Ternary positive electrode material and preparation method and application thereof

Abstract

The invention provides a ternary positive electrode material and a preparation method and application thereof. According to the invention, the pentavalent metal cations are doped with the ternary material, and then the surface of the material is coated with a layer of hydrophobic organic polymer material polydimethylsiloxane in a wet ball milling manner, so that the prepared ternary positive electrode material has higher storage stability and cycling stability; and the lithium ion battery can have more stable durability in long-term infiltration of an electrolyte, side reaction of the electrolyte and a positive electrode material is prevented, and the problems of poor electrochemical performance, poor cycle performance and the like of the lithium battery under high voltage are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a ternary positive electrode material and a preparation method and application thereof, and more specifically relates to a high-voltage single crystal ternary positive electrode material with high cycle stability and a preparation method and application thereof. Background Art

[0002] Positive electrode materials play a decisive role in the energy density, safety and service life of lithium-ion batteries. Among the many positive electrode materials, nickel-cobalt-manganese (NCM) ternary positive electrode materials, especially NCM materials with higher nickel content, have been widely studied. However, relevant studies have shown that nickel-rich layered oxide positive electrode materials face a series of challenges such as crystal structure stability, phase change, interfacial side reactions, and oxygen release at higher charging cut-off voltages. This series of side reactions will accelerate the structural distortion of the positive electrode and cause the decline of electrochemical performance, making it impossible to simultaneously meet the requirements of higher cycle life and energy density. At the same time, because high-nickel ternary materials have certain air instability, the surface of the material will degrade after being left in humid air, which seriously affects the performance of the material. This is also an important factor limiting the production and application of materials. Therefore, it is of practical significance to develop a ternary positive electrode material that has both good rate performance and good storage stability and cycle stability at high voltage. Summary of the invention

[0003] The object of the present invention is to provide a ternary positive electrode material and a preparation method thereof, wherein the ternary positive electrode material has both good rate performance and good storage stability and cycle stability under high voltage, thereby solving the problem of limitations of ternary materials in production and application.

[0004] The ternary positive electrode material provided by the present invention is prepared by a method comprising the following steps: 1) Using nickel salt, cobalt salt and manganese salt as raw materials, a ternary precursor is synthesized by hydrothermal method; 2) The ternary precursor, the lithium source and the oxide of the pentavalent metal cation are mixed and ground, and sintered at high temperature in an oxygen-rich atmosphere to obtain a ternary matrix material; 3) The obtained ternary matrix material and the hydrophobic polymer material are dispersed in an organic solvent, mixed and ball-milled, and dried to obtain a ternary positive electrode material.

[0005] The present invention adopts pentavalent metal cations to dope ternary materials, and then coats a layer of hydrophobic organic polymer polydimethylsiloxane on the surface of the material by wet ball milling. The ternary positive electrode material thus prepared has higher storage stability and cycle stability, and can also have more stable durability in long-term infiltration of electrolyte, preventing the occurrence of side reactions between electrolyte and positive electrode material, and solving the problems of poor electrochemical performance and poor cycle performance of lithium batteries under high voltage.

[0006] In step 1) of the above method, the nickel salt may be selected from at least one of nickel nitrate, nickel acetate, nickel chloride and nickel sulfate; The cobalt salt may be selected from at least one of nitrate, acetate, chloride and sulfate of cobalt; The manganese salt may be selected from at least one of manganese nitrate, acetate, chloride and sulfate; Calculated in terms of nickel element, cobalt element and manganese element, the molar ratios of the nickel salt, cobalt salt and manganese salt are 0.6-0.8: 0.05-0.1: 0.1-0.3, specifically 0.7: 0.1: 0.2 and 0.65: 0.1: 0.25.

[0007] The operation of step 1) is: dissolving nickel salt, cobalt salt and manganese salt in a mixed solution of ethanol and water, then slowly adding a mixed solution of ammonia water and sodium hydroxide (the concentration of ammonia water and sodium hydroxide is 0.2 mol / L) to the solution dropwise, stirring for a certain period of time, and then hydrothermally assisted synthesis of the ternary precursor. Wherein, in the mixed solution of ethanol and water, the volume ratio of ethanol to water is 2:3; The stirring time is 6 to 10 hours; The hydrothermal time can be 10-12 hours, and the temperature can be 180-200°C.

