Prelithiation of Lithium-Ion Battery Anodes

Abstract

The present invention provides a process for prelithiating anode materials for lithium-ion batteries.

Description

[Technical field]

[0001] The present invention relates to a new process for prelithiating anode materials for lithium-ion batteries. [Background technology]

[0002] Lithium-ion batteries are used in a variety of consumer electronics and are increasingly being adopted in electric vehicles. Researchers and developers are focusing on improving the performance of lithium-ion batteries for such applications. A problem with some anode materials is the loss of lithium during battery cycling, especially during the first charge / discharge cycle, which is usually irreversible and can be relatively large. Graphite, silicon materials, and mixtures of graphite and silicon materials are often used as anode materials in lithium-ion batteries.

[0003] Irreversible first cycle lithium loss can be caused by the consumption of lithium ions in the formation of a solid electrolyte interface layer (SEI). To minimize lithium loss through this pathway, anodes are often prelithiated, and several techniques have been developed. Prelithiated anodes can be formed by intercalation or alloying reactions of lithium ions with carbon-based or silicon-based anode materials. Another prelithiation method, called the "direct contact" or "internal short" method, involves bringing lithium metal into direct contact with the anode in the presence of an electrolyte solution, which releases electrons to ionize the lithium metal; lithium foil or lithium powder is often used as the lithium metal source.

[0004] In the direct contact prelithiation method, both lithium foil and lithium metal powder have drawbacks as lithium sources. Thin (20 μm or less) lithium foil can uniformly cover the anode surface, but is fragile and expensive. Thick lithium foil (50 μm or more) must be cut into strips to prevent overloading the anode, but this does not uniformly cover the anode surface. Lithium metal powder can uniformly cover the anode surface, but the increased pressure required to break the passivation layer of lithium metal powder can damage the anode, and the high surface area of ​​lithium metal powder can enhance the reaction rate with the electrolyte, thereby increasing the temperature of the electrochemical cell.

[0005] Thus, there is a need for new and improved methods for prelithiation of lithium-ion battery anodes that minimize or eliminate the irreversible loss of lithium during the first charge / discharge cycle. Summary of the Invention

[0006] The present invention provides a process for prelithiation of anode materials. An advantage of the process described herein is that it allows for control of the lithium loading on the anode material. Another advantage provided by the present invention is that thick lithium foils (50 μm or greater) can be used without experiencing the drawbacks normally associated with such foils.

[0007] One embodiment of the present invention is a process for prelithiating an anode material, the process comprising contacting the anode material with a substrate surface of a substrate material in an electrochemical cell, the substrate surface comprising patterned lithium, to form a prelithiated anode material.

[0008] Another embodiment of the present invention is a process for preparing a patterned lithium-containing substrate surface. The process comprises: forming a layered sheet from a protective material, a lithium-containing foil, and a substrate material, the protective material contacting one side of the lithium-containing foil and a substrate surface of the substrate material contacting the other side of the lithium-containing foil; placing the layered sheet on a patterning device, patterning the layered sheet with the patterning device, and removing the layered sheet from the patterning device; removing the protective material and the lithium-containing foil from the substrate surface of the substrate material to obtain a substrate material comprising a substrate surface comprising patterned lithium.

[0009] Another embodiment of the invention includes a process for prelithiating an anode material, the process comprising preparing a substrate material comprising a substrate surface comprising patterned lithium, and contacting the anode material with the substrate surface of the substrate material in an electrochemical cell to form a prelithiated anode material, the substrate surface comprising patterned lithium.

[0010] These and other embodiments and features of the present invention will become further apparent from the following description, drawings, and appended claims. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagrammatic representation of a protective layer, a lithium-containing foil, a substrate material, and layered sheets formed therefrom. [Diagram 2] FIG. 1 shows two pseudo-shaded confocal micrographs showing different heights of Li on the Cu foil due to two different patterning pressures using the same die. [Figure 3A] 1 is a photograph of a copper foil substrate having lithium patterned thereon. [Figure 3B] Photograph of the same copper foil substrate after prelithiation of the anode material.

