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

Abstract

The invention provides a double-coating type anode material and a preparation method and application thereof, wherein the double-coating type anode material comprises a manganese-containing anode material core, a first shell and a second shell, wherein the first shell and the second shell 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. The invention takes manganese-containing anode material as a core, takes a boron coating layer coated on the surface of the core as a first shell layer, and takes a carbon coating layer coated on the surface of the first shell layer as a second shell layer, thereby forming the double-coating type anode material. The boron coating layer is used as the first shell layer, so that the conductivity and the structural stability of the anode material can be improved, the interaction between the carbon coating layer and the manganese-containing anode material core is enhanced under the action of the boron coating layer, the carbon coating layer can realize uniform coating, the conductivity of the double-coated anode material is effectively improved, and meanwhile, the double-coated anode material can keep higher capacity under high rate and has excellent high rate capacity retention rate.

Description

Double-coated positive electrode material and preparation method and application thereof

Technical Field

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

Background

In recent years, as the energy density of lithium iron phosphate has approached the theoretical limit, lithium iron manganese phosphate has received increasing attention as an advanced version of lithium iron phosphate. Compared with lithium iron phosphate, the lithium iron manganese phosphate has the characteristic of high voltage, the voltage can be increased by introducing manganese into the positive electrode material, the higher voltage represents the higher energy density, and the voltage platform of the lithium iron manganese phosphate is as high as 4.1V and far higher than 3.4V of the lithium iron phosphate, so that the theoretical energy density of the lithium iron manganese phosphate can be higher than that of the lithium iron phosphate by more than 15% under the same condition, and the lithium iron manganese phosphate has a good development prospect. However, since manganese is a metal element having very poor conductivity, the conductivity of lithium manganese iron phosphate is further lowered than that of lithium iron phosphate, and the electron conductivity is only 10 ^-13 S/cm。

Generally improving the conductivity of lithium manganese iron phosphate in a carbon coating mode, for example, CN102738465B discloses a preparation method of a lithium manganese iron phosphate anode composite material, which comprises the steps of putting a lithium source, a ferric iron source, manganese dioxide and a carbon source into a ball milling tank, adding a proper amount of a dispersing agent and a complexing agent, and then putting the ball milling tank on a ball mill for ball milling for 4-6 hours at 200-500 r/min; drying and grinding the mixture obtained after ball milling again to obtain LiMn _x Fe _1-x PO ₄ A precursor; and calcining to obtain the carbon-coated lithium manganese iron phosphate cathode material. However, since the particles of lithium manganese iron phosphate are small, onlyOne third of the ternary cathode materials have large specific surface area, complex surface structure and poor affinity with carbon, so that a uniform carbon coating layer cannot be obtained by using the above method, and a carbon source with a proportion of up to 30wt% is required for complete coating, thus resulting in a decrease in gram capacity.

CN111900344B discloses a preparation method of a carbon-coated lithium manganese iron phosphate positive electrode material, which comprises the steps of firstly, preparing a transition metal salt solution A, a phosphorus solution B and an ammonia water solution C according to the molar ratio of Mn to Fe, and simultaneously dropwise adding the transition metal salt solution A, the phosphorus solution B and the ammonia water solution C into a reaction kettle to prepare a precursor of the lithium manganese iron phosphate positive electrode material; and then, matching a lithium source with the precursor according to a molar ratio, adding a coated carbon source and a doped metal compound, and calcining under the protection of an inert atmosphere to obtain the carbon-coated lithium manganese iron phosphate cathode material. The above method uses simple solid phase coating, is difficult to form a uniform coating layer on the surface, and the coating layer is easy to fall off in the circulation process.

CN109888205A discloses a nano-micro spherical carbon-coated lithium manganese iron phosphate composite material, a preparation method thereof, a lithium battery anode material and a lithium battery, wherein the composite material comprises lithium manganese iron phosphate and an outer carbon layer coated outside the lithium manganese iron phosphate, and the chemical composition of the lithium manganese iron phosphate is LiMn _1-x Fe _x PO ₄ Wherein x is more than or equal to 0.1 and less than or equal to 1, the particle size D50 of the composite material is 1-10 mu m, and the mass content of carbon element in the lithium manganese iron phosphate is 1-10%. The patent uses the nanometer spherical lithium manganese iron phosphate, is difficult to form a uniform coating layer on the surface, and aggravates the falling off of the coating layer in the circulating process.

