Solid polymer electrolyte comprising at least one polymer comprising at least one unit obtained from a styrenic monomer and a specific polymer

Abstract

The present invention relates to a solid polymer electrolyte comprising: a) at least one polymer comprising at least one unit obtained from a reaction of at least one styrenic monomer with at least one polymer P selected from polyethers; and b) at least one electrolyte salt.

Description

[0001] DESCRIPTION

[0002] TITLE: Solid polymer electrolyte comprising at least one polymer comprising at least one unit obtained from a styrenic monomer and a particular polymer

[0003] Technical field

[0004] The present invention relates to the field of solid polymer electrolytes; More particularly, the present invention relates to a solid polymer electrolyte comprising a) at least one electrolyte salt, and b) at least one polymer comprising at least one unit obtained from a reaction of at least one styrenic monomer with at least one particular polymer P. The invention also relates to a process for preparing said solid polymer electrolyte. The present invention also relates to an all-solid battery cell comprising said solid polymer electrolyte, as well as to an all-solid battery comprising said cell.

[0005] Previous techniques

[0006] Conventionally, all-solid-state batteries comprise one or more positive electrodes, one or more negative electrodes, a solid electrolyte forming a separator, an anode current collector and a cathode current collector.

[0007] Battery performance 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. For such a battery to function, this network is percolated, forming ionic conduction paths throughout the entire volume of the electrode, to ensure the transport of ions to or from all the active material particles.

[0008] All-solid-state batteries use different types of materials such as solid electrolytes. In particular, there are two main branches within the field of solid (or solid-state) electrolytes: ceramics (or inorganic electrolytes) and solid polymer electrolytes, which can be referred to as EPS in the following.

[0009] Generally, ceramics have superior ionic conductivity and electrochemical stability window, but their chemical stability and mechanical properties are poor. On the other hand, solid polymer electrolyte has superior chemical stability and mechanical properties, but the main problem is the low ionic conductivity at room temperature. The Bolloré Bluecar (registered trademark) is a good example. This car is the first electric car (and the only one commercially available to date) that uses a Li metal battery with a solid polymer electrolyte. But the battery system of this car requires a high operating temperature (around 80°C) to achieve suitable ionic conductivity of the solid polymer electrolyte.

[0010] It turns out that the performance of the Bolloré Bluecar is reduced at room temperature. In particular, the ionic conductivity is low (less than 10" 4 S / cm) due to the presence of crystalline domains in the EPS. It should be noted that this ionic conductivity value should be much higher than this to achieve good performance in electric cars. This is why the Bluecar Bolloré battery system includes a heater. This is efficient enough to allow the fusion of the crystalline domains and therefore improve the molecular dynamics of the polymer chains and thus ionic transport.

[0011] To address this issue, the introduction of an amorphous region into a poly(ethylene oxide)-based solid polymer electrolyte, which can be referred to as POE in the following, was explored. POE is one of the most well-known host polymers for the preparation of EPS. However, the introduction of an amorphous region into POE may decrease the mechanical properties of EPS and cause structural failure in the battery system.

[0012] Therefore, there is a need to develop a novel solid polymer electrolyte that can overcome the above drawbacks.

[0013] Thus, the aim of the present invention is to design a solid polymer electrolyte making it possible to obtain improved performances, in particular better ionic conductivity at room temperature and better thermal stability.

[0014] Statement of the invention

[0015] The subject of the invention is therefore a solid polymer electrolyte comprising: a) at least one polymer comprising at least one unit obtained from a reaction of at least one styrenic monomer with at least one polymer P chosen from polyethers; and b) at least one electrolyte salt.

[0016] Thanks to the solid polymer electrolyte according to the invention, improved performances are obtained, in particular a better ionic conductivity at room temperature. Furthermore, the polymer a) does not have a crystalline domain. The invention also relates to a process for preparing the solid polymer electrolyte according to the invention, comprising the following steps: i) bringing at least said styrene monomer into contact with at least said polymer P; ii) polymerizing the product obtained at the end of step i); iii) recovering said solid polymer electrolyte; said electrolyte salt being added during step ii) and / or step iii).

[0017] Another subject of the invention is an all-solid-state battery cell comprising the solid polymer electrolyte according to the invention, as well as an all-solid-state battery comprising the cell according to the invention.

[0018] Other advantages and characteristics of the invention will appear more clearly on examining the detailed description and the attached drawings in which: [Fig 1] is a differential scanning calorimetry (DSC) graph characterizing a solid polymer electrolyte according to the invention;

[0019] [Fig 2] represents the evolution of the ionic conductivity as a function of the temperature of a solid polymer electrolyte according to the invention and of a comparative solid polymer electrolyte.

[0020] It is specified that the expression “from... to...” used in the present description of the invention must be understood as including each of the terminals mentioned.

