Method for the production of a tellurium-doped lithium cobaltate precursor

Abstract

A process for the preparation of a lithium cobaltate precursor, comprising the following steps: S1: Addition of a cobalt salt solution, a precipitating agent, and a complexing agent to a base solution for reaction in an inert atmosphere to obtain a reaction material, wherein the precipitating agent is a mixed solution of tellurium dioxide dissolved in a sodium hydroxide solution, and the base solution is a mixed solution of ammonia water and a thiosulfate; wherein in step S1 the concentration of sodium hydroxide in the precipitating agent is 2.0 to 4.0 mol / L, and the amount of tellurium dioxide added is 1 to 10% of the molar amount of sodium hydroxide, and the base solution has a pH of 10-11, an ammonia concentration of 5-10 g / L, and a thiosulfate concentration of 0.1-3.0 mol / L;andS2: When the reaction material reaches a target particle size, it is subjected to aging and solid-liquid separation to obtain the lithium cobaltate precursor; in the process, tellurium is reduced to tellura anion with the thiosulfate to produce cobalt telluride, and the cobalt telluride is co-precipitated with cobalt hydroxide, thereby achieving tellurium doping in the precursor.

Description

TECHNICAL AREA

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates in particular to a method for producing a tellurium-doped lithium cobaltate precursor and its use. BACKGROUND

[0002] Lithium cobaltate is widely used as a cathode material for lithium-ion batteries due to its high operating voltage and energy density, ease of synthesis, and rapid charging / discharging capabilities. However, in recent years, the increasing miniaturization and multifunctionality of electronic products have placed higher demands on battery energy density, demands that conventional lithium cobaltates can no longer meet. Improving the energy density of lithium batteries while ensuring safety and adequate cycle life will remain a fundamental focus for small lithium batteries in the coming years.

[0003] The most important ways to improve energy density are to increase the capacity of the electrode material and / or to increase the battery's operating voltage, and increasing both voltage and capacity is currently the main focus in the development of cathode materials for 3K lithium batteries. The operating voltage of existing lithium-ion batteries is essentially between 3.0 V and 4.3 V, and the capacity of a lithium-ion battery using lithium cobaltate as the cathode material can be increased by about 20% when charged to 4.5 V. If the operating voltage exceeds 4.2 V, the deintercalation coefficient x of Li 1-x CoO2 ≥ 0.5, which leads to the breakdown of the structure inside the material, causing problems such as a poor charge-discharge cycle at high voltage and poor storage performance at high temperature.

[0004] A high-voltage lithium cobaltate cathode material is known in the prior art. The product made from it can achieve a compacted density of 4.1–4.15 g / cm³. 3 It exhibits a particle size distribution D50 of 17.0–19.0 ​​µm, which falls into the category of large particles in the lithium cobaltate industry. The rate performance of particles with this size needs improvement due to the long diffusion path of lithium ions. During charging and discharging, the volume changes within the large particles tend to cause microcracks in the material, leading to a significant decrease in cycle performance. Since most of the lithium cobaltate materials currently on the market primarily have a polycrystalline morphology with a compacted density of 3.6 g / cm³, this is a significant challenge. 3or less, it is also an urgent task to increase the compacted density and thus increase the volumetric energy density of lithium cobaltate materials. SUMMARY

[0005] The present invention aims to solve at least one of the aforementioned technical problems that exist in the prior art. Therefore, the present invention proposes a method for producing a tellurium-doped lithium cobaltate precursor and its use.

[0006] According to one aspect of the present invention, a method for producing a lithium cobaltate precursor is provided, comprising the following steps: S1: Addition of a cobalt salt solution, a precipitating agent, and a complexing agent to a base solution for reaction in an inert atmosphere to obtain a reaction material, wherein the precipitating agent is a mixed solution of tellurium dioxide dissolved in sodium hydroxide, and the base solution is a mixed solution of ammonia water and thiosulfate; and S2: When the reaction material reaches a target particle size, it is subjected to aging and solid-liquid separation to obtain the lithium cobaltate precursor.

[0007] In some embodiments of the present invention, in step S1 the cobalt salt solution is at least one of the group consisting of cobalt sulfate, cobalt nitrate, cobalt chloride and a mixture thereof.

[0008] In some embodiments of the present invention, the cobalt salt solution in step S1 has a concentration of 1.0-2.0 mol / L.