[0008] In step 2) of the above method, the lithium source is at least one of lithium chloride, lithium acetate, lithium hydroxide and lithium carbonate, and specifically can be lithium carbonate; The molar ratio of the lithium element in the lithium source to all the metal elements in the ternary precursor may be (1-1.08): 1; The oxide of the pentavalent metal cation may be at least one of V2O5, Nb2O5, Sb2O5, and Ta2O5, and the molar ratio of the pentavalent metal cation to all metal elements in the ternary precursor may be (0.005-0.01):1; The high temperature sintering is divided into two stages: pre-sintering and sintering. The pre-sintering temperature is 650-750°C for 5-10 hours; the sintering temperature is 800-950°C for 10-15 hours.

[0009] High-temperature sintering is divided into two stages. The first stage is to thermally decompose lithium salts (especially lithium carbonate) and precursors to promote the lithiation reaction and the conversion of precursors into transition metal oxides. The second stage is to promote crystal growth and make the transition metal oxide grow to the required size.

[0010] In step 3) of the above method, the hydrophobic polymer material is at least one of polydimethylsiloxane and polytetrafluoroethylene. The mass ratio of the ternary matrix material to the hydrophobic polymer material is 1:(0.01-0.05); The organic solvent may be at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol; The weight of the mixing balls in the ball mill: the weight of the materials is 1:2, and the ball milling time is 3-6 hours; The drying is vacuum drying; The vacuum drying process is carried out at a pressure of -0.1 MPa, a temperature of 100-120°C, and a time of 6-8 hours.

[0011] The above method further comprises a washing and drying process of the hydrothermally obtained ternary precursor material after step 1), and a crushing and screening step of the sintered ternary matrix material after step 2).

[0012] The application of the above-mentioned ternary positive electrode material in lithium-ion batteries also falls within the protection scope of the present invention.

[0013] The ternary positive electrode material has both good rate performance and good storage stability and cycle stability at high voltage.

[0014] The invention also provides a lithium ion battery.

[0015] The positive electrode of the lithium-ion battery is made of the above-mentioned ternary positive electrode material.

[0016] The present invention has the following beneficial effects: (1) The present invention adopts pentavalent metal cation doping ternary materials. The doping of pentavalent metal cations helps to increase the interlayer spacing, electron transport and structural stability of the lithium layer, thereby significantly improving Li + The electrical conductivity further improves the electrochemical performance of the material.

[0017] (2) The present invention uses pentavalent metal cations to dope ternary materials. There is a strong interaction between pentavalent metal cations and oxygen, which can stabilize the structure of the material and effectively inhibit the loss of oxygen and the dissolution of the metal. This doping method greatly improves the situation in which the electrochemical performance of the ternary material is degraded due to structural distortion caused by the redox of anions.

[0018] (3) The present invention coats the polydimethylsiloxane on the surface of the material by wet ball milling. The coating layer is uniform and the polymer material forms a hydrophobic layer on the surface of the material. This coating method improves the storage performance of the material and avoids the increase of the residual alkali content on the surface of the material during long-term storage. On the other hand, it prevents the material from being eroded by the electrolyte during long-term immersion in the electrolyte, alleviates the attenuation of voltage and capacity, and enables the material to have higher cycle stability. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0020] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0021] Example 1 Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in a mixed solution of ethanol and water in a volume ratio of 2:3 according to a metal molar ratio of 0.7:0.1:0.2, and then a mixed solution of ammonia water and sodium hydroxide with a concentration of 0.2 mol / L was slowly added dropwise to the solution. After being fully stirred for 6 hours, the solution was transferred into a reactor, and after being kept warm at a hydrothermal temperature of 200°C for 12 hours, the material was washed and dried to obtain a ternary precursor powder; The obtained ternary precursor, lithium carbonate and V2O5 are fully mixed and ground in a certain ratio, wherein the molar ratio of lithium element, vanadium element and all metal elements in the ternary precursor is 1.08:0.01:1. The ground material is sintered in an oxygen-rich atmosphere at a pre-sintering temperature of 650°C for 5 hours, and then heated to 900°C for 12 hours to obtain a ternary matrix material; The ternary matrix material and polydimethylsiloxane are dispersed in a n-hexane solvent at a mass ratio of 1:0.01. After complete dispersion, the formed solution is placed in a ball mill with a ball-to-material ratio of 1:2, mixed and ball-milled for 6 hours, and then the material is vacuum dried at 100°C for 6 hours (pressure -0.1MPa) to obtain the ternary positive electrode material.

[0022] Example 2 Compared with Example 1, the molar ratio of lithium element, vanadium element and all metal elements in the ternary precursor is 1.08:0.0075:1, and other steps, raw materials and parameters remain unchanged.

[0023] Example 3 Compared with Example 1, the molar ratio of lithium element, vanadium element and all metal elements in the ternary precursor is 1.08:0.005:1, and other steps, raw materials and parameters remain unchanged.

