Lithium-doped electrode in an electrode roll, and a secondary cell

Abstract

A negative electrode material (2, 5) adapted for an electrode assembly (10), and adapted to be provided onto on at least one side of a conductive substrate (1, 4), wherein the negative electrode material comprises SiOx and particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode, and in that said particulate lithium metal is encapsulated with a polymeric material or substance.

Description

[0001] LITHIUM-DOPED ELECTRODE IN AN ELECTRODE ROLL, AND

[0002] A SECONDARY CELL

[0003] TECHNICAL FIELD

[0004] The present disclosure generally pertains to a negative electrode material comprising an encapsulated lithium metal powder, an electrode assembly for secondary cells comprising said negative electrode material, and a method of manufacturing said negative electrode material and electrode assembly.

[0005] BACKGROUND

[0006] In addressing climate change, there is an increasing demand for rechargeable batteries, e.g., to enable electrification of transportation and to supplement renewable energy. Such batteries typically comprise a number of cells, often referred to as secondary cells.

[0007] In battery manufacturing it is known in the art to provide an electrically conductive sheet with a coating that is rolled up into a cylinder.

[0008] A conventional method for producing lithium-ion batteries consists of coating a metal oxide positive electrode onto a first side of an electrically conductive sheet, usually a foil of aluminum as a current collector, and coating a negative electrode made from carbon / graphite onto a second side of the electrically conductive sheet, providing a suitable separator and electrolyte made of lithium salt in an organic solvent.

[0009] Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g '), low density (0.59 g cm3) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode).

[0010] In recent years, silicon (Si) thin film has become more interesting to use as anode material, instead of the conventionally used carbon-based coatings. A drawback of Si thin films is the low electronic conductivity and volume changes that occur during lithiation / delithiation of the anode. Various attempts have been made to improve the Si thin film to form a doped and more reactive Si film. One such way is to provide an oxidized silicon reaction product i.e., lithium silicate, lithiated silicon and lithium oxide (Doped and reactive silicon thin film anodes for lithium-ion batteries: A review, Salah M, et al, Journal of Power Sources, Volume 506, 15 September 2021, 230194). A drawback of these Li doped Si materials is that they can cause uneven Li concentration in the anode electrode and uneven solid electrolyte interface (SEI) formation at a first charge step.

[0011] Further to this, in the production of the anode usually a water based solvent system for the anode slurry is used, and lithium is extremely reactive when it comes into contact with water.

[0012] As the demand for rechargeable batteries increases, more and more focus is also being placed on production speed. To achieve an effective production of rechargeable batteries, the production method and composition of the batteries can be optimized with fewer defects compromising the performance of the battery cell.

[0013] SUMMARY

[0014] It is in view of the above considerations and others that the embodiments of the present invention have been made. The present disclosure aims at providing highly performance secondary cells that are efficient in manufacture.

[0015] According to a first aspect, the present disclosure provides a negative electrode material for an electrode assembly, adapted to be provided onto on at least one side of a conductive substrate of said electrode assembly, wherein the negative electrode material comprises at least 10 wt.- % SiOx and particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode, and in that said particulate lithium metal is encapsulated with a polymeric material.

[0016] By pre-doping of lithium (Li) into the negative electrode material or the anode electrode material, the irreversible capacity can be minimized especially for Si and SiO anode. By adding lithium metal powder, or a particulate lithium metal, into the negative electrode material during the mixing process, a uniform SEI formation reaction is achieved as well as improved cell performance. By encapsulating the lithium metal powder particles with a polymeric material, the risk of the lithium reacting with the water in the anode coating slurry is eliminated.

[0017] According to one example, the polymeric material may be provided as a surface coating on said particulate lithium metal. The polymeric material may comprise any one of polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVdF). An advantage of particulate lithium metal encapsulated with a polymeric material comprising any one of PE, PP, and PVdF, where preferably the polymeric material comprising PE, is that such encapsulation is hydrophobic. Such hydrophobicity enables increased chemical stability in water-based slurries of the particulate lithium metal, over e.g. encapsulations comprising more hydrophilic polymers, such as poly(methyl methacrylate) (PMMA).

[0018] According to the first aspect, the particles of said particulate lithium metal may have a mean particle size (D50, volumetric mean value) in the range of 100 to 500 nm.

[0019] The D50, based on volumetric mean, of the particles of this disclosure may be measured by any method known to the person skilled in the art. Suitably, however, laser diffraction is used. Suitable methodologies for measuring particle size and particle size distributions by laser diffraction are detailed in ISO 13320:2020.

[0020] According to a second aspect there is provided a method of manufacturing a negative electrode material, comprising providing an aqueous slurry comprising at least 10 wt.-% SiOx, wherein said aqueous slurry further comprises particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode and in that said particulate lithium metal is encapsulated with a polymeric material / substance.

