CN113277557B - Amorphous calcium vanadate, preparation method thereof, battery cathode and battery - Google Patents

Amorphous calcium vanadate, preparation method thereof, battery cathode and battery Download PDF

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CN113277557B
CN113277557B CN202110529981.9A CN202110529981A CN113277557B CN 113277557 B CN113277557 B CN 113277557B CN 202110529981 A CN202110529981 A CN 202110529981A CN 113277557 B CN113277557 B CN 113277557B
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calcium
calcium vanadate
vanadium
vanadate
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CN113277557A (en
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徐小明
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Ningde Amperex Technology Ltd
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    • C01GCOMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G31/00Compounds of vanadium
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/054Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/48Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
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    • C01P2002/70Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
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    • C01P2004/62Submicrometer sized, i.e. from 0.1-1 micrometer
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M2004/026Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027Negative electrodes
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract

The embodiment of the application discloses amorphous calcium vanadate, a preparation method thereof, a battery cathode and a battery, wherein the molar ratio of calcium element to vanadium element of the amorphous calcium vanadate is 0.07-0.50: 1, the preparation method comprises the following steps: a) Dissolving a vanadium source in a first solvent to form a solution A, and dissolving a calcium source in a second solvent to form a solution B; b) Uniformly mixing the solution A and the solution B, and adding a complexing agent to obtain a solution C; c) Pretreating the solution C to obtain a calcium vanadate precursor; d) And carrying out sintering heat treatment on the calcium vanadate precursor to obtain amorphous calcium vanadate. The amorphous calcium vanadate is used as a battery cathode active material, has higher specific capacity, can ensure good cycling stability of the material, and provides rich ion diffusion channels.

Description

Amorphous calcium vanadate, preparation method thereof, battery cathode and battery
Technical Field
The embodiment of the application relates to the technical field of material chemistry, in particular to amorphous calcium vanadate, a preparation method thereof, a battery cathode and a battery.
Background
Lithium ion batteries have been widely used in portable electronic devices (such as mobile phones, notebook computers, electronic watches, etc.) and electric automobiles, and become an indispensable part of life of people in modern society. With the development of portable electronic devices and electric automobiles, the energy density of lithium ion batteries is also increasingly required.
The positive and negative electrode materials are the most central factors for determining the energy density of the lithium ion battery, most of developed and mature negative electrode materials are mainly graphite, but the theoretical specific capacity of the graphite is limited, about 372mAh/g, the energy density of the lithium ion battery based on the graphite is close to the limit at present, and the development of new negative electrode materials becomes a research hot spot in recent years. As a high-capacity anode material, the silicon-based anode material has high specific capacity, but has large volume expansion after lithium intercalation, rapid cycle attenuation, low compaction density and limited improvement of volume energy density, and still has great challenges in application.
Due to the scarcity of lithium metal, researchers are looking for alternatives to high energy density lithium ion batteries while continuing to develop them. Sodium Ion Batteries (SIBs) and Lithium Ion Batteries (LIBs) have similar electrochemical energy storage mechanisms and are a promising battery technology; however, sodium ions have a larger diameter than lithium ions, and the sodium ions need to overcome a larger potential barrier during charge and discharge, resulting in a greatly reduced diffusion rate. Therefore, developing a suitable high-efficiency anode material which can be active in lithium/sodium ion batteries has more application prospect.
Disclosure of Invention
The technical problem mainly solved by the embodiment of the application is to provide amorphous calcium vanadate, a preparation method thereof, a battery cathode and a battery, wherein the amorphous calcium vanadate has higher specific capacity, can ensure good cycling stability of materials, and provides rich ion diffusion channels.
In order to achieve the above object, in a first aspect, an embodiment of the present application provides amorphous calcium vanadate, wherein the amorphous calcium vanadate has a molar ratio of calcium element to vanadium element of 0.07 to 0.50:1.
in some embodiments, the amorphous calcium vanadate has a molar ratio of elemental calcium to elemental vanadium of from 0.15 to 0.35:1.
in a second aspect, an embodiment of the present application provides a method for preparing amorphous calcium vanadate as described above, comprising the steps of:
a) Dissolving a vanadium source in a first solvent to form a solution A, and dissolving a calcium source in a second solvent to form a solution B;
b) Uniformly mixing the solution A and the solution B, and then adding a complexing agent to obtain a solution C;
c) Pretreating the solution C to obtain a calcium vanadate precursor;
d) And carrying out sintering heat treatment on the calcium vanadate precursor to obtain the amorphous calcium vanadate.