[0024] Example 4 Compared with Example 1, the metal molar ratio of nickel sulfate, cobalt sulfate and manganese sulfate is 0.65:0.1:0.25, and other steps, raw materials and parameters remain unchanged.

[0025] Example 5 Compared with Example 1, the mass ratio of the ternary matrix material to polydimethylsiloxane is 1:0.05, and the other steps, raw materials and parameters remain unchanged.

[0026] Example 6 Compared with Example 1, the pentavalent metal cation oxide is Nb2O5, and the other steps, raw materials and parameters remain unchanged.

[0027] Example 7 Compared with Example 1, the pentavalent metal cation oxide is Ta2O5, and the other steps, raw materials and parameters remain unchanged.

[0028] Example 8 Compared with Example 1, the hydrophobic polymer material coated on the surface is polytetrafluoroethylene, and the other steps, raw materials and parameters remain unchanged.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that the doping step of pentavalent metal cation oxide in step 2 is omitted, the ternary precursor and lithium carbonate are fully mixed and ground in a certain proportion, and the molar ratio of lithium element to all metal elements in the ternary precursor is 1.08:1.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that the coating step of step 3 is omitted, and the ternary precursor, lithium carbonate and V2O5 obtained in step 1 are fully mixed and ground in a metal ion molar ratio of 1:1.08:0.01 and then sintered to obtain the ternary material.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that the doping and coating steps in step 2 and step 3 are omitted, and the ternary precursor is directly synthesized by the hydrothermal method, which is then fully mixed with lithium carbonate in a metal ion molar ratio of 1:1.08, ground and sintered to obtain the ternary material.

[0032] Effect verification 1. pH and residual alkali detection: The ternary cathode materials prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1. The pH test method is to mix the lithium ion battery cathode material with distilled water at a solid-liquid ratio of 1:10, and then test it with a pH meter; the residual alkali is determined by acid-base titration; the free lithium content in Table 1 is the sum of the lithium ion content in the residual alkali (lithium carbonate and lithium hydroxide).

[0033] Table 1 Residual alkali content of positive electrode materials in different embodiments

[0034] Comparing Example 1 with Comparative Example 3, it can be seen that the residual alkali content on the surface of the ternary positive electrode material prepared by the method of the present invention is significantly reduced. Comparing Examples 1, 2, 3 and Comparative Example 1, it can be seen that the doping of pentavalent metal cation oxides can also reduce the content of residual alkali (mainly lithium carbonate) on the surface of the material. This is because the doping of pentavalent metal cations consumes lithium carbonate on the surface and forms a layer of fast ion conductor containing pentavalent metals on the surface of the material, thereby greatly reducing the content of residual alkali. Comparing Examples 1 and 8, polytetrafluoroethylene, as a common surface-coated hydrophobic polymer material, is not as good as polydimethylsiloxane in its ability to reduce surface residual alkali. At the same time, compared with Comparative Example 2, it is shown that the coating of polydimethylsiloxane significantly reduces the residual alkali content on the surface of the material.

[0035] The ternary positive electrode materials prepared in Example 1, Example 8 and the comparative example were exposed to air for 3 days, and the changes in the surface pH and the residual alkali content of the materials were compared. The results are shown in Table 2.

[0036] Table 2 Residual alkali content of positive electrode materials in different embodiments after exposure

[0037] It can be seen from the data after placement that the ternary positive electrode material provided by the present invention improves the storage performance of the material, avoids the increase of residual alkali content on the surface of the material during long-term storage, makes the storage performance of the material more stable, and is conducive to solving the problem of limitations caused by the storage environment in the production and application of ternary materials.

[0038] 2. Electrical performance test method: The materials prepared in the above embodiments and comparative examples are used as positive electrode active materials, and conductive carbon black and polyvinylidene fluoride are mixed and dissolved in N-methylpyrrolidone solution at a mass ratio of 90:5:5, and then evenly coated on aluminum foil, dried at 120°C for 12 hours, and made into a compacted density of 3.5g / cm 3The positive electrode sheet was prepared; 1.0 mol / L LiPF61M LiPF6 was dissolved in EC / DMC / DEC (1:1:1 in wt.%) electrolyte, and the positive electrode sheet, separator (Celgard 24), electrolyte, and metal lithium negative electrode were assembled into a CR2016 button battery in a glove box.

[0039] The assembled button cell was subjected to electrochemical performance test at 25°C, with a starting voltage of 2.8V and a cut-off voltage of 4.5V. First, the battery was charged and discharged at the rates of 0.2C / 0.2C, 0.33C / 0.33C, 1C / 1C and 0.2C / 0.2C in the first 4 weeks, and then charged and discharged at the rate of 1C / 1C until 300 cycles. The above test results are shown in Table 3.

