Polymer electrolyte for all-solid-state batteries, particularly lithium-metal batteries

Abstract

Polymer electrolyte comprising at least one polymer and at least one electrolyte salt, the polymer comprising polyethylene glycol borate ester and poly(4-vinylpyridine).

Description

Title of the invention: Polymer electrolyte for all-solid-state batteries, in particular for lithium-metal batteries technical field

[0001] The present invention relates to the field of all-solid-state batteries, such as lithium-metal batteries.

[0002] More particularly, the present invention relates to a polymer electrolyte and a method for preparing said electrolyte. The invention also relates to an electrochemical battery cell comprising said electrolyte, an all-solid-state battery comprising said electrochemical cell, and a motor vehicle comprising such a battery. Previous techniques

[0003] In a conventional manner, all-solid-state batteries comprise one or more positive electrodes, one or more negative electrodes, a solid electrolyte forming a separator, an anodic current collector and a cathodic current collector.

[0004] The performance of a battery depends on its ionic and electronic transport properties. In the case of an all-solid-state battery, ionic transport at the electrode scale occurs through the network formed by the solid electrolyte, which creates ionic conduction pathways throughout the entire volume of the electrode for the transport of ions to or from all the particles of active material.

[0005] All-solid-state batteries use different types of solid electrolyte materials. In particular, there are two main branches in the field of solid (or solid-state) electrolytes: ceramics (or inorganic electrolytes) and solid polymer electrolytes, which can be called EPS.

[0006] Poly(ethylene glycol) borate ester polymer, abbreviated BPEG or BPEO, is attracting increasing interest as a polymer electrolyte due to its high electrochemical stability towards lithium metal and its ability to increase the number of transfers by immobilizing the lithium salt counter-anion.

[0007] It also exhibits a higher ionic conductivity than a linear polymer electrolyte based on poly(ethylene glycol) (PEG).

[0008] In BPEO, the crystallinity of the PEG polymer is reduced by the presence of boron atoms which give BPEO a dendrimer-type structure.

[0009] However, although the decrease in crystallinity induces an increase in the ionic conductivity of BPEO compared to PEG, it also leads to a decrease in its mechanical stability.

[0010] Due to its low mechanical stability, BPEO does not prevent the formation of lithium dendrites, so its use as a solid polymer electrolyte is limited.

[0011] In addition, the ionic conductivity and self-healing capabilities of BPEO can be improved.

[0012] There is therefore a need to develop a new polymer electrolyte to overcome the above disadvantages. Description of the invention

[0013] The present invention therefore aims to overcome the aforementioned drawbacks and to improve the mechanical stability, ionic transport properties and self-healing capacity of a polymer electrolyte incorporating poly(ethylene glycol) borate ester (BPEO).

[0014] 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".

[0015] 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.

[0016] The present invention relates to a polymer electrolyte for a battery, in particular an all-solid battery, comprising at least one polymer and at least one electrolyte salt.

[0017] The polymer comprises poly(ethylene glycol) borate ester and poly(4-vinylpyridine).

[0018] Preferably, the polymer is derived from a monomer of the following formula (I):

[0019] Where n, m and p represent integers, identical or different, ranging from 1 to 22800, preferably between 1 and 45.

[0020] RI, R2 and R3 are identical or different groups, selected from: a borate group (-O-BR4), a hydroxyl group (-OH), an alkyl chain comprising from 1 to 10 carbon atoms, preferably from 1 to 6, for example a methyl group (-CH3) or ethyl group (-CH2CH3), a polymerizable group, preferably a group comprising at least one C=C double bond, such as a vinyl group (-CH=CH2), an azide group (-N3), an alkyne group and possibly the combination of an azide group (-N3) and an alkyne group.

[0021] R4 is selected from: a hydroxyl group (-OH), an alkyl chain comprising from 1 to 10 carbon atoms, preferably from 1 to 6, for example a methyl group (-CH3) or ethyl group (-CH2CH3), a polymerizable group, preferably a group comprising at least one C=C double bond, such as a vinyl group (-CH=CH2), an azide group (-N3), an alkyne group and possibly the combination of an azide group and an alkyne group.

