Electrolytes and methods for their use

Abstract

In one example of a method for improving the performance of a silicon-based negative electrode, the silicon-based negative electrode is pre-lithiated in an electrolyte containing a lithium salt dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC). DME and FEC are present in a volume-to-volume ratio of 10:1 to 1:10. The pre-lithiation forms a solid electrolyte intermediate phase on an exposed surface of the negative electrode.

Description

BACKGROUND

[0001] Secondary or rechargeable lithium-sulfur batteries, or lithium-ion batteries, are commonly used in numerous stationary and portable devices, for example, in the consumer electronics, automotive, and aerospace industries. Lithium batteries have become popular for several reasons, including their relatively high energy density, the general absence of memory effects compared to other types of rechargeable batteries, relatively low internal resistance, and low self-discharge when not in use. The fact that lithium batteries can be repeatedly switched on and off during their service life makes them an attractive and reliable power source. SUMMARY

[0002] In one example of a method for improving the performance of a silicon-based negative electrode, the silicon-based negative electrode is pre-lithiated in an electrolyte containing a lithium salt dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC). DME and FEC are present in a volume-to-volume ratio of 10:1 to 1:10. The pre-lithiation forms a solid electrolyte intermediate phase on an exposed surface of the silicon-based negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Features of examples of the present disclosure will become apparent by reference to the following detailed description and the drawings, in which the same reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features with a previously described function may or may not be described in conjunction with other drawings in which they appear. Fig. Figure 1 is a schematic perspective view of a silicon-sulfur example battery showing the charge and discharge state, the battery comprising an electrolyte according to an example of the present disclosure; Fig. Figure 2 is a schematic perspective view of an example lithium-ion battery showing the state of discharge, the battery including an example of a pre-lithiated negative electrode disclosed herein; Fig. Figure 3 is a graph showing the capacity (mAh / g).s , left Y-axis, labelled “C”) compared to the cycle number (X-axis, labelled “#”) and the Coulomb efficiency (%, right Y-axis, labelled “%”) compared to the cycle number (X-axis, labelled “#”) for a silicon-sulfur example battery with a pre-lithiated negative example electrode disclosed herein and a silicon-sulfur comparison battery with a pre-lithiated negative comparison electrode; and Fig. Figure 4 is a graph showing the specific capacity based on sulfur (mAh / g, left Y-axis labeled "Y"). l“) compared to the cycle number (X-axis labeled “#”) and the Coulomb efficiency (right Y-axis labeled “Y2”) compared to the cycle number (X-axis labeled “#”) for a silicon-sulfur example battery with an example electrolyte including a lithium salt additive as disclosed herein, and represents a silicon-sulfur comparison battery with an unmodified electrolyte (i.e., without lithium salt additive). DETAILED DESCRIPTION

[0004] Lithium-sulfur and lithium-ion batteries generally operate on the principle of conducting lithium ions from a negative electrode (sometimes called the anode) to a positive electrode (sometimes called the cathode) and back again. The negative and positive electrodes are located on opposite sides of a porous polymer separator impregnated with an electrolyte solution suitable for conducting lithium ions. Each electrode is also connected to its associated current collector, which is connected to an interruptible external circuit through which electric current can flow between the negative and positive electrodes. Examples of active materials for the negative electrode of a lithium-sulfur or lithium-ion battery include silicon and silicon alloys.If the lithium-sulfur battery contains silicon or a silicon alloy as the active material, the battery can be called a silicon-sulfur battery or a silicon (lithium)-sulfur battery.

[0005] Silicon or a silicon alloy can be a desirable material for the negative electrode of a lithium-sulfur or lithium-ion battery, at least in part, due to its high theoretical capacity (e.g., 4200 mAh / g). Additionally, a solid electrolyte interphase (SEI) can form on exposed surface(s) of the silicon-based negative electrode, and this layer can influence cell performance if desired. Generally, the SEI layer forms from i) electrolyte components that decompose when exposed to a low voltage potential, and ii) electrolyte decomposition products that deposit on the exposed surfaces of the silicon-based negative electrode. It is desirable for the SEI layer to form in a controlled environment to create an electronic insulating layer of the desired thickness.Theoretically, the SEI layer covers the surface of the negative electrode and prevents electrons from diffusing out; otherwise, the electrolyte would inevitably be consumed by electrochemical reduction. Furthermore, the SEI layer can also provide kinetic stability for the electrolyte against further reduction in subsequent cycles. The SEI layer is therefore typically an ionically conductive layer, allowing lithium ions to migrate through it. Overall, the SEI layer should contribute to efficient battery cycling.

[0006] While silicon and silicon alloys offer significant theoretical capacity advantages, their use can lead to a shorter battery lifespan. For example, silicon and silicon alloys can undergo significant expansion and contraction during charging and discharging. Extreme expansion and contraction can cause breakage, material fatigue, or other mechanical damage, resulting in loss of electrical contact and a reduced battery lifespan. Additionally, extreme expansion and contraction of silicon or silicon alloys can damage the unstable SEI layer(s), exposing portions of the underlying silicon / silicon alloy to additional electrolyte.This can lead to further decomposition of the electrolyte solution at the exposed areas, resulting in the formation of an additional SEI layer(s). Due to the constant rupture and formation of the SEI layer, lithium can become irreversibly trapped within it, the electrolyte can be consumed, and / or the SEI layer can grow unintentionally.

