阅读说明：本技术 一种三维碳纳米管复合硅酸亚铁锂微球及其制备方法 (Three-dimensional carbon nano tube composite lithium iron silicate microsphere and preparation method thereof ) 是由 颜海燕 李晨 张改 董经纬 王昭 刘玉君 于 2020-05-20 设计创作，主要内容包括：本发明公开一种三维碳纳米管复合硅酸亚铁锂微球及其制备方法,涉及锂电池电极制备技术领域,所述制备方法主要包括以下几步：首先以碳纳米管、分散剂、溶剂配置碳纳米管浆料；然后将氢氧化锂、草酸亚铁和二氧化硅充分混合后溶解于碳纳米管浆料中并进行球磨,球磨完成后继续搅拌并通过分散剂调节浆料的粘稠度；再通过喷雾干燥得到前驱体并依次经过烧结、微波辐照后得到三维碳纳米管复合硅酸亚铁锂微球。采用本发的三维碳纳米管复合硅酸亚铁锂微球制备的锂电池性能优异,在500次循环后,在5C时依然具有优异的倍率性能和循环稳定性,容量保持率约为91.2％。(The invention discloses a three-dimensional carbon nano tube composite lithium ferrous silicate microsphere and a preparation method thereof, relating to the technical field of lithium battery electrode preparation, wherein the preparation method mainly comprises the following steps: firstly, preparing carbon nanotube slurry by using a carbon nanotube, a dispersant and a solvent; then fully mixing lithium hydroxide, ferrous oxalate and silicon dioxide, dissolving the mixture in carbon nanotube slurry, carrying out ball milling, continuously stirring the mixture after the ball milling is finished, and adjusting the viscosity of the slurry through a dispersing agent; and then spray drying to obtain a precursor, and sintering and microwave irradiation are carried out in sequence to obtain the three-dimensional carbon nanotube composite lithium iron silicate microsphere. The lithium battery prepared by adopting the three-dimensional carbon nanotube composite lithium iron silicate microsphere has excellent performance, and still has excellent rate performance and cycle stability at 5 ℃ after 500 cycles, and the capacity retention rate is about 91.2%.)

1. A preparation method of a three-dimensional carbon nanotube composite lithium iron silicate microsphere is characterized by mainly comprising the following steps:

s1: preparing carbon nanotube slurry by using a carbon nanotube, a dispersant and a solvent;

s2: fully mixing lithium hydroxide, ferrous oxalate and silicon dioxide, dissolving the mixture into the carbon nanotube slurry obtained in the step S1, performing ball milling, continuously stirring the mixture after the ball milling is finished, and adjusting the viscosity of the slurry through a dispersing agent;

s3: obtaining a precursor by spray-drying the slurry of step S2;

s4: sintering and microwave irradiating the precursor in sequence to obtain the three-dimensional carbon nano tube composite lithium ferrous silicate microsphere.

2. The method for preparing the three-dimensional carbon nanotube composite lithium ferrous silicate microsphere of claim 1, wherein the dispersant is one of sodium dodecyl sulfate, N-vinyl pyrrolidone and sodium dodecyl sulfate.

3. The preparation method of the three-dimensional carbon nanotube composite lithium iron silicate microsphere according to claim 1, wherein the carbon nanotube, the dispersant and the solvent are in a mass ratio of: 1-10: 0.2-5: 85-98.8.

4. The preparation method of the three-dimensional carbon nanotube composite lithium iron silicate microsphere according to claim 3, wherein the mass ratio of the carbon nanotube, the dispersant and the solvent is 5:3: 92.

5. The preparation method of the three-dimensional carbon nanotube composite lithium ferrous silicate microsphere according to claim 1, wherein the mass ratio of the lithium hydroxide, the ferrous oxalate and the silicon dioxide is 1:1: 1.

6. The method for preparing the three-dimensional carbon nanotube composite lithium iron silicate microsphere according to claim 1, wherein the mass ratio of the lithium hydroxide to the carbon nanotube is 1.5: 1.

