CN111653755A - A kind of lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material and a preparation method thereof. A certain quality of nickel cobalt lithium aluminate precursor is weighed, mixed with lithium and sintered to obtain nickel cobalt aluminum Lithium oxide primary sintered material, then the nickel cobalt lithium aluminate primary sintered material is stirred and washed with water, and vacuum dried to obtain a nickel cobalt lithium aluminate cathode material matrix. Then, the base positive electrode material and the coating lithium iron phosphate-boric acid are mixed, and then sintered at a high temperature to obtain a nickel cobalt lithium aluminate positive electrode material co-coated with lithium iron phosphate-boric acid. The co-coated nickel-cobalt lithium aluminate positive electrode material of the present invention has good electrical conductivity, and the coating layer is uniform, which can prevent the direct reaction between the positive electrode material matrix and the electrolyte, and effectively improve the cycle performance and safety performance of the material. In addition, the invention has the advantages of simple process, excellent product performance and low cost, and is suitable for large-scale industrial production.

Description

A kind of lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material and preparation thereof method

technical field

The invention belongs to the technical field of positive electrode materials for lithium ion batteries, and in particular relates to a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material and a preparation method thereof.

Background technique

With the increasing rise of the new energy vehicle industry, the lithium-ion battery industry has developed rapidly. The cathode material plays a key role as an important component. Among the cathode materials, lithium nickel cobalt aluminate has been widely studied and applied due to its high energy density, good thermal stability, and good cycle performance. However, the nickel cobalt lithium aluminate cathode material also has certain defects. Due to its high nickel content, the material is prone to mix lithium and nickel, resulting in structural instability of the material; in addition, high-priced nickel will react with the electrolyte, resulting in an irreversible phase transition , the material structure collapses, which in turn leads to the deterioration of the cycle performance and safety performance of the material.

In view of the above problems, surface coating active agent is an effective improvement method. The coating material can effectively prevent the direct contact between the positive electrode material and the electrolyte, prevent the reaction between nickel ions and the electrolyte, and ensure the stability of the positive electrode material and the electrolyte, thereby improving the cycle performance and safety performance. This method has high technical requirements and will cause a certain loss of capacity, and it is difficult to guarantee the uniformity of the coating layer.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material and a preparation method thereof, to overcome the problems such as the cycle performance and safety performance of the prior art nickel cobalt lithium aluminate, the present invention can It can effectively prevent the reaction between the cathode material and the electrolyte, and improve the cycle performance and safety performance of the material.

To achieve the above object, the present invention adopts the following technical solutions:

A lithium iron phosphate-boric acid co-coated nickel-cobalt lithium aluminate positive electrode material, the nickel-cobalt lithium aluminate positive electrode material is composed of a matrix positive electrode material and a lithium iron phosphate-boric acid co-coating layer, the matrix positive electrode material The molecular formula of is Li _a Ni _0.91 Co _0.06 Al _0.03 O ₂ , where 1.01≤a≤1.06.

Further, the lithium iron phosphate-boric acid co-coating layer includes a lithiated layer of phosphoric acid, a lithiated layer of iron phosphate, and a lithiated layer of boric acid.

Further, in the raw materials for preparing the lithium iron phosphate-boric acid co-coating layer, the mass fraction of lithium iron phosphate in the matrix cathode material is 0.02wt%-0.30wt%; the mass fraction of boric acid in the matrix cathode material is 0.01wt%-0.30 wt%.

Further, in the lithium iron phosphate-boric acid co-coating layer, the mass fraction of lithium iron phosphate in the matrix cathode material is 0.05wt%-0.20wt%; the mass fraction of boric acid in the matrix cathode material is 0.03wt%-0.15wt% %.

A preparation method of a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material, comprising the following steps:

Step 1: Weigh the nickel cobalt lithium aluminate precursor, mix it with lithium and sinter to obtain the nickel cobalt lithium aluminate primary sintering material;

Step 2: adding the nickel cobalt lithium aluminate primary sintering material into deionized water for stirring and washing, and vacuum drying after solid-liquid separation to obtain a matrix cathode material;

Step 3: mixing the base positive electrode material and the coating lithium iron phosphate-boric acid, and then sintering at a high temperature to obtain a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material.