Optionally, the vanadium source is V 2 O 5 Or NH 4 VO 3
The calcium source is selected from Ca (OH) 2 、CaCl 2 、CaSO 4 、CaC 2 O 4 One or more of the following.
In some embodiments, the vanadium source is V 2 O 5 The calcium source is Ca (OH) 2
The first solvent is a mixture of 30% hydrogen peroxide and water, and the volume ratio of the 30% hydrogen peroxide to the water is 1-2: 10.
the second solvent is a mixture of small molecular alcohol and water, and the volume ratio of the small molecular alcohol to the water is 2:1 to 8.
Optionally, the step b) specifically includes:
mixing and stirring the solution A and the solution B for 30-60 min, then adding a complexing agent, and continuously stirring for 1-2 h at the temperature of 70-100 ℃ to obtain a solution C.
As a further improvement of the above technical solution, the step c) specifically includes:
putting the solution C into a baking oven at 70-150 ℃ and baking for 24-48 hours to obtain a gel-like substance;
and then raising the temperature of the oven to 200-300 ℃, and continuously baking for 24-48 h to obtain the calcium vanadate precursor.
In some embodiments, in said step d), the sintering temperature is 400-500 ℃ and the sintering time is 4-8 h.
In a third aspect, embodiments of the present application provide a battery anode comprising an anode current collector and an anode active material distributed on the anode current collector, the anode active material comprising amorphous calcium vanadate as described above.
In a fourth aspect, embodiments of the present application provide a battery comprising a battery anode as described above.
Unlike the related art, the amorphous calcium vanadate provided by the embodiment of the application can be applied to a battery cathode, is used as a cathode active material, and has the following technical effects:
1) The electron taking and losing is carried out based on the vanadium element as an active center, and the vanadium has multiple valence states, so that multiple electrons can be taken and lost, and higher specific capacity is realized;
2) The introduction of calcium ions can improve the carrier concentration of the material on one hand, so as to improve the electronic conductivity of the material, and the calcium ions do not participate in electrochemical reaction on the other hand, so that the volume change of the active material in the charge-discharge process can be effectively relieved, the agglomeration of active components is inhibited, and the good cycling stability of the material is ensured;
3) The amorphous structure can provide a large and rich ion diffusion channel, and the multiplying power performance of the material is improved, so that the amorphous calcium vanadate can be applied to not only a lithium ion battery cathode but also a sodium ion battery cathode.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present application, one or more embodiments are illustrated by the accompanying drawings corresponding thereto, and these illustrations do not constitute limitations of the embodiments.
Fig. 1 is a capacity-cycle diagram of an amorphous calcium vanadate material provided by an embodiment of the application as a negative electrode active material for a lithium ion battery;
fig. 2 is a graph of capacity versus voltage of an amorphous calcium vanadate material provided by an embodiment of the application as a negative electrode active material for a lithium ion battery at different rates;
FIG. 3 is an XRD pattern for materials obtained at different sintering temperatures provided by the examples of the application;
FIG. 4 is an SEM image of the material obtained at different sintering temperatures provided by an embodiment of the application;
fig. 5 is an EDS spectrum of a material obtained at a sintering temperature of 450 ℃ provided by an embodiment of the present application.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. In addition, the technical features of the different embodiments of the present application described below may be combined with each other as long as they do not collide with each other.
The technical scheme in the embodiment of the application will be described below with reference to the accompanying drawings.
