and the phosphorus iron source includes but is not limited to iron phosphate. Sources of materials that can form lithium iron pyrophosphate include lithium sources, iron sources and phosphorus sources, wherein lithium sources include but are not limited to lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate; iron sources include but are not limited to trioxide Diiron, ferric acetate or ferric phosphate, phosphorus sources include but are not limited to phosphoric acid, lithium dihydrogen phosphate, lithium phosphate. Sources of materials from which lithium manganese pyrophosphate can be formed include lithium sources, manganese sources, and phosphorus sources. Wherein lithium sources include but are not limited to lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate or lithium phosphate; manganese sources include but are not limited to manganese dioxide, manganese carbonate, manganese acetate or manganese tetroxide; phosphorus sources include but are not limited to phosphoric acid Lithium dihydrogen phosphate or lithium phosphate. Sources of materials that can form silver oxide include, but are not limited to, silver oxide, silver acetate, silver nitrate, or silver hydroxide.

In a preferred embodiment of the present invention, the above preparation method further includes the following steps: S3 uses the intermediate product obtained in S2 as a base material, and forms a conductive carbon layer on the surface of the intermediate product. The steps of forming the conductive carbon layer may refer to conventional methods and conventional process parameters in the art. In the present invention, preferably, the S3 includes the following steps: mixing the intermediate product obtained in S2 with the second carbon source (in a solvent, such as water), and drying to obtain a third dry mixture; heating the third dry mixture to 600 After -750°C, the temperature is maintained for 3-10 h to form the conductive carbon layer on the surface of the active component.

In S3 of the above preparation method, there is no special requirement for the mixing method of the intermediate product and the second carbon source, as long as the two are relatively uniformly dispersed in the solvent, for example, the two can be mixed relatively by stirring. Evenly, the stirring time is 15-50min.

In S3 of the above preparation method, the drying process may include, but is not limited to, vacuum drying, heating drying under inert gas protection, spray drying, freeze drying or flash drying, etc., among which spray drying is preferred. For the conditions of spray drying, refer to The process conditions conventionally selected in the art will not be repeated here.

In S3 of the above preparation method, there is no special requirement for the heating treatment, as long as the temperature of the third dry mixture is raised to 600-750° C. for 3-10 hours. In the present invention, the third dry mixture is preferably heated to 300-500°C at a rate of 2-10°C/min. The temperature of the second dry mixture to 300-500°C at a rate of 2-10°C/min is beneficial to better form an amorphous coating layer on the surface.

In the above preparation method of the present invention, it is preferred that both S1 and S2 are carried out in the presence of an inert gas throughout the entire process. Carrying out S1 (preparation of active components) and S2 (preparation of inner cladding layer with amorphous metal compound structure) in the presence of inert gas is beneficial to avoid the introduction of impurities and optimize the electrochemical performance of the prepared lithium manganese iron phosphate materials . The inert gas that can be used includes, but is not limited to, a mixture of one or more of nitrogen, argon, and helium.

Meanwhile, according to the third aspect of the present invention, a lithium iron manganese phosphate material is also provided, and the lithium iron manganese phosphate material is prepared by the above-mentioned preparation method of the present invention. The lithium iron manganese phosphate material includes an active component with a LiMn _x Fe _{1-xy My PO 4} /C structure, wherein 0≤x≤1, 0≤y≤1, and M is Co, Ni, Mg, Zn, one or more of V and Ti; and a coating layer containing an amorphous metal compound wrapped on the surface of the active component. Preferably, the particle size _D50 of the active component is 0.5-1.0 μm, and the thickness of the coating layer of the inorganic amorphous material is 1-5 nm.

Preferably, the amorphous metal compound in the coating layer is selected from amorphous aluminum oxide, amorphous lithium phosphate, amorphous lithium pyrophosphate, amorphous iron pyrophosphate, amorphous pyrophosphate One or several mixtures of lithium iron, amorphous lithium manganese pyrophosphate, and amorphous silver oxide

Preferably, the lithium iron manganese phosphate material further comprises a conductive carbon layer coated on the surface of the coating layer; preferably, the thickness of the conductive carbon layer is 2-10 nm.

