WO2022104899A1 - Preparation method for positive electrode material for lithium ion battery - Google Patents

Abstract

A preparation method for a positive electrode material for a lithium ion battery, characterized in that a metal salt of a fatty acid is mixed with the positive electrode material for a lithium battery, and a coated positive electrode material is prepared by high-temperature solid-phase reaction sintering. The preparation method provided by the present invention can quickly realize uniform coating of a positive electrode material, enhancing the interface stability of a positive electrode material for a lithium ion battery, thereby enhancing the safety, stability and cycle life of the material and significantly eliminating resistance rise after the use of the battery material.

Description

Preparation method of positive electrode material for lithium ion battery technical field

The invention relates to a preparation method of an electrode material, in particular to a preparation method of a positive electrode material of a lithium battery, which further improves various performances of the battery.

Background technique

Lithium-ion batteries, as a green energy storage technology with high energy density and good cycle life, are widely used in various energy storage devices. Especially recently, electric vehicles, which have been vigorously developed in order to alleviate environmental pollution, have brought broad business opportunities to the lithium-ion battery industry. Large-scale commercial production of lithium-ion batteries with superior performance and low cost requires continuous innovation in advanced production technologies. In particular, the innovation in the production process of lithium-ion battery materials will greatly improve the performance of the entire lithium-ion battery and reduce production costs. As an indispensable part of lithium-ion batteries, the production process and cost of cathode materials have always been an important factor restricting the performance and price of lithium-ion batteries. The continuous pursuit of high energy density of lithium-ion batteries in the industry has forced the cycle cut-off voltage of cathode materials to be higher and higher. A higher cycle cut-off voltage will cause greater stress on the interfacial stability of the cathode material. How to realize the stability of the cathode material interface plays an important role in realizing the stability of the cathode material under high cut-off voltage. At present, the widely adopted technical means is to directly modify the surface of the positive electrode material, usually using oxides, fluorides and other non-electrochemical active materials to directly modify or coat the surface of the positive electrode material. Oxides, fluorides and other substances coated on the surface of the positive electrode material are used to avoid direct contact between the surface of the positive electrode material and the electrolyte, thereby reducing the surface reactivity of the positive electrode material, reducing the dissolution of metal ions, and delaying the transformation of the surface of the positive electrode material. By coating the positive electrode material, the overall cycle life and safety performance of the battery can be improved.

The industry uses the gas phase method, the liquid phase method and the solid phase method to coat the cathode material, of which the solid phase method has the lowest production cost and is the most suitable for large-scale production. However, the solid-phase method often results in poor material coating effect due to the uneven dispersion of the coating in the early stage. How to achieve uniform coating of cathode materials by solid-phase method has always been a difficulty in the industry.

CN108172826A discloses a method for coating high nickel ternary material. The technology firstly mixes the coating material lithium iron phosphate nanoparticles with the high nickel ternary material at low speed, and then performs high speed mechanical mixing to fuse and coat the coating material lithium iron phosphate and the high nickel ternary material to complete the coating experiment. The solid-phase coating method provided by this technology requires too much production equipment and is difficult to produce on a large scale.

CN108767221A discloses a method for coating the positive electrode material of lithium ion battery. This technology prepares a cathode material coated with an aluminum-titanium alloy by ball-milling the titanium-aluminum mixed oxide and the cathode material and then sintering at a high temperature. Also, the production steps of this technology are complicated and the equipment requirements are too high, which is not conducive to large-scale production.

CN111554907A discloses the application of fatty acid in preparing lithium ion battery and the method for preparing electrode material. In this technology, fatty acid is used as dispersant, and fatty acid is mixed with coating material as coating precursor, and then the coating is used as a coating precursor. The coating precursor is mixed with the electrode material for solid-phase sintering. After high temperature sintering, the fatty acid will turn into a liquid state to help the coating disperse on the surface of the electrode material, thereby forming a uniformly coated electrode material. This technology solves the problem of large-scale production of solid-state coating, but still needs to add a little more than 1% of coating materials such as metal oxides and metal fluorides, and ideal materials for lithium-ion batteries hope to reduce The amount of these coating materials further improves the battery performance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for preparing a positive electrode material for a lithium ion battery, which reduces the amount of coating material and further improves the performance of the material.