[0009] In some embodiments of the present invention, in step S1 the concentration of sodium hydroxide in the precipitating agent is 2.0 to 4.0 mol / l and the amount of tellurium dioxide added is 1 to 10% of the molar amount of sodium hydroxide.

[0010] In some embodiments of the present invention, the complexing agent in step S1 is ammonia water with a concentration of 6.0-12.0 mol / L.

[0011] In some embodiments of the present invention, the base solution in step S1 has a pH of 10-11, an ammonia concentration of 5-10 g / L and a thiosulfate concentration of 0.1-3.0 mol / L.

[0012] In some embodiments of the present invention, the reaction in step S1 is carried out at a temperature of 55-65°C, a pH of 10-11 and an ammonia concentration of 5-10 g / L.

[0013] In some embodiments of the present invention, the reaction in step S1 is carried out in a reactor, and the volume of the base solution is 8-12% of the volume of the reactor.

[0014] In some embodiments of the present invention, the reaction in step S1 is carried out with a stirring speed of 200-500 rpm.

[0015] In some embodiments of the present invention, aging is carried out for 24-48 hours in step S2.

[0016] In some embodiments of the present invention, the target particle size distribution D50 of the reaction material in step S2 is 2.0-5.0 µm.

[0017] In some embodiments of the present invention, step S2 further comprises washing and drying a solid phase obtained by solid-liquid separation with water, and the drying is optionally carried out at a temperature of 100-120°C for 4-6 h.

[0018] The present invention also provides for the use of the lithium cobaltate precursor described above for the production of lithium cobaltate. In some embodiments of the present invention, the process for producing lithium cobaltate comprises: mixing the lithium cobaltate precursor with a lithium source and calcining the resulting mixture in an oxygen-containing atmosphere to obtain the lithium cobaltate. Doping with tellurium, as well as reduction synthesis and low-temperature sintering of the precursor, yields a long-cycle, highly dense monocrystalline lithium cobalt cathode material.

[0019] In some embodiments of the present invention, the lithium source is at least one from the group consisting of lithium carbonate, lithium hydroxide and a mixture thereof.

[0020] In some embodiments of the present invention, the calcination is carried out at a temperature of 700-800°C. Furthermore, the calcination is carried out for 12-18 hours.

[0021] In some embodiments of the present invention, the molar ratio of the cobalt element in the lithium cobaltate precursor to the lithium element in the lithium source is 1: (1.0-1.2).

[0022] The present invention also provides for the use of the lithium cobaltate precursor produced according to the method described above in the manufacture of a cathode material for a lithium-ion battery.

[0023] The present invention also provides for the use of the lithium cobaltate precursor produced according to the method described above in the manufacture of a lithium-ion battery.

[0024] According to a preferred embodiment of the present invention, the present invention has at least the following advantageous effects. 1. In this disclosure, a tellurium-doped cobalt hydroxide is obtained by the co-precipitation of a cobalt salt, a complexing agent, and a precipitating agent, followed by doping with tellurium. Because tellurium is soluble, it is difficult to precipitate it together with cobalt. In this disclosure, tellurium is reduced to the tellura anion with thiosulfate to generate cobalt telluride, which is then precipitated with cobalt hydroxide, thereby achieving the doping of the tellurium in the precursor. The reaction equations involved are as follows: 4Co 2+ +4TeO3 2- +3S2O3 2- +6OH - =4CoTe↓+6SO4 2- +3H2O; Co 2+ +2OH - =Co(OH)2↓. 2. The oxidation of cobalt alters the crystalline phase, weakens the whiskers, and makes the material loose and porous. However, in the present disclosure, the reaction during coprecipitation always takes place in a reducing atmosphere, thus preventing the oxidation of cobalt. Therefore, the precursor produced is denser, and the lithium cobaltate material produced by subsequent sintering has a higher density. 3. After calcination of the lithium cobaltate precursor and the lithium source, a tellurium-doped lithium cobaltate cathode material is obtained. Tellurium is used to replace the oxygen atoms in lithium cobaltate, and cobalt telluride is gradually oxidized to oxygen during subsequent sintering (CoTe + 2O₂ = CoTeO₄). In its anionic form, tellurium can contribute to further stabilization of the crystal skeleton. Since tellurium also has a larger ionic radius, the interlayer spacing is further increased, which further enhances the lithium capacity and the specific capacity of the material. 4. The difference between the doping of tellurium and the doping of other elements lies in the fact that, as a non-metallic element, it can form a stable anion group to exist stably, unlike sulfur and selenium in the same group, which are extremely volatile after oxidation at high temperatures, making the removal of impurities difficult. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is described below in conjunction with the drawings and examples in which: Fig. Figure 1 shows a scanning electron microscope (SEM) image of the lithium cobaltate produced in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The following section clearly and completely describes the concept of the present invention and the technical effects it produces, in conjunction with the examples, to fully understand its purpose, features, and effects. It is evident that the examples described represent only a subset of the examples of the present invention, and not all of them. All other examples, which could have been determined by those skilled in the art based on the examples of the present invention without any inventive work, fall within the scope of the present invention. Example 1

