Process for preparing a negative electrode comprising lithium carbonate

Abstract

The present invention relates to a method for preparing a negative electrode for a Li-ion battery comprising: a) mixing a solution S1 comprising at least one binder L1 with a solution S2 comprising lithium carbonate; b) adding at least one active material for a negative electrode to the solution obtained at the end of step a).

Description

Title of the invention: Process for preparing a negative electrode comprising lithium carbonate Technical field

[0001] The present invention relates to the field of lithium-ion (Li-ion) batteries. More particularly, the present invention relates to a method for preparing a negative electrode incorporating lithium carbonate. The invention also relates to a method for preparing an assembly formed by the negative electrode and a current collector comprising preparing said negative electrode by the method for preparing the negative electrode. The present invention also relates to a Li-ion battery cell comprising said negative electrode or said assembly formed by the negative electrode and the current collector, as well as a vehicle comprising said battery. Previous techniques

[0002] Conventionally, Li-ion batteries comprise one or more positive electrodes, one or more negative electrodes, an anode current collector, a cathode current collector, an electrolyte and a separator.

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

[0004] Li-ion batteries comprise active electrode materials that allow the insertion and deinsertion of lithium ions during charging and discharging processes. These insertions and deinsertions 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 the automotive application 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 an electrolyte liquid, generally based on carbonate solvent, combined with active electrode materials. In industry, a so-called formation step is carried out after battery manufacture, in which a specific charge / discharge program is applied to enable the creation of stable interfaces and in particular the SEI (Solid Electrolyte Interphase) on the anode side.

[0007] This electrolyte reduction reaction nevertheless causes difficulties. Lithium is consumed during the formation of the SEI, thus causing an irreversible capacity to be obtained. In addition, a poorly controlled SEI on the active materials for the negative electrode can lead to reduced cyclability and therefore a vehicle mileage range directly impacted over the charge and discharge cycles.

[0008] However, it is found that the SEI is often poorly controlled, thus impairing the proper functioning of Li-ion batteries. The SEI is then not robust enough.

[0009] Thus, there is a need to develop negative electrodes allowing Li-ion batteries to have improved performance. Statement of the invention

[0010] The subject of the invention is therefore a method for preparing a negative electrode for a Li-ion battery comprising:

[0011] a) mixing a solution SI comprising at least one binder L1 with a solution S2 comprising lithium carbonate;

[0012] b) adding at least one active material for a negative electrode to the solution obtained at the end of step a).

[0013] The method for preparing a negative electrode for a Li-ion battery according to the invention makes it possible to lead to the formation of a more robust SEI, thus leading to the production of Li-ion batteries having improved performance. Indeed, a more robust SEI results in an improvement in the irreversible capacity in the first charge and discharge cycle. In addition, the capacity retention is improved. Thus, a more robust SEI has a positive impact on the cyclability, and which therefore has a positive impact on the durability of the Li-ion battery.

[0014] The invention also relates to a method for preparing an assembly formed by the negative electrode and a current collector comprising:

[0015] i) the preparation of the negative electrode by the method of preparation according to the invention of the negative electrode;

[0016] ii) coating said negative electrode on said current collector.

[0017] Another object of the invention is a Li-ion battery cell comprising at least a negative electrode obtained by the preparation method according to the invention or at least one assembly formed by the negative electrode and a current collector obtained by the method according to the invention.

[0018] The invention also relates to a battery comprising at least one Li-ion battery cell according to the invention and a vehicle comprising at least one battery according to the invention.

[0019] Other advantages and characteristics of the invention will appear more clearly on examining the detailed description and the attached drawings in which:

[0020] [Fig. 1] is a diagram representing a negative electrode obtained by the preparation method according to the invention of the negative electrode;

[0021] [Fig.2] is a diagram representing an assembly formed by the negative electrode and a current collector obtained by the preparation method according to the invention of said assembly.

[0022] 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.

[0023] As indicated above, the method of preparing a negative electrode according to the invention comprises a) mixing a solution SI comprising at least one binder L1 with a solution S2 comprising lithium carbonate.

[0024] According to a preferred embodiment, the solution S1 comprises water. Thus, according to this preferred embodiment, the solution S1 is an aqueous solution.

[0025] Advantageously, the binder L1 is chosen from saccharides and their mixtures, preferably from oligosaccharides, polysaccharides and their mixtures, such as carboxymethyl cellulose, hydroxyethylcellulose, chitosan, alginates, pectins, amylose, xanthan gum, gum arabic, gellan gum, karaya gum, guar gum, more preferably from celluloses, such as carboxymethyl cellulose, hydroxyethylcellulose, and their mixtures, even more preferably from carboxymethyl cellulose.

[0026] Advantageously, the content of binder L1 ranges from 0.1 to 5% by weight, preferably from 0.5 to 4% by weight, more preferably from 1 to 3% by weight, even more preferably from 1.5 to 2.5% by weight relative to the weight of the solution SI.

