CN106784815B - A kind of iron-based sulfide electrode material, preparation method and the application in solid state battery - Google Patents

Abstract

The present invention provides a kind of iron-based sulfide electrode material, preparation method and the applications in solid state battery, belong to lithium secondary battery technical field.Iron-based sulfide electrode material based on conversion reaction is selected from the one or more of ferrous sulfide, ferriferrous sulfide and eight seven iron of vulcanization.The preparation method of this iron-based sulfide electrode material has the advantages that simple time saving.

Description

A kind of iron-based sulfide electrode material, preparation method and application in solid-state battery application

technical field

The invention belongs to the technical field of lithium secondary batteries, and relates to an iron-based sulfide electrode material, a preparation method and its application in solid-state batteries.

Background technique

Due to the advantages of high energy density, high discharge voltage, long cycle life and no memory effect, lithium-ion batteries have been widely used in consumer electronics and communications. In the future, they will have broad applications in the fields of hybrid electric vehicles and large-scale energy storage. Prospects. However, traditional lithium-ion batteries usually use organic electrolyte as the lithium-ion conductive medium, which has safety problems such as flammability, corrosion, and poor thermal stability, which limits the application of lithium-ion batteries. At the same time, metal lithium will undergo a series of side reactions with the liquid electrolyte in the liquid battery. For example, a chemical reaction will occur when the metal lithium surface directly contacts the electrolyte, and an uneven solid electrolyte film will be formed on the metal lithium surface. In the process of charging and discharging, due to the uneven distribution of current density, the solid electrolyte film on the surface of lithium metal will crack or even fall off, and the negative electrode of lithium metal will continue to dissolve. In addition, the growth of lithium dendrites can cause the separator to puncture, eventually causing the battery to short-circuit and fail.

Solid-state batteries use inorganic solid electrolytes or polymer electrolytes to replace the organic electrolytes in traditional lithium-ion batteries, which have higher safety performance and thermal stability, and are considered to be the ultimate solution to completely solve the safety problem of lithium-ion batteries. The most studied inorganic solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes. Inorganic solid electrolyte materials have high room temperature ionic conductivity and mechanical strength, wide electrochemical window, and good thermal stability. The polymer solid electrolyte is mainly a material system based on polyethylene oxide. This kind of material has high high-temperature ionic conductivity, easy film formation, and good machinability. The safety performance of the all-solid lithium battery made of solid electrolyte is obviously better than that of the liquid battery, which effectively solves the danger of leakage, combustion and explosion of the organic electrolyte during use. On the other hand, the high mechanical strength of the solid electrolyte can effectively inhibit the growth of lithium dendrites, and there is no interfacial side reaction, and the cycle stability and safety performance are significantly improved. At the same time, it also makes it possible for metal lithium to be used as a negative electrode material in batteries, further improving the energy density of batteries.

At present, most of the cathode materials widely used are lithium-containing transition metal oxides and phosphate electrodes (LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ ), which have high working voltage and cycle stability, but the theoretical ratio The capacity is generally low, and the ability to increase the energy density of the battery is limited. Although sulfur-based and transition metal sulfide electrodes have low operating voltages, their theoretical specific capacities are high, which helps to increase the energy density of batteries. In solid-state batteries, how to reduce the interface resistance is the key to improving the cycle stability of the battery and giving full play to the capacity of the positive electrode. The use of transition metal sulfides as cathode materials is usually accompanied by significant volume changes during charge and discharge, which may lead to electrode pulverization or poor contact at the contact interface between the electrode and the electrolyte. The flake-like transition metal sulfide electrode material can relieve the internal stress during cycling and inhibit the destruction of the electrode structure caused by the volume change effect. At the same time, the two-dimensional sheet structure has a large specific surface area, which can increase the contact area between the electrode and the solid electrolyte, reduce the interface contact resistance, and increase the active sites for electrochemical reactions. The thin nanosheets also help shorten the transport distance of lithium ions and electrons and improve electrochemical reaction kinetics.

Iron-based sulfide electrodes have good research prospects because of their cheap raw materials, abundant reserves, environmental friendliness and high specific capacity. Currently, complex and time-consuming solvothermal and hydrothermal methods are usually used to synthesize transition metal sulfide electrode materials with certain microscopic morphology. Therefore, it is crucial to develop facile and time-saving synthetic methods to obtain iron-based sulfide electrode materials with specific morphologies.

