阅读说明：本技术 一种溶胶凝胶-固相烧结法制备低钴正极材料的方法 (Method for preparing low-cobalt cathode material by sol-gel-solid phase sintering method ) 是由 陆和杰 孙旭 王浩 梁正 李海强 李永红 卢瑶 黄凯 吴平 于 2021-07-22 设计创作，主要内容包括：本发明涉及C01G,更具体地,本发明涉及一种溶胶凝胶-固相烧结法制备低钴正极材料的方法。包括：锂盐溶胶制备、前驱体分散液制备、混合凝胶制备、正极材料制备。本发明通过锂盐溶胶作为最直接的锂源,和低钴或的三元前驱体形成复合溶胶凝胶,消除了粉体混料的局部差异性问题,且利用溶胶锂盐一定的流动性通过低三元前驱体的孔隙,实现由内到外的渗透混合,最后再采用固相烧结的方式获得优异电化学性能的低钴三元正极材料。通过溶胶凝胶-固相烧结法获得了具有良好晶体结构的低钴三元正极材料,在应用于锂离子电池中表现出优异的首次库伦效率、首次克容量和良好的循环稳定性。(The invention relates to C01G, in particular to a method for preparing a low-cobalt cathode material by a sol-gel-solid phase sintering method. The method comprises the following steps: lithium salt sol preparation, precursor dispersion liquid preparation, mixed gel preparation and positive electrode material preparation. According to the invention, the lithium salt sol is used as the most direct lithium source to form the composite sol gel with the low-cobalt or ternary precursor, the problem of local difference of powder mixed materials is solved, the permeation mixing from inside to outside is realized by utilizing certain fluidity of the sol lithium salt through the pores of the low-ternary precursor, and finally, the low-cobalt ternary cathode material with excellent electrochemical performance is obtained by adopting a solid-phase sintering mode. The low-cobalt ternary cathode material with a good crystal structure is obtained by a sol-gel-solid phase sintering method, and shows excellent first coulombic efficiency, first gram capacity and good cycling stability when being applied to a lithium ion battery.)

1. A method for preparing a low-cobalt cathode material by a sol-gel-solid phase sintering method is characterized by comprising the following steps:

lithium salt sol preparation: adding lithium salt and a boron source into water and a diluting solvent to obtain lithium salt sol;

preparing low-cobalt precursor dispersion liquid: adding a low-cobalt precursor into an organic solvent to obtain a low-cobalt precursor dispersion liquid;

preparing mixed gel: adding the low-cobalt precursor dispersion liquid into the lithium salt sol, mixing and drying to obtain mixed gel;

preparing a low-cobalt cathode material: and (3) performing solid-phase sintering on the mixed gel to obtain the low-cobalt cathode material of the lithium ion battery.

2. The method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 1, wherein the lithium salt is selected from one or more of lithium alkyl alkoxide, lithium inorganic acid, lithium hydroxide and lithium organic acid.

3. The method for preparing the low-cobalt cathode material by the sol-gel solid-phase sintering method according to claim 1, wherein the boron source is one or more selected from boric acid, ammonium borate and boric acid ester.

4. The method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 1, wherein the volume ratio of the lithium salt to the boron source is (0.5-1): 1.

5. the method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 1, wherein the mass concentration of the low-cobalt precursor in the precursor dispersion liquid is 10-100 g/L.

6. The method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 1, wherein the low-cobalt precursor is a metal compound, the metal in the precursor comprises at least one of nickel, cobalt and manganese, and the molar ratio of cobalt to the total molar amount of nickel, cobalt and manganese in the precursor is (0-1): 1.

7. the method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 1, wherein the particle size of the low-cobalt precursor is 2-5 μm.

8. The method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to any one of claims 1 to 7, wherein in the preparation of the lithium salt sol, after adding the lithium salt into water and a diluting solvent, adding a boron source, and stirring for 0.5 to 5 hours, the lithium salt sol is obtained.

