Pretreatment process for an anode for an electrochemical cell of an electric battery

Abstract

A pretreatment process for an anode for an electrochemical battery cell, comprising the following steps: a) supplying an anode, b) placing the anode in the presence of sulfuryl fluoride (SO2F2) gas until a layer comprising the -F and -SO2F groups forms on the surface of the anode, c) removing the SO2F2 gas to stop the reaction between the SO2F2 and the anode material, and d) recovering the pretreated anode obtained.

Description

Title of the invention: Method for pretreating an anode for an electrochemical cell of an electric battery technical field

[0001] The present invention relates, in general, to electric batteries, such as an electric battery for a motor vehicle and, more specifically, to the lifespan of an electric battery.

[0002] More specifically, the invention relates to a method for pretreating an anode for an electrochemical cell of an electric battery, as well as to an anode assembly comprising a pretreated anode, an electrochemical cell incorporating such an anode assembly and an electric battery comprising such an electrochemical cell. Previous techniques

[0003] An electrochemical cell of an electric battery comprises a positive electrode called the "cathode", a negative electrode called the "anode", an electrolyte allowing the circulation of ions between the anode and the cathode, and anodic and cathodic current collectors carrying, respectively, the anode and the cathode and connecting them to the external circuit.

[0004] The performance of a battery depends on the ionic and electronic transport properties.

[0005] Thermodynamic reactions are initiated during the first charging cycle of the electrochemical cell, and the first ion exchanges between the electrodes take place. Products resulting from these reactions accumulate on the surface of the electrodes to form a layer called the solid-electrolyte interface or SEI layer.

[0006] In a lithium-ion battery, this layer is an essential element for the proper functioning of the electric battery because it conducts lithium ions very well and has the advantage of stopping the catalytic decomposition of the liquid electrolyte solvent.

[0007] The quality of the SEI layer determines the battery life and its formation is therefore an important step.

[0008] Alkali metal anodes such as lithium are the most attractive candidates because of their high energy density.

[0009] However, their volume is considerably altered during the cycle, which can lead to various mechanical problems in the electrochemical cell. The radical change in volume results in continuous exposure of the anode to the reactive contents of the electrolyte. In addition, the SEI layer is strongly bonded to the anode surface so that the SEI layer can be strongly deformed during the cycle.

[0010] It is well known that a high lithium fluoride (LiF) SEI layer, formed on an anode, exhibits exceptional stability during cycles, suppressing SEI deformation by anode volume change and dendrite formation.

[0011] Classically, the LiF-rich SEI layer is formed in-situ by the addition of additives and / or solvents, such as fluoroethylene carbonate (FEC).

[0012] FEC or its derivatives confer remarkable ring stability, but its transport properties, such as ionic conductivity and transfer number, are limited. In other words, the use of such fluorine-containing materials for the formation of the LiF-rich SEI layer therefore limits the electrolyte design.

[0013] Furthermore, the use of fluorine-containing materials to form the LiF-rich SEI layer on an anode generates certain adverse effects.

[0014] In particular, LiPF6 was selected several decades ago for Li-ion batteries because it can serve as a source of LiF for the SEI layer on the anode and as a passivation layer on the current collector. The decomposition of LiPF6 leads, in the presence of water, to the formation of HF. However, HF is a highly corrosive compound and can destroy the electrodes, the SEI layer, and the passivation layer of the current collector. Description of the invention

[0015] The present invention therefore aims to overcome the aforementioned disadvantages and to improve the stability of an electrochemical cell during its charge and discharge cycles in order to increase its lifespan and the lifespan of the electric battery incorporating such an electrochemical cell.

[0016] In the description of the invention which will be given, the expression "at least one" used shall be considered equivalent to the expression "one or more".

[0017] Furthermore, it is specified that the expression "between ... and ..." used in this description of the invention should be understood as including each of the limits mentioned.

[0018] The present invention relates to a pretreatment method for an anode for an electrochemical cell of an electric battery, comprising the following steps:

[0019] a) provide an anode,

[0020] b) place the anode in the presence of sulfuryl fluoride gas (SO2F2) until a layer comprising the -F and -SO2F groups forms on the surface of the anode,

[0021] c) remove the SO2F2 gas, and

[0022] d) recover the pre-treated anode obtained.

