CN117525403A - High-voltage high-capacity medium-high nickel monocrystal ternary positive electrode material, preparation method thereof and battery - Google Patents

Abstract

The invention belongs to the field of new energy and discloses a high-voltage, high-capacity, medium-high nickel single crystal ternary cathode material, which is characterized in that it includes a core layer, an inner cladding layer, and an outer cladding layer, and the inner cladding layer is a hydroxyl group. Aluminum oxide is coated on the surface of the core layer through a wet coating method at 0-10°C; the outer cladding layer is a boron source coated on the surface of the inner cladding layer through a dry coating method; The molar content of nickel in the core layer accounts for more than 60% of the total molar amount of nickel, cobalt and manganese. The cathode material has excellent first charge and discharge capacity. At the same time, the invention also provides a preparation method of the cathode material and a lithium-ion battery.

Description

A high voltage, high capacity, medium and high nickel single crystal ternary cathode material and its preparation method and Battery

Technical field

The invention relates to the field of new energy, specifically a high-voltage, high-capacity medium-high nickel single crystal ternary cathode material and a preparation method and battery thereof.

Background technique

With the progress of human society and the upgrading of consumption, consumers have put forward higher and higher requirements for energy storage devices. The current mainstream energy storage device is lithium-ion battery, which is divided into power lithium-ion battery and consumer electronics lithium-ion battery. Batteries, commercial lithium-ion batteries not only require good safety, but also must meet the characteristics of high energy density and low economic cost. The key factor that restricts the energy density of lithium-ion batteries is the performance of the cathode material. High-nickel, single-crystal, and high-voltage cathode materials are currently the more mainstream technical routes for improving energy density, but the problems that follow are High nickelization increases the residual lithium on the surface of the material, causing a series of safety, storage, processing and other problems. Single crystallization makes the lithium ion transmission path of the material longer and the particle uniformity becomes worse. The surface and internal structure of the material under high voltage Problems such as poor stability and increased side reactions can cause structural collapse and short cycle life. Therefore, if you want to obtain a high voltage, high capacity, medium and high nickel single crystal ternary cathode material, you need to focus on solving the above problems.

D1: CN202210721702.3 discloses a low-temperature high-power ternary cathode material and a preparation method thereof, which belongs to the technical field of lithium-ion batteries. The preparation method of the low-temperature high-power ternary cathode material includes the following steps: uniformly mixing the ternary precursor, lithium salt, magnesium chromate, and lithium titanium zirconium phosphate to obtain a mixed material; sintering the mixed material in an oxygen-containing atmosphere, After sintering, the sample is crushed to obtain pulverized material; finally, the outer surface of the pulverized material is coated in layers to form an aluminum fluoride layer and a boron oxide layer to obtain the target product.

Its instructions state that it is double-coated with boron oxide and aluminum fluoride. The aluminum fluoride coating blocks contact with the electrolyte during battery charging and discharging, reduces the occurrence of side reactions on the surface of the material, and improves the cycle performance of the material. Boron oxide is more likely to absorb moisture in the air to generate boric acid, thereby reducing the water absorption of lithium oxide on the material surface and converting it into lithium hydroxide and lithium carbonate, thereby reducing the residual alkali on the material surface. The boric acid generated can further acidify the material surface and reduce electrolysis. The liquid corrodes the material surface and further improves the material's cycle performance.

Embodiment 1 records that the outer surface of the pulverized material is coated with an aluminum fluoride layer and a boron oxide layer in layers. The method is: the aluminum fluoride and the pulverized material are uniformly mixed together in a mass ratio of 0.015:1, and then placed. Sintering in a muffle furnace at 650°C for 8 hours. After the sintering is completed, the material is crushed in a universal crusher for 30 seconds and sieved in a 400 mesh screen to obtain the material coated with the aluminum fluoride layer.

It can be seen that this solution uses dry coating.

D2: CN201910959426.2 discloses quaternary cathode materials for lithium-ion batteries and their preparation methods and lithium-ion batteries. The quaternary cathode material includes a core and a cladding layer. The cladding layer is formed on at least part of the surface of the core. The quaternary cathode material has a composition as shown in formula (I), LixNiaCobMncAldMyO2 (I) formula In (I), 1.00≤x≤1.05, 0.00≤y≤0.05, 0.3≤a≤0.92, 0.03≤b≤0.06, 0.01≤c≤0.03, 0.01≤d≤0.03, a+b+c+d=1 , M is at least one selected from the group consisting of second main group elements, third main group elements, fourth main group elements, fifth main group elements, fourth sub-group elements, and fifth sub-group elements.