[0007] An example of the electrolyte disclosed herein can be used for the pre-lithiation of a silicon-based negative electrode and to form a stable SEI layer on the electrode surface. "Stable" means that the SEI layer formed is relatively resistant to degradation when discharged during the discharge process of the silicon-sulfur battery with migrating, diffusing, or oscillating lithium polysulfide (LiS) intermediates. x, where x is 2 <x<8) der Schwefel-basierten positiven Elektrode in Kontakt kommt. Lithium-Polysulfid-Zwischenprodukte, die an der Schwefel-basierten positiven Elektrode gebildet werden, sind im Allgemeinen im Batterieelektrolyt lösbar und können zur siliziumbasierten negativen Elektrode wandern, wo sie mit der negativen Elektrode in parasitischer Art reagieren, um Lithium-Polysulfid-Zwischenprodukte niedrigerer Ordnung zu erzeugen. Diese Lithium-Polysulfid-Zwischenprodukte diffundieren zurück zur positiven Elektrode und regenerieren die höheren Formen der Lithium-Polysulfid-Zwischenprodukte. Infolgedessen kommt es in der Batterie zu einem Pendel-Effekt. Weiterhin, sind diese Polysulfid-Zwischenprodukt-Anionen eine starke Lewis-Base, da sie reich an Elektronen sind und greifen so Chemikalien an, die elektronenziehende Gruppen enthalten, wie Carbonylgruppen.The stable SEI layer disclosed herein, formed using the prelithiation electrolyte disclosed herein, remains intact when exposed to lithium polysulfide intermediates, thus consuming less electrolyte and acting as a barrier layer that prevents the lithium polysulfide intermediates from migrating to the silicon-based negative electrode. Additionally, the stable SEI layer is believed to be more tolerant of the volume expansion of the silicon or silicon alloy. Overall, the use of the prelithiation electrolyte disclosed herein can contribute to improved battery life.

[0008] Another example of the electrolyte disclosed herein can be used during the cycling of the silicon-sulfur battery. This electrolyte includes an additive(s) that can contribute to the stability of the SEI layer during battery operation.

[0009] As noted above, one of the electrolytes disclosed herein is a pre-lithiation electrolyte used for the pre-lithiation of an example of a silicon-based negative electrode (reference numeral 12 in Fig. 1) and for the formation of an SEI layer (reference numeral 19 in Fig. 1 and Fig. 2) is used on an exposed surface(s) of the silicon-based negative electrode 12. The pre-lithiation electrolyte solution disclosed herein may be included in a pre-lithiation kit with the silicon-based negative electrode 12. As explained in more detail below, the pre-lithiation process produces active Li + added to the silicon-based negative electrode 12, making it suitable for use in a lithium-based battery.

[0010] The pre-lithiation electrolyte and the process for forming and pre-lithiating the silicon-based negative electrode 12 are now described. Fig. Point 1 is referenced in the discussion.

[0011] The pre-lithiation electrolyte contains a lithium salt. This can be, for example, one of the following lithium salts: LiPF6, LiAlCl4, LiI, LiBr, LiSCN, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiPF4(C2O4) (LiFOP), LiNO3, LiBF4, LiClO4, LiN(CF3SO2)2 (LiTFSI), LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiN(FSO2)2 (LiFSI), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF3(CF3)3, etc. In one example, the lithium salt in the pre-lithiation electrolyte is 1M LiPF6.

[0012] The lithium salt is dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC). The volume-to-volume ratio of the solvents (DME to FEC) ranges from 10:1 to 1:10. In one example, the volume-to-volume ratio of DME to FEC is 3:1. It was found that the use of FEC as an additional solvent results in the formation of the desired SEI layer 19 on the exposed surface(s) of the silicon-based negative electrode 12 during the pre-lithiation process.

[0013] The FEC is active and easily degradable during prelithiation and forms the SEI layer 19.

[0014] Prior to prelithiation of the silicon-based negative electrode 12, the electrode 12 is purchased or manufactured. In one example, the manufacture of the electrode 12 involves dispersing silicon or a silicon alloy, conductive carbon, and a binder in a specific ratio in an organic solvent or water. The dispersion can be mixed to obtain a homogeneous solution. The solution can then be applied to copper or other suitable current collectors on the negative side using a doctor blade (or by other means).

[0015] The silicon-based negative electrode 12 comprises any silicon-based lithium host material (i.e., active material) that is sufficiently alloyable with lithium and can be intercalated in copper or another suitable current collector acting as the negative pole 12a. Examples of the active silicon material include crystalline silicon, amorphous silicon, and silicon dioxide (SiO₂). x ), silicon alloys (e.g. Si-Sn), etc. The active silicon material can be used in the form of powder, particles, etc., from nanoscale to microscale.

[0016] The silicon-based negative electrode 12 can also incorporate the aforementioned polymer binder to structurally hold the active silicon material together. Examples of binders include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), styrene-butadiene rubber carboxymethylcellulose (SBR-CMC), polyacrylic acid (PAA), cross-linked polyacrylic acid-polyethyleneimine, poly(acrylamide-co-diallyl and dimethylammonium chloride), polyethylene oxide (PEO), or polyimide (PI). Other suitable binders include polyvinyl alcohol (PVA), sodium alginate, or other water-soluble binders.

[0017] Furthermore, the silicon-based negative electrode 12 can also include the previously mentioned conductive carbon material. The conductive carbon can be a carbon with a large specific surface area, such as acetylene black (i.e., carbon black), and is included to facilitate electron transfer between the active silicon material and, for example, the current collector on the negative side (reference numeral 12a in [reference number]). Fig. 1) to ensure. Other examples of suitable conductive fillers that can be used alone or in combination with carbon black include graphene, graphite, carbon nanotubes, and / or carbon nanofibers. A specific example of a combination of conductive fillers is carbon black with carbon nanofibers.