The embodiment of the application provides amorphous calcium vanadate, which comprises the following calcium elements in a molar ratio of 0.07-0.50: 1, the amorphous calcium vanadate can be applied to a battery cathode and used as a cathode active material. As vanadium has multiple valence states, the amorphous calcium vanadate takes vanadium element as an active center to conduct electron losing and electron losing, and multiple electron losing can be achieved, so that higher specific capacity is achieved; secondly, the introduction of calcium ions can improve the carrier concentration of the material on one hand, so that the electronic conductivity of the material is improved, and on the other hand, the calcium ions belong to inactive elements and do not participate in electrochemical reaction, so that the volume change of the active material in the charge and discharge process can be effectively relieved, the agglomeration of the active components is inhibited, and the good cycling stability of the material is ensured; furthermore, the amorphous structure can provide a larger and rich ion diffusion channel, and the multiplying power performance of the material is improved, so that the amorphous calcium vanadate can be applied to not only a lithium ion battery cathode but also a sodium ion battery cathode.
The electrochemical properties of the material, including but not limited to specific capacity, cycle performance, rate capability, etc., can be adjusted by adjusting the molar ratio of the calcium element to the vanadium element of the amorphous calcium vanadate.
As an example, when the amorphous calcium vanadate has a molar ratio of calcium element to vanadium element of 0.32:1, fig. 1 and 2 show a capacity-cycle chart of a lithium ion button cell assembled from the amorphous calcium vanadate as a negative electrode active material, and a capacity-voltage chart at different rates, respectively, and it is seen from the chart that the capacity after 60 cycles is 100% compared to the capacity retention at the second cycle, and the rate performance is 55% (retention of capacity at a current density of 1.0A/g compared to a current density of 0.1A/g).
The molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate is 0.32:1, table 1 shows the effect of different calcium element and vanadium element molar ratios of amorphous calcium vanadate on the electrochemical performance of the material.
TABLE 1
As the amorphous calcium vanadate takes the vanadium element as an active center to conduct electron gain and loss, the molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate has a remarkable influence on the electrochemical performance of the material as can be seen from table 1. The molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate is 0.32:1, when the molar ratio of the calcium element to the vanadium element of the amorphous calcium vanadate is increased, the specific capacity is reduced, and the rate performance is reduced, but the cycle performance is increased, and when the molar ratio of the calcium element to the vanadium element is 0.38:1, the specific capacity is reduced from 723mAh/g to 680mAh/g; when the molar ratio of the calcium element to the vanadium element is 0.49:1, the specific capacity is reduced to 465mAh/g, the rate performance is deteriorated by 6%, but the rate performance is maintained to be more than 50%.
When the molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate is gradually reduced, the specific capacity is increased and then reduced, and when the molar ratio of the calcium element and the vanadium element is respectively 0.20:1 and 0.175:1, the specific capacity is increased, the cycle performance is not greatly different, and the rate performance is improved by 2%; the molar ratio of the calcium element to the vanadium element is 0.15: when the specific capacity reaches the maximum of 801mAh/g, the rate performance is improved by 2%, but the cycle performance is deteriorated by 3%.
The molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate is continuously reduced, the specific capacity, the cycle performance and the multiplying power performance are all reduced, and the molar ratio of the calcium element to the vanadium element is 0.075: at 1, the specific capacity was 709mAh/g, and the cycle performance and the rate performance were both deteriorated by 3%.
In the crystalline vanadium oxide, though the specific capacity is larger than the molar ratio of calcium element and vanadium element is 0.15: the specific capacity at 1, however, is remarkably deteriorated in both cycle performance and rate performance, and in crystalline CaO, electrochemical activity is not exhibited. It can be seen that the introduction of calcium ions is critical to the performance of amorphous calcium vanadate, and that the molar ratio of calcium element to vanadium element is both too low and too high, when the molar ratio of calcium element to vanadium element is too low, the optimization effect (improvement of electron conductivity, alleviation of volume change, and preparation of agglomeration of active ingredient) caused by calcium ions is not significant, and when the molar ratio of calcium element to vanadium element is too high, the excessive ratio of inactive ingredient can negatively affect the reactivity (mainly expressed in specific capacity) of the material.
In some embodiments, the amorphous calcium vanadate has a molar ratio of elemental calcium to elemental vanadium of from 0.15 to 0.35: when the molar ratio of the calcium element to the vanadium element is within the above range, the cathode active material has a specific capacity of 720mAh/g or more, and is excellent in cycle performance and rate performance.
The embodiment of the application also provides a battery anode, which comprises an anode current collector and anode active materials distributed on the anode current collector, wherein the anode active materials comprise the amorphous calcium vanadate. The negative electrode current collector is also distributed with an adhesive, a conductive agent and the like, and the materials are mixed with amorphous calcium vanadate to form a negative electrode active material layer on the negative electrode current collector.
