Patent Application
20240429442
The present invention concerns the field of energy storage, and particularly solid-state batteries.
Lithium ion (Li-ion) batteries offer outstanding energy density and are widely used for portable devices and electric and hybrid vehicles for example.
They are based on the reversible exchange of the lithium ion between the positive and negative electrodes, separated by an ionic conductive liquid electrolyte. Such liquid electrolytes are key to allow a good mobility of Li+ cations in the battery cell. Nevertheless, they are based upon organic solvents that are flammable, which can give rise to potential thermal runaways in case of incident. In this context, polymer electrolytes have been developed as ionic conductive solid electrolytes for solid state batteries notably to promote the safety of the systems and to potentially increase the stored energy. Nevertheless, most of these batteries suffer from lithium dendrites growth over charge/discharge cycles which may affect their morphological integrity potentially leading to internal short circuits. In other words, such batteries still have a limited lifetime, and are not as safe as they should be.
In the view of optimizing the solid-state batteries, ionic conductive solid electrolytes must therefore provide excellent ionic conductivity (to be able to work in a power range comparable with Li-ion) together with high mechanical properties (to promote the integrity of battery cells).
Various polymer electrolytes for Li-ion batteries have been explored.
EP3761398 teaches solid polymer electrolytes based on solvents, (co) polymers and crosslinking agents. However, the system proposed ends up with a complete crosslinked system that cannot be reprocessed once obtained. In addition, the system needs to be shaped in its application before crosslinking.
US 2019/0319303 discloses solid electrolyte composition containing an inorganic solid electrolyte and a polymeric binder, such as HNBR.
US 2009/0162754 discloses a solid polymer electrolyte for lithium batteries comprising a first polymer, a lithium salt and a second polymer, partially miscible in the first polymer and partially crystalline or vitreous acting as a mechanical reinforcement. However, first these polymers need to be crystalline or vitreous at the operating temperature to be effective as mechanical strengthener, second no elastic properties are brought to the system. Moreover, such polymers have generally very low ionic conductivity when in the vitreous state or when crystalline, preventing this phase from possible impact on the ionic conductivity.
Caradant et al., ACS Appl. Polym. Mater. 2020, 2, 11, 4943-4951 report a blend of poly (ethylene oxide) and hydrogenated nitrile butadiene rubber as a solid polymer electrolyte in lithium-ion batteries. However, in this publication uncrosslinked HNBR is used and no dopant molecules are involved.
The invention has for objective to solve the technical problem linked to supplying an ionic conductive electrolyte securing the battery storage.
The invention in particular aims at supplying an ionic conductive solid electrolyte for solid state batteries. The invention notably aims at supplying an Lit ionic conductive solid electrolyte with high mechanical properties.
The invention also has for objective to provide an industrial preparation method of an ionic conductive electrolyte, in particular an easy and secure industrialized process and simple to set up. Particularly, the invention aims at solving the above technical problems with cost effective and time efficient solutions.
The present invention thus provides for the first time thermoplastic vulcanizates (TPV) based solid polymer electrolytes hereafter called TPV SPEs.
According to a first object, the present invention thus concerns a solid polymer electrolyte (SPE) comprising an alkali metal salt and a thermoplastic vulcanizate (TPV) matrix, wherein said TPV comprises a mixture of at least one crosslinked elastomer phase and at least one thermoplastic polymer phase.
The TPV matrix is thus based on a blend of at least two polymeric phases, preferably two polymeric phases: the crosslinked elastomer phase and the thermoplastic polymer phase.
TPV SPEs exhibit improved properties over usual polymer electrolytes, including better electrochemical stability than polyethylene oxide (demonstrated below with high potential electrodes, e.g. NMC 111), high mechanical properties, and a high strength under pressure (including at room temperature and at elevated temperature) making them particularly adequate for doped/gelified system.
They may also involve a large frame of advantages such as:
As used herein, an «alkali metal» is an element such as lithium (Li), sodium (Na), potassium (K). Particularly, the alkali metal is lithium.
The salt of the alkali salt is typically the cation salt thereof, such as Li+.
“Elastomer phase” refers to a homogenous polymeric phase in terms of chemical composition and/or texture, constituted by a polymer that displays rubber-like elasticity as defined by the IUPAC.
Said phase is referred to as “crosslinked” or vulcanizated in that it has been subjected to a crosslinking reaction by the action of one or more crosslinking agents. The elastomer is crosslinked in that it comprises covalent bonds or relatively short sequences of chemical bonds to join two polymer chains together, that have been formed by the crosslinking reaction.
Suitable crosslinking agents generally depend on the elastomer polymer that is considered.
