Electrode and electrolyte for lithium ion battery, incorporating a polymer compound

Abstract

An assembly for a lithium-ion battery, comprising an electrolyte and an electrode, wherein the electrolyte comprises poly(acrylonitrile-co-methyl acrylate) and lithium salt and / or the electrode incorporates a polymer binder comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt.

Description

[0001] DESCRIPTION

[0002] TITLE: Electrode and electrolyte for lithium-ion battery incorporating a polymer compound

[0003] The present invention relates, in general, to all-solid-state batteries, and in particular all-solid-state lithium-ion batteries.

[0004] More specifically, the invention relates to an electrolyte material and an electrode material for an all-solid lithium-ion battery incorporating a polymer compound and, more particularly, to an electrolyte and a polymeric binder comprising poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) and lithium salt.

[0005] Today, the vast majority of electrochemical energy storage systems sold in electric vehicles are batteries using “Lithium-ion” technology.

[0006] These lithium technologies have seen increasing interest over the last thirty years compared to other battery technologies. They use electrode materials called "active materials" which must allow the reversible insertion and deinsertion of lithium ions during the charging and discharging processes.

[0007] However, conventional Li-ion technology is close to its performance limits as there can be no compromise on lifespan or safety.

[0008] Common liquid electrolytes are composed of flammable carbonate solvents that can act as fuel in the event of accidental behavior. This flammability poses a problem regarding the possibility of rapid charging. Indeed, high charging currents will cause a rise in temperature inside the cells, posing a problem with the liquid electrolyte.

[0009] The use of a solid electrolyte as a separator would reduce these safety problems while increasing the energy density of the so-called "all-solid" battery with the use of metallic lithium at the negative electrode. Good ionic conductivity greater than 10-2 S / cm, electronic insulation as well as high potential stability greater than 4.5V are necessary to compete with conventional liquid electrolytes from an electrochemical performance point of view.

[0010] The solid electrolyte must fulfill its role as a separator and therefore also have sufficient mechanical properties to prevent the growth of Li-metal dendrites at the negative electrode.

[0011] It is known to use poly(ethylene oxide) (POE) polymer in an all-solid-state battery for electric vehicles with iron phosphate (LiFePO4) as the positive electrode and POE-LiTF SI complex for the all-solid-state electrolyte.

[0012] POE is easy to form, has good mechanical strength and thermal stability well above 100°C, unlike carbonate-based liquid electrolytes.

[0013] However, POE only operates at a high temperature of 80°C and its potential stability window is reduced, ranging from 0 to 3.8V vs Li+ / Li, which limits its use as a separator but also as a polymeric electrode binder, when used against high potential active materials. This prevents the use of high potential cathode materials, limiting the energy density of such cells.

[0014] Thus, there is a need to develop new all-solid-state battery materials that can overcome the drawbacks mentioned below.

[0015] The invention therefore aims to overcome these drawbacks and to propose a material for an all-solid lithium-ion battery providing improved electrochemical stability in potential and allowing operation at a temperature below 80°C.

[0016] There is therefore provided a lithium-ion battery assembly, comprising an electrolyte and an electrode, the electrolyte comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt and / or the electrode incorporating a polymeric binder comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0017] In a first embodiment, the electrolyte comprises poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0018] The integration of PAN-co-MA allows to obtain potential stability beyond 4.5V vs Li / Li + facing lithium metal. In a second embodiment, the polymeric binder of the electrode comprises poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0019] The integration of PAN-co-MA into the electrode does not cause parasitic reactions and allows good electrode retention. Its use is suitable as an electrode binder.

[0020] In a third embodiment, the electrolyte and the polymeric binder of the electrode comprise poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0021] The simultaneous integration of PAN-co-MA into the electrode and electrolyte of an all-solid-state lithium-ion battery is particularly advantageous.

[0022] It has been found that the poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) compound allows operation of the all-solid-state lithium battery at room temperature, and having a wide potential stability window, makes it possible to use high potential cathode materials. In addition, the energy density of cells incorporating this polymeric compound is high.

[0023] Other characteristics, aspects, objects and advantages will emerge from the description which follows and from the following examples, given purely for illustrative purposes.

[0024] In this description, the expression "at least one" used is equivalent to the expression "one or more".

[0025] The invention relates to a lithium-ion battery assembly, comprising an electrolyte and an electrode, the electrolyte comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt and / or the electrode incorporating a polymeric binder comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0026] The lithium-ion battery assembly according to the invention can be incorporated into an all-solid or semi-solid lithium-ion battery cell.

[0027] Polymeric Binder for Electrode In one embodiment, the electrode of the lithium-ion battery assembly may comprise a polymeric binder comprising PAN-co-MA and lithium salt.