Therefore, how to improve the affinity between the core of the positive electrode material and the carbon coating layer to form a uniform carbon coating layer, so that the conductivity of the positive electrode material is further improved, and the positive electrode material can maintain higher capacity at high rate is a technical problem to be solved urgently

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a double-coated positive electrode material and a preparation method and application thereof. The invention takes a manganese-containing anode material as a core, takes a boron coating layer coated on the surface of the core as a first shell and takes a carbon coating layer coated on the surface of the first shell as a second shell, thereby forming the double-coating type anode material. The boron coating layer is used as the first shell layer, so that the conductivity and the structural stability of the anode material can be improved, the interaction between the carbon coating layer and the manganese-containing anode material core is enhanced under the action of the boron coating layer, the carbon coating layer can realize uniform coating, the conductivity of the double-coated anode material is effectively improved, and meanwhile, the double-coated anode material can keep higher capacity under high rate and has excellent high rate capacity retention rate.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a double-coating type anode material, which comprises 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.

The invention takes a manganese-containing anode material as a core, takes a boron coating layer coated on the surface of the core as a first shell and takes a carbon coating layer coated on the surface of the first shell as a second shell, thereby forming the double-coating type anode material. The boron coating layer is used as a first shell layer, boron in the boron coating layer can form a Mn-B bond with manganese in the core, so that the conductivity of the material is improved, mn can be prevented from being separated from the surface of the positive electrode material in the charging and discharging processes, and the structure of the material is stabilized; in addition, the boron coating layer is used as an intermediate layer of the core and the carbon coating layer, so that an important bridge function is achieved, under the action of the boron coating layer, the interaction between the carbon coating layer and the manganese-containing cathode material core is enhanced, the carbon coating layer can realize uniform coating, the conductivity of the double-coated cathode material is effectively improved, and meanwhile, the double-coated cathode material can keep higher capacity under high rate and has excellent high rate capacity retention rate.

In the invention, the affinity of the manganese-containing cathode material core and the carbon coating layer is poor, if the boron coating layer is not added, a uniform carbon coating layer is difficult to obtain, and the carbon coating layer is easy to fall off from the manganese-containing cathode material in the circulation process.

Preferably, the mass fraction of the boron coating layer is 1 to 3% based on 100% by mass of the double-coated positive electrode material, and may be, for example, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or the like.

In the invention, if the mass fraction of the boron coating layer is too low, the uniformity of the subsequent carbon coating layer is influenced, so that the conductivity and the rate capability of the material cannot be improved; if the mass fraction of the boron coating is too high, the gram volume will be affected.

Preferably, the mass ratio of the boron coating layer to the carbon coating layer is 1 (0.5-2), and may be, for example, 1.

In the present invention, if the mass ratio of the boron coating layer to 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 conductivity; if the mass ratio of the boron 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 is lowered because the conductivity of boron is lower than that of carbon.

Preferably, the mass content of the manganese-containing cathode material core is 91-98.5% based on 100% of the mass of the double-coated cathode material, and may be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, or the like, for example.

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

In a second aspect, the present invention provides a method for preparing the double-coated positive electrode material according to the first aspect, the method 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.

According to the invention, the interaction between the carbon source and the manganese-containing anode material can be enhanced by coating boron on the surface of the manganese-containing anode material, so that the carbon source can be uniformly coated on the surface of the intermediate product to form a uniform carbon coating layer, thereby remarkably improving the conductivity of the double-coated anode material and improving the electrochemical performance of the material.

Preferably, the boron source is a boron based lewis acid.

It is noted that boron-based lewis acids can attract groups having lone pair electrons.

Preferably, the boron-based lewis acid includes any one or a combination of at least two of boric acid, borate, or boron oxide, and illustratively, the borate may be, for example, lithium borate, manganese borate, sodium tetraborate, or iron borate, and the like.

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

Preferably, the carbon source is an organic carbon source.