Such agents may be chosen from organic peroxides, including dialkyle peroxydes, such as Luperox® peroxydes such as Luperox® DI marketed by Arkema.
According to an embodiment, the elastomer is a thermosetting polymer, typically chosen from cis-1,4-polyisoprene (NR) and trans-1,4-polyisoprene, Synthetic polyisoprene, Polybutadiene, Chloroprene rubber (CR), polychloroprene, Neoprene, Baypren, Butyl rubber, halogenated butyl rubbers such as chloro butyl rubber: CIIR and bromo butyl rubber: BIIR, Styrene-butadiene rubber (SBR), Nitrile rubber (NBR), Hydrogenated nitrile rubbers (HNBR), EPM (ethylene propylene rubber), EPDM rubber (ethylene propylene diene rubber), Epichlorohydrin rubber (ECO), Polyacrylic rubber (ACM, ABR), Silicone rubber (SI, Q, VMQ), Fluorosilicone rubber (FVMQ), Fluoroelastomers (FKM for fluorocarbon-based fluoroelastomer materials defined by the ASTM International standard D1418, and FEPM), Perfluoroelastomers (FFKM), Polyether block amides (PEBA), Chlorosulfonated polyethylene (CSM), Ethylene-vinyl acetate (EVA).
More particularly, the elastomer is chosen from unsaturated or saturated rubber, more particularly, the elastomer is hydrogenated nitrile butadiene rubber (HNBR).
As used herein, “the thermoplastic polymer phase” refers to a polymeric phase constituted by a plastic polymer that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
According to an embodiment, the thermoplastic polymer is chosen from Acrylic, ABS, Polybenzimidazole, Polycarbonate, Polyether sulfone, Polyoxymethylene, Polyether ether ketone, Polyetherimide, Polyethylene, Polyphenylene oxide, Polyphenylene sulfide, Polypropylene, Polystyrene, Polyvinyl chloride, Polyvinylidene fluoride, Polytetrafluoroethylene (Teflon), Poly(ethylene oxide) (PEO), Polycaprolactone (PCL).
According to an embodiment, the thermoplastic polymer is Poly(ethylene oxide) (PEO) or Polycaprolactone (PCL), typically Polycaprolactone (PCL).
The electrolyte salt may be chosen from a variety of lithium-ion conducting electrolyte salts typically used for lithium batteries.
Various types of lithium salts used to conduct Li+ ions in electrolyte solutions for lithium rechargeable batteries are disclosed in particular Xu et al. Formulation of Blended-Lithium-Salt Electrolytes for Lithium Batteries Angew. Chem. Int. Ed. 2020, 59, 3400, and Auger et al. Materials Science and Engineering: R: Reports 2018, 134, 1-21.
Lithium hexafluorophosphate (LiPF6) which is the dominant Li-salt used in commercial rechargeable lithium-ion batteries. Further illustrative Li-salts include Lithium-bis(trifluoromethanesulfonyl)imide (TFSI), -bis(fluorosulfonyl)imide (FSI), -hexafluoroarsenate (AsF6−), -perchlorate (ClO4−), -hexafluorophosphate (PF6−), -tetrafluoroborate (BF4−), -trifluoromethanesulfonate, -triflate (Tf) (CF3SO3−), -bis(oxalato)borate (BOB) and -difluoro(oxalato)borate (BODFB).
The electrolyte salt may generally be present in a dissolved form, either in one or more of the polymeric phases, or into one or more of the optional additives that may be present.
The SPE according to the invention may further comprise one or more additional ingredients such as dopants and/or additives such as those usually used in solid polymer electrolytes, including dopants and/or additives.
According to an embodiment, the TPV may further comprise one or more dopant, typically to improve the ionic conductivity. Such dopant may be organic molecules chosen from trimethylphosphate (TMP), triethylphosphate (TEP), fluoroethylene carbonate (FEC), vinylene carbonate (VC).
According to an embodiment, the TPV may further comprise one or more additives, such as solvents, plasticizers, lithium ceramic, inorganic fillers and radical trappers.
Solvents may be chosen from organic liquid, water, ionic liquids, Illustrative solvents include trimethylphosphate (TMP), triethylphosphate (TEP), fluoroethylene carbonate (FEC), vinylene carbonate (VC).
The solvents may be chosen from a variety of lithium-ion conducting liquids typically used for lithium batteries. Various types of solvents used for lithium rechargeable batteries are disclosed in Chem. Rev. 2004, 104, 4303-4417 and Chem. Rev. 2014, 114, 11503-1161.
Plasticizers can be chosen from the variety of known plasticizers from the polymer melt processing industry but can also be any oligomer allowing a reduction in viscosity of the overall formulation. Plasticizers can be compounds such as synthetic or natural oils or polymer oligomers such as glyme molecules for example.
