CN115810744A - Double-coated positive electrode material and preparation method and application thereof - Google Patents

Abstract

The invention provides a double-coated positive electrode material and its preparation method and application. The double-coated positive electrode material includes an inner core of a positive electrode material containing manganese, and a first shell layer and a second shell layer coated on the surface of the inner core in turn. Shell layer; the first shell layer is a boron coating layer, and the second shell layer is a carbon coating layer. In the present invention, the manganese-containing positive electrode material is used as the core, the boron coating layer coated on the surface of the core is used as the first shell layer, and the carbon coating layer coated on the surface of the first shell layer is used as the second shell layer, thereby forming double-coated cathode material. As the first shell layer, the boron coating can not only improve the electrical conductivity and structural stability of the cathode material, but also enhance the interaction between the carbon coating and the inner core of the cathode material containing manganese under the action of the boron coating. , so that the carbon coating layer can be uniformly coated, which effectively improves the electrical conductivity of the double-coated cathode material. At the same time, the double-coated cathode material can maintain a high capacity at a high rate, and has an excellent high-rate capacity retention rate.

Description

A double-coated positive electrode material and its preparation method and application

technical field

The invention belongs to the field of electrode materials, and in particular relates to a double-coated positive electrode material and a preparation method and application thereof.

Background technique

In recent years, as the energy density of lithium iron phosphate has approached the theoretical limit, lithium iron manganese phosphate, as an advanced version of lithium iron phosphate, has received more and more attention. Compared with lithium iron phosphate, lithium iron phosphate has more "manganese" elements. Manganese has the characteristics of high voltage. The introduction of manganese into the positive electrode material can increase the voltage. The higher the voltage, the higher the energy density. The voltage of lithium iron phosphate The platform is as high as 4.1V, which is much higher than the 3.4V of lithium iron phosphate, so its theoretical energy density under the same conditions can be more than 15% higher than that of lithium iron phosphate, which has a good development prospect. However, manganese is a metal element with very poor conductivity, so the conductivity of lithium iron phosphate is further lower than that of lithium iron phosphate, and the electronic conductivity is only 10 ^-13 S/cm.

Generally, the conductivity of lithium manganese iron phosphate is improved by carbon coating. For example, CN102738465B discloses a preparation method of lithium manganese iron phosphate positive electrode composite material, by combining lithium source, ferric iron source, manganese dioxide and carbon source Put it into a ball mill jar, add an appropriate amount of dispersant and complexing agent, then put the ball mill jar on a ball mill and mill at 200-500r/min for 4-6h; then dry the mixed material obtained after ball milling and grind again, A LiMn _x Fe _1-x PO ₄ precursor is obtained; after calcination, a carbon-coated lithium manganese iron phosphate cathode material is obtained. However, because the particles of lithium manganese iron phosphate are small, only one-third of the ternary cathode material, the specific surface area is large, the surface structure is complex, and the affinity with carbon is too poor, so the above method cannot be used to obtain a uniform carbon coating. Coating, and in order to coat completely, it is necessary to use a carbon source with a proportion as high as 30wt%, which leads to a decrease in gram capacity.

CN111900344B discloses a method for preparing a carbon-coated lithium manganese iron phosphate positive electrode material. First, the transition metal salt solution A, the phosphorus solution B and the ammonia solution C are added dropwise to the reactor at the same time according to the molar ratio of Mn and Fe to form a The precursor of lithium manganese iron phosphate cathode material; then the precursor is mixed with lithium source according to the molar ratio, and coated carbon source and doping metal compound are added, and calcined under the protection of an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate cathode material. The above method uses simple solid phase coating, it is difficult to form a uniform coating layer on the surface, and the coating layer is easy to fall off during the cycle.

CN109888205A discloses a nano-micro spherical carbon-coated lithium manganese iron phosphate composite material and its preparation method, lithium battery anode material, and lithium battery. The outer carbon layer, the chemical composition of the lithium manganese iron phosphate is LiMn _1-x Fe _x PO ₄ , wherein, 0.1≤x≤1, the particle size D50 of the composite material is 1 to 10 μm, and the lithium manganese iron phosphate The mass content of carbon element is 1% to 10%. The patent uses nano-spherical lithium manganese iron phosphate, which makes it difficult to form a uniform coating layer on the surface, which will aggravate the shedding of the coating layer during cycling.

