A surface modification method for metal oxide positive electrode materials for lithium ion batteries based on carbon disulfide gas phase modification and application thereof

Abstract

A kind of surface modification method of metal oxide positive electrode material for lithium ion battery based on carbon disulfide gas phase modification and its application.The present application belongs to the field of metal oxide positive electrode material for lithium ion battery.Aiming at the deficiency of prior art, the present application first introduces CS2 gas phase treatment into the post-treatment process of metal oxide positive electrode material, injects carbon disulfide vapor under the protection of inert atmosphere (Ar or N2), heats to a certain temperature and keeps warm; then, the reaction gas containing O2 is introduced and heated, and the oxidation treatment is carried out, and the surface modification is completed after cooling. The method of the present application realizes the synergistic effect of residual lithium elimination and functional coating construction, and obtains a special interface structure with electronic insulation and ion conductivity through reaction kinetics regulation. Moreover, the process parameters are accurately controllable, the treatment time is less than 2 hours, no subsequent washing process is needed, and it is suitable for continuous production.

Description

Technical Field

[0001] This invention belongs to the field of metal oxide cathode materials for lithium-ion batteries, specifically relating to a surface modification method for metal oxide cathode materials for lithium-ion batteries based on carbon disulfide vapor phase modification and its application. Background Technology

[0002] The global energy crisis and environmental damage caused by increasing energy demand and the continued use of traditional fossil fuels have had a significant negative impact. To address this contradiction, vigorously developing green and sustainable energy is crucial, and electrochemical energy storage and conversion technology has proven highly effective. Since its commercialization in 1991, lithium-ion batteries have gradually demonstrated significant advantages, capturing the largest share of the global rechargeable battery market. Their high energy density and long cycle life have led to their widespread application in electric vehicles, grid energy storage, and electronic devices. The performance of lithium-ion batteries largely depends on the cathode material. Among various cathode materials, metal oxide cathode materials have attracted widespread attention due to their high energy density, high plateau potential, good rate performance, and low cost, and are currently one of the main research hotspots in cathode materials.

[0003] Although metal oxide cathode materials offer many advantages, such as low cost and higher specific capacity, several problems have arisen in practical applications, severely hindering their development. For example, cation mixing induces the formation of a disordered rock-salt phase structure, leading to a decrease in the material's specific capacity. This disordered structure can impede the application of Li... + The diffusion and electron transfer of these substances degrade the cycle performance and rate performance of the cathode material. Furthermore, the unstable surface of the material makes it prone to various side reactions upon contact with carbonate-based electrolytes, increasing interfacial impedance and reducing cycle stability. During charge and discharge, heat accumulation and gas release caused by side reactions accelerate the thermal runaway process, leading to decreased battery safety.

[0004] Surface coating modification is the most common method to solve the above problems. Its main purpose is to form a uniform coating material on the surface of the cathode material. This coating material can act as a physical barrier to prevent direct contact between the material surface and the electrolyte, thereby reducing the generation of side reactions. It can also consume the generated HF, reduce the dissolution of transition metals in the active material and the damage to the surface structure. Some coatings can convert these residues into reasonably conductive lithium compounds, such as phosphates and garnets, thereby improving rate performance. Some researchers also use full-surface polymer coatings, which can prevent cracking by providing elastic support to secondary particles. Specifically, the composition of these coatings can be divided into three main categories. One is oxides, such as Al2O3, TiO2, ZrO2, etc. The advantage of these oxide materials is that they can be well integrated with the surface of the cathode material and can exist stably in the electrolyte, playing a protective role. However, since these oxides usually have poor conductivity, they will increase the surface impedance, which is not conducive to the transport and diffusion of lithium ions. Another type is inorganic compounds, including various phosphates and lithium-containing compounds such as lithium titanate. These materials are characterized by a certain degree of lithium-ion conductivity and do not hinder ion transport. However, their synthesis process is relatively complex, and achieving uniform surface coating is difficult. Another type of coating material is organic conductive polymers. The advantage of this type of coating is its good mechanical properties; it can elastically change with the expansion and contraction of secondary particles, effectively preventing electrolyte intrusion into the particles due to particle breakage. However, its disadvantage remains poor ionic conductivity. Summary of the Invention

[0005] To overcome the above-mentioned technical defects, the present invention provides a method for surface modification of metal oxide cathode materials for lithium-ion batteries based on carbon disulfide vapor phase modification and its application.