Its instruction manual records: the method of quaternary cathode materials includes:

(1) Mix the quaternary cathode material precursor, lithium source and dopant to obtain the first mixture;

(2) Perform a first sintering process on the first mixed material to obtain a core of quaternary positive electrode material;

(3) Mix the quaternary positive electrode material core with the first coating agent to obtain a second mixture;

(4) Perform a second sintering treatment on the second mixture to obtain a primary coating product;

(5) Mix the primary coating product with the second coating agent to obtain a third mixture;

(6) Calcining the third mixture to obtain the quaternary cathode material.

The first coating agent includes at least one selected from aluminum oxide, aluminum hydroxide, aluminum nitrate, and aluminum oxyhydroxide;

The second coating agent includes at least one selected from the group consisting of boric acid, boron oxide, lithium phosphate, and lithium niobate.

The description states: In order to further improve the quality of the prepared quaternary cathode material, according to embodiments of the present invention, the primary coating product can be washed and dried before S500. As a result, impurities contained in the primary coated product can be effectively removed. During the research, the inventor found that the primary coating product contained some residual alkali Li2CO3, LiOH, Li2O and other impurities. If impurities are not removed during the battery manufacturing process, the viscosity of the battery slurry will increase or even become gel-like or jelly-like, making the material unable to enter the next stage of the process.

The embodiments describe that alumina is used for dry coating.

From the records of this case, we can find that the case tends to remove residual lithium through water washing.

D3: CN201910831610.9 discloses a cathode material. The chemical formula of the cathode material is Li1.01~1.12NixCoyMn(1-xy)M0.001~0.008B0.001~0.015O2, where 0.45<x<0.75, 0.15<y<0.35, 0<x+y<1, M is one or more of Al, Ti, Sn, and Nb. The positive electrode material includes a lithium nickel cobalt manganese oxide matrix and is coated with the lithium Glassy composite coating of LiMO ₂ -B ₂ O ₃ on nickel cobalt manganese oxide substrate.

The instruction manual records: S2: Put the lithium nickel cobalt manganese oxide matrix and the metal compound containing M into a ball mill tank for ball milling. After the first heat treatment, a lithium nickel cobalt manganese oxide package coated with a metal oxide film is obtained. Covering matrix, M is at least one or more of Al, Ti, Sn, and Nb. The M-containing metal compound is one or more of aluminum nitrate, aluminum acetate, aluminum hydroxide, aluminum oxyhydroxide, titanium dioxide, titanium hydroxide, tin oxide, and niobium pentoxide. The molar ratio of the metal compound to the lithium nickel cobalt manganese oxide matrix is 0.001 to 0.008:1. The ball milling time is 1 to 3 hours. The ball to material ratio is 1.3:1. The first heat treatment temperature is 600~900℃, and the first heat treatment time is 8~16h.

S3: uniformly mix the lithium nickel cobalt manganese oxide coating matrix coated with the metal oxide film and the boron-containing compound in a high-speed mixer, and obtain the cathode material after the second heat treatment.

The boron-containing compound is one of boric acid, metaboric acid, pyoboric acid (H ₂ B ₄ O ₇ ), and boron oxide. The molar ratio of the boron-containing compound to the lithium nickel cobalt manganese oxide coating matrix is 0.001 to 0.015:1. The mixing time is 5 to 15 minutes. The temperature of the second heat treatment is 300~600℃, and the time of the second heat treatment is 4~12h.

D4: CN202210287611.3 discloses a method for preparing an Al/B co-coated cathode material. Mix the precursor material and the lithium source evenly, and sinter in an air or oxygen atmosphere to obtain a cathode material matrix; mix the cathode material matrix and the nanoscale Al source in a mixer at high speed, and then add the lithium source and micron-scale B source Mix at low speed to obtain a mixture; sinter the mixture in an air or oxygen atmosphere to obtain an Al/B co-coated cathode material. The Al source is at least one of nanometer-sized aluminum oxide, aluminum oxyhydroxide, and aluminum hydroxide; the B source is at least one of micron-sized boron oxide, boron nitride, and boric acid.