Contents of the invention

The invention provides an iron-based sulfide electrode material. The iron-based sulfide electrode material can improve the electrochemical performance of a solid-state battery. On the one hand, because the iron-based sulfide has a higher theoretical specific capacity and a moderate working voltage, Application in solid-state lithium batteries can increase the energy density of solid-state batteries; on the other hand, the microscopic morphology of the iron-based sulfide electrode material in this application is a two-dimensional sheet structure, which can increase the contact area between the electrode and the solid electrolyte and reduce the interface contact resistance. At the same time, the nanosheet structure can effectively shorten the lithium ion transmission distance and improve the electrochemical reaction kinetics, thereby improving the electrochemical performance of solid-state batteries. Therefore, the iron-based sulfide electrode material prepared in this application has better cycle performance.

The present invention also provides a method for preparing an iron-based sulfide electrode material. The preparation method for an iron-based sulfide electrode material provided by this application can improve the performance of a solid-state battery. Specifically, by synthesizing a two-dimensional sheet-like active material, its The contact area with the electrolyte and conductive additives can reduce the interface contact resistance while alleviating the volume effect during cycling, and ultimately improve the energy density and cycle stability of solid-state batteries.

The application provides a method for preparing an iron-based sulfide electrode material, comprising the following steps:

A) Add the ferrous salt solution into the polyvinyl alcohol aqueous solution, and stir to obtain a mixed solution; under the protection of an inert atmosphere, stir and mix the above mixed solution with the sodium sulfide aqueous solution, and obtain a black precipitate after reaction.

B) The black precipitate is washed by centrifugation and then dried to obtain the final iron-based sulfide electrode material.

Preferably, in the aqueous solution of the raw materials, the concentration of ferrous salt is 1wt%-80wt%, the concentration of polyvinyl alcohol aqueous solution is 0.01wt%-30%, and the concentration of sodium sulfate aqueous solution is 1wt%-80wt%.

Preferably, the mixing and stirring temperature is 0-100° C., and the stirring time is 0.001-10 h.

Preferably, the drying is freeze drying or vacuum drying at 80°C, and the drying time is 12-36 hours.

Preferably, the selected ferrous salt is one or more of FeSO ₄ ·7H ₂ O and FeCl ₂ ·4H ₂ O.

The present application also provides a solid-state battery, including the iron-based sulfide electrode material prepared by the preparation method described in the above scheme.

The present application provides a method for preparing an iron-based sulfide electrode material, which includes the following steps: adding a ferrous salt solution into an aqueous solution of polyvinyl alcohol, and stirring to obtain a mixed solution. Under the protection of an inert atmosphere, the above mixed solution was stirred and mixed with an aqueous solution of sodium sulfide, and a black precipitate was obtained after the reaction. The black precipitate was washed by centrifugation and then dried to obtain the final iron-based sulfide electrode material. This application adopts polyvinyl alcohol-assisted co-precipitation method to obtain iron-based sulfide electrode materials. In the process of mixing ferrous salt solution and polyvinyl alcohol aqueous solution, ferrous ions and polyvinyl alcohol undergo a complex reaction, and then react with sodium sulfide In the process of co-precipitation in aqueous solution, the long chain of polyvinyl alcohol can not only make the co-precipitation reaction proceed slowly, but also effectively control the morphology of the precipitate. Finally, an iron-based sulfide electrode material with a nanoflower structure composed of nanosheets is obtained. The electrode material with a two-dimensional sheet structure helps to improve the contact between the electrode and the solid electrolyte and shorten the transmission distance of lithium ions and electrons.

The iron-based sulfide electrode material in this application can improve the electrochemical performance of solid-state batteries. On the one hand, because iron-based sulfide has a high theoretical specific capacity and moderate working voltage, it can improve the energy density of solid-state batteries when used in solid-state batteries On the other hand, the microscopic morphology of the iron-based sulfide electrode material in this application is a two-dimensional sheet structure, which can increase the contact area between the electrode and the solid electrolyte, alleviate the volume effect during the cycle, and improve the cycle stability of the solid-state battery; therefore , the iron-based sulfide electrode material prepared in this application has better cycle performance.

Description of drawings

FIG. 1 is a scanning electron micrograph of the iron-based sulfide electrode material prepared in Example 1 of the present invention.