7. The method for preparing the three-dimensional carbon nanotube composite lithium iron silicate microspheres according to claim 1, wherein the temperature of the spray drying is 115 ℃.

8. The method for preparing the three-dimensional carbon nanotube composite lithium iron silicate microsphere as claimed in claim 1, wherein the sintering process of step S4 is pre-sintering at 350-400 ℃ for 3-5 h, and then sintering at 700 ℃ under argon/hydrogen protection for 6-9 h.

9. The method for preparing three-dimensional carbon nanotube composite lithium iron silicate microspheres as claimed in claim 1, wherein the microwave irradiation time is 5-8 minutes, and the microwave power is 600-750W.

10. A three-dimensional carbon nanotube composite lithium iron silicate microsphere prepared by the method for preparing the three-dimensional carbon nanotube composite lithium iron silicate microsphere of any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a three-dimensional carbon nanotube composite lithium iron silicate microsphere and a preparation method thereof.

Background

Lithium ion batteries have become the primary power source for a variety of applications due to their excellent lithium storage properties. Then, the development of a novel electrode with good rate performance, excellent cycle life and high reversible capacity is of great importance for the development and application of lithium ion battery materials and devices. Recently, many new electrode materials, such as LiCoMnO₄、Li₃V₂(PO)₃、Li₂MnSiO₄、LiVPO₄F and Li₂FeSiO₄And the like are widely studied. Among these novel electrode materials, polyanionic type Li₂FeSiO₄It is considered to be a promising positive electrode material due to its high stability and excellent safety. In addition, Li was shown by two electron reaction₂FeSiO₄Has a theoretical capacity of 332mAhg^-1. However, Li₂FeSiO₄The electron conductivity of the conductive layer is 10 to 14Scm^-1The ionic conductivity is 10 to 14Scm^-1Exhibit low electron mobility and Li⁺Diffusion rate, difficult in Li₂FeSiO₄In the presence of two Li⁺This greatly hinders its practical application in lithium storage devices.

Disclosure of Invention

In order to solve the problems, the invention provides a three-dimensional carbon nano tube composite lithium iron silicate microsphere (3D-L)i₂FeSiO 4/CNTs) and a preparation method thereof, and the three-dimensional carbon nano tube composite lithium ferrous silicate microspheres are prepared by combining spray drying, sintering and microwave irradiation to improve Li₂FeSiO₄The lithium ion battery positive electrode material has lithium storage performance.

In order to achieve the purpose, one of the technical schemes adopted by the invention is as follows: a preparation method of a three-dimensional carbon nanotube composite lithium iron silicate microsphere mainly comprises the following steps:

s1: preparing carbon nanotube slurry by using a carbon nanotube, a dispersant and a solvent;

s2: fully mixing lithium hydroxide, ferrous oxalate and silicon dioxide, dissolving the mixture into the carbon nanotube slurry obtained in the step S1, performing ball milling, continuously stirring the mixture after the ball milling is finished, and adjusting the viscosity of the slurry through a dispersing agent;

s3: obtaining a precursor by spray-drying the slurry of step S2;

s4: sintering and microwave irradiating the precursor in sequence to obtain the three-dimensional carbon nano tube composite lithium ferrous silicate microsphere.

Further, the dispersing agent is one of sodium dodecyl sulfate, N-vinyl pyrrolidone and sodium dodecyl sulfate.

Furthermore, the carbon nano tube, the dispersing agent and the solvent are in the mass ratio of: 1-10: 0.2-5: 85-98.8.

Furthermore, the mass ratio of the carbon nano tube to the dispersing agent to the solvent is 5:3: 92.

Furthermore, the mass ratio of the lithium hydroxide, the ferrous oxalate and the silicon dioxide is 1:1: 1.

Furthermore, the mass ratio of the lithium hydroxide to the carbon nano tube is 1.5: 1.

Still further, the temperature of the spray drying was 115 ℃.

Furthermore, the sintering process of step S4 is pre-sintering at 350-400 ℃ for 3-5 h, and then sintering at 700 ℃ under the protection of argon/hydrogen for 6-9 h.

