Sulfate and ferrous electrode material with orthorhombic structure

Abstract

Electrode material of formula A2Fe3(SO4)4 in which A is an alkali selected from sodium (Na), lithium (Li), potassium (K) and mixtures thereof, the electrode material having a crystallographic structure.

Description

Title of the invention: Sulfated and ferrous electrode material with an orthorhombic structure technical field

[0001] The present invention relates to a material for forming a positive electrode of a battery, in particular a sodium-ion battery. It also relates to a method for manufacturing such a material. Previous technique

[0002] Iron-containing sulfated materials are of interest to the battery industry, particularly for forming a positive electrode of a sodium-ion battery.

[0003] Four Fe-containing sulfated materials are known to inventors. They exhibit electrochemical properties potentially of interest for forming a battery component. Barpanda P. et al. A 3.8-V earth-abundant sodium battery electrode / / Nat Commun. Nature Publishing Group, 2014. Vol. 5, p. 4358 describes a material of formula Na2Fe2(SO4)3 whose structure is described in the space group C2 / c, with Fe in an oxidation state of +2, and exhibiting a theoretical capacity of 120 mAh / g. It is also known from Pan IV. et al. Na2Fe(SO4)2: An anhydrous 3.6 V, low-cost and good-safety cathode for a rechargeable sodium-ion battery / / J Mater Chem A Mater. Royal Society of Chemistry, 2019. Vol. 7, No. 21. P. 13197-13204 a Na2Fe(SO4)2 material whose structure is described in the space group C2 / c, with Fe in an oxidation state +2, and exhibiting a theoretical capacity of 91 mAh / g. It is also known from Park H. et al.Monoclinic Fe2(SO4)3: A new Fe-based cathode material with superior electrochemical performances for Na-ion batteries / / J Power Sources. Elsevier BV, 2019. Vol. 434, p. 226750. A material with the formula Fe2(SO4)3 whose structure is described in the space group P2; / a, with Fe in an oxidation state of +3, and exhibiting a theoretical capacity of 133 mAh / g. It is finally known from Balic-Zunic T. et al. Eldfellite, NaFe(SO4)2, a new fumarolic ore from Eldfell volcano, Iceland 7 / Mineral Mag. Mineralogical Society, 2009. Vol. 73, No. 1. Pp. 51-57 a material with the formula NaFe(SO4)2, whose structure is described in the space group C2 / m, with Fe in an oxidation state of +3. The material has a theoretical capacity of 99 mAh / g and its electrochemical properties were reported by Singh P. et al. Eldfellite, NaFe(SO4)2: an intercalation cathode host for low-cost Na-ion batteries / / Energy Environ Sci. Royal Society of Chemistry, 2015. Vol. 8, No. 10. P.3000-3005. .

[0004] A battery that would include a material containing Fe in an oxidation state of +3 would be in a charged state, which would require a negative electrode presodium in In practice, these iron-containing sulfate materials generally require solid-state synthesis, which must be carried out under an inert atmosphere. This is because the pure phases within these materials are sensitive to humidity and can absorb water molecules, and those containing Fe2+ ions tend to oxidize readily in the presence of oxygen. Furthermore, in the cases described, grinding is performed to homogenize a mixture of precursors before a subsequent annealing step.

[0005] It is also known from Gao J. et al. Preparation, structure and properties of Na2Mn3(SO4)4: A new potential candidate with high voltage for Na-ion batteries / / J Mater Chem A Mater. Royal Society of Chemistry, 2016. Vol. 4, No. 30. P. 11870-11877 and Ben Yahia H. Crystal structure of a new polymorphic modification of Na2Mn3(SO4)4 / / Zeitschrift für Kristallo graphie - Crystalline Materials, 2019. Vol. 234, No. 11-12, P. 697-705 two polymorphic materials containing Mn of formula Na2Mn3(SO4)4. These materials crystallize in orthorhombic structures described in the space groups Cmc2 and Pbca. The Cmc2 structure is obtained from amorphous precursors of Na2SO4 and MnSO4H2O in a molar ratio of 1:3, they are mixed and annealed at 300 °C for 6 h, then annealed again for a day with several intermediate grinding steps.To obtain the Pbca structural material, the same precursors are mixed in mass proportions of 0.298 g and 1.046 g (and in molar proportions with an excess of 2 mol.% Na2SO4) and annealed at 600°C for 12 h. However, no electrochemical activity was reported for these materials.

[0006] A theoretical study conducted by Phung B. Na 2 Fe 3 (SO 4 ) 4 As a New High-Voltage Potential Cathode Material for Sodium-Ion Batteries 7 / Hue University Journal of Science: Natural Science, 2021. Vol. 130, Ne IB. P. 59-67 predicts that the compound Na2Fe3(SO4)4 would exhibit, if it existed, a potential of 4.0 V vs. Na7Na at the positive electrode of Na-ion batteries and a structure described in the space group C mc2 1.