Preferably, in the active component having the structure of LiMn _x Fe _{1-xy My PO 4} /C, the molar ratio of Li to the sum of Mn, Fe and M is 0.98-1.02:1; The content of element C in the component is 0.5-3.5 wt % of the total weight of the active component.

In addition, according to the fourth aspect of the present invention, a battery slurry is also provided, the battery slurry includes a lithium iron manganese phosphate material and a solvent, and the lithium iron manganese phosphate material is the above-mentioned lithium manganese iron phosphate of the present invention. Material. The solvent that can be used in the above battery slurry includes but is not limited to one of water and N-methylpyrrolidone.

There is no special requirement for the solid content of the battery slurry in the process of preparing the above-mentioned battery slurry, and an appropriate selection can be made according to the usage requirements of the battery slurry. Generally, the solid content in the battery slurry is 30-60 wt %, preferably 40-50 wt %, more preferably 45-50 wt %.

The above-mentioned battery paste of the present invention further includes a solvent, a binder and a conductive agent. The raw materials and dosages of the binder, the conductive agent and the solvent can all be selected with reference to the routine in the field. For example, the binder can be polyvinylidene fluoride, the conductive agent can be acetylene black, and lithium manganese iron phosphate materials (positive electrode active materials) The weight ratio to conductive agent and binder is 80:10:10. Solvents that can be used in the above battery slurry include, but are not limited to, one or more of water, ethanol, and methanol.

According to a fifth aspect of the present invention, there is further provided a positive electrode, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer comprises the lithium manganese iron phosphate of the present invention Material. The positive electrode provided by the present invention is prepared by using the battery slurry containing the lithium manganese iron phosphate material of the present invention. In view of the low water absorption rate of the lithium manganese iron phosphate material of the present invention, the water absorption rate of the positive electrode is also higher than that of the present invention. Low. Preferably, the current collectors can refer to conductive metal materials conventionally used in the art, for example, including but not limited to platinum (Pt) foil, palladium (Pd) foil, aluminum (Al) foil, and the like.

The present invention further provides a lithium battery, the lithium battery is equipped with a positive electrode, and the positive electrode is the above positive electrode. For the lithium battery provided by the present invention, by using the positive electrode material with low water content provided by the present invention, the residual water content in the battery pole piece is low, especially under high temperature storage, the water and electrolysis are reduced. The possibility of irreversible side reactions of the liquid to generate HF components avoids the deterioration of the electrode material being dissolved, and improves the storage capacity retention rate of the battery at high temperatures.

The following will further illustrate the lithium iron manganese phosphate material of the present invention, its preparation method, the positive electrode and the lithium battery, and its beneficial effects with reference to specific embodiments and comparative examples.

The test items and test methods involved in the following preparation examples, preparation comparative examples, examples and comparative examples are as follows:

In the following preparation examples and comparative preparation examples, inductively coupled plasma emission spectrometry (ICP) was used to determine the composition of the lithium iron manganese phosphate material of the present invention; transmission electron microscopy (TEM) was used to observe the composition of the lithium iron manganese phosphate material of the present invention. shape and particle size.

In the following preparation examples and comparative preparation examples, a laser particle size analyzer commercially available from Chengdu Jingxin Powder Testing Equipment Co., Ltd. was used to measure the average particle size (volume average particle size) of the lithium iron manganese phosphate material of the present invention. The thickness of the middle cladding layer of the lithium manganese iron phosphate material of the present invention is estimated and observed by using the particle size comparison method before and after, and the transmission electron microscope (TEM) pattern.

In the following preparation examples and comparative preparation examples, the same process conditions were adopted for the spray drying step, including the inlet air temperature being 200-300°C and the outlet air temperature being 80-200°C.

