Mn-doped FeS/CN bimetallic sulfide material with large lattice spacing as well as preparation method and application thereof
Technical Field
The invention belongs to the technical field of storage of nano materials and electrochemical energy, and particularly relates to a Mn-doped FeS/CN bimetal sulfide material with a large lattice spacing, and a preparation method and application thereof.
Background
Under the current increasingly severe ecological environment, new energy has evolved into a powerful alternative to fossil energy, and the development of a material with efficient energy conversion and storage is an urgent need to utilize these new energy sources. Lithium Ion Batteries (LIBs) are known for their light weight, high energy density, and fast charge and discharge. However, the shortage and maldistribution of lithium sources have made it difficult to meet the increasing demand for power equipment. The sodium source is cheap ($150 t) -1 ) And are widely distributed on the earth (23.6X 103 mg/kg) -1 ) And is easy to obtain. The working principle of the sodium ion battery is very similar to that of the lithium ion battery, and the sodium ion battery has the same rocking chair charging and discharging principle with the lithium ion battery and is a reasonable substitute of the lithium ion battery. The charging and discharging processes of both batteries are generally accomplished by shuttling and de-intercalation of charged ions in the battery between the electrode materials of the battery. Sodium ion batteries, like lithium ion batteries, are also affiliated with ion transfer rocking chair batteries. This concept was originally defined by Armand et al in the 80's of the 20 th century by using a layered compound with a low intercalation potential as the negative electrode material of a lithium ion battery and a layered compound comprising lithium element with a high intercalation potential as the positive electrode material, creating a battery model in which lithium ions cycle back and forth between the two electrode materials during charge-discharge cycles. In the process of charging the battery, sodium ions are released from the anode material of the battery into the electrolyte by the electric field force, move to the cathode material of the battery through the electrolyte, meet with electrons reaching the cathode material of the battery through an external circuit, and are finally embedded into the cathode material of the sodium ion battery in a sodium simple substance state. In the process of discharging the battery, sodium in the negative electrode material of the sodium-ion battery outputs an electron to be changed into a sodium ion to enter electrolyte, the sodium ion moves to the positive electrode through the electrolyte and is combined with the electron passing through an external circuit, the sodium ion is changed into a sodium simple substance again and then is embedded into the positive electrode material of the sodium-ion battery, and finally a charge-discharge cycle is completed.
However, sodium ion (Na) + ) Radius ratio lithium ion (Li) + ) Large mass ratio of Li + The structural damage to the active electrode material during the circulation process is larger; this results in a number of suitable lithiumThe electrode material of the ion battery cannot be used for the sodium ion battery. Therefore, it is important to prepare an electrode material suitable for a sodium ion battery.
Transition metal chalcogenides have proven to be an alternative anode material due to their open framework structure, high theoretical capacity and low cost. Iron sulfide is a typical transition metal sulfide, and the theoretical specific capacity is up to 609mAh g -1 Low cost, environment protection and rich resources. Unfortunately, FeS expands in volume during cycling and has low conductivity, resulting in poor electrochemical performance. Heteroatom doping is considered to be a simple and feasible way to improve the electrochemical performance of single metal sulfides. Doping can enhance electron/ion transport by creating chemical bonds between iron, sulfur, and heteroatoms. Greater atomic doping also improves the lattice parameter to accommodate more sodium ions. In addition, some doping can change the structure and the form of the material, and the problem of single metal sulfide is fundamentally solved.
In the prior art, e.g. < Na > 2 MnFe(CN) 6 @Na 2 NiFe(CN) 6 The synthesis and application thereof in sodium-ion batteries (Zhongyue, Gejia, et al, research and design of power technology, 2020, 08 months, 1108- 2 MnFe(CN) 6 @Na 2 NiFe(CN) 6 The first discharge specific capacity of the sodium ion half battery adopting the material is 137.1mAh/g, and the capacity retention rate reaches 94.91% after the charge-discharge cycle is 200 times. However, the presence of crystal water in this material affects the stability and capacity of the material, and when the material is used in an electrode material of a sodium ion battery, the capacity and cycle stability of the material are to be improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a Mn-doped FeS/CN bimetallic sulfide material with large lattice spacing, and the Mn-doped FeS is prepared by first utilizing PVP, ferrous sulfate, manganese chloride, thiourea and sulfur powder 2 and/PVP precursor, and then carbonizing the precursor under a multi-property environment to prepare a finished product. When the finished product is applied to the cathode material of the sodium-ion batteryAnd has higher capacity and longer-lasting cycle stability. Specifically, the following technique is used.