The embodiment of the application also provides a battery, which comprises the battery cathode, a battery anode, a separation film which is arranged between the battery anode and the battery cathode, and electrolyte. The battery can be a lithium ion battery or a sodium ion battery, wherein the negative electrode active material in the negative electrode of the battery comprises calcium element and vanadium element with the molar ratio of 0.07-0.50: 1, amorphous calcium vanadate.
The embodiment of the application also provides a preparation method of the amorphous calcium vanadate, which comprises the following steps:
a) Dissolving a vanadium source in a first solvent to form a solution A, and dissolving a calcium source in a second solvent to form a solution B;
b) Uniformly mixing the solution A and the solution B, and adding a complexing agent to obtain a solution C;
c) Pretreating the solution C to obtain a calcium vanadate precursor;
d) And carrying out sintering heat treatment on the calcium vanadate precursor to obtain amorphous calcium vanadate.
Wherein in step a), the vanadium source may be V 2 O 5 Or NH 4 VO 3 An appropriate solvent may be selected as the first solvent according to the dissolution characteristics of the above-mentioned substances. For example, when V is adopted 2 O 5 When the vanadium source is used, the first solvent is a mixed solvent of 30% hydrogen peroxide and water to formIs orange-red clear vanadium-containing solution; when NH is used 4 VO 3 As a vanadium source, the first solvent is water (heated to above 60 ℃) and the solution a formed is a colorless or pale yellow clear vanadium-containing solution. ( Wherein 30% hydrogen peroxide represents that 100g hydrogen peroxide solution contains 30g hydrogen peroxide and 70g water; namely, 30% is the mass fraction of hydrogen peroxide in the application. )
The source of calcium may be selected from Ca (OH) 2 、CaCl 2 、CaSO 4 、CaC 2 O 4 According to the dissolution characteristics of the above substances, an appropriate solvent may be selected as the second solvent. For example, when CaCl is used 2 As a source of calcium, the second solvent is water, and when Ca (OH) is used 2 、CaSO 4 Or CaC 2 O 4 As a calcium source, the second solvent also needs to include an appropriate amount of an acid or a small molecule alcohol.
In some embodiments, the vanadium source is V 2 O 5 The calcium source is Ca (OH) 2 The first solvent is a mixture of 30% hydrogen peroxide and water, and the volume ratio of the 30% hydrogen peroxide to the water is 1-2: 10, the second solvent is a mixture of small molecular alcohol and water, and the volume ratio of the small molecular alcohol to the water is 2:1 to 8, the small molecular alcohol can be glycerol, glycol, n-butanol and other alcohols with molecular weight below 300.
In step b), the complexing agent is Dimethylformamide (DMF) or N-methylpyrrolidone (NMP), and is used for carrying out a complexing reaction on the calcium source and the vanadium source in the solution C so as to form calcium vanadate compound. In one embodiment, step b) specifically includes: and (3) uniformly mixing the solution A and the solution B, stirring for 30-60 min, adding a complexing agent, and continuously stirring for 1-2 h at the temperature of 70-100 ℃ to obtain a solution C.
In step C), the solution C is pretreated to obtain a calcium vanadate precursor, namely, the solution C is baked to obtain an organic-inorganic complex solid. As a preferred embodiment, step c) specifically includes: putting the solution C into a baking oven at 70-150 ℃ and baking for 24-48 h to obtain a gelatinous substance; then the temperature of the oven is increased to 200-300 ℃ and baking is continued for 24-48 hours, so as to obtain the calcium vanadate precursor. The calcium vanadate precursor is obtained after two-step baking, so that the obtained precursor has uniform granularity and uniform components.
In step d) the sintering temperature is 400-500 ℃ and the sintering time is 4-8 hours, which is critical for the formation of amorphous calcium vanadate, too short sintering time or too low sintering temperature, resulting in reduced performance of the formed amorphous calcium vanadate, while the sintering temperature is too high, the resulting sintered body is no longer in an amorphous form.
The technical scheme of the preparation method of amorphous calcium vanadate provided by the application is further described below by combining specific examples.