1. Preparation Example and Comparative Preparation Example

Preparation Example 1

It is used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound in the coating layer is amorphous aluminum oxide)

(1) Weigh 3.69 grams of lithium carbonate, 11.50 grams of ammonium dihydrogen phosphate, 7.98 grams of ferric oxide and 1.42 grams of sucrose, add them to a sand mill, grind at 2000 rpm for 3 hours, spray dry, and under nitrogen protection, at 0.1 ° C The heating rate of /min was slowly heated to 680 °C, the constant temperature was 5 h, and the natural cooling was performed to obtain an active component with a LiFePO ₄ /C structure, and the particle size D ₅₀ of the active component was 0.58 μm;

(2) Weigh 0.58 g of aluminum nitrate nonahydrate, add 1 L of water and 15.75 g of the above _- mentioned active component with LiFePO structure, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up 500°C with a temperature ramp rate of 30°C/min ℃, the temperature is directly lowered without heat preservation, and an amorphous aluminum oxide coating layer is formed on the surface of the active component to obtain an intermediate product, wherein the thickness of the coating layer is 3.9 nm;

(3) Weigh 1.16 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 5 ° C/min, maintain a constant temperature for 3 hours, and cool down the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P1, wherein the thickness of the conductive carbon layer is 8.2 nm.

(4) JEM-2010 (HR) transmission electron microscope tester was used to test the above-mentioned final product P1. Test conditions: The acceleration voltage is 200KV, and the vacuum degree is less than 2×10 ^-5 Pa. Test method: Disperse the final product P1 in ethanol solution, ultrasonically disperse it for 30min, drop it on the copper mesh, and vacuum dry it for 2h.

Test results: The TEM spectrum of the particle morphology of P1 prepared in Preparation Example 1 is shown in Figure 1. In Figure 1, it can be clearly seen that there are two coating layers on the surface of the active component, and the inner layer is an amorphous metal compound coating. The coating layer (low water absorption rate), and the outer layer is a conductive carbon layer (good conductivity). , has good electrical conductivity.

Preparation Example 2

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous lithium phosphate)

(1) Weigh 3.69 grams of lithium carbonate, 11.50 grams of ammonium dihydrogen phosphate, 7.98 grams of ferric oxide and 1.42 grams of sucrose, add them to a sand mill, grind at 2000 rpm for 3 hours, spray dry, and under nitrogen protection, at 2°C The heating rate of /min was slowly heated to 800 °C, the constant temperature was 20 h, and the natural cooling was performed to obtain an active component with a LiFePO ₄ /C structure, and the particle size D ₅₀ of the active component was 0.61 μm;

(2) Weigh 0.16 g of phosphoric acid (content 85wt%) and 0.17 g of lithium hydroxide monohydrate, add 1 L of water and 15.78 g of the above-mentioned active components, stir for 30 min, spray dry, under nitrogen protection, at a temperature of 80°C/min The heating rate is slowly increased to 300 ° C, and the temperature is directly lowered without heat preservation, and an amorphous lithium phosphate coating layer is formed on the surface of the active component to obtain an intermediate product, and the thickness of the coating layer in the obtained intermediate product is 3.5 nm;

(3) Weigh 1.16 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, under nitrogen protection, slowly heat up to 600 ° C at a heating rate of 10 ° C/min, keep the temperature for 10 h, and cool down, the obtained The final product P2, in which the thickness of the conductive carbon layer is 8.2 nm.