[0021] For the purposes of the present invention, the term “styrenic monomer” means a monomer having at least the chemical structure of styrene.

[0022] As indicated above, the solid polymer electrolyte according to the invention comprises a) at least one polymer comprising at least one unit obtained from a reaction of at least one styrenic monomer with at least one polymer P chosen from polyethers.

[0023] Advantageously, the polyethers which can be used according to the invention can be poly(alkylene oxide), such as poly(ethylene oxide), poly(propylene oxide), etc., cyclic polyethers such as 12-crown-4 ether, 15-crown-5 ether, 18-crown-6 ether, etc.

[0024] According to a preferred embodiment, the polymer P is chosen from poly(ethylene oxide), poly(propylene oxide) and their mixture, preferably the polymer P is poly(ethylene oxide). Advantageously, the poly(ethylene oxide) has a molar mass ranging from 100 to 3000 g / mol, preferably from 200 to 2000 g / mol, more preferably from 400 to 2000 g / mol, even more preferably from 400 to 1000 g / mol.

[0025] The solid polymer electrolyte according to the invention further comprises b) at least one electrolyte salt.

[0026] Advantageously, said electrolyte salt is chosen from alkaline earth metal salts, alkali metal salts and their mixtures, preferably from alkali metal salts, more preferably from sodium salts, lithium salts and their mixtures.

[0027] Among the sodium salts that can be used according to the invention, mention may be made of NaCE3SO3, NaSCN, NaBE4, NaN(CE3SO3)2, or even NaClO4.

[0028] Even more preferably, said electrolyte salt is chosen from lithium salts.

[0029] Among the lithium salts which can be used according to the invention, mention may be made, in addition to those cited below, of lithium polyanion salts, such as, for example, lithium polystyrene sulfonate salt.

[0030] Advantageously, said electrolyte salt is chosen from LiPEô, LiFSI (LiN(SO2E)2), LiTESI (LiN(CF3SO2)2), LiClO4, LiAsE6, LiBE4, Liil, LiCF3SO3, LiN(CE3CE2SO2)2, LiCH3SO3, LiN(CF3SO2)(CF2HSO2), LiN(RFSO2)2, LiC(RFSO2)3, RF being a group chosen from a fluorine atom and a perfluoroalkyl group comprising from one to eight carbon atoms.

[0031] Preferably, said electrolyte salt is lithium bis(trifluoromethanesulfonyl)imide LiTFSI (LiN(CF3SO2)2).

[0032] When present, according to a preferred embodiment, the electrolyte salt is present in a content ranging from 10 to 50% by weight, preferably from 10 to 30% by weight relative to the total weight of the solid polymer electrolyte.

[0033] In this embodiment, and according to a preferred embodiment, the polymer a) is present in a content ranging from 50 to 90% by weight, preferably from 70 to 90% by weight relative to the total weight of the solid polymer electrolyte.

[0034] Advantageously, said styrenic monomer is chosen from styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, m-chlorostyrene, p-chlorostyrene, vinylanisole, styrene sulfonate and mixtures thereof, preferably chosen from styrene and styrene sulfonate, more preferably styrene sulfonate. According to a preferred embodiment, the weight ratio between the polymer P and the styrenic monomer ranges from 0.6 to 9, preferably from 0.95 to 7.5, more preferably from 1.3 to 6.5.

[0035] According to a particularly preferred embodiment, said motif is of the following formula (I):

[0036] (I), in which m ranges from 3 to 68, preferably from 3 to 23.

[0037] The total content of styrenic monomer may range from 10 to 60% by weight, preferably from 12 to 51% by weight, more preferably from 14 to 35% by weight, even more preferably from 18 to 33% by weight relative to the total weight of the polymer a).

[0038] The total content of polymer P may range from 40 to 90% by weight, preferably from 49 to 88% by weight, more preferably from 65 to 86% by weight, even more preferably from 67 to 82% by weight relative to the total weight of the polymer a).

[0039] The present invention also relates to a process for preparing a solid polymer electrolyte according to the invention and as mentioned above.

[0040] Said preparation process comprises the following steps: i) bringing at least said styrenic monomer as defined above into contact with at least said polymer P as defined above; ii) polymerizing the product obtained at the end of step i); iii) recovering said solid polymer electrolyte; said electrolyte salt as defined above being added during step ii) and / or step iii). Thus, the electrolyte salt can be added either during step (ii) of polymerization, or during step (iii) during recovery, or during step (ii) and also step (iii).

[0041] Preferably, the electrolyte salt is added during step ii). More preferably, the electrolyte salt is added only during step ii).

[0042] Step i) may take place for a period ranging from 1 hour to 72 hours, preferably from 5 to 60 hours, more preferably from 8 to 36 hours.

[0043] Step i) may take place in the presence of a solvent, such as for example acetonitrile or THF.