Fig. 2 is a cycle performance test chart of the iron-based sulfide electrode material prepared in Example 1 of the present invention applied to a solid-state battery.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

The embodiment of the present invention discloses a method for preparing a composite polymer electrolyte, comprising the following steps:

A) adding the ferrous salt solution to the polyvinyl alcohol aqueous solution, stirring to obtain a mixed solution; under the protection of an inert atmosphere, stirring and mixing the above mixed solution with the sodium sulfide aqueous solution, and obtaining a black precipitate after the reaction;

B) drying the black precipitate after centrifugal washing to obtain the final iron-based sulfide electrode material;

This application adopts the method of co-precipitation assisted by polyvinyl alcohol to prepare iron-based sulfide electrode materials, that is, the present invention adopts the method of co-precipitation preparation to obtain iron-based sulfide electrodes with a nanoflower structure composed of nanosheets and good cycle stability Material. The preparation method of the iron-based sulfide electrode material provided by this application enables the self-assembly of iron-based sulfide nanosheets into a nano-flower microstructure, which helps to alleviate the volume effect, increases the contact area between the electrode and the solid electrolyte, and improves the overall performance of the solid-state battery. performance.

In the present invention, firstly, the ferrous salt solution and the polyvinyl alcohol aqueous solution are mixed, and the complexation reaction occurs after stirring. Then the above mixed solution is mixed with sodium sulfide aqueous solution, stirred and reacted for a period of time, centrifuged, washed, and dried to obtain the final product.

In the above-mentioned process of preparing the mixed solution, the ferrous salt is well known to those skilled in the art, and the present application is not particularly limited. For example, the ferrous salt described in the present application is preferably FeSO ₄ ·7H ₂ O, One or more of FeCl ₂ ·4H ₂ O, in an embodiment, the polymer matrix is more preferably FeSO ₄ ·7H ₂ O. The preferred grades of polyvinyl alcohol described in the present application are four types: polyvinyl alcohol 2499, polyvinyl alcohol 1799, polyvinyl alcohol 1788 and polyvinyl alcohol 1750. The polyvinyl alcohol described in this application is used as a complexing agent, which performs coordination complexation with ferrous ions to form Fe ²⁺ -polyvinyl alcohol, and then mixes with S ^2- to undergo co-precipitation reaction to form iron with a certain nano-morphology sulfide-based electrode materials.

The mixing and stirring temperature is preferably 0-100° C., and the stirring time is 0.001-10 h. The optimum is 1.0h. The drying is freeze-drying or vacuum drying at 80° C., and the drying time is preferably 12-36 hours. In an embodiment, it is more preferably 18 to 32 hours, most preferably 24 hours. If the stirring temperature is too high, Fe ²⁺ is easily oxidized to Fe ³⁺ , resulting in impurities;

In the iron-based sulfide electrode material prepared by the present application, Fe ²⁺ undergoes a complex reaction with polyvinyl alcohol chains, which can effectively control the reaction rate and product morphology, and the iron-based sulfide electrode material with a two-dimensional nanosheet structure can reduce the volume Effect, increase the contact area between the electrode and the solid electrolyte, and shorten the lithium ion transmission distance.

The present application also provides a solid-state battery, which includes the iron-based sulfide electrode material prepared by the preparation method described in the above scheme.

The iron-based sulfide electrode material prepared by this application is used as the positive electrode of the solid-state battery. Because the iron-based sulfide electrode has good electronic conductivity and special nanostructure, the lithium secondary battery has good rate performance and cycle stability. sex.

In order to further understand the present invention, the preparation method of the iron-based sulfide electrode material provided by the present invention will be described in detail below in conjunction with the examples, and the protection scope of the present invention is not limited by the following examples.

Example 1

FeSO ₄ ·7H ₂ O aqueous solution was added to the aqueous solution of polyvinyl alcohol 1750 with a concentration of 1.0wt%, and after stirring at room temperature for 0.5h, a mixed solution was obtained; then, under the protection of an argon atmosphere, the mixed solution was added to a concentration of In 20wt% Na ₂ S·9H ₂ O aqueous solution, react at room temperature for 0.5 h, centrifuge to wash the black precipitate, and freeze-dry for 24 h to obtain the iron-based sulfide electrode material. The iron-based sulfide electrode material with a microscopic morphology of two-dimensional nanosheets is shown in Figure 1.