Preparation Example 3

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous lithium pyrophosphate)

(1) Weigh 3.69 grams of lithium carbonate, 18.68 grams of iron phosphate dihydrate and 1.42 grams of sucrose, add to a sand mill, grind at 1000 rpm for 3 hours, spray dry, and slowly heat up at a heating rate of 0.1°C/min under nitrogen protection 800°C, constant temperature for 5h, and natural cooling to obtain an active component with a LiFePO ₄ /C structure, and the particle size D ₅₀ of the active component is 0.75 μm;

(2) Weigh 0.31 g of phosphoric acid (content 85wt%) and 0.34 g of lithium hydroxide, add 1 L of water and 15.75 g of the above-mentioned active components, stir for 30 min, spray dry, under nitrogen protection, at a heating rate of 30°C/min Slowly raise the temperature to 500°C, and directly drop the temperature without heat preservation to form an amorphous lithium pyrophosphate coating layer on the surface of the active component to obtain an intermediate product, wherein the thickness of the amorphous lithium pyrophosphate coating layer is 2.4 nm;

(3) Weigh 1.0 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 750 ° C at a heating rate of 10 ° C/min, maintain a constant temperature for 6 h, and cool down the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P3, wherein the thickness of the conductive carbon layer is 7.1 nm.

Preparation Example 4

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous iron pyrophosphate)

(1) In the same way as step (1) in Preparation Example 3, an active component having a LiFePO ₄ /C structure is obtained, and the particle size D ₅₀ of the active component is 0.74 μm;

(2) Weigh 0.24 g of ferric phosphate dihydrate, add 1 L of water and 15.75 g of the above-mentioned active components, stir for 30 min, spray-dry, under nitrogen protection, slowly heat up to 700 ° C with a heating rate of 30 ° C/min, directly without insulation Cooling to form an amorphous iron pyrophosphate coating layer on the surface of the active component to obtain an intermediate product, wherein the thickness of the coating layer is 2.1 nm;

(3) Weigh 1.16 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 10 ° C/min, keep the temperature for 10 hours, and cool down the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P4, wherein the thickness of the conductive carbon layer is 7.0 nm.

Preparation Example 5

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous lithium iron pyrophosphate)

(1) In the same way as step (1) in Preparation Example 3, an active component having a LiFePO ₄ /C structure is obtained, and the particle size D ₅₀ of the active component is 0.74 μm;

(2) Weigh 0.10 g of ferric phosphate dihydrate, 0.08 g of phosphoric acid (content 85wt%) and 0.02 g of lithium carbonate, add 1 L of water and 15.75 g of the above-mentioned active components, stir for 30 min, spray dry, under nitrogen protection, at 30 The heating rate of ℃/min is slowly increased to 500 ℃, and the temperature is directly lowered without heat preservation to form an amorphous lithium ferrous pyrophosphate coating layer on the surface of the active component to obtain an intermediate product, wherein the thickness of the coating layer is 1.4 nm;

(3) Weigh 0.50 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 10 ° C/min, maintain a constant temperature for 10 h, and cool the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P5, wherein the thickness of the conductive carbon layer is 3.5 nm.

Preparation Example 6

It is used to describe the lithium manganese iron phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous lithium manganese pyrophosphate)

(1) In the same way as step (1) in Preparation Example 3, an active component having a LiFePO ₄ /C structure is obtained, and the particle size D ₅₀ of the active component is 0.75 μm;

(2) Weigh 0.12 g of manganese carbonate, 0.12 g of phosphoric acid (content 85% by weight) and 0.07 g of lithium carbonate, add 1 L of water and 15.75 g of the above-mentioned active components, stir for 30 min, spray dry, under nitrogen protection, at 30°C/ The heating rate of min is slowly heated to 500 °C, and the temperature is directly lowered without heat preservation to form an amorphous lithium manganese pyrophosphate coating layer on the surface of the active component, and an intermediate product is obtained, wherein the thickness of the coating layer is 1.4 nm;

(3) Weigh 1.00 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 10 ° C/min, maintain a constant temperature for 10 h, and cool down the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P6, wherein the thickness of the conductive carbon layer is 7.1 nm.

