CN111987308A - Rechargeable magnesium battery positive electrode material and preparation method and application thereof - Google Patents

Rechargeable magnesium battery positive electrode material and preparation method and application thereof Download PDF

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CN111987308A
CN111987308A CN202010803639.9A CN202010803639A CN111987308A CN 111987308 A CN111987308 A CN 111987308A CN 202010803639 A CN202010803639 A CN 202010803639A CN 111987308 A CN111987308 A CN 111987308A
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positive electrode
anion
electrode material
magnesium
magnesium battery
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索鎏敏
毛明磊
陈立泉
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Abstract

The invention relates to a chargeable magnesium battery anode material, a preparation method and application thereof, and the chargeable magnesium battery anode material is characterized in thatThe positive electrode material of the rechargeable magnesium battery comprises a pyrite type compound with a chemical general formula of MTx(ii) a Wherein M is a transition metal cation comprising: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V; t is anion, including one or more of O, S, Se, Te, As, Cl, Br and I; 1<x<3, and the anion is not in the lowest valence state; in the pyrite type compound, a d orbit of a transition metal cation and a p orbit of an anion are highly hybridized to form a strong covalent bond, so that the transition metal and the anion in the rechargeable magnesium battery positive electrode material jointly participate in an oxidation-reduction process in the charging and discharging processes of the magnesium battery, and the joint valence change of the anions and the cations is generated.

Description

Rechargeable magnesium battery positive electrode material and preparation method and application thereof
Technical Field
The invention relates to the technical field of materials, in particular to a rechargeable magnesium battery anode material and a preparation method and application thereof.
Background
Since the last 90 s, lithium ion battery technology has gradually dominated the energy storage field. However, as the energy density of lithium ion batteries approaches the theoretical limit of intercalation chemistry, further improvements in energy density are difficult to achieve. Much attention has been paid to the research of lithium metal batteries in recent years because of their ability to combine lithium metal with a high capacity lithium-free positive electrode, which theoretically allows higher energy densities to be achieved. But the application of lithium metal cathodes is limited by the lower deposition dissolution coulombic efficiency and dendrite induced safety issues. While magnesium metal has a high capacity (particularly a volume capacity of 3833mA h/cm)3) Low reduction potential (-2.4V vs. SHE), abundant reserves, and easy processing. More importantly, the magnesium metal cathode can realize the deposition and dissolution with coulombic efficiency close to 100%, and has no dendritic crystal and high safety performance. All these advantages make magnesium battery systems a promising next-generation energy storage technology.
The development of magnesium batteries has been limited by the lack of suitable positive electrode materials. Generally, there are two main directions to find a magnesium battery positive electrode material with high energy density: high operating potential oxides and high capacity sulfides. There is a strong interaction between the highly polarized magnesium ions and the oxide positive electrode material, which results in slow reaction kinetics and a low degree of magnesium ion intercalation. In addition, magnesium ions tend to extract oxygen from the oxide to form an amorphous interface comprising magnesium oxide. This amorphization results from the thermodynamic instability of the magnesium intercalation product, preventing magnesium ions from penetrating into the bulk phase of the cathode material. Currently, magnesium-free sulfide positive electrode materials, such as layered and spinel TiS2And spinel ZrS2And is used as a magnesium battery cathode material in large quantities, however it is limited by low capacity and less than ideal kinetics. Traditional embedded chemistry is based on the redox of simple transition metal cations, in most cases only one electron transfer per transition metal, which essentially limits its capacity release. In addition, localized electrons in the cation redox process do not readily accommodate the charge carried by the magnesium ion, compromising the kinetics of magnesium ion diffusion.
If a positive electrode material capable of overcoming the above defects can be found, the positive electrode material plays a crucial role in the wide application of the rechargeable magnesium battery.
Disclosure of Invention
The embodiment of the invention provides a rechargeable magnesium battery positive electrode material and a preparation method and application thereof. The pyrite type compound included in the positive electrode material of the rechargeable magnesium battery can simultaneously realize the oxidation-reduction valence change of cations and anions, so that the capacity and voltage of the positive electrode material are improved, and the dynamic performance of electrode reaction is favorably improved.
In a first aspect, embodiments of the present invention provide a rechargeable magnesium battery positive electrode material, where the rechargeable magnesium battery positive electrode material includes a pyrite-type compound with a chemical formula of MTx(ii) a Wherein M is a transition metal cation comprising: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V; t is anion, including one or more of O, S, Se, Te, As, Cl, Br and I; 1<x<3, and the anion is not in the lowest valence state;
in the pyrite type compound, a d orbital of a transition metal cation and a p orbital of an anion are hybridized to form a covalent bond, so that the transition metal and the anion in the rechargeable magnesium battery positive electrode material jointly participate in an oxidation-reduction process in the charging and discharging processes of the magnesium battery, and the joint valence change of the anion and the cation is generated.
Preferably, the crystal structure of the pyrite-type compound belongs to an isometric crystal system,
Figure BDA0002628300330000021
the point group is a group of points,
Figure BDA0002628300330000022
space group, standard card # 42-1340.
