Surface modification method of metal oxide positive electrode material for lithium ion battery based on carbon disulfide gas phase modification and application of surface modification method

Abstract

The invention discloses a surface modification method of a metal oxide positive electrode material for a lithium ion battery based on carbon disulfide gas phase modification and application thereof. The invention belongs to the field of metal oxide positive electrode materials for lithium ion batteries. In order to overcome the defects in the prior art, CS2 gas-phase treatment is introduced into a metal oxide positive electrode material post-treatment process for the first time, carbon disulfide steam is injected under the protection of inert atmosphere (Ar or N2), and the mixture is heated to a certain temperature for heat preservation; and then introducing reaction gas containing O2, heating, carrying out oxidation treatment, and cooling to finish surface modification. According to the method, the synergistic effect of residual lithium elimination and functional coating construction is achieved, and a special interface structure with both electronic insulativity and ion conductivity is obtained through reaction kinetics regulation and control. The process parameters are accurate and controllable, and the treatment time is lt; the method does not need a subsequent washing process, and is suitable for continuous production.

Description

Technical Field

[0001] The present invention belongs to the field of metal oxide positive electrode materials for lithium ion batteries, and particularly relates to a surface modification method of metal oxide positive electrode materials for lithium ion batteries based on carbon disulfide gas phase modification and application thereof. Background Art

[0002] Due to the increasing demand for energy and the continuous use of traditional fossil fuels, the global energy crisis and environmental damage have had a significant negative impact. In order to resolve this contradiction, it is very important to vigorously develop green and sustainable energy, among which electrochemical energy storage and conversion technology has been proven to be very effective. Since its commercialization in 1991, lithium-ion batteries have gradually demonstrated great advantages and occupied the largest market share of rechargeable batteries in the world. Due to their high energy density and long cycle life, they have been widely used in electric vehicles, grid energy storage and electronic devices. The performance of lithium-ion batteries depends largely on the positive electrode material. Among the many positive electrode materials, metal oxide positive electrode materials have attracted widespread attention due to their advantages such as high energy density, high platform potential, good rate performance and low cost. They are also one of the main research hotspots of positive electrode materials.

[0003] Although metal oxide cathode materials have many advantages, such as low cost and higher specific capacity, they also cause many problems in practical applications that seriously restrict their application process. For example, the cation mixing induces the formation of disordered rock salt phase structure, resulting in a decrease in the specific capacity of the material. This disordered structure will hinder the Li + The diffusion and electron transfer of the cathode material deteriorate the cycling and rate performance of the cathode material. Furthermore, the material's surface is unstable, and contact with carbonate-based electrolytes easily triggers various side reactions, which increase interfacial impedance and reduce cycling stability. During charge and discharge, heat accumulation and gas release caused by these side reactions accelerate the material's thermal runaway process, resulting in a decrease in battery safety.

[0004] Surface coating modification is the most commonly used method to solve the above problems. Its main purpose is to form a uniform coating material on the surface of the positive electrode material. This coating material can act as a physical barrier to prevent direct contact between the material surface and the electrolyte, thereby reducing the occurrence of side reactions. It can also consume the generated HF, reduce the dissolution of transition metals in the active material and the destruction of the surface structure. Some coatings can convert these residues into reasonably conductive lithium compounds, such as phosphates and garnets, thereby improving rate performance. Other researchers use full-surface polymer coatings to prevent rupture by providing elastic support to secondary particles. The specific composition of these coatings can be divided into three categories. One is oxides, such as Al2O3, TiO2, ZrO2, etc. The advantage is that these oxide materials can be well integrated with the surface of the positive electrode material and can exist stably in the electrolyte to play a protective role. However, since these oxides usually have poor conductivity, they will increase the surface impedance, which is not conducive to the transmission and diffusion of lithium ions. The other type is inorganic compounds, including various phosphates and lithium-containing compounds such as lithium titanate. These substances are characterized by a certain degree of lithium ion conductivity and do not hinder ion transport. However, their disadvantage is that the 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 coating is that it has good mechanical properties and can elastically change with the expansion and contraction of the secondary particles, effectively preventing the secondary particles from rupturing and causing the electrolyte to invade the particles. However, its disadvantage is still poor ionic conductivity. Summary of the Invention

[0005] In order to overcome the above technical defects, the present invention provides a surface modification method of metal oxide positive electrode materials for lithium ion batteries based on carbon disulfide gas phase modification and its application.