9. The method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to claim 8, wherein in the preparation of the mixed gel, the low-cobalt precursor dispersion liquid is added into the lithium salt sol, mixed for 3-6 hours, and dried at 30-40 ℃ to obtain the mixed gel.

10. The application of the cathode material prepared by the method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method according to any one of claims 1 to 9 in a battery.

Technical Field

The invention relates to C01G, in particular to a method for preparing a low-cobalt cathode material by a sol-gel-solid phase sintering method.

Background

The anode material is the most critical raw material of the lithium ion battery, the metal cobalt has an important function of stabilizing the structure in the ternary anode material, but the global metal cobalt-reserve is limited and the price is high, so the raw material cost and the application cost of the anode material of the lithium ion battery are increased to a great extent. Therefore, the reduction of the proportion of the cobalt content in the ternary material is an important measure for effectively reducing the cost and the application of the ternary cathode material. The metal cobalt has an important function of stabilizing the structure in the ternary material, and the crystal structure is easy to collapse after the cobalt content is reduced under the general condition, so that the reversibility of the deintercalation of lithium ions in the charge-discharge process is influenced, and the extremely low first coulombic efficiency is shown.

Compared with the method of directly using lithium salt and a precursor to carry out solid-phase mixing and sintering, the method can promote the lithium salt and the precursor to be mixed with CN108232135A and CN111924896A to provide the cathode material and the preparation method thereof, and the performance of the cathode material is improved by using reduced graphene oxide and sulfur sol to form gel or forming a stable sol-gel system by using nickel, cobalt, manganese metal salt and lithium.

However, when the sol-gel method is used for preparing the low-cobalt and cobalt-free cathode material, the obtained porous structure has uneven pore size, and is easy to shrink and collapse in the drying and sintering processes, so that the crystal structure and the electrical properties of the low-cobalt and even cobalt-free cathode material are affected.

Disclosure of Invention

In order to solve the above problems, a first aspect of the present invention provides a method for preparing a positive electrode material by a sol-gel-solid phase sintering method, comprising:

lithium salt sol preparation: adding lithium salt and a boron source into water and a diluting solvent to obtain lithium salt sol;

preparing low-cobalt precursor dispersion liquid: adding a low-cobalt precursor into an organic solvent to obtain a low-cobalt precursor dispersion liquid;

preparing mixed gel: adding the low-cobalt precursor dispersion liquid into the lithium salt sol, mixing and drying to obtain mixed gel;

preparing a positive electrode material: and (3) performing solid-phase sintering on the mixed gel to obtain the low-cobalt cathode material of the lithium ion battery.

Preparation of lithium salt sols

In one embodiment, the lithium salt of the present invention is selected from one or more of lithium alkyl alkoxide, lithium inorganic acid, lithium hydroxide, and lithium organic acid. Examples of lithium alkyl alkoxides include, but are not limited to, lithium ethoxide, lithium methoxide, lithium isopropoxide, lithium butoxide, preferably lithium alkyl alkoxides of C1-C3; examples of the inorganic acid lithium include, but are not limited to, LiNO₃、LiNO₂、Li₂CO₃、Li₂SO₄、Li₂SO₃、LiClO₄、LiMnO₄(ii) a Examples of the lithium organic acid include, but are not limited to, lithium acetate and lithium formate. Lithium alkylalkoxides are preferred.

Preferably, the boron source of the present invention is selected from one or more of boric acid, ammonium borate, and borate esters. Boric acid esters are preferred, and examples include trimethyl borate, triethyl borate, tri-n-butyl borate, tripropyl borate and tri-n-hexyl borate, with tri-C1-C4 alkyl borates being preferred.