Therefore, how to improve the affinity between the core of the positive electrode material and the carbon coating layer, so as to form a uniform carbon coating layer, so that the electrical conductivity of the positive electrode material can be further improved, and at the same time, the positive electrode material can maintain a high capacity at a high rate. technical issues to be resolved

Contents of the invention

Aiming at the deficiencies of the prior art, the object of the present invention is to provide a double-coated positive electrode material and its preparation method and application. In the present invention, the manganese-containing positive electrode material is used as the core, the boron coating layer coated on the surface of the core is used as the first shell layer, and the carbon coating layer coated on the surface of the first shell layer is used as the second shell layer, thereby forming Double-coated cathode material. As the first shell layer, the boron coating can not only improve the electrical conductivity and structural stability of the cathode material, but also enhance the interaction between the carbon coating and the inner core of the manganese-containing cathode material under the action of the boron coating. , so that the carbon coating layer can be uniformly coated, which effectively improves the electrical conductivity of the double-coated cathode material. At the same time, the double-coated cathode material can maintain a high capacity at a high rate, and has an excellent high-rate capacity retention rate.

To achieve this purpose of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a double-coated positive electrode material, the double-coated positive electrode material includes a core of a positive electrode material containing manganese, and a first shell layer and a second shell layer that are sequentially coated on the surface of the core core ;

The first shell layer is a boron clad layer, and the second shell layer is a carbon clad layer.

In the present invention, the manganese-containing positive electrode material is used as the core, the boron coating layer coated on the surface of the core is used as the first shell layer, and the carbon coating layer coated on the surface of the first shell layer is used as the second shell layer, thereby forming Double-coated cathode material. The boron coating layer is used as the first shell layer, and the boron in it can form Mn-B bond with the manganese in the inner core to improve the conductivity of the material, and at the same time prevent Mn from detaching from the surface of the positive electrode material during charging and discharging, stabilizing the material. structure; in addition, the boron coating, as the middle layer between the inner core and the carbon coating, plays an important role as a bridge. Under the action of the boron coating, the interaction between the carbon coating and the inner core of the manganese-containing cathode material is obtained. Enhanced, so that the carbon coating layer can be uniformly coated, effectively improving the conductivity of the double-coated cathode material, and at the same time, the double-coated cathode material can maintain a high capacity at a high rate, and has excellent high-rate capacity retention Rate.

In the present invention, the inner core of the manganese-containing positive electrode material has poor affinity with the carbon coating layer. If the boron coating layer is not added, it is difficult to obtain a uniform carbon coating layer, and the carbon coating layer is easily removed from the manganese-containing positive electrode material during the cycle. fall off.

Preferably, based on 100% of the mass of the double-coated positive electrode material, the mass fraction of the boron coating layer is 1-3%, such as 1%, 1.2%, 1.4%, 1.6%, 1.8% %, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%, etc.

In the present invention, if the mass fraction of the boron coating layer is too low, the uniformity of the subsequent carbon coating layer will be affected, resulting in the inability to improve the conductivity and rate performance of the material; if the mass fraction of the boron coating layer is too high, then Will affect the gram capacity.

Preferably, the mass ratio of the boron coating layer and the carbon coating layer is 1:(0.5-2), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1 :1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2 etc.

In the present invention, if the mass ratio of the boron coating layer and the carbon coating layer is too small, that is, the proportion of the boron coating layer is too low, it is difficult to form a uniform carbon coating layer, resulting in a decrease in electrical conductivity; if the boron coating layer If the mass ratio of the carbon coating layer to the carbon coating layer is too large, that is, the proportion of the boron coating layer is too high, the conductivity of the material will be reduced because the conductivity of boron is lower than that of carbon.

Preferably, based on 100% of the mass of the double-coated positive electrode material, the mass content of the inner core of the manganese-containing positive electrode material is 91-98.5%, for example, it can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 98.5%, etc.

Preferably, the manganese-containing positive electrode material includes any one of lithium manganese iron phosphate, lithium manganate or lithium-rich manganese-based materials, preferably lithium manganese iron phosphate.

In a second aspect, the present invention provides a method for preparing the double-coated positive electrode material as described in the first aspect, the preparation method comprising the following steps:

(1) Mixing the raw material of the manganese-containing positive electrode material with the boron source, and obtaining an intermediate product after one calcining;

(2) Mixing the intermediate product described in step (1) with a carbon source, followed by secondary calcination to obtain the double-coated positive electrode material.