[0023] In step b), the SO2F2 gas reacts with the anode material. The reaction leads to the formation of a layer comprising a compound including the anode material and an -F group and a compound including the anode material and an -SO2F group.

[0024] The layer obtained, with a high content of -F and -SO2F groups, forms on the surface of the anode. Such anode pretreatment is particularly advantageous for using the resulting layer as an SEI layer in an electrochemical battery cell.

[0025] The pretreatment process according to the invention makes it possible to manufacture, by a simple, fast, and inexpensive means, an artificial SEI layer on the anode by an ex situ method.

[0026] The resulting SEI layer is rich in fluorine, the SO2F2 gas being a source of both -F and -SO2F groups. Due to the presence of such an SEI layer, the stability of the anode and the electrochemical cell is improved.

[0027] Furthermore, the pretreatment process according to the invention does not require any solvent or additive so that it can be easily adapted for large-scale use.

[0028] In one embodiment, the anode provided in step a) can be an alkali metal anode, such as lithium, potassium or sodium, or a mixture of alkali metals.

[0029] For example, the alkali metal of the anode can be lithium. The SEI layer thus formed in step b) has a high content of LiF and LiSO2F compounds. The SO2F2 gas alone acts as the source of LiF and LiSO2F.

[0030] In another embodiment, the anode provided in step a) can be a graphite anode for the formation in the presence of SO2F2 in step b), of a layer comprising the -F and -SO2F groups on the surface of the graphite anode.

[0031] When the anode is made of graphite, step b) is preferably carried out in the presence of at least one base and at least one solvent, in addition to the SO2F2 gas.

[0032] Advantageously, step b) can be carried out in the presence of a solvent such as toluene and a base such as 4-dimethylaminopyridine (DMAP).

[0033] For example, the base, which may be DMAP, may be present in a content of between 1 and 2% by weight.

[0034] The surface of graphite is generally not uniform and contains many defects, such as -OH, -OOC, -OOH groups, etc. The reaction between the graphite anode and the SO2F2 gas allows these defects to be replaced by -F and -SO2F groups, in order to improve the stability of the graphite anode.

[0035] The presence of a layer containing the -F and -SO2F groups to replace defects on the surface of the graphite improves the overall reactivity of the The surface of the graphite relative to the electrolyte when the anode is incorporated into an electrochemical cell. In this way, the SEI layer can be formed more homogeneously across the entire surface of the anode.

[0036] Furthermore, the replacement of defects, in particular -OH, by the -F and -SO2F groups makes it possible to avoid the formation of the HF compound which is corrosive, in gaseous phase at room temperature, and which has the disadvantage of destructuring the graphite in the electrochemical cell.

[0037] Also, the -SO2F group on the graphite defects is likely to facilitate the formation of the SEI layer on the graphite anode.

[0038] Depending on the desired thickness of the SEI layer, the duration of the gas contact with the anode in step b) can be adjusted.

[0039] Preferably, step b) is carried out for a duration of between 5 and 60 s.

[0040] According to examples, the duration of step b) can be 5 s, 15 s, 30 s or 60 s.

[0041] Preferably, step c) is carried out by replacing the SO2F2 gas with an atmosphere An inert atmosphere, such as argon, is used to stop the reaction and prevent any unwanted side effects. Replacing the SO2F2 gas with an inert atmosphere also allows for better control of the thickness of the SEI layer formed.

[0042] Advantageously, the anode comprises a first face intended to come into contact with an electrolyte of the electrochemical cell, and a second face opposite to the first face.

[0043] The pretreatment process may include, prior to step b), a masking step of the second face of the anode so as to form the SEI layer only on the first face intended to come into contact with the electrolyte.

[0044] The invention also relates to an anode assembly for an electrochemical cell of an electric battery comprising an anode and an SEI layer disposed on the surface of the anode and comprising the -F and -SO2F groups.

[0045] The anode of the anode assembly can be made of alkali metal, such as lithium, potassium or sodium.

[0046] According to an alternative, the anode of the anode assembly can be made of graphite.

[0047] Advantageously, the SEI layer is disposed on the first face of the anode intended to come into contact with the electrolyte.

[0048] Preferably, the thickness of the SEI layer formed is on the order of a few nm to 100 nm.