[0007] There is therefore a need for a new sulfated crystalline material, comprising an alkali metal and iron, for the production of a battery electrode, as well as for a manufacturing process for this material which can be implemented industrially in a simple way. Description of the invention

[0008] The invention relates to an electrode material of formula A2Fe3(SO4)4 in which A is an alkali selected from sodium (Na), lithium (Li), potassium (K) and mixtures thereof, the electrode material having an orthorhombic crystallographic structure.

[0009] Advantageously, the electrode material according to the invention has an average discharge voltage and a theoretical capacity that are interesting for forming a positive electrode of an A-ion battery, in particular a sodium-ion battery.

[0010] Preferably, the orthorhombic structure of the electrode material is in the space group Pbca.

[0011] An example of a crystallographic structure in the space group Pbca is described in Ben Yahia H., Crystal structure of a new polymorphie modification of Na 2 Mn 3 (SO 4 ) 4 / / Zeitschrift für Kristallo graphie - Crystalline Materials, 2019. Vol. 234, N° 11-12, P. 697-705.

[0012] The invention also relates to a manufacturing process comprising:

[0013] a) the supply of an alkali precursor comprising alkali A and a ferrous precursor comprising Fe, at least one of the alkali and ferrous precursors comprising SO4 sulfate groups, b) the repetition of a synthesis cycle until formation of the electrode material according to the invention, the synthesis cycle being carried out in an inert atmosphere and comprising, or even consisting of, grinding the alkali and ferrous precursors in a grinding tank and a successive, or even consecutive, rest after the grinding has stopped.

[0014] The inventors have noted that repeating the synthesis cycle from the alkali precursor and the ferrous precursor makes it easy to obtain the electrode material.

[0015] During rest, the grinding tank is held stationary. In particular, it is not rotating.

[0016] Furthermore, the invention relates to a positive battery electrode, in particular selected from a positive lithium-ion (Li-ion) battery electrode, a positive sodium-ion (Na-ion) battery electrode, a positive potassium-ion (K-ion) battery electrode, a positive lithium (Li) battery electrode, a positive sodium (Na) battery electrode and a positive potassium (K) battery electrode, said positive battery electrode comprising the electrode material according to the invention or obtained according to the process of the invention.

[0017] Finally, the invention relates to a battery, preferably chosen from a lithium-ion (Li-ion) battery, a sodium-ion (Na-ion) battery, a potassium-ion (K-ion) battery, a sodium metal (Na) battery, a lithium metal (Li) battery, a potassium metal (K) battery, the battery comprising a positive battery electrode according to the invention.

[0018] Preferably, the alkali A is sodium.

[0019] The alkali precursor may have the formula A2SO4.

[0020] According to the variant where A is Na, the alkali precursor is preferably Na2SO4.

[0021] According to the variant where A is a mixture of at least two alkalis from Na, Li and K, the alkali precursor can be a mixture of at least two compounds from Na2SO4, Li2 SO4 and K2SO4 respectively.

[0022] The ferrous precursor can be of formula FeSO4xH2O, with 0 < x < 0.5.

[0023] The ferrous precursor can be dehydrated. Preferably, it is dehydrated Prior to the implementation of step a), the dehydration of the hydrated precursor is carried out under an inert atmosphere. It can be carried out at a temperature between 150 °C and 400 °C, in particular at 250 °C for a period exceeding 2 h, in particular equal to 3 h. In step a), a mixture of an alkali precursor and a ferrous precursor can be formed, in particular from a powder comprising, or even consisting of, particles made of the alkali precursor and a powder comprising, or even consisting of, particles made of the ferrous precursor.

[0024] Preferably, in step a), the alkali and ferrous precursors are supplied in a Fe / A molar ratio between 1.2 and 1.5, preferably equal to 1.25, the Fe / A molar ratio being equal to the ratio between the number of moles of Fe of the ferrous precursor and the number of moles of A of the alkali precursor.

[0025] In step b), the atmosphere is inert, which limits the oxidation of Fe. It is preferably made up of at least one inert gas, preferably argon (Ar).

[0026] Preferably, the grinding tank is airtight, except where necessary for the circulation of the gas ensuring the maintenance of an inert atmosphere within the tank. Preferably, the grinding time carried out in step b) is between 5 and 25 minutes, for example 10 minutes, and the resting time is between 3 and 40 minutes, for example 5 minutes.

[0027] Preferably, the synthesis cycle is repeated less than 150 times, for example 99 times. It can be repeated more than 100 times.