In the present invention, the boron coating on the surface of the manganese-containing positive electrode material can enhance the interaction between the carbon source and the manganese-containing positive electrode material, so that the carbon source can be evenly coated on the surface of the intermediate product, forming a uniform carbon coating layer, thereby significantly Improve the conductivity of the double-coated positive electrode material and improve the electrochemical performance of the material.

Preferably, the boron source is boron-based Lewis acid.

It should be noted that boron-based Lewis acids can attract groups with lone pairs of electrons.

Preferably, the boron-based Lewis acid includes any one or a combination of at least two of boric acid, borate or boron oxide. Exemplarily, the borate can be, for example, lithium borate, manganese borate, sodium tetraborate or Ferric borate, etc.

Preferably, the mass content of the boron source is 1-5% based on 100% of the raw material of the manganese-containing positive electrode material. For example, it may be 1%, 2%, 3%, 4% or 5%.

Preferably, the carbon source is an organic carbon source.

In the present invention, the boron-based Lewis acid can attract the organic carbon source with a lone pair of electrons, thereby enhancing the interaction between the organic carbon source and lithium manganese iron phosphate, so that the organic carbon source can be uniformly coated on the boron-coated The surface of the layer effectively improves the conductivity of the double-coated positive electrode material.

Preferably, the functional group of the organic carbon source includes any one or a combination of at least two of hydroxyl, imino or amino groups. Exemplarily, the organic carbon source may be glucose or 2-mercaptoimidazole.

Preferably, based on 100% of the raw material of the manganese-containing positive electrode material, the mass content of the carbon source is 1-6%, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5% , 4%, 4.5%, 5%, 5.5% or 6%, etc.

In the present invention, if the mass content of the carbon source is too high, the formed carbon coating layer is too thick, which will reduce the gram capacity of the positive electrode material; if the mass content of the carbon source is too low, the rate performance of the positive electrode material will be reduced.

As a preferred embodiment, the raw materials of the manganese-containing positive electrode material include manganese source, lithium source, phosphorus source and iron source.

Preferably, the manganese source includes any one or a combination of at least two of manganese carbonate, manganese dioxide, manganese acetate or manganese nitrate.

Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate.

Preferably, the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate or phosphorus pentoxide.

Preferably, the iron source includes any one or a combination of at least two of iron phosphate, iron oxide, iron oxalate or iron sulfate, such as iron phosphate, ferric iron tetroxide , iron oxalate or iron sulfate, etc.

Preferably, the way of mixing in the step (1) is ball milling, the speed of the ball milling is 300-600rpm, for example, it can be 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm or 600rpm, etc., the time of the ball milling is 2-8h, such as 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc.

Preferably, the method of mixing in the step (2) is ball milling, the speed of the ball milling is 200-500rpm, such as 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500rpm, etc., the time of the ball milling is 2-8h, for example, can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc.

Preferably, the temperature of the primary calcination is 500-600°C, such as 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C wait.

Preferably, the time for the primary calcination is 4-10 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

Preferably, the secondary calcination temperature is 600-800°C, such as 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C or 800°C ℃ and so on.

Preferably, the time for the secondary calcination is 4-10 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

Preferably, the atmosphere for the primary calcination and the secondary calcination is an inert atmosphere, and the gas in the inert atmosphere includes any one or a combination of at least two of nitrogen, helium or argon.

As a preferred technical solution, the preparation method comprises the following steps:

(1) Manganese source, lithium source, phosphorus source, iron source and boron-based Lewis acid with a mass content of 1-5% are mixed by ball milling at 300-600rpm for 2-8h, and calcined at 500-600°C for 4-10h once, get intermediate products;

(2) The intermediate product described in step (1) is mixed with the organic carbon source with a mass content of 1-6% at 200-500rpm for 2-8h, and then calcined for 4-10h in an inert atmosphere at 600-800°C, The double-coated positive electrode material was obtained.

In a third aspect, the present invention provides a lithium ion battery, wherein the positive electrode of the lithium ion battery includes the double-coated positive electrode material described in the first aspect.

