Composite material for the negative electrode of a battery comprising an active material whose surface is at least partially covered with a particular material

Abstract

The present invention relates to a composite material for a negative electrode of a battery comprising at least one active material for a negative electrode, the surface of which is at least partially covered with a layer of at least ZrW2O8.

Description

Title of the invention: Composite material for the negative electrode of a battery comprising an active material whose surface is at least partially covered with a particular material Technical field

[0001] The present invention relates to the field of batteries, such as Na-ion, K-ion, Li-ion and all-solid-state batteries. More particularly, the present invention relates to a particular composite material for a negative electrode. The invention also relates to a method for preparing said composite material. The present invention also relates to a negative electrode comprising the composite material, a battery cell comprising said negative electrode, a battery comprising said battery cell, as well as a vehicle comprising said battery. Previous techniques

[0002] Today, electrochemical energy storage systems have numerous applications in the fields of portable electronics (smartphones, laptops, portable tools, etc.) and more recently in the field of electric vehicles, a booming field. The most developed technology is Li-ion battery technology.

[0003] Indeed, Li-ion batteries developed since the 1990s are widely used as energy storage devices for mobility applications. This trend is explained in particular by mass and volume energy densities significantly higher than those of conventional nickel cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) accumulators, an absence of memory effect, low self-discharge compared to other accumulators and also by a reduction in costs per kilowatt-hour linked to this technology.

[0004] Li-ion batteries comprise active electrode materials that allow the insertion and removal of lithium ions during charging and discharging processes. These insertions and removals must be reversible so that the accumulator can store energy over several cycles.

[0005] Good mobility of the lithium ion in the structure as well as good electrical conductivity of the electrode material are essential properties allowing these batteries to be used at high charging and discharging speeds, allowing significant electrical power. The specific power of a battery is an important issue for automotive applications because it allows lighter batteries to be used for the same effort or it allows batteries to be used in safer conditions.

[0006] One of the classic Li-ion battery systems consists of the use of a liquid electrolyte, generally based on carbonate solvent, associated with active electrode materials, for example graphite for the negative electrode.

[0007] However, research is accelerating to develop batteries that can carry more energy, involving the use of innovative materials that allow the storage of a greater quantity of lithium. If we take the example of silicon, it has a theoretical specific capacity of approximately 3600 mAh / g, which is 10 times greater than that of graphite. If we take the example of silicon oxides SiOx, these have a theoretical specific capacity of approximately 2500-2700 mAh / g. These materials can be combined with other chemistries such as Na-ion and K-ion.

[0008] This intrinsic advantage of the materials nevertheless leads to a very significant volume expansion (> 300% for silicon, approximately 160% for silicon oxides SiOx) causing cracking of the particles as well as contact losses in the microstructure of the electrode, negatively affecting the electrochemical performances.

[0009] Indeed, lithiation-related expansion is normal and unavoidable in Li-ion batteries, and it occurs on a microscopic scale. However, when it becomes excessive due to factors such as overcharging, rapid charging / discharging, or design issues, it can lead to mechanical stresses that damage the battery. Battery swelling is often the result of this excessive expansion, and it can cause safety issues by causing chemical leaks or even short circuits.

[0010] This phenomenon can be exacerbated in the case of all-solid batteries which have an all-solid electrolyte where the mechanical constraints linked to expansion are greater.

[0011] On the other hand, the application of electric vehicles requires specific specifications such as fast charging. If silicon (and silicon oxides SiOx) has demonstrated its effectiveness, the (dis)charge is accompanied by a strong rise in temperature, in other words lost energy.

[0012] Thus, there is a need to develop active materials for negative electrodes that make it possible to have batteries with improved performance. Presentation of the invention

[0013] The subject of the invention is therefore a composite material for the negative electrode of a battery comprising at least one active material for the negative electrode, the surface of which is covered at least partially with a layer of at least ZrW2O8.

[0014] The composite material according to the invention makes it possible to contain volume expansion during (de)lithiation and the increase in temperature. It also makes it possible to obtain a negative electrode with good mechanical strength, thus leading to the preservation of excellent electrochemical properties of the battery. The composite material according to the invention therefore has a positive impact on the durability of the battery.

[0015] Another subject of the invention is a negative electrode of a battery comprising at least one composite material according to the invention. The invention also relates to a battery cell comprising at least one negative electrode according to the invention, a battery comprising at least one battery cell according to the invention, as well as a vehicle comprising at least one battery according to the invention.

[0016] The invention also relates to a process for preparing a composite material as defined above, comprising:

[0017] i) mixing the active material for negative electrode as defined above with at least ZrW2O8;

[0018] ii) spray drying of the mixture obtained at the end of step i);

[0019] iii) recovery of the material obtained at the end of step ii).

[0020] Other advantages and characteristics of the invention will appear more clearly upon examination of the detailed description.