[0028] Preferably, the total duration of step b) is less than 40 hours, for example equal to 25 hours.

[0029] Preferably, the grinding in step b) is carried out in a ball mill. Preferably, the ratio of the mass of the balls to the total mass of the ferrous and alkali precursors is between 5 and 30, in particular between 5 and 20, for example equal to 10, the rotational speed of the mill being in particular between 450 rpm and 1000 rpm [revolutions per minute], for example equal to 750 rpm.

[0030] A person skilled in the art knows how to adjust the duration and power of the grinding, as well as the rest period and the number of synthesis cycles, so that the electrode material is formed. In particular, they know how to ensure that the heat supplied by the grinding is sufficient to ensure the formation of the electrode material. Preferably, the temperature of the grinding chamber at the end of step b) is above 30 °C. For example, it is between 50 °C and 250 °C. A person skilled in the art knows also avoid the formation of other undesired crystallographic phases, for example of the alluaudite type. Preferably, the temperature of the grinding vessel is less than or equal to 350 °C, preferably less than or equal to 300 °C, preferably less than or equal to 250 °C throughout the duration of step b).

[0031] The temperature of the grinding tank is for example measured by means of a thermocouple disposed in the grinding tank, for example in contact with the inner face of the wall of the grinding tank.

[0032] The invention will now be illustrated by means of the accompanying examples and figure plates in which:

[0033] [Fig. 1] represents a diffractogram of an example of the electrode material according to the invention,

[0034] [Fig.2] is a Mössbauer spectrum of the example electrode material according to the invention,

[0035] [Fig.3] are images acquired by scanning electron microscopy at magnifications different from the example of the material according to the invention,

[0036] [Fig.4] are discharge curves at different speeds representing the evolution of the voltage relative to the Na7Na couple in volts as a function of the capacitance in mAh / g of an example of electrode according to the invention. Examples

[0037] The following non-limiting examples are given for the purpose of illustrating the invention. The following raw materials were used in the examples: - alkaline precursor: Na2SO4 reference 238597-25G marketed by the company Sigma Aldrich. - Ferrous precursor: FeSO4·7H2O powder, with a purity greater than 99%, marketed by the company ReagentPlus®,

[0038] In all examples according to the invention, the ferrous precursor was first dehydrated in an argon oven at a temperature of 250 °C for 3 hours until FeSO4«%H2O was obtained with x«0.08. Example 1#:

[0039] The precursors Na2SO4 and FeSO4·%H2O with x ≈ 0.08 were mixed in a mortar, with a ratio of the number of moles of Fe to the number of moles of Na of 1.25, under an inert atmosphere. The mixture was placed in a sealed, reference ZrO2 Pulverisette Premium Line ball mill marketed by Fritsch®. The ratio of the mass of the balls to the mass of the precursor mixture was 10. A synthesis cycle consisted of 10 minutes of grinding at a speed of 750 rpm [revolutions per minute] followed by a rest period of 5 minutes. This cycle was then repeated 99 times. A total of 100 cycles were therefore performed. The final powder, designated compound 1, was extracted from the grinder.

[0040] Figure 1 shows a powder X-ray diffractogram of compound 1, refined using the Rietveld method. The structure of compound 1 is described in the Pbca space group. The X-ray diffraction measurement was performed with a Bruker D8 Discover diffractometer with a molybdenum source (Kai = 0.7093 Å, Ka2 = 0.7135 Å). The measurement was carried out in the Debye-Scherrer configuration, and compound 1 was sealed in a capillary under an inert atmosphere to prevent any possible evolution.

[0041] Figure 2 shows a Mössbauer spectrum of compound 1, which contains only iron in the form of Fe2+ ions in a high-spin state, typical of the Fe2+ ion in sulfates. Deconcentration of the spectrum allows us to distinguish two different local environments for the Fe2+ ions; the first doublet with a lower shift can be attributed to an Fe2+ ion surrounded by less oxygen in the structure than the second Fe2+ site.

[0042] Figure 3 shows two images of compound 1 obtained by scanning electron microscopy. The sample obtained consists of aggregates composed of small particles without a precise morphology, typical of a homogenate. Example 2#:

[0043] To prepare an electrode, the powder of compound 1 was mixed in a mortar with carbon black and polytetrafluoroethylene (PTFE, of the Sigma-Aldrich brand at 99.9% purity) for a total of 100% by mass distributed as follows: 75% of compound 1, 20% of carbon black and 5% of PTFE.

[0044] The theoretical capacity for the electrode material of formula Na2Fe3(SO4)4 of structure Pb ca is 90 mAh / g.