In a second aspect, an embodiment of the present invention provides a preparation method of the rechargeable magnesium battery positive electrode material according to the first aspect, where the preparation method includes:
weighing a proper amount of transition metal salt and an anion source according to the requirement, placing the transition metal salt and the anion source in a reaction kettle, adding a certain amount of solvent, keeping the temperature at 100-300 ℃ for 1-72 hours, washing a reaction product with water, and drying the reaction product in a vacuum oven to obtain the pyrite type compound rechargeable magnesium battery positive electrode material.
Preferably, the transition metal salt comprises at least one of an acetate, sulfate, nitrate, or halide salt of M; wherein M is a transition metal cation, comprising: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V;
the anion source comprises a simple substance T or an inorganic compound containing T; wherein T is anion, including one or more of O, S, Se, Te, As, Cl, Br and I;
the solvent is dimethylformamide DMF and/or ethylene glycol EG.
In a third aspect, an embodiment of the present invention provides a preparation method of the rechargeable magnesium battery positive electrode material in the first aspect, where the preparation method includes:
and weighing a proper amount of transition metal simple substances and anion sources according to the requirement, placing the transition metal simple substances and the anion sources in a ball milling tank, and performing sealed ball milling for 1-72 hours to obtain the pyrite type compound rechargeable magnesium battery positive electrode material.
Preferably, the transition metal simple substance includes: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V;
the anion source comprises a simple substance T or an inorganic compound containing T; wherein T is anion, including one or more of O, S, Se, Te, As, Cl, Br and I.
In a fourth aspect, an embodiment of the present invention provides a positive electrode of a rechargeable magnesium battery, including: the rechargeable magnesium battery positive electrode material according to the first aspect; in the positive electrode, the pyrite type compound accounts for 40-95% by mass.
Preferably, the positive electrode further comprises a conductive additive and a binder;
the mass percentage of the conductive additive in the positive electrode is 1-30%; the conductive additive specifically includes: one or more of graphene, ketjen black, carbon nanotubes, acetylene black and Super-P carbon black;
the mass percentage of the binder in the positive electrode is 1-10%; the binder specifically includes: one or more of Polytetrafluoroethylene (PTFE), hydroxymethyl cellulose (CMC), sodium alginate, polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and Styrene Butadiene Rubber (SBR).
In a fifth aspect, an embodiment of the present invention provides a rechargeable magnesium battery, including: the positive electrode according to the fourth aspect.
Preferably, the rechargeable magnesium battery further comprises a magnesium ion electrolyte and a magnesium metal negative electrode;
the concentration of the magnesium ion electrolyte is 0.01-2 mol/L; the solute comprises MgCl2、AlCl3、PhMgCl、Mg(TFSI)2、Mg(BH4)2、Mg(oTf)2The solvent comprises one or more of tetrahydrofuran, dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether;
the magnesium metal negative electrode comprises one or more of metal magnesium foil, magnesium powder, magnesium net and magnesium alloy.
The rechargeable magnesium battery positive electrode material provided by the embodiment of the invention adopts the pyrite type compound as the positive electrode material, and can obtain high capacity, long cycle and better dynamic performance. Firstly, because the energy of the d orbit of the pyrite type compound transition metal is close to that of the p orbit of the anion, a strong covalent bond is formed, so that the joint valence change of the transition metal and the anion can be realized, and the capacity is improved. Hybridization of the transition metal d-orbitals and the anion p-orbitals results in highly delocalized electron clouds that favor the accommodation of the charge brought by the magnesium ions, improving the kinetics of the reaction. In addition, the transition metal elements forming the pyrite mineral compound mainly come from VIII (Fe, Co and Ni) groups, generally have lower d orbitals, and can obtain higher working voltage, thereby being beneficial to improving the energy density of the rechargeable magnesium battery.
Drawings
The technical solutions of the embodiments of the present invention are further described in detail with reference to the accompanying drawings and embodiments.
FIG. 1 is a schematic diagram of a spatial structure of a pyrite-type compound provided in an embodiment of the present invention;
FIG. 2 is an X-ray diffraction diagram of a pyrite-type compound provided in examples 1-5 of the present invention;
FIG. 3 shows Fe provided in example 1 of the present invention0.5Co0.5S2Scanning electron microscopy images of (a);
FIG. 4 shows Fe provided in example 1 of the present invention0.5Co0.5S2Transmission electron microscopy images of (a);
FIG. 5 shows Fe provided in example 1 of the present invention0.5Co0.5S2Element distribution diagram of transmission electron microscope;
FIG. 6 shows Fe provided in example 1 of the present invention0.5Co0.5S2Constant current charge and discharge curve of magnesium battery as anode material;
FIG. 7 shows Fe provided in example 1 of the present invention0.5Co0.5S2The cycle performance of the magnesium battery is a positive electrode material;
FIG. 8 shows Fe provided in example 1 of the present invention0.5Co0.5S2A rate performance diagram of the magnesium battery which is a positive electrode material;
FIG. 9 shows Fe provided in example 1 of the present invention0.5Co0.5S2Constant current charge and discharge curves of the magnesium battery which is made of the anode material and mark marks of I, II, III, IV and V;
