阅读说明：本技术 一种锂离子电池复合正极活性材料及其制备方法 (Composite positive electrode active material of lithium ion battery and preparation method thereof ) 是由 梁子钦 唐安平 徐国荣 宋海申 陈核章 于 2021-07-19 设计创作，主要内容包括：本发明提供一种锂离子电池复合正极活性材料及制备方法。所述复合正极活性材料由V-(2)O-(3)和Li-(3)PO-(4)复合而成,Li-(3)PO-(4)的Li～(+)和PO-(4)～(3-)离子分别作为锂源和电荷中和剂参与钒元素的氧化还原反应；所述复合正极活性材料以V-(2)O-(3)作为氧化还原电对和PO-(4)～(3-)受体,通过转化反应机理实现或的可逆转化。尽管V-(2)O-(3)和Li-(3)PO-(4)这两个组分在2-4.5V电压区间都没有明显的电化学储锂活性,但由原位生成的V-(2)O-(3)颗粒和Li-(3)PO-(4)颗粒组成的复合正极活性材料在2-4.5V电压区间不仅表现出电化学储锂活性,而且具有良好的比容量和优良的循环性能。(The invention provides a composite anode active material of a lithium ion battery and a preparation method thereof. The composite positive electrode active material consists of V 2 O 3 And Li 3 PO 4 Is compounded of Li 3 PO 4 Li of (2) + And PO 4 3‑ Ions respectively serve as a lithium source and a charge neutralizer to participate in the oxidation-reduction reaction of the vanadium element; the composite positive electrode active material is represented by V 2 O 3 As redox couples and PO 4 3‑ Receptor, by conversion reaction mechanism Or The reversible transformation of (2). Although V 2 O 3 And Li 3 PO 4 The two components have no obvious electrochemical lithium storage activity in the voltage range of 2-4.5V, but the in-situ generated V 2 O 3 Particles and Li 3 PO 4 The composite positive active material composed of the particles not only shows electrochemical lithium storage activity in a voltage range of 2-4.5V, but also has good specific capacity and excellent cycle performance.)

1. A composite positive electrode active material for Li-ion battery is prepared from V₂O₃And Li₃PO₄The composite material is characterized in that:

the composite positive electrode active material uses Li₃PO₄Li of (2)⁺And PO₄ ^3-Ions respectively serve as a lithium source and a charge neutralizer to participate in the oxidation-reduction reaction of the vanadium element;

② the composite positive electrode active material is represented by V₂O₃As redox couples and PO₄ ^3-Receptor, by conversion reaction mechanismOrThe reversible transformation of (2).

2. The lithium ion battery composite positive electrode active material according to claim 1, characterized in that: in the lithium ion battery composite positive electrode active material, V₂O₃With Li₃PO₄The ratio of the amount of the substance is 3:2 to 4.

3. The method for preparing the composite positive active material of the lithium ion battery according to claim 1 or 2, comprising the steps of:

firstly, oxalic acid and ammonium metavanadate or vanadium pentoxide are put into distilled water to form a solution;

dissolving lithium acetate and ammonium dihydrogen phosphate in the solution obtained in the step I to prepare a precursor solution;

dispersing or dissolving ketjen black in the precursor solution obtained in the step two, and performing spray drying to obtain precursor powder;

fourthly, sintering the precursor powder obtained in the third step for 1 to 6 hours at the temperature of between 400 and 700 ℃ in an inert atmosphere, and then cooling the precursor powder to room temperature to obtain the lithium ion battery compositeA positive electrode active material, i.e. V having a carbon content of 0 to 20 wt%₂O₃-Li₃PO₄A composite positive electrode active material.

Technical Field

The invention relates to the field of chemical power sources, in particular to a composite positive active material of a lithium ion battery and a preparation method thereof.