A solid-state battery was assembled with Li ₁₀ GeP ₂ S ₁₂ -75Li ₂ S 25P ₂ S ₅ 1% P ₂ O ₅ double-layer solid electrolyte as the conductive medium, and metal lithium as the counter electrode, and the electrochemical performance was tested at room temperature . The curve in Fig. 2 is the cycle performance of the iron-based sulfide electrode material prepared in Example 1. As can be seen from Fig. 2, at room temperature, this electrode has good cycle performance when applied to solid-state batteries. After 30 cycles, the reversible capacity still maintains about 436mAh/g.

Example 2

FeSO ₄ ·7H ₂ O aqueous solution was added to the aqueous solution of polyvinyl alcohol 1799 with a concentration of 0.5wt%, and after stirring at room temperature for 0.5h, a mixed solution was obtained; then, under the protection of an argon atmosphere, the mixed solution was added to a concentration of In a 5wt% Na ₂ S·9H ₂ O aqueous solution, react at room temperature for 0.5 h, centrifuge to wash the black precipitate, and vacuum dry at 80° C. for 24 h to obtain an iron-based sulfide electrode material. The microscopic morphology is an iron-based sulfide electrode material in the shape of two-dimensional nanosheets.

A solid-state battery was assembled with Li ₁₀ GeP ₂ S ₁₂ -70Li ₂ S·30P ₂ S ₅ double-layer solid electrolyte as the conductive medium and metal lithium as the counter electrode, and the electrochemical performance was tested at room temperature. The iron-based sulfide electrode material prepared in Example 2 was used to assemble a solid-state battery. After 30 cycles at a current density of 800mA/g, the reversible capacity remained at about 423mAh/g.

Example 3

FeCl ₂ ·4H ₂ O aqueous solution was added to the aqueous solution of 3.0wt% polyvinyl alcohol 1788 and stirred at room temperature for 0.5h to obtain a mixed solution; then, under the protection of argon atmosphere, the mixed solution was added to a concentration of In 20wt% Na ₂ S·9H ₂ O aqueous solution, react at room temperature for 0.5 h, centrifuge to wash the black precipitate, and freeze-dry to obtain the iron-based sulfide electrode material. The microscopic appearance is a nanoflower structure formed by the self-assembly of nanosheets.

A solid-state battery was assembled with Li ₁₀ GeP ₂ S ₁₂ -80Li ₂ S·20P ₂ S ₅ double-layer solid electrolyte as the conductive medium and metal lithium as the counter electrode, and the electrochemical performance was tested at room temperature. The iron-based sulfide electrode material prepared in Example 3 was used to assemble a solid-state battery. After 30 cycles at a current density of 500 mA/g, the reversible capacity remained at about 352 mAh/g.

Comparative example 1

Under the protection of argon atmosphere, FeSO ₄ 7H ₂ O aqueous solution was added to 20wt% Na ₂ S 9H ₂ O aqueous solution, reacted at room temperature for 0.5h, centrifuged to wash the black precipitate, and freeze-dried for 24h to obtain iron-based sulfide The electrode material has a microscopic appearance of secondary particles formed by agglomeration of nanoparticles.

A solid-state battery was assembled with Li ₁₀ GeP ₂ S ₁₂ -75Li ₂ S 25P ₂ S ₅ 1% P ₂ O ₅ double-layer solid electrolyte as the conductive medium, and metal lithium as the counter electrode, and the electrochemical performance was tested at room temperature . The charge-discharge cycle at a current density of 1000mA/g has a reversible capacity of only about 264mAh/g. This is mainly because the agglomeration of nanoparticles leads to a decrease in the contact area between the active material and the solid electrolyte and an increase in the interfacial resistance. Moreover, the large volume expansion during the cycle leads to the destruction of the electrode and the decrease of the cycle stability.

Comparative example 2

Under the protection of argon atmosphere, FeSO ₄ 7H ₂ O aqueous solution was added to 20wt% Na ₂ S 9H ₂ O aqueous solution, reacted at room temperature for 0.5h, centrifuged to wash the black precipitate, and vacuum dried at 80°C for 24h to obtain iron sulfide-based electrode materials. The microscopic appearance is micron granular.

A solid-state battery was assembled with Li ₁₀ GeP ₂ S ₁₂ -70Li ₂ S·30P ₂ S ₅ double-layer solid electrolyte as the conductive medium and metal lithium as the counter electrode, and the electrochemical performance was tested at room temperature. At room temperature, this electrode is used in solid-state batteries. After 30 charge-discharge cycles at a current density of 800mA/g, the reversible capacity is only 282mAh/g.