Preparation Example 7

It is used to describe the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous silver oxide)

(1) In the same way as step (1) in Preparation Example 3, an active component having a LiFePO ₄ /C structure is obtained, and the particle size D ₅₀ of the active component is 0.75 μm;

(2) Weigh 0.08 g of silver oxide, add 1 L of water and 15.78 g of the above-mentioned active components, stir for 30 min, spray-dry, under nitrogen protection, slowly heat up to 500 ° C with a heating rate of 30 ° C/min, directly cool down at 500 ° C without insulation An amorphous silver oxide coating layer is formed on the surface of the active component to obtain an intermediate product, wherein the thickness of the coating layer is 1.2 nm;

(3) Weigh 1.0 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned intermediate product, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 10 ° C/min, maintain a constant temperature for 10 h, and cool down the intermediate product The surface is coated with a conductive carbon layer to obtain the final product P7, wherein the thickness of the conductive carbon layer is 6.0 nm.

Preparation Example 8

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous iron pyrophosphate)

Preparation method of lithium iron manganese phosphate material: refer to Preparation Example 3, the difference is:

(1) Weigh 3.69 grams of lithium carbonate, 4.60 grams of manganese carbonate, 9.34 grams of iron phosphate, 1.19 grams of cobalt carbonate and 1.42 grams of sucrose, add to a sand mill, grind at 1000 rpm for 3 hours, spray dry, and under nitrogen protection, at 0.1 The heating rate of ℃/min was slowly heated to 750 ℃, the constant temperature was 5 h, and the natural cooling was performed to obtain an active component with a structure of LiMn _0.4 Fe _0.5 Co _0.1 PO ₄ , and the particle size D ₅₀ of the active component was 0.76 μm; The final product obtained is designated as P8.

Preparation Example 9

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous iron pyrophosphate)

Preparation method of lithium iron manganese phosphate material: refer to Preparation Example 3, the difference is:

In step (1), the temperature is slowly increased to 800°C at a heating rate of 3°C/min, the temperature is kept constant for 5 hours, and then cooled naturally to obtain an active component with a LiFePO ₄ /C structure. The particle size D ₅₀ of the active component is 0.77 μm. The final product obtained by this method is designated P9.

Preparation Examples 10-11

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous iron pyrophosphate)

Preparation method of lithium iron manganese phosphate material: refer to Preparation Example 3, the difference is:

In step (2), the temperature is slowly increased to 500°C at the heating rate of 20 and 100°C/min respectively, and the temperature is directly lowered without heat preservation to form an amorphous lithium pyrophosphate coating layer on the surface of the active component to obtain an intermediate product, wherein the amorphous lithium pyrophosphate is obtained. The thicknesses of the lithium pyrophosphate coating layers are 2.2 nm and 2.9 nm, respectively. The final products obtained by this method are designated P10 and P11.

Preparation Example 12

Used to illustrate the lithium iron manganese phosphate material of the present invention and its preparation method (wherein the amorphous metal compound is amorphous iron pyrophosphate)

Preparation method of lithium iron manganese phosphate material: refer to Preparation Example 3, the difference is:

In step (3), the temperature is slowly increased to 750°C at a heating rate of 15°C/min, the temperature is kept constant for 6 hours, and the surface of the intermediate product is cooled to coat a conductive carbon layer to obtain the final product P12, wherein the thickness of the conductive carbon layer is 6.8 nm. The final product obtained by this method is designated P12.

Comparative Preparation Example 1

For comparative description of the present invention, lithium iron manganese phosphate material and preparation method thereof

(1) with step (1) in embodiment ₁ , obtain the active component with LiFePO structure;

(2) Weigh 1.16 g of sucrose, add 100 mL of water and 15.75 g of the above-mentioned active components, stir for 30 min, spray dry, and under nitrogen protection, slowly heat up to 700 ° C at a heating rate of 5 ° C/min, maintain a constant temperature for 3 hours, and cool down to obtain the final Product DP1.

(3) JEM-2010 (HR) transmission electron microscope tester was used to test the above-mentioned final product P1. Test conditions: The acceleration voltage is 200KV, and the vacuum degree is less than 2×10 ^-5 Pa. Test method: Disperse the final product DP1 in ethanol solution, ultrasonically disperse it for 30min, drop it on the copper mesh, and dry it in vacuum for 2h.