[0044] A catalyst may be present during step i), such as pyridine.

[0045] Step i) may be carried out at a temperature ranging from room temperature to 40°C, preferably at room temperature. Room temperature is a temperature ranging from 20 to 25°C.

[0046] Advantageously, step ii) takes place at a temperature ranging from 40 to 120°C, preferably from 60 to 120°C.

[0047] According to a particular embodiment, step ii) takes place over a period ranging from 2 hours to 48 hours, preferably from 5 hours to 24 hours.

[0048] Step ii) may take place in the presence of a polymerization initiator, such as AIBN.

[0049] A solvent may be present during step ii), such as ethanol or THF.

[0050] Step iii) of recovering said solid polymer electrolyte can be carried out by evaporation of any solvent present, followed by drying, for example at 80°C for a period which can be 24 hours.

[0051] The invention also relates to an all-solid battery cell comprising at least one solid polymer electrolyte according to the invention as defined above.

[0052] Another object of the present invention is an all-solid-state battery comprising at least one cell as defined above.

[0053] The present invention is illustrated in a non-limiting manner by the following examples.

[0054] Measurement methods

[0055] Measurement of melting temperatures

[0056] Melting temperatures Tf are measured in a known manner by differential scanning calorimetry, or DSC (Differential Scanning Calorimetry) for melting and crystallization temperatures and enthalpies by varying the temperature from -70 to 100°C, under an inert gas atmosphere (argon), with an applied temperature ramp of 10 K / min.

[0057] Measurement of ionic conductivity

[0058] The ionic conductivity of the samples was measured by AC impedance spectroscopy. The sample was placed in a controlled environment sample holder (CESH, Biology) to maintain an inert gas atmosphere. The AC impedance spectrum was recorded by an MTZ-35 frequency response analyzer (BioLogic) in a temperature range of 25°C to 100°C. The samples were preheated to 80°C for one hour before measurement. A 50 mV sinusoidal voltage perturbation was applied between 107 and 0.05 Hz. The temperature was controlled by an intermediate temperature system (ITS, BioLogic). The temperature increased slowly (1 K / min) and was maintained for 15 minutes to ensure that the sample reached thermal equilibrium.

[0059] Examples

[0060] Example 1: Preparation of a solid polymer electrolyte according to the invention

[0061] 1 mL of oxalyl chloride was added to 20 mL of dry acetonitrile to form a solution. After stirring for 5 minutes, 3 drops of DMF, acting as a catalyst, were added to the solution. The solution was stirred for 5 hours. After the solution turned yellow, 1 g of 4-styrene sulfonic acid sodium salt was added. A white particle (NaCl) was observed upon addition.

[0062] The mixture was stirred overnight (> 15H) at room temperature. The resulting mixture was filtered and the solid was removed. The solution portion was loaded into a pre-dried round flask and stirred in an ice bath.

[0063] 4.8 g of monomethoxy poly(ethylene oxide), having a molecular weight by weight of 1000 g / mol, and 1.3 mL of triethylamine were dissolved in 15 mL of dry acetonitrile (DMAP or pyridine can be added as a catalyst). The solution was added to the round flask in an ice bath. Then, it was stirred for up to 3 days.

[0064] After the reaction, the solvent was evaporated in vacuo at 65 °C. The resulting crude product was dissolved in dichloromethane (DCM) and washed with aqueous NaHCO3 solution (0.3M) three times and then washed again with 10 mL of HC1 (1M) once. The DCM portion was collected and the solvent was evaporated. A dark yellow solid was obtained.

[0065] The resulting solid was dissolved in a small amount of DMSO and AIBN (10 mol%) was added. The solution was bubbled using argon gas to remove oxygen in the DMSO. The solution was heated at 120°C overnight. The resulting solid was washed with THE to remove unreacted monomers.

[0066] The resulting polymer was dissolved in ethanol (or acetonitrile) and 25% by weight of LiTESI was added. The solution was stirred overnight. The solvent was removed under vacuum at 65°C and then dried at 80°C for 24 hours.

[0067] A solid polymer electrolyte according to the invention was obtained. The mass content of poly(ethylene oxide) is 85.6% by weight relative to the total weight of the polymer.

[0068] Example 2: Performance Evaluation a. Melting Temperature (Tf)

[0069] The polymer as prepared in Example 1 is used, and called Pol 1.

[0070] Different comparative polymers were also used. These polymers were prepared according to the protocol described in WO 2007 / 113236. They are copolymers of the following formula (II):

[0071] These are therefore PS-POE-PS (polystyrene-b-poly(ethylene oxide)-b-polystyrene) block copolymers.

[0072] Two copolymers, Pol 2 and Pol 3, were used. Pol 2 is a copolymer comprising 75% by mass of POE. Pol 3 is a copolymer comprising 56% by mass of POE.