Comparative example 3

FeCl ₃ ·6H ₂ O (0.5mmol), Na ₂ S·9H ₂ O (2mmol) and S (2mmol) were dissolved in 30mL deionized water to form a homogeneous aqueous solution. Then 10 mL of ethylenediamine was slowly added to the above-mentioned mixed solution which was continuously stirred, and then transferred to a hydrothermal reaction kettle, heated to 160°C and kept for 12 hours. After the temperature was naturally cooled to room temperature, the precursor was obtained by ultrasonically cleaning with deionized water and absolute ethanol and then drying at 60°C for 5 hours. The precursor was placed in a vacuum furnace and heated to 250 °C for 2 h to obtain FeS.

The organic electrolyte was used as the conductive medium, and metal lithium was used as the counter electrode to assemble a half-cell, and the electrochemical performance was tested at room temperature. After 30 charge-discharge cycles at a current density of 1000mA/g, the reversible capacity is only 257mAh/g. Its cycle performance is significantly lower than that of solid-state batteries. And the organic electrolyte is used to avoid the potential safety hazards of leakage, combustion and explosion.

Comparative example 4

2g FeSO ₄ 7H ₂ O and 0.216g sucrose were dissolved in 7.5mL of deionized water to form a mixed solution, 3.45g of Na ₂ S 9H ₂ O was dissolved in 7.5mL of deionized water, and then the above two solutions were dissolved in 15mL of Uniformly disperse in absolute ethanol to obtain a suspension. Finally, the above mixed solution was transferred to a hydrothermal reaction kettle and heated to 180° C. for 18 hours. After the temperature was naturally cooled to room temperature, it was washed with deionized water and absolute ethanol and then dried to obtain the final product FeS.

The organic electrolyte was used as the conductive medium, and metal lithium was used as the counter electrode to assemble a half-cell. The electrochemical performance test was carried out at room temperature, and it was found that its reversible capacity decayed seriously. At room temperature, this electrode is used in solid-state batteries, and the reversible capacity is only 243mAh/g after 30 charge-discharge cycles at a current density of 500mA/g.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. a kind of iron-based sulfide electrode material is in the application in solid state battery, which is characterized in that the iron-based sulfide electrode Material is selected from FeS, Fe₃S₄And Fe₇S₈It is one or more；The FeS and Fe₇S₈Belong to four directions or hexagonal crystal system, the Fe₃S₄Belong to Cubic system；Also, described FeS, Fe₇S₈、Fe₃S₄Microscopic appearance be the nanometer flower structure being made of nanometer sheet, wherein appointing Dimension is lower than 100nm；

Also, the preparation method of the iron-based sulfide electrode material the following steps are included:

A) ferrous salt solution is added in polyvinyl alcohol water solution, stirs, obtains mixed solution；

B) under inert atmosphere protection, above-mentioned mixed solution is stirred with sodium sulfide solution and is reacted, reaction temperature be 0~ 100 DEG C, the time is 0.001~10h, is precipitated after reaction；

C) will be dry after precipitating centrifuge washing, obtain iron-based sulfide electrode material.

2. a kind of preparation method of iron-based sulfide electrode material, which comprises the following steps:

A) ferrous salt solution is added in polyvinyl alcohol water solution, stirs, obtains mixed solution；

B) under inert atmosphere protection, above-mentioned mixed solution is stirred with sodium sulfide solution and is reacted, reaction temperature be 0~ 100 DEG C, the time is 0.001~10h, is precipitated after reaction；

C) will be dry after precipitating centrifuge washing, obtain iron-based sulfide electrode material.

3. preparation method according to claim 2, which is characterized in that the concentration of the ferrous salt solution be 1wt%~ 80wt%；The concentration of the polyvinyl alcohol water solution is 0.01wt%~30wt%；The concentration of the sodium sulfide solution is 1wt%~80wt%.

4. preparation method according to claim 2, which is characterized in that step C) described in drying be freeze-drying or 80 DEG C of vacuum drying, drying time are 12~36h.

5. preparation method according to claim 2, which is characterized in that the ferrous salt is selected from FeSO₄·7H₂O and FeCl₂·4H₂O's is one or more.

6. a kind of solid state battery, which is characterized in that including iron prepared by preparation method described in any one of claim 2~5 Base sulfide electrode material.