[0018] The silicon-based negative electrode 12 can contain approximately 40% to approximately 90% by weight (i.e., 90 wt%) of active silicon material. The negative electrode 12 can contain between 0 wt% and approximately 30 wt% of conductive filler. Additionally, the negative electrode 12 can contain between 0 wt% and approximately 20 wt% of polymer binder. In one example, the silicon-based negative electrode 12 contains approximately 70 wt% of active silicon material, approximately 15 wt% of conductive carbon material, and approximately 15 wt% of polymer binder material. As briefly described above, the solution resulting from the dispersion of these materials can be prepared, poured onto the negative-side current collector (e.g., copper), and dried to form the silicon-based negative electrode 12.

[0019] The silicon-based negative electrode 12 can then be pre-lithiated using the lithium-silicon half-cell method. Specifically, the Li-Si half-cell is assembled using the silicon-based negative electrode 12, which is immersed in the previously described pre-lithiation electrolyte. A voltage potential is applied to the half-cell, causing the FEC in the pre-lithiation electrode to decompose. The decomposition product is deposited on the exposed surface(s) 13 of the silicon-based negative electrode 12, forming the SEI layer 19. The decomposition product can be LiF, Li₂CO₃, Li x PF y O zThe material used could be F-exchanged lithium ethylene dicarbonate (F-LEDC), an unsaturated polyolefin, etc. The voltage potential is applied for a time sufficient to form the SEI layer 19. The time the voltage potential is applied can range from 1 hour to 100 hours. In one example, the voltage potential is applied for approximately 20 hours. In an example with a higher current, the duration may be shorter. Likewise, with a lower current, the duration may be longer. The SEI layer 19 can be approximately 10 nm thick or less.

[0020] In another example, the silicon-based negative electrode 12 can be pre-lithiated by short-circuiting lithium-silicon after the previously described pre-lithiation electrolyte has been placed between them. This can be carried out for a period of approximately 1 hour up to approximately 24 hours.

[0021] During pre-lithiation, lithium ions are dissolved (or removed or stripped) from the lithium metal of the Li-Si half-cell and alloy with silicon through an electrochemical reaction with the pre-lithiation electrolyte (which can conduct the lithium ions). The lithium ions can then alloy with the silicon-based active material, thereby lithiating the silicon-based negative electrode 12.

[0022] When the pre-lithiation is complete, the lithiated silicon-based negative electrode 12, on which the SEI layer 19 has formed, can be washed off to remove the remaining pre-lithiation electrolyte, and then it can be used either in a lithium-ion battery 30 or in a silicon-sulfur battery 10.

[0023] When used in a lithium-sulfur battery or a silicon-sulfur battery 10, the lithiated silicon-based negative electrode 12 disclosed herein can be combined with a positive electrode 14 consisting of any sulfur-based active material that is sufficiently alloyable with lithium and alloys with aluminum, or with another suitable current collector that acts as the positive terminal of the battery 10. In one example, the sulfur-based active material can be a sulfur-carbon composite. In another example, the weight ratio of S to C in the positive electrode 14 is between 1:9 and 8:1.

[0024] The positive electrode 14 may also contain a polymer binder to structurally hold the sulfur-based active material together. The polymer binder may consist of at least one of the following: polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), an ethylene propylene diene monomer (EPDM) rubber, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), styrene-butadiene rubber carboxymethylcellulose (SBR-CMC), polyacrylic acid (PAA), cross-linked polyacrylic acid-polyethyleneimine, polyimides or polyvinyl alcohol (PVA), sodium alginate, or other water-soluble binders.

[0025] Furthermore, the positive electrode 14 can contain a conductive carbon material. In one example, the conductive carbon material is a carbon with a large specific surface area, such as acetylene black (i.e., carbon black) or activated carbon. Other examples of suitable conductive fillers that can be used alone or in combination with carbon black include graphene, graphite, carbon nanotubes, and / or carbon nanofibers. A specific example of a combination of conductive fillers is carbon black with carbon nanofibers.

[0026] The positive electrode 14 can contain approximately 40% to approximately 90% by weight (i.e., 90 wt%) of the sulfur-based active material. The positive electrode 14 can contain 0 wt% to approximately 30 wt% of the conductive filler. Additionally, the positive electrode 14 can contain between 0 wt% and approximately 20 wt% of polymer binder. In one example, the positive electrode 14 contains approximately 80 wt% sulfur-based active material, approximately 10 wt% conductive carbon material, and approximately 10 wt% polymer binder.

[0027] The silicon-sulfur battery 10 will now be described in more detail. As in Fig. As shown in Figure 1, the silicon-sulfur battery 10 includes the positive-side current collectors 14a and the previously mentioned negative-side current collectors 12a, which are positioned in contact with the positive electrode 14 and the silicon-based negative electrode 12 to receive and release free electrons from an external circuit 24. The positive-side current collectors 14a can be made of aluminum or any other suitable electrically conductive material. The negative-side current collectors 12a can be made of aluminum or any other suitable electrically conductive material.

[0028] It is self-evident that the silicon-sulfur battery 10 can include the pre-lithiated silicon-based negative electrode 12 on which the SEI layer 19 was formed.

[0029] As in Fig. As shown in Figure 1, the silicon-sulfur battery 10 includes the pre-lithiated, silicon-based negative electrode 12 (which has an SEI layer 19 formed on it) and the sulfur-based positive electrode 14, separated by a porous separator 16.