Another object of the present invention is to provide a method for preparing a positive electrode material for a lithium ion battery, which improves the energy retention rate of the material and is beneficial to the application in the lithium ion battery.

Another object of the present invention is to provide a method for preparing a positive electrode material of a lithium ion battery, which reduces the increase in resistance and is beneficial to the application in the lithium ion battery.

A method for preparing a positive electrode material for a lithium ion battery, adding metal salts of C10-C34 fatty acids, maintaining the coating uniformity of the electrode material prepared by the solid-phase method, and reducing the amount of the coating material.

The fatty acid provided by the present invention contains at least one carboxyl group. For example: but not limited to saturated or unsaturated monobasic acid, saturated or unsaturated dibasic acid, and saturated or unsaturated tribasic acid, etc., the number of single atoms contained in it is greater than 10, especially 10 to 34, such as: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 and 34.

Another specific compound embodiment is a saturated fatty acid, which includes substituents such as, but not limited to, hydroxyl, mercapto, amino, ester, alkane, alkene, and alkyne groups, and the like.

Another specific compound embodiment is an unsaturated fatty acid, including at least one saturated double bond or triple bond, and substituents such as, but not limited to, hydroxyl, mercapto, amino, ester, alkane, alkene, and alkyne groups .

In order to make lithium-ion battery electrode materials have higher thermal stability and cycle life. The use of fatty acids at room temperature contains two states of liquid phase and solid phase, that is, with the increase of the carbon chain length of fatty acids, fatty acids gradually change from liquid phase to solid phase. That is, when the number of carbon atoms of the saturated fatty acid is 10 or more, the fatty acid is in a solid phase at room temperature. Therefore, it can be matched with the method of coating battery materials with solid phase, and has practical feasibility, and can realize more economical and simpler manufacture of electrode materials.

Another specific embodiment of the metal salt of fatty acid is shown in the formula Me ^t+ [CH ₃ (CH ₂ ) _n COO] _t , where n is an integer from 8 to 32, such as: 8, 9, 10, 11, 12, 13 , 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 and 32. t is an integer from 1 to 7, such as: 1, 2, 3, 4, 5, 6 and 7. Me is a metal ion, such as but not limited to Li, Mg, Zn, Cu, Ca, Fe, Al, Ni, Co, Mn, Ti, Cr, Zr, Nb, W and other metal ions.

When the electrode material is prepared by the solid-phase method, the above-mentioned metal salt of the fatty acid is used to coat the lithium ion battery material. The fatty acids are volatilized during the heating process, and the metal salts are oxidized at high temperature to form metal oxides (such as but not limited to Li ₂ O, MgO, ZnO, CaO, CuO, NiO, CoO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , MnO ₂ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ and WO ₃ , etc.), and will not have any effect on lithium-ion battery materials.

When the battery material is prepared by the solid-phase method, the metal salts of the above-mentioned various fatty acids can coat the lithium-ion battery material, and form uniformly distributed oxides on the material, so that the amount of the used coating material is further reduced. , such as: 1% or less, such as: but not limited to 0.5%, also improves the energy retention rate of the material and reduces the resistance growth.

As known to those skilled in the art, the materials used to manufacture the positive electrode include: layered structure materials such as Li _1±m Ni _x Co _y Mn _z M _1-xyz O ₂ , where M is a trace element such as: but not limited to Cr , Mg, Al, Ti, Zr, Zn, Ca, Nb and W, etc.; m ranges from 0.005 to 0.2; x, y and z are independently selected from 0 to 1, and the sum of x, y and z is 0.8～1, such as but not limited to: x=0.8, y=0.1, z=0.1 or x=0.8, y=0, z=0.15. Common ternary materials such as: but not limited to NCM622 (chemical formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ), NCM811 (chemical formula LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ) and NCA (chemical formula LiNi _0.8 Co _0.15 Al _0.5 O _{2 )} )Wait. These materials are used in the present invention alone or in combination.