[0012] The drawings depict embodiments of certain aspects of the invention and are not intended to impose limitations on the scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] To prepare a substrate material that includes a patterned lithium-containing substrate surface, the first step is generally to form a layered sheet from a protective material, a lithium-containing foil, and a substrate material. In the layered sheet, the protective material is in contact with one side of the lithium-containing foil and the substrate is in contact with the other side of the lithium-containing foil. In the layered sheet, the lithium-containing foil is an intermediate layer between the protective material and the substrate. This is illustrated in FIG. 1, which shows a protective layer 2, a lithium-containing foil 4, a substrate material 6, and a layered sheet 8 formed therefrom. The substrate material 6 has a substrate surface 6a that contacts the lithium-containing foil 4 to form a patterned lithium-containing substrate surface of the substrate material.

[0014] The purpose of the protective material is to prevent the lithium-containing foil from adhering to the surface of the patterning device, and the protective material can be any convenient material that does not tear under the patterning conditions. Typically, the protective material is a plastic film, such as a polyethylene or polypropylene film.

[0015] Suitable lithium-containing foils include lithium metal foils and lithium alloy foils, including LiMg foils, LiAl foils, LiAg foils, LiSn foils, and LiZn foils. In many cases, lithium metal foils are preferred.

[0016] The lithium-containing foils typically have a thickness ranging from about 30 μm to about 200 μm, more often from about 40 μm to about 150 μm. Although this parameter has not been optimized, it is recognized that thicker foils will transfer more lithium under the same patterning conditions.

[0017] The substrate material can be any convenient material, including metal foils and plastic films such as polyethylene or polypropylene films. Metal foils are the preferred substrate material and are generally selected from metals such as nickel or copper. Preferred metal foils include copper foil and nickel foil, with copper foil being more preferred.

[0018] It is recommended and preferred that the lithium-containing foil be handled in the absence of water (e.g., about 1.5% humidity or less). This can be accomplished in a vacuum or an inert atmosphere such as helium, nitrogen, or argon. An inert atmosphere is preferred. Incidental amounts of water may be present. When the layered sheet is formed, the lithium-containing foil is essentially encased between the protective material layer and the substrate material layer, so there is no need to drain the moisture.

[0019] The layered sheet is placed into a patterning device and subjected to the patterning instructions of the device, which include die presses, automated stamping machines, and roll presses, where the pattern is transferred from the roller to the layered sheet.

[0020] A variety of patterns can be punched to transfer the lithium to the substrate material. Examples of patterns that can be used include dot matrices and parallel lines. The density of some patterns can vary. For example, in a dot matrix pattern, the number of dots per unit area can be varied, and in the case of parallel lines, the line width and / or spacing between the lines of the pattern can be different. Such variations in the pattern usually require the use of different patterning elements (dies or rollers) for each variation of the pattern. Varying the pattern is one way to vary the amount of lithium transferred from the lithium-containing foil to the substrate material.

[0021] When a die and press are used, the type of press used to apply pressure to the die is not believed to be particularly important. A floor press can be used. When the patterning device is a floor press die, the layered sheet is placed in the die and typically stamped with a pressure of about 1000 psi to about 3000 psi (about 6.89 MPa to about 20.7 MPa), preferably about 1500 psi to about 2500 psi (about 10.3 MPa to about 17.2 MPa). This parameter has not been optimized.

[0022] This process forms a shaped layered sheet that is removed from the patterning device. The patterning process transfers the lithium (and other metal(s) if alloys are used) from the foil to the substrate surface in the pattern from the patterning device.

[0023] It will be understood that throughout this document, the lithium (and other metals, if alloyed) is transferred onto the surface of the substrate material, although some of the transferred metal atoms may be below the surface of the substrate material, and results to date indicate that most of the transferred metal(s) remain at the surface of the substrate material, and the extent to which the transferred metal atoms penetrate below the surface, if at all, is not known.

[0024] Removal of the protective layer and lithium-containing foil results in a substrate material comprising a substrate surface containing patterned lithium. It may be possible to remove the substrate material from the lithium-containing foil and protective material in one step, the protective material and lithium-containing foil remaining together, which is not recommended as this may result in some of the transferred lithium being removed from the substrate material. Preferably, the protective layer is removed from the lithium-containing foil, and then the lithium-containing foil is removed from the substrate. A factor to consider when selecting a foil is the ease of removal of the lithium-containing foil from the patterned substrate material.

[0025] There are advantages gained by this patterning process. The amount of lithium transferred to the substrate material can be controlled by varying the thickness of the lithium foil and / or by varying the conditions used in the patterning device. The same patterning device can be used at different conditions, such as different pressures, to transfer different amounts of lithium to the substrate material without changing the composition of the layered sheet fed to the device. Another way to vary the amount of lithium transferred to the substrate material is to feed layered sheets containing lithium-containing foils of different thicknesses to the patterning device without changing the patterning conditions. Both the thickness of the lithium-containing foil and the conditions of the patterning device can be varied to transfer a wider range of lithium amounts without the need to use different patterning dies, rollers, or devices.

[0026] An illustration of different amounts of transferable lithium is shown in Figure 2, which are two pseudo-shadow micrographs from a confocal microscope showing different heights of lithium transferred onto a copper foil (substrate material). In Figure 2, the height of lithium 10 on the substrate surface 6a of substrate material A is about 10 μm, and the height of lithium 10 on the substrate surface 6a of substrate material B is about 35 μm. The different heights indicate different amounts of lithium transferred to the substrate surface of the substrate materials.

[0027] The ability to control the height of the transferred lithium pattern allows the same patterning element in the same patterning device to transfer different amounts of lithium to a substrate, eliminating the need to change the patterning element (e.g., die or roller) to transfer more or less amounts of lithium. In some preferred embodiments, a greater amount of lithium can be transferred by, for example, using the same die at a higher pressure. In other embodiments, a greater amount of lithium can be transferred at the same pressure by changing the die or roller to one with a denser pattern, such as a dot matrix die with more dots per unit area.

[0028] In the prelithiation process, the anode material and a substrate surface of a substrate material are contacted in an electrochemical cell, where the substrate surface contains patterned lithium to form a prelithiated anode material (and an at least partially delithiated substrate surface).

[0029] The anode material may be any anode material that can be used to form a lithium battery, including graphite, one or more silicon materials, mixtures of graphite and one or more silicon materials, various metals and alloys, which may be lithium alloys. In particular, the anode material for lithium batteries is often graphite or a mixture of graphite and one or more silicon materials.

[0030] The substrate material comprising the patterned lithium-containing surface can be prepared as described above. The substrate materials and their preferences are described above.

[0031] The patterned lithium-containing substrate surface (the patterned side of the substrate material) is contacted with the anode material to be prelithiated. Typically, the material is placed in an electrochemical cell after contacting. The contacted material may remain in the electrochemical cell for a period of time sufficient to prelithiate the anode material. The prelithiation process at least partially delithiates the substrate surface of the patterned lithium-containing substrate material. On a laboratory scale, the length of time required to prelithiate the anode material was about 30 minutes to about 60 minutes.

[0032] Liquid media for electrochemical cells are typically comprised of one or more solvents that are polar, aprotic, stable to electrochemical cycling, and preferably low viscosity, forming a liquid medium for the solutions used in lithium batteries. These solvents typically include acyclic carbonates, cyclic carbonates, ethers, sulfur-containing compounds, and esters of boric acid.

[0033] Solvents that can form the liquid medium for the electrochemical cell in the practice of this invention include ethylene carbonate (1,3-dioxolan-2-one), dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dioxolane, dimethoxyethane (glyme), tetrahydrofuran, ethylene sulfite, 1,3-propylene glycol borate, bis(2,2,2-trifluoroethyl) ether, and mixtures of any two or more of the foregoing.

[0034] Preferred solvents include ethylene carbonate, ethyl methyl carbonate, and mixtures thereof. More preferred are mixtures of ethylene carbonate and ethyl methyl carbonate, especially in a volume ratio of about 20:80 to about 40:60, more preferably about 25:75 to about 35:65 ethylene carbonate:ethyl methyl carbonate.