Furthermore, the microwave irradiation time is 5-8 minutes, and the power of the microwave is 600-750W.

The second technical scheme adopted by the invention is as follows: the three-dimensional carbon nanotube composite ferrous silicate lithium microsphere prepared by the preparation method of any one of the three-dimensional carbon nanotube composite ferrous silicate lithium microspheres in the technical scheme.

The invention has the beneficial effects that:

(1) the spray drying method is combined with sintering and microwave irradiation process modes, and the in-situ coating method is combined to prepare the 3D-Li₂FeSiO₄The preparation method integrates the advantages of direct drying of solution or emulsion into powder or granular products by spray drying, short reaction time of microwave radiation technology, uniform in-situ coating and strong interface bonding, and can prepare high-quality 3D-Li on a large scale in a short time₂FeSiO₄The preparation method of the/CNTs composite electrode material designs and constructs 3D-Li with nano-scale size₂FeSiO₄The method is a brand new and effective method in the aspect of the/CNTs composite electrode material.

(2) The carbon nano tube with excellent conductivity, high chemical stability and good mechanical property is selected as a carrier and an additive, and a carbon film coated on the surface of an electrode material is combined, so that a space network structure with higher conductivity can be formed in the composite material, and the problem of Li is better solved₂FeSiO₄The cathode material has low electronic conductivity, thereby greatly improving the high rate performance and the cycling stability of the electrode material, and is Li₂FeSiO₄The industrialization of the anode material lays a foundation.

3D-Li prepared by the invention₂FeSiO₄the/CNTs electrode shows 169.1 mA-h/g high discharge capacity at 0.1C multiplying power, and shows stable cycle characteristics after 60 cycles, and the capacity retention rate is 99.6%; prepared 3D-Li₂FeSiO₄the/CNTs electrodes showed discharge capacities of 144.3, 134.2, 124.5, 112.1 and 94.7 mA-h/g at 0.5, 1, 2, 5 and 10C, respectively, and the prepared 3D-Li₂FeSiO₄the/CNTs electrode has excellent rate performance and cycling stability at 5 ℃ after 500 cycles, and the capacity retention rate is about 91.2%.

In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a flow chart of a process for preparing a three-dimensional carbon nanotube composite lithium iron silicate microsphere according to an embodiment of the present invention;

FIG. 2 is a scanning electron microscope image of a three-dimensional carbon nanotube composite lithium iron silicate microsphere according to embodiment 1 of the present invention;

fig. 3 is an XRD and raman spectra of an electrode material micro-prepared from a three-dimensional carbon nanotube and lithium iron silicate in embodiment 1 of the present invention;

fig. 4 is a graph of a charging and discharging curve and battery performance of a lithium battery electrode micro-fabricated by a three-dimensional carbon nanotube and lithium iron silicate in embodiment 1 of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A preparation method of a three-dimensional carbon nanotube composite lithium iron silicate microsphere mainly comprises the following steps:

s1: preparing carbon nanotube slurry by using a carbon nanotube, a dispersant and a solvent;

s2: fully mixing lithium hydroxide, ferrous oxalate and silicon dioxide, dissolving the mixture into the carbon nanotube slurry obtained in the step S1, performing ball milling, continuously stirring the mixture after the ball milling is finished, and adjusting the viscosity of the slurry through a dispersing agent;

s3: obtaining a precursor by spray-drying the slurry of step S2;

s4: sintering and microwave irradiating the precursor in sequence to obtain the three-dimensional carbon nano tube composite lithium ferrous silicate microsphere.

In one embodiment, the dispersant is one of sodium dodecyl sulfate, N-vinyl pyrrolidone and sodium dodecyl sulfate. The reason why sodium dodecyl sulfate is used as the dispersant in the preferred embodiment of the present invention is that sodium dodecyl sulfate has a low Krafft point (8 ℃ C.), and is suitable for effective dispersion of carbon nanotubes at room temperature.