Further, the lithium source used in the first step of mixing lithium is lithium hydroxide LiOH·H ₂ O, the precursor of lithium nickel cobalt aluminate is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , and the precursor of lithium nickel cobalt aluminate is Ni 0.91 Co 0.06 Al 0.03 (OH) 2 . The molar ratio of the lithium source is 1:(1.01-1.06), the sintering temperature is 650-750°C, and the holding time is 9-15h.

Further, in step 2, the mass ratio of deionized water to the primary sintered material of nickel cobalt lithium aluminate is (1-5):1.

Further, in step 2, the stirring and water washing time is 10-60 min, and the stirring linear speed is 500 rpm; the solid-liquid separation method is one of centrifugation and suction filtration; the vacuum drying temperature is 100-150 ° C, and the time is 4-10 h.

Further, the mixing method of the base positive electrode material and the coating lithium iron phosphate-boric acid is one of ball milling and high mixing.

Further, after the matrix cathode material is mixed with the coating lithium iron phosphate-boric acid, the sintering temperature is 250-450°C, and the holding time is 6-10h; the atmosphere in the sintering process is an oxygen-rich atmosphere, the pressure is 20Pa-40Pa, and the oxygen volume is The content is 90%-99%.

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

The present invention takes the nickel-cobalt lithium aluminate cathode material as the matrix, uses lithium iron phosphate and boric acid as coating raw materials, and prepares the nickel-cobalt alumina lithium anode material co-coated with lithium iron phosphate and boric acid; the residual total alkali in the boric acid and the matrix material The reaction of (lithium hydroxide and lithium carbonate) to generate lithium borate can effectively reduce the total alkali of the material and improve the processing performance of the material; and the boric acid has good melting aid, combined with the good conductivity of lithium iron phosphate, through sintering can make the co-polymer The coating layer is more uniformly distributed on the surface of the matrix material, which significantly improves the conductivity of the material, and effectively prevents the interface reaction between the cathode material matrix and the electrolyte, thereby improving the cycle performance and safety performance of the material.

Description of drawings

FIG. 1 is a schematic diagram of the co-coated lithium iron phosphate-cobalt nickel cobalt lithium aluminate positive electrode material sample prepared in Example 1 of the present invention under a 50k times electron microscope.

FIG. 2 is the first charge-discharge curve at 0.1C of the co-coated lithium iron phosphate-nickel borate cobalt lithium aluminate positive electrode material sample prepared in Example 1 of the present invention.

3 is a cycle curve of the co-coated lithium iron phosphate-nickel cobalt borate lithium aluminate cathode material sample prepared in Example 1 of the present invention at a rate of 1C.

Detailed ways

The present invention will be specifically described by the following examples, which are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention.

A lithium iron phosphate-boric acid co-coated nickel-cobalt lithium aluminate positive electrode material, the nickel-cobalt lithium aluminate positive electrode material is composed of a matrix positive electrode material and a lithium iron phosphate-boric acid co-coating layer, the matrix positive electrode material The molecular formula is Li _a Ni _0.91 Co _0.06 Al _0.03 O ₂ , where 1.01≤a≤1.06; the molecular formulas of the lithium iron phosphate and boric acid are LiFePO ₄ , H ₃ BO ₃ respectively, and the lithium iron phosphate is used by coating iron carbon phosphate Lithium, lithium iron phosphate-boric acid co-coating layer (finally formed lithium iron phosphate-boric acid co-coating layer) contains a lithiated layer of phosphoric acid, a lithiated layer of iron phosphate, and a lithiated layer of boric acid. In the raw material of the lithium iron phosphate-boric acid co-coating layer, the mass fraction of lithium iron phosphate in the matrix cathode material is 0.02wt%-0.30wt%, preferably 0.05wt%-0.20wt%; the mass fraction of boric acid in the matrix cathode material The fraction is 0.01wt%-0.30wt%, preferably 0.03wt%-0.15wt%.