[0021] According to a third aspect there is provided an electrode assembly adapted for a secondary battery cell, the electrode assembly comprising: a first conductive substrate; a first electrode coating material provided on at least one side of the first conductive substrate; a second electrode substrate; a second electrode coating material provided on at least one side of the second conductive substrate; and a separator layer sandwiched between the first and second conductive substrate; wherein the first and second electrode coating material is at least partially coated on the first and second conductive substrate respectively, whereby said first and second conductive substrates exhibits uncoated portions and coated portions, wherein the first or second coating material comprises either a negative or a positive electrode material, wherein said negative electrode material comprises SiOx and particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode, and in that said particulate lithium metal is encapsulated with a polymeric material. According to a fourth aspect there is provided a secondary battery cell comprising the electrode assembly according to the third aspect. According to one example, said cell may be any one of a cylindrical, prismatic and pouch type cell.

[0022] According to a fifth aspect there is provided the use of a secondary battery cell according to the fourth aspect, in an electrical vehicle.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The embodiments disclosed herein are illustrated by way of example, and by not by way of limitation, in the figures of the accompanying drawing. Like reference numerals refer to corresponding parts throughout the drawings.

[0025] Fig. 1 schematically shows an illustration of an exemplary electrode assembly.

[0026] Fig. 2 shows the result for discharge capacity at different rates for examples 1-2

[0027] Fig. 3 shows the result for capacity retention for examples 1-2 as rated to example 2

[0028] Fig. 4 shows the result for capacity retention for examples 1-2 as rated to the respective example

[0029] DETAILED DESCRIPTION

[0030] Embodiments of the present disclosure will now be described more fully hereinafter. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art.

[0031] Figure 1 illustrates an electrode assembly 10, or a so-called jelly roll 7 or Swiss roll, with a first conductive substrate material 1 coated with a first electrode coating material 2, 2’, at least one insulating sheet or separator 3, and a second conductive substrate material 4 coated with a second electrode coating material 5, 5’ in a layered or sandwich design. The sandwiched layers may be rolled into the so-called jelly roll 7 and inserted into a hollow casing 6 to form a battery cell 8, which is then sealed. Fig. 1 is only a schematic representation of an exemplary battery cell. The battery cell may also be a prismatic or pouch type cell.

[0032] Said first or second electrode coating materials 2, 5 may be one of a cathode (negative electrode), or anode (positive electrode) material, and may be provided on one or both sides of the conductive substrate material. The first or second conductive substrate material 1, 4 may be a metal foil, such as a copper foil or aluminium foil, depending on the electrode coating.

[0033] The respective electrode material 2, 5 is conventionally coated onto the respective conductive substrate material 1, 4 as a liquid or aqueous slurry.

[0034] The positive electrode (cathode) material 2, 2’, 5, 5’ may be a conventional lithium-nickel- manganese-cobalt-oxide (LiNiMnCoO2), i.e., a NMC material. A typical NMC powder blend consists of 33% nickel, 33% manganese and 33% cobalt.

[0035] The negative electrode (anode) material or layer 2, 2’, 5, 5’ comprises an aqueous slurry or a mixture or composition, comprising silicon or silicon oxide SiOxand a particulate lithium (Li) metal or a lithium (Li) metal powder.

[0036] The slurry preferably comprises more than 10 % by weight of SiOxor SiOxin a range of 10 wt.-% to 100 wt.-%. SiOx is an anode active material, and it can be used with or without other active material like graphite.

[0037] The slurry preferably comprises particulate Li metal or Li metal powder in a range of about 5 to 30 wt.% in total solid component after drying the electrode. The indicated range of wt.% of particulate Li in the slurry is decided considering the amount of SiOx material in the cell.

[0038] The lithium metal particles in the powder are encapsulated or coated with a polymeric substance or material. The polymeric material may be provided as a surface coating layer. By “encapsulated with” is meant that the particles are rendered inert from reacting with solvent water in the anode slurry.

[0039] The thickness of said coating layer is preferably less than 200 nm. The encapsulation process of Li or Li powder may be performed as follows; provide a solution comprising a polymeric material and comprising as a solvent any one of an ethyl methyl carbonate (EMC), diethyl carbonate (DEC) dimethyl carbonate (DMC) and said polymeric material as a solute. The lithium metal powder may be polymer coated by spray-drying of said solution comprising said polymeric material. The polymeric material may comprise a polymer such as polyethylene (PE), polypropylene (PP), or polyvinylidene fluoride (PVdF), preferably PE. The encapsulation material may comprise an electrolyte-soluble polymer.