Test results: The TEM spectrum of the particle morphology of DP1 prepared in Comparative Preparation Example 1 is shown in Figure 2. In Figure 2, it can be clearly seen that there is a conductive carbon layer coating on the surface of the active component, which does not exist. Amorphous metal compound coating. Although the lithium manganese iron phosphate material with this structure increases the thickness of the conductive carbon layer, there is no amorphous metal compound coating layer in it. Li binding.

Comparative Preparation Example 2

Referring to the lithium iron manganese phosphate material prepared by the method in Example 1 of the Chinese Patent Application No. 200910053346, it is denoted as DP2.

Comparative Preparation Example 3

Referring to the lithium iron manganese phosphate material prepared by the method in Example 1 in the Chinese patent application with the application number of 200910044154, it is denoted as DP3.

Two, embodiment 1-12 and comparative example 1-3

It is used to describe the positive electrode of the present invention and its preparation method.

Preparation method: Dissolve lithium manganese iron phosphate materials, acetylene black, and polyvinylidene fluoride (purchased from Dongguan Qingfeng Plastic Materials Co., Ltd., brand name FR900) in N-methylpyrrolidone in a weight ratio of 80:10:10 A battery slurry with a solid content of 50 wt % was formed in the medium, and the slurry obtained after stirring was coated on an aluminum foil with a thickness of 25 μm, and baked at 110 ° C ± 5 ° C to form a material layer with a thickness of 20 μm, A positive electrode material is obtained. Table 1 shows the comparison relationship between the prepared positive electrode and the lithium iron manganese phosphate materials contained therein.

Table 1.

Positive electrode material Lithium Iron Manganese Phosphate Materials Positive electrode material Lithium Iron Manganese Phosphate Materials S1 P1 S2 P2 S3 P3 S4 P4 S5 P5 S6 P6 S7 P7 S8 P8 S9 P9 S10 P10 S11 P11 S12 P12 DS1 DP1 DS2 DP2 DS3 DP3

test:

The lithium iron manganese phosphate materials P1-P12 and DP1-DP3 prepared in Preparation Examples 1-12 of the present invention and Comparative Preparation Examples 1-3, respectively, as well as the positive electrodes prepared in Examples 1-12 of the present invention and Comparative Examples 1-3 S1-S12 and DS1-DS12 for performance testing.

(1) Moisture content of lithium iron manganese phosphate materials: Prepare lithium iron manganese phosphate materials according to the methods in Preparation Examples 1 to 12 and Comparative Preparation Examples 1 to 3, and directly test the lithium iron manganese phosphate materials after sintering. moisture content.

The test method includes: first test the moisture content M0 of the blank bottle, then weigh 0.2g of the sample, and under the condition of the air flow rate of 40ml/min, the temperature is raised to 200°C at a heating rate of 15°C/min to obtain the total moisture content M1 , then, the moisture content of the lithium iron manganese phosphate material is M2=M1-M0.

Test results: as shown in Table 2:

Table 2

Example Moisture content (ppm) Example Moisture content (ppm) P1 980.4 P2 863.7 P3 250.3 P4 525.2 P5 343.3 P6 344.6 P7 350.0 P8 258.3 P9 325.6 P10 550.0 P11 725.0 P12 601.2 DP1 3860 DP2 2068.3 DP3 2845.2

(2) Moisture content of the positive electrode (equivalent to the water absorption rate of the lithium iron manganese phosphate materials): The lithium iron manganese phosphate materials prepared in Preparation Examples 1 to 12 and Comparative Preparation Examples 1 to 3 were mixed in the same time period. The water content of the positive electrodes S1-S12 and DS1-DS3 was measured after the positive electrode was prepared inside.