[0030] The porous separator 16 can, for example, consist of a polyolefin. The polyolefin can be a homopolymer (derived from a single monomer component) or a heteropolymer (derived from more than one monomer component), either linear or branched. If a heteropolymer derived from two monomer components is used, the polyolefin can adopt any copolymer chain arrangement, including that of a block copolymer or a random copolymer. The same applies if the polyolefin is a heteropolymer derived from more than two monomer components. For example, the polyolefin can be polyethylene (PE), polypropylene (PP), or a mixture of PE and PP, or a multilayer structured porous film of PE and / or PP. Commercially available porous separators 16 contain a single-layer polypropylene membrane, such as CELGARD 2400 and CELGARD 2500 from Celgard, LLC (Charlotte, NC).It goes without saying that the porous separator 16 can be coated or treated, or uncoated or untreated. For example, the porous separator 16 can be coated or uncoated, or it can have a surface active ingredient treatment.

[0031] In other examples, the porous separator 16 may consist of a different polymer, selected from polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), polyamides (nylon), polyurethanes, polycarbonates, polyesters, polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI), polyamideimides, polyethers, polyoxymethylene (e.g., acetal), polybutylene terephthalate, polyethylene naphthenate, polybutene, polyolefin copolymers, acrylonitrile butadiene styrene copolymers (ABS), polystyrene copolymers, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polysiloxane polymers (such as polydimethylsiloxane (PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), polyphenylenes (e.g., PARMAX™ (Mississippi Polymer Technologies, Inc., Bay Saint Louis, Mississippi)). Polyaryletherketones, poly(perfluorocyclobutane), polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers and terpolymers, polyvinylidene chloride, polyvinyl fluoride, liquid crystalline polymers (e.g.VECTRAN™ (Hoechst AG, Germany) and ZENITE® (DuPont, Wilmington, Germany), polyaramides, polyphenylene oxide, and / or combinations thereof. Another example of a liquid-crystalline polymer that can be used for the porous separator 16 is poly(p-hydroxybenzoic acid). In yet another example, the porous separator 16 can be selected from a combination of polyolefin (such as PE and / or PP) and one or more of the other polymers listed above.

[0032] The porous separator 16 can be a single layer or a multilayer laminate (e.g., two-layer, three-layer, etc.) produced by either a dry or wet process. The entire separator 16 can, for example, consist of a single layer of polyolefin and / or another listed polymer. Alternatively, the separator 16 can be composed of several separate layers of the same or a similar polyolefin and / or polymer. In one example, the separator 16 can be formed by coating a separate layer of polyolefin with one or more layers of polymers. Furthermore, the polyolefin (and / or other polymer) layer and other optional polymer layers can also be incorporated into the separator 16 as a fibrous layer to provide the separator with suitable structural and porosity characteristics.Other suitable separators 16 can include a layer of ceramic material or a ceramic filler in the polymer matrix (i.e., an organic-inorganic composite matrix). In further embodiments, a ceramic membrane, such as Al₂O₃, Si₃N₄, and SiC, can itself be used as the separator 16.

[0033] The porous separator 16 serves as an electrical insulator (preventing a short circuit), as mechanical support, and as a barrier to prevent physical contact between the two electrodes 12 and 14. The porous separator 16 also prevents the passage of lithium ions (denoted Li). + ) by an electrolyte 18 that fills its pores, safely.

[0034] As in Fig. Figure 1 shows both the silicon-based negative electrode 12 (including the SEI layer 19) and the positive electrode 14 and the porous separator 16 impregnated in battery electrolyte 18. In the examples disclosed herein, the battery electrolyte 18 (not to be confused with the pre-lithiation electrolyte described above) consists of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and / or LiPF6, a solvent mixture of dimethoxyethane (DME) and 1,3-dioxolane (DIOX), a lithium salt additive selected from a group consisting of LiBF2(C2O4) (LiODFB), LiPF6, and / or LiB(C2O4)2, and optionally LiNO3.

[0035] The lithium salt additive is present in a small amount, between approximately 0.1 wt.% and approximately 10 wt.% of a total wt.% of the electrolyte solution. It is believed that the small amount of lithium salt additive disclosed herein can significantly increase the cycle life and the Coulomb efficiency of the battery. The lithium salt additive can contribute to the formation of a stable SEI layer 19.

[0036] It is self-evident that in cases where LiPF6 is present in the battery electrolyte 18, the electrolyte solution also contains a Lewis base to stabilize the LiPF6. Examples of suitable Lewis bases include dimethylacetamide (DMAc) and tributylamine (TBA). The Lewis base can be present in an amount between approximately 0.1 wt% and approximately 5 wt%.

[0037] The battery electrolyte 18 disclosed herein improves the performance of the silicon-sulfur solid cell. A specific example of the battery electrolyte 18 comprises approximately 0.1 M to approximately 0.5 M LiNO3 plus approximately 0.1 M to approximately 1 M LiTFSI and approximately 0.1 M to approximately 1 M LiPF6 in dimethoxyethane (DME):1,3-dioxolane (DIOX) (v:v = 10:1 to 1:10) and approximately 0.1 M to approximately 0.5 M LiODFB as a lithium salt additive. This example of the battery electrolyte 18 may or may not contain a trace amount (approximately 0.1 wt% to approximately 3 wt%) of DMAc or TBA as a PF5 scavenger. This electrolyte system can significantly improve the Coulomb efficiency of a prepared silicon-sulfur solid cell, although it is assumed that the low Coulomb efficiency for silicon-sulfur solid cells can be improved even further.