[0027] In this example, a tellurium-doped lithium cobaltate cathode material was produced as follows: Step 1. A cobalt sulfate solution with a concentration of 1.0 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 2.0 mol / L was prepared as a precipitating agent, and tellurium dioxide was added in an amount equal to 1% of the molar amount of sodium hydroxide to dissolve it completely and obtain a mixed solution. Step 3. Ammonia water with a concentration of 6.0 mol / L was prepared as a complexing agent. Step 4. A base solution was placed in a reactor and nitrogen was added. The volume of the base solution was 12% of the reactor volume, and the base solution was adjusted to a pH of 11 and an ammonia concentration of 10 g / L. Then, sodium thiosulfate was added so that the sodium thiosulfate concentration in the base solution was 0.1 mol / L. Step 5. The cobalt sulfate solution prepared in step 1, the mixed solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 200 rpm, a pH of 11, a temperature of 55 °C, and an ammonia concentration of 10 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 2.0 µm, the feeding process was stopped. Aging was then carried out for 24 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried for 6 hours at 100 °C to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium carbonate in a molar ratio of cobalt to lithium of 1:1 and calcined in an oxygen atmosphere at a temperature of 700°C for 18 hours. It was then crushed, sieved, and de-ironed. The tellurium-doped lithium cobaltate cathode material was subsequently obtained.

[0028] Fig. shows an SEM image of the lithium cobaltate produced in this example, which reveals that the material has a very dense bulk structure. Example 2

[0029] In this example, a tellurium-doped lithium cobaltate cathode material was produced as follows: Step 1. A cobalt nitrate solution with a concentration of 1.5 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 3.0 mol / L was prepared as a precipitating agent, and tellurium dioxide was added in an amount equal to 5% of the molar amount of sodium hydroxide to dissolve it completely and obtain a mixed solution. Step 3. Ammonia water with a concentration of 9.0 mol / L was prepared as a complexing agent. Step 4. A base solution was placed in a reactor and nitrogen was added. The volume of the base solution corresponded to 10% of the reactor volume, and the base solution was adjusted to a pH of 10.5 and an ammonia concentration of 8 g / L. Then, sodium thiosulfate was added so that the sodium thiosulfate concentration in the base solution was 1.5 mol / L. Step 5. The cobalt nitrate solution prepared in step 1, the mixed solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 350 rpm, a pH of 10.5, a temperature of 58 °C, and an ammonia concentration of 8 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 3.5 µm, the feeding process was stopped. Aging was then carried out for 36 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried at 110 °C for 5 hours to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium hydroxide in a molar ratio of cobalt to lithium of 1:1.1 and calcined in an oxygen atmosphere at a temperature of 750°C for 15 hours. The mixture was then crushed, sieved, and de-ironed. The tellurium-doped lithium cobaltate cathode material was subsequently obtained. Example 3

[0030] In this example, a tellurium-doped lithium cobaltate cathode material was produced as follows: Step 1. A cobalt chloride solution with a concentration of 2.0 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 4.0 mol / L was prepared as a precipitating agent, and tellurium dioxide was added in an amount equal to 10% of the molar amount of sodium hydroxide to dissolve it completely and obtain a mixed solution. Step 3. Ammonia water with a concentration of 12.0 mol / L was prepared as a complexing agent. Step 4. A base solution was added to a reactor and argon was introduced. The volume of the base solution corresponded to 12% of the reactor volume, and the base solution was adjusted to a pH of 10 and an ammonia concentration of 5 g / L. Then, sodium thiosulfate was added so that the sodium thiosulfate concentration in the base solution was 3.0 mol / L. Step 5. The cobalt chloride solution prepared in step 1, the mixed solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 500 rpm, a pH of 10, a temperature of 65 °C, and an ammonia concentration of 5 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 5.0 µm, the feeding process was stopped. Aging was then carried out for 48 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried at 120 °C for 4 hours to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium hydroxide in a molar ratio of cobalt to lithium of 1:1.2 and calcined in an oxygen atmosphere at a temperature of 800°C for 12 hours. It was then crushed, sieved, and de-ironed. The tellurium-doped lithium cobaltate cathode material was subsequently obtained. Comparative Example 1