FIG. 10 shows Fe provided in example 1 of the present invention0.5Co0.5S2Fe L collected at FIG. 9 marker3Electron energy loss spectrum of (a);
FIG. 11 shows Fe provided in example 1 of the present invention0.5Co0.5S2Co L collected at FIG. 9 mark3Electron energy loss spectrum of (a);
FIG. 12 shows Fe provided in example 1 of the present invention0.5Co0.5S2S L collected at the label of FIG. 93Electron energy loss spectrum of (a);
FIG. 13 shows Fe provided in example 1 of the present invention0.5Co0.5S2X-ray photoelectron spectroscopy of S2 p collected at the label of fig. 9;
FIG. 14 shows the constant-current intermittent titration (GITT) measurement of Fe provided in example 1 of the present invention0.5Co0.5S2A quasi-equilibrium voltage distribution diagram of the Mg soft package battery;
FIG. 15 shows Fe obtained from GITT provided in example 1 of the present invention0.5Co0.5S2Overpotential of the Mg soft package battery in the charge and discharge process;
FIG. 16 is a graph of the dynamic potential response after current interruption during GITT measurement provided in embodiment 1 of the present invention;
FIG. 17 is an AC impedance spectrum obtained after every 2 hours of relaxation in a first cycle of GITT measurements provided in example 1 of the present invention;
FIG. 18 shows Fe provided in example 2 of the present invention0.7Co0.3S2Scanning electron microscopy images of (a);
FIG. 19 shows Fe provided in example 2 of the present invention0.7Co0.3S2A constant current charge-discharge diagram of the magnesium battery which is a positive electrode material;
FIG. 20 shows Fe provided in example 2 of the present invention0.7Co0.3S2The cycle performance of the magnesium battery is a positive electrode material;
FIG. 21 shows Fe provided in example 3 of the present invention0.9Co0.1S2Scanning electron microscopy images of (a);
FIG. 22 shows Fe provided in example 3 of the present invention0.9Co0.1S2A constant current charge-discharge diagram of the magnesium battery which is a positive electrode material;
FIG. 23 illustrates an embodiment of the present inventionFe provided in example 30.9Co0.1S2The cycle performance of the magnesium battery is a positive electrode material;
FIG. 24 shows FeS provided in example 4 of the present invention2Scanning electron microscopy images of (a);
FIG. 25 is a FeS provided in example 4 of the present invention2A constant current charge-discharge diagram of the magnesium battery which is a positive electrode material;
FIG. 26 is a FeS provided in example 4 of the present invention2The cycle performance of the magnesium battery is a positive electrode material;
FIG. 27 shows CoS provided in example 5 of the present invention2Scanning electron microscopy images of (a);
FIG. 28 shows CoS provided in embodiment 5 of the present invention2A constant current charge-discharge diagram of the magnesium battery which is a positive electrode material;
FIG. 29 shows CoS provided in example 5 of the present invention2The cycle performance of the magnesium battery is shown as a positive electrode material.
Detailed Description
The invention is further illustrated by the following figures and specific examples, but it should be understood that these examples are for the purpose of illustration only and are not to be construed as in any way limiting the present invention, i.e., as in no way limiting its scope.
The positive electrode material of the rechargeable magnesium battery comprises a pyrite type compound with a chemical general formula of MTx(ii) a Wherein M is a transition metal cation comprising: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V; t is anion, including one or more of O, S, Se, Te, As, Cl, Br and I; 1<x<3, and the anion is not in the lowest valence state;
the pyrite type compound refers to FeS which is mixed with pyrite2Compound material with same crystal structure, or FeS with pyrite caused lattice distortion by doping2Compound materials with similar crystal structures. Fig. 1 is a schematic spatial structure diagram of a pyrite-type compound provided by the present invention. The crystal structure of the pyrite type compound belongs to an isometric crystal system,
Figure BDA0002628300330000071
the point group is a group of points,
Figure BDA0002628300330000072
space group, standard card # 42-1340.
In the pyrite type compound, a d orbital of a transition metal cation and a p orbital of an anion are hybridized to form a covalent bond, so that the transition metal and the anion in the rechargeable magnesium battery positive electrode material jointly participate in an oxidation-reduction process in the charge-discharge process of the magnesium battery, and the joint valence change of the anion and the cation is generated.
With FeXCo1-XS2(0. ltoreq. X. ltoreq.1) as an example, the d orbitals of the transition metals and the valence bands of the sulfur element overlap partially in terms of energy. The initially empty d orbital will be filled by the electrons of the valence band of the sulfur element, resulting in a hole at the top of its valence band. The high concentration of holes causes two sulfide ions to condense into (S)2)2-Producing pyrite-type compounds. That is, electrons on the 3p orbital of S are filled into the d orbitals of Fe and Co to form a compound having redox activity (S)2)2-(ii) a Transition metals also have redox activity and are referred to as combined anion and cation redox chemistry, i.e., in redox, both transition metal cations and anions participate in the redox process and achieve valence change.
In addition to the predictable high capacity of the co-valence transition of cations and anions, the d orbital of the transition metal and the 3p orbital of sulfur in the pyrite type compound are highly hybridized to generate highly delocalized electrons on the metal and the sulfur, which is beneficial to accommodating the charge of magnesium ions and improving the dynamic performance of the reaction. In addition, transition metal elements such as Fe, Co, etc. forming pyrite-type compounds having a lower d-orbital can output higher operating voltages.
The rechargeable magnesium battery positive electrode material can be obtained by a hydrothermal method or a ball milling method.
The preparation method comprises the following steps: weighing a proper amount of transition metal salt and an anion source according to the requirement, placing the transition metal salt and the anion source in a reaction kettle, adding a certain amount of solvent, keeping the mixture at the temperature of between 100 and 300 ℃ for 1 to 72 hours, washing a reaction product with water, and drying the reaction product in a vacuum oven to obtain a pyrite type compound rechargeable magnesium battery positive electrode material; or weighing a proper amount of transition metal simple substance and anion source according to the requirement, placing the transition metal simple substance and anion source in a ball milling tank, and performing sealed ball milling for 1-72 hours to obtain the pyrite type compound rechargeable magnesium battery positive electrode material.
In the above preparation method, the transition metal simple substance includes: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V; the anion source comprises a simple substance T or an inorganic compound containing T; t is anion, including one or more of O, S, Se, Te, As, Cl, Br and I; the solvent is Dimethylformamide (DMF) and/or Ethylene Glycol (EG).
The rechargeable magnesium battery positive electrode material can be used as a rechargeable magnesium battery positive electrode, and a conductive additive and a binder can be added into the rechargeable magnesium battery positive electrode.
Specifically, in the positive electrode, the pyrite type compound accounts for 40-95% by mass.
The mass percentage of the conductive additive in the anode is 1-30%; the conductive additive specifically includes: one or more of graphene, ketjen black, carbon nanotubes, acetylene black and Super-P carbon black; the mass percentage of the binder in the anode is 1-10%; the binder specifically includes: one or more of Polytetrafluoroethylene (PTFE), hydroxymethyl cellulose (CMC), sodium alginate, polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and Styrene Butadiene Rubber (SBR).
The obtained positive electrode can be combined with magnesium ion electrolyte and a magnesium metal negative electrode to form a rechargeable magnesium battery.
In the specific implementation, the concentration of the magnesium ion electrolyte is 0.01-2 mol/L; the solute comprises MgCl2、AlCl3、PhMgCl、Mg(TFSI)2、Mg(BH4)2、Mg(oTf)2The solvent comprises one or more of tetrahydrofuran, dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether. The magnesium metal cathode can be selected from one or more of metal magnesium foil, magnesium powder, magnesium net and magnesium alloy.
In order to better understand the technical scheme provided by the invention, the following describes the specific composition and characteristics of the rechargeable magnesium battery positive electrode material applied by the invention by using a plurality of specific examples.
Example 1
This example provides a pyrite type of Fe0.5Co0.5S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Fe0.5Co0.5S2The synthesis of (2): weighing 1mmol of FeSO4，1mmol CoSO4And 10mmol urea, dissolved in 30mL Dimethylformamide (DMF) and 40mL Ethylene Glycol (EG), and then 25mmol of sulfur powder added; after stirring for one hour, the suspension was transferred to a reaction kettle and held at 180 ℃ for 12 hours. Repeatedly washing the obtained product with deionized water and ethanol for three times, and drying in a vacuum oven at 60 ℃ to obtain pyrite type Fe0.5Co0.5S2。
(2) And (3) adding the following components in percentage by weight of 7: 1: 1: 1 weight ratio of Fe0.5Co0.5S2And uniformly grinding the Ketjen black, the carbon nano tube and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, the magnesium foil, and 0.4mol/L MgCl were put2-AlCl3And assembling the electrolyte dissolved in the dimethyl ether into the soft package battery. Performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 20 mA/g.
FIG. 2 is an X-ray diffraction pattern of a pyrite-type compound provided in examples 1-5 of the present invention. FIG. 3 shows Fe provided in example 1 of the present invention0.5Co0.5S2Scanning electron microscopy of (a). FIG. 4 is a transmission electron microscope photograph provided in example 1 of the present invention. FIG. 5 is a distribution diagram of transmission electron microscope elements provided in example 1 of the present invention. FIG. 6 shows Fe provided in example 1 of the present invention0.5Co0.5S2Constant current charge and discharge curve of magnesium battery as anode material. FIG. 7 shows Fe provided in example 1 of the present invention0.5Co0.5S2The cycle performance of the magnesium battery is shown as a positive electrode material. FIG. 8 shows Fe provided in example 1 of the present invention0.5Co0.5S2The rate performance diagram of the magnesium battery is the positive electrode material. FIG. 9 shows Fe provided in example 1 of the present invention0.5Co0.5S2The constant current charge-discharge curve and I, II, III, IV and V marks of the magnesium battery which is the anode material are respectively tested at each mark by an electron energy loss spectrum and an X-ray photoelectron spectrum, and the results are shown in FIGS. 10-13. FIG. 10 shows Fe provided in example 1 of the present invention0.5Co0.5S2Fe L collected at FIG. 8 marker3Electron energy loss spectrum of (1). FIG. 11 shows Fe provided in example 1 of the present invention0.5Co0.5S2Co L collected at FIG. 8 mark3Electron energy loss spectrum of (1). FIG. 12 shows Fe provided in example 1 of the present invention0.5Co0.5S2S L collected at the label of FIG. 83Electron energy loss spectrum of (1). FIG. 13 shows Fe provided in example 1 of the present invention0.5Co0.5S2X-ray photoelectron spectra of S2 p collected at the label of fig. 8. As can be seen from FIG. 2, the compounds provided in examples 1 to 5 of the present invention all have the same standard FeS pyrite content2And