[0006] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for surface modification of metal oxide cathode materials for lithium-ion batteries based on carbon disulfide vapor-phase modification, the method comprising the following steps: S1: Place the lithium-ion battery with residual alkaline lithium compounds on the surface into a sealed reaction vessel using a metal oxide positive electrode material, evacuate the vessel, and then introduce an inert gas to atmospheric pressure. S2: Inject carbon disulfide vapor, heat to a certain temperature and hold for heat preservation; S3: Introduce a reaction gas containing O2 and heat it to carry out oxidation treatment. After cooling, the surface modification is completed.

[0007] Further specifying, the lithium-ion battery metal oxide cathode material with residual alkaline lithium compounds on the surface of S1 includes LiNiO2 and LiNi x Co y Mn 1-x-yO2 (x > 0.5, y > 0, x + y < 1) or LiNi x Mn 1-x O2 (1 > x > 0.5).

[0008] Further specifying, the alkaline lithium compound in S1 is Li2CO3 or LiOH.

[0009] Further specified, S1 is evacuated to 10 -3 Pa.

[0010] Further specifying, the inert gas in S1 is either Ar or N2.

[0011] Further specified, the partial pressure of carbon disulfide vapor (CS2) in S2 is 5-50 kPa.

[0012] Further specified, the heating temperature in S2 is 80-120 ℃, and the holding time is 30-90 min.

[0013] Further specifying, the reaction gas containing O2 in S3 includes N2 or Ar, wherein the O2 content is 1-80 vol.

[0014] Further specified, the oxidation treatment temperature in S3 is 100-300 ℃.

[0015] The second objective of this invention is to provide a lithium-ion battery metal oxide cathode material with a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the above method.

[0016] Further specified, the thickness of the composite coating is 2-5 nm.

[0017] The third objective of this invention is to provide an application of a lithium-ion battery metal oxide cathode material with a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the above method in lithium-ion batteries.

[0018] The fourth objective of this invention is to provide a positive electrode sheet for a lithium-ion battery, wherein the positive electrode sheet is formed by coating a substrate with a slurry made of a lithium-ion battery metal oxide positive electrode material with a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the above method, a binder, and a conductive agent.

[0019] The advantages of this invention compared to existing technologies are: (1) The main innovation of this invention is the introduction of CS2 vapor phase modification into the post-processing technology of metal oxide cathode materials. Under the protection of an inert atmosphere (Ar or N2), the residual alkaline lithium compounds such as Li2CO3 and LiOH on the material surface undergo a selective chemical reaction with CS2 vapor through a programmed temperature-controlled reaction device (50-200℃). Then, oxidation treatment is carried out under an O2 atmosphere to generate a sulfide composite coating (Li2SO3 / Li2SO4) with a three-dimensional network structure in situ, realizing the synergistic effect of residual lithium elimination and functional coating construction. Through reaction kinetic control, a special interface structure with both electronic insulation and ion conductivity is obtained. Experimental data show that the NCM811 material treated by this process exhibits significantly optimized electrochemical performance in the voltage range of 2.8-4.3V: the capacity retention rate after 100 cycles at 1C is increased to 94.6% (comparative example 84.6%).