The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above-mentioned numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention will not exhaustively list the ranges. The specific pip value to include.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention provides a double-coated positive electrode material. The double-coated positive electrode material uses a manganese-containing positive electrode material as the core, and a boron coating layer coated on the surface of the core as the first shell layer. The carbon coating layer coated on the surface of the first shell layer is the second shell layer. As the first shell layer, the boron coating layer can not only improve the electrical conductivity and structural stability of the cathode material, but also under the action of the boron coating layer, the interaction between the carbon coating layer and the inner core of the cathode material containing manganese has been improved. Enhanced, so that the carbon coating layer can achieve uniform coating, effectively improving the conductivity of the double-coated positive electrode material;

(2) The double-coated positive electrode material provided by the present invention can maintain a high capacity at a high rate, and has an excellent high rate capacity retention rate.

Description of drawings

FIG. 1 is an SEM image of the double-coated cathode material provided in Example 1 of the present invention.

FIG. 2 is a charge-discharge curve diagram of the double-coated positive electrode material provided in Example 1 of the present invention.

Detailed ways

It should be understood that the terms "first", "second" and so on are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features.

The technical solutions of the present invention will be further described below through specific embodiments. It should be clear to those skilled in the art that the embodiments are only for helping to understand the present invention, and should not be regarded as specific limitations on the present invention.

Example 1

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 96.9%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 2%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :2.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric phosphate, manganous carbonate, phosphoric acid, lithium carbonate, boron oxide, and reducing agent glucose according to the molar ratio of 1.6:0.4:0.4:1:0.05:0.07, mill in a ball mill at 600rpm for 2h, and then place Calcined at 600°C for 4 hours at 600°C in a nitrogen atmosphere furnace, and obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boron oxide is 1.1%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add glucose, and ball mill for 2 hours at 500 rpm, then place it in an atmosphere furnace fed with nitrogen for secondary calcination at 800°C for 10 hours , the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of glucose is 5%.

Figure 1 shows the SEM image of the double-coated positive electrode material provided in this example. It can be seen from the figure that the lithium manganese iron phosphate positive electrode material prepared in this example has complete particles and uniform particle size distribution.

Figure 2 shows the charge and discharge curves of the double-coated positive electrode material provided in this example. It can be seen from the figure that the gram capacity of the lithium manganese iron phosphate positive electrode material prepared in this example can reach 156.3mAh/g.

Example 2

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 98.3%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 0.6%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :0.6.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric phosphate, manganous carbonate, phosphoric acid, lithium carbonate, boron oxide, and reducing agent glucose according to the molar ratio of 1.6:0.4:0.4:1:0.05:0.07, mill in a ball mill at 600rpm for 2h, and then place Calcined at 600°C for 4 hours at 600°C in a nitrogen atmosphere furnace, and obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boron oxide is 1.1%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add glucose, and ball mill at 600rpm for 2h, then place it in an atmosphere furnace fed with nitrogen for secondary calcination at 800°C for 10h , the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of glucose is 1.5%.

Example 3

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 97.1%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 1.8%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :1.8.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric phosphate, manganous carbonate, phosphoric acid, lithium carbonate, boron oxide, and reducing agent glucose according to the molar ratio of 1.6:0.4:0.4:1:0.05:0.07, mill in a ball mill at 600rpm for 2h, and then place Calcined at 600°C for 4 hours at 600°C in a nitrogen atmosphere furnace, and obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boron oxide is 1.1%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add 2-mercaptoimidazole, and ball mill it at 600rpm for 2h, then place it in an atmosphere furnace fed with nitrogen gas at 800°C for two Secondary calcination for 10 hours, and the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of 2-mercaptoimidazole is 5%.

Example 4

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 96.9%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 2%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :2.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric phosphate, manganous carbonate, phosphoric acid, lithium carbonate, boron oxide, and reducing agent glucose according to the molar ratio of 1.6:0.4:0.4:1:0.05:0.07, mill in a ball mill at 600rpm for 2h, and then place Calcined at 500°C for 4 hours at 500°C in an atmosphere furnace filled with nitrogen, and then obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boron oxide is 1.1%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add glucose, ball mill at 600rpm for 2h, and place it in an atmosphere furnace fed with nitrogen for secondary calcination at 700°C for 10h , the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of glucose is 5%.