[0038] The silicon-sulfur battery 10 also includes the interruptible external circuit 24, which connects the positive electrode 14 and the negative electrode 12. The silicon-sulfur battery 10 can also power a load 26, which can be operationally connected to the external circuit 24. The load 26 is supplied with electrical energy from the electric current flowing through the external circuit 24 when the silicon-sulfur battery 10 is discharged. While the load 26 can be any number of electrically powered devices, some specific examples of a power-consuming load include an electric motor for a hybrid vehicle or an electric car, a laptop computer, a mobile phone, and a cordless power tool. However, the load 26 can also be an energy-generating device that charges the silicon-sulfur battery 10 to store the energy.The tendency of wind turbines or solar power plants to generate electricity with fluctuations and / or interruptions often means, for example, that the excess energy has to be stored for later use.

[0039] The silicon-sulfur battery 10 may comprise a variety of other components which, although not shown here, are well known to experts. For example, the silicon-sulfur battery 10 may include a casing, seals, terminals, tabs, and other useful components or materials arranged between or around the positive electrode 14 and the silicon-based negative electrode 12 for performance or practical reasons. Additionally, the size and shape of the silicon-sulfur battery 10, as well as the design and chemical composition of its main components, may vary depending on the specific application for which it is designed. Battery-powered automobiles and portable consumer electronics devices, for example, are two embodiments in which the silicon-sulfur battery 10 would likely have a different size, capacity, and power output.The silicon-sulfur battery 10 can also be connected in series and / or parallel with other similar silicon-sulfur batteries 10 to produce a higher voltage output and current (in parallel connection) or a higher voltage output (in series connection) if the consumer 26 requires it.

[0040] The silicon-sulfur battery 10 can provide a usable electrical current during battery discharge (shown under reference numeral 20 in Fig. 1) generate. During discharge, chemical processes occur in battery 10, including the production of lithium (Li). + ) from the negative electrode 12 and a reaction occurs between lithium cations and alkali metal polysulfide salts (i.e. Li2S). n, such as Li₂S₈, Li₂S₆, Li₂S₄, Li₂S₂, and Li₂S) in the positive electrode 14. As such, polysulfides (sulfur reduction) are sequentially formed in the positive electrode 14 as the battery 10 discharges. The chemical potential difference between the positive electrode 14 and the negative electrode 12 (in the range of approximately 1.5 to 3.0 volts, depending on the exact chemical composition of electrodes 12 and 14) drives the electrons generated by the dissolution of lithium at the negative electrode 12 through the external circuit 24 to the positive electrode 14. The resulting electric current flowing through the external circuit 24 can be used and passed through the load 26 until the lithium in the negative electrode 12 is depleted and the capacity of the silicon-sulfur battery 10 decreases.

[0041] The silicon-sulfur battery 10 can be recharged and made usable at any time by connecting an external power source to the silicon-sulfur battery 10 to reverse the electrochemical reactions of battery discharge. During charging (shown under reference 22 in Fig. 1) Lithium alloys with the negative electrode 12, and sulfur is formed at the positive electrode 14. Connecting an external power source to the silicon-sulfur battery 10 forces the otherwise non-spontaneous oxidation of lithium at the positive electrode 14 to generate electrons and lithium ions. The electrons flow back to the negative electrode 12 through the external circuit 24, and the lithium ions (Li) +The lithium molecules, which are transported back to the negative electrode 12 through the separator 16 via the electrolyte 18, reconnect at the negative electrode 12 and replenish it with lithium for use in the next battery discharge cycle 20. The external power source that can be used to charge the silicon-sulfur battery 10 can vary in size, design, and specific end application. Some suitable external power sources include a battery charger that plugs into an AC wall outlet or an automotive AC generator.

[0042] With reference to Fig. 2. If the pre-lithiated silicon-based negative electrode 12 described herein is used in a lithium-ion battery 30, any known separator 16, current collector, etc., can be used with the pre-lithiated silicon-based negative electrode 12 and a suitable positive electrode 14'. It is understood that the porous separator 16 used in the lithium-ion battery 30 can be of the same type as the porous separator 16 used in Fig. Figure 1 is shown for the silicon-sulfur battery 10. Furthermore, the current collector of the negative side 12a and the current collector of the positive side 14a, which are described herein for the silicon-sulfur battery 10, can also be used in the lithium-ion battery 30.

[0043] It is self-evident that the lithium-ion battery 30 can contain the pre-lithiated silicon-based negative electrode 12 on which an SEI layer 19 has been formed.

[0044] In Fig. 2 The lithiated silicon-based negative electrode 12 disclosed herein can be paired with the positive electrode 14', which consists of any lithium-based active material capable of sufficiently good lithium insertion and removal while acting as the positive terminal of the lithium-ion battery 30. A common group of known lithium-based active materials suitable for the positive electrode 14' includes transition metal oxides with layered lithium. Some specific examples of a lithium-based active material are spinel lithium manganese oxide (LiMn₂O₄), lithium cobalt oxide (LiCoO₂), and a nickel manganese oxide spinel [Li(Ni)₂O₄]⁻. 0.5 Mn1.5)O2], a layered nickel-manganese-cobalt oxide [Li(Ni x Mn y Co z)O2] or a lithium iron polyanion oxide, such as lithium iron phosphate (LiFePO4) or lithium iron fluorophosphate (Li2FePO4F). Other lithium-based active materials can also be used, such as lithium nickel cobalt oxide (LiNi). x Co 1-x O2), aluminium-stabilized lithium manganese oxide spinel (Li x Mn 2-x Al y O4) and lithium vanadium oxide (LiV2O5). Li2MSiO4 (M is any mixture of Co, Fe, and / or Mn), xLi2MnO 3- (1-x)LiMO2 (M is any mixture of Ni, Mn and / or Co) and any other high-efficiency nickel-manganese-cobalt material. "Any mixture" means that each element can be present in any quantity. M could, for example, be Al, with or without Co and / or Mg, or any other combination of the listed elements.