[0040] Table 3 Electrochemical properties of positive electrode materials prepared in different embodiments

[0041] Combining the data of Examples 1-7 in Table 1 and Table 3, it can be seen that the polydimethylsiloxane-coated pentavalent metal cation-doped ternary positive electrode material provided by the present invention has a low surface residual alkali content, and has excellent initial charge and discharge specific capacity and cycle performance; It can be seen from the data of Examples 1, 6, and 7 in Table 3 that the doping of pentavalent metal cations has a significant effect on the improvement of material capacity and rate performance. It can be seen from the comparison between Example 1 and Comparative Example 2 that the coating of polydimethylsiloxane has a significant improvement in the cycle performance of the material. The 0.2C discharge capacity of Example 1 is 210.3mAh / g, and the capacity retention rate is 88.7% after 300 cycles. The 0.2C discharge capacity of Comparative Example 3 is 193.4mAh / g, and the capacity retention rate is 75.7% after 300 cycles. Example 1 is significantly better than Comparative Example 3, indicating that the ternary positive electrode material prepared using the method of the present invention is more conducive to improving the rate performance of the material, especially the capacity at high rates, and has an important influence on the cycle stability of the material.

[0042] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principles of the present invention, the application is intended to include any changes, uses or improvements to the present invention, including departure from the disclosed scope in the application, and changes made with conventional techniques known in the art.

Claims

1. A method for preparing a ternary positive electrode material, characterized in that: The method comprises the following steps: 1) Using nickel salt, cobalt salt and manganese salt as raw materials, a ternary precursor is synthesized by hydrothermal method; 2) The ternary precursor, the lithium source and the oxide of the pentavalent metal cation are mixed and ground, and sintered at high temperature in an oxygen-rich atmosphere to obtain a ternary matrix material; 3) The obtained ternary matrix material and the hydrophobic polymer material are dispersed in an organic solvent, mixed and ball-milled, and dried to obtain a ternary positive electrode material.

2. The method according to claim 1, characterized in that In step 1), the nickel salt is selected from at least one of nickel nitrate, nickel acetate, nickel chloride and nickel sulfate; The cobalt salt is selected from at least one of nitrate, acetate, chloride and sulfate of cobalt; The manganese salt is selected from at least one of manganese nitrate, acetate, chloride and sulfate; Calculated in terms of nickel element, cobalt element and manganese element, the molar ratios of the nickel salt, cobalt salt and manganese salt are 0.6-0.8: 0.05-0.1: 0.1-0.3 respectively.

3. The method according to claim 1, characterized in that The operation of step 1) is: dissolving nickel salt, cobalt salt and manganese salt in a mixed solution of ethanol and water, then adding ammonia water and sodium hydroxide mixed solution to the solution, stirring thoroughly, and then hydrothermally assisted synthesis of the ternary precursor. Wherein, the stirring time is 6 to 10 hours; The hydrothermal time is 10-12h, and the temperature is 180-200℃.

4. The method according to claim 1, characterized in that: In step 2), the lithium source is at least one of lithium chloride, lithium acetate, lithium hydroxide and lithium carbonate; The molar ratio of the lithium element in the lithium source to all the metal elements in the ternary precursor is (1-1.08): 1; The oxide of the pentavalent metal cation is at least one of V2O5, Nb2O5, Sb2O5, and Ta2O5; The molar ratio of the pentavalent metal cation to all metal elements in the ternary precursor is (0.005-0.01):

1.

5. The method according to claim 1, characterized in that In step 2), the high temperature sintering is divided into two stages: pre-sintering and sintering. The pre-sintering temperature is 650-750°C for 5-10 hours; the sintering temperature is 800-950°C for 10-15 hours.

6. The method according to claim 1, characterized in that In step 3), the hydrophobic polymer material is at least one of polydimethylsiloxane and polytetrafluoroethylene; The mass ratio of the ternary matrix material to the hydrophobic polymer material is 1:(0.01-0.05).

7. The method according to claim 1, characterized in that In step 3), the organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol; The ball milling time is 3 to 6 hours; The drying is vacuum drying; The vacuum drying process is carried out at a pressure of -0.1 MPa, a temperature of 100-120°C, and a time of 6-8 hours.

8. A ternary positive electrode material prepared by the method according to any one of claims 1 to 7.

9. Use of the ternary cathode material according to claim 8 in lithium-ion batteries.

10. A lithium ion battery, characterized in that: The positive electrode of the lithium-ion battery is made of the ternary positive electrode material according to claim 8.

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