Example 5

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 96.9%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 2%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :2.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric phosphate, manganous carbonate, phosphoric acid, lithium carbonate, boron oxide, and reducing agent glucose according to the molar ratio of 1.2:0.8:0.4:1:0.05:0.055, mill in a ball mill at 600rpm for 2h, and then place Calcined at 600°C for 4 hours at 600°C in a nitrogen atmosphere furnace, and obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boron oxide is 1.1%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add glucose, and ball mill at 600rpm for 2h, then place it in an atmosphere furnace fed with nitrogen for secondary calcination at 800°C for 10h , the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of glucose is 5%.

Example 6

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 97.82%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 1.08%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :1.08.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric oxalate, manganese dioxide, phosphoric acid, lithium nitrate, boric acid and reducing agent glucose according to the molar ratio of 1.6:0.4:2:1:0.1:0.035, mill in a ball mill at 450rpm for 5h, and then put into Calcined at 600°C for 7 hours in a helium atmosphere furnace, and obtained boron-coated lithium manganese iron phosphate after cooling;

Wherein, the mass content of boric acid is 3.9%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add 2-mercaptoimidazole, and ball mill it at 350rpm for 5h, then place it in an atmosphere furnace with helium at 800°C Secondary calcination for 4 hours, and the double-coated positive electrode material is obtained after cooling;

Wherein, the mass content of 2-mercaptoimidazole is 3%.

Example 7

This embodiment provides a double-coated positive electrode material. The double-coated positive electrode material includes a core of lithium manganese iron phosphate, and a boron coating layer and a carbon coating layer sequentially coated on the surface of the core.

Wherein, the mass content of the lithium manganese iron phosphate core is 98.5%, the mass fraction of the boron coating layer is 1.1%, the mass fraction of the carbon coating layer is 1.5%, and the mass ratio of the boron coating layer and the carbon coating layer is 1.1 :1.5.

This embodiment also provides a method for preparing a double-coated positive electrode material, the preparation method comprising the following steps:

(1) Mix ferric sulfate, manganese acetate, phosphoric acid, lithium nitrate and sodium tetraborate in a molar ratio of 1.6:0.4:2:1:0.025, mill in a ball mill at 300rpm for 8 hours, and then place in an atmosphere furnace with argon Calcined at 550°C for 10 hours once, and after cooling, lithium manganese iron phosphate coated with boron was obtained;

Wherein, the mass content of sodium tetraborate is 1.6%;

(2) Transfer the boron-coated lithium manganese iron phosphate described in step (1) to a ball mill, add glucose, and ball mill it at 200rpm for 8h, then place it in an atmosphere furnace filled with argon for secondary calcination at 600°C 7h, obtain the double-coated positive electrode material after cooling;

Wherein, the mass content of glucose is 5%.

Example 8

The difference between this embodiment and Example 1 is that the mass fraction of the boron coating layer is 0.8%, the mass fraction of the carbon coating layer is 1.45%, the mass content of the lithium manganese iron phosphate core is 97.75%, and the boron coating layer The mass ratio of the clad layer to the carbon clad layer was not changed.

All the other preparation methods and parameters are consistent with Example 1.

Example 9

The difference between this embodiment and Example 1 is that the mass fraction of the boron coating layer is 3.5%, the mass fraction of the carbon coating layer is 5.82%, the mass content of the lithium manganese iron phosphate core is 90.68%, and the boron coating layer The mass ratio of the clad layer to the carbon clad layer was not changed.

All the other preparation methods and parameters are consistent with Example 1.

Example 10

The difference between this embodiment and Example 1 is that the mass ratio of the boron coating layer and the carbon coating layer is 1:0.3, then the mass fraction of the carbon coating layer is 0.33%, and the mass fraction of the boron coating layer is 1.1%, the mass content of lithium manganese iron phosphate core is 98.57%.

All the other preparation methods and parameters are consistent with Example 1.

Example 11

The difference between this embodiment and Example 1 is that the mass ratio of the boron coating layer and the carbon coating layer is 1:3, then the mass fraction of the carbon coating layer is 3.3%, and the mass fraction of the boron coating layer is 1.1%, the mass content of lithium manganese iron phosphate core is 95.6%.

All the other preparation methods and parameters are consistent with Example 1.