[0049] The invention also relates to an electrochemical cell for an electric battery comprising an assembly as previously described.

[0050] The electrochemical cell may comprise a cathode, and an anode assembly as previously described, an electrolyte allowing the circulation of ions between the anode and the cathode, and anodic and cathodic current collectors carrying, res Specifically, the anode and the cathode. The SEI layer of the anode assembly is positioned opposite the electrolyte.

[0051] The invention also relates to an electric battery comprising at least one electrochemical cell as previously described.

[0052] The electric battery may incorporate a lithium metal anode, an anode of an alkali metal other than lithium, for example sodium or potassium, an anode of a mixture of alkali metals, or a graphite anode.

[0053] The electric battery can be a lithium-ion battery, a lithium-air battery, a lithium-sulfur battery or a battery incorporating an anode of an alkali metal other than lithium.

[0054] In one embodiment, the anode assembly may include a lithium metal anode and an SEI layer comprising LiF and LiSO2F compounds.

[0055] The presence of the SEI layer, and in particular of the LiF and LiSO2F compounds, leads to stabilizing the anode during charge and discharge cycles by curbing the increase in the volume of the anode and the formation of dendrites, which results in a prolonged battery life.

[0056] LiF, which gives high mechanical properties to the SEI layer, contributes greatly to improving the stability of the anode.

[0057] LiSO2F also participates in the stability of the anode and compensates for the low ionic conductivity of LiF by contributing to a uniform transfer of Li+ in the plane of the SEI layer.

[0058] This results in significant stability of the Li metal during cycling obtained by a synergistic effect of LiF and LiSO2F.

[0059] The invention also relates to a motor vehicle comprising at least one electric battery as previously described. Example

[0060] Ex situ formation of a SEI layer on a lithium metal anode

[0061] A lithium metal plate is placed on a glass or polytetrafluoroethylene (PTFE) plate. PTFE tape is applied to the edges of one side of the lithium metal plate so that the second side, opposite the first and in contact with the glass or PTFE plate, is masked. The plate is then placed in a double-necked flask, the flask is sealed with a rubber stopper, and then placed under an argon atmosphere using a medical needle inserted through the stopper.

[0062] Under a fume hood, a stream of SO2F2 gas is introduced into the balloon using a medical needle inserted through the stopper. The argon atmosphere is replaced by SO2F2. After a period of a few seconds to 1 minute, depending on the desired thickness, a SEI layer is formed on the first face of the lithium metal plate. The balloon is then purged with argon to stop the reaction.

[0063] The pretreated lithium metal plate obtained is stored in a glove box filled with argon until its use in an electrochemical cell.

Claims

Demands

1. A method for pretreating an anode for an electrochemical cell of an electric battery, comprising the following steps: a) providing an anode, b) placing the anode in the presence of sulfuryl fluoride (SO2F2) gas until a layer comprising the -F and -SO2F groups forms on the surface of the anode, c) removing the SO2F2 gas to stop the reaction between the SO2F2 and the anode material, and d) recovering the pretreated anode obtained.

2. A method according to claim 1, wherein the anode supplied in step a) is an alkali metal anode.

3. A method according to claim 2, wherein the alkali metal of the anode is lithium metal, the layer formed in step b) comprising LiF and LiSO2F compounds.

4. A method according to claim 1, wherein the anode supplied in step a) is a graphite anode, step b) is carried out in the presence of at least one base and at least one solvent.

5. A method according to any one of the preceding claims, wherein step c) is carried out by replacing the SO2F2 gas with an inert atmosphere, such as argon.

6. A method according to any one of the preceding claims, wherein step b) is carried out for a duration of between 5 and 60 s.

7. Anode assembly for an electrochemical cell of an electric battery comprising an anode and a layer disposed on the surface of the anode comprising the -F and -SO2F groups.

8. Anode assembly according to claim 7, wherein the anode is made of alkali metal, such as lithium, sodium or potassium, of a mixture of alkali metals, or of graphite.

9. Electrochemical cell for electric battery comprising an anode assembly as defined in claim 7 or 8.

10. Electric battery comprising at least one electrochemical cell as defined in claim 9.

11. Motor vehicle comprising at least one electric battery as defined in claim 10.