[0028] Advantageously, the lithium salt may comprise lithium bis(trifluoromethanesulfonyl)imide (LiTF SI).

[0029] According to one characteristic, the lithium salt may consist of LiTF SI.

[0030] Preferably, the polymeric binder of the electrode incorporates between 1 and 40% by weight of PAN-co-MA relative to the total weight of the electrode, and more preferably, the polymeric binder of the electrode incorporates between 20 and 40% by weight of PAN-co-MA relative to the total weight of the electrode.

[0031] Preferably, the polymeric binder of the electrode incorporates between 1 and 20% by weight of lithium salt, preferably between 5 and 15% by weight of lithium salt.

[0032] Preferably, the PAN-co-MA comprises between 50 and 99% by weight of acrylonitrile, and more preferably between 80 and 99% by weight, relative to the total weight of the PAN-co-MA in the polymeric binder of the electrode.

[0033] Electrolyte

[0034] In one embodiment, the electrolyte of the lithium-ion battery assembly may comprise PAN-co-MA and lithium salt.

[0035] Preferably, the electrolyte incorporates between 50 and 95% by weight of PAN-co-MA, and more preferably between 70 and 90% by weight, relative to the total weight of the electrolyte.

[0036] Preferably, the electrolyte incorporates between 5 and 60% by weight of lithium salt, and more preferably between 15 and 35% by weight, relative to the total weight of the electrolyte.

[0037] In one embodiment, the electrolyte may incorporate liquid electrolyte comprising lithium salt.

[0038] According to one example, the liquid electrolyte may be a carbonate-based liquid electrolyte. Preferably, the electrolyte comprises between 40 and 80% of liquid electrolyte relative to the total weight of the electrolyte.

[0039] Preferably, the PAN-co-MA comprises between 50 and 99% by weight of acrylonitrile, and more preferably between 80 and 99% by weight, relative to the total weight of the PAN-co-MA in the electrolyte.

[0040] The invention also relates to a method of manufacturing an electrolyte for a lithium-ion battery.

[0041] In a first step, PAN-co-MA and lithium salt are mixed in an aprotic polar solvent.

[0042] In one example, the solvent may be dimethyl sulfoxide (DMSO).

[0043] The resulting mixture is stirred at room temperature until the PAN-co-MA and the lithium salt dissolve in the solvent.

[0044] Once dissolved, the mixture is coated onto a current collector.

[0045] The coating is then dried until the solvent evaporates and a solid electrolyte is obtained.

[0046] The current collector is, for example, an aluminum foil.

[0047] Preferably, in the first step, between 50 and 95% by weight of PAN-co-MA, preferably between 70 and 90% by weight, is mixed in the solvent. These mass proportions are considered relative to the total weight of PAN-co-MA and lithium salt.

[0048] After drying the coating, it will be possible to add liquid electrolyte containing lithium salt to obtain a semi-solid electrolyte.

[0049] Advantageously, a carbonate-based liquid electrolyte can be added after the coating has dried.

[0050] Preferably, an aprotic solvent is also added to the coating, for example DMSO.

[0051] Preferably, between 40 and 80% by weight of liquid electrolyte may be added. These mass proportions are considered relative to the total weight of the semi-solid electrolyte.

[0052] Lithium-ion battery The invention relates to a cell for a lithium-ion battery comprising an assembly as described above.

[0053] Advantageously, the lithium-ion battery cell may comprise an anode, a cathode, and an electrolyte. The cathode and the electrolyte may be formed by an assembly incorporating PAN-co-MA and lithium salt as described above.

[0054] The invention also relates to a lithium-ion battery, comprising at least one cell or at least one assembly as described previously.

[0055] The lithium-ion battery can be an all-solid-state battery or a semi-solid-state battery.

[0056] The invention further relates to a motor vehicle comprising at least one lithium-ion battery as described above.

[0057] It may be provided that the lithium-ion battery assembly as described above is incorporated into a lithium-ion traction battery, for example a motor vehicle.

[0058] It may also be provided that the lithium-ion battery assembly as described above is incorporated into any other type of lithium-ion battery, not intended to be involved in a traction movement.

[0059] The invention also relates to a use of an assembly as described above in a lithium-ion battery for operation of the lithium-ion battery at room temperature.

[0060] The present invention is illustrated in a non-limiting manner by the following examples of a method of forming an electrode binder and an electrolyte incorporating PAN-co-MA polymer and lithium salt.

[0061] Example 1: Electrode comprising a polymeric binder

[0062] A composite electrode was formulated using PAN-co-MA polymer as a binder.