The metal salts of fatty acids of the present invention are in the form of solid powders, with particle sizes ranging from 10 nm to 2 μm, particularly powders with particle sizes ranging from 10 nm to 500 nm.

The metal salts of fatty acids of the present invention are aluminum stearate and aluminum laurate.

The metal salts of fatty acids of the present invention are magnesium stearate and magnesium laurate.

The present invention provides a method for preparing a positive electrode material for a lithium ion battery. The metal salt of the fatty acid is mixed with the positive electrode material for the lithium ion battery, and the surface of the electrode material for the lithium ion battery prepared by sintering (eg, at a temperature of 200° C. to 1000° C.) is uniform. Metal oxides are dispersed.

For the positive electrode material of the lithium ion battery applied to the preparation method of the present invention, the form of the positive electrode material is preferably powder.

The present invention provides a preparation method for preparing a lithium ion positive electrode material. The metal salt of fatty acid is mixed with the positive electrode material for lithium battery, and it is prepared by high-temperature solid-phase reaction sintering. ℃, the sintering time is such as: but not limited to 1 hour to 24 hours.

Another preparation method for preparing a lithium ion positive electrode material is to mix a metal salt of a fatty acid with a positive electrode material for a lithium battery. The temperature is raised to 200°C to 1000°C and sintered for 1 hour to 24 hours, so as to complete the solid-phase reaction between the coating material and the lithium ion battery material. After the sintering reaction is completed, the material is dispersed and sieved to obtain a uniformly coated positive electrode material.

In the various preparation methods provided by the present invention, the addition amount of the metal salt is correspondingly determined according to the content of the metal oxide in the prepared positive electrode material (for example: 0.6%±0.1%).

Another preparation method for preparing lithium ion positive electrode material, the metal salt of fatty acid is mixed with the positive electrode material for lithium battery, and it is prepared by high-temperature solid-phase reaction sintering, and in the obtained coated positive electrode material, the metal oxide accounts for The mass percentage is: 0.6% ± 0.1%, such as: 0.5%, 0.6% and 0.7%.

In the various preparation methods provided by the present invention, during the sintering process, the temperature is usually raised to 200°C to 1000°C at a rate of 1°C/min to 10°C/min, and then kept for 1 hour to 24 hours.

Another preparation method for preparing a lithium ion positive electrode material is that aluminum stearate or aluminum laurate is mixed with a positive electrode material for lithium batteries, and the temperature is raised to 200°C to 1000°C at a rate of 1 to 10°C/min. The temperature is maintained for another 1 to 24 hours, thereby completing the solid-phase reaction between the coating material and the lithium ion battery material. After the sintering reaction is completed, the material is dispersed and sieved to obtain a uniformly coated positive electrode material.

In the preparation method of the present invention, the specific sintering temperature and sintering time are determined according to the decomposition temperature of the fatty acid salt used.

The beneficial effects brought by the present invention are:

By using the metal salt of fatty acid as the coating material, the present invention can directly carry out uniform coating on the surface of the positive electrode material through high-temperature solid-phase reaction, the operation is simple, the cost is low, and it is very suitable for large-scale industrial production. After the reaction, except for the target coating (such as metal oxide) formed on the surface of the positive electrode material, no impurities will be generated, and the amount of the coating contained in the material is further reduced, so that the performance of the material is further improved.

The preparation method of the positive electrode material of the lithium battery provided by the present invention can quickly realize the uniform coating of the positive electrode material, enhance the interface stability of the positive electrode material of the lithium ion battery, thereby enhancing the safety stability and cycle life of the material, and at the same time significantly Improve the resistance increase that occurs when the battery material is used.

Description of drawings

Fig. 1 is magnesium stearate TGA curve figure;

Fig. 2 is aluminum stearate TGA curve figure;

Fig. 3 is aluminum laurate TGA curve diagram;

Fig. 4 is the surface element analysis diagram of comparative example 1;

Fig. 5 is the magnesium distribution diagram of the materials prepared in Example 1A, Example 1B and Example 1C;

6 is the XRD patterns of Comparative Example 1, Comparative Example 2, Example 1A, Example 1B, Example 1C and Example 2;

FIG. 7 is a comparison diagram of charge-discharge curves of materials for battery positive electrodes prepared in Comparative Example 1, Comparative Example 2, Example 1A, Example 1B, Example 1C and Example 2;

FIG. 8 is a comparison diagram of DCIR changes during the cycle of materials for battery positive electrodes prepared in Comparative Example 1, Comparative Example 2, Example 1A, Example 1B, Example 1C and Example 2;

9 is a comparison chart of the cycle performance test of the materials for battery positive electrodes prepared in Comparative Example 1, Comparative Example 2, and Example 2;

Fig. 10 is the XRD pattern of comparative example 3, embodiment 3 and embodiment 4;

FIG. 11 is a comparison diagram of charge-discharge curves of the materials for battery positive electrodes prepared in Comparative Example 3, Example 3 and Example 4;

Fig. 12 is the XRD pattern of comparative example 4, embodiment 5 and embodiment 6;

FIG. 13 is a comparison diagram of charge-discharge curves of the materials for battery positive electrodes prepared in Comparative Example 4, Example 5 and Example 6;

FIG. 14 is a comparison chart of the cycle performance test of the materials for battery positive electrodes prepared in Comparative Example 4 and Example 5. FIG.

Detailed ways

The technical solutions of the present invention are described in detail below with reference to the accompanying drawings. The embodiments of the present invention are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. , without departing from the spirit and scope of the technical solutions of the present invention, and should be included in the scope of the claims of the present invention.

The various test methods used in the following examples of the present invention are specifically described as follows:

1) X-ray diffraction (XRD) structure characterization

The test equipment for X-ray diffraction is Bruker D2-XE-T, the target material used in this instrument is a copper target, and the X-ray wavelength is

First, weigh 1g to 2g of sample, spread the sample as flat as possible in the center of the sample stage, and then use a glass slide to smooth it to ensure that the sample is flush with the sample groove and that no sample is outside the groove. Finally, put the prepared sample stage into Bruker D2-XE-T for testing. The scanning range of X-ray 2θ is set to 10°～80°, the scanning step is 0.01°, and the X-ray exposure time of each step is is 0.1s.

2) Scanning electron microscope (SEM) morphology characterization

First, a small amount of powder sample is bonded to the conductive tape of the sample stage to ensure that the sample is evenly dispersed without agglomeration. The samples were then placed in a Nippon Electronics Joel JCM-7000 NeoScope desktop scanning electron microscope for observation. The elements of the particle cross section were analyzed by Joel JED-2300 energy dispersive spectrometer, and energy dispersive X-ray spectroscopy (EDS) data were collected.

3) Electrochemical performance test

The prepared lithium ion battery cathode material is mixed with a conductive agent (such as: carbon black), a binder (such as: polyvinylidene fluoride) and a solvent (such as: N-methylpyrrolidone) to prepare an electrode slurry, and then It was coated on an aluminum-based current collector, dried to prepare an electrode, and the electrode was assembled into a button battery, and electrochemical tests were carried out using a Neware (CT-4008) battery charge-discharge instrument. The coin cell battery was firstly cycled between 2.75-4.4V with a current of 0.1C for 4 turns, and then the cycle test was performed with a current of 0.2C or 0.5C in the same voltage range.

At the same time as the cyclic test of the button battery, the discharge DC resistance (DCIR) of the button battery is also tested.