[0027] The SI solution may further comprise at least one electronic conduction agent, preferably chosen from a carbon material, more preferably chosen from carbon black, acetylene black, graphite, carbon nanotubes, and mixtures thereof, even more preferably carbon black.

[0028] According to a preferred embodiment, solution S2 comprises water. Thus, according to this preferred embodiment, solution S2 is an aqueous solution.

[0029] According to a preferred embodiment, the lithium carbonate is in the form of particles. Lithium carbonate has the advantage of being a water-soluble lithium additive.

[0030] Advantageously, the lithium carbonate content ranges from 0.1 to 10% by weight, preferably from 0.5 to 6% by weight, more preferably from 2 to 4% by weight relative to the weight of solution S2.

[0031] The method of preparing the negative electrode according to the invention further comprises b) adding at least one active material for a negative electrode with the solution obtained at the end of step a).

[0032] The negative electrode active material is not specifically limited and may be any negative electrode active material generally known to those skilled in the art in the world of Li-ion batteries.

[0033] Advantageously, said active material for negative electrode is chosen from: graphite, silicon oxides, silicon carbides, and mixtures thereof, preferably among graphite, silicon carbides and mixtures thereof.

[0034] The method of preparing the negative electrode according to the invention may further comprise c) mixing a solution S3 comprising at least one binder L2 with the solution obtained at the end of step b).

[0035] According to a preferred embodiment, solution S3 comprises water. Thus, according to this preferred embodiment, solution S3 is an aqueous solution.

[0036] Preferably, the binder L2 is chosen from ethylene and propylene copolymers, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and mixtures thereof, preferably from styrene-butadiene copolymers.

[0037] Advantageously, the content of binder L2 ranges from 1 to 60% by weight, preferably from 10 to 55% by weight, more preferably from 20 to 50% by weight, even more preferably from 30 to 50% by weight relative to the weight of the solution S3.

[0038] The present invention also relates to a method for preparing an assembly formed by the negative electrode and a current collector.

[0039] Said preparation process comprises:

[0040] i) the preparation of the negative electrode by the process as defined above;

[0041] ii) coating said negative electrode on said current collector.

[0042] Coating step ii) may be carried out by casting said negative electrode obtained at the end of step i) onto a current collector, such as an anodic current collector.

[0043] Preferably, the current collector is a copper current collector.

[0044] The assembly obtained can then be dried by heating at a temperature ranging from 50 to 120°C, preferably from 60 to 100°C, more preferably from 70 to 90°C.

[0045] After drying, the assembly can be calendered.

[0046] Reference will be made to Figures 1 and 2 which are diagrams representing, respectively, a negative electrode obtained by the preparation method according to the invention as defined above, and an assembly formed by the negative electrode and a current collector obtained by the preparation method according to the invention of said assembly.

[0047] As seen in [Fig.l], the negative electrode 1 comprises negative electrode active material 2 which is in the form of spheres in two rows. The negative electrode 1 also comprises an electronic conduction agent 3, typically carbon black, and also a mixture of binders L1 and L2 4, typically a mixture of carboxymethyl cellulose and styrene-butadiene copolymer.

[0048] Finally, the negative electrode 1 comprises lithium carbonate 5, the particles of which are distributed over the entire negative electrode 1. Thus, the lithium carbonate 5 is present within the microstructure of the negative electrode 1.

[0049] These lithium carbonate particles 5 can form a film and make it possible to obtain a robust SEI.

[0050] Furthermore, after coating the negative electrode on a current collector, such as an anode current collector, the negative electrode 1 is obtained, as seen in [Fig.2], coated on the anode current collector 6, such as a copper current collector.

[0051] The invention also relates to a Li-ion battery cell comprising at least one negative electrode obtained by the method as defined above or at least one assembly formed by the negative electrode and a current collector obtained by the method as defined above.

[0052] Another object of the present invention is a battery comprising at least one Li-ion battery cell as defined above, as well as a vehicle comprising at least one battery as defined above.

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

[0054] Example 1: Preparation of a negative electrode comprising graphite as active material

[0055] An SI solution comprising carboxymethyl cellulose (CMC) was prepared in water by stirring with a magnetic bar. The content of carboxymethyl cellulose is 2% by weight relative to the total weight of the SL solution. Then, the SI solution was mixed with carbon black in a planetary mixer for 5 min at 1500 rpm.

[0056] A solution S2 comprising lithium carbonate was also prepared in water by stirring with a magnetic bar. The lithium carbonate content is 3% by weight relative to the total weight of the solution S2.

[0057] The two solutions S1 and S2 were then mixed in the planetary mixer for 5 min at 1500 rpm.

[0058] Then, graphite was added into the solution resulting from the mixture of the two SI solutions and S2. After adding the graphite, the whole was mixed in the planetary mixer for 5 min at 1500 rpm.

[0059] The viscosity was then adjusted with water and then a solution S3 comprising the styrene-butadiene copolymer (styrene-butadiene rubber SBR) was prepared in water. The content of styrene-butadiene copolymer is 40% by weight relative to the total weight of the solution S3.

[0060] Solution S3 was added to the solution resulting from the mixture of the two solutions S1 and S2 and graphite, then mixed again in the planetary mixer for 5 min at 1500 rpm.

[0061] The resulting electrode contains the following weight percentages of Graphite / Carbon Black / CMC / SBR / Lithium Carbonate: 96 / 1 / 1 / 1 / 1.

[0062] Example 2: preparation of an assembly formed by the negative electrode prepared in example 1 and the current collector

[0063] After mixing all the ingredients as described in Example 1, the electrode was cast as a film (having a thickness of 150 micrometers) onto the copper current collector.

[0064] The assembly obtained was then dried at 80°C for 10 hours in an oven. The assembly obtained was then calendered and is now ready for use in a Li-ion battery.

[0065] Example 3: Preparation of a negative electrode comprising silicon carbide as active material

[0066] An SI solution comprising carboxymethyl cellulose (CMC) was prepared in water by stirring with a magnetic bar. The content of carboxymethyl cellulose is 2% by weight relative to the total weight of the SL solution. Then, the SI solution was mixed with carbon black in a planetary mixer for 5 min at 1500 rpm.

[0067] A solution S2 comprising lithium carbonate was also prepared in water by stirring with a magnetic bar. The lithium carbonate content is 3% by weight relative to the total weight of the solution S2.

[0068] The two solutions S1 and S2 were then mixed in the planetary mixer for 5 min at 1500 rpm.

[0069] Then, silicon carbide (SiC) was added to the solution resulting from the mixture of the two solutions SI and S2. After adding the graphite, the whole was mixed in the planetary mixer for 5 min at 1500 rpm.

[0070] The viscosity was then adjusted with water and then a solution S3 comprising the styrene-butadiene copolymer (styrene-butadiene rubber SBR) was prepared in water. The content of styrene-butadiene copolymer is 40% by weight relative to the total weight of the solution S3.

[0071] Solution S3 was added to the solution resulting from the mixture of the two solutions SI and S2 and silicon carbide, then mixed again in the planetary mixer for 5 min at 1500 rpm.

[0072] The resulting electrode contains the following weight percentages of SiC / Carbon Black / CMC / SBR / Lithium Carbonate: 92 / 2 / 2 / 2 / 2.

[0073] Example 4: preparation of an assembly formed by the negative electrode prepared at example 3 and the current collector

[0074] After mixing all the ingredients as described in Example 3, the electrode was cast as a film (having a thickness of 150 micrometers) onto the copper current collector.

[0075] The assembly obtained was then dried at 80°C for 10 hours in an oven. The assembly obtained was then calendered and is now ready for use in a Li-ion battery.

Claims

Claims

1. A method for preparing a negative electrode for a Li-ion battery comprising: a) mixing a solution SI comprising at least one binder L1 with a solution S2 comprising lithium carbonate; b) adding at least one active material for a negative electrode to the solution obtained at the end of step a).

2. Method according to claim 1, characterized in that the binder L1 is chosen from saccharides and their mixtures, preferably from oligosaccharides, polysaccharides and their mixtures, more preferably from celluloses, such as carboxymethyl cellulose, hydroxyethylcellulose, and their mixtures, even more preferably from carboxymethyl cellulose.

3. Method according to claim 1 or 2, characterized in that the SI solution further comprises at least one electronic conduction agent, preferably chosen from a carbon material, more preferably chosen from carbon black, acetylene black, graphite, carbon nanotubes, and mixtures thereof, even more preferably carbon black.

4. Method according to any one of the preceding claims, characterized in that the active material for negative electrode is chosen from graphite, silicon oxides, silicon carbides, and mixtures thereof, preferably from graphite, silicon carbides and mixtures thereof.

5. Method according to any one of the preceding claims, characterized in that the method further comprises: c) mixing a solution S3 comprising at least one binder L2 with the solution obtained at the end of step b).

6. Method according to claim 5, characterized in that the binder L2 is chosen from ethylene and propylene copolymers, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and mixtures thereof, preferably from styrene-butadiene copolymers.

7. A method of preparing an assembly formed by the negative electrode and a current collector comprising: i) preparing the negative electrode by the method as defined in any one of the preceding claims; ii) coating said negative electrode on said current collector; fluent.

8. Li-ion battery cell comprising at least one negative electrode obtained by the method as defined in any one of claims 1 to 6 or at least one assembly formed by the negative electrode and a current collector obtained by the method as defined in claim 7.

9. A battery comprising at least one Li-ion battery cell as defined in claim 8.

10. Vehicle comprising at least one battery as defined in claim 9.

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