A preparation method of a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material, comprising the following steps:

Step 1: Weigh the nickel cobalt lithium aluminate precursor, mix it with lithium and sinter to obtain the nickel cobalt lithium aluminate primary sintering material; the lithium source used when mixing lithium is lithium hydroxide, and the nickel cobalt lithium aluminate precursor is mixed with the lithium nickel cobalt aluminate. The molar ratio of the lithium source is 1:(1.01-1.06), the sintering temperature is 650-750°C, and the holding time is 9-15hh;

Step 2: adding the nickel cobalt lithium aluminate primary sintering material into deionized water for stirring and washing, the mass ratio of the deionized water to the nickel cobalt lithium aluminate primary sintering material is (1-5): 1, and the stirring and washing time is 10- 60min, the stirring line speed is 500rpm, the solid-liquid separation is followed by vacuum drying to obtain the matrix cathode material, and the solid-liquid separation method is one of centrifugation and suction filtration; the vacuum drying temperature is 100-150 ℃, and the time is 4-10h;

Step 3: Mix the matrix cathode material and the coating lithium iron phosphate-boric acid, and then sinter at high temperature to obtain a nickel cobalt lithium aluminate cathode material co-coated with lithium iron phosphate and boric acid; the matrix cathode material and the coating lithium iron phosphate -The mixing method of boric acid is one of ball milling and high mixing. After the matrix cathode material is mixed with the coating lithium iron phosphate-boric acid, the sintering temperature is 250-450 ℃, and the holding time is 6-10h; the atmosphere during the sintering process It is an oxygen-rich atmosphere, slightly positive pressure (20Pa ~ 40Pa), and the oxygen volume content is 90%-99%.

Example 1

Step 1: Weigh a certain mass of nickel-cobalt aluminate precursor, the molecular formula is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , mix with lithium hydroxide (LiOH·H ₂ O) and sinter to obtain lithium nickel-cobalt aluminate Initial sintering material. The molar ratio of nickel-cobalt aluminate precursor to lithium source is 1:1.01, the sintering temperature is 650°C, and the holding time is 9h.

Step 2: Weigh a certain mass of nickel-cobalt lithium aluminate primary sintering material, add a certain mass of deionized water at a water-to-material ratio of 1:1, and stir and wash with a stirring speed of 500 rpm and a washing time of 10 minutes. Then, suction filtration, and vacuum drying for 4 hours at a temperature of 100° C. to obtain a nickel-cobalt lithium aluminate cathode material matrix.

Step 3: mixing the matrix cathode material and the coating lithium iron phosphate-boric acid by ball milling, wherein the mass fraction of lithium iron phosphate in the matrix cathode material is 0.05wt%, and the mass fraction of boric acid in the matrix cathode material is 0.03wt%. After high temperature sintering, a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material was obtained, wherein the sintering temperature was 250°C, the holding time was 6h, the oxygen volume content was more than 90%, and the slight positive pressure (20±2Pa) .

The co-coated nickel cobalt lithium aluminate Li _1.01 Ni _0.91 Co _0.06 Al _0.03 O ₂ cathode material prepared in this example has a 0.1C discharge specific capacity of 210.2mAh/g, and the capacity basically does not decay for 100 cycles.

Example 2

Step 1: Weigh a certain mass of nickel-cobalt aluminate precursor, the molecular formula is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , mix with lithium hydroxide (LiOH·H ₂ O) and sinter to obtain lithium nickel-cobalt aluminate Initial sintering material. The molar ratio of nickel-cobalt aluminate precursor to lithium source is 1:1.02, the sintering temperature is 710°C, and the holding time is 12h.

Step 2: Weigh a certain mass of nickel-cobalt lithium aluminate primary sintering material, add a certain mass of deionized water at a water-to-material ratio of 2:1 for stirring and washing, the stirring speed is 500rpm, and the washing time is 30min. After centrifugation, and vacuum drying for 6 hours at a temperature of 120° C., a matrix of nickel-cobalt lithium aluminate cathode material was obtained.

Step 3: Mix the base cathode material and the coating lithium iron phosphate-boric acid through a high-mixer, wherein the mass fraction of lithium iron phosphate in the base cathode material is 0.10 wt %, and the mass fraction of boric acid in the base cathode material is 0.06 wt % . After high temperature sintering, a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material was obtained, wherein the sintering temperature was 290°C, the holding time was 8h, the oxygen volume content was more than 90%, and the slight positive pressure (25±2Pa) .

The co-coated nickel cobalt lithium aluminate Li _1.02 Ni _0.91 Co _0.06 Al _0.03 O ₂ cathode material prepared in this example has a discharge specific capacity of 211.1 mAh/g at 0.1C, and the capacity basically does not decay for 100 cycles.