[0035] Lithium-containing salts suitable for the practice of the present invention include lithium perchlorate, lithium nitrate, lithium thiocyanate, lithium aluminate, lithium tetrachloroaluminate, lithium tetrafluoroaluminate, lithium tetraphenylborate, lithium tetrafluoroborate, lithium bis(oxolato)borate (LiBOB), lithium di(fluoro)(oxalato)borate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium titanate, lithium manganate, lithium cobaltate (LiCoO 2 ), lithium nickel oxide (LiNiO 2), lithium alkyl carbonates in which the alkyl group has 1 to 6 carbon atoms, lithium methylsulfonate, lithium trifluoromethylsulfonate, lithium pentafluoroethylsulfonate, lithium pentafluorophenylsulfonate, lithium fluorosulfonate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium (ethylsulfonyl)(trifluoromethylsulfonyl)imide, and mixtures of any two or more of the foregoing. Preferred lithium-containing salts include lithium hexafluorophosphate, lithium tetrafluoroborate, lithium di(fluoro)(oxolato)borate, and lithium bis(oxolato)borate.

[0036] Typical concentrations of lithium-containing salts in solutions for electrochemical cells range from about 0.1 M to about 2.5 M, preferably from about 0.5 M to about 2 M, more preferably from about 0.75 M to about 1.75 M, and even more preferably from about 0.95 M to about 1.5 M. When multiple lithium-containing salts form a lithium-containing electrolyte, the concentration refers to the total concentration of all lithium-containing salts present in the electrolyte solution.

[0037] After the prelithiation step, the contacted materials are removed from the electrochemical cell and the substrate material is separated from the prelithiated anode material.

[0038] FIG. 3A shows a patterned copper foil (substrate material 6 having a patterned lithium-containing substrate surface 6a) where the lithium is visible in dotted, lighter shaded areas 10, and FIG. 3B shows the same copper foil (substrate material 6 having a substrate surface 6a) after a prelithiation step, where no lithium (lighter shaded areas) is observed.

[0039] Another embodiment of the present invention is a lithium-ion battery having an anode, characterized in that at least a portion of the anode is formed from the prelithiated anode material prepared as described above. This is a process for assembling a silicon battery.

[0040] Yet another embodiment of the present invention is a lithium battery having an anode, characterized in that at least a portion of the anode is composed of the prelithiated anode material prepared as described above.

[0041] The initial coulombic efficiency of lithium ion cells formed from prelithiated anode materials prepared according to the present invention can be further enhanced by increasing the loading of lithium in the anode material by modifying the patterning process as described above to increase the amount of lithium transferred to the substrate material. EXAMPLES

[0042] The following examples are presented for illustrative purposes and are not intended to impose limitations on the scope of the invention.

[0043] Example 1 For patterning of the substrate with lithium-containing foils, in all experiments the protective layer was a polyethylene or polypropylene film, the lithium metal foil was about 127 μm thick, and the substrate was a copper foil. The lithium metal foil was placed on top of the copper foil, and a polyethylene or polypropylene film was placed on top of the lithium metal foil to form a layered sheet. The preparation of the layered sheet was carried out in an atmosphere with a humidity of about 1%.

[0044] In this example implementation, one of the dot matrix dies has a diameter of 0.20 mm, a dot-to-dot spacing of 0.69 mm, and approximately 2.25 dots / cm 2 The other dot matrix die had a tip of 0.20 mm in diameter, 0.97 mm spacing between dots, and approximately 4.5 dots / cm 2 Each die (Danley Die Set, Anchor Danly, Ontario, Canada) was mounted on a 25 ton floor press. The layered sheet was placed in the die set with the die oriented so that it was on top of the protective layer, and the lithium metal foil was pressed into the copper foil. Pressure was then applied. 4.5 dots / cm 2In the runs using this die, the applied pressure was 2000 psi (13.8 MPa).