Background

In recent years, it has been found that Li is not contained in the crystal structure⁺Lithium-free transition metal oxides conducting channels, e.g. FeO, MnO, NiO, CoO, Mn₂O₃、Mn₃O₄、NiMn₂O₄And after the surface of the metal oxide is initially modified by the nano LiF, the metal oxide can be converted into a high-capacity anode material. Such unusual electrochemical properties are attributed to the surface conversion reaction mechanism, in contrast to the conventional lithium intercalation mechanism. This finding is because it is not only independent of the specific crystal structure, but also makes it possible to break through the intercalation compound LiMO₂The reached capacity barrier of 250mAh/g, and is worthy of further study. In particular, MnO-LiF system attracts people's attention. In the MnO-LiF system, Mn³⁺/Mn²⁺(redox potential 2.5V) and Mn⁴⁺/Mn³⁺(redox potential-3.75V) couples all participate in electrochemical reaction, wherein Mn⁴⁺/Mn³⁺The couple of electrons is mainly involved in the redox reaction in the high voltage region, Mn³⁺/Mn²⁺The couple of Electrodes participates in the redox reaction of the whole voltage interval (S-K Jung, et al, Lithium-Free Transition metals for Positive Electrodes in Lithium-Ion batteries. Nat. energy 2017,2, 16208). Therefore, the surface conversion reaction of the MnO-LiF system can utilize the high-valence oxidation-reduction reaction of the transition metal, thereby obtaining higher discharge capacity and energy density.

In 2016, Tomita task group found that neither NiO sample nor LiF sample after high energy ball milling has obvious discharge capacity, and after 144h of high energy ball milling, the mixture of NiO and LiF has first discharge capacity as high as 216mAh/g at 0.05C rate in 2-5V interval (Y Tomita, et al, Synthesis and charge-discharge properties of LiF-NiO composite as a catalyst for Li-ion batteries, J.Power Sources,2016,329,406). Therefore, the surface conversion reaction can only occur when the metal oxide, such as MnO or NiO, is uniformly dispersed and closely contacted with LiF in two phases of submicron, even nanoscale. How to realize the nanoscale uniform dispersion and close contact of LiF and metal oxides such as MnO, NiO and the like and establish a nano active micro-area suitable for the conversion reaction is a very critical problem. At present, the metal oxide/LiF compound is prepared by a high-energy ball milling method. Meanwhile, LiF is a stable ionic compound, so that the Li-F bond needs to be broken in the charging process to overcome high activation energy, and the electronic conductivity and the ionic conductivity of the LiF are poor.

In contrast to LiF, Li₃PO₄Is a kind of lithium fast ion conductor, and has acceptable ion conductivity (10) at 25 DEG C^-8～10^-7Scm^-1) And phosphate ions are larger than fluoride ions, and electrochemical splitting is easier to occur. Similar to Mn, metal V is also a transition metal element with a rich valence state. In thatIn the system, two lithium ions are embedded in a safe voltage window of the electrolyte to obtain the theoretical specific capacity of up to 318mAh/g, so that the lithium ion battery is a high-energy-density positive electrode material with a very good prospect. However, with VOPO₄As an initial positive active material of the battery, metallic lithium must be used as a negative electrode, and this defect affects its commercial application. LiVOPO₄Only one Li can be supplied as an initial positive electrode active material⁺The source of (a). And Li₂VOPO₄Two Li can be formally allowed⁺With respect to Li, however₂VOPO₄No literature has been reported on studies of the initial positive electrode active material.

Disclosure of Invention

In view of the problems in the background art, an object of the present invention is to provide a composite positive active material for a lithium ion battery, which has a good specific capacity and excellent cycle performance, and a method for preparing the same.

In order to achieve the above object, in a first aspect of the present invention, there is provided a composite positive electrode active material for a lithium ion battery, consisting of V₂O₃And Li₃PO₄And compounding. The composite positive electrode active material is formed with Li₃PO₄Li of (2)⁺And PO₄ ^3-Ions respectively used as a lithium source and a charge neutralizer (providing a negative ion source for charge compensation during the oxidation and reduction reaction of transition metal ions) participate in the oxidation-reduction reaction of the vanadium element; the composite positive electrode active material is represented by V₂O₃As redox couples and PO₄ ^3-Receptor, by conversion reaction mechanismOrThe reversible transformation of (2).

In a second aspect of the present invention, the present invention provides a method for preparing a lithium ion battery composite positive active material, for preparing the lithium ion battery composite positive active material according to the first aspect of the present invention, comprising the steps of: firstly, oxalic acid and ammonium metavanadate or vanadium pentoxide are put into distilled water to form a solution; dissolving lithium acetate and ammonium dihydrogen phosphate in the solution obtained in the step I to prepare a precursor solution; dispersing or dissolving ketjen black in the precursor solution obtained in the step two, and performing spray drying to obtain precursor powder; fourthly, sintering the precursor powder obtained in the third step for 1 to 6 hours at the temperature of between 400 and 700 ℃ in an inert atmosphere, and then cooling the precursor powder to room temperature to obtain the lithium ion battery composite positive electrode active material, namely V with the carbon content of between 0 and 20 weight percent₂O₃-Li₃PO₄A composite positive electrode active material.