[0020] (2) The process parameters of the method of the present invention are precise and controllable, suitable for continuous production, with a processing time of <2 h and no need for subsequent washing process. This technology effectively solves common industry problems such as gas generation, interfacial side reactions and cycle degradation caused by residual lithium on the surface of metal oxide cathode materials, and provides an innovative solution for the development of high-safety and long-life lithium-ion batteries. Attached Figure Description

[0021] Figure 1 The image shows a scanning electron microscope (SEM) image of the metal oxide cathode material prepared in step (2) of Example 2. Figure 2 Scanning electron microscope (SEM) images of the modified cathode material prepared in Example 2; Figure 3 The cycling stability of the cathode materials obtained in Examples 1-3 and the comparative examples in half-cells is shown. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0024] Example 1 A surface modification method for lithium-ion battery metal oxide cathode materials based on carbon disulfide vapor-phase modification includes the following steps: (1) Prepare a 2 mol / L mixed metal salt solution by dissolving nickel, cobalt and manganese sulfate solution in a molar ratio of 8:1:1. Mix the solution with 1 mol / L sodium hydroxide solution and 0.4 mol / L ammonia solution and feed it into the reactor at a rate of 1.2 mL / min using a peristaltic pump. Control the pH at 10.60, the temperature at 60 °C, and the stirring rate at 650 rpm. After the reaction is completed, wash and dry the product to obtain the metal oxide precursor. (2) The above metal oxide precursor and lithium hydroxide are mixed evenly at a molar ratio of 1:1.05. Under an oxygen atmosphere, the temperature is first raised to 500 °C at a rate of 2 °C / min and calcined for 6 h. Then the temperature is raised to 850 °C at a rate of 2 °C / min and calcined for 18 h. After ball milling, the metal oxide cathode material is obtained. (3) Place the above-mentioned metal oxide cathode material in a sealed reactor and evacuate to 10 °C. -3 After Pa, N2 is introduced until atmospheric pressure is reached; (4) Inject carbon disulfide vapor to a partial pressure of 5 kPa, heat to 80 °C, and hold for 60 min; (5) Introduce an O2 / N2 mixture containing 60 vol% O2 as the reaction gas, heat to 180 ℃ and hold for 5 h, and after cooling, obtain a modified cathode material with a surface coated with a Li2SO3 / Li2SO4 composite coating, denoted as NCM-CS2-1.

[0025] Example 2 A surface modification method for lithium-ion battery metal oxide cathode materials based on carbon disulfide vapor-phase modification includes the following steps: (1) Prepare a 2 mol / L mixed metal salt solution by dissolving nickel, cobalt and manganese sulfate solution in a molar ratio of 8:1:1. Mix the solution with 1 mol / L sodium hydroxide solution and 0.4 mol / L ammonia solution and feed it into the reactor at a rate of 1.2 mL / min using a peristaltic pump. Control the pH at 10.60, the temperature at 60 °C, and the stirring rate at 650 rpm. After the reaction is completed, wash and dry the product to obtain the metal oxide precursor. (2) The above metal oxide precursor and lithium hydroxide were mixed evenly at a molar ratio of 1:1.05. Under an oxygen atmosphere, the temperature was first increased to 500 °C at a rate of 2 °C / min and calcined for 6 h, then increased to 850 °C at a rate of 2 °C / min and calcined for 18 h. After ball milling, the metal oxide cathode material was obtained; SEM images are shown below. Figure 1 As shown; (3) Place the above-mentioned metal oxide cathode material in a sealed reactor and evacuate to 10 °C. -3 After Pa, N2 is introduced until atmospheric pressure is reached; (4) Inject carbon disulfide vapor to a partial pressure of 20 kPa, heat to 80 °C, and hold for 60 min; (5) An O2 / N2 mixture containing 60 vol% O2 was introduced as the reaction gas, and the temperature was raised to 180 ℃ and held for 5 h. After cooling, a modified cathode material with a Li2SO3 / Li2SO4 composite coating on the surface was obtained, denoted as NCM-CS2-2; SEM images are shown below. Figure 2 As shown, after with Figure 1 As can be seen from the comparison, the method of the present invention does not change the morphology and structure of the metal oxide cathode material.