[0021] 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.

[0022] As indicated above, the composite material for the negative electrode of a battery according to the invention comprises at least one active material for the negative electrode, the surface of which is covered at least partially with a layer of at least ZrW 2O8.

[0023] Advantageously, the surface of the active material for negative electrode is completely covered with a layer of at least ZrW2O8.

[0024] Thus, the composite material according to the invention is a coated material. The negative electrode active material is coated with a layer of at least ZrW2O8, with the surface of the negative electrode active material being covered at least partially, preferably completely, with a layer of at least ZrW2O8.

[0025] The ZrW2O8 material has the particularity of having a negative coefficient of thermal expansion. This coefficient of thermal expansion can be measured according to the ISO 17562:2016 standard between -196°C and 2000°C and expressed in K1.

[0026] Advantageously, the active material for the negative electrode is chosen from silicon and silicon oxides.

[0027] Advantageously, said layer has a thickness ranging from 5 to 200 nm, preferably from 5 to 100 nm, more preferably from 5 to 30 nm, even more preferably from 5 to 20 nm.

[0028] According to a particularly preferred embodiment, said layer is made of a material consisting solely of ZrW2O8.

[0029] The present invention also relates to a process for preparing a composite material as defined above, comprising:

[0030] i) mixing the active material for negative electrode as defined above with at least ZrW2O8;

[0031] ii) spray drying of the mixture obtained at the end of step i);

[0032] iii) recovery of the material obtained at the end of step ii).

[0033] This method makes it possible to obtain a composite material as defined above, making it possible to contain the volume expansion during (de)lithiation and the increase in temperature and making it possible to minimize the volume variations of the active material during (de)charging. The composite material according to the invention therefore ensures mechanical stability and provides an improvement in electronic conductivity compared to an active material in the form of a silicon oxide particle, or silicon particles, which is not coated, or whose surface is "bare".

[0034] Indeed, during the battery charging mechanism using such a “bare” silicon oxide particle or “bare” silicon, we witness the oxidation of the positive active material leading to the disinsertion of the Li+ cations which pass through the separator thanks to the electrolyte and are inserted into the negative active material, in our case silicon oxide or silicon, by reduction.

[0035] The quantity of theoretically insertable Li+ being high (volume variations of up to 400%), mechanical problems are generally observed, in particular cracks leading to contact losses within the silicon oxide particle (from 1 to 30 microns) or silicon. This phenomenon is reinforced by the increase in temperature which occurs during electrochemical reactions and particularly for high charging regimes (-20°C to 150°C), with an active material of silicon oxide or silicon.

[0036] Thus, swelling and fracturing of the silicon oxide particle, or silicon, are observed during lithiation.

[0037] Conversely, thanks to the composite material according to the invention, the layer of at least ZrW2O8 makes it possible to absorb the volume variation of the SiOx, or of the silicon, due to the increase in temperature during charging and to minimize the volume expansion of the SiOx, or of the silicon, due to the insertion of the Li+ cations.

[0038] Thus, swelling is limited and no fracturing of the active material is observed.

[0039] Advantageously, the method according to the invention further comprises iv) an application of heat at a temperature of at least 500°C, preferably for at least 5 minutes.

[0040] According to a preferred embodiment, the temperature is at least 600°C, preferably ranging from 600 to 800°C.

[0041] Advantageously, the heat may be applied for at least 1 hour, preferably for at least 4 hours, more preferably for at least 10 hours, even more preferably the heat may be applied for a period ranging from 10 to 14 hours.

[0042] The method according to the invention may also comprise a second application of heat at a temperature different from that applied during the application of heat iv).

[0043] Preferably, the temperature of the second heat application is higher than that applied during heat application iv).

[0044] Preferably, the temperature of the second heat application is greater than or equal to 900°C, preferably ranging from 900 to 1300°C.

[0045] According to a preferred embodiment, the second heat application is carried out for at least 5 minutes, preferably for at least 1 hour, more preferably for at least 3 hours, even more preferably the second heat application is carried out for a period ranging from 3 to 7 hours.

[0046] The invention also relates to a negative electrode of a battery comprising at least one composite material as defined above, and a battery cell comprising at least one negative electrode as defined above.

[0047] Another object of the present invention is a battery comprising at least one battery cell as defined above.

[0048] Preferably, the battery is a Na-ion, K-ion, Li-ion or all-solid-state battery.

[0049] The present invention also relates to a vehicle comprising at least one battery as defined above.

[0050] The present invention is illustrated in a non-limiting manner by the following examples. Examples Example 1: Preparation of an active material

[0051] An aqueous solution containing hydrated ammonium metatungstate ((NH4)6H2Wi2 O40.nH2O), hydrated zirconyl chloride (ZrOCl2.nH2O) and citric acid (C6H8 O7) was prepared. The pH of the solution was brought to a value of 6 by the addition of ammonia (NH3).