Example 3

Step 1: Weigh a certain mass of nickel-cobalt aluminate precursor, the molecular formula is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , mix with lithium hydroxide (LiOH·H ₂ O) and sinter to obtain lithium nickel-cobalt aluminate Initial sintering material. The molar ratio of nickel-cobalt aluminate precursor to lithium source is 1:1.01, the sintering temperature is 705°C, and the holding time is 10h.

Step 2: Weigh a certain mass of nickel-cobalt lithium aluminate primary sintering material, add a certain mass of deionized water at a water-to-material ratio of 1:1 for stirring and washing, the stirring speed is 500rpm, and the washing time is 15min. After that, suction filtration, and vacuum drying for 8 hours at a temperature of 120° C. to obtain a nickel-cobalt lithium aluminate cathode material matrix.

Step 3: mixing the matrix cathode material and the coating lithium iron phosphate-boric acid by ball milling, wherein the mass fraction of lithium iron phosphate in the matrix cathode material is 0.10wt%, and the mass fraction of boric acid in the matrix cathode material is 0.10wt%. After high temperature sintering, a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material was obtained, wherein the sintering temperature was 270°C, the holding time was 6h, the oxygen volume content was more than 90%, and the slight positive pressure (30±2Pa) .

The co-coated nickel cobalt lithium aluminate Li _1.01 Ni _0.91 Co _0.06 Al _0.03 O ₂ cathode material prepared in this example has a 0.1C discharge specific capacity of 214.7 mAh/g, and the capacity basically does not decay for 100 cycles.

Example 4

Step 1: Weigh a certain mass of nickel-cobalt aluminate lithium precursor, the molecular formula is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , mix with lithium hydroxide (LiOH·H ₂ O) and sinter to obtain lithium nickel-cobalt aluminate Initial sintering material. The molar ratio of nickel cobalt aluminate precursor to lithium source is 1:1.03, the sintering temperature is 715°C, and the holding time is 12h.

Step 2: Weigh a certain quality of primary sintered material of nickel cobalt lithium aluminate, add a certain quality of deionized water at a water-to-material ratio of 3:1 for stirring and washing, the stirring speed is 500rpm, and the washing time is 30min. Then, suction filtration, and vacuum drying for 6 hours at a temperature of 120° C. to obtain a nickel-cobalt lithium aluminate cathode material matrix.

Step 3: mixing the base cathode material and the coating lithium iron phosphate-boric acid by ball milling, wherein the mass fraction of lithium iron phosphate in the base cathode material is 0.10wt%, and the mass fraction of boric acid in the base cathode material is 0.08wt%. After high temperature sintering, a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material was obtained, wherein the sintering temperature was 350°C, the holding time was 8h, the oxygen volume content was more than 95%, and the slight positive pressure (25±2Pa) .

The 0.1C discharge specific capacity of the finished product of the co-coated nickel cobalt lithium aluminate Li _1.03 Ni _0.91 Co _0.06 Al _0.03 O ₂ cathode material prepared in this example is 213.1 mAh/g, and the capacity is basically not attenuated for 100 cycles.

Example 5

Step 1: Weigh a certain mass of nickel-cobalt aluminate precursor, the molecular formula is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , mix with lithium hydroxide (LiOH·H ₂ O) and sinter to obtain lithium nickel-cobalt aluminate Initial sintering material. The molar ratio of nickel cobalt aluminate precursor to lithium source is 1:1.06, the sintering temperature is 750°C, and the holding time is 15h.

Step 2: Weigh a certain mass of nickel-cobalt lithium aluminate primary sintering material, add a certain mass of deionized water at a water-to-material ratio of 5:1, and stir and wash with a stirring speed of 500 rpm and a washing time of 60 minutes. After centrifugation, and vacuum drying for 10 hours at a temperature of 150° C., a matrix of nickel-cobalt lithium aluminate cathode material was obtained.

Step 3: Mix the base cathode material and the coating lithium iron phosphate-boric acid with a high-mixer, wherein the mass fraction of lithium iron phosphate in the base cathode material is 0.20 wt %, and the mass fraction of boric acid in the base cathode material is 0.15 wt % . After high temperature sintering, a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate cathode material was obtained, wherein the sintering temperature was 450°C, the holding time was 10h, the oxygen volume content was more than 95%, and the slight positive pressure (30±2Pa) .