[0063] A composition was formed by adding 6% by weight of PAN-co-MA in N-methyl-2-pyrrolidone (NMP) solvent, then 2% by weight of lithium salt LiTF SI. These mass proportions are calculated relative to the total weight of the mixture consisting of the solvent, PAN-co-MA and the lithium salt.

[0064] The composition is mixed using a mechanical mixer overnight at 50°C to obtain a polymer binder in the form of a gel.

[0065] In a thinky pot, 50 wt% LiFePO4 (LFP), 10 wt% Timcal SuperC65 carbon and 40 wt% of the previously obtained polymer gel are deposited so as to obtain 30 wt% PAN-co-MA and 10 wt% LiTF SI in the composite electrode.

[0066] The mixture is mixed in a thinky mixer several times for 5 minutes at 1000 rpm before being coated on a carbon-coated aluminum foil. The coating is left to dry overnight at 80°C in the open air.

[0067] The electrode thus obtained is then tested electrochemically, against lithium metal in the presence of a liquid LPX electrolyte based on carbonate and a lithium salt.

[0068] The composition of the LPX liquid electrolyte is 1 mol / L of lithium salt LiPFe in Ethylene carbonate (EC): Dimethyl carbonate (DMC): Ethyl methyl carbonate (EMC) in the following proportions 1:1:1 by volume.

[0069] The performance of a lithium-ion half-cell formed by the obtained PAN-co-MA based electrode and the LPX liquid electrolyte is tested. Galvanostatic cycling was performed at room temperature (25°C), from a BioLogic potentiostat at a potential of 5V vs Li / Li +and at a cycling rate of C / 20. A reversible capacity of around 140 mAh / g was observed in the first cycle, which stabilizes at 130 mAh / g after 50 cycles.

[0070] PAN-co-MA provides good electrode retention and does not cause parasitic reactions. Its use is therefore suitable and particularly advantageous as an electrode binder.

[0071] Example 2: Electrolyte

[0072] A solid electrolyte film was formulated using PAN-co-MA polymer. A composition is formulated by adding, in dimethyl sulfoxide (DMSO) solvent, 5% by weight of PAN-co-MA relative to the weight of DMSO in the composition, and 25% by weight of lithium salt LiTF SI relative to the weight of PAN-co-MA in the composition.

[0073] The composition is mixed using a mechanical mixer for 24 hours.

[0074] The composition is then coated onto an aluminum foil using a doctor blade set at 800 pm.

[0075] First, the electrolyte sample is dried in an oven in the open air at 80°C overnight.

[0076] In a second step, the electrolyte sample is dried for 4 hours under vacuum at 80°C in order to remove impurities due to the solvent and the water present in the air.

[0077] After drying, a solid electrolyte is obtained.

[0078] A two-electrode electrochemical cell was produced in a glove box using a 10 mm diameter button cell device.

[0079] In the device, a solid electrolyte pellet incorporating previously obtained PAN-co-MA, as well as a piece of lithium 4 mm in diameter were placed between two stainless steel shims. 2 drops of conventional liquid electrolyte based on LPX carbonates were then added, i.e. 58% by weight of liquid electrolyte relative to the total weight of solid and liquid electrolyte.

[0080] The cell is subjected to electrochemical tests on a BioLogic potentiostat. A potential stability test by cyclic voltammetry is carried out up to 5.5V vs Li / Li + and at a temperature of 25°C. Potential stability of the cell up to 5V vs Li / Li + was observed.

[0081] Example 3: Assembly comprising an electrolyte and an electrode comprising a polymeric binder

[0082] An electrode was formulated to observe the galvanostatic cycling behavior of the PAN-co-MA based electrolyte obtained in Example 2. The electrode, composed of 50% by mass of LiFePO4 (LFP) as well as 10% by mass of Timcal SuperC65 carbon, 30% by mass of PAN-co-MA and 10% by mass of LiTF SI, is obtained according to the method described in Example 1.

[0083] A two-electrode electrochemical cell was produced in a glove box using a 10 mm diameter button cell device.

[0084] In the device, an electrode pellet of 8 mm diameter incorporating PAN-co-MA obtained according to the method described in Example 1, a solid electrolyte pellet incorporating PAN-co-MA obtained according to the method described in Example 2, as well as a piece of lithium of 4 mm diameter, were placed between two stainless steel shims. 2 drops of conventional liquid electrolyte based on LPX carbonates were then added, i.e. 58% by weight of liquid electrolyte relative to the total weight of solid and liquid electrolyte.

[0085] The cell is subjected to electrochemical tests on a BioLogic potentiostat. A potential stability test by cyclic voltammetry is carried out between 3.65V and 2.5V vs Li / Li + at a temperature of 40°C and a cycling regime of C / 20.