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material with large lattice spacing comprises the following steps:
s1, adding inorganic ferrous salt and inorganic manganese salt into a glycol solution of polyvinylpyrrolidone, and stirring until the inorganic ferrous salt and the inorganic manganese salt are dissolved; then adding thiourea and sulfur powder, stirring, performing ultrasonic treatment for 10-30min, keeping at 180 ℃ for 18h, centrifuging and collecting to obtain black powdery Mn-dots FeS 2 A PVP precursor; washing with deionized water and ethanol, and vacuum drying (drying at 65 deg.C in vacuum oven);
s2, mixing the Mn-coped FeS obtained in the step S1 2 The PVP precursor is carbonized for 2-4h at 800 ℃ in the environment of inert gas (generally nitrogen, argon and the like) to obtain the Mn-coped FeS bimetallic sulfide material.
In the preparation method of the Mn-doped FeS/CN bimetallic sulfide material, the inorganic ferrous salt and the inorganic manganese salt in the step S1 need to be salts capable of being dissolved in ethylene glycol. To facilitate the dissolution of these salts, inorganic ferrous and manganese salts may be milled/ground to reduce their particle size, typically 10-100 μm. In order to promote the dissolution of the sulfur powder in the ethylene glycol, methods such as ultrasonic treatment are used.
Preferably, in step S1, the ratio of the mass of the polyvinylpyrrolidone to the total amount of the inorganic ferrous salt and the inorganic manganese salt is 50-250g/mol, and the ratio of the total amount of the inorganic ferrous salt and the inorganic manganese salt to the amount of the thiourea and the sulfur powder is 1:1 (1-2).
More preferably, in step S1 of the above preparation method, the mass ratio of the inorganic ferrous salt to the inorganic manganese salt is 4 (1-4).
Further preferably, in step S1 of the above preparation method, the ratio of the amount of the inorganic ferrous salt to the inorganic manganese salt is 3: 1.
Preferably, in step S1 of the above preparation method, after adding thiourea and sulfur powder and ultrasonically stirring, 180 ℃ is maintained for 18 hours.
More preferably, in step S1, the ratio of the mass of the polyvinylpyrrolidone to the total amount of the inorganic ferrous salt and the inorganic manganese salt is 100g/mol, and the ratio of the total amount of the inorganic ferrous salt and the inorganic manganese salt to the amount of the thiourea and the sulfur powder is 2:2: 3.
Preferably, the inorganic ferrous salt is ferrous sulfate or ferrous chloride, and the inorganic manganese salt is manganese chloride.
The invention also provides the Mn-doped FeS/CN bimetallic sulfide material with large lattice spacing prepared by the preparation method and a method for applying the material to the preparation of a cathode material of a sodium-ion battery.
The Mn-doped FeS/CN bimetallic sulfide material with large lattice spacing provided by the invention adopts a one-time solvothermal and annealing process to synthesize the multinuclear Mn-doped FeS/CN. The selection of Mn atoms as doping atoms in the present invention has four important reasons: (1) the premise of doping is that the radius of matrix atoms (Fe) is similar to that of doping atoms (Mn); (2) the atomic radius (0.067nm) of Mn is slightly larger than that (0.061nm) of Fe, so that the lattice spacing can be properly increased to enhance the storage capacity of sodium; (3) the reserves of manganese ore and iron ore on the earth are also abundant, and the price is also low; (4) due to the difference of the extra-nuclear electrons, Mn doping brings a large number of holes, thereby improving the conductivity.
Compared with the prior art, the invention has the advantages that:
1. the invention uses larger lattice spacing caused by Mn atom doping, and provides more space for the storage of sodium ions; the doping of atoms increases the conductivity and enhances the transport and rate performance of carriers;
2. the existence of the multi-core structure and carbon can improve the tolerance of volume expansion, thereby being beneficial to long-term cycle performance;
3. the detection result of the electrochemical performance of the Mn-doped FeS/CN bimetallic sulfide material shows that the Mn-doped FeS/CN bimetallic sulfide material has higher reversible capacity of 0.5 A.g as a sib anode -1 When the ratio is 563.3mAh g -1 (ii) a Has more excellent rate capability, 8 A.g -1 The average molecular weight is 442.8mAh g -1 (ii) a More durable circulation stability, 206.2mAh g after 8000 times of circulation -1 (ii) a Has higher energyDensity and capacity retention; provides a promising strategy for improving the electrochemical performance of the single metal sulfide.