According to the method, a microwave radiation technology is adopted after sintering, the sintering temperature is reached at a higher temperature rise rate, the crystal structure of the lithium ferrous silicate is further optimized, and in the process, the material is heated uniformly and segregation caused by nonuniform crystallization is avoided; and controlling and adjusting the formula to obtain the three-dimensional carbon nanotube/lithium ferrous silicate composite material with a controllable structure.

The method adopts a spray drying method, combines sintering and microwave irradiation process modes, and combines an in-situ coating method to prepare the 3D-Li₂FeSiO₄The preparation method integrates the advantages of direct drying of solution or emulsion into powder or granular products by spray drying, short reaction time of microwave radiation technology, uniform in-situ coating and strong interface bonding, and can prepare high-quality 3D-Li on a large scale in a short time₂FeSiO₄The preparation method of the/CNTs composite electrode material designs and constructs 3D-Li with nano-scale size₂FeSiO₄The method is a brand new and effective method in the aspect of the/CNTs composite electrode material.

The three-dimensional structure can enable the electrode to have efficient electrolyte storage, and reduce Li⁺Thereby increasing Li⁺The ability to diffuse.

In one embodiment, the carbon nanotube is prepared by a graphite arc method, and the catalyst is one of iron, cobalt, nickel and yttrium oxide.

In one embodiment, the carbon nanotube, the dispersant and the solvent are mixed in a mass ratio of 1-10: 0.2-5: 85-98.8. Illustratively, the mass ratio of the carbon nanotubes to the dispersant to the solvent is 1:0.2:98.8 or 10:5: 95.

In a more preferred embodiment, the mass ratio of the carbon nanotubes to the dispersant to the solvent is 5:3: 92. The lithium ion battery electrode material prepared by adopting the carbon nanotube slurry with the proportion has excellent performance.

In one embodiment, the mass ratio of the lithium hydroxide, the ferrous oxalate and the silicon dioxide is 1:1: 1.

In one embodiment, the mass ratio of the lithium hydroxide to the carbon nanotubes is 1.5: 1.

In one embodiment, the stirring time in step S2 is 1.5-3 h. Illustratively, it may be 1.2h, 1.8h, 2h, 2.5h, 3 h.

In one embodiment, the temperature of the spray drying is 115 ℃. Spray drying at the temperature can quickly remove water and other volatile micromolecules, and dry powder is directly prepared, has good powder dispersibility and is not easy to agglomerate.

In one embodiment, the sintering process of step S4 is pre-sintering at 350-400 ℃ for 3-5 h, and then sintering at 700 ℃ under the protection of argon/hydrogen for 6-9 h.

According to the method, the ferrous silicate lithium is sintered at 700 ℃, so that the ferrous iron in the ferrous silicate lithium can be ensured to be ferrous, no ferric iron or other iron impurities exist, and the ion migration and crystallization rate of the anode material can be controlled by the fixed sintering temperature. Low sintering temperatures may result in insufficient ion transport and failure to form a conductive network. Over-high temperature can cause over-burning, partial volatilization of lithium and generation of oxygen defects, so that the density of a sample is low, and the ion mobility in the electrochemical process is influenced.

In the experimental process, the ferrous silicate lithium crystal structure particles can be obtained by sintering at 700 ℃ for 6-9 h, wherein the crystal structure integrity obtained by sintering at 700 ℃ for 9h under the protection of nitrogen is the best, but the difference from the sintering in 6 hours is not very large, and the over-sintering phenomenon occurs when the time exceeds 9 hours.

Therefore, in the most preferred embodiment of the present invention, the sintering conditions are as follows: after sintering at 360 ℃ for 3.5h, sintering at 700 ℃ under argon/nitrogen shield for 9 h.

In one embodiment, the microwave irradiation time is 5-8 minutes, and the power of the microwave is 600-750W.

Referring to fig. 1 to 4, an embodiment of a method for preparing a three-dimensional carbon nanotube composite lithium iron silicate microsphere of the present invention is as follows: