Sodium iron hydroxysulfide compound, method for producing said compound, active material containing said compound, and electrochemical electrode produced from said active material

Abstract

A sodium iron hydroxysulfide compound, a method for making the compound, an active material containing the compound, and an electrochemical electrode made from the active material. x [Fe(OH)2] y A method for producing a compound of FeS, said method comprising the following steps: a. mixing equimolar amounts of iron and sodium sulfide in an aqueous NaOH solution, b. heating the mixture obtained to a temperature comprised between 110°C and 210°C for a period comprised between 1 hour and 1 week, c. recovering the active material by filtration and drying in a neutral atmosphere.

Description

[Technical field]

[0001] Energy storage electrochemical systems have important applications in the fields of mobile electronics and electric vehicles. One of the most commonly used battery accumulator technologies is based on the use of lithium ions.

[0002] The very widespread popularity of these lithium technologies currently raises many questions in terms of the cost of lithium and in terms of the associated mineral reserves. Indeed, the price of lithiated precursors (e.g. Li2CO3) has tripled in the last 20 years, and the sources of lithium are geographically very limited (Slater, MD, Kim, D., Lee, E., & Johnson, CS (2013). Sodium‐ion batteries. Advanced Functional Materials, 23(8), 947-958). For these reasons, much research is being carried out to develop alternative technologies. Of these, sodium‐ion based batteries are of particular interest.

[0003] Like Li-ion batteries, Na-ion batteries use electrode materials, so-called "active materials", that allow the insertion and de-insertion of sodium ions during the charging and discharging process. These insertions and de-insertions should be reversible so that the accumulator can store energy over many cycles. A good mobility of the sodium ions in the structure, and also a good electrical conductivity of the electrode materials, are essential properties to allow these batteries to be used at high charging and discharging rates and to allow high power. The specific power (W / kg) of the battery is of great interest for vehicle applications, since this allows the use of lighter batteries for the same effort and also allows the batteries to be used in safer conditions.

[0004] Although many anode materials (sulfides, oxides, carbon-based materials) are listed in the Li-ion battery literature, few have proven to be of real interest as anode active materials for Na-ion batteries. In particular, the sulfide and hydroxysulfide classes have been little studied. However, the high valency of the sulfides ensures good mobility for sodium ions and good electron mobility (which ensures good electrical conductivity). Many transition metal sulfides (MoS2, TiS2) have a lamellar structure, and sodium can diffuse rapidly and in large quantities between the lamellae, giving the compounds good capacity (the number of sodium ions or charges that can be inserted by the mass of the electrode, expressed in mAh). Furthermore, the disadvantage of sulfides is related to the mass of sulfur and also to the soft nature (in a mechanical sense) of these compounds, which leads to considerable deformations during sodium insertion / deinsertion, often resulting in mechanical ageing and battery swelling. In addition, these compounds do not contain sodium, and batteries should be made with metallic sodium in mind, or with low potential compounds that already contain sodium.

[0005] Prior Art In the prior art, Li et al. (Large-scale synthesis of highly uniform Fe1-xS nanostructures as a high-rate anode for sodium ion batteries - Nano Energy - Volume 37, 1 July 2017, Pages 81-89 - DOI: 10.1016 / j.nanoen.2017.05.012), Li, L., Peng, S., Bucher, N., Chen, H.-Y., Shen, N., Nagasubramanian, A., Eldho, E., Hartung, S., Ramakrishna, S., Srinivasan, M) disclose the use of iron sulfide in sodium battery anodes and their high charge capacity in certain structures, however, the product does not initially contain sodium.

[0006] Disclosure of the Invention The subject of the present invention is a compound of formula (NaOH) x [Fe(OH)2] y It is a compound of FeS (wherein x and y are in the range between 0 and 1).

[0007] Another subject of the invention is a compound of formula (NaOH) x [Fe(OH)2] y A method for producing a compound of FeS, wherein x and y are in the range of 0 to 1, comprising the steps of: a. Mixing equimolar amounts of iron and sodium sulfide in an aqueous NaOH solution; b. heating the mixture obtained to a temperature comprised between 110°C and 210°C for a period comprised between 1 hour and 1 week; c. A step of recovering the active material by filtering and drying in a neutral atmosphere. Includes.

[0008] The iron content (by mass) may be 0.56 g and the sodium sulfide content (by mass) may be 2.6 g.

[0009] The concentration of the aqueous NaOH solution may be in the range of 1 to 10 mol / l, preferably 1 mol / l.