Drawings
FIG. 1 is an SEM image of an Mn-doped FeS/CN electrode material of example 1;
FIGS. 2 and 3 are TEM images of Mn-dots FeS/CN electrode material of example 1;
FIG. 4 is a HRTEM image of the Mn-doped FeS/CN electrode material in example 1;
FIG. 5 is an SEM image of the Mn-doped FeS/CN electrode material of example 2;
FIG. 6 is an SEM image of the Mn-doped FeS/CN electrode material of example 3;
FIG. 7 is an SEM image of a composite MnS/FeS electrode material prepared in comparative example 1;
FIG. 8 shows Mn-doped FeS/CN electrode materials prepared in examples 1-3 at 4A g -1 A cycle plot of 1000 cycles under conditions;
FIG. 9 shows FeS electrode material prepared in comparative example 2 at 4A g -1 A cycle chart for 1000 cycles under the conditions;
FIG. 10 shows MnS electrode material prepared in comparative example 3 at 4 A.g -1 A cycle chart of 500 cycles performed under the conditions;
FIG. 11 shows Mn-doped FeS/CN electrode material prepared in example 1 at 0.5 A.g -1 A cycle chart of cycling 100 times under the conditions;
FIG. 12 is a graph of rate capability of the Mn-doped FeS/CN electrode material prepared in example 1;
FIG. 13 shows the Mn-doped FeS/CN electrode material prepared in example 1 at 8 A.g -1 A cycle chart after 8000 cycles under the condition;
FIG. 14 is an XRD pattern of Mn-doped FeS/CN electrode materials prepared in examples 1-3;
FIG. 15 shows Mn-doped FeS of example 1 2 XRD pattern of PVP precursor.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following examples and comparative examples, polyvinylpyrrolidone (PVP) used was purchased from the national pharmaceutical group, having a molecular weight of about 5800 and a polymerization degree of monomer polymerization; the used inorganic ferrous salt is ferrous chloride tetrahydrate and ferrous sulfate tetrahydrate, the used inorganic manganous salt is manganese chloride tetrahydrate, purchased from national medicine group company, and is firstly ground to the grain diameter of 10-100 mu m when in use; thiourea (chemical formula is CH 4 N 2 S) and sulfur powder are purchased from national medicine group company, and the purity is 99.8 percent.
Example 1
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided by the embodiment comprises the following steps:
s1, adding 0.4g of polyvinylpyrrolidone into 50ml of ethylene glycol, and stirring for 30min until the polyvinylpyrrolidone is dissolved to prepare a solution; adding 3mmol ferrous sulfate tetrahydrate and 1mmol manganese chloride tetrahydrate, and stirring until the mixture is dissolved; then adding 4mmol of thiourea and 6mmol of sulfur powder, stirring, performing ultrasonic treatment for 30min, then placing the mixture into an oven for keeping the temperature of 180 ℃ for 18h, and centrifugally collecting to obtain black powdery Mn-dots FeS 2 A PVP precursor; washing with deionized water and alcohol, and drying in a vacuum oven at 65 ℃;
s2, mixing 100mg of Mn-doped FeS obtained in the step S1 2 Carbonizing PVP precursor in a tube furnace protected by argon at 600 deg.C for 3h to obtain carbonized PVP and Mn-coped FeS 2 And (4) carrying out phase change to obtain the Mn-doped FeS bimetallic sulfide material.
Example 2
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided in this embodiment is different from that in embodiment 1 in that 3.5mmol of ferrous sulfate tetrahydrate and 0.5mmol of manganese chloride tetrahydrate are used; thiourea was 4mmol and sulphur powder 4 mmol. Namely, the amount of substances of ferrous sulfate tetrahydrate and manganese chloride tetrahydrate is 7:1, and the ratio of the total amount of substances of ferrous sulfate tetrahydrate and manganese chloride tetrahydrate to the amount of substances of thiourea and sulfur powder is 1:1: 1.
Example 3
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided by the embodiment is different from the preparation method of the embodiment 1 in that 2mmol of ferrous sulfate tetrahydrate and 2mmol of manganese chloride tetrahydrate are used; thiourea was 4mmol and sulphur powder was 8 mmol. Namely, the amount of substances of ferrous sulfate tetrahydrate and manganese chloride tetrahydrate is 1:1, and the ratio of the total amount of substances of ferrous sulfate tetrahydrate and manganese chloride tetrahydrate to the amount of substances of thiourea and sulfur powder is 1:1: 2.