Example 1
The preparation method of the amorphous calcium vanadate comprises the following steps:
(1) Will be 1.8kg V 2 O 5 Dissolving in 50L deionized water, stirring for 30min, and slowly adding 10L 30% H under stirring 2 O 2 Continuing stirring for 1h after the addition is completed to obtain a solution A; 0.5kg of Ca (OH) 2 The adding volume ratio is 1:1 (the total volume of the mixed solution is 40L) and stirring for 1-2 h to obtain a solution B;
(2) Mixing and stirring the solution A and the solution B prepared in the step (1) for 30-60 min, then adding 50L of N, N-Dimethylformamide (DMF), and stirring for 1-2 h at the temperature of 70 ℃ to obtain a solution C;
(3) Baking the solution C prepared in the step (2) in a baking oven at 70 ℃ for 24-48 hours to obtain a gel-like substance;
(4) Raising the temperature of the oven to 250 ℃, and continuously baking for 24-48 hours to obtain a calcium vanadate precursor;
(5) And (3) sintering the calcium vanadate precursor powder obtained in the step (4) for 5 hours at 500 ℃ in an argon atmosphere to obtain amorphous calcium vanadate.
Example 2:
the whole of the preparation method was identical to that of example 1, except that the sintering temperature in the step (5) was adjusted to 450 ℃.
Example 3:
the whole of the preparation method was identical to that of example 1, except that the sintering temperature in the step (5) was adjusted to 400 ℃.
Example 4:
the whole was identical to the preparation method of example 1, except that the sintering time in the step (5) was adjusted to 4h.
Example 5:
the whole was identical to the preparation method of example 1, except that the sintering time in the step (5) was adjusted to 6h.
Example 6:
the whole of the preparation method was identical to that of example 1, except that the sintering time in the step (5) was adjusted to 8 hours.
Example 7:
the whole of the preparation method was identical to that of example 1, except that the sintering atmosphere in the step (5) was adjusted to nitrogen.
Example 8:
the whole of the preparation method was identical to that of example 1, except that the sintering atmosphere in the step (5) was argon/hydrogen (95/5, V/V) mixed gas.
Example 9:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 The amount of (C) used was reduced to 0.25kg.
Example 10:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 The amount of (C) is reduced to 0.1kg.
Example 11:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 The amount of (C) was increased to 0.75kg.
Example 12:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 The amount of (C) used was increased to 1.0kg.
Example 13:
the overall procedure was as in example 1, except that the ratio of glycerin to distilled water in step (1) was adjusted to 1:2.
example 14:
the overall procedure was as in example 1, except that the ratio of glycerin to distilled water in step (1) was adjusted to 1:4.
example 15:
the overall procedure was as in example 1, except that the ratio of glycerin to distilled water in step (1) was adjusted to 2:1.
example 16:
the whole was identical to the preparation method of example 1, except that the glycerol in step (1) was changed to ethylene glycol.
Example 17:
the whole was identical to the preparation method of example 1, except that the glycerol in the step (1) was changed to n-butanol.
Example 18:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 CaCl is changed into 2 While maintaining the molar amount of Ca unchanged.
Example 19:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 CaCl is changed into 2 And glycerin was removed while keeping the molar amount of Ca unchanged.
Example 20:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 Change to CaSO 4 While maintaining the molar amount of Ca unchanged.
Example 21:
the whole was identical to the preparation method of example 1, except that Ca (OH) in the step (1) was added 2 Change to CaC 2 O 4 While maintaining the molar amount of Ca unchanged.
Example 22:
in general agreement with the preparation method of example 1, except that V in step (1) was used 2 O 5 Changing to NH 4 VO 3 While keeping the molar amount of V unchanged.
Example 23:
the whole was identical to the preparation method of example 1, except thatH in step (1) 2 O 2 The addition amount was adjusted from 10L to 5L.
Example 24:
in general agreement with the preparation method of example 1, except that V in step (1) was used 2 O 5 Changing to NH 4 VO 3 Heating water to 60-70 ℃ and heating H 2 O 2 Removed while keeping the molar amount of V unchanged.
Example 25:
in general agreement with the preparation method of example 1, except that V in step (1) was used 2 O 5 The amount of (C) was adjusted to 2.5kg.