[0045] Electrochemical tests were performed using the formed electrode as the positive electrode of a CR2032 format battery, with a sodium reference electrode, the assembly having been installed under an argon atmosphere. Two sheets of Viledon and Celgard® tempered glass fibers were placed between the two electrodes to act as a separator and electrolyte reservoir. The electrolyte consisted of IM NaPF6 dissolved in a mixture of ethylene carbonate and dimethyl carbonate. The ratio of the volume of ethylene carbonate to the mass of dimethyl carbonate was 1. In addition, the electrolyte contained fluoroethylene carbonate, which constituted 2% of its mass. The battery containing compound 1 was electrochemically tested at constant current in a series of cycles, each consisting of a charge followed by a discharge, at a temperature of 25°C.

[0046] Figure 4 shows the discharge curves of compound 1 obtained with different current densities of D / 30, D / 20, D / 10, D / 5, D / 2, and D, calculated considering the exchange of two electrons. At a current density of D / 30, the electrode containing the electrode material according to the invention has a capacity of 62 mAh / g with an active material mass charge of 18 mg / cm², or 1.4 mAh / cm². At a current density of D, the electrode containing the electrode material according to the invention has a capacity of 53 mAh / g with an active material mass charge of 18 mg / cm², or 0.954 mAh / cm². This value is more than three times higher than that obtained for other Na, Fe and S based phases such as Na2Fe2(SO4)3 which delivers 80 mAh / g at D / 5 with a mass charge of active material of 3 mg / cm2 or 0.24 mAh / cm2.

[0047] As is apparent from reading the description, the electrode material according to the invention has electrochemical properties which make it particularly well suited for a battery electrode application.

Claims

Demands

1. Electrode material of formula A2Fe3(SO4)4 in which A is an alkali selected from sodium (Na), lithium (Li), potassium (K) and mixtures thereof, the electrode material having an orthorhombic crystallographic structure.

2. Electrode material according to claim 1, the orthorhombic structure of the electrode material being in the space group Pbca.

3. Electrode material according to any one of claims 1 and 2, alkali A being sodium.

4. A manufacturing process comprising: a) supplying an alkali precursor comprising alkali A and a ferrous precursor comprising Fe, at least one of the alkali and ferrous precursors comprising SO4 sulfate groups, b) repeating a synthesis cycle until formation of the electrode material according to any one of the preceding claims, the synthesis cycle being carried out in an inert atmosphere and comprising, or even consisting of, grinding the alkali and ferrous precursors in a grinding tank and successive, or even consecutive, rest after stopping the grinding.

5. Method according to the preceding claim, the ferrous precursor being FeSO4xH2O, with 0 < x < 0.

5.

6. A process according to any one of claims 4 and 5, the alkali precursor having the formula A2SO4, preferably being Na2SO4

7. 4* Method according to any one of claims 4 to 6, the alkali and ferrous precursors being supplied in a Fe / A molar ratio of between 1.2 and 1.5, preferably equal to 1.25, the Fe / A molar ratio being equal to the ratio of the number of moles of Fe of the ferrous precursor to the number of moles of A of the alkali precursor.

8. A method according to any one of claims 4 to 7, the grinding time being between 5 and 25 minutes, for example equal to 10 minutes, and the resting time being between 3 and 40 minutes, for example equal to 5 minutes.

9. A method according to any one of claims 4 to 8, the cycle being repeated less than 150 times, for example 99 times.

10. A method according to any one of claims 4 to 9, the total duration of step b) being less than 40 hours, for example equal to 25 hours.

11. A method according to any one of claims 4 to 10, the grinding being carried out in a ball mill, preferably with a ratio of the mass of the balls to the total mass of the ferrous and alkali precursor between 5 and 30, for example equal to 10, the rotation speed of the mill being in particular between 450 rpm and 1000 rpm [rotations per minute], for example equal to 750 rpm.

12. A method according to any one of claims 4 to 11, the inert atmosphere being formed of at least one inert gas, preferably argon.

13. Positive battery electrode, in particular selected from a positive lithium-ion (Li-ion) battery electrode, a positive sodium-ion (Na-ion) battery electrode, a positive potassium-ion (K-ion) battery electrode, a positive lithium (Li) battery electrode, a positive sodium (Na) battery electrode and a positive potassium (K) battery electrode, said positive battery electrode comprising the electrode material according to any one of claims 1 to 3 or obtained by the process according to any one of claims 4 to 12.

14. Battery, preferably selected from a lithium-ion (Li-ion) battery, a sodium-ion (Na-ion) battery, a potassium-ion (K-ion) battery, a sodium metal (Na) battery, a lithium metal (Li) battery, a potassium metal (K) battery, the battery comprising a positive battery electrode according to the preceding claim.

Images