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

Abstract

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.

Description

Title of the invention: Electrode and electrolyte for lithium-ion battery incorporating a polymer compound

[0001] The present invention relates, in general, to all-solid-state batteries, and in particular to all-solid-state lithium-ion batteries.

[0002] More specifically, the invention relates to an electrolyte material and an all-solid lithium-ion battery electrode material incorporating a polymer compound and, more particularly, to an electrolyte and a polymer binder comprising poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) and lithium salt.

[0003] Today the vast majority of electrochemical energy storage systems sold in electric vehicles are batteries using “Lithium-ion” technology.

[0004] These lithium technologies have seen increasing interest over the last thirty years compared to other battery technologies. They employ electrode materials called "active material" which must allow the reversible insertion and insertion of lithium ions during the charging and discharging processes.

[0005] However, conventional Li-ion technology is close to its performance limits insofar as there can be no compromise on lifespan or safety.

[0006] Conventional liquid electrolytes are composed of flammable carbonate solvents that can act as fuel in the event of accidental damage. This flammability poses a problem regarding the possibility of rapid charging. Indeed, high charging currents will induce a temperature rise inside the cells, which presents a problem with the liquid electrolyte.

[0007] The use of a solid electrolyte acting as a separator would reduce these safety problems while increasing the energy density of the so-called "all-solid-state" battery with the use of metallic lithium at the negative electrode. Good ionic conductivity greater than 10⁻² S / cm, electronic insulation, and high-potential stability greater than 4.5V are necessary to compete with conventional liquid electrolytes from an electrochemical performance standpoint.

[0008] 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.

[0009] It is known to use the poly(ethylene oxide) (POE) polymer in an all-solid-state battery for electric vehicles with iron phosphate (LiFePO4) as the positive electrode and the POE-LiTFSI complex for the all-solid-state electrolyte.

[0010] POE is easy to shape, has good mechanical strength and thermal stability well above 100°C, unlike liquid carbonate-based electrolytes.

[0011] However, POE only operates at a high temperature of 80°C and its potential stability window is narrow, ranging from 0 to 3.8V compared to Li+ / Li, which limits its use as a separator and also as a polymeric electrode binder when used with high-potential active materials. This prevents the use of high-potential cathode materials, thus limiting the energy density of such cells.

[0012] Thus, there is a need to develop new materials for all-solid-state batteries to overcome the disadvantages mentioned below.

[0013] The invention therefore aims to remedy these drawbacks and to propose a material for all-solid lithium-ion batteries providing improved electrochemical stability in potential and allowing operation at a temperature below 80°C.

[0014] A lithium-ion battery assembly is therefore proposed, 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.

[0015] In a first embodiment, the electrolyte comprises poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0016] The integration of PAN-co-MA makes it possible to obtain potential stability beyond 4.5 V vs Li / Li+ compared to lithium metal.

[0017] In a second embodiment, the polymeric binder of the electrode comprises poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0018] The integration of PAN-co-MA into the electrode does not cause parasitic reactions and ensures good electrode retention. Its use is suitable as an electrode binder.

[0019] In a third embodiment, the electrolyte and the polymeric binder of the electrode comprise poly(acrylonitrile-co-methyl acrylate) and lithium salt.

[0020] The simultaneous integration of PAN-co-MA in the electrode and in the electrolyte of an all-solid lithium-ion battery is particularly advantageous.

[0021] It has been observed that the compound poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) allows the all-solid-state lithium battery to operate at room temperature, and, exhibiting a wide potential stability window, makes it possible to use high-potential cathode materials. Furthermore, the energy density of cells incorporating this polymer compound is high.

[0022] Other features, aspects, objects and advantages will become apparent from the description that follows and from the following examples, given purely for illustrative purposes.

[0023] In this description, the expression "at least one" used is equivalent to the expression "one or more".

[0024] The invention relates to an assembly for a lithium-ion battery, 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.

[0025] The lithium-ion battery assembly according to the invention can be incorporated into an all-solid or semi-solid lithium-ion battery cell. Polymeric binder for electrode

[0026] In one embodiment, the electrode of the lithium-ion battery assembly may include a polymeric binder comprising PAN-co-MA and lithium salt.

[0027] Advantageously, the lithium salt may contain lithium bis(trifluoromethanesulfonyl)imidide (LiTFSI).

[0028] According to one feature, the lithium salt may consist of LiTFSI.

[0029] 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.

[0030] 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.

[0031] 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. Electrolyte

[0032] In one embodiment, the electrolyte of the lithium-ion battery assembly may comprise PAN-co-MA and lithium salt.