Comparative example 1

The difference between this comparative example and Example 5 is that the double-coated positive electrode material does not add a boron coating layer, that is, no boron oxide is added to the raw material in step (1), and the mass of the lithium manganese iron phosphate core is The content is 98%.

All the other preparation methods and parameters are consistent with Example 5.

Comparative example 2

The difference between this comparative example and Example 5 is that the double-coated positive electrode material does not add a carbon coating layer, that is, only step (1) is performed, and step (2) is not performed, the core of the lithium manganese iron phosphate core The mass content is 98.9%.

All the other preparation methods and parameters are consistent with Example 5.

Comparative example 3

The difference between this comparative example and Example 5 is that the double-coated positive electrode material is lithium manganese iron phosphate without coating, that is, there is no step (2), and no boron oxide is added in step (1) .

All the other preparation methods and parameters are consistent with Example 5.

Comparative example 4

The difference between this comparative example and Example 5 is that carbon coating is performed on the surface of the lithium manganese iron phosphate inner core first, and then boron coating is performed.

All the other preparation methods and parameters are consistent with Example 5.

Performance Testing

In order to verify the performance of the double-wrapped positive electrode material prepared by the present invention, the double-wrapped positive electrode material provided by Examples 1-11 and Comparative Examples 1-4, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) is mixed according to the mass ratio of 8:1:1, and a certain amount of organic solvent N-methylpyrrolidone (NMP) is added, and after stirring, it is coated on an aluminum foil to make a positive electrode sheet; the negative electrode is made of metal lithium sheet; the diaphragm is Celgard2400 polypropylene porous membrane; the solvent in the electrolyte is a solution composed of EC, DMC and EMC at a mass ratio of 1:1:1, the solute is LiPF ₆ , and the concentration of LiPF ₆ is 1.0mol/L; the 2023 model is assembled in the glove box Button batteries.

The charge-discharge cycle performance test was carried out on the above-mentioned battery, and the discharge specific capacity at 0.2C and 1C was tested within the cut-off voltage range of 2.2-4.3V.

The test results are shown in Table 1.

Table 1

analyze:

According to the data results of Examples 1-7, it can be seen that the positive electrode material prepared by the method provided by the present invention has better gram capacity and rate performance, because this scheme is pre-coated with Lewis acid to obtain a uniformly coated The carbon coating layer, and then in the case of using a lower mass fraction of the carbon coating layer, a good rate performance can be obtained.

From the comparison of the data results of Example 1 and Examples 8-9, it can be seen that when the mass fraction of the boron coating layer is too low, the conductivity and rate performance of the material are reduced, but because the total content of inactive substances is reduced, the The gram capacity of the material is increased; and when the mass fraction of the boron coating is too high, because the conductivity of boron is lower than that of carbon, too much boron will also reduce the conductivity of the coating and affect the gram capacity of the material and rate performance.

From the comparison of the data results of Example 1 and Examples 10-11, it can be seen that when the mass ratio of the boron coating layer and the carbon coating layer is too large, because the content of the carbon coating layer is too low, a uniform carbon coating cannot be formed. layer, the conductivity is reduced, but because the surface of the positive electrode material has a boron coating layer, it still has good conductivity. When the mass ratio of the boron coating layer to the carbon coating layer is too small, the carbon coating layer is too thick, which will reduce the gram capacity of the material.

From the comparison of the data results of Example 5 and Comparative Example 1, it can be seen that if no boron coating layer is added, it is difficult to obtain a uniform carbon coating layer, and the carbon coating layer is easy to fall off from the manganese-containing positive electrode material during the cycle.

From the comparison of the data results of Example 5 and Comparative Example 2, it can be seen that although the initial discharge specific capacity of Comparative Example 2 at 0.1C does not show a downward trend, but due to the poor affinity between the manganese-containing positive electrode material and the carbon coating layer, the For ratio 2, the first discharge specific capacity at 1C showed a trend of a significant decrease.

From the comparison of the data results of Example 5 and Comparative Example 3, it can be seen that for the positive electrode material without coating, its performance is the worst in terms of gram capacity and rate performance.

From the comparison of the data results of Example 5 and Comparative Example 4, it can be known that carbon coating is carried out first and then boron coating is carried out, and the effect of the boron coating layer on forming a uniform carbon coating layer cannot be brought into play, so its performance is poor, so it is not as good as implementing Example 5.