[0052] Silicon oxide (SiOx), with x = 1, in the form of particles having a D90 particle size equal to 10 pm, was then introduced into the solution such that the final mass ratio was equivalent to 0.5% zirconium tungstate (ZrW2O8) and 99.5% SiOx.

[0053] The mixture obtained was then sprayed using the atomization drying technique. mization (or the so-called "Spray-Drying" technique) thanks to its passage through a bifluid nozzle at a temperature of 200 °C, using the B-290 mini atomizer from Buchi.

[0054] The material was recovered in powder form from the equipment recipe and then heated to 700°C for 12 hours, then to 1180°C for 5 hours to ensure the formation of the ZrW2O8 compound.

[0055] The composite material comprising the active material SiOx coated with a layer of approximately 10 nm of ZrW2O8 is thus formed.

[0056] Example 2: Thermal evolution of the composite material between -10 and 50°C

[0057] The composite material prepared in Example 1 underwent a temperature increase of 60 °C in an oven. The total diameter of the composite particles is approximately 10 pm at -10 °C. The thermal stresses at 50 °C were calculated independently for SiOx and ZrW2O8 from their Young's modulus (respectively 150 Gpa and 88 Gpa) leading to the following values: 5.5 Gpa for SiOx and -7.9 Gpa for the ZrW2O8 coating. The stresses acting on the composite material amounting to -2.4 Gpa, the total diameter at 50 °C was determined by calculation and estimated at 9.82 pm including the coating while it was estimated at 10.363 pm for a particle without coating.

[0058] Example 3: Preparation of a negative electrode and preparation of a Li-ion battery

[0059] The negative electrode was prepared by mixing the composite material from Example 1 (84% by weight), an electronically conductive agent (Super P, 8% by weight) and a binder (polyacrylic acid, 8% by weight) dissolved in demineralized water. The ink was mixed using a Thinky ARE 250 and coated onto a copper current collector to obtain a basis weight approximately equal to 1.5 mg / cm2.

[0060] The button cell (CR2032) was then assembled using a cathode composed of lithium nickel manganese cobalt oxide (NMC622), Super P and polyvinylidene fluoride (CH2-CF2)n and coated on aluminum. The separator is Celgard 2320. The liquid electrolyte is composed of 1 M of LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a ratio of 50 / 50 by volume. The complete battery based on the composite material was thus manufactured.

[0061] Example 4: Preparation of a negative electrode and preparation of a Li-ion battery all-solid

[0062] The negative electrode was prepared by mixing in mortar the composite material from Example 1 (70% by weight), a solid argyrodite electrolyte (Li6PS5Cl, 20% by weight) and an electronic conductive agent (Super P, 10% by weight) by dry method.

[0063] The first step in manufacturing the battery consisted of introducing 60 mg of Li6PS5 Cl pressed at 100 MPa for 3 minutes into a poly(methyl methacrylate) (PMMA) mold with a diameter of 10 mm, to obtain the separator layer also playing the role of ionic conductor.

[0064] The second step was to add 10 mg of the previously prepared negative electrode to the separator and press at 200 MPa for 3 minutes.

[0065] Finally, the positive electrode composed of NMC622, Li6PS5Cl and Super P was added on the other side of the separator and pressed at 300 MPa for 3 minutes.

[0066] The entire system was maintained under a pressure of 100 MPa for cycling. The all-solid-state battery was thus manufactured.

Claims

Claims

1. Composite material for a negative electrode of a battery comprising at least one active material for a negative electrode whose surface is at least partially covered with a layer of at least ZrW2O8.

2. Composite material according to claim 1, characterized in that the surface of the active material for negative electrode is completely covered with a layer of at least ZrW2O8.

3. Composite material according to claim 1 or 2, characterized in that the active material for negative electrode is chosen from silicon and silicon oxides.

4. Composite material according to any one of the preceding claims, characterized in that said layer has a thickness ranging from 5 to 200 nm, preferably from 5 to 100 nm, more preferably from 5 to 30 nm, even more preferably from 5 to 20 nm.

5. Negative electrode of a battery comprising at least one composite material as defined in any one of the preceding claims.

6. Battery cell comprising at least one negative electrode as defined in claim 5.

7. A battery, such as a Na-ion, K-ion, Li-ion or all-solid-state battery, comprising at least one battery cell as defined in claim 6.

8. Vehicle comprising at least one battery as defined in claim 7.

9. A process for preparing a composite material as defined in any one of claims 1 to 4, comprising: i) mixing said active material for negative electrode with at least ZrW2O8; ii) spray drying the mixture obtained at the end of step i); iii) recovering the material obtained at the end of step ii).

10. Method according to the preceding claim, characterized in that it further comprises iv) an application of heat at a temperature of at least 500°C, preferably for at least 5 minutes.