[0033] 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.

[0034] 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.

[0035] In one embodiment, the electrolyte may incorporate liquid electrolyte comprising lithium salt.

[0036] According to one example, the liquid electrolyte can be a carbonate-based liquid electrolyte.

[0037] Preferably, the electrolyte comprises between 40 and 80% liquid electrolyte relative to the total weight of the electrolyte.

[0038] 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.

[0039] The invention also relates to a method for manufacturing an electrolyte for lithium-ion batteries.

[0040] In a first step, PAN-co-MA and lithium salt are mixed in a polar aprotic solvent.

[0041] According to one example, the solvent can be dimethyl sulfoxide (DMSO).

[0042] The resulting mixture is stirred at room temperature until the PAN-co-MA and lithium salt dissolve in the solvent.

[0043] Once dissolved, the mixture is coated onto a current collector.

[0044] The coating is then dried until the solvent evaporates and a solid electrolyte is obtained.

[0045] The current collector is, for example, an aluminum sheet.

[0046] Preferably, in the first step, 50 to 95% by weight of PAN- is mixed co-MA, preferably between 70 and 90% by weight, in the solvent. These mass proportions are considered relative to the total weight of PAN-co-MA and lithium salt.

[0047] After drying of the coating, it may be possible to add liquid electrolyte containing lithium salt to obtain a semi-solid electrolyte.

[0048] Advantageously, a liquid electrolyte based on carbonates can be added after the coating has dried.

[0049] Preferably, an aprotic solvent is also added to the coating, for example DMSO.

[0050] Preferably, between 40 and 80% by weight of liquid electrolyte can be added. These mass proportions are considered relative to the total weight of the semi-solid electrolyte. Lithium-ion battery

[0051] The invention relates to a lithium-ion battery cell comprising an assembly as described above.

[0052] 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.

[0053] The invention also relates to a lithium-ion battery, comprising at least one cell or at least one assembly as described above.

[0054] The lithium-ion battery can be an all-solid-state battery or a semi-solid-state battery.

[0055] The invention further relates to a motor vehicle comprising at least one lithium-ion battery as described above.

[0056] It may be envisaged that the lithium-ion battery assembly as described above may be incorporated into a traction lithium-ion battery, for example in a motor vehicle.

[0057] 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.

[0058] The invention also relates to the use of an assembly as described above in a lithium-ion battery for operation of the lithium-ion battery at room temperature.

[0059] The present invention is illustrated in a non-limiting manner by the following examples of a process for forming an electrode binder and an electrolyte incorporating PAN-co-MA polymer and lithium salt.

[0060] Example 1: Electrode comprising a polymeric binder

[0061] A composite electrode has been formulated using PAN-co-MA polymer as a binder.

[0062] A composition was formed by adding 6% by weight of PAN-co-MA to the solvent N-methyl-2-pyrrolidone (NMP), followed by 2% by weight of lithium salt LiTFSI. These mass proportions are calculated with respect to the total weight of the mixture consisting of the solvent, PAN-co-MA, and lithium salt.

[0063] The composition is mixed using a mechanical mixer overnight at 50°C to obtain a polymeric binder in gel form.

[0064] In a thinky pot, 50% by weight of LiFePO4 (LFP), 10% by weight of Timcal SuperC65 carbon and 40% by weight of the polymer gel obtained previously are deposited so as to obtain 30% by weight of PAN-co-MA and 10% by weight of LiTFSI in the composite electrode.

[0065] The mixture is mixed in a Thinky mixer several times for 5 minutes at 1000 rpm before being coated onto a carbon-coated aluminum strip. The coating is left to dry overnight at 80°C in open air.

[0066] The electrode thus obtained is then electrochemically tested against lithium metal in the presence of a liquid electrolyte LPX based on carbonate and a lithium salt

[0067] The composition of the liquid electrolyte LPX is 1 mol / L of lithium salt LiPF6 in Ethylene carbonate (EC): Dimethyl carbonate (DMC): Ethyl methyl carbonate (EMC) in the following proportions 1:1:1 by volume.

[0068] The performance of a half-cell of lithium-ion formed by the obtained PAN-co-MA-based electrode and the LPX liquid electrolyte is tested. Galvanostatic cycling was carried out at room temperature (25°C), using 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 during the first cycle, stabilizing at 130 mAh / g after 50 cycles.

[0069] PAN-co-MA ensures good electrode retention and does not cause unwanted reactions. Its use is therefore suitable and particularly advantageous as an electrode binder. Example 2: Electrolyte

[0070] A solid electrolyte film was formulated using the PAN-co-MA polymer.