The lithium nickel cobalt aluminate Li _1.06 Ni _0.91 Co _0.06 Al _0.03 O ₂ cathode material prepared in this example has a 0.1C discharge specific capacity of 211.5mAh/g, and the capacity basically does not decay for 100 cycles.

Claims (10)

1. a lithium iron phosphate-boric acid co-coated nickel-cobalt lithium aluminate anode material, is characterized in that, the nickel-cobalt lithium aluminate anode material is made up of matrix cathode material and lithium iron phosphate-boric acid co-coating layer, The molecular formula of the base positive electrode material is Li _a Ni _0.91 Co _0.06 Al _0.03 O ₂ , where 1.01≤a≤1.06. 2. a kind of lithium iron phosphate-boric acid co-coated nickel-cobalt lithium aluminate positive electrode material according to claim 1, is characterized in that, described lithium iron phosphate-boric acid co-coated layer comprises the lithiated layer of phosphoric acid, The lithiated layer of iron phosphate and the lithiated layer of boric acid. 3. a kind of lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material according to claim 1 is characterized in that, in the raw material of preparing lithium iron phosphate-boric acid co-coated layer, lithium iron phosphate accounts for The mass fraction of the matrix cathode material is 0.02wt%-0.30wt%; the mass fraction of the boric acid in the matrix cathode material is 0.01wt%-0.30wt%. 4. A kind of lithium iron phosphate-boric acid co-coated nickel-cobalt lithium aluminate positive electrode material according to claim 1, characterized in that, in the lithium iron phosphate-boric acid co-coated layer, lithium iron phosphate accounts for the matrix The mass fraction of the positive electrode material is 0.05wt%-0.20wt%; the mass fraction of the boric acid in the matrix positive electrode material is 0.03wt%-0.15wt%. 5. the preparation method of the lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material according to any one of claims 1-4, is characterized in that, comprises the following steps: Step 1: Weigh the nickel cobalt lithium aluminate precursor, mix it with lithium and sinter to obtain the nickel cobalt lithium aluminate primary sintering material; Step 2: adding the nickel cobalt lithium aluminate primary sintering material into deionized water for stirring and washing, and vacuum drying after solid-liquid separation to obtain a matrix cathode material; Step 3: mixing the base positive electrode material and the coating lithium iron phosphate-boric acid, and then sintering at a high temperature to obtain a lithium iron phosphate-boric acid co-coated nickel cobalt lithium aluminate positive electrode material. 6. the preparation method of the lithium iron phosphate-boric acid co-coated nickel-cobalt aluminate positive electrode material according to claim 5, is characterized in that, the lithium source that adopts when mixing lithium in step 1 is lithium hydroxide LiOH·H ₂ O, the precursor of nickel cobalt aluminate is Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ , and the molar ratio of the precursor of nickel cobalt aluminate to lithium source is 1:(1.01-1.06), and the sintering temperature is 650-750 ℃, the holding time is 9-15h. 7. the preparation method of the nickel cobalt lithium aluminate positive electrode material of lithium iron phosphate-boric acid co-coated according to claim 5, is characterized in that, in step 2, the quality of deionized water and nickel cobalt lithium aluminate primary sintering material The ratio is (1-5):1. 8. the preparation method of the lithium iron phosphate-boric acid co-coated nickel-cobalt aluminate positive electrode material according to claim 5, is characterized in that, in step 2, stirring and washing time is 10-60min, and stirring linear velocity is 500rpm; The method of solid-liquid separation is one of centrifugation and suction filtration; the vacuum drying temperature is 100-150°C, and the time is 4-10h. 9. the preparation method of the nickel cobalt lithium aluminate anode material of the co-coated lithium iron phosphate-boric acid according to claim 5, is characterized in that, the mixing mode of matrix cathode material and coating lithium iron phosphate-boric acid is ball milling And one of the high mixes. 10. The preparation method of the lithium iron phosphate-boric acid co-coated nickel-cobalt aluminate cathode material according to claim 5, characterized in that, after the matrix cathode material is mixed with the coating lithium iron phosphate-boric acid, the sintering temperature The temperature is 250-450°C, and the holding time is 6-10h; the atmosphere in the sintering process is an oxygen-rich atmosphere, the pressure is 20Pa-40Pa, and the oxygen volume content is 90%-99%.

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