[0045] After releasing the pressure, the layered sheet was removed from the die, the protective layer was peeled off from the lithium metal foil, and then the lithium metal foil was peeled off from the copper foil. Visual inspection of the copper foil shows that the pattern of the die has been transferred to the copper foil (see FIG. 3A). By observing the copper foil under a scanning electron microscope, the height of the pattern on the copper foil can be measured, which is reported in Table 1. [Table 1]

[0046] Example 2 Prelithiation was performed in coin cells. The anode was 16 mm in diameter, and the lithium-patterned copper foil was slightly larger than 16 mm in diameter to ensure complete coverage of the anode material surface. The electrolyte was 1.2 M LiPF with a 30:70 ratio (by weight) of ethylene carbonate:diethylene carbonate. 6 A volume of 200 μL was used. Slight pressure was applied by holding (pinching) the coin cell battery case and the battery was left for either 30 or 60 minutes.

[0047] At the end of the 30 or 60 minutes, the cells were disassembled. The patterned copper foil of the coin cells was inspected and in all cases showed the absence of lithium metal by visual inspection. Figure 3 shows one of the copper foils used in this example patterned with lithium in a dot matrix pattern (A) and the same copper foil after the prelithiation step (B). The absence of lithium on the copper foil after the prelithiation step indicates that lithium has been transferred to the anode material.

[0048] Example 3 A portion of the prelithiated anode material from Example 2 was used in the formation of batteries to evaluate the amount of lithium transferred from the Li foil. Half-cell batteries were formed from prelithiated graphite or Li-patterned Cu foil, a polypropylene separator (Celgard, LLC), and a matte Li metal foil as the counter electrode. The electrolyte for both half-cell batteries was 1.2 M LiPF with a ratio of ethylene carbonate:diethylene carbonate = 30:70 (by weight). 6 A volume of 200 μL was used. Constant current charging at a current of 15 μA was applied to each battery cell. The battery cell containing the Li-patterned Cu foil had a capacity of 0.3 mAh / cm 2 The battery cell containing prelithiated graphite has an open circuit voltage drop of 3 V to 0.4 V and a delithiation capacity of 10 mAh / g. graphite It had a capacity of .

[0049] Example 4 A complete battery cell was formed from prelithiated graphite using lithium nickel cobalt manganese oxide (NCM622) as the cathode in a 1:1 negative:positive (N / P) ratio, based on the anode material and ignoring the lithium present in the prelithiation step. The electrolyte was 1.2 M LiPF in ethylene carbonate:diethylene carbonate:30:70 (by weight). 6 The cells were subjected to one electrochemical cycle of CCCV charging. The results are summarized in Table 2. The increase in initial coulombic efficiency observed in the cells containing prelithiated anodes indicates that prelithiation compensates for the irreversible lithium loss normally observed during the first charge / discharge cycle. [Table 2]

[0050] Any component referred to anywhere in this specification or claims by chemical name or formula, whether referred to in the singular or plural, is identified as being present prior to contact with another substance (e.g., another component, solvent, etc.) referred to by its chemical name or chemical type. Any chemical changes, transformations, and reactions that occur in the resulting mixture or solution are not included. It does not matter what changes, transformations, and / or reactions (if any) occur, because such changes, transformations, and / or reactions are the natural result of bringing together the specified components under the conditions required in accordance with this disclosure. Thus, the components are identified as components that are brought together in connection with performing a desired operation or in forming a desired composition. Also, even if the claims herein may refer to substances, components, and / or ingredients in the present tense (such as "comprising," "is," etc.), the reference refers to the substances, components, or ingredients that were present immediately before they were first contacted, blended, or mixed with one or more other substances, components, and / or ingredients in accordance with this disclosure. Thus, the fact that the substances, components, or ingredients may have lost their original identity due to chemical reaction or chemical change in the course of a contacting, blending, or mixing operation, when performed in accordance with this disclosure by the ordinary skill of a chemist, is of no practical importance.

[0051] The present invention may comprise, consist of, or consist essentially of the materials and / or procedures recited herein.

[0052] As used herein, the term "about" modifying the amount of an ingredient in the composition or used in the process of the present invention refers to the variation in the numerical amount that may occur due to, for example, typical measuring procedures and liquid handling procedures used to make concentrates or use solutions in the real world, inadvertent errors in these procedures, differences in manufacture, source, or purity of ingredients used to make the composition or carry out the method. The term about also encompasses amounts that differ due to different equilibrium conditions of the composition obtained from a particular initial mixture. Whether or not modified by the term "about", the claims include the equivalent of the amount.