[0040] The particles of said particulate lithium metal have a mean particle size (D50) in the range of 100 to 500 nm.

[0041] The particles of said polymeric material have a mean particle size (D50) in the range of 10 to 100 um prior to encapsulation process of the particulate lithium metal.

[0042] The encapsulation or coating material does not substantially affect the cycling of Li / Li+in the charging / discharging operation of the battery cell.

[0043] The encapsulated lithium powder may be added together with other active material powder to secure homogenous distribution in the slurry.

[0044] The slurry may also contain any one of the following active materials, artificial graphite in a range of 0% to 90%, and natural graphite in a range of 0 % to 90%.

[0045] Carbon based material can be used as conducting agent, e.g., carbon black, carbon nanotubes (CNT), or flake type graphite. Organic and polymeric materials may be used as a binding agent, e.g., carboxymethyl cellulose (CMC), Styrene-Butadiene Rubber (SBR), poly acrylic acid (PAA), and polyvinyl alcohol (PVA).

[0046] The aqueous slurry formed may be controlled by checking the pH of the final slurry to detect if lithium reacts with water during the mixing, and / or by gas generation measurement for the final slurry to check if lithium reacts with water during the mixing. A rheology measurement may be performed to check the distribution uniformity.

[0047] The secondary battery cell may be an electrode-roll or cylindrical secondary cell, and may be for, or comprised in a vehicle battery or battery pack for propelling a vehicle. The secondary cell may also be any one of a cylindrical, prismatic and pouch type cell.

[0048] The vehicle may for example be a fully electrically propelled vehicle or a hybrid vehicle. The electrode coating material 2, 5 may be provided onto said conductive substrate material 1, 4 such that an entire long edge portion, or longitudinal edge portion, of the conductive substrate is left uncoated (not shown).

[0049] Further, the electrode coating material may be provided onto the conductive substrate 1, 4, such that there is a gap of uncoated conductive substrate between two portions of electrode coating 2, 5. This is often referred to as intermittent coating.

[0050] By high electrical voltage stability is meant V vs Li / Li+ in the range of 2.5 to 5.

[0051] Examples

[0052] Preparation of PE-coated Li metal powder

[0053] PE coated Li metal powder was prepared following the procedure below. Li metal powder (D50 at 500 nm), low-density PE (LDPE) powder (Mw at 50,000 g / mol, and D50 at 20 pm) and hexane were mixed in 1 : 1 :3 wt. ratio, for 30 minutes at room temperature in inert atmosphere. The mixture was heated to 160°C and passed through a spray drying process using a nozzle in inert atmosphere, where the inlet temperature was 160°C, outlet temperature was 80°C, using a spray pressure of 3 bar. The formed PE coated Li metal powder was subsequently heated at 90°C to remove the solvent.

[0054] Preparation example 1 - Preparation of Electrode including Li metal powder

[0055] The anode slurry was prepared mixing non-doped SiOx, Graphite, PAA binder and PE coated Li metal powder in 45:45:5:5 in wt.% in water-based system.

[0056] An anode electrode was prepared by applying the prepared anode slurry to a copper current collector, followed by doctor blading and drying. The anode electrode was pressed to the target electrode density, 1.2g / cc in this example, whereafter the pressed anode electrode was dried at 130°C for 8 hours under reduced pressure.

[0057] Preparation example 2 - Comparative example for preparation of Electrode without Li metal powder The anode slurry is prepared mixing non-doped SiOx, Graphite and PAA binder in 47.5:47.5:5 in wt.% in water-based system.

[0058] An anode electrode was prepared by applying the prepared anode slurry to a copper current collector, followed by doctor blading and drying. The anode electrode was pressed to the target electrode density, 1.2g / cc in this example, whereafter the pressed anode electrode was dried at 130°C for 8 hours under reduced pressure.

[0059] Example 1. Preparation of Pouch cell including Li metal powder

[0060] A pouch cell was assembled using the anode electrode prepared according to example 1, together with cathode electrode including an active layer comprising NCM811, a conductive agent, and a binder; and a ceramic-coated PE-based separator. The cell also contained nonaqueous electrolyte comprising a carbonate-based solvent and LiPFe salt.

[0061] Example 2. Preparation of Pouch cell without Li metal powder - comparative example

[0062] A pouch cell was assembled using the anode electrode prepared according to example 2, together with cathode electrode including an active layer comprising NCM811, a conductive agent, and a binder; and a ceramic-coated PE-based separator. The cell also contained nonaqueous electrolyte comprising a carbonate-based solvent and LiPFe salt.