The description states: The present invention uses a pure dry coating process to form Al/B co-coating on the surface of the cathode material. First, the Al source is coated on the surface of the cathode material matrix under high-speed mixing conditions, and the Al source is evenly attached to the surface of the particles; then the B source is coated on the surface of the cathode material matrix under low-speed conditions, and the lithium source is supplemented. The coated Al source combines with the residual alkali on the surface, and the coated B source combines with the supplementary Li source. After secondary sintering, a double-layer coating film of Li-Al-O/Li-B-O is formed respectively. The ions of the cathode material The conductivity is further improved. At the same time, the cathode material is evenly covered with a double-layer film and has less contact with the electrolyte. The HF corrosion resistance is enhanced, and the cycle and rate performance are improved.

D5: CN201610223367.9 discloses a high-voltage single crystal ternary cathode material and its preparation method. The general formula of this material can be expressed as LixNi1-m-nComMnnO ₂ (0.96<x<1.12, 0<m<1, 0<n<1, and m+n<1). Using nickel salt, cobalt salt and manganese salt as raw materials, the precursor is prepared by co-precipitation method or chemical synthesis method, and the precursor is mixed with the lithium source. After pretreatment, the modifier is added to it, mixed evenly and then High voltage single crystal ternary cathode material is obtained by sintering, crushing and sieving. The prepared high-voltage single-crystal ternary cathode material has a grain size of 2 to 15 μm and a compacted density of 3.8 to 3.9 g/cm3. At the same time, the surface of the ternary cathode material is modified by wet coating with Al to stabilize the material structure and inhibit side reactions between the material and the electrolyte.

The instructions state: (4) wet-coat aluminum with the material LixNi1-m-nComMnnO2 obtained in step (3): slowly add the prepared aluminum compound-containing solution to the aqueous phase system or organic phase system through a peristaltic pump. into LixNi1-m-nComMnnO2 obtained in step (3), control the pH value of the reaction in the range of 5.5 to 10.5, and the reaction temperature in the range of 25 to 65°C; stir for 0.5 to 4h, with a stirring speed of 300 to 800r/min, and then After suction filtration, drying, and finally calcining at 400 to 800°C for 5 to 10 hours, the LixNi1-m-nComMnnO2 material with uniform aluminum surface coating is obtained.

The solution containing the aluminum compound adopts at least one of aluminum nitrate, aluminum isopropoxide, aluminum ethoxide, aluminum acetylacetonate, aluminum stearate, aluminum oxyhydroxide, aluminum chloride, and nano-alumina. The coating amount of aluminum In 0.01~5wt%.

After Al is wet-coated, there is a uniform coating layer on the surface of the grain, which can prevent the reaction between the material and the electrolyte, and effectively improve the cycle performance, high-temperature storage performance and safety performance of lithium-ion batteries at high voltage. It has been actually tested that the wet Al-packing method effectively improves the cycle performance, high-temperature storage performance and safety performance of lithium-ion batteries at high voltages of 4.4 and 4.5V.

D6: The positive electrode disclosed in CN202010842563.0 includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. The above-mentioned non-aqueous electrolyte solution contains lithium fluorosulfonate. The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material layer contains aluminum oxide hydrate at least in a surface layer portion. The aluminum oxide hydrate is aluminum hydroxide or aluminum oxyhydroxide.

The following conclusions can be drawn from the above documents:

Conclusion 1: The coating of aluminum and boron was disclosed in D1-D4. Boron is mainly used to remove residual alkali, reduce the corrosion of the electrolyte on the material surface, and further improve the cycle performance of the material; in some comparison documents, it is believed that Al can Combined with residual alkali and boron, a double-layer coating film of Li-Al-O/Li-B-O can be formed; however, dry coating is used in D1-D4.

Conclusion 2: D5 disclosed wet coating of Al, while D6 did not disclose the method used for coating.

From the above analysis, it can be seen that aluminum and boron have the effect of reducing residual alkali, the inner layer of aluminum can play an isolation role, and aluminum and boron can form a double coating film.

At the same time, wet-coated aluminum has a uniform coating layer on the surface of the grains, which can prevent the reaction between the material and the electrolyte, effectively improving the cycle performance, high-temperature storage performance and safety performance of lithium-ion batteries at high voltages.

But overall, there is no significant difference between dry aluminum cladding and wet aluminum cladding.

The technical problem solved in this case is: how to further improve the first charge and discharge capacity of the cathode material.

Contents of the invention

The object of the present invention is to provide a high voltage, high capacity, medium and high nickel single crystal ternary cathode material, which has excellent first charge and discharge capacity.