[0071] A composition is formulated by adding, in dimethyl sulfoxide solvent (DMSO), 5% by weight of PAN-co-MA relative to the weight of DMSO in the composition, and 25% by weight of lithium salt LiTFSI relative to the weight of PAN-co-MA in the composition.

[0072] The composition is mixed using a mechanical mixer for 24 hours.

[0073] The composition is then coated onto an aluminum strip using a doctor- blade set to 800 pm.

[0074] Initially, the electrolyte sample is dried in an open-air oven at 80°C overnight.

[0075] 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 water present in the air.

[0076] After drying, a solid electrolyte is obtained.

[0077] A two-electrode electrochemical cell was made in a glove box using a 10 mm diameter button cell device.

[0078] In the device, a pellet of solid electrolyte incorporating previously obtained PAN-co-MA, and a piece of lithium 4 mm in diameter, were placed between two stainless steel spacers. Two drops of conventional liquid electrolyte based on LPX carbonates were then added, representing 58% by weight of liquid electrolyte relative to the total weight of solid and liquid electrolyte.

[0079] The cell is subjected to electrochemical tests on a BioLogic potentiostat. A potential stability test by cyclic voltammetry is performed up to 5.5V vs Li / Li+ and at a temperature of 25°C. Potential stability of the cell was observed up to 5V vs Li / Li+.

[0080] Example 3: Assembly comprising an electrolyte and an electrode comprising a polymeric binder

[0081] 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 LiTFSI, is obtained according to the process described in Example 1.

[0082] A two-electrode electrochemical cell was made in a glove box using a 10 mm diameter button cell device.

[0083] In the device, an 8 mm diameter electrode pellet incorporating PAN-co-MA obtained according to the process described in Example 1, a solid electrolyte pellet incorporating PAN-co-MA obtained according to the process described in Example 2, and a 4 mm diameter piece of lithium were placed between two stainless steel spacers. Two drops of conventional liquid electrolyte based on LPX carbonates were then added, representing 58% by weight of liquid electrolyte relative to the total weight of solid and liquid electrolytes.

[0084] 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 at a cycling regime of C / 20.

[0085] A high capacity of 150 mAh / ga ​​was obtained during the first cycle and during the fifth charging cycle at 40°C.

[0086] Such capacities at 40°C are superior to those obtained with a POE-based material placed against LFP.

[0087] Example 4: Assembly comprising an electrolyte and an electrode comprising a polymeric binder

[0088] An electrochemical cell was formulated according to the process described in Example 3 in which, not 2 drops, but 4 drops of conventional liquid carbonate-based electrolyte (LPX) were added.

[0089] 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 at a cycling regime of C / 20.

[0090] The capacity obtained is greater 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.

[0091] Tests at 25°C were also carried out at higher cycling rates. At AC / 10 and C / 5, a capacity of 80 and 60 mAh / g, respectively, was observed.

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

[0093] The addition of 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 a solid or semi-solid electrolyte and as an 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 for galvanostatic cycling at room temperature and electrochemical stability above 4.5 V compared to Li / Li+ at room temperature, in relation to lithium metal.

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

Claims

Demands

1. Lithium-ion battery assembly, comprising an electrolyte and an electrode, the electrolyte comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt, and the electrolyte incorporating between 70 and 90% by weight of poly(acrylonitrile-co-methyl acrylate), relative to the total weight of the electrolyte.

2. Assembly according to claim 1, wherein the electrode incorporates a polymeric binder comprising poly(acrylonitrile-co-methyl acrylate) and lithium salt.

3. Assembly according to claim 1 or 2, wherein the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imidide.

4. Assembly according to any one of claims 1 to 3, wherein the polymeric binder of the electrode incorporates between 1 and 40 wt% of poly(acrylonitrile-co-methyl acrylate), preferably between 20 and 40 wt%, relative to the total weight of the electrode.

5. 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, wherein 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. 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-state lithium-ion battery at room temperature.

11. A method for manufacturing an electrolyte for a lithium-ion battery, comprising the following successive steps:

12. - lithium salt is mixed with between 70 and 90% by weight of poly(acrylonitrile-co-methyl acrylate), relative to the total weight of poly(acrylonitrile-co-methyl acrylate) and lithium salt, in a polar aprotic solvent; - Stir at room temperature until dissolved; - the mixture is coated onto a current collector; - it is left to dry until the solvent evaporates and a solid electrolyte is obtained. A manufacturing process according to claim 11, wherein 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.