Example 26:
in general agreement with the preparation method of example 1, except that V in step (1) was used 2 O 5 The amount of (C) was adjusted to 3.6kg.
Example 27:
the overall procedure was as in example 1, except that the amount of DMF in step (2) was adjusted to 25L.
Example 28:
the overall procedure was as in example 1, except that the amount of DMF in step (2) was adjusted to 80L.
Example 29:
the overall procedure was as in example 1, except that DMF in step (2) was changed to N-methylpyrrolidone (NMP).
Example 30:
the whole of the preparation method was identical to that of example 1, except that the stirring temperature after DMF addition in the step (2) was adjusted to 90℃and the baking temperature in the step (3) was also adjusted to 90 ℃.
Example 31:
the whole of the preparation method was identical to that of example 1, except that the baking temperature in the step (3) was adjusted to 120 ℃.
Example 32:
the whole of the preparation method was identical to that of example 1, except that the baking temperature in the step (3) was adjusted to 150 ℃.
Example 33:
the whole of the preparation method was identical to that of example 1, except that the baking temperature in the step (4) was adjusted to 200 ℃.
Example 34:
the whole of the preparation method was identical to that of example 1, except that the baking temperature in the step (4) was adjusted to 300 ℃.
Comparative example 1:
the overall procedure is as in example 1, except that the calcium source in step (1) is removed.
Comparative example 2:
the whole was identical to the preparation method of example 1, except that the vanadium source in step (1) was removed.
Comparative example 3:
the overall procedure was as in example 1, except that the complexing agent in step (2) was removed.
Comparative example 4:
the whole was identical to the preparation method of example 1, except that the sintering temperature in the step (5) was adjusted to 550 ℃.
Comparative example 5:
the whole of the preparation method was identical to that of example 1, except that the sintering temperature in the step (5) was adjusted to 600 ℃.
The reaction conditions and test results of the respective examples and comparative examples are shown in tables 2 and 3, respectively.
TABLE 2
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TABLE 3 Table 3
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From examples 1-3 and comparative examples 4-5, and from fig. 3-5, it can be seen that the sintering temperature is critical to whether or not an amorphous form of calcium vanadate is formed. When the sintering temperature is not higher than 500 ℃, the XRD pattern of the obtained material shows no obvious sharp diffraction peak, the SEM pattern shows random arrangement, the formed material is in an amorphous form, and the obtained material is amorphous calcium vanadate as shown in the combination of figure 5.
Whereas at temperatures above 500 c, the calcium vanadate formed is no longer in an amorphous state. For example, when the sintering temperature is 550 ℃, the XRD pattern of the prepared material shows obvious diffraction peaks, which indicate that the prepared material is not in an amorphous state. When the sintering temperature is 600 ℃, the XRD pattern diffraction peak of the prepared material is stronger, which indicates that the sintering temperature is increased, the crystallinity is further improved, and the SEM also shows that crystals exist.
Further, according to examples 1 to 3, it is understood that the sintering temperature also has some influence on the cycle performance and the rate performance, and when the sintering temperature is 400 ℃, the material is also in an amorphous state, but the cycle performance is 5% worse than that of example 1, and the sintering temperature may be too low, so that the surface functional groups of the material are more, and more byproducts are easily generated in the cycle process. In contrast, according to examples 4 to 6, at a sintering time of 4 to 6 hours, the effect on the material is small, and at a sintering time of 8 hours, the specific capacity and the rate performance are lowered, so that the sintering time is not more than 8 hours.
According to examples 1, 9-12, 25-26 and comparative examples 1-2, it can be seen that the addition amounts and proportions of the vanadium source and the calcium source in step (1) are positively correlated with the molar ratio of the calcium element to the vanadium element in the finally obtained amorphous calcium vanadate, and by adjusting the addition amounts of the vanadium source and the calcium source in step (1), the molar ratio of the calcium element to the vanadium element in the finally obtained amorphous calcium vanadate can be adjusted, and the molar ratio of the calcium element to the vanadium element has a significant influence on the properties of the final material.