[0045] The lithium-based active material of the positive electrode 14' can be mixed with a polymeric binder and a conductive filler (e.g., carbon with a large specific surface area). Any binder previously described for the negative electrode 12 can be used for the positive electrode 14'. The polymeric binder structurally binds the lithium-based active material and the carbon with a large specific surface area together. An example of carbon with a large specific surface area is carbon black. The carbon with a large specific surface area ensures the electron transfer between the current collector of the positive side 14a and the particles of the active material of the positive electrode 14'.

[0046] The porous separator 16 in Fig. 2, which serves as an electrical insulator and mechanical support, is inserted between the negative electrode 12 and the positive electrode 14' to prevent physical contact between the two electrodes 12, 14' and to avoid the occurrence of a short circuit. In addition to forming a physical barrier between the two electrodes 12, 14', the porous separator 16 prevents the passage of lithium ions (through the black dots and the open circles with a (+) charge) in Fig. 2 marked) and associated anions (through the open circles with a (-) charge in Fig. 2 marked) by an electrolyte solution that fills its pores, ensuring that the lithium-ion battery 30 functions correctly.

[0047] Any suitable electrolyte solution 21 capable of conducting lithium ions between the negative electrode 12 and the positive electrode 14' can be used in the lithium-ion battery 30. For example, the electrolyte solution 21 can be an anhydrous liquid electrolyte solution, a lithium salt dissolved in an organic solvent, or a mixture of organic solvents. Experts are familiar with the many non-aqueous liquid electrolyte solutions that can be used in the lithium-ion battery 30, as well as how to manufacture and purchase them commercially. Some examples of lithium salts that can be used are LiClO4, LiAlCl4, LiI, LiBr, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(FSO2)2 (LIFSI), LiN(CF3SO2)2 (LITFSI), LiPF6, LiPF4(C2O4) (LiFOP), LiNO3 and mixtures thereof.The following can be used as organic solvents: cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate), linear carbonates (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate), aliphatic carboxylic acid esters (methyl formate, methyl acetate, methyl propionate), γ-lactones (γ-butyrolactone, γ-valerolactone), chain structure ethers (1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane) and mixtures thereof.

[0048] As in Fig. As shown in Figure 2, the lithium-ion battery 30 also includes an interruptible external circuit 24 that connects the negative electrode 12 and the positive electrode 14'. The lithium-ion battery 30 can also power a load 26, which may be operationally connected to the external circuit 24. The load 26 is supplied with electrical energy from the electric current flowing through the external circuit 24 when the lithium-ion battery 30 is discharged. While the load 26 can be any number of electrically powered devices, some specific examples of a power-consuming load 26 include an electric motor for a hybrid vehicle or electric car, a laptop computer, a mobile phone, and a cordless power tool. However, the load 26 can also be a power generation device that charges the lithium-ion battery 30 to store energy.The tendency of wind turbines or solar power plants to generate electricity with fluctuations and / or interruptions often means, for example, that the excess energy has to be stored for later use.

[0049] The lithium-ion battery 30 may also include a variety of other components which, although not shown here, are well known to experts. For example, the lithium-ion battery 30 may contain a casing, seals, terminals, tabs, and other useful components or materials arranged between or around the negative electrode 12 and the positive electrode 14' for performance or practical reasons. Additionally, the size and shape of the lithium-ion battery 30, as well as the design and chemical composition of its main components, may vary depending on the specific application for which it is designed. Battery-powered automobiles and portable consumer electronics devices, for example, are two embodiments in which the lithium-ion battery 30 would likely have a different size, capacity, and power output.The lithium-ion battery 30 can also be connected in series and / or parallel with other similar lithium-ion batteries to produce a higher voltage output and current (in parallel connection) or a higher voltage output (in series connection) if the consumer 26 requires it.

[0050] The lithium-ion battery 30 generally operates on the flow of lithium ions from a negative electrode 12 to a positive electrode 14' and back again. In a fully charged state, the voltage of the battery 30 is at its maximum value (usually in the range of 2.0 V to 5.0 V); while in a fully discharged state, the voltage of the battery 30 is at its minimum value (usually in the range of 0 V to 2.0 V). Essentially, the Fermi energy levels of the active materials in the positive and negative electrodes 14', 12 change during battery operation, and this also applies to the difference between the two, known as the battery voltage. During discharge, the battery voltage decreases and the Fermi levels approach each other. During charging, the reverse process occurs, with the battery voltage increasing while the Fermi levels move further apart.During battery discharge, the external load 26 enables a current flow in the external circuit 24 in such a direction that the difference between the Fermi levels (and consequently the cell voltage) decreases. During battery charging, the opposite occurs: the battery charger forces a current flow in the external circuit 24 in such a direction that the difference between the Fermi levels (and consequently the cell voltage) increases.