The invention has the following beneficial effects:

1. the lithium ion battery composite anode active material not only can solve the problemThe fundamental problems of the multi-electron reaction system and the metal oxide/LiF composite are now starting with Li₃PO₄Li of (2)⁺And PO₄ ^3-Study on conversion reaction of ions as carriers and charge neutralizers respectively to realizeOr Provides a feasible way and shows different research angles for developing a conversion reaction cathode active material system.

2. The preparation method of the lithium ion battery composite anode active material is beneficial to good contact and uniform dispersion among the components in the lithium ion battery composite anode active material and establishment of a proper active reaction micro-area environment, thereby improving V₂O₃-Li₃PO₄The conversion reaction kinetics performance of the composite anode active material. In addition, the carbon component in the composite positive electrode active material will avoid agglomeration of material particles and Li during discharge₃PO₄The segregation of the active component improves the uniformity of the particle size and distribution of the material obviously, thereby improving the utilization rate of the active component and improving the specific discharge capacity and the cycle performance of the active component.

Drawings

FIG. 1 shows X-ray diffraction patterns of samples of examples 1, 2, 3, 4 and 5 according to the present invention.

FIG. 2 is a sample of example 3 of the invention and Li-free prepared under the same conditions₃PO₄V of₂O₃Charge and discharge curves of the samples.

FIG. 3 is a cycle performance curve of example 3 of the present invention.

FIG. 4 is a cyclic voltammogram of example 3 of the present invention at a scan rate of 1.0 mV/s.

Detailed Description

For a better understanding of the present invention, the present invention will be further described with reference to the following examples and drawings, but the scope of the present invention is not limited to the examples shown.

Example 1

3.7821g of oxalic acid and 2.3396g of ammonium metavanadate (NH)₄VO₃) Dispersed in 200ml of distilled water and stirred at 75 ℃ until a solution is formed.

② 3.0606g of lithium acetate dihydrate (CH)₃COOLi·2H₂O), 1.1503g of ammonium dihydrogen phosphate (NH)₄H₂PO₄) And 12.0984g citric acid monohydrate (C)₆H₈O₇·H₂And O) dissolving in the solution obtained in the step I to form a precursor solution.

And thirdly, spray drying the precursor solution to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the third step for 1 hour at 700 ℃ under the argon atmosphere, and naturally cooling to room temperature to obtain the precursor powder with 10 wt% of carbon and V₂O₃With Li₃PO₄V in a molar ratio of 1:1₂O₃-Li₃PO₄And (c) a complex.

Example 1 the samples were measured using a Brucker model D8 Advance X-ray diffractometer. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data and V of the sample of example 1₂O₃JCPDS standard card (card number: 34-0187) and Li₃PO₄The JCPDS standard card (card number: 15-0760) is well conformed, and V does not exist in a spectrogram₂O₅、VO₂、Li₃V₂(PO₄)₃And waiting for impurity peaks, which indicates that the sample has high purity.

Example 2

3.7821g of oxalic acid and 1.8188g of vanadium pentoxide are dispersed in 200ml of distilled water and stirred at 75 ℃ until a solution is formed.

And dissolving 4.0808g of lithium acetate dihydrate and 1.5337g of ammonium dihydrogen phosphate in the solution obtained in the step (i) to form a precursor solution.

And thirdly, spray drying the precursor solution to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the third step for 2 hours at 500 ℃ in an argon atmosphere, and naturally cooling to room temperature to obtain the carbon-free V₂O₃With Li₃PO₄V in a molar ratio of 3:4₂O₃-Li₃PO₄And (c) a complex.

Example 2 the samples were measured using a Brucker model D8 Advance X-ray diffractometer. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data and V of the sample of example 2₂O₃JCPDS standard card (card number: 34-0187) and Li₃PO₄The JCPDS standard card (card number: 15-0760) is well conformed, and V does not exist in a spectrogram₂O₅、VO₂、Li₃V₂(PO₄)₃And waiting for impurity peaks, which indicates that the sample has high purity.

Example 3

3.7821g of oxalic acid and 2.3396g of ammonium metavanadate were dispersed in 200ml of distilled water and stirred at 75 ℃ until a solution was formed.

And dissolving 3.0606g of lithium acetate dihydrate and 1.1503g of ammonium dihydrogen phosphate in the solution obtained in the step (i) to form a precursor solution.