The method for the instrument to calculate the DCIR is: after the charging step is over, the next step is the shelving step, and the voltage (V ₁ ) at the last point of the shelving step is recorded. After the shelving step is over, the next step is the discharge step, the battery is discharged with a constant current (I), and the voltage (V ₂ ) at the first point of the discharge step is recorded at the same time. The calculation formula of DCIR is: DCIR=(V ₁ -V ₂ )/I

4) Thermogravimetric Analysis Test (TGA)

Thermogravimetric analysis of the fatty acid salts used was performed on a PerkinElmer-STA-8000 instrument. First, weigh 6 mg to 20 mg of fatty acid salt into the crucible and put the crucible lid on it. Put the crucible containing the fatty acid salt and another empty crucible into the instrument furnace at the same time. Next, oxygen was injected into the furnace as the reaction atmosphere, and argon was used as the protective gas of the furnace body, and the material was heated to 800 degrees Celsius with a heating rate of 5°C/min to conduct a thermogravimetric analysis experiment on the material.

Comparative Example 1

The chemical formula of the positive electrode material NCM523 used in this comparative example is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and the material has not undergone any coating treatment.

The comparative samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Comparative Example 2

The chemical formula of the positive electrode material NCM523 used in this comparative example is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and stearic acid and nano-alumina (Al ₂ O ₃ ) are used at the same time, and the Al ₂ O ₃ particle size is between 20-30 nanometers The mixture of NCM523 was used as the coating material to conduct coating experiments on NCM523.

First, a mixture of 3 g of stearic acid and nano-Al ₂ O ₃ is prepared, wherein the mass percentage of stearic acid is controlled at 3% to 30%. 10g to 30g of ball milling beads are added to the above mixture for high-speed ball milling, the ball milling time is set to 1 hour to 5 hours, and the ball milling speed is set to 100 to 600 rmp. After the mixing, the mixture of stearic acid and nano-Al ₂ O ₃ was collected, that is, the coating material. An appropriate amount of NCM523 was taken, and the corresponding coating material (ie a mixture of stearic acid and nano-Al ₂ O ₃ ) was added to achieve a mass percentage of Al ₂ O ₃ of 0.5%. The NCM523 and the coating precursor are placed in a mixer and mixed for 1 to 8 hours. The above mixture is heated to 200°C to 1000°C at a rate of 1°C/min to 10°C/min, maintained at this temperature for 1 to 24 hours, and then cooled to room temperature with the furnace to complete the coating process. The comparative samples were tested for electrochemical cycle life and DCIR.

Comparative Example 3

The chemical formula of the positive electrode material NCM622 used in this comparative example is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and the material has not undergone any coating treatment.

The comparative samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Comparative Example 4

The chemical formula of the positive electrode material NCM811 used in this comparative example is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the material has not undergone any coating treatment.

The comparative samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 1

The positive electrode material used in this example is the same NCM523 as in Comparative Example 1, its chemical formula is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and the fatty acid salt used is magnesium stearate (C ₃₆ H ₇₀ MgO ₄ ).

Put an appropriate amount of NCM523 and magnesium stearate into a mixer, mix and stir for 8 hours, so that NCM523 and magnesium stearate are fully mixed.

The above mixture was heated to 650°C at a rate of 5°C/min and held for 10 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The addition of magnesium stearate is equivalent to the content of magnesium oxide in the above-mentioned comparative example and is converted. In this example, the mass percentages of magnesium oxide-coated NCM523 finally prepared are: 0.5% (marked as: Example 1A), 1% (marked as: Example 1B) and 2% (marked as: Example 1C).

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 2

The positive electrode material used in this example is the same NCM523 as in Comparative Example 1, its chemical formula is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and the fatty acid salt used is aluminum stearate (C ₅₄ H ₁₀₅ AlO ₆ ).

Put an appropriate amount of NCM523 and aluminum stearate into a mixer, mix and stir for 8 hours, so that NCM523 and aluminum stearate are fully mixed.

The above mixture was heated to 650°C at a rate of 5°C/min and held for 10 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The added amount of aluminum stearate is equivalent to the content of aluminum oxide in the above-mentioned comparative example. In this example, the mass percentage of alumina-coated NCM523 is finally 0.5%.

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 3

The positive electrode material used in this example is the same NCM622 as in Comparative Example 3, its chemical formula is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and the fatty acid salt used is aluminum stearate (C ₅₄ H ₁₀₅ AlO ₆ ).