[0010] The heating period may be for 4 days.

[0011] The heating temperature may be 160°C.

[0012] Drying may be carried out at 90° C. for 4 hours under a dry nitrogen atmosphere.

[0013] Another subject of the invention is a negative electrode for a sodium-ion battery, comprising at least one active material according to the above compound.

[0014] The content of the active material may be in the range of 50% by weight to 97% by weight, and is preferably 97% by weight, based on the total weight of the negative electrode.

[0015] The negative electrode may further comprise at least one additional conductive compound.

[0016] The further conductive compound may be selected from metal particles, carbon, and mixtures thereof, preferably carbon.

[0017] The carbon may be in the form of graphite, carbon black, carbon fibers, carbon nanowires, carbon nanotubes, or carbon nanospheres, and is preferably in the form of carbon black.

[0018] The content of the further conductive compound is in the range of 3 to 50% by weight, preferably in the range of 3 to 20% by weight, based on the total weight of the negative electrode.

[0019] Another subject of the invention is a sodium-ion battery comprising at least one negative electrode as defined above.

[0020] In particular, the negative electrode for a Na-ion battery has the following advantages: Na4Ti5O in low and high regimes 12 Larger capacity than the material, up to 110mAh / g after 10 hours of charging and discharging - Made from materials produced by aqueous synthesis, which shortens the synthesis time compared to conventional technologies; and Made of materials that promote good reversible mobility of sodium.

[0021] Other objects, features and advantages of the present invention will appear more clearly on reading the following description, given by way of non-limiting example only and referring to the accompanying drawings, in which: [Brief description of the drawings]

[0022] [Figure 1] The galvanostatic regime behaviour of the compounds is shown. [Diagram 2]1 shows the evolution of the capacity of an electrochemical half-cell with two electrodes under different charging regimes. [Diagram 3] The galvanostatic regime behavior of the compound in an electrochemical half-cell with two electrodes (active material / electrolyte / metallic sodium) is shown in different discharge regimes.

[0023] Detailed Description Formula (NaOH) x [Fe(OH)2] y The iron sodium hydroxysulfide compound FeS, where x and y are in the range between 0 and 1, has a lamellar structure in which iron sulfide FeS lamellae alternate with sodium hydroxide and / or iron hydroxide lamellae. The compound thus formed is of the ionic covalent type.

[0024] Sodium iron hydroxysulfide compound (NaOH) x [Fe(OH)2] y The method for producing FeS is based on a reaction involving an equimolar mixture of iron and sulfur in aqueous NaOH. Heating may be required to obtain a stoichiometric and well-crystallized phase.

[0025] A first embodiment of the manufacturing method is as follows: 0.56 g of iron powder and 2.6 g of sodium sulfide nonahydrate (Na2S,9H2O) are mixed in 30 ml of an aqueous solution of sodium hydroxide (NaOH) (concentration 1 mol / l). The whole is heated without stirring at 160°C for 4 days in a closed pressure-resistant space, in particular an autoclave. After cooling to room temperature, the solution contains a black precipitate. The solution is filtered to isolate the precipitate, which is then dried for 4 hours at 90°C under a dry nitrogen atmosphere. After drying, the precipitate is crushed, revealing (NaOH) x [Fe(OH)2] y A fine powder of FeS (where x=0.5, y=0.75) is obtained.

[0026] This compound can then be used as the active material in an electrode. For example, an electrode made of the active material can be made of (NaOH) x [Fe(OH)2] y The compound is prepared by grinding 200 mg of FeS with 50 mg of Timcal® SuperC65 carbon (used as an additional conductive compound) (80:20 mixture) in an agate mortar. In some specific embodiments, (NaOH) x [Fe(OH)2] y The mixture of FeS compounds and carbon may contain additives, especially polymers, that enable it to maintain its cohesion.

[0027] To perform electrochemical characterization of the active material electrodes by electrostatic cycling, an electrochemical cell with two electrodes is prepared in a glove box using a device (Swagelok®, diameter 12 mm). In the Swagelok® device, a first layer of 25 mg of the active material-carbon mixture and two layers (a separator made of glass microfiber (Whatman® CAT No. 1823-070), cut to the appropriate diameter and saturated with electrolyte, and a pure sodium sheet (Sigma-Aldrich®), cut with a die and pressure bonded) are placed against a current collector made of stainless steel (Alfa Aesar®). The electrolyte used is sodium salt (NaPF6) at a concentration of 1.0 mol / l dissolved in an equal volume mixture of ethyl carbonate and diethyl carbonate.