Lithium ceramic may be in the form of lithium aluminum titanium phosphate (LATP, Li1.3Al0.3Ti1.7(PO4)3), lithium lanthanum zirconium oxide (LLZO, Li7La3Zr2O12).
Radical trappers may be used to extend compounding times by controlling the crosslinking reaction rate. Radical trappers include 2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO), more example is presented by Bertin et al. Kinetic subtleties of nitroxide mediated polymerization. Chemical Society Reviews 2011, 40 (5), 2189-2198.
Inorganic fillers can be used to further reinforce the polymeric phases. They may be added in the elastomeric phase with the crosslinking agents to ensure that these stay in the wanted phase when the crosslinking occurs. Representative inorganic fillers include ceramic fillers such as TiO2, SiO2.
According to an embodiment, the SPE composition of the invention comprises a thermoplastic vulcanizate (TPV) matrix, wherein:
Typically, the crosslinked elastomer phase(s) and the thermoplastic polymer phase(s) may be present in a 50/50 volume ratio.
Their respective weight content typically depends on their respective density.
According to an embodiment, the SPE according to the invention may comprise:
The invention has for further objective to supply a solid-state battery that may be easily produced on the industrial scale.
According to a further object, the present invention also concerns a process for preparing the TPVs SPE of the invention comprising the steps of:
The melting temperature of the elastomer polymer is defined as the temperature for its melting point where the polymer transitions from the solid to the molten form.
The crosslinking agent is defined as above. Its activation temperature is defined as the temperature triggering the crosslinking reaction.
T1 and T2 depend on the nature of the elastomer polymer and the crosslinking agent.
Optional additional ingredients as defined above may be added during step a) and/or step b), as appropriate.
Typically, dopants may be added in step a) or b).
Typically, additives may be added in step a) or b).
According to an embodiment, the process of the invention may be carried out by extrusion.
Typically, the mixing steps a) and b) may be carried out in one or more heated extruder(s) or internal mixer(s).
Suitable extruders may be of the twin screws type.
Following step c), the resulting composition may be further processed to shape it in the desired form.
The final product is not limited in its form. It can be in the form of granules (e.g. at the exit of the extruder) or shaped in the form of a film.
According to a further object, the present invention also concerns an electrochemical all-solid-state cell comprising a solid polymer electrolyte according to the invention.
As used herein, an electrochemical cell, an elementary cell including a positive electrode/electrolyte/negative electrode assembly configured to store the electrical energy that is produced by a chemical reaction and to release it as an electric current.
Typically, the cell of the invention is a Li-ion cell.
According to a further object, the present invention also concerns an electrochemical module comprising the stack of at least two cells according to the invention, each cell being electrically connected with one or more other cell(s).
The term “module” therefore designates the assembly of several electrochemical cells, said assembly being able to be in series and/or parallel.
According to another object, the invention also relates to a battery or “accumulator” comprising one or more modules according to the invention. The term “battery” thus means the assembly of one or more modules according to the invention.
List of acronyms:
The HNBR-PCL thermoplastic vulcanizate (TPV) was made with an extruder (15 mL volume Xplore®) using the following protocol:
The TMP doped HNBR-PCL based TPV is obtained using the following protocol:
The same procedure and amounts as for example 1 were used except no crosslinking agents were added to the HNBR elastomeric phase. The composition obtained is as follows:
The TMP doped HNBR-PCL blend is obtained using the following protocol:
The HNBR-PEO thermoplastic vulcanizate (TPV) was made with an extruder (15 mL volume Xplore®) using the following protocol:
1. First the elastomer, here the HNBR was introduced in the Xplore at T=115° C. during 3 min (rotation speed of 80 rpm). Then, 2 phr of Luperox DI was added and mixed for 5 min with a rotation speed of 80/120 rpm in order to obtain the elastomeric phase containing the active peroxide.
2. The mixture HNBR+DI was removed from the Xplore.
3. 6.18 g of the HNBR+DI mixture was introduced in the Xplore at 115° C.
4. As the temperature is increased to 170° C., 7 g of PEO and 4.22 g of LiTFSI are rapidly added around 140°° C.
5. The mixture is left in the Xplore during 10 min at 170° C. in order to completely activate the peroxide crosslinking agent with a rotation speed of 140 rpm in order to obtain the TPV SPE with the following composition:
6. The resulting TPV SPE compound is removed from the Xplore and shaped into a film through compression with a press (pressure of 7 bars at 170° C. during 30 s) to obtain a film (thickness of 100 μm).