[0006] The technical solutions of the present invention are as follows: One of the objectives of the present 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 being carried out according to the following steps: S1: placing a metal oxide cathode material for a lithium-ion battery with residual alkaline lithium compounds on its surface in a closed reactor, evacuating the reactor and introducing an inert gas to atmospheric pressure; S2: inject carbon disulfide vapor, heat to a certain temperature and keep warm; S3: introducing reaction gas containing O2 and heating to carry out oxidation treatment, and completing surface modification after cooling.

[0007] It is further defined that the metal oxide positive electrode materials for lithium ion batteries with alkaline lithium compounds remaining on the surface of S1 include LiNiO2, 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] It is further defined that the alkaline lithium compound in S1 is Li2CO3 or LiOH.

[0009] Further limit, vacuum in S1 to 10 -3 Pa.

[0010] It is further defined that the inert gas in S1 is Ar or N2.

[0011] It is further defined that the partial pressure of carbon disulfide vapor (CS2) in S2 is 5-50 kPa.

[0012] It is further defined that the heating temperature in S2 is 80-120°C and the holding time is 30-90 min.

[0013] It is further defined that the reaction gas containing O2 in S3 includes N2 or Ar, wherein the O2 content is 1-80 vol%.

[0014] It is further defined that the oxidation treatment temperature in S3 is 100-300°C.

[0015] The second object of the present invention is to provide a metal oxide positive electrode material for lithium ion batteries with a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the above method.

[0016] It is further defined that the composite coating thickness is 2-5 nm.

[0017] The third object of the present invention is to provide a metal oxide positive electrode material for lithium ion batteries with a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the above method and its application in lithium ion batteries.

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

[0019] Compared with the prior art, the present invention has the following advantages: (1) The present invention proposes a surface modification method for metal oxide cathode materials based on carbon disulfide gas phase modification and its application. The main innovation lies in: for the first time, CS2 gas phase treatment is introduced into the post-treatment process of metal oxide cathode materials. Under the protection of an inert atmosphere (Ar or N2), a program-controlled temperature reaction device (50-200°C) is used to selectively react the alkaline lithium compounds such as Li2CO3 and LiOH remaining on the surface of the material with CS2 vapor. The material is then oxidized in an O2 atmosphere to in situ generate a sulfur-based composite coating (Li2SO3 / Li2SO4) with a three-dimensional network structure, achieving a synergistic effect of residual lithium elimination and functional coating construction; through reaction kinetics regulation, 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 improved electrochemical performance in the voltage range of 2.8-4.3V: the capacity retention rate after 100 cycles of 1 C is increased to 94.6% (84.6% for the comparative example).

[0020] (2) The process parameters of the method of the present invention are precisely controllable, suitable for continuous production, with a processing time of less than 2 h and no need for subsequent washing steps. This technology effectively solves common industry problems such as gas production, interfacial side reactions, and cycle degradation caused by residual lithium on the surface of metal oxide cathode materials, providing an innovative solution for the development of highly safe and long-life lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope image of the metal oxide positive electrode material prepared in step (2) of Example 2; Figure 2 This is a scanning electron microscope image of the modified positive electrode material prepared in Example 2; Figure 3 The cycle stability performance of the positive electrode materials obtained in Examples 1-3 and the comparative example in the half-cell. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

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

[0024] Example 1 A surface modification method for a metal oxide cathode material for a lithium-ion battery based on carbon disulfide vapor phase modification comprises the following steps: (1) A 2 mol / L mixed metal salt solution of nickel, cobalt and manganese sulfate solution was prepared in a molar ratio of 8:1:1, and then mixed evenly with a 1 mol / L sodium hydroxide solution and a 0.4 mol / L ammonia solution. The mixture was fed into a reactor at a rate of 1.2 mL / min via a peristaltic pump. The pH was controlled at 10.60, the temperature was 60 °C, and the stirring rate was 650 rpm. After the reaction, the mixture was washed and dried to obtain a metal oxide precursor. (2) The above-mentioned metal oxide precursor and lithium hydroxide were mixed uniformly in a molar ratio of 1:1.05, and the mixture was heated to 500 °C at a rate of 2 °C / min in an oxygen atmosphere, and fired for 6 h, and then heated to 850 °C at a rate of 2 °C / min, and fired for 18 h. The metal oxide positive electrode material was obtained after ball milling; (3) Place the above metal oxide cathode material in a closed reactor and evacuate to 10 -3 Pa, and then N2 was introduced to normal pressure; (4) Inject carbon disulfide vapor to a partial pressure of 5 kPa, heat to 80 °C, and keep warm for 60 min; (5) An O2 / N2 mixed gas containing 60 vol% O2 was introduced as the reaction gas, the temperature was raised to 180 °C and kept warm for 5 h, and after cooling, a modified positive electrode material with a surface coated with a Li2SO3 / Li2SO4 composite coating was obtained, which was recorded as NCM-CS2-1.