In one embodiment, the low-cobalt precursor is a metal compound, the metal in the precursor includes at least one of nickel, cobalt and manganese, and the molar ratio of cobalt to the total molar amount of nickel, cobalt and manganese in the precursor is (0-1): 1, preferably (0-0.2): 1, more preferably (0 to 0.1): 1.

the invention uses nickel, cobalt and manganese as the precursor of metal elements, and the metal compound can be metal hydroxide, metal carbonate, metal oxide, metal sulfate and the like, such as Ni_xCo_yMn_(1-x-y)(OH)₂、Ni_xCo_yMn_(1-x-y)CO₃、Ni_xCo_yMn_(1-x-y)O、Ni_xCo_yMn_(1-x-y)SO₄And x and y are respectively the molar ratio of nickel and cobalt in the nickel-cobalt-manganese precursor to the total molar weight of nickel, cobalt and manganese, wherein y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than or equal to 1, and x + y is less than or equal to 1.

Preferably, the particle size of the low-cobalt precursor of the invention is 2-5 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, and preferably 3-4 μm. The size of the particles is referred to as the "particle size", also known as the "particle size" or "diameter". When a certain physical property or physical behavior of the measured particle is most similar to a homogeneous sphere of a certain diameter, the diameter of the sphere is taken as the average particle diameter of the measured particle. The average particle diameter of the invention is D measured by a laser particle sizer₅₀The value is obtained.

More preferably, in the low cobalt precursor dispersion liquid of the present invention, the mass concentration of the low cobalt precursor is 10 to 100g/L, which may be, for example, 10g/L, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, or 100 g/L.

Further preferably, the organic solvent of the present invention is selected from one or more of alcohols and ketones, more preferably alcohols, and further preferably, the organic solvent of the present invention and the alcohol in the dilution solvent are the same in kind.

Preferably, in the preparation of the low-cobalt precursor dispersion liquid, a low-cobalt precursor is added into an organic solvent, and the mixture is stirred for 2-3 hours at a speed of 300-800 r/min, so as to obtain the low-cobalt precursor dispersion liquid.

In one embodiment, the molar ratio of lithium element in the lithium salt to the total moles of nickel, cobalt and manganese in the precursor is (1-1.1): 1.

mixed gel preparation

In one embodiment, in the preparation of the mixed gel, the low-cobalt precursor dispersion is added into the lithium salt sol, mixed for 3-6 hours, and dried at 30-40 ℃ to obtain the mixed gel. Preferably, in the preparation of the mixed gel, the precursor dispersion liquid is added into the lithium salt sol, mixed for 3-6 h at 300-800 r/min, and dried for 8-24 h at 30-40 ℃ to obtain the mixed gel.

The method adopts low-temperature drying, and controls the drying time and the drying temperature, wherein the drying temperature is 30-40 ℃, and 30 ℃, 32 ℃, 34 ℃, 35 ℃, 37 ℃ and 40 ℃ can be enumerated; the drying time is 8-24 h, and can be exemplified by 8h, 12h, 14h, 16h, 18h, 20h, 22h and 24 h.

Preparation of cathode material

According to the invention, the low-cobalt cathode material is prepared by solid-phase sintering, and in one embodiment, in the preparation of the cathode material, the mixed gel is subjected to low-temperature sintering and high-temperature sintering in sequence to obtain the low-cobalt ternary cathode material.

Preferably, the low-temperature sintering temperature is 300-800 ℃, and the low-temperature sintering time is 3-12 h at 300 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃ and 800 ℃, and the low-temperature sintering time is 3-10 h at 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h and 12h, and the heating rate is 1-10 ℃/min at 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min and 10 ℃/min.

Preferably, the low-temperature sintering temperature is 300-800 ℃, and the low-temperature sintering time is 3-12 h at 300 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃ and 800 ℃, and the low-temperature sintering time is 3-10 h at 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h and 12h, and the heating rate is 1-10 ℃/min at 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min and 10 ℃/min.

More preferably, the high-temperature sintering temperature is 700-1100 ℃, which can be enumerated by 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃ and 3-12 h, which can be enumerated by 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h and 12h, and the heating rate is 1-10 ℃/min, which can be enumerated by 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min and 10 ℃/min. In the low-temperature sintering and high-temperature sintering processes, the temperature is the temperature which is increased to the highest temperature, and the time is the time for keeping the temperature after the temperature is increased to the highest temperature.