According to the invention, the boron-based Lewis acid can attract the organic carbon source with the group of lone pair electrons, so that the interaction between the organic carbon source and the lithium manganese iron phosphate is enhanced, the organic carbon source can be uniformly coated on the surface of the boron coating layer, and the conductivity of the double-coated positive electrode material is effectively improved.

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

Preferably, the carbon source may be present in an amount of 1 to 6% by mass, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or the like, based on 100% by mass of the raw material of the manganese-containing positive electrode material.

In the invention, if the mass content of the carbon source is too high, the formed carbon coating layer is too thick, and the gram volume of the cathode material is reduced; if the mass content of the carbon source is too low, the rate capability of the positive electrode material is lowered.

As a preferred embodiment, 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 iron phosphate, iron oxide, iron oxalate or iron sulfate or a combination of at least two of them, and may be iron phosphate, ferroferric oxide, iron oxalate or iron sulfate, for example.

Preferably, the mixing in step (1) is ball milling, the speed of the ball milling is 300-600rpm, such as 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm or 600rpm, and the like, and the time of the ball milling is 2-8h, such as 2h, 3h, 4h, 5h, 6h, 7h or 8h, and the like

Preferably, the mixing manner in the step (2) is ball milling, the ball milling rate is 200-500rpm, such as 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500rpm, and the like, and the ball milling time is 2-8h, such as 2h, 3h, 4h, 5h, 6h, 7h or 8h, and the like.

Preferably, the temperature of the primary calcination is 500-600 ℃, for example, 500 ℃, 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, or 600 ℃.

Preferably, the time of the primary calcination is 4 to 10 hours, and for example, the primary calcination can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or the like.

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

Preferably, the time of the secondary calcination is 4 to 10 hours, and for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or the like can be used.

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

As a preferable technical scheme, the preparation method 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.

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

The recitation of numerical ranges herein includes not only the above-recited values, but also any values between any of the above-recited numerical ranges not recited, and for brevity and clarity, is not intended to be exhaustive of the specific values encompassed within the range.

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

(1) The invention provides a double-coating type anode material, which takes a manganese-containing anode material as an inner core, takes a boron coating layer coated on the surface of the inner core as a first shell and takes a carbon coating layer coated on the surface of the first shell as a second shell. The boron coating layer is used as a first shell layer, so that the conductivity and the structural stability of the positive electrode material can be improved, and the interaction between the carbon coating layer and the manganese-containing positive electrode material core is enhanced under the action of the boron coating layer, so that the carbon coating layer can realize uniform coating, and the conductivity of the double-coated positive electrode material is effectively improved;

(2) The double-coated positive electrode material provided by the invention can keep higher capacity under high rate and has excellent high rate capacity retention rate.

Drawings

Fig. 1 is an SEM image of a double-coated positive electrode 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 embodiment 1 of the present invention.

Detailed Description

It is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitation of the present invention.

Example 1

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated cathode material, which comprises the following steps:

(1) Mixing iron phosphate, manganese carbonate, phosphoric acid, lithium carbonate, boron oxide and a reducing agent glucose according to a molar ratio of 1.6;

wherein the mass content of the boron oxide is 1.1%;

(2) Transferring the lithium manganese iron phosphate coated with boron on the surface in the step (1) into a ball mill, adding glucose, performing ball milling for 2h at 500rpm, placing the mixture into an atmosphere furnace with nitrogen introduced, performing secondary calcination for 10h at 800 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the glucose is 5 percent.

Fig. 1 shows an SEM image of the double-coated cathode material provided in this embodiment, and it can be seen from the SEM image that the lithium iron manganese phosphate cathode material prepared in this embodiment has complete particles and uniform particle size distribution.

Fig. 2 shows a charge-discharge curve diagram of the double-coated positive electrode material provided in this embodiment, and it can be known that the gram capacity of the lithium iron manganese phosphate positive electrode material prepared in this embodiment can reach 156.3mAh/g.

Example 2

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated positive electrode material, which comprises the following steps:

(1) Mixing iron phosphate, manganese carbonate, phosphoric acid, lithium carbonate, boron oxide and a reducing agent glucose according to a molar ratio of 1.6;

wherein the mass content of the boron oxide is 1.1%;

(2) Transferring the lithium manganese iron phosphate coated with boron on the surface in the step (1) into a ball mill, adding glucose, performing ball milling for 2h at 600rpm, placing the mixture into an atmosphere furnace with nitrogen introduced, performing secondary calcination for 10h at 800 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the glucose is 1.5 percent.