The test method includes: first test the moisture content N0 of the blank bottle, then weigh 0.2g of the sample, and under the condition of the air flow rate of 40ml/min, the temperature is raised to 200°C at a heating rate of 15°C/min to obtain the total moisture content N1 , then the water absorption rate of the lithium iron manganese phosphate material is N2=N1-N0-M2, where M2 is the water content of the lithium iron manganese phosphate material.

Test results: as shown in Table 3:

table 3.

Example Moisture content (%) Example Moisture content (%) S1 876.5 S2 1106.4 S3 412.7 S4 875.4 S5 572.1 S6 574.3 S7 583.3 S8 418.7 S9 1041.7 S10 916.7 S11 1208.3 S12 1002.3 DS1 2880.2 DS2 2106.4 DS3 3670.4

As can be seen from the data in Table 2 and Table 3: the water content and water absorption of the lithium iron manganese phosphate materials prepared according to Examples 1 to 12 of the preparation method of the present invention are relatively low, which is obviously better than that of the comparative examples. 1-3 The prepared lithium iron manganese phosphate materials have both water content and water absorption.

3. Implementation Application Example 1-12 and Comparative Application Example 1-3

It is used to describe the lithium battery of the present invention and its preparation method.

Preparation method: Lithium-ion monolithic batteries T1-T12 and DT1-DT3 were fabricated by implementing the positive electrodes S1-S12 and DS1-DS3 prepared in Application Examples 1-12 and Comparative Examples 1-3. The negative electrode material in the fabricated batteries was graphite. The diaphragm material is PVDF (polyvinylidene fluoride, which is commercially available from Arkema (Changshu) Fluorine Chemical Co., Ltd. with the brand name of PVDF HSV900), and the electrolyte is 1mol/ _LLiPF6 /(EC+DMC) (wherein LiPF6 is lithium hexafluorophosphate, EC is ethylene carbonate, DMC is dimethyl carbonate, and the volume ratio of EC to DMC is 1:1).

The comparison relationship between the prepared lithium battery and the positive electrode material contained therein is shown in Table 4.

Table 4.

Positive electrode material Lithium Iron Manganese Phosphate Materials Positive electrode material Lithium Iron Manganese Phosphate Materials T1 S1 T2 S2 T3 S3 T4 S4 T5 S5 T6 S6 T7 S7 T8 S8 T9 S9 T10 S10 T11 S11 T12 S12 DT1 DS1 DT2 DS2 DT3 DS3

test:

The performance tests were performed on the lithium batteries T1-T12 and DT1-DT3 prepared by the application examples 1-12 and the comparative application examples 1-3, respectively.

(1) Test items and methods:

①, mass specific capacity: put the lithium-ion batteries prepared above on the test cabinet, first charge at 0.1C with constant current and constant voltage, the charging range is 2.5-4.35V, record the first discharge capacity of the battery, and record the battery again. Discharge capacity, and calculate the mass specific capacity of the battery according to the following formula.

Mass specific capacity = battery first discharge capacity (mAh)/positive electrode material weight (g).

②、Capacity retention rate of lithium battery stored at high temperature (60℃) for 25 days: first charge and discharge the battery at 0.1C current for one week, and record the discharge capacity C0; After 7 days of storage, take out the battery to cool, discharge to the cut-off voltage of 2.5V, record the remaining capacity C1, then the high temperature capacity retention rate = (C0/C1)*100%.

(3) Test results: as shown in Table 5:

table 5.

As can be seen from the data in Table 5, the initial capacity of the batteries T1-T3 prepared according to the application examples 1 to 12 according to the present invention was adversely affected (see mass specific capacity data), and had excellent high temperature capacity retention; and The initial capacity of the batteries DT1-DT3 prepared according to Comparative Application Examples 1 to 3 was significantly affected, and the high temperature capacity retention rate was also relatively poor.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, These simple modifications belong to the protection scope of the present invention.

In addition, it should be noted that each specific technical feature described in the above-mentioned specific implementation manner may be combined in any suitable manner under the circumstance that there is no contradiction. In order to avoid unnecessary repetition, the present invention will not describe various possible combinations.