Put an appropriate amount of NCM622 and aluminum stearate into a mixer, mix and stir for 8 hours, so that NCM622 and aluminum stearate are fully mixed.

The above mixture was heated to 650°C at a rate of 5°C/min and held for 10 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The added amount of aluminum stearate is equivalent to the content of aluminum oxide in the above-mentioned comparative example. In this example, the mass percentage of alumina-coated NCM622 is finally 0.5%.

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 4

The positive electrode material used in this example is the same NCM622 as in Comparative Example 3, its chemical formula is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and the fatty acid salt used is aluminum laurate (C ₃₆ H ₆₉ AlO ₆ ).

Put an appropriate amount of NCM622 and aluminum laurate into the mixer, mix and stir for 8 hours, so that NCM622 and aluminum laurate are fully mixed.

The above mixture was heated to 500°C at a rate of 5°C/min and held for 10 to 24 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The added amount of aluminum laurate is equivalent to the content of alumina in the above-mentioned comparative example. In this example, the mass percentage of alumina-coated NCM622 is finally 0.5%.

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 5

The positive electrode material used in this example is the same NCM811 as in Comparative Example 4, its chemical formula is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the fatty acid salt used is aluminum stearate (C ₅₄ H ₁₀₅ AlO ₆ ).

Put an appropriate amount of NCM811 and aluminum stearate into the mixer, mix and stir for 8 hours, so that NCM811 and aluminum stearate are fully mixed.

The above mixture was heated to 650°C at a rate of 5°C/min and held for 10 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The added amount of aluminum stearate is equivalent to the content of aluminum oxide in the above-mentioned comparative example. In this example, the mass percentage of alumina-coated NCM811 is finally 0.25%.

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

Example 6

The positive electrode material used in this example is the same NCM811 as in Comparative Example 4, its chemical formula is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the fatty acid salt used is magnesium stearate (C ₃₆ H ₇₀ MgO ₄ ).

Take an appropriate amount of NCM811 and magnesium stearate into the mixer, mix and stir for 8 hours, so that NCM811 and magnesium stearate are fully mixed.

The above mixture was heated to 650°C at a rate of 5°C/min and held for 10 hours. After cooling to room temperature with the furnace, the above-mentioned materials prepared by sintering are dispersed and sieved to obtain the final coated positive electrode material, and the coating experiment is completed.

The addition of magnesium stearate is equivalent to the content of magnesium oxide in the above-mentioned comparative example and is converted. In this example, the mass percentage of magnesium oxide-coated NCM811 was finally prepared to be 0.25%.

The synthesized samples were characterized by XRD, SEM and EDS, electrochemical cycle life and DCIR tests.

In the above embodiments of the present invention, three fatty acid salts are used as examples, namely: magnesium stearate, aluminum stearate and aluminum laurate. The TGA results for these three fatty acid salts are shown in FIGS. 1 to 3 . In the experiment of thermogravimetric analysis, all three fatty acid salts decomposed with the increase of heating temperature. When the heating temperature is high enough, the weight of the fatty acid salt will remain unchanged, and all fatty acid salts will eventually be converted into the corresponding metal oxides after calculation: when the temperature is greater than 650 ℃, magnesium stearate will eventually become magnesium oxide (as shown in Figure 1), aluminum stearate will eventually become alumina (as shown in Figure 2); when the temperature is greater than 500 °C, aluminum laurate will eventually become alumina (as shown in Figure 3). Through thermogravimetric analysis, the reaction temperature required for the solid-phase reaction coating of the positive electrode material with the fatty acid salt can be known.

The SEM/EDS characterization of Comparative Example 1 was carried out. As shown in Figure 4, only the main elements nickel, cobalt and manganese of NCM523 were detected in Comparative Example 1, and no other metal elements were detected, indicating that Comparative Example 1 was uncoated NCM523 does not have magnesium. The NCM523 coated with magnesium stearate was subjected to SEM/EDS (i.e., Example 1A, Example 1B and Example 1C), and the main elements nickel, cobalt, and manganese could be found at the same time, and the oxidation after coating could be observed at the same time. The magnesium element in magnesium, as shown in Figure 5, wherein the magnesium element in Example 1A, Example 1B and Example 1C are uniformly distributed on the surface of the positive electrode material particles, and with the increase of the amount of coating material, the signal of Mg It is gradually enhanced, which proves that the coating amount of MgO gradually increases.