CoS2The same crystal structure, and as the Fe content increases, the position of the X-ray diffraction peak shifts to the right, indicating that the lattice spacing becomes gradually larger. As can be seen from FIG. 3, Fe0.5Co0.5S2Is nano-sized small spherical particles with uniform particle size distribution. As can be seen from FIG. 4, Fe0.5Co0.5S2The particle diameter of (A) is in the range of 100-200 nm. As can be seen from FIG. 5, Fe0.5Co0.5S2The distribution of each element in the alloy is uniform. As can be seen from FIG. 6, the discharge capacity was 206mAh/g and the charge capacity was 200 mAh/g. No obvious voltage platform exists in the charging and discharging process, which indicates that the pyrite Fe0.5Co0.5S2What is carried out in a magnesium battery is an embedded reaction. As can be seen from FIG. 7, the capacity of the first 100 turns was maintained at 154mAh/g, and the coulombic efficiency was close to 100%, indicating Fe0.5Co0.5S2The material has excellent circulation stabilityAnd (4) sex. As can be seen from FIG. 8, Fe was present even at current densities of 50mA/g and 100mA/g0.5Co0.5S2The positive electrode can still respectively obtain the capacities of 154mA h/g and 101mA h/g, which shows that the positive electrode has better rate capability. As can be seen from fig. 10, the valence state of Fe gradually decreases during the discharging process, gradually increases during the charging process, and returns to almost the initial state at the end of the charging process. As can be seen from fig. 11, the valence state of Co gradually decreases during discharging, gradually increases during charging, and finally returns to the initial state. As can be seen from fig. 12, the valence state of S gradually decreases during discharging, gradually increases during charging, and finally returns to the initial state. As can be seen from fig. 13, the valence state of S gradually decreases during discharging, gradually increases during charging, and finally returns to the initial state. As can be seen from FIGS. 10-13, magnesium is intercalated and deintercalated in the pyrite type Fe0.5Co0.5S2In the process, cations Fe and Co and anions S are subjected to valence change, namely, the valence change of the cations and the anions is carried out together.
The kinetic properties are discussed further below. To further understand the pyrite type Fe0.5Co0.5S2Reaction kinetics of the samples, the overpotentials of the quasi-equilibrium state of the samples were tested using the constant current intermittent titration technique (GITT). In the first cycle, after a discharge or charge cycle of 20 milliamps/gram every 1 hour, the cell was allowed to relax at open circuit for 2 hours to reach quasi-equilibrium. Constant current intermittent titration method (GITT) for measuring Fe0.5Co0.5S2The quasi-equilibrium voltage distribution of the/Mg soft package battery is shown in figure 14, the battery is relaxed for 2 hours after discharging or charging every 1 hour under the condition of 20mA/g and room temperature, and the hollow point in the figure represents the equilibrium open-circuit potential. The cumulative capacity was 272 mAmp-hrs/g at discharge and 258 mAmp-hrs/g at charge, both exceeding the capacity at constant current discharge/charge. A diagonal line can be drawn at the open dots of FIG. 14, and FIG. 15 shows Fe obtained from GITT0.5Co0.5S2Overpotential of/Mg soft package battery in the process of charging and discharging. During charging and discharging, Fe0.5Co0.5S2Does not change greatly, which shows thatIn the process of magnesium ion intercalation and deintercalation, Fe0.5Co0.5S2The kinetics of (a) remain stable.
To explore the source of the potential, the dynamic potential response after current cutoff during GITT measurements was carefully analyzed, as shown in fig. 16. During the discharge process, it can be seen that once the current is removed, the voltage jumps first by a small value (0.09 volts) due to charge transfer and ohmic resistance. It was then gradually increased by 0.29 volt, corresponding to elimination of concentration polarization by ion diffusion, until it approached the quasi-equilibrium condition after 2 hours of relaxation; the opposite occurs during charging. It is evident that most of the overpotential during discharge and charge comes from concentration polarization, probably because of Mg2+And strong covalent bonding between the host lattice.
The pyrite type Fe can be further studied by obtaining ac impedance spectra after each 2 hours of relaxation in the first cycle of GITT measurements shown in fig. 170.5Co0.5S2Redox mechanism (2). R at different oxidation degrees during discharging and chargingctThe value was between 3k ohm and 3.5k ohm, indicating that the reaction process is highly reversible. In our Fe0.5Co0.5S2In the/Mg system, symmetrical RctIs characteristic of the intercalation reaction. In addition, R during chargingctSlightly higher than R in discharge processctThis is consistent with the large overpotential of the GITT demagging process.
Example 2
This example provides a pyrite type of Fe0.7Co0.3S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Fe0.7Co0.3S2The synthesis of (2): weighing 1.4mmol FeCl2，0.6mmol CoCl2And 10mmol urea, dissolved in 30mL DMF and 40mL EG, then added with 25mmol sulfur powder; after stirring for one hour, the suspension was transferred to a reaction kettle and held at 180 ℃ for 12 hours. Repeatedly washing the obtained product with deionized water and ethanol for three times, and drying in a vacuum oven at 80 ℃ to obtain pyrite type Fe0.7Co0.3S2。
(2) And (3) adding the following components in percentage by weight of 8: 1: 1 weight ratio of Fe0.7Co0.3S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 1mg/cm2。
(3) In a glove box filled with argon, the positive plate, the magnesium foil, and 0.25 mol/l PhMgCl-AlCl3And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 20 mA/g.
FIG. 18 shows Fe provided in example 2 of the present invention0.7Co0.3S2Scanning electron microscopy of (a). FIG. 19 shows Fe provided in example 2 of the present invention0.7Co0.3S2Constant current charge and discharge curve of magnesium battery as anode material. FIG. 20 shows Fe provided in example 2 of the present invention0.7Co0.3S2The cycle performance of the magnesium battery is shown as a positive electrode material. As can be seen from FIG. 21, Fe0.7Co0.3S2Are spherical particles with a size distribution in a large range from 100nm to 1000 nm. As can be seen from FIG. 19, Fe0.7Co0.3S2The discharge capacity was 170mAh/g and the charge capacity was 167 mAh/g. As can be seen from FIG. 20, the capacity of the first 60 cycles is maintained at 114mAh/g, and the coulombic efficiency approaches 100%, indicating Fe0.7Co0.3S2The material has better cycling stability.
Example 3
This example provides a pyrite type of Fe0.9Co0.1S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Fe0.9Co0.1S2The synthesis of (2): 1.8mmol of Fe (NO) are weighed3)2，0.2mmol CoCl2And 10mmol urea, dissolved in 30mL DMF and 40mL EG, then added with 25mmol sulfur powder; after stirring for one hour, the suspension was transferred to a reaction vesselAnd 180 degrees celsius for 12 hours. Repeatedly washing the obtained product with deionized water and ethanol for three times, and drying in a vacuum oven at 120 ℃ to obtain pyrite type Fe0.9Co0.1S2。
(2) And (3) adding the following components in percentage by weight of 6: 3: 1 weight ratio of Fe0.9Co0.1S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 3mg/cm2。
(3) In a glove box filled with argon, the positive plate, the magnesium foil, and 0.25 mol/l PhMgCl-AlCl3And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 10 mA/g.
FIG. 21 shows Fe provided in example 3 of the present invention0.9Co0.1S2Scanning electron microscopy of (a). FIG. 22 shows Fe provided in example 3 of the present invention0.9Co0.1S2Constant current charge and discharge curve of magnesium battery as anode material. FIG. 23 shows Fe provided in example 3 of the present invention0.9Co0.1S2The cycle performance of the magnesium battery is shown as a positive electrode material. As can be seen from FIG. 21, Fe0.9Co0.1S2The majority are spherical particles with the size of 200-500 nm. As can be seen from FIG. 22, Fe0.9Co0.1S2The discharge capacity was 110mAh/g and the charge capacity was 107 mAh/g. As can be seen from FIG. 23, the capacity of the first 60 turns remained at 60 mAh/g.
From examples 1 to 3, as the cobalt content was decreased, the capacity of the pyrite-type iron-cobalt sulfide solid solution was gradually decreased, and the cycle stability was also gradually decreased, indicating that an increase in the cobalt content in a certain range has a promoting effect on the electrochemical performance.
Example 4
This example provides a pyrite type FeS2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)FeS2The synthesis of (2): weighing 2mmol Fe (Ac)2And 10mmol urea, dissolved in 20mL DMF and 50mL EG, then 25mmol sulfur powder added; after stirring for one hour, the suspension was transferred to a reaction kettle and held at 170 ℃ for 14 hours. Repeatedly washing the obtained product with deionized water and ethanol for three times, and drying in a vacuum oven at 100 ℃ to obtain the pyrite type FeS2。
(2) And (3) adding the following components in percentage by weight of 7: 2: 1, respectively weighing FeS according to the mass ratio2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (TFSI)2-AlCl3And (3) assembling the electrolyte dissolved in the ethylene glycol dimethyl ether into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 10 mA/g.
FIG. 24 shows FeS provided in example 4 of the present invention2Scanning electron microscopy of (a). FIG. 25 is a FeS provided in example 4 of the present invention2Constant current charge and discharge curve of magnesium battery as anode material. FIG. 26 is a FeS provided in example 4 of the present invention2The cycle performance of the magnesium battery is shown as a positive electrode material. As can be seen from FIG. 24, FeS2Presenting a non-uniform distribution of micro-spherical particles with a size between 1 and 5 microns. As can be seen from FIG. 25, FeS2The discharge capacity of (2) was 35mAh/g, and the charge capacity was 34 mAh/g. As can be seen from FIG. 26, the capacity of the first 60 cycles was maintained at 18mAh/g, indicating that the pyrite type FeS2The electrochemical activity of (2) is low.
Example 5
This example provides a pyrite type CoS2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)CoS2The synthesis of (2): weighing 2mmol of CoSO4And 10mmol urea, dissolved in 10mL DMF and 60mL EG, then 20mmol sulfur powder added; after stirring for one hour, the suspension was transferred to a reaction vessel at 200 fThe degree is maintained for 24 hours. Repeatedly washing the obtained product with deionized water and ethanol for three times, and then drying in a vacuum oven at 100 ℃ to obtain the pyrite type CoS2。
(2) And (3) adding the following components in an amount of 8.5: 0.5: 1 weight ratio of CoS2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 5mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (OTf)2-MgCl2And (4) assembling the electrolyte dissolved in the diethylene glycol dimethyl ether into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 10 mA/g.
FIG. 27 shows CoS provided in example 5 of the present invention2Scanning electron microscopy of (a). FIG. 28 shows CoS provided in embodiment 5 of the present invention2Constant current charge and discharge curve of magnesium battery as anode material. FIG. 29 shows CoS provided in example 5 of the present invention2The cycle performance of the magnesium battery is shown as a positive electrode material. As can be seen from FIG. 27, CoS2The particle size of the microspheres is about 2 microns. As can be seen from FIG. 24, CoS2The discharge capacity of (2) was 75mAh/g, and the charge capacity was 74 mAh/g. As can be seen from FIG. 25, the capacity of the first 60 cycles was maintained at 58mAh/g, indicating that the pyrite type CoS2The electrochemical activity of (2) is low.
Example 6
This example provides a pyrite type of Fe0.5Ni0.5S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Fe0.5Ni0.5S2The synthesis of (2): weighing 1mmol of FeSO4，1mmol NiCl2And 10mmol urea, dissolved in 30mL DMF and 40mL EG, then 20mmol sulfur powder added; after stirring for one hour, the suspension was transferred to a reaction kettle and held at 180 ℃ for 24 hours. The obtained product was repeatedly washed three times with deionized water and ethanol, and then at 50 ℃Drying in a vacuum oven to obtain pyrite type Fe0.5Ni0.5S2。
(2) And (3) adding the following components in percentage by weight of 8: 1: 1 weight ratio of Fe0.5Ni0.5S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 3mg/cm2。
(3) In a glove box filled with argon, the positive plate, the magnesium foil, and 0.25 mol/l PhMgCl-MgCl2And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.2-3V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 10 mA/g.
Example 7
This example provides a pyrite type Mn0.5Ni0.5S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Mn0.5Ni0.5S2The synthesis of (2): weighing 100mmol Mn powder, 100mmol Ni powder and 400mmol sulfur powder, placing in a ball milling tank, sealing and ball milling for 48 hours to obtain Mn0.5Ni0.5S2。
(2) And (3) adding the following components in percentage by weight of 8: 1: 1 by weight ratio of Mn to Mn0.5Ni0.5S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, the magnesium foil, and 0.25 mol/l PhMgCl-MgCl2And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.2-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 10 mA/g.
Example 8
This example provides a pyrite type of Fe0.9Cr0.1S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Fe0.9Cr0.1S2The synthesis of (2): weighing 180mmol of Fe powder, 20mmol of Cr powder and 400mmol of sulfur powder, placing the materials in a ball milling tank, and carrying out sealed ball milling for 24 hours to obtain Fe0.9Cr0.1S2。
(2) And (3) adding the following components in percentage by weight of 8: 1: 1 weight ratio of Fe0.9Cr0.1S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (TFSI)2-AlCl3-MgCl2And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 50 mA/g.
Example 9
This example provides a pyrite type Cu0.5Cr0.5S2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Cu0.5Cr0.5S2The synthesis of (2): weighing 100mmol of Cu powder, 100mmol of Cr powder and 400mmol of sulfur powder, placing the materials in a ball milling tank, and carrying out sealed ball milling for 24 hours to obtain Cu0.5Cr0.5S2。
(2) And (3) adding the following components in percentage by weight of 8: 1: 1 weight ratio of Cu0.5Cr0.5S2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (TFSI)2-AlCl3-MgCl2And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 50 mA/g.
Example 10
The true bookThe embodiment provides pyrite type Cu0.5Cr0.5Se2And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Cu0.5Cr0.5Se2The synthesis of (2): weighing 100mmol of Cu powder, 100mmol of Cr powder and 400mmol of Se powder, placing the powder in a ball milling tank, and carrying out sealed ball milling for 24 hours to obtain Cu0.5Cr0.5Se2。
(2) And (3) adding 9: 0.5: 0.5 weight ratio of Cu0.5Cr0.5Se2And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (TFSI)2-AlCl3-MgCl2And (4) assembling the electrolyte dissolved in tetrahydrofuran into the soft package battery. And performing cyclic voltammetry test on the battery, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 50 mA/g.
Example 11
This example provides a pyrite type Zn0.5Ti0.5Se1.5I0.5And preparing a positive electrode material and testing the performance of the positive electrode material.
(1)Zn0.5Ti0.5Se1.5I0.5The synthesis of (2): weighing 100mmol Zn powder, 100mmol Ti powder, 300mmol selenium powder and 100mmol iodine powder, placing in a ball milling tank, sealing and ball milling for 24 hours to obtain Zn0.5Ti0.5Se1.5I0.5。
(2) And (3) adding the following components in percentage by weight of 7: 2: 1, respectively weighing Zn according to the mass ratio0.5Ti0.5Se1.5I0.5And uniformly grinding the Ketjen black and the polytetrafluoroethylene, rolling to form a film, and drying to obtain the positive pole piece. Wherein the content of active substance is 2mg/cm2。
(3) In a glove box filled with argon, the positive plate, magnesium foil, and 1 mol/L Mg (oTf)2-MgCl2And assembling the electrolyte dissolved in the dimethyl ether into the soft package battery. And to the batteryPerforming cyclic voltammetry test, wherein the scanning voltage range is 0.5-2.5V vs. Mg/Mg2+. Then, the battery is subjected to a constant current charge and discharge test, and the current density is 50 mA/g.
The pyrite type compound cathode material disclosed by the invention utilizes the hybridization of the d-orbit of the transition metal and the 3 p-orbit of the anion, has a strong covalent bond, can simultaneously realize the joint valence change of the cation and the sulfur anion of the transition metal, can obtain the cathode capacity of more than 200mAh/g, and has a better capacity retention rate.
The pyrite-type compound has stable ligand hole chemistry, which results from the 3p orbital electron portion of S entering the d orbital of the transition metal, resulting in a sulfur ligand having a ratio to S2-Higher oxidation state. The initially empty d-orbitals are filled with electrons of the transition metal valence band, resulting in holes at the top of the valence band. The high concentration of holes causes two sulfide ions to condense into (S)2)2-Producing pyrite-type compounds. Wherein the transition metal and the sulfur have redox activity to generate cation and anion covalence.
In addition to the predictable high capacity contributed by the co-valency of the anions and cations, the d-orbitals of transition metals and the 3 p-orbitals of sulfur are highly hybridized in the pyrite structure, generating highly delocalized electrons in the metal and ligand units, facilitating the accommodation of the charge of magnesium ions and improving the reaction kinetics. In addition, pyrites of the VIII (Fe, Co, and Ni) main group, in particular, have a lower d-orbital and are capable of outputting higher operating voltages.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. The rechargeable magnesium battery positive electrode material is characterized by comprising a pyrite type compound with a chemical general formula of MTx(ii) a WhereinAnd M is a transition metal cation, including: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V; t is anion, including one or more of O, S, Se, Te, As, Cl, Br and I; 1<x<3, and the anion is not in the lowest valence state;
in the pyrite type compound, a d orbital of a transition metal cation and a p orbital of an anion are hybridized to form a covalent bond, so that the transition metal and the anion in the rechargeable magnesium battery positive electrode material jointly participate in an oxidation-reduction process in the charging and discharging processes of the magnesium battery, and the joint valence change of the anion and the cation is generated.
2. The rechargeable magnesium battery positive electrode material according to claim 1, wherein the pyrite-type compound has a crystal structure belonging to an isometric system,
Figure FDA0002628300320000011
the point group is a group of points,
Figure FDA0002628300320000012
space group, standard card # 42-1340.
3. A method for preparing the rechargeable magnesium battery positive electrode material as claimed in any one of claims 1-2, wherein the method comprises:
weighing a proper amount of transition metal salt and an anion source according to the requirement, placing the transition metal salt and the anion source in a reaction kettle, adding a certain amount of solvent, keeping the temperature at 100-300 ℃ for 1-72 hours, washing a reaction product with water, and drying the reaction product in a vacuum oven to obtain the pyrite type compound rechargeable magnesium battery positive electrode material.
4. The production method according to claim 3, wherein the transition metal salt includes at least one of an acetate, sulfate, nitrate, or halide salt of M; wherein M is a transition metal cation, comprising: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V;
the anion source comprises a simple substance T or an inorganic compound containing T; wherein T is anion, including one or more of O, S, Se, Te, As, Cl, Br and I;
the solvent is dimethylformamide DMF and/or ethylene glycol EG.
5. The method for preparing the positive electrode material of the rechargeable magnesium battery as claimed in any one of claims 1 to 2, wherein the method comprises the following steps:
and weighing a proper amount of transition metal simple substances and anion sources according to the requirement, placing the transition metal simple substances and the anion sources in a ball milling tank, and performing sealed ball milling for 1-72 hours to obtain the pyrite type compound rechargeable magnesium battery positive electrode material.
6. The production method according to claim 5, wherein the elemental transition metal includes: fe. One or more of Co, Ni, Mn, Zn, W, Nb, Zr, Mo, Ti, Cu and V;
the anion source comprises a simple substance T or an inorganic compound containing T; wherein T is anion, including one or more of O, S, Se, Te, As, Cl, Br and I.
7. A positive electrode for a rechargeable magnesium battery, the positive electrode comprising: a rechargeable magnesium battery positive electrode material according to any one of the claims 1-2; in the positive electrode, the pyrite type compound accounts for 40-95% by mass.
8. The positive electrode according to claim 7, further comprising a conductive additive and a binder;
the mass percentage of the conductive additive in the positive electrode is 1-30%; the conductive additive specifically includes: one or more of graphene, ketjen black, carbon nanotubes, acetylene black and Super-P carbon black;
the mass percentage of the binder in the positive electrode is 1-10%; the binder specifically includes: one or more of Polytetrafluoroethylene (PTFE), hydroxymethyl cellulose (CMC), sodium alginate, polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and Styrene Butadiene Rubber (SBR).
9. A rechargeable magnesium battery, characterized in that the rechargeable magnesium battery comprises: the positive electrode according to any one of claims 7 or 8.
10. The rechargeable magnesium battery of claim 9, further comprising a magnesium ion electrolyte and a magnesium metal negative electrode;
the concentration of the magnesium ion electrolyte is 0.01-2 mol/L; the solute comprises MgCl2、AlCl3、PhMgCl、Mg(TFSI)2、Mg(BH4)2、Mg(oTf)2The solvent comprises one or more of tetrahydrofuran, dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether;
the magnesium metal negative electrode comprises one or more of metal magnesium foil, magnesium powder, magnesium net and magnesium alloy.
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