[0063] Evaluation 1 of example cells - coulombic efficiency

[0064] Pouch cells made according to examples 1-2 above were charged and discharged between 2.8- 4.2 V using a rate of O. IC.The electric current was recorded during the first charge and first discharge. A coulombic efficiency was calculated for each example, based on the total charge during charge and discharge. Example 1 had a coulombic efficiency of 90 %, whereas example 2 only had a coulombic efficiency 76 %, showing that the encapsulated particulate lithium metal improves the coulombic efficiency of a comparative cell.

[0065] Evaluation 2 of example cells - rated discharge capacity Pouch cells made according to examples 1-2 above were charged and discharged between 2.8-

[0066] 4.2 V using an increasing rate for each charge / discharge cycle, using the rates C / 3, C / 2, C, 2C, and 3C, while recording the electric current.The discharge capacity retention in relation to the discharge capacity at C / 3 was calculated. Figure 2 shows the results of this test for examples 1-2, where it is evident that the addition of encapsulated particulate lithium metal did not alter the capacity retention at higher rates.

[0067] Evaluation 3 of example cells - capacity

[0068] Pouch cells made according to examples 1-2 above were charged and discharged between 2.8-

[0069] 4.2 V using a rate of 1C, except every fiftieth charge / discharge cycle starting at the first charge / discharge cycle where instead the rate was C / 3. The electric current was recorded and the discharge capacity retention in relation to the first discharge of a cell according to example 2 was calculated. Figure 3 shows the results of these measurements, providing the data points for each fiftieth cycle at C / 3 as described above. It is evident that example 1 shows a higher capacity retention than example 2, illustrating the effect of the added particulate lithium metal, as well as the effect of the encapsulation providing chemical stability during electrode production.

[0070] Evaluation 4 of example cells - cycle life

[0071] Pouch cells made according to examples 1-2 above were charged and discharged between 2.8-

[0072] 4.2 V using a rate of 1C, except every fiftieth charge / discharge cycle starting at the first charge / discharge cycle where instead the rate was C / 3. The electric current was recorded and the discharge capacity retention for each example in relation to the first discharge of respective example was calculated. Figure 4 shows the results of these measurements, providing the data points for each fiftieth cycle at C / 3 as described above. It is evident that example 1 shows a higher capacity retention over long term charge / discharge cycling than example 2, illustrating the effect of the added particulate lithium metal, as well as the effect of the encapsulation providing chemical stability during electrode production.

[0073] Modifications and other variants of the described embodiments will come to mind to ones skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure.

[0074] Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “comprise / comprises” or “include / includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS1. A negative electrode material (2, 5) for an electrode assembly (10), adapted to be provided onto on at least one side of a conductive substrate (1, 4) of said electrode assembly (10); characterized in that the negative electrode material comprises at least 10 wt.-% SiOxand particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode, and in that said particulate lithium metal is encapsulated with a polymeric material.

2. The negative electrode material (2, 5) according to claim 1, wherein said polymeric material is provided as a surface coating on said particulate lithium metal.

3. The negative electrode material (2, 5) according to claims 1-2, wherein said polymeric material comprises any one of polyethylene (PE), polypropylene (PP) and poly vinylidene fluoride (PVdF), preferably comprises polyethylene (PE).

4. The negative electrode material (2, 5) according to any of the preceding claims wherein said particles of said particulate lithium metal have a mean particle size in the range of 100 to 500 nm.

5. A method of manufacturing a negative electrode material (2, 5), comprising providing an aqueous slurry comprising at least 10 wt.-% SiOx, characterized in that said aqueous slurry further comprises particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode and in that said particulate lithium metal is encapsulated with a polymeric material.

6. An electrode assembly (10) adapted for a secondary battery cell, the electrode assembly comprising: a first conductive substrate (1); a first electrode coating material (2, 2’) provided on at least one side of the first conductive substrate (1); a second electrodesubstrate (4); a second electrode coating material (5, 5’) provided on at least one side of the second conductive substrate (4); and at least one separator layer (3) sandwiched between the first and second conductive substrate (1, 4); wherein the first and second electrode coating material (2, 5) is at least partially coated on the first and second conductive substrate (1, 4) respectively, whereby said first and second conductive substrates (1, 4) exhibits uncoated portions and coated portions (2, 5), wherein the first or second coating material (2, 5) comprises either a negative or a positive electrode material, characterized in that said negative electrode material comprises SiOx and particulate lithium metal in a range of about 5 to 30 wt.% in total solid component after drying the electrode, and in that said particulate lithium metal is encapsulated with a polymeric material.

7. A secondary battery cell (8) comprising the electrode assembly (10) according to claim 6.

8. The secondary battery cell (8) according to claim 7, wherein said cell is any one of a cylindrical, prismatic and pouch type cell.

9. Use of a secondary battery cell (8) according to claim 7 or 8, in an electrical vehicle.

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