[0051] At the beginning of the discharge, the negative electrode 12 of the lithium-ion battery 30 contains a high concentration of intercalated lithium, while the positive electrode 14' is relatively empty. When the negative electrode 12 contains a sufficiently higher amount of intercalated lithium, the lithium-ion battery 30 can generate a usable electric current through reversible electrochemical reactions that occur when the external circuit 24 is closed to connect the negative electrode 12 and the positive electrode 14'. Under these circumstances, closing the external circuit causes the extraction of intercalated lithium from the negative electrode 12. The extracted lithium atoms are split into lithium ions (indicated by the black dots and the open circles with a (+) charge) and electrons (e -) while leaving an intercalation host at the interface between the negative electrode and the electrolyte.

[0052] The chemical potential difference between the positive electrode 14' and the negative electrode 12 (in the range of approximately 2.0 V to approximately 5.0 V, depending on the exact chemical composition of the electrodes 12, 14') drives the electrons (e - The electrons (e) generated by the oxidation of the intercalated lithium at the negative electrode 12 are transported through the external circuit 24 to the positive electrode 14'. Simultaneously, the lithium ions are transported from the electrolyte solution through the porous separator 16 to the positive electrode 14'. -The lithium ions flowing through the external circuit 24 and the lithium ions migrating through the porous separator 16 in the electrolyte solution are eventually recombined and form intercalated lithium at the positive electrode 14'. The electric current flowing through the external circuit 24 can be used and passed through the load 26 until the level of intercalated lithium at the negative electrode 12 falls below a minimum level or there is no longer a need for electrical energy.

[0053] The lithium-ion battery 30 can be recharged after a partial or full discharge of its available capacity. To recharge the lithium-ion battery 30, an external battery charger is connected to the positive and negative electrodes 14', 12 to repeat the electrochemical reactions of the battery discharge in reverse order. During recharging, the electrons (e- ) back to the negative electrode 12 through the external circuit 24 and the lithium ions are transported through the electrolyte through the porous separator 16 back to the negative electrode 12. The electrons (e - ) and the lithium ions are recombined at the negative electrode 12, thereby intercalating lithium in this electrode for use in the next battery discharge cycle.

[0054] The external battery charger used to charge the 30-cell lithium-ion battery can vary in size, design, and specific end-use application. Some suitable external battery chargers include a battery charger that plugs into an AC wall outlet and an automotive AC generator.

[0055] Examples of batteries 10 and 30 can be used in a wide variety of applications. For instance, batteries 10 and 30 can be used in various devices, such as battery-powered or hybrid vehicles, laptop computers, mobile phones, cordless power tools, and similar items.

[0056] Examples are given herein to further illustrate the present disclosure. It is understood that these examples are for illustrative purposes only and are not intended to limit the scope of the disclosed example(s). EXAMPLE 1

[0057] A silicon-based negative electrode was fabricated and prelithiated. The silicon-based negative electrode contained 70% silicon or a silicon alloy, 15% conductive carbon material, and 15% binder. The silicon-based negative electrode was prelithiated in a half-cell using a prelithiation electrolyte of 1 M LiPF6 in DME:FEC (v:v = 3:1). The half-cell was prelithiated to 10 mV relative to Li / Li + Unloaded in 10 to 48 hours.

[0058] After prelithiation, the silicon-based negative electrode was purged with DME and installed in a complete silicon-sulfur sample battery. The complete silicon-sulfur sample battery contained a sulfur-based positive electrode and a separator. The sulfur cathode was composed of 80% elemental sulfur, 10% conductive carbon material, and 10% binder. Polypropylene (PP2500) was used as the separator. The battery electrolyte used in the complete silicon-sulfur sample battery was 0.3 M LiNO3 plus 0.7 M LiTFSI in dimethoxyethane (DME):1,3-dioxolane (DIOX) (v:v = 1:1).

[0059] A complete silicon-sulfur reference battery was also fabricated. The complete silicon-sulfur reference battery contained a silicon-based negative reference electrode pre-lithiated with a pre-lithiation reference electrolyte of 1M LiTFSI in DME:DIOX (v:v = 1:1) plus 5% FEC. The pre-lithiation of the silicon-based negative reference electrode was performed in the same manner as described for the silicon-based negative example electrode.

[0060] The full silicon-sulfur comparison battery contained a sulfur-based positive electrode, separator and battery electrolyte of the same type (i.e. 0.3 M LiNO3 plus 0.7 M LiTFSI in DME:DIOX (v:v = 1:1)) as previously described for the full silicon-sulfur example battery.

[0061] The galvanostatic cycling performance of the full silicon-sulfur sample battery (1) and the full silicon-sulfur comparison battery (2) was tested by cycling between 1.3 V and 2.6 V at a rate of C / 10 at room temperature for up to 40 cycles.

[0062] The results of the cycling performance and the Coulomb efficiency are in Fig. 3 is shown. In particular, the capacity (mAh / g) is shown. sThe graph shows the voltage on the left y-axis (labeled "C"), the coulomb efficiency (%) on the right y-axis (labeled "%), and the cycle number on the x-axis (labeled "#"). As noted above, "1" represents the results of the full silicon-sulfur sample battery, and "2" represents the results of the full silicon-sulfur comparison battery. Overall, the full silicon-sulfur sample battery with the negative electrode pre-lithiated with 1M LiPF6 in DME:FEC (v:v = 3:1) showed more stable performance. This is thought to be due to the SEI layer formed during the pre-lithiation process. EXAMPLE 2

[0063] A complete silicon-sulfur example battery was prepared with a pre-lithiated silicon-based negative electrode, a sulfur-based positive electrode, and a separator, as previously described in Example 1. The battery electrolyte used in this complete silicon-sulfur example battery was 0.3 M LiNO3 plus 0.5 M LiTFSI and 0.2 M LiPF6 in dimethoxyethane (DME):1,3-dioxolane (DIOX) (v:v = 1:1) and approximately 0.1 M LiODFB as a lithium salt additive.