Dispersing 0.4688g Keqin black in the precursor solution obtained in the step II, and performing spray drying to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the fifth step for 4 hours at 500 ℃ under the argon atmosphere, and naturally cooling to room temperature to obtain the precursor powder with 15 wt% of carbon and V₂O₃With Li₃PO₄V in a molar ratio of 1:1₂O₃-Li₃PO₄And (c) a complex. .

Example 3 the samples were measured using a Brucker model D8 Advance X-ray diffractometer. The XRD spectrum is shown in figure 1. From FIG. 1As can be seen, the X-ray powder diffraction data and V of the sample of example 3₂O₃JCPDS standard card (card number: 34-0187) and Li₃PO₄The JCPDS standard card (card number: 15-0760) is well conformed, and V does not exist in a spectrogram₂O₅、VO₂、Li₃V₂(PO₄)₃And waiting for impurity peaks, which indicates that the sample has high purity.

In example 3, a positive electrode sheet was prepared from a sample of acetylene black and PVDF in a mass ratio of 7:2:1, and the positive electrode sheet was assembled into a button cell, and a charge/discharge test was performed at a rate of 0.05C in a voltage range of 2 to 4.5V. The first charge and discharge curves of the samples are shown in fig. 2, and the cycle performance curves are shown in fig. 3. As can be seen from FIGS. 2 and 3, under the set charge-discharge system, the first specific discharge capacity of the sample is 181.1mAh/g, the specific discharge capacity after 50 cycles is maintained at 152.9mAh/g, and the capacity retention rate is 84.4%. Under the same charge-discharge system and under the same process conditions, the prepared material does not contain Li₃PO₄V of₂O₃The sample had little electrochemical activity. From the cyclic voltammogram as shown in fig. 4, it can be seen that three reduction peaks appear in order around 2.4, 2.8 and 3.5V, and the corresponding oxidation peaks appear in order around 2.8, 3.2 and 3.8V.

Example 4

3.7821g of oxalic acid and 2.3396g of ammonium metavanadate were dissolved in 200ml of distilled water and stirred at 75 ℃ until a solution was formed.

And dissolving 2.0404g of lithium acetate dihydrate and 0.7669g of ammonium dihydrogen phosphate in the solution obtained in the step (i) to form a precursor.

Dispersing 0.5677g Keqin black in the precursor solution obtained in the step II, and performing spray drying to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the third step for 4 hours at 500 ℃ in an argon atmosphere, and naturally cooling to room temperature to obtain the precursor powder with 20 wt% of carbon and V₂O₃With Li₃PO₄V with a molar ratio of 3:2₂O₃-Li₃PO₄And (c) a complex.

Example 4 samples were X-ray diffracted using the Brucker model D8 AdvanceAnd (6) measuring by an instrument. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data and V of the sample of example 4₂O₃JCPDS standard card (card number: 34-0187) and Li₃PO₄The JCPDS standard card (card number: 15-0760) is well conformed, and V does not exist in a spectrogram₂O₅、VO₂、Li₃V₂(PO₄)₃And waiting for impurity peaks, which indicates that the sample has high purity.

Example 5

3.7821g of oxalic acid and 2.3396g of ammonium metavanadate were dissolved in 200ml of distilled water and stirred at 75 ℃ until a solution was formed.

② 4.0808g of lithium acetate dihydrate and 1.5337g of ammonium dihydrogen phosphate were dissolved in the solution obtained in (i) to form a precursor solution.

Dispersing 0.1603g Keqin black in the precursor solution obtained in the step II, and performing spray drying to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the third step for 6 hours at 400 ℃ in an argon atmosphere, and naturally cooling to room temperature to obtain the precursor powder with the carbon content of 5 wt% and V₂O₃With Li₃PO₄V in a molar ratio of 3:4₂O₃-Li₃PO₄And (c) a complex.

Example 5 the samples were measured using a Brucker model D8 Advance X-ray diffractometer. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data and V of the sample of example 5₂O₃JCPDS standard card (card number: 34-0187) and Li₃PO₄The JCPDS standard card (card number: 15-0760) is basically consistent, but no sharp characteristic diffraction peak appears in the spectrogram, which indicates that V in the sample₂O₃With Li₃PO₄Poorly crystalline or in the amorphous state.

The above is only a preferred embodiment of the present invention, and various modifications and changes can be made by those skilled in the art based on the above concept of the present invention, for example, combinations and changes of the ratio and the process conditions within the scope of the ratio and the process conditions given in the present invention, and such changes and modifications are within the spirit of the present invention.