As shown in the XRD data of Figure 6, the uncoated NCM523 (ie, Comparative Example 1) is a pure R-3m layered structure. Simultaneously using fatty acid salts to form oxide-coated NCM523 (ie, Example 1A, Example 1B, Example 1C, and Example 2), characterized by XRD, it is also a pure R-3m layered structure. The data show that NCM523 coated with fatty acid salts does not generate any impurity phase. Therefore, the use of fatty acid salts will not affect the original positive electrode material due to the introduction of impurity phases during the coating process.

The electrochemical performance of uncoated NCM523 and NCM523 coated with fatty acid salts were compared. Since the coating material is an oxide and has no electrochemical activity, the charge-discharge capacity of the positive electrode material will decrease with the increase of the quality of the coating material. The charge-discharge curves of the three examples and Comparative Example 1 are compared as shown in Figure 7. As the content of MgO coating increases, the charge-discharge capacity of NCM523 gradually decreases. The charge-discharge capacity of Example 1A is comparable to that of Comparative Example 1. At the same time, compared with the uncoated NCM523, the MgO-coated NCM523 also showed a smaller increase in resistance during cycling, as shown in Fig. It shows high interface stability. Table 1 summarizes the energy retention rate of each of the above samples. After 50 cycles, all NCM523 coated with magnesium stearate have higher energy retention rate compared with the uncoated NCM523, which is coated with 0.5% MgO. The covered NCM523 has the highest energy retention rate of 94.3%. By comparing the initial charge-discharge capacity, DC resistance growth and energy retention rate, NCM523 (Example 1A) using magnesium stearate to achieve 0.5% MgO coating is the optimal coating condition. Therefore, the total coating amount of 0.5% oxide is still taken, and NCM523 is coated with aluminum stearate to obtain Example 2. At the same time, NCM523 was coated with stearic acid and alumina to obtain Comparative Example 2.

Comparative Example 1, Comparative Example 2 and Example 2 were compared. The XRD test shows that Comparative Example 1, Comparative Example 2 and Example 2 are all pure R-3m layered structures (see FIG. 6 ), and no impurities are found. The electrochemical test of the three shows that Comparative Example 1, Comparative Example 2 and Example 2 all have comparable initial charge and discharge capacities (see Figure 7); among them, Example 2 has the smallest increase in DC resistance (see Figure 8). After 50 cycles, the energy retention rate of Example 2 can reach 95.3%, which is the sample with the highest energy retention rate. As shown in FIG. 9 , comparing the energy retention rates of Example 2 and Comparative Example 2, Example 2 has a better energy retention rate. From the comparison of the resistance growth rate and the energy retention rate of the positive electrode material, it can be seen from the comparison of the effect of using aluminum stearate to directly coat NCM523 and using stearic acid and aluminum oxide to coat NCM523 directly. The effect of coating the material is better, and the purpose of further reducing the amount of coating material is achieved.

As shown by the XRD data in Figure 10, the uncoated NCM622 (Comparative Example 3) is a pure R-3m layered structure. Using aluminum stearate and aluminum laurate as fatty acid salts to carry out 0.5% Al ₂ O ₃ coating on NCM622 to obtain Example 3 and Example 4, which are also pure R-3m layered structure through XRD characterization. The data show that NCM622 coated with aluminum stearate and aluminum laurate as fatty acid salts does not produce any impurity phase. Therefore, the use of fatty acid salts will not affect the original positive electrode material due to the introduction of impurity phases during the coating process.