The invention provides an application of the cathode material prepared by the method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method in a battery.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, the lithium salt sol is used as the most direct lithium source to form the composite sol gel with the low-cobalt ternary precursor, the problem of local difference of powder mixed materials is solved, the permeation mixing from inside to outside is realized by utilizing certain fluidity of the sol lithium salt through the pores of the low-cobalt ternary precursor, and finally, the low-cobalt ternary cathode material with excellent electrochemical performance is obtained by adopting a solid-phase sintering mode.

(2) Compared with the method of directly mixing lithium salt and a low-cobalt precursor, the method has the advantages that the mixing mode is changed from solid particle mixing to gel-state atomic-level mixing, the gel-state lithium salt is infiltrated into the pores in the precursor, the mixing is uniform, the high-adhesion lithium salt has high adhesion and is more sufficient in reaction, and the dust problem is avoided.

(3) The inventors have found that the use of a liquid lithium salt, particularly a lithium alkylol salt, in the liquid state and a boron salt, for example, in the dehydration condensation in comparison with conventional lithium inorganic salts such as lithium oxide or lithium hydroxide, is advantageous (BO)₃Six-ring gel center is formed and combined with lithium ions, and the inventor finds that with the addition of the lithium ionThe stirring time after the lithium salt is added into the boron source is increased, the center of the gel is gradually increased, and crosslinking is gradually carried out, so that the viscosity of the lithium salt sol is gradually increased, and the lithium salt sol is beneficial to infiltration and permeation with the low-cobalt precursor.

(4) The inventor finds that in the preparation process of the mixed gel, the formation of a gel center cross-linked network can be promoted by adding the low-cobalt precursor dispersion liquid with a certain size into the lithium salt sol and stirring for a period of time, and the size and the drying temperature of the low-cobalt precursor are controlled, so that the low-cobalt precursor is favorable for supporting the cross-linked network, the shrinkage and collapse in the drying process are reduced, and when the low-cobalt precursor is sintered, secondary polycrystalline particles with uniform crystal size and good crystallinity are more easily obtained, and the cycle performance and the coulombic efficiency are improved.

(5) The low-cobalt ternary cathode material is prepared by controlling the using amount of cobalt in the precursor, the cost of the ternary material can be reduced, the crystallinity is good, the low-cobalt ternary cathode material can be used for a lithium ion battery, and the low-cobalt ternary cathode material has high first coulombic efficiency and first gram capacity and excellent cycle stability.

Drawings

Fig. 1 is an X-ray diffraction pattern (XRD) of the low-cobalt ternary cathode materials prepared in example a and comparative example B.

Fig. 2 is a Scanning Electron Microscope (SEM) image of the low-cobalt ternary cathode material prepared in the example a and the comparative example B.

Fig. 3 is a first charge-discharge curve diagram of the low-cobalt ternary cathode material prepared in the embodiment a and the comparative embodiment B.

Fig. 4 is a graph of the cycle performance of the low-cobalt ternary cathode materials prepared in example a and comparative example B.

Detailed Description

Examples

Example of the implementation

The present example provides a method of preparing a positive electrode material, comprising:

lithium salt sol preparation: taking 35mL of methanol, adding 2.5mL of lithium methoxide under a stirring state, adding 10mL of water and 35mL of tetrahydrofuran, mixing, adding 50mL of tri-n-butyl borate at the speed of 20mL/h, and stirring for 30min to obtain lithium salt sol;

preparing low-cobalt precursor dispersion liquid: taking D prepared by a batch coprecipitation method₅₀3.5 mu m low-cobalt ternary hydroxide precursor Ni_0.55Co_0.05Mn_0.40(OH)₂Adding 10.0g of the precursor into methanol, and stirring for 2.5 hours at 500r/min to obtain low-cobalt precursor dispersion liquid; the molar ratio of lithium element in the lithium methoxide to the total moles of nickel, cobalt and manganese in the precursor is 1.045: 1;

preparing mixed gel: adding the low-cobalt precursor dispersion liquid into the lithium salt sol, stirring for 4.0h at 300r/min, and storing for 12h at 35 ℃ in a forced air drying oven to obtain mixed gel;

preparing a low-cobalt cathode material: and roasting the mixed gel at 650 ℃ for 8h, heating to 940 ℃ for 12h, coarsely crushing by using an alligator crusher, finely crushing by using a mechanical crusher, and sieving by using a 325-mesh vibrating screen to obtain the low-cobalt ternary cathode material.