The TMP doped HNBR-PEO based TPV is obtained using the following protocol:
The same procedure and amounts as for example 3 were used except no crosslinking agents were added to the HNBR elastomeric phase. The composition obtained is as follows:
Counter Example 4 (CE4): SPE Based on a HNBR-PEO Blend (Without Crosslinking) Doped With TMP
The TMP doped HNBR-PEO blend is obtained using the following protocol:
a. Pressure and Temperature Tests
After complete drying at 60° C. for 12 hours, samples with a thickness of 1000 μm and 16 mm in diameter were placed in an oven at 80°° C. during 1 hour with a weight of 2.8kg on it in order to apply near 20 psi of pressure. The thickness and the surface of each sample were measured after the test. For samples containing dopants, they were added after the drying procedure in the glove box.
The surface expansions for the compositions of Example 1 and 2 as well as Counter Example 1 and 2 are illustrated in
The thickness changes for the compositions of Example 1 and 2 as well as Counter Example 1 and 2 are illustrated in
b. Ionic Conductivity
The conductivity measurements were performed using a MTZ-35 impedance analyzer and ITS (Intermediate Temperature System) between 20° C. and 80° C. with scanned frequencies between 3.5×107 Hz and 5×10−2 Hz and a voltage amplitude of 100 mV.
The conductivity for the compositions of Example 1 and 2 as well as Counter Example 1 and 2 are illustrated in
The NMC electrode was made with an extruder (15 mL volume Xplore®) using the following protocol:
The same procedure and amounts as for example 3 were used except the SPE used was the one from counter example 1. The same amount of TMP is added in the glove box on the electrode (20% wt versus SPE content). The composition obtained is as follows:
The NMC electrode was made with an extruder (15 mL volume Xplore®) using the following protocol:
The same procedure and amounts as for example 3 were used except the SPE used was the one from counter example 1. The same amount of TMP is added in the glove box on the electrode (20% wt versus SPE content). The composition obtained is as follows:
Cycling tests were performed in coin cell at 60° C. with a cycling rate of C/20 (half charge-discharge cycle in 20 hours).
Coin cell Li|E2 SPE|E3 NMC.
E2 SPE was laminated on the E3 NMC electrode (140° C. in a dry atmosphere Ar-filled glovebox) and then, the stack Li|E2 SPE|E3 NMC was laminated at 140° C.
E3 Electrode loading: 4.3 mg/cm2.
Theoretical capacity: 145 mAh/g.
E2 SPE thickness: 125±25 μm.
Voltage limits: 2.8 V in discharge and 4.2 V in charge with a voltage stabilization at 4.2 V during 2 hours after each charge.
The cycling test for Assembly 1 (A1) is represented in
Coin cell Li|CE2 SPE|CE3 NMC.
CE2 SPE was laminated on the CE3 NMC electrode (120° C. in a dry atmosphere Ar-filled glovebox) and then, the stack Li|CE2 SPE|CE3 NMC was laminated at 120° C.
CE3 Electrode loading: 4.8 mg/cm2.
Theoretical capacity: 145 mAh/g.
CE2 SPE thickness: 125±25 μm.
Voltage limits: 2.8 V in discharge and 4.2 V in charge.
The cycling test for Assembly 2 (A2) is represented in
Coin cell Li|E4 SPE|E6 NMC.
E4 SPE was laminated on the E6 NMC electrode (140° C. in a dry atmosphere Ar-filled glovebox) and then, the stack Li|E4 SPE|E6 NMC was laminated at 140° C.
E6 Electrode loading: 4.8 mg/cm2.
Theoretical capacity: 145 mAh/g.
E4 SPE thickness: 125±25 μm.
Voltage limits: 2.8 V in discharge and 4.2 V in charge with a voltage stabilization at 4.2 V during 2 hours after each charge.
The cycling test for Assembly 3 (A3) is represented in
Coin cell Li|CE4 SPE|CE6 NMC.
CE4 SPE was laminated on the CE6 NMC electrode (120° C. in a dry atmosphere Ar-filled glovebox) and then, the stack Li|CE2 SPE|CE3 NMC was laminated at 120° C.
CE6 Electrode loading: 4.4 mg/cm2.
Theoretical capacity: 145 mAh/g.
CE4 SPE thickness: 125±25 μm.
Voltage limits: 2.8 V in discharge and 4.2 V in charge.
The cycling test for Assembly 4 (A4) is represented in
The electrochemical performances of Assembly 1 and 2 are compared in
Altogether, the results show the improved mechanical resistance (
| Number | Date | Country | Kind |
|---|---|---|---|
| 21306574.1 | Nov 2021 | EP | regional |
The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2022/081114 filed Nov. 8, 2022, which claims priority of European Patent Application No. 21306574.1 filed Nov. 10, 2022. The entire contents of which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/081114 | 11/8/2022 | WO |