[0026] Example 3 A surface modification method for lithium-ion battery metal oxide cathode materials based on carbon disulfide vapor-phase modification includes the following steps: (1) Prepare a 2 mol / L mixed metal salt solution by dissolving nickel, cobalt and manganese sulfate solution in a molar ratio of 8:1:1. Mix the solution with 1 mol / L sodium hydroxide solution and 0.4 mol / L ammonia solution and feed it into the reactor at a rate of 1.2 mL / min using a peristaltic pump. Control the pH at 10.60, the temperature at 60 °C, and the stirring rate at 650 rpm. After the reaction is completed, wash and dry the product to obtain the metal oxide precursor. (2) The above metal oxide precursor and lithium hydroxide are mixed evenly at a molar ratio of 1:1.05. Under an oxygen atmosphere, the temperature is first raised to 500 °C at a rate of 2 °C / min and calcined for 6 h. Then the temperature is raised to 850 °C at a rate of 2 °C / min and calcined for 18 h. After ball milling, the metal oxide cathode material is obtained. (3) Place the above-mentioned metal oxide cathode material in a sealed reactor and evacuate to 10 °C. -3 After Pa, N2 is introduced until atmospheric pressure is reached; (4) Inject carbon disulfide vapor to a partial pressure of 30 kPa, heat to 80 °C, and hold for 60 min; (5) Introduce an O2 / N2 mixture containing 60 vol% O2 as the reaction gas, heat to 180 ℃ and hold for 5 h, and after cooling, obtain a modified cathode material with a surface coated with a Li2SO3 / Li2SO4 composite coating, denoted as NCM-CS2-3.

[0027] Comparative Example A method for preparing a metal oxide cathode material includes the following steps: (1) Prepare a 2 mol / L mixed metal salt solution by dissolving nickel, cobalt and manganese sulfate solution in a molar ratio of 8:1:1. Mix the solution with 1 mol / L sodium hydroxide solution and 0.4 mol / L ammonia solution and feed it into the reactor at a rate of 1.2 mL / min using a peristaltic pump. Control the pH at 10.60, the temperature at 60 °C, and the stirring rate at 650 rpm. After the reaction is completed, wash and dry the product to obtain the metal oxide precursor. (2) The above metal oxide precursor and lithium hydroxide are mixed evenly at a molar ratio of 1:1.05. Under an oxygen atmosphere, the temperature is first raised to 500 °C at a rate of 2 °C / min and calcined for 6 h. Then the temperature is raised to 850 °C at a rate of 2 °C / min and calcined for 18 h. After ball milling, the metal oxide cathode material is obtained. (3) Place the above-mentioned metal oxide cathode material in a sealed reactor and evacuate to 10 °C. -3 After Pa, N2 is introduced until atmospheric pressure is reached; (4) Heat to 80 ℃ and keep warm for 60 min; (5) Introduce an O2 / N2 mixture containing 60 vol% O2 as the reaction gas, heat to 180 ℃ and hold for 5 h, and then cool to obtain the modified material, which is denoted as NCM-CS2-0.

[0028] Application examples Using the metal oxide cathode materials prepared in Examples 1-3 and the comparative examples as raw materials, cathode sheets were prepared, coin cells were assembled, and electrochemical performance was tested.

[0029] (1) The preparation method of the positive electrode sheet is as follows: any one of the metal oxide positive electrode materials prepared in Examples 1-3 and the comparative example, conductive carbon (Super P) and polyvinylidene fluoride (PVDF) are dissolved in 2 mL of N-methylpyrrolidone (NMP) at a weight ratio of 8:1:1 and stirred thoroughly to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on aluminum foil using a coating machine and vacuum dried at 120 °C for 10 h to obtain a positive electrode sheet; the positive electrode sheet is cut into 14 mm circular electrode sheets using a punching machine.