[0073] The data are collected in Table 1 below. [Table 1]

[0074] In Figure 1, it is clearly visible that no specific peak is visible in the temperature range from -50 to 100°C (curve A). The Pol 1 polymer according to the invention therefore does not have a melting temperature.

[0075] Conversely, it was possible to measure melting temperatures for the comparative Pol 2 and Pol 3 polymers, of 59°C and 48°C respectively, with very specific peaks, as can be seen in WO 2007 / 113236.

[0076] Therefore, the polymer used in the context of the invention, Pol 1, does not have crystalline domains unlike Pol 2 and Pol 3, comparative polymers of the prior art. b. Ionic conductivity

[0077] The solid polymer electrolyte according to the invention as obtained in Example 1 is used, and called EPS 1. The molar ratio Li (lithium salt LiTFSI): EO (ethylene oxide) is 1:15).

[0078] A solid polymer electrolyte comprising the reference polymer, poly(ethylene oxide) and lithium salt LiTFSI in a molar ratio (Li:EO (ethylene oxide) = 1:20) was used. It is referred to as EPS 2 in the following.

[0079] The evolution of ionic conductivity as a function of temperature of solid polymer electrolytes EPS1 (curve B) and EPS2 (curve C) can be observed in Figure 2.

[0080] Thus, it clearly appears that the EPS 1 electrolyte according to the invention has better ionic conductivity than that of the EPS 2 electrolyte in the temperature range from room temperature up to 50°C.

[0081] This represents a significant advance for all-solid-state batteries, the main problem of which remains low ionic conductivity at room temperature.

[0082] The solid polymer electrolyte according to the invention is therefore a high-potential candidate for application within an all-solid-state battery.

Claims

CLAIMS 1. Solid polymer electrolyte comprising: a) at least one polymer comprising at least one unit obtained from a reaction of at least one styrenic monomer with at least one polymer P chosen from polyethers; and b) at least one electrolyte salt.

2. Solid polymer electrolyte according to claim 1, characterized in that the polymer P is chosen from poly(ethylene oxide), poly(propylene oxide) and their mixture, preferably the polymer P is poly(ethylene oxide).

3. Solid polymer electrolyte according to claim 2, characterized in that the poly(ethylene oxide) has a molar mass ranging from 100 to 3000 g / mol, preferably from 200 to 2000 g / mol, more preferably from 400 to 2000 g / mol, even more preferably from 400 to 1000 g / mol.

4. Solid polymer electrolyte according to any one of the preceding claims, characterized in that said electrolyte salt is chosen from alkaline earth metal salts, alkali metal salts and their mixtures, preferably from alkali metal salts, more preferably from sodium salts, lithium salts and their mixtures, even more preferably from lithium salts.

5. Solid polymer electrolyte according to any one of the preceding claims, characterized in that said electrolyte salt is chosen from LiPF6, LiFSI, LiTFSI, LiCIC, LiAsF6, LiBF4, LiI1, LiCF3SO3, LiN(CF3CF2SO2)2, LiCH3SO3, LiN(CF3SO2)(CF2HSO2), LiN(RFSO2)2, LiC(RFSO2)3, RF being a group chosen from a fluorine atom and a perfluoroalkyl group comprising from one to eight carbon atoms.

6. Solid polymer electrolyte according to any one of the preceding claims, characterized in that said styrenic monomer is chosen from styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, m-chlorostyrene, p-chlorostyrene, vinylanisole, styrene sulfonate and mixtures thereof, preferably chosen from styrene and styrene sulfonate, more preferably styrene sulfonate.

7. Solid polymer electrolyte according to any one of the following claims, characterized in that said unit is of the following formula (I): in which m ranges from 3 to 68, preferably from 3 to 23.

8. Process for preparing a solid polymer electrolyte according to any one of the preceding claims, characterized in that it comprises the following steps: i) bringing at least said styrenic monomer into contact with at least said polymer P; ii) polymerizing the product obtained at the end of step i); iii) recovering said solid polymer electrolyte; said electrolyte salt being added during step ii) and / or step iii).

9. Method according to claim 8, characterized in that the electrolyte salt is added during step ii).

10. Method according to claim 8 or 9, characterized in that step i) takes place for a period ranging from 1 hour to 72 hours, preferably from 5 to 60 hours, more preferably from 8 to 36 hours.

11. Process according to any one of claims 8 to 10, characterized in that step ii) takes place at a temperature ranging from 40 to 120°C, preferably from 60 to 120°C.

12. Method according to any one of claims 8 to 11, characterized in that step ii) takes place for a period ranging from 2 hours to 48 hours, preferably from 5 hours to 24 hours.

13. All-solid battery cell comprising at least one solid polymer electrolyte as defined in any one of claims 1 to 7.

14. All-solid-state battery comprising at least one cell as defined in claim 13.

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