The electrochemical performance of Comparative Example 3 was compared with that of Examples 3 and 4. Since the coating material is an oxide and has no electrochemical activity, the charge-discharge capacity of the positive electrode material will decrease with the increase of the quality of the coating material. Figure 11 shows the comparison of the charge-discharge curves of Comparative Example 3, Example 3 and Example 4. The charge-discharge capacity of Example 3 and Example 4 is slightly lower than that of Comparative Example 3. After 50 cycles, the energy retention rates of Example 3 and Example 4 can reach 92.2% and 90.8%, respectively, which are higher than 89.2% of Comparative Example 3. It can be seen from Table 1 that after 50 cycles, the resistances of Example 3 and Example 4 can reach 25.9 ohm and 30.98 ohm, which are both lower than the 31.76 ohm of Comparative Example 3.

As shown by the XRD data in Figure 12, the uncoated NCM811 (Comparative Example 4) is a pure R-3m layered structure. And using aluminum stearate and magnesium stearate as fatty acid salts, NCM811 was coated with 0.25% Al ₂ O ₃ and MgO to obtain Examples 5 and 6, which were characterized by XRD and were also pure R-3m layered structure. . The data show that NCM811 coated with aluminum stearate and magnesium stearate as fatty acid salts does not produce any impurity phase. Therefore, the use of fatty acid salts will not affect the original positive electrode material due to the introduction of impurity phases during the coating process.

The electrochemical performance of Comparative Example 4 was compared with that of Examples 5 and 6. Although the coating material is an oxide and has no electrochemical activity, the mass of the coating material of 0.25% has little effect on the charge-discharge capacity of the positive electrode material NCM811. For the comparison of the charge-discharge curves of Comparative Example 4, Example 5 and Example 6, see FIG. 13 . After 50 cycles, the energy retention rates of Example 5 and Example 6 can reach 88.3% and 85.6%, respectively, which are higher than 85.5% of Comparative Example 4, but compared with Example 3 and Example 4, the value is lower, It is shown that it is inferior to Example 3 and Example 4 in terms of energy retention. FIG. 14 compares the discharge capacity of Example 5 and Comparative Example 4, and the discharge capacity retention rate of Example 5 is better than that of Comparative Example 4.

Table 1 Energy retention rate of various coated and uncoated cathode materials after 50 cycles

Claims (10)

1. A method for preparing a positive electrode material for a lithium ion battery, which is characterized in that a metal salt of a fatty acid is mixed with a positive electrode material for a lithium battery, and a coated positive electrode material is obtained by high-temperature solid-phase reaction sintering. The metal salt is represented by the formula Me ^t+ [CH ₃ (CH ₂ ) _n COO] _t , wherein n is an integer from 8 to 32, t is an integer from 1 to 7, and Me is a metal ion.
2. The preparation method according to claim 1, wherein said n is 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 or 32.
3. The preparation method according to claim 1, wherein the metal ions are selected from Li, Mg, Zn, Cu, Ca, Fe, Al, Ni, Co, Mn, Ti, Cr, Zr, Nb and An ion composed of one or more metals of W.
4. The preparation method according to claim 1, wherein the fatty acid is volatilized during the heating process, and the metal salt is oxidized at high temperature to form a metal oxide, and in the coated positive electrode material, The mass percentage of the metal oxide is 0.6%±0.1%.
5. The preparation method according to claim 1, wherein the metal salt of the fatty acid is selected from aluminum stearate and aluminum laurate.
6. The preparation method according to claim 1, wherein the metal salt of the fatty acid is selected from magnesium stearate and magnesium laurate.
7. The preparation method according to claim 1, wherein the solid-phase reaction is heated to 200°C to 1000°C and sintered for 1 hour to 24 hours.
8. The preparation method according to claim 1, wherein the solid-phase reaction is heated to 200°C to 1000°C at a rate of 1°C/min to 10°C/min, and then incubated for 1 hour to 24 hours.
9. The preparation method according to claim 1, wherein the metal salt of the fatty acid is in the form of a solid powder, and the particle size is 10 nm to 2 μm.
10. The preparation method according to claim 1, wherein the cathode material for lithium battery is selected from one or more of NCM622, NCM811 and NCA.

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