[0030] The assembly method of the button cell battery is as follows: Assemble in a glove box with an argon content of 99.999%, an actual oxygen content of <0.01 ppm, and a moisture content of <0.01 ppm; assemble the battery in the following order: negative electrode shell, positive electrode plate, polypropylene (PP) separator, electrolyte, negative electrode plate, gasket, spring contact, and positive electrode shell; wherein, the electrolyte is prepared by mixing 1 M lithium hexafluorophosphate with an organic solvent, the organic solvent being composed of ethylene carbonate, diethyl carbonate, and propylene carbonate in a volume ratio of 1:1:1, and the negative electrode plate is a lithium metal sheet.

[0031] The electrochemical performance testing method and steps are as follows: In a 25 ℃ constant temperature test chamber, the coin cell lithium-ion battery was placed for 10 h, then charged at a constant current rate of 0.1 C to 4.3 V, and discharged at a constant current rate to 3.0 V. This cycle was repeated three times for activation. The initial coulombic efficiency can be obtained from the initial charge and discharge capacity. Then, a constant current charge and discharge test was performed at a rate of 1 C between 3.0 V and 4.3 V. After 100 cycles, the capacity retention rate of the battery after 100 cycles can be obtained to measure the cycle stability of the battery.

[0032] The performance test results of the cathode materials prepared in the examples and comparative examples are shown in Table 1.

[0033] Table 1 Performance Parameter Results

[0034] As can be seen from the table above, the modified metal oxide cathode material has significantly improved electrochemical performance, especially when the partial pressure of carbon disulfide is 20 kPa.

[0035] In summary, this invention provides a novel surface modification method for metal oxide cathode materials. By employing an in-situ induced chemical reaction using carbon disulfide, the alkalinity of the material surface is significantly reduced, inhibiting electrolyte decomposition and structural degradation on the surface of the high-nickel ternary cathode material. This improves the reversible capacity of the high-nickel ternary cathode material while significantly enhancing its cycle stability.

[0036] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for surface modification of metal oxide cathode materials for lithium-ion batteries based on carbon disulfide vapor-phase modification, characterized in that, The method described: S1: The lithium-ion battery with residual alkaline lithium compounds on its surface is placed in a sealed reaction vessel using a metal oxide positive electrode material. After evacuation, an inert gas is introduced to atmospheric pressure. The alkaline lithium compound is Li2CO3 or LiOH. S2: Inject carbon disulfide vapor, heat to a certain temperature and hold; CS2 partial pressure is 5-50 kPa, heating temperature is 80-120 ℃, and holding time is 30-90 min; S3: Introduce a reaction gas containing O2 and heat it to carry out oxidation treatment. The oxidation treatment temperature is 100-300 ℃. After cooling, the surface modification is completed.

2. The method according to claim 1, characterized in that, The metal oxide cathode materials for lithium-ion batteries with residual alkaline lithium compounds on the surface of S1 include LiNiO2 and LiNi. x Co y Mn 1-x-y O2, where x > 0.5, y > 0, x + y < 1 or LiNi x Mn 1-x O2, where 1 > x > 0.

5.

3. The method according to claim 1, characterized in that, The reaction gas containing O2 in S3 includes N2 or Ar, with an O2 content of 1-80 vol.

4. The lithium-ion battery metal oxide cathode material with a surface coated with a composite coating of Li₂SO₃ and Li₂SO₄ obtained by the method according to any one of claims 1-3, characterized in that, The thickness of the composite coating is 2-5 nm.

5. The application of the metal oxide cathode material for lithium-ion batteries with a surface coating of Li2SO3 and Li2SO4 composite as described in claim 4 in lithium-ion batteries.

6. A positive electrode sheet for a lithium-ion battery, characterized in that, The substrate is formed by coating a slurry with a lithium-ion battery metal oxide cathode material with a surface coated with a composite coating of Li2SO3 and Li2SO4 as described in claim 4, a binder, and a conductive agent.

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