Example 4
The difference between the preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided by the embodiment and the embodiment 1 is that ferrous sulfate tetrahydrate is replaced by ferrous chloride hydrate.
Example 5
The difference between the preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided in this embodiment and embodiment 1 is that the amount of polyvinylpyrrolidone used is 1g, i.e., the ratio of the mass of polyvinylpyrrolidone to the total amount of the inorganic ferrous salt and the inorganic manganese salt is 250 g/mol.
Example 6
The difference between the preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided in this embodiment and embodiment 1 is that the amount of polyvinylpyrrolidone used is 0.2g, i.e., the ratio of the mass of polyvinylpyrrolidone to the total amount of the inorganic ferrous salt and the inorganic manganese salt is 50 g/mol.
Comparative example 1
The sodium-ion battery negative electrode material provided by the comparative example is different from that of example 1 in that manganese chloride tetrahydrate is replaced by manganese oxalate during preparation. The specific preparation method is the same as that of example 1.
Comparative example 2
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided by the comparative example comprises the following steps: the difference from example 1 is that in step S1, any manganese salt such as manganese chloride tetrahydrate is not used, that is, 4mmol of ferrous sulfate tetrahydrate is directly used; the preparation method is the same as that of example 1.
Comparative example 3
The preparation method of the Mn-doped FeS/CN bimetallic sulfide material provided by the comparative example comprises the following steps: the difference from the embodiment 1 is that in the step S1, any ferrous salt such as ferrous sulfate tetrahydrate is not used, that is, 4mmol of manganese chloride tetrahydrate is directly used; the preparation method is the same as that of example 1.
Test example: microscopic morphology of electrode materials prepared in examples 1 to 3 and comparative example 1, and examples 1 to 5 and comparative examples 1 to 3 and electrochemical Performance test
The microscopic morphologies of the Mn-doped FeS/CN bimetallic sulfide material prepared in example 1 are shown in FIGS. 1-4, and the microscopic morphologies of the Mn-doped FeS/CN bimetallic sulfide materials prepared in examples 2 and 3 are shown in FIGS. 5 and 6. Comparative example 1 the microstructure of the prepared composite MnS/FeS is shown in fig. 7, and the composite is not a doped sample and has a low reversible capacity when used as an electrode material for a sodium ion battery.
As shown in FIG. 8, at 4A · g -1 Under the conditions, the Mn-doped FeS/CN electrode materials prepared in examples 1 to 3 respectively have a reversible capacity of 488mAh g after 1000 cycles by using a blue battery test system -1 、370mAh·g -1 、368mAh·g -1 。
As shown in FIG. 9, the FeS electrode material prepared in comparative example 2 had a reversible capacity of 300mAh g after 1000 cycles -1 。
As shown in FIG. 10, the MnS electrode material prepared in comparative example 3 has a reversible capacity of 117mAh g after 500 cycles, respectively -1 。
As shown in FIG. 11, at 0.5A · g -1 Under the conditions, the Mn-doped FeS/CN electrode material prepared in example 1 has a reversible capacity of 562.7mAh g after 100 cycles by using a blue battery test system -1 。
As shown in FIG. 12, at 8A · g -1 Under the conditions, the Mn-doped FeS/CN electrode material prepared in example 1 has excellent rate capability (270.4 mAh.g) -1 )。
As shown in FIG. 13, at 8A · g -1 Under the condition, the Mn-dots FeS/CN electrode material prepared in the example 1 can still maintain 206.2 mAh.g after 8000 cycles -1 Of the battery.
FIG. 14 is an XRD pattern of the electrode materials of examples 1-3; FIG. 15 is Mn-coped FeS of step S1 of example 1 2 XRD pattern of PVP precursor.
From the test results, the Mn-doped FeS/CN electrode material prepared by the preparation method provided by the invention has higher reversible capacity (0.5 A.g) as a sib anode -1 When the ratio is 563.3mAh g -1 ) Excellent rate capability (8 A.g) -1 The average molecular weight is 442.8mAh g -1 ) And a long-lasting circulation stability (206.2 mAh g after 8000 cycles) -1 ) I.e., higher energy density and capacity retention.
The practice of the present invention has been described in detail with reference to the foregoing detailed description, but the invention is not limited to the specific details of the foregoing embodiment. Within the scope of the claims and the technical idea of the invention, a number of simple modifications and changes can be made to the technical solution of the invention, and these simple modifications are within the scope of protection of the invention.