In addition, the various embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the contents disclosed in the present invention.

Claims (13)

1. The lithium iron manganese phosphate material is characterized by comprising LiMn_xFe_{1-x- y}M_yPO₄The active component of the structure/C, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and M is one or more of Co, Ni, Mg, Zn, V and Ti; and a coating layer coated on the surface of the active component, wherein the coating layer contains an amorphous metal compound,

the particle size D50 of the active component is 0.5-1.0 μm, and the thickness of the coating layer is 1-5 nm;

the lithium iron manganese phosphate material also comprises a conductive carbon layer coated on the surface of the coating layer;

the amorphous metal compound is selected from one or a mixture of more of amorphous ferric pyrophosphate, amorphous ferrous lithium pyrophosphate, amorphous manganese lithium pyrophosphate and amorphous silver oxide;

the thickness of the conductive carbon layer is 2-10 nm;

the compound has LiMn_xFe_1-x-yM_yPO₄In the active component of the structure/C, the molar ratio of Li to the sum of Mn, Fe and M is 0.98-1.02: 1;

the content of the C element in the active component is 0.5-3.5 wt% of the total weight of the active component.

2. The preparation method of the lithium iron manganese phosphate-based material according to claim 1, comprising the steps of:

s1, providing LiMn_xFe_1-x-yM_yPO₄The active component of the structure/C, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and M is one or more of Co, Ni, Mg, Zn, V and Ti;

and S2, taking the active component as a base material, and forming a coating layer containing an amorphous metal compound on the surface of the active component.

3. The preparation method according to claim 2, wherein the preparation method of the active ingredient in S1 comprises the following steps:

s11, mixing a lithium source, an optional iron source, an optional manganese source, an optional M source, a phosphorus source and a first carbon source in proportion, and drying to obtain a first dry mixture;

s12, sintering the first dry mixture at 600-800 ℃ for 5-30h at constant temperature to form the active component.

4. The preparation method as claimed in claim 3, wherein the first dry mixture is heated to 600-800 ℃ at a rate of 0.1-2 ℃/min in the S12.

5. The preparation method according to claim 3, wherein in the S11, the molar ratio of the lithium source calculated as Li to the optional iron source, the optional manganese source and the optional M source calculated as Fe + Mn + M is 0.98-1.02: 1.

6. the preparation method according to claim 2, wherein the S2 includes the steps of:

s21, mixing the active component with a material source for forming the amorphous metal compound, and drying to obtain a second dry mixture;

s22, heating the second dry mixture to 300-500 ℃ and directly cooling without heat preservation to form the coating layer containing the amorphous metal compound on the surface of the active component.

7. The preparation method as claimed in claim 6, wherein the temperature of the second dry mixture in the step S22 is raised to 300-500 ℃ at a rate of 30-80 ℃/min.

8. The method of manufacturing of claim 2, wherein the method of manufacturing further comprises the steps of:

s3, mixing the intermediate product obtained in the S2 with a second carbon source, drying to obtain a third dry mixture, heating the third dry mixture to 600-750 ℃, and then preserving heat for 3-10h to form a conductive carbon layer on the surface of the intermediate product.

9. The preparation method as claimed in claim 8, wherein the third dry mixture is heated to 600-750 ℃ at a rate of 2-10 ℃/min in the S3.

10. A lithium iron manganese phosphate-based material, characterized in that the lithium iron manganese phosphate-based material is prepared by the preparation method of any one of claims 2 to 9.

11. A battery paste comprising a lithium iron manganese phosphate-based material and a solvent, characterized in that the lithium iron manganese phosphate-based material is the lithium iron manganese phosphate-based material of claim 1 or 10.

12. A positive electrode comprising a current collector and a positive active material layer disposed on the current collector, characterized in that the positive active material layer comprises the lithium iron manganese phosphate-based material of claim 1 or 10.

13. A lithium battery having a positive electrode mounted therein, wherein the positive electrode material comprises the positive electrode according to claim 12.

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