At the same time, the invention also provides a preparation method of the cathode material and a lithium-ion battery.

In order to achieve the above objects, the present invention provides the following technical solution: a high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including a core layer, an inner cladding layer, and an outer cladding layer. The inner cladding layer is made of hydroxyl oxidation. Aluminum is coated on the surface of the core layer through a wet coating method at 0-10°C; the outer cladding layer is a boron source and is coated on the surface of the inner cladding layer through a dry coating method; The molar content of nickel in the core layer accounts for more than 60% of the total molar amount of nickel, cobalt and manganese.

After the cathode material is treated with a special coating process, the residual lithium hydroxide on the surface can be reduced to less than 500ppm, and the total residual lithium can be reduced to less than 2500ppm. The lower residual lithium can not only reduce the processing difficulty of subsequent preparation of lithium-ion battery slurry, It can also improve the high-temperature storage performance of the battery. The Al in the solution can fully and efficiently combine with residual lithium to form a "Li-Al-O" structural material, reducing the residual lithium content and forming a uniform and dense coating layer on the inner surface of the material, which can effectively isolate the core of the cathode material from the electrolyte. Contact, reducing side reaction activity, thereby effectively inhibiting the occurrence of side reactions, consumption of electrolyte and dissolution of cathode material elements, thus improving cycle under high voltage conditions. The outer layer is coated with LixBO3-containing substances, and the B-containing substances in the outer layer are isolated by the Al coating layer. The outer layer can avoid combining with the structural Li in the core of the material, and preferentially combines with the residual lithium that has not reacted with Al and captures part of the "Li- The Li in "Al-O" forms a "Li-B-O" structural material. Because the Li in the "Li-B-O" structure is in the outermost layer, it can be preferentially used to form the positive electrode CEI film and migrate to the negative electrode for SEI film formation, reducing The active lithium in the first charge and discharge is lost, and the Li-B-O material formed is a fast ion conductor layer, which can accelerate the deintercalation of lithium ions on the surface of the cathode material, further reducing polarization and increasing the first charge and discharge capacity.

In the above-mentioned high voltage, high capacity, medium and high nickel single crystal ternary cathode material, the coating amount of the inner coating layer is 1%-5%. Preferably, it is 2.86-4.29%; the % here represents the amount of aluminum oxyhydroxide required for 100g of the cathode material, which is equivalent to the percentage content of the cathode material;

In the above-mentioned high voltage, high capacity, medium and high nickel single crystal ternary cathode material, the coating amount of the outer coating layer is 0.1%-0.6%, and the boron source is boron oxide or boron oxyhydroxide. The % here represents the amount of boron source required for 100 g of cathode material, which is equivalent to the percentage content of the cathode material; preferably, the coating amount of the outer coating layer is 0.11%-0.35%.

In the above-mentioned high voltage, high capacity, medium and high nickel single crystal ternary cathode material, the chemical formula of the core layer is: _LiNix Co _y Mn _1-xy O ₂ , where 0.6<x<0.8, 0.05≤y≤0.10.

Although the embodiments of the present invention only show specific cases where x is 0.72 and y is 0.07, it is actually found during repeated experiments that for high-nickel single crystal ternary materials, the method of the present invention can The same trend appears within the above range.

At the same time, the invention also discloses a method for preparing the cathode material as described in any one of the above, including the following steps:

Step 1: Coat aluminum oxyhydroxide on the surface of the core layer through wet coating to form an inner coating layer; the temperature of wet coating is 0-10°C;

Step 2: Coat boric acid on the surface of the inner coating layer through dry coating to form an outer coating layer.

In the above preparation method of cathode material, in step 1, the ratio of core layer to solvent is 0.5-2:1.

In the above preparation method of cathode material, the solvent is water or absolute ethanol or aqueous ethanol of any concentration;

Coating time is 5-60min;

The wet coating method is as follows: adding the aluminum oxyhydroxide solution to the solvent, stirring, then adding the positive electrode material, and continuing to stir;

After step 1, filter the material with the inner coating layer and proceed to step 2 after drying.

In the above preparation method of positive electrode material, the weight ratio of the boric acid and the material with an outer coating layer obtained in step 1 is 1000:1-6.

In the above-mentioned preparation method of the positive electrode material, a ball mill is used for dry coating, and then the material is sintered at a temperature of 300-450°C.

Finally, the present invention also discloses a lithium ion battery, which is characterized in that it includes a positive electrode, a negative electrode, an electrolyte and a separator, and the active ingredients in the positive electrode are as described above.

Compared with the prior art, the beneficial effects of the present invention are:

The surface residual lithium hydroxide of the cathode material of the present invention can be reduced to less than 500 ppm, and the total residual lithium can be reduced to less than 2500 ppm. The lower surface residual lithium can not only reduce the processing difficulty of subsequent preparation of lithium ion battery slurry, but also improve the performance of the battery. High temperature storage performance. The Al in the solution can fully and efficiently combine with residual lithium to form a "Li-Al-O" structural material, reducing the residual lithium content and forming a uniform and dense coating layer on the inner surface of the material, which can effectively isolate the core of the cathode material from the electrolyte. contact, reducing the side reaction activity, thereby effectively inhibiting the occurrence of side reactions, the consumption of electrolyte and the dissolution of cathode material elements, thus improving the cycle under high voltage conditions. The outer layer is coated with LixBO3-containing substances, and the B-containing substances on the outer layer are isolated by the Al coating layer. The outer layer can avoid combining with the structural Li in the core of the material, and preferentially combines with the residual lithium that has not reacted with Al and captures part of the "Li- Li in "Al-O" forms a "Li-B-O" structural material. Because Li in the "Li-B-O" structure is in the outermost layer, it can be preferentially used for positive electrode CEI film formation and migrate to the negative electrode for SEI film formation, reducing The active lithium in the first charge and discharge is lost, and the Li-B-O material formed is a fast ion conductor layer, which can accelerate the deintercalation of lithium ions on the surface of the cathode material, further reducing polarization and increasing the first charge and discharge capacity.

Description of drawings

Figure 1 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Example 1;

Figure 2 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Example 2;

Figure 3 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Example 3;

Figure 4 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Example 4;

Figure 5 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Example 5;

Figure 6 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Comparative Example 1;

Figure 7 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Comparative Example 2;

Figure 8 is a scanning electron microscope image of the high-voltage single crystal low-cobalt ternary cathode material of Comparative Example 3.

Detailed ways

The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1

A method for preparing high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including the following steps:

1) Add a solution containing 2.86g aluminum oxyhydroxide to 100ml deionized water, control the water temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of cathode material and continue stirring for 30 minutes; the chemical formula of the cathode material is (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ )

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Mix the thoroughly dried coating with 0.18g boric acid in a ball mill for 30 minutes, and then transfer it to a muffle furnace for sintering at 350°C/6h;

6) Cool to room temperature and then take it out to obtain a surface-coated high-voltage, high-capacity, medium-to-high nickel single crystal ternary cathode material.

Example 2

A method for preparing high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including the following steps:

1) Add a solution containing 2.86g aluminum oxyhydroxide to 100ml absolute ethanol, control the temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of cathode material and continue stirring for 30 minutes; the chemical formula of the cathode material is (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ )

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Mix the thoroughly dried coating with 0.18g boric acid in a ball mill for 30 minutes, and then transfer it to a muffle furnace for sintering at 300°C/6h;

6) Cool to room temperature and then take it out to obtain a surface-coated high-voltage, high-capacity, medium-to-high nickel single crystal ternary cathode material.

Example 3

A method for preparing high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including the following steps:

1) Add a solution containing 4.29g aluminum oxyhydroxide to 100ml deionized water, control the temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of cathode material and continue stirring for 30 minutes; the chemical formula of the cathode material is (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ )

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Mix the thoroughly dried coating with 0.18g boric acid in a ball mill for 30 minutes, and then transfer it to a muffle furnace for sintering at 350°C/6h;

6) Cool to room temperature and then take it out to obtain a surface-coated high-voltage, high-capacity, medium-to-high nickel single crystal ternary cathode material.

Example 4

A method for preparing high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including the following steps:

1) Add a solution containing 2.86g aluminum oxyhydroxide to 100ml deionized water, control the temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of cathode material and continue stirring for 30 minutes; the chemical formula of the cathode material is (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ )

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Mix the thoroughly dried coating and 0.18g nano boron oxide in a ball mill for 30 minutes, and then transfer it to a muffle furnace for sintering at 350°C/6h;

6) Cool to room temperature and then take it out to obtain a surface-coated high-voltage, high-capacity, medium-to-high nickel single crystal ternary cathode material.

Example 5

A method for preparing high voltage, high capacity, medium and high nickel single crystal ternary cathode material, including the following steps:

1) Add a solution containing 2.86g aluminum oxyhydroxide to 100ml deionized water, control the temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of positive electrode material and continue stirring for 30 minutes;

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Mix the thoroughly dried coating and 0.27g nano boron oxide in a ball mill for 30 minutes, then transfer to a muffle furnace for sintering at 350°C/6h;

6) Cool to room temperature and then take it out to obtain a surface-coated high-voltage, high-capacity, medium-to-high nickel single crystal ternary cathode material.

Example 6

It is roughly the same as Example 1, except that the amount of aluminum oxyhydroxide is 3g and the amount of boric acid is 0.11g. The stirring time for step 1 is 20 minutes, and the stirring time for step 2 is 20 minutes. The sintering temperature in step 5 is 300°C, and the sintering time is 5 hours.

Example 7

It is roughly the same as Example 1, except that the amount of aluminum oxyhydroxide is 3.5g and the amount of boric acid is 0.22g. The stirring time for step 1 is 10 minutes, and the stirring time for step 2 is 15 minutes. The sintering temperature in step 5 is 350°C, and the sintering time is 6 hours.

Example 8

It is roughly the same as Example 1, except that the amount of aluminum oxyhydroxide is 3.8g and the amount of boric acid is 0.35g. The stirring time for step 1 is 30 minutes, and the stirring time for step 2 is 30 minutes. The sintering temperature in step 5 is 400°C, and the sintering time is 4h.

Comparative example 1

A method for preparing a ternary cathode material, including the following steps:

1) Add 2.86g aluminum oxyhydroxide solution to 100ml deionized water, control the water temperature within 0-10°C, and stir for 15 minutes;

2) Then add 100g of cathode material (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ ) and continue stirring for 30 minutes;

3) Use an ice bath while stirring to ensure that the solution is within 0-10°C throughout the process, and obtain a preliminary inner surface coating slurry after vacuuming and dehydration;

4) Transfer to a constant temperature drying oven and dry thoroughly at 100°C/3h;

5) Sinter at 350°C/6h in a muffle furnace, cool to room temperature and then take it out to obtain the single crystal ternary cathode material of Comparative Example 1.

Comparative example 2

A method for preparing a ternary cathode material, including the following steps:

1) Mix 100g of a calcined matrix and 0.18g of nano boron oxide in a ball mill for 30 minutes, then transfer to a muffle furnace for sintering at 350°C/6h; the chemical formula of a calcined matrix is LiNi _0.72 Co _0.07 Mn _0.21 O ₂ ;

2) Cool to room temperature and take it out to obtain the ternary cathode material of Comparative Example 2.

Comparative example 3

It is basically the same as Example 1, except that the final sintering coating temperature is 500°C/6h.

Comparative example 4

A method for preparing a ternary cathode material: mix 0.23g nano-alumina (the same Al content as 2.86g aluminum oxyhydroxide solution) and 100g cathode material (LiNi _0.72 Co _0.07 Mn _0.21 O ₂ ), ball mill, and muffle furnace It is sintered at 350℃/6h.

Comparative example 5

It is roughly the same as Example 1, except that the aluminum oxyhydroxide is replaced by aluminum nitrate in an equal molar amount.

Comparative example 6

It is roughly the same as Example 1, except that the aluminum oxyhydroxide is replaced by aluminum hydroxide in an equal molar amount.

Comparative example 7

It is basically the same as Example 1, except that steps 1-3 are carried out at room temperature.

Performance Testing

Test items: 0.1C first charge, 0.1C first discharge, 0.1C first effect, 50-week cycle retention rate and residual alkali detection.

The test method is:

0.1C first charge test: Under normal temperature, constant current charge at 0.1C rate to 4.45V, constant voltage charge until the cut-off current is less than 0.05C, first charge capacity is the sum of constant current charge and constant voltage charge capacity;

0.1C first discharge test: at room temperature, 0.1C constant current discharge to 3.0V;

0.1C first effect test: ratio of first discharge capacity to first charge capacity;

50-cycle cycle retention test: 1C charge and discharge cycle for 50 weeks at room temperature.

The test results can be seen in Table 1 and Table 2

Table 1 shows the capacitance comparison of high-voltage single crystal low-cobalt ternary cathode materials in Examples and Comparative Examples.