In examples 11 and 12, based on example 1, when the molar ratio of the calcium element to the vanadium element of amorphous calcium vanadate increases, the specific capacity decreases, and the rate performance decreases. When the molar ratio of the calcium element and the vanadium element of the amorphous calcium vanadate is gradually reduced, the specific capacity is increased and then reduced, and when the molar ratio of the calcium element and the vanadium element is respectively 0.20:1 (corresponding to example 25) and 0.175:1 (corresponding to example 9), the specific capacity is increased, the cycle performance is the same as or slightly different from the level, and the rate performance is improved by 2%; the molar ratio of the calcium element to the vanadium element is 0.15: when 1 (corresponding to example 26), the specific capacity reached the maximum of 801mAh/g, the rate performance was improved by 2%, but the cycle performance was deteriorated by 3%.
In comparative example 1, the obtained product was crystalline vanadium oxide with significantly deteriorated cycle performance and rate performance without the addition of a calcium source, and in comparative example 2, the material was finally obtained as crystalline CaO with no electrochemical activity without the addition of a vanadium source; it can be seen that the addition of the calcium source and the vanadium source is critical to the finally obtained amorphous calcium vanadate and the performance of the material, and the molar ratio of the calcium element and the vanadium element is too low and too high, when the ratio is too low, the optimization effect (improvement of the electronic conductivity, alleviation of the volume change and preparation of the agglomeration of the active ingredient) caused by the calcium ion is not obvious, and when the ratio is too high, the proportion of the inactive ingredient is too high, the reaction activity of the material is negatively influenced.
According to examples 1, 27-29 and comparative example 3, the addition of complexing agent is also critical to the final product formed, and in the case of comparative example 3 where no complexing agent is added, the final product is a crystalline vanadium oxide, indicating that no complexing reaction between the calcium source and the vanadium source in solution occurs to form the final calcium vanadate compound without the addition of complexing agent.
The above embodiments are only for illustrating the technical solution of the present application, and are not limiting; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the application, the steps may be implemented in any order, and there are many other variations of the different aspects of the application as described above, which are not provided in detail for the sake of brevity; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application.

Claims (7)

1. A method for preparing amorphous calcium vanadate, comprising the following steps:
a) Dissolving a vanadium source in a first solvent to form a solution A, and dissolving a calcium source in a second solvent to form a solution B;
b) Uniformly mixing the solution A and the solution B, and then adding a complexing agent to obtain a solution C;
c) Pretreating the solution C to obtain a calcium vanadate precursor;
d) Sintering the calcium vanadate precursor to obtain the amorphous calcium vanadate, wherein the sintering temperature is 400-500 ℃ and the sintering time is 4-8 hours, so that the molar ratio of calcium element to vanadium element of the amorphous calcium vanadate is 0.15-0.35: 1.
2. the method according to claim 1, wherein,
the vanadium source is V 2 O 5 Or NH 4 VO 3
The calcium source is selected from Ca (OH) 2 、CaCl 2 、CaSO 4 、CaC 2 O 4 One or more of the following.
3. The method according to claim 2, wherein,
the vanadium source is V 2 O 5 The calcium source is Ca (OH) 2
The first solvent is a mixture of 30% hydrogen peroxide and water, and the volume ratio of the 30% hydrogen peroxide to the water is 1-2: 10.
the second solvent is a mixture of small molecular alcohol and water, and the volume ratio of the small molecular alcohol to the water is 2:1 to 8.
4. The method according to claim 1, wherein,
the step b) specifically comprises the following steps:
mixing and stirring the solution A and the solution B for 30-60 min, then adding a complexing agent, and continuously stirring for 1-2 h at the temperature of 70-100 ℃ to obtain a solution C.
5. The process according to any one of claim 1 to 4, wherein,
the step c) specifically comprises the following steps:
putting the solution C into a baking oven at 70-150 ℃ and baking for 24-48 hours to obtain a gel-like substance;
and then raising the temperature of the oven to 200-300 ℃, and continuously baking for 24-48 h to obtain the calcium vanadate precursor.
6. A battery negative electrode comprising a negative electrode current collector and a negative electrode active material distributed on the negative electrode current collector, characterized in that the negative electrode active material comprises amorphous calcium vanadate, which is prepared by the preparation method of any one of claims 1 to 5.
7. A battery comprising the battery anode of claim 6.
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