[0086] A high capacity of 150 mAh / g was achieved during the first cycle and during the fifth charge cycle at 40°C.

[0087] Such capacities at 40°C are superior to those obtained with a POE-based material placed against LFP.

[0088] Example 4: Assembly comprising an electrolyte and an electrode comprising a polymeric binder

[0089] An electrochemical cell was formulated according to the method described in Example 3 in which, not 2 drops, but 4 drops of conventional carbonate-based liquid electrolyte (LPX) were added.

[0090] The cell is subjected to electrochemical tests on a BioLogic potentiostat. A potential stability test by cyclic voltammetry is carried out between 3.65V and 2.5V vs Li / Li + at a temperature of 25°C and a cycling regime of C / 20.

[0091] The capacity obtained is higher than the capacity obtained in Example 3. A high capacity of 170 mAh / g was obtained during the first charging cycle at 25°C and then, during the fifth cycle, a capacity of 125 mAh / g. Tests at 25°C were also carried out at higher cycling rates. AC / 10 and C / 5, a capacity of 80 and 60 mAh / g, respectively, are observed.

[0092] Such capacities at 25°C are superior to those obtained with a POE-based material placed against LFP.

[0093] Adding a small amount of liquid electrolyte, such as a carbonate-based electrolyte, to the solid electrolyte material incorporating the PAN-co-MA polymer is sufficient to obtain a higher capacity at room temperature.

[0094] PAN-co-MA-based polymer compounds are therefore particularly advantageous for use as solid or semi-solid electrolyte and as electrode binder in lithium-ion batteries.

[0095] The integration of PAN-co-MA into the electrolyte and / or electrode of a lithium-ion battery cell allows galvanostatic cycling at room temperature, electrochemical stability above 4.5 V vs Li / Li+ at room temperature, compared to lithium metal

[0096] PAN-co-MA thus allows operation at room temperature, and has a wide potential stability window, allowing the use of high potential cathode materials. The energy density of such cells is optimized.

Claims

CLAIMS 1. A lithium-ion battery assembly, comprising an electrolyte and an electrode, the electrolyte comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt and / or the electrode incorporating a polymeric binder comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt.

2. Assembly according to claim 1, in which the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide.

3. Assembly according to claim 1 or 2, in which the polymeric binder of the electrode incorporates between 1 and 40% by weight of poly(acrylonitrile-co-methyl acrylate), preferably between 20 and 40% by weight, relative to the total weight of the electrode.

4. Assembly according to any one of the preceding claims, in which the electrolyte incorporates between 50 and 95% by weight of poly(acrylonitrile-co-methyl acrylate), preferably between 70 and 90% by weight, relative to the total weight of the electrolyte.

5. An assembly according to any one of the preceding claims, wherein the electrolyte incorporates liquid electrolyte comprising lithium salt, such as a carbonate-based liquid electrolyte, and preferably between 40 and 80% by weight of liquid electrolyte relative to the total weight of the electrolyte.

6. Assembly according to any one of the preceding claims, in which the poly(acrylonitrile-co-methyl acrylate) comprises between 50 and 99% by weight of acrylonitrile, preferably between 80 and 99% by weight, relative to the total weight of the poly(acrylonitrile-co-methyl acrylate).

7. A lithium-ion battery cell comprising an assembly according to any one of the preceding claims.

8. Lithium-ion battery comprising at least one cell according to claim 7 or at least one assembly according to any one of claims 1 to 6.

9. Motor vehicle comprising at least one lithium-ion battery according to claim 8.

10. Use of an assembly according to any one of claims 1 to 6 in an all-solid lithium-ion battery at room temperature. 1 1 . Method for manufacturing an electrolyte for a lithium-ion battery, comprising the following successive steps: poly(acrylonitrile-co-methyl acrylate) and lithium salt are mixed in an aprotic polar solvent; the mixture is stirred at room temperature until dissolved; the mixture is coated on a current collector; the mixture is left to dry until the solvent has evaporated and a solid electrolyte is obtained.

12. Manufacturing method according to claim 11, in which between 50 and 95% by weight of poly(acrylonitrile-co-methyl acrylate), preferably between 70 and 90% by weight, relative to the total weight of poly(acrylonitrile-co-methyl acrylate) and lithium salt, are mixed.

13. Manufacturing method according to claim 11 or 12, in which liquid electrolyte comprising lithium salt, such as a carbonate-based liquid electrolyte, is added to the solid electrolyte obtained after drying to obtain a semi-solid electrolyte, preferably between 40 and 80% by weight of liquid electrolyte relative to the total weight of the semi-solid electrolyte.