This example also provides a low cobalt positive electrode material prepared as described above.

Comparative example

The embodiment provides a method for preparing a low-cobalt cathode material, which comprises the following steps:

will D₅₀Low cobalt precursor Ni of 3.5 μm_0.55Co_0.05Mn_0.40(OH)₂Mixing with powder lithium carbonate, wherein the molar ratio of lithium element in the lithium carbonate to the total moles of nickel, cobalt and manganese in the precursor is 1.045: 1; sintering at 940 ℃ for 10h, coarsely crushing by an alligator crusher after sintering, finely crushing by a mechanical crusher, and sieving by a 325-mesh vibrating screen to obtain the LiNi with low cobalt_0.55Co_0.05Mn_0.40O₂A ternary positive electrode material.

This example also provides a low cobalt positive electrode material prepared as described above.

Evaluation of Performance

1. Crystallinity: the positive electrode materials provided by the embodiment and the comparison example are subjected to X-ray diffraction, the obtained diffraction patterns are shown in figure 1, and from figure 1, the full width at half maximum (FWHM) of the main peak (003) of the embodiment is obviously higher than that of the comparison example, so that the low-cobalt positive electrode material obtained by using the sol-gel method has better crystallinity.

2. Crystal size: SEM tests are carried out on the cathode materials provided by the implementation case and the comparison case, and as shown in figure 2, the low-cobalt cathode material obtained by the sol-gel method is found to be composed of compact secondary microspheres, the particle size of primary particles of the cut secondary microspheres is about 4.5 mu m, and compared with the low-cobalt cathode material obtained by the traditional comparison case, the sphericity of the microspheres is more uniform and perfect.

3. And (3) charge and discharge test: the low cobalt positive electrode materials provided by the implementation case and the comparison case are respectively used as the positive electrodes of the lithium ion battery, and a first charge-discharge experiment is carried out, so that an obtained first charge-discharge curve graph is shown in fig. 3, wherein 1-1 and 1-2 in fig. 3 are charge-discharge curves of the implementation case, 2-1 and 2-2 are charge-discharge curves of the comparison case, and as can be seen from fig. 3, the low cobalt positive electrode material obtained by using the sol-gel-solid phase sintering method of the invention has a first discharge gram capacity of 170.2mAh/g and a first coulomb efficiency of 88.6% when charged and discharged at a current density of 0.2C multiplying power of charging within a voltage range of 3.0-4.3V, and shows excellent first coulomb efficiency and first gram capacity compared with the comparison case.

4. And (3) cyclic stability: the low-cobalt positive electrode materials provided by the implementation case and the comparison case are respectively used as the positive electrodes of the lithium ion batteries, and a cyclic charge-discharge stability test is carried out in a room temperature environment, as shown in fig. 4, under the current density conditions of 0.5C rate charge and 1.0C rate discharge, the capacity of the first circle of the implementation case is 155.6mAh/g, the capacity is kept at 150.6mAh/g after 50 cycles, and the high capacity retention rate is 96.8%; in contrast to the comparative example, the capacity retention rate is 93.5% after 50 cycles, which shows that the cycle stability of the low-cobalt cathode material obtained by the gel sol-solid phase sintering method provided by the invention is remarkably improved.

According to the test result, the method for preparing the low-cobalt cathode material by the sol-gel-solid phase sintering method can be used for preparing the low-cobalt cathode material, can improve the crystal structure and the electrical property of the cathode material while reducing the cost, and can be used as the cathode material of the lithium ion battery.