Example 3

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated cathode material, which comprises the following steps:

(1) Mixing iron phosphate, manganese carbonate, phosphoric acid, lithium carbonate, boron oxide and a reducing agent glucose according to a molar ratio of 1.6;

wherein the mass content of the boron oxide is 1.1%;

(2) Transferring the lithium manganese iron phosphate with the surface coated with boron in the step (1) into a ball mill, adding 2-mercaptoimidazole, performing ball milling for 2 hours at 600rpm, placing the mixture into an atmosphere furnace with nitrogen introduced, performing secondary calcination for 10 hours at 800 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the 2-mercaptoimidazole is 5 percent.

Example 4

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated cathode material, which comprises the following steps:

(1) Mixing iron phosphate, manganese carbonate, phosphoric acid, lithium carbonate, boron oxide and a reducing agent glucose according to a molar ratio of 1.6;

wherein the mass content of the boron oxide is 1.1%;

(2) Transferring the lithium manganese iron phosphate coated with boron on the surface in the step (1) into a ball mill, adding glucose, performing ball milling for 2h at 600rpm, placing the mixture into an atmosphere furnace with nitrogen introduced, performing secondary calcination for 10h at 700 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the glucose is 5 percent.

Example 5

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated cathode material, which comprises the following steps:

(1) Mixing iron phosphate, manganese carbonate, phosphoric acid, lithium carbonate, boron oxide and a reducing agent glucose according to a molar ratio of 1.2;

wherein the mass content of the boron oxide is 1.1%;

(2) Transferring the lithium manganese iron phosphate coated with boron on the surface in the step (1) into a ball mill, adding glucose, performing ball milling for 2h at 600rpm, placing the mixture into an atmosphere furnace with nitrogen introduced, performing secondary calcination for 10h at 800 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the glucose is 5 percent.

Example 6

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated positive electrode material, which comprises the following steps:

(1) Mixing ferric oxalate, manganese dioxide, phosphoric acid, lithium nitrate, boric acid and a reducing agent glucose according to a molar ratio of 1.6;

wherein, the mass content of the boric acid is 3.9 percent;

(2) Transferring the lithium manganese iron phosphate with the surface coated with boron in the step (1) into a ball mill, adding 2-mercaptoimidazole, performing ball milling for 5 hours at 350rpm, placing the mixture into an atmosphere furnace with helium introduced, performing secondary calcination for 4 hours at 800 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the 2-mercaptoimidazole is 3 percent.

Example 7

The embodiment provides a two cladding type cathode material, two cladding type cathode material include the lithium iron manganese phosphate kernel, and the cladding is in proper order in boron coating and the carbon coating on kernel surface.

The mass content of the manganese lithium 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 to the carbon coating layer is 1.1.

The embodiment also provides a preparation method of the double-coated positive electrode material, which comprises the following steps:

(1) Mixing ferric sulfate, manganese acetate, phosphoric acid, lithium nitrate and sodium tetraborate according to a molar ratio of 1.6;

wherein the mass content of the sodium tetraborate is 1.6%;

(2) Transferring the lithium manganese iron phosphate coated with boron on the surface in the step (1) into a ball mill, adding glucose, performing ball milling for 8 hours at 200rpm, placing the mixture into an argon-filled atmosphere furnace, performing secondary calcination for 7 hours at 600 ℃, and cooling to obtain the double-coated positive electrode material;

wherein the mass content of the glucose is 5 percent.

Example 8

The difference between this example 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 iron manganese phosphate core is 97.75%, and the mass ratio of the boron coating layer to the carbon coating layer is unchanged.

The remaining preparation methods and parameters were in accordance with example 1.

Example 9

The difference between the present example 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 iron manganese phosphate core is 90.68%, and the mass ratio of the boron coating layer to the carbon coating layer is unchanged.

The remaining preparation methods and parameters were in accordance with example 1.