[0022] The nitrogen atoms of the poly(4-vinylpyridine) form a covalent coordination bond with the boron atoms of the BPEO so that the nitrogen atoms thus act as crosslinking agents in the BPEO-based polymer matrix.

[0023] The self-healing capacity of polymers depends on the quantity of reversible bonds. The reversible covalent coordination bond between boron and nitrogen adds to the reversible bonds formed between the boron and oxygen atoms of BPEO, so that the self-healing properties of the polymer electrolyte according to the invention are improved.

[0024] The covalent coordination bond between boron and nitrogen further implies a significant increase in the mechanical stability of BPEO.

[0025] Furthermore, the presence of nitrogen limits the intermolecular interactions between the PEG chains of BPEO, leading to the suppression of BPEO crystallinity. This results in an increase in the ionic conductivity of the polymer electrolyte according to the invention compared to the BPEO polymer.

[0026] In one embodiment, the polymer electrolyte consists of at least one polymer and at least one electrolyte salt, the polymer consisting of poly(ethylene glycol) borate ester and poly(4-vinylpyridine).

[0027] In one embodiment, the polymer electrolyte consists of at least one polymer and at least one electrolyte salt, the polymer comprising poly(ethylene glycol) borate ester and poly(4-vinylpyridine).

[0028] Advantageously, the molecular weight of PEG can be between 62 g / mol and 100,000,000 g / mol, preferably between 200 g / mol and 10,000 g / mol, more preferably between 400 g / mol and 2,000 g / mol.

[0029] Advantageously, the molecular weight of poly(4-vinylpyridine) can be between 500 g / mol and 100,000 g / mol.

[0030] Preferably, the molar ratio of 4-vinylpyridine to BPEO can be between 0.1 and 20, preferably between 0.1 and 10.

[0031] Preferably, the molar ratio of the electrolyte salt, such as a lithium salt, to the 4-vinylpyridine is between 0.1 and 5.

[0032] Preferably, the electrolyte salt is a lithium salt.

[0033] Advantageously, said electrolyte salt is selected from LiPF6, LiFSI, LiTFSI, LiClO4, LiAsF6, LiBF4, Lil, LiN(CF3SO2)2, LiCF3SO3, LiN(CF3CF2SO2)2, LiCH3SO3, LiN(CF3 SO2)(CF2HSO2), LiN(RFSO2)2, LiC(RFSO2)3, RF being a group selected from a fluorine atom and a perfluoroalkyl group comprising from one to eight carbon atoms.

[0034] Preferably, said electrolyte salt is LiTFSI.

[0035] Another object of the invention relates to a process for manufacturing a polymer electrolyte, comprising the following steps:

[0036] i) bring at least polyethylene glycol borate ester and 4-vinylpyridine into contact;

[0037] ii) polymerize the product obtained at the end of step i); and

[0038] iii) recover the polymer electrolyte;

[0039] at least one electrolyte salt being added before and / or after step ii).

[0040] Advantageously, in step i), the molecular weight of the PEG chains of BPEO can be between 62 g / mol and 100,000,000 g / mol, preferably between 200 g / mol and 10,000 g / mol, more preferably between 400 g / mol and 2,000 g / mol.

[0041] Advantageously, the molecular weight of the poly(4-vinylpyridine) of the polymer electrolyte obtained in step iii) can be between 500 g / mol and 100,000 g / mol.

[0042] Preferably, in step i), the molar ratio of 4-vinylpyridine to BPEO can be between 0.1 and 20, preferably between 0.1 and 10.

[0043] Preferably, the molar ratio of the electrolyte salt, such as a lithium salt, to the 4-vinylpyridine is between 0.1 and 5.

[0044] Preferably, the electrolyte salt is a lithium salt.

[0045] Advantageously, said electrolyte salt before and / or after step ii) is selected from LiPF6, LiFSI, LiTFSI, LiClO4, LiAsF6, LiBF4, Lil, LiN(CF3SO2)2, LiCF3SO3, LiN(CF3 CF2SO2)2, LiCH3SO3, LiN(CF3SO2)(CF2HSO2), LiN(RFSO2)2, LiC(RFSO2)3, RF being a group selected from a fluorine atom and a perfluoroalkyl group comprising from one to eight carbon atoms.

[0046] Preferably, said electrolyte salt added before and / or after step ii) is LiTFSI.

[0047] Preferably, step ii) is carried out in the presence of a radicle initiator, such as azobisisobutyronitrile (AIBN).

[0048] Step ii) of polymerization can be carried out at a temperature between 25 and 100°C, preferably between 30 and 90°C.

[0049] The embodiments described for the polymer electrolyte are applicable to said polymer electrolyte preparation process.

[0050] The invention also relates to an electrochemical battery cell comprising a polymer electrolyte as previously described.

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

[0052] Advantageously, the battery is an all-solid-state battery.

[0053] The battery may 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, such as potassium or sodium.

[0054] Preferably, the battery is an all-solid-state lithium-metal battery.

[0055] The invention also relates to a motor vehicle comprising at least one battery as previously described. Examples

[0056] Example 1: Formation of a polymer electrolyte comprising poly(ethylene glycol) borate ester (BPEO), poly(4-vinylpyridine) and EiFSI according to a first embodiment

[0057] 1.1. Preparation of the BPEO

[0058] The preparation of the polyethylene glycol borate ester was carried out according to the synthesis process reported in the publication Chem. Commun., 2023,59, 1066-1069.

[0059] Poly(ethylene glycol) (PEG) was dissolved in acetonitrile, in an amount of 10 mL of acetonitrile per gram of PEG, under an argon atmosphere. The molecular weight of PEG is between 62 g / mol and 100,000 g / mol, preferably between 200 g / mol and 10,000 g / mol, more preferably between 400 g / mol and 2,000 g / mol.

[0060] Two-thirds of a mole equivalent of triethyl borate was then added and the mixture was heated to 80°C. The solution was stirred overnight under an argon atmosphere.

[0061] The solvent was removed using a rotary evaporator at 40°C, then the resulting polymer was washed with ice-cold diethyl ether.

[0062] The resulting white solid was dried under vacuum at 60°C for 12h. The resulting BPEO polymer powder was then stored in a glove box under argon in which the amount of O2 and H2O is less than 5 ppm.

[0063] 1.2. Formation of the polymer electrolyte

[0064] The BPEO obtained in step 1.1 was dissolved in acetonitrile, in an amount of 10 mL per gram of BPEO.

[0065] A 4-vinylpyridine solution was prepared by diluting the monomer in acetonitrile, using 10 mL of acetonitrile per gram of monomer. This solution was slowly added to the BPEO solution, and the mixture was then stirred for 6 hours at room temperature. The molar ratio of 4-vinylpyridine to BPEG can range from 0.1 to 20.

[0066] LiFTSI and the initiator azobisisobutyronitrile (AIBN) were then slowly added to the solution, which was left to stand for 3 hours.

[0067] The molar ratio of LiFTSI to 4-vinylpyridine is between 0.1 and 5.

[0068] The amount of AIBN is between 0.1 and 20% by weight of 4-vinylpyridine.

[0069] The solution was dried at 30°C under vacuum to concentrate the solution, then the concentrated solution was poured onto a Teflon plate and heated to 80°C for 6 hours to carry out polymerization.

[0070] The resulting polymer was then dried under vacuum at 60°C.

[0071] Example 2: Formation of a polymer electrolyte comprising poly(ethylene glycol) borate ester (BPEO), poly(4-vinylpyridine) and EiFSI according to a second embodiment

[0072] 2.1. Preparation of the BPEO

[0073] The BPEO was prepared in the same way as in point 1.1.

[0074] 2.2. Formation of the polymer electrolyte

[0075] The BPEO obtained in step 2.1 was dissolved in acetonitrile, in an amount of 10 mL per gram of BPEO.

[0076] A 4-vinylpyridine solution was prepared by diluting the monomer in acetonitrile, using 10 mL of acetonitrile per gram of monomer. This solution was slowly added to the BPEO solution, and the mixture was then stirred for 6 hours at 40°C. The molar ratio of 4-vinylpyridine to BPEO can be between 0.1 and 10.

[0077] The molecular weight of poly(4-vinylpyridine) is between 500 g / mol and 100,000,000 g / mol.

[0078] LiFTSI was slowly added to the solution which was then maintained at 40°C for 3h.

[0079] The molar ratio of LiFTSI to 4-vinylpyridine is between 0.1 and 5.

[0080] The resulting polymer was then dried under vacuum at 60°C for 6 hours in order to remove acetonitrile and traces of water.

Claims

Demands

1. Polymer electrolyte comprising at least one polymer and at least one electrolyte salt, the polymer comprising polyethylene glycol borate ester and poly(4-vinylpyridine).

2. Electrolyte according to claim 1, wherein the polymer is derived from a monomer of the following formula (I): Where n, m and p represent integers, identical or different, from 1 to 22800, preferably from 1 to 45; RI, R2 and R3 are identical or different groups, chosen from: a borate group (-O-BR4), a hydroxyl group (-OH), an alkyl chain comprising from 1 to 10 carbon atoms, preferably from 1 to 6, for example a methyl group (-CH3) or ethyl group (-CH2CH3), a polymerizable group, preferably a group comprising at least one C=C double bond, such as a vinyl group (-CH=CH2), an azide group (-N3), an alkyne group and possibly the combination of an azide group (-N3) and an alkyne group; R4 being chosen from: a hydroxyl group (-OH), an alkyl chain comprising from 1 to 10 carbon atoms, preferably from 1 to 6, for example a methyl group (-CH3) or ethyl group (-CH2CH3), a polymerizable group, preferably a group comprising at least one C=C double bond, such as a vinyl group (-CH=CH2), a group azide (-N3), an alkyne group and possibly the combination of an azide group and an alkyne group.

3. Electrolyte according to claim 1 or 2, wherein the molecular weight of poly(ethylene glycol) is between 62 g / mol and 100,000 g / mol, preferably between 200 g / mol and 10,000 g / mol, more preferably between 400 g / mol and 2,000 g / mol.

4. Electrolyte according to any one of the preceding claims, wherein the molecular weight of poly(4-vinylpyridine) is between 500 g / mol and 100,000 g / mol.

5. Electrolyte according to any one of the preceding claims, wherein the molar ratio of 4-vinylpyridine to polyethylene glycol borate ester is between 0.1 and 20.

6. Electrolyte according to any one of the preceding claims, wherein the molar ratio of the electrolyte salt to the 4-vinylpyridine is between 0.1 and 5.

7. Electrolyte according to any one of the preceding claims, wherein said electrolyte salt comprises lithium, said electrolyte salt preferably being selected from LiPF6, LiFSI, LiTFSI, LiClO4, LiAsF6, LiBF4, LiN(CF3SO2)2, LiCF3SO3, LiN(CF3CF2SO2)2, LiCH3SO3, LiN(CF3SO2)(CF2HSO2), LiN(RFSO2)2, LiC(RFSO2)3, RF being a group selected from a fluorine atom and a perfluoroalkyl group comprising from one to eight carbon atoms.

8. A process for preparing a polymer electrolyte, characterized in that it comprises the following steps: i) contacting at least polyethylene glycol borate ester and 4-vinylpyridine; ii) polymerizing the product obtained at the end of step i); and iii) recovering the polymer electrolyte; at least one electrolyte salt being added before and / or after step ii).

9. Electrochemical cell for all-solid-state battery, in particular lithium-metal battery, comprising a polymer electrolyte as defined in any one of claims 1 to 7.

10. All-solid-state battery comprising at least one electrochemical cell as defined in claim 9.

11. Motor vehicle comprising at least one all-solid-state battery as defined in claim 10.