[0028] After installation was completed, the cell was cycled in a BioLogic® cycle tester at C / 10 (charge and discharge in 10 hours) with Na / Na + The pair is subjected to electrochemical testing in a static cycle operated between 3 V and 1 V relative to the potential.

[0029] FIG. 1 shows the electrostatic regime behavior of the compound in an electrochemical half-cell with two electrodes (active material / electrolyte / metallic sodium) (charged for 10 h). The first discharge makes it possible to reach an irreversible capacity of 75 mAh / g with the insertion of 0.5 Na. The next cycle leads to a reversible capacity of 110 mAh / g with the insertion of 0.7 Na. The average potential reached during the reversible cycle is Na / Na + Therefore, this active material can be used as a negative electrode.

[0030] Figure 2 shows the evolution of the capacity of an electrochemical half-cell with two electrodes under different charging regimes (charge / discharge times of 10, 5, 3, 1, 2 and 12 min). A fast charge of 20 min results in a loss of 50% of the capacity (compared to a charge / discharge time of 10 h).

[0031] In a second embodiment of the present method, the concentration of the aqueous sodium hydroxide solution is different. The second embodiment of the present method is as follows: 0.56 g of iron powder and 2.6 g of sodium sulfide nonahydrate (Na2S,9H2O) are mixed in 30 ml of aqueous NaOH solution (concentration 3 mol / l). The set is heated without stirring at 160°C for 4 days in a closed pressure-resistant space, in particular an autoclave. After cooling to room temperature, the solution contains a black precipitate. The solution is filtered to isolate the precipitate, which is then dried for 4 hours at 90°C under a dry nitrogen atmosphere. After drying in this way, the precipitate is ground, revealing (NaOH) x [Fe(OH)2] y A fine powder of the compound FeS (where x=0.5, y=0.25) is obtained (yield about 80%).

[0032] The compound obtained by the second embodiment of the process is characterized in a similar manner to the compound obtained by the first embodiment of the process.

[0033] Figure 3 shows the electrostatic regime behavior of the compound in an electrochemical half-cell with two electrodes (active material / electrolyte / metallic sodium) at different discharge regimes. The capacity of the compound is 70 mAh / g in the C / 10 regime (charge / discharge in 10 h) and 43 mAh / g when charged in 20 min.

Claims

1. Formula (NaOH) ｘ [Fe(OH) ２ ] ｙ A compound of FeS.

2. 2. The compound of claim 1, wherein the molar fractions of x and y range between 0 and 1.

3. Formula (NaOH) ｘ [Fe(OH) ２ ] ｙ 1. A method for producing a compound of FeS, comprising the steps of: a. Mixing equimolar amounts of iron and sodium sulfide in an aqueous NaOH solution; b. Heating the resulting mixture to a temperature comprised between 110°C and 210°C for a period comprised between 1 hour and 1 week; c. Recovering the active material by filtering and drying in a neutral atmosphere. A manufacturing method comprising:

4. 4. The method of claim 3, wherein the mass of iron is 0.56 g and the mass of sodium sulfide is 2.6 g.

5. 4. The method according to claim 3, wherein the concentration of the aqueous NaOH solution is in the range of 1 to 10 mol / l, preferably 1 mol / l.

6. The method according to claim 3, wherein the heating period is 4 days.

7. The method according to claim 3, wherein the heating temperature is 160°C.

8. 4. The process of claim 3, wherein drying is carried out at 90° C. for 4 hours under a dry nitrogen atmosphere.

9. 10. A negative electrode for a sodium-ion battery comprising at least one active material according to the compound of claim 1.

10. 10. The negative electrode according to claim 9, characterized in that the content of active material is in the range of 50 to 97% by weight, preferably 97% by weight, relative to the total weight of the negative electrode.

11. 10. The negative electrode of claim 9, further comprising at least one additional conductive compound.

12. 12. Anode according to claim 11, characterized in that the further conductive compound is selected from metal particles, carbon and mixtures thereof, preferably carbon.

13. 13. The anode of claim 12, wherein the carbon is in the form of graphite, carbon black, carbon fibers, carbon nanowires, carbon nanotubes, or carbon nanospheres, preferably in the form of carbon black.

14. 12. Anode according to claim 11, characterized in that the content of the further conductive compound is in the range of 3 to 50% by weight, preferably in the range of 3 to 20% by weight, relative to the total weight of the anode.

15. A sodium-ion battery comprising at least one negative electrode according to claim 9.

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