[0025] Example 2 A surface modification method for a metal oxide cathode material for a lithium-ion battery based on carbon disulfide vapor phase modification comprises the following steps: (1) A 2 mol / L mixed metal salt solution of nickel, cobalt and manganese sulfate solution was prepared in a molar ratio of 8:1:1, and then mixed evenly with a 1 mol / L sodium hydroxide solution and a 0.4 mol / L ammonia solution. The mixture was fed into a reactor at a rate of 1.2 mL / min via a peristaltic pump. The pH was controlled at 10.60, the temperature was 60 °C, and the stirring rate was 650 rpm. After the reaction, the mixture was washed and dried to obtain a metal oxide precursor. (2) The above metal oxide precursor and lithium hydroxide were mixed evenly in a molar ratio of 1:1.05. In an oxygen atmosphere, the temperature was first raised to 500 °C at a rate of 2 °C / min and fired for 6 h. Then the temperature was raised to 850 °C at a rate of 2 °C / min and fired for 18 h. The metal oxide positive electrode material was obtained after ball milling. SEM analysis showed that Figure 1 As shown; (3) Place the above metal oxide cathode material in a closed reactor and evacuate to 10 -3 Pa, and then N2 was introduced to normal pressure; (4) Inject carbon disulfide vapor to a partial pressure of 20 kPa, heat to 80 °C, and keep warm for 60 min; (5) An O2 / N2 mixed gas containing 60 vol% O2 was introduced as the reaction gas, the temperature was raised to 180 °C and kept for 5 h, and after cooling, a modified positive electrode material with a surface coated with a Li2SO3 / Li2SO4 composite coating was obtained, which was recorded as NCM-CS2-2; SEM is shown in FIG. Figure 2 As shown, after Figure 1 By comparison, it can be seen that the method of the present invention does not change the morphology and structure of the metal oxide positive electrode material.

[0026] Example 3 A surface modification method for a metal oxide cathode material for a lithium-ion battery based on carbon disulfide vapor phase modification comprises the following steps: (1) A 2 mol / L mixed metal salt solution of nickel, cobalt and manganese sulfate solution was prepared in a molar ratio of 8:1:1, and then mixed evenly with a 1 mol / L sodium hydroxide solution and a 0.4 mol / L ammonia solution. The mixture was fed into a reactor at a rate of 1.2 mL / min via a peristaltic pump. The pH was controlled at 10.60, the temperature was 60 °C, and the stirring rate was 650 rpm. After the reaction, the mixture was washed and dried to obtain a metal oxide precursor. (2) The above-mentioned metal oxide precursor and lithium hydroxide were mixed uniformly in a molar ratio of 1:1.05, and the mixture was heated to 500 °C at a rate of 2 °C / min in an oxygen atmosphere, and fired for 6 h, and then heated to 850 °C at a rate of 2 °C / min, and fired for 18 h. The metal oxide positive electrode material was obtained after ball milling; (3) Place the above metal oxide cathode material in a closed reactor and evacuate to 10 -3 Pa, and then N2 was introduced to normal pressure; (4) Inject carbon disulfide vapor to a partial pressure of 30 kPa, heat to 80 °C, and keep warm for 60 min; (5) An O2 / N2 mixed gas containing 60 vol% O2 was introduced as the reaction gas, the temperature was raised to 180 °C and kept warm for 5 h, and after cooling, a modified positive electrode material with a surface coated with a Li2SO3 / Li2SO4 composite coating was obtained, which was recorded as NCM-CS2-3.

[0027] Comparative Example A method for preparing a metal oxide positive electrode material comprises the following steps: (1) A 2 mol / L mixed metal salt solution of nickel, cobalt and manganese sulfate solution was prepared in a molar ratio of 8:1:1, and then mixed evenly with a 1 mol / L sodium hydroxide solution and a 0.4 mol / L ammonia solution. The mixture was fed into a reactor at a rate of 1.2 mL / min via a peristaltic pump. The pH was controlled at 10.60, the temperature was 60 °C, and the stirring rate was 650 rpm. After the reaction, the mixture was washed and dried to obtain a metal oxide precursor. (2) The above-mentioned metal oxide precursor and lithium hydroxide were mixed uniformly in a molar ratio of 1:1.05, and the mixture was heated to 500 °C at a rate of 2 °C / min in an oxygen atmosphere, and fired for 6 h, and then heated to 850 °C at a rate of 2 °C / min, and fired for 18 h. The metal oxide positive electrode material was obtained after ball milling; (3) Place the above metal oxide cathode material in a closed reactor and evacuate to 10 -3 Pa, and then N2 was introduced to normal pressure; (4) Heat to 80°C and keep warm for 60 min; (5) An O2 / N2 mixed gas containing 60 vol% O2 was introduced as the reaction gas, the temperature was raised to 180 °C and kept at this temperature for 5 h, and the modified material was obtained after cooling, which was recorded as NCM-CS2-0.