Table 2 Comparison of residual lithium in high-voltage single crystal low-cobalt ternary cathode materials of Examples and Comparative Examples

Conclusion analysis:

1. Through the analysis of Comparative Example 1 and Comparative Example 4, it can be seen that there is a big difference in the electrical properties of the two methods of aluminum coating by wet method and dry aluminum coating, in terms of the reduction of residual alkali;

2. Through the comparison between Example 1 and Comparative Example 1, it can be found that if boron is not coated, its first discharge, first effect and cycle retention rate deteriorate; Aluminum, its first release, first effect and cycle retention rate are even worse.

3. Through the comparison between Example 1 and Comparative Example 3, it can be found that the material is relatively sensitive to sintering temperature, and excessive temperature will lead to coating failure;

4. Through the comparison between Example 1 and Comparative Examples 5 and 6, it can be found that other aluminum sources are not as effective as aluminum oxyhydroxide in improving electrical properties and residual alkali;

5. Through the comparison between Example 1 and Comparative Example 7, it can be found that the temperature of wet coating is a very important process parameter in the entire experiment.

Figures 1-8 are electron microscopy images of Examples 1-5 and Comparative Examples 1-3. From Figures 1-8 we can see that compared with dry mixing, wet coating can significantly reduce residual lithium on the material surface and improve surface coating. Cover uniformity;

Based on the above analysis, we believe that wet coating at low temperatures is conducive to the dissociation of lithium into the liquid, and as the coating proceeds, it can be evenly combined with aluminum on the surface of the material, which is important for first charge, first discharge, and first effect. , cycle maintenance are beneficial;

Compared with free aluminum ions and aluminum hydroxide, aluminum oxyhydroxide has a molecular structure, is insoluble in water, and will not be taken away by the filtration process. When it is coated on the surface of the cathode material, it behaves uniformly Stable coating; it is combined with the dry-coated boron source to form an inner and outer double coating layer to further improve the electrical performance.

Claims (10)

1. A high voltage, high capacity, medium and high nickel single crystal ternary cathode material, characterized in that it includes a core layer, an inner cladding layer, and an outer cladding layer. The inner cladding layer is aluminum oxyhydroxide coated by a wet method. The method is coated on the surface of the core layer under the conditions of 0-10°C; the outer coating layer is a boron source and is coated on the surface of the inner coating layer by dry coating; the nickel in the core layer The molar content accounts for more than 60% of the total molar amount of nickel, cobalt and manganese. 2. The high voltage, high capacity, medium and high nickel single crystal ternary cathode material according to claim 1, characterized in that the coating amount of the inner coating layer is 1%-5%. 3. The high voltage, high capacity, medium and high nickel single crystal ternary cathode material according to claim 1, characterized in that the coating amount of the outer coating layer is 0.1%-0.6%, and the boron source is boron oxide. or boron oxyhydroxide. 4. The high voltage, high capacity _, medium and high nickel single crystal ternary cathode material according to claim 1, characterized in that the chemical formula of the core layer is: _{LiNixCoyMn1 -xyO2 ,} wherein, 0.6<x <0.8, 0.05≤y≤0.10. 5. A method for preparing the cathode material according to any one of claims 1 to 4, characterized in that it includes the following steps: Step 1: Coat aluminum oxyhydroxide on the surface of the core layer through wet coating to form an inner coating layer; the temperature of wet coating is 0-10°C; Step 2: Coat boric acid on the surface of the inner coating layer through dry coating to form an outer coating layer. 6. The preparation method of the cathode material according to claim 5, characterized in that in step 1, the ratio of the core layer to the solvent is 0.5-2:1. 7. The preparation method of the cathode material according to claim 6, wherein the solvent is water or absolute ethanol or aqueous ethanol of any concentration; Coating time is 5-60min; The wet coating method is as follows: adding the aluminum oxyhydroxide solution to the solvent, stirring, then adding the positive electrode material, and continuing to stir; After step 1, filter the material with the inner coating layer and proceed to step 2 after drying. 8. The method for preparing a cathode material according to claim 5, wherein the weight ratio of the material with the inner cladding layer obtained in step 1 to boric acid is 1000:1-6. 9. The preparation method of the cathode material according to claim 5, characterized in that a ball mill is used for dry coating and then sintering at a temperature of 300-450°C. 10. A lithium-ion battery, characterized in that it includes a positive electrode, a negative electrode, an electrolyte and a separator, and the active component in the positive electrode is as described in any one of claims 1-4.