[0031] In this comparative example, a lithium cobaltate cathode material was produced, which differs from Example 1 in that tellurium dioxide and sodium thiosulfate were not added in Comparative Example 1, as follows: Step 1. A cobalt sulfate solution with a concentration of 1.0 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 2.0 mol / L was prepared as a precipitating agent. Step 3. Ammonia water with a concentration of 6.0 mol / L was prepared as a complexing agent. Step 4. A base solution was added to a reactor and nitrogen was introduced. The volume of the base solution corresponded to 12% of the reactor volume, and the base solution was adjusted to a pH of 11 and an ammonia concentration of 10 g / L. Step 5. The cobalt sulfate solution prepared in step 1, the sodium hydroxide solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 200 rpm, a pH of 11, a temperature of 55 °C, and an ammonia concentration of 10 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 2.0 µm, the feeding process was stopped. Aging was then carried out for 24 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried for 6 hours at 100 °C to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium carbonate in a molar ratio of cobalt to lithium of 1:1 and calcined in an oxygen atmosphere at a temperature of 700°C for 18 hours. It was then crushed, sieved, and de-ironed. The lithium cobaltate cathode material was subsequently obtained. Comparative Example 2

[0032] In this example, a lithium cobaltate cathode material was produced, which differs from Example 2 in that tellurium dioxide and sodium thiosulfate were not added in Comparative Example 2, as follows: Step 1. A cobalt nitrate solution with a concentration of 1.5 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 3.0 mol / L was prepared as a precipitating agent. Step 3. Ammonia water with a concentration of 9.0 mol / L was prepared as a complexing agent. Step 4. A base solution was added to a reactor and nitrogen was introduced. The volume of the base solution corresponded to 10% of the reactor volume, and the base solution was adjusted to a pH of 10.5 and an ammonia concentration of 8 g / L. Step 5. The cobalt nitrate solution prepared in step 1, the mixed solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 350 rpm, a pH of 10.5, a temperature of 58 °C, and an ammonia concentration of 8 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 3.5 µm, the feeding process was stopped. Aging was then carried out for 36 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried at 110 °C for 5 hours to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium hydroxide in a molar ratio of cobalt to lithium of 1:1.1 and calcined in an oxygen atmosphere at a temperature of 750°C for 15 hours. It was then crushed, sieved, and de-ironed. The lithium cobaltate cathode material was subsequently obtained. Comparative Example 3

[0033] In this example, a lithium cobaltate cathode material was produced, which differs from Example 3 in that tellurium dioxide and sodium thiosulfate were not added in Comparative Example 3, as follows: Step 1. A cobalt chloride solution with a concentration of 2.0 mol / L was prepared. Step 2. A sodium hydroxide solution with a concentration of 4.0 mol / L was prepared as a precipitating agent. Step 3. Ammonia water with a concentration of 12.0 mol / L was prepared as a complexing agent. Step 4. A base solution was added to a reactor and argon was introduced. The volume of the base solution corresponded to 12% of the reactor volume, and the base solution was adjusted to a pH of 10 and an ammonia concentration of 5 g / L. Step 5. The cobalt chloride solution prepared in step 1, the mixed solution prepared in step 2, and the ammonia solution prepared in step 3 were added to the reactor for cocurrent reaction. The reactor was set to a stirring speed of 500 rpm, a pH of 10, a temperature of 65 °C, and an ammonia concentration of 5 g / L. Step 6. When it was determined that the D50 value of the material in the reactor reached 5.0 µm, the feeding process was stopped. Aging was then carried out for 48 hours. Step 7. The material in the reactor was subjected to solid-liquid separation to obtain a precipitate, which was then washed with pure water and dried at 120 °C for 4 hours to obtain a lithium cobaltate precursor material. Step 8. The precursor material obtained in step 7 was mixed with lithium hydroxide in a molar ratio of cobalt to lithium of 1:1.2 and calcined in an oxygen atmosphere at a temperature of 800°C for 12 hours. The mixture was then crushed, sieved, and iron-free. The lithium cobaltate cathode material was subsequently obtained. Table 1. Proof of compacted density Compacted density g / cm³ 3 Example 1 4.23 Example 2 4.21 Example 3 4.25 Comparative Example 1 3.81 Comparative Example 2 3.76 Comparative Example 3 3.83 Test example