Example 10

The difference between the present example and example 1 is that, when the mass ratio of the boron coating layer to the carbon coating layer is 1.3, the mass fraction of the carbon coating layer is 0.33%, the mass fraction of the boron coating layer is 1.1%, and the mass content of the lithium iron manganese phosphate core is 98.57%.

The remaining preparation methods and parameters were in accordance with example 1.

Example 11

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

The remaining preparation methods and parameters were in accordance with example 1.

Comparative example 1

The difference between the comparative example and the example 5 is that the boron coating layer is not added to the double-coated cathode material, that is, boron oxide is not added to the raw material in the step (1), and the mass content of the manganese iron phosphate lithium core is 98%.

The remaining preparation methods and parameters were in accordance with example 5.

Comparative example 2

The difference between the comparative example and the example 5 is that the double-coated positive electrode material is only subjected to the step (1) and not subjected to the step (2) without adding a carbon coating, and the mass content of the lithium iron manganese phosphate core is 98.9%.

The remaining preparation methods and parameters were in accordance with example 5.

Comparative example 3

The comparative example is different from example 5 in that the double-coated positive electrode material is lithium manganese iron phosphate, no coating is performed, that is, step (2) is omitted, and no boron oxide is added in step (1).

The remaining preparation methods and parameters were in accordance with example 5.

Comparative example 4

The comparative example is different from example 5 in that the surface of the lithium iron manganese phosphate core is coated with carbon and then coated with boron.

The remaining preparation methods and parameters were in accordance with example 5.

Performance testing

In order to verify the performance of the double-coated cathode material prepared by the present invention, the double-coated cathode materials provided in examples 1 to 11 and comparative examples 1 to 4, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 8Preparing a positive plate; the negative electrode adopts a metal lithium sheet; the diaphragm is Celgard2400 polypropylene porous membrane; the solvent in the electrolyte is a solution composed of EC, DMC and EMC according to a mass ratio of 1 ₆ ，LiPF ₆ The concentration of (A) is 1.0mol/L; a 2023 button cell battery was assembled in a glove box.

And (3) carrying out charge-discharge cycle performance test on the battery, and testing the discharge specific capacity of the battery under 0.2C and 1C within the range of cut-off voltage of 2.2-4.3V.

The test results are shown in table 1.

TABLE 1

And (3) analysis:

according to the data results of the examples 1 to 7, the positive electrode material prepared by the method provided by the invention has better gram capacity and rate capability, because the scheme is used for obtaining the uniformly coated carbon coating layer by coating the Lewis acid in advance, and further, the good rate capability can be obtained under the condition of using the carbon coating layer with lower mass fraction.

From the comparison of the data 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 capability of the material are reduced, while the gram volume of the material is increased due to the reduced total content of inactive substances; when the mass fraction of the boron coating layer is too high, the conductivity of boron is lower than that of carbon, so that too much boron can reduce the conductivity of the coating layer, and the gram volume and rate capability of the material are affected.

As is clear from comparison of the data results of example 1 and examples 10 to 11, when the mass ratio of the boron coating layer to the carbon coating layer is too large, a uniform carbon coating layer cannot be formed due to too low content of the carbon coating layer, and the conductivity is lowered, but the positive electrode material still has good conductivity due to the boron coating layer on the surface thereof. 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 reduces the gram volume of the material.

As can be seen from comparison of the data results of example 5 and comparative example 1, it is difficult to obtain a uniform carbon coating layer without adding a boron coating layer, and the carbon coating layer is easily detached from the manganese-containing cathode material during the cycle.

As can be seen from comparison of the data results of example 5 and comparative example 2, although comparative example 2 did not show a tendency of a decrease in the specific first discharge capacity at 0.1C, comparative example 2 showed a tendency of a large decrease in the specific first discharge capacity at 1C due to the poor affinity of the manganese-containing cathode material with the carbon coating layer.

As can be seen from the comparison of the data results of example 5 and comparative example 3, the performance of the positive electrode material without coating was the worst in both gram capacity and rate capability.

As is clear from the comparison of the data results of example 5 and comparative example 4, the effect of the boron coating layer on the formation of a uniform carbon coating layer cannot be exerted by performing carbon coating first and then boron coating, and thus the performance is inferior to that of example 5.

The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by 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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