[0028] Application Examples Positive electrode sheets were prepared using the metal oxide positive electrode materials prepared in Examples 1-3 and the comparative example as raw materials, button batteries were assembled, and electrochemical performance tests were performed.

[0029] (1) A method for preparing a positive electrode sheet, comprising the following steps: dissolving 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) in 2 mL of N-methylpyrrolidone (NMP) at a weight ratio of 8:1:1, and stirring thoroughly to obtain a positive electrode slurry; using a coater to evenly coat the positive electrode slurry on aluminum foil, and vacuum drying at 120°C for 10 h to obtain a positive electrode sheet, and using a punching machine to cut the positive electrode sheet into 14 mm circular sheets.

[0030] The button battery assembly method comprises the following steps: assembling in a glove box, wherein the argon content in the glove box is 99.999%, the actual oxygen content is less than 0.01 ppm, and the moisture content is less than 0.01 ppm; assembling the battery in the order of a negative electrode shell, a positive electrode sheet, a diaphragm polypropylene PP, an electrolyte, a negative electrode sheet, a gasket, a spring, and a positive electrode shell; wherein the electrolyte is prepared by mixing 1 M lithium hexafluorophosphate with an organic solvent, wherein the organic solvent is composed of ethylene carbonate, diethyl carbonate, and propylene carbonate in a volume ratio of 1:1:1, and the negative electrode sheet is a metal lithium sheet.

[0031] The electrochemical performance test method is as follows: In a constant temperature test room at 25°C, the button lithium-ion battery was placed for 10 hours, then charged to 4.3 V at a constant current rate of 0.1 C, and discharged to 3.0 V at a constant current for three cycles for activation. The first coulombic efficiency can be obtained through the first charge and discharge capacity; then a constant current charge and discharge test was performed between 3.0 V and 4.3 V at a rate of 1 C. After 100 cycles, the capacity retention rate of the battery after 100 cycles can be obtained to measure the battery's cycle stability.

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

[0033] Table 1 Performance parameter results

[0034] It can be seen from the above table that 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, the present invention provides a novel surface modification method for metal oxide cathode materials. By using carbon disulfide to induce an in-situ chemical reaction, 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 method increases the reversible capacity of the high-nickel ternary cathode material while significantly improving its cycling stability.

[0036] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope 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 based on the scope of protection 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: S1: placing a metal oxide cathode material for a lithium-ion battery with residual alkaline lithium compounds on its surface in a closed reactor, evacuating the reactor and introducing an inert gas to atmospheric pressure; S2: inject carbon disulfide vapor, heat to a certain temperature and keep warm; S3: introducing reaction gas containing O2 and heating to carry out oxidation treatment, and completing surface modification after cooling.

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

3. The method according to claim 1, characterized in that The alkaline lithium compound in S1 is Li2CO3 or LiOH.

4. The method according to claim 1, wherein The partial pressure of CS2 in S2 is 5-50 kPa.

5. The method according to claim 1, wherein The heating temperature in S2 is 80-120°C and the holding time is 30-90 min.

6. The method according to claim 1, characterized in that The O2-containing reaction gas in S3 includes N2 or Ar, wherein the O2 content is 1-80 vol%.

7. The method according to claim 1, characterized in that The oxidation treatment temperature in S3 is 100-300°C.

8. A metal oxide positive electrode material for lithium ion batteries having a surface coated with a Li2SO3 / Li2SO4 composite coating obtained by the method according to any one of claims 1 to 7, characterized in that: The composite coating thickness is 2-5 nm.

9. Use of the metal oxide positive electrode material for lithium ion batteries with a surface coated with a Li2SO3 / Li2SO4 composite coating as claimed in claim 8 in lithium ion batteries.

10. A positive electrode plate for a lithium-ion battery, characterized in that: The substrate is coated with a slurry made of a metal oxide positive electrode material for a lithium ion battery with a surface covered with a Li2SO3 / Li2SO4 composite coating as claimed in claim 8, a binder and a conductive agent.

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