[0053] Unless expressly indicated otherwise, the article "a" or "an" as used herein is not intended, and should not be construed as, limiting the description or claims to the single element to which the article refers. Rather, as used herein, the article "a" or "an" is intended to cover one or more such elements, unless the context expressly indicates otherwise.

[0054] This invention is susceptible to considerable variation in its practice, and therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove.

Claims

Claim 1 A process for prelithiation of an anode material, the process comprising contacting an anode material with a substrate surface of a substrate material within an electrochemical cell to form a prelithiated anode material, the substrate surface comprising patterned lithium, said process. Claim 2 The process according to claim 1, wherein the anode material is graphite, one or more silicon materials, or a mixture of graphite and one or more silicon materials. Claim 3 The substrate surface comprising the patterned lithium is forming a layered sheet from a protective material, a lithium-containing foil, and a substrate material, the protective material being in contact with one side of the lithium-containing foil, and the substrate surface of the substrate material being in contact with the other side of the lithium-containing foil, said forming; placing the layered sheet on a patterning device, patterning the layered sheet with the patterning device to form a shaped layered sheet, and removing the shaped layered sheet from the patterning device; removing the protective material and the lithium-containing foil from the substrate surface of the substrate material to obtain a substrate material comprising the substrate surface comprising patterned lithium, prepared by the process according to claim 1. Claim 4 The process according to claim 3, wherein the lithium-containing foil is a lithium metal foil. Claim 5 The process according to claim 3 or 4, wherein the lithium-containing foil has a thickness of about 30 μm to about 200 μm. Claim 6 The process according to claim 3, wherein said forming of the layered sheet is performed under vacuum or in an inert atmosphere. Claim 7 The process according to any one of claims 3, 4, and 6, wherein the patterning device provides a dot matrix pattern. Claim 8 The process according to any one of claims 3, 4, and 6, wherein the protective material is a plastic film. Claim 9 The process according to claim 8, wherein the plastic film is a polyethylene film or a polypropylene film. Claim 10 The process according to any one of claims 1 to 4 and 6, wherein the substrate material is a metal foil. Claim 11 The process according to any one of claims 1 to 4 and 6, wherein the substrate material is a copper foil. Claim 12 A process for prelithiation of an anode material, the process comprising: forming a layered sheet from a protective material, a lithium-containing foil, and a substrate material, the protective material contacting one surface of the lithium-containing foil, and a substrate surface of the substrate material contacting the other surface of the lithium-containing foil; placing the layered sheet on a patterning device, patterning the layered sheet with the patterning device, and removing the layered sheet from the patterning device; removing the protective material and the lithium-containing foil from the substrate surface of the substrate material to obtain the substrate material having a patterned lithium-containing substrate surface; contacting, in an electrochemical cell, an anode material with the substrate surface of the substrate material, the substrate surface containing patterned lithium, to form a prelithiated anode material.

13. The process according to claim 12, wherein the lithium-containing foil is a lithium metal foil.

14. The process according to claim 12 or 13, wherein the lithium-containing foil has a thickness of about 30 μm to about 200 μm.

15. The process according to claim 12 or 13, wherein the forming of the layered sheet is performed under vacuum or in an inert atmosphere.

16. The process according to any one of claims 12 or 13, wherein the patterning device provides a dot matrix pattern.

17. The process according to any one of claims 12 or 13, wherein the protective material is a plastic film.

18. The process according to claim 17, wherein the plastic film is a polyethylene film or a polypropylene film.

19. The process according to claim 13, wherein the anode material is graphite, one or more silicon materials, or a mixture of graphite and one or more silicon materials.

20. The process according to any one of claims 1 to 4, 6, and 12 to 13, wherein the substrate material is a metal foil.

21. The process according to any one of claims 1 to 4, 6, and 12 to 13, wherein the substrate material is a copper foil.

22. A process for assembling a lithium battery having said anode, wherein at least a part of the anode is formed from a prelithiated anode material formed according to any of claims 1 to 2 and 13. [

23. ] A lithium battery having said anode, wherein at least a part of the anode is composed of a prelithiated anode material formed according to any of claims 1 to 2 and 13.

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