[0034] The lithium cobaltate material obtained in each of the examples and comparison examples, used as the active material, acetylene black as the conductive agent, and PVDF as the binder, were mixed in a 92:4:4 ratio. A specific amount of the organic solvent NMP was then added, stirred, and applied to aluminum foil to produce a positive electrode foil. A metallic lithium foil was used as the negative electrode. Subsequently, a CR2430 button cell battery was prepared in an argon-filled glove compartment. The button cell was tested for its electrical performance in the Lanhe CT2001A test system at 3.0 V–4.48 V, a current density of 1C = 180 mAh / g, and a temperature of 25 ± 1 °C. The test results are shown in Table 2. Table 2. Electrochemical performance of batteries made from lithium cobaltate Discharge capacity at 0.1 C / 4.48 V, mAh / g Capacity maintenance rate after 600 cycles at 0.1 C / 4.48 V Example 1 246.3 84% Example 2 241.4 87% Example 3 238.7 89% Comparative Example 1 207.8 74% Comparative Example 2 208.1 77% Comparative Example 3 208.1 73%

[0035] As can be seen from Table 2, the discharge capacity and cycle performance in the comparison examples were significantly lower than in the examples. This is due to the addition of tellurium dioxide and sodium thiosulfate in the examples. The resulting cobalt telluride was gradually oxidized during sintering. In its anionic form, tellurium can contribute to stabilizing the crystal skeleton. Furthermore, since tellurium had a larger ionic radius, the interlayer spacing was increased, which further improved the lithium capacity and the specific capacity and cycle performance of the material. In addition, Table 1 shows that the examples exhibited a higher compact density and a higher volumetric energy density.

[0036] The examples of the present invention have been described in detail above in conjunction with the drawings. However, the present invention is not limited to the examples mentioned above, and various modifications can be made without departing from the purpose of the present invention within the scope of the knowledge of those possessing ordinary technical expertise. Furthermore, the examples of the present invention and the features in the examples can be combined with one another, provided they do not contradict each other.

Claims

[1] A process for producing a lithium cobaltate precursor comprising the following steps: S1: Adding a cobalt salt solution, a precipitating agent, and a complexing agent to a base solution for reaction in an inert atmosphere to obtain a reaction material, wherein the precipitating agent is a mixed solution of tellurium dioxide dissolved in sodium hydroxide, and the base solution is a mixed solution of ammonia water and thiosulfate; and S2: When the reaction material reaches a target particle size, the reaction material is subjected to aging and solid-liquid separation to obtain the lithium cobaltate precursor. [2] The method according to claim 1, wherein in step S1, the cobalt salt solution is at least one solution selected from the group consisting of cobalt sulfate, cobalt nitrate, cobalt chloride and a mixture thereof. [3] The method according to claim 1, wherein in step S1 the cobalt salt solution has a concentration of 1.0-2.0 mol / L. [4] The process according to claim 1, wherein in step S1 the concentration of sodium hydroxide in the precipitant is 2.0 to 4.0 mol / l and the amount of tellurium dioxide added is 1 to 10% of the molar amount of sodium hydroxide. [5] The process according to claim 1, wherein in step S 1 the complexing agent is ammonia water having a concentration of 6.0-12.0 mol / L. [6] The method according to claim 1, wherein in step S1 the base solution has a pH of 10-11, an ammonia concentration of 5-10 g / L and a thiosulfate concentration of 0.1-3.0 mol / L. [7] The process according to claim 1, wherein in step S1 the reaction is carried out at a temperature of 55-65°C, a pH of 10-11 and an ammonia concentration of 5-10 g / L. [8] Use of the lithium cobaltate precursor prepared according to any one of claims 1 to 7 for producing lithium cobaltate, a cathode material for lithium-ion batteries or a lithium-ion battery. [9] Use according to claim 8, wherein the lithium cobaltate is prepared by a process comprising: mixing the lithium cobaltate precursor with a lithium source and calcining a resulting mixture in an oxygen-containing atmosphere, wherein the lithium source is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, and a mixture thereof. [10] Use according to claim 8, wherein the lithium cobaltate is prepared by a process comprising: mixing the lithium cobaltate precursor with a lithium source and calcining a resulting mixture in an oxygen-containing atmosphere, wherein the calcination is carried out at a temperature of 700-800°C.