The applicant declares that the present invention illustrates the process method of the present invention through the above examples, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of selected raw materials in the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. The double-coating type anode material is characterized by comprising a manganese-containing anode material core, a first shell layer and a second shell layer, wherein the first shell layer and the second shell layer are sequentially coated on the surface of the core;

the first shell layer is a boron coating layer, and the second shell layer is a carbon coating layer.

2. The double-coated positive electrode material according to claim 1, wherein the mass fraction of the boron coating layer is 1 to 3% based on 100% by mass of the double-coated positive electrode material;

preferably, the mass ratio of the boron coating layer to the carbon coating layer is 1 (0.5-2).

3. The double-clad positive electrode material according to claim 1 or 2, wherein the manganese-containing positive electrode material core has a mass content of 91 to 98.5% based on 100% by mass of the double-clad positive electrode material.

4. The double-clad positive electrode material according to any one of claims 1 to 3, wherein the manganese-containing positive electrode material comprises any one of lithium iron manganese phosphate, lithium manganate or a lithium-rich manganese-based material, preferably lithium iron manganese phosphate.

5. A method for preparing the double-coated positive electrode material according to any one of claims 1 to 4, comprising the steps of:

(1) Mixing a raw material of a manganese-containing cathode material with a boron source, and calcining for one time to obtain an intermediate product;

(2) And (2) mixing the intermediate product obtained in the step (1) with a carbon source, and performing secondary calcination to obtain the double-coated positive electrode material.

6. The production method according to claim 5, wherein the boron source is a boron-based Lewis acid;

preferably, the boron-based lewis acid comprises any one or a combination of at least two of boric acid, a borate, or boron oxide;

preferably, the mass content of the boron source is 1-5% based on 100% of the raw material of the manganese-containing cathode material;

preferably, the carbon source is an organic carbon source;

preferably, the functional group of the organic carbon source comprises any one of a hydroxyl group, an imino group, or an amino group, or a combination of at least two thereof;

preferably, the mass content of the carbon source is 1-6% based on 100% of the raw material of the manganese-containing cathode material.

7. The production method according to any one of claims 5 to 6, wherein the raw materials of the manganese-containing positive electrode material include a manganese source, a lithium source, a phosphorus source, and an iron source;

preferably, the manganese source comprises any one of manganese carbonate, manganese dioxide, manganese acetate or manganese nitrate or a combination of at least two thereof;

preferably, the lithium source comprises any one of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate or a combination of at least two thereof;

preferably, the phosphorus source comprises any one of phosphoric acid, ammonium dihydrogen phosphate or phosphorus pentoxide, or a combination of at least two thereof;

preferably, the iron source comprises any one of or a combination of at least two of iron phosphate, iron oxide, iron oxalate or iron sulphate.

8. The preparation method according to any one of claims 5 to 7, wherein the mixing in step (1) is ball milling, the ball milling speed is 300-600rpm, and the ball milling time is 2-8h;

preferably, the mixing in the step (2) is ball milling, the speed of the ball milling is 200-500rpm, and the time of the ball milling is 2-8h;

preferably, the temperature of the primary calcination is 500-600 ℃;

preferably, the time of the primary calcination is 4-10h;

preferably, the temperature of the secondary calcination is 600-800 ℃;

preferably, the time of the secondary calcination is 4 to 10 hours;

preferably, the atmosphere of the primary calcination and the atmosphere of the secondary calcination are both inert atmosphere, and the gas in the inert atmosphere comprises any one or a combination of at least two of nitrogen, helium or argon.

9. The method according to any one of claims 5 to 8, characterized in that it comprises the following steps:

(1) Ball-milling and mixing a manganese source, a lithium source, a phosphorus source, an iron source and 1-5% by mass of boron-based Lewis acid at 300-600rpm for 2-8h, and calcining for 4-10h at 500-600 ℃ for one time to obtain an intermediate product;

(2) And (2) ball-milling and mixing the intermediate product obtained in the step (1) and an organic carbon source with the mass content of 1-6% for 2-8h at 200-500rpm, and calcining for 4-10h in an inert atmosphere at 600-800 ℃ for the second time to obtain the double-coated positive electrode material.

10. A lithium ion battery, characterized in that the double-coated positive electrode material of any one of claims 1 to 4 is included in the positive electrode of the lithium ion battery.

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