[0064] A full silicon-sulfur reference battery was also prepared. The full silicon-sulfur reference battery contained a pre-lithiated silicon-based negative electrode, a sulfur-based positive electrode, and a separator of the same type as the full silicon-sulfur example battery. The reference battery electrolyte used in this full silicon-sulfur example battery was 0.3 M LiNO3 plus 0.7 M LiTFSI in dimethoxyethane (DME):1,3-dioxolane (DIOX) (v:v = 1:1). No lithium salt additive was included.

[0065] The galvanostatic cycling performance of the full silicon-sulfur example battery (3) and the full silicon-sulfur comparison battery (4) was tested by cycling between 1.3 V and 2.6 V at a rate of C / 10 at room temperature for up to 90 cycles.

[0066] The results of the cycling performance and the Coulomb efficiency are in Fig.Figure 4 shows the specific capacity, specifically based on sulfur (mAh / g) on ​​the left y-axis (labeled "y1"), the coulomb efficiency (%) on the right y-axis (labeled "y2"), and the cycle count on the x-axis (labeled "#"). As noted above, Figure 3 shows the results for the full silicon-sulfur sample battery tested with the lithium salt electrolyte, and Figure 4 shows the results for the full silicon-sulfur comparison battery tested with a non-lithium salt electrolyte. Overall, the full silicon-sulfur sample battery with the lithium salt electrolyte showed better cycle life (e.g., see results at 50 cycles and above) and coulomb efficiency.

[0067] It is understood that the ranges provided here include the specified range and any value or subrange within that range. For example, a range from approximately 0.1 wt% to approximately 10 wt% should be interpreted as encompassing not only the explicitly stated limits of approximately 0.1 wt% to approximately 10 wt%, but also individual values ​​such as 1 wt%, 5.5 wt%, 7.25 wt%, etc., and subranges such as from 2 wt% to approximately 8 wt%; from approximately 0.2 wt% to approximately 9 wt%, etc. Furthermore, when "approximately" is used to describe a value, it is understood to include small variations from the specified value (up to + / - 5%).

[0068] References in the description to "an example," "another example," "example," etc., mean that a specific element (e.g., feature, structure, and / or property) described in connection with the example is included in at least one example described herein and may or may not be present in other examples. Furthermore, it is understood that the described elements for each example may be combined in any suitable way across the various examples, unless the context clearly dictates otherwise.

[0069] When describing and claiming the examples disclosed herein, the singular forms “ein”, “eine” and “der / die / das” imply plural references unless the context clearly dictates otherwise.

[0070] Although several examples have been described in detail, it goes without saying that the disclosed examples can be modified. Therefore, the foregoing description should be considered non-restrictive.

Claims

[1] Method for improving the performance of a silicon-based negative electrode, the method comprising: Prelithiation of the silicon-based negative electrode in an electrolyte containing a lithium salt dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC) in a volume:volume ratio of 10:1 to 1:10, forming a solid electrolyte intermediate phase on an exposed surface of the silicon-based negative electrode. [2] Method according to the definition in claim 1, wherein the silicon-based negative electrode comprises an active material selected from silicon or a silicon alloy. [3] Method according to the definition in claim 1, wherein the prelithiation is carried out by: Integrating the silicon-based negative electrode into a half-cell; Immersion of the silicon-based negative electrode in the electrolyte; and Applying a voltage potential to the silicon-based negative electrode for a time sufficient to form the solid electrolyte intermediate phase. [4] Method according to the definition in claim 1, wherein the prelithiation is carried out by: Integrating the silicon-based negative electrode into a half-cell with a lithium-based counter electrode; Immersion of the silicon-based negative electrode in the electrolyte; and Short-circuiting the half-cell. [5] Method according to the definition in claim 1, wherein the lithium salt is selected from a group consisting of: LiPF6, LiAlCl4, LiI, LiBr, LiSCN, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiPF4(C2O4) (LiFOP), LiNO3, LiBF4, LiClO4, LiN(CF3SO2)2 (LiTFSI), LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiN(FSO2)2 (LiFSI), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF3(CF3)3 and combinations thereof. [6] Electrolyte for prelithiation of a silicon-based negative electrode, the electrolyte comprising: a lithium salt; and a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC) in a volume: volume ratio of 10:1 to 1:

10. [7] Electrolyte as defined in claim 6, wherein the lithium salt is selected from the group consisting of LiPF6, LiAlCl4, LiI, LiBr, LiSCN, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiPF4(C2O4) (LiFOP), LiNO3, LiBF4, LiClO4, LiN(CF3SO2)2 (LiTFSI), LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiN(FSO2)2 (LiFSI), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF3(CF3)3 and combinations thereof. [8] A method for improving the performance of a silicon-sulfur battery, the method comprising the addition of a lithium salt selected from a group consisting of LiBF2(C2O4) (LiODFB), LiPF6, LiB(C2O4)2, and combinations thereof, to an electrolyte to be used in the silicon-sulfur battery, wherein the electrolyte consists of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), LiPF6 or combinations thereof in a solvent mixture of dimethoxyethane (DME) and 1,3-dioxolane (DIOX), optionally LiNO3 and optionally a Lewis base if LiPF6 is present. [9] Silicon-sulfur battery, comprising: a negative electrode containing a silicon-based active material; a positive electrode containing a sulfur-based active material; a separator positioned between the negative electrode and the positive electrode; and an electrolyte solution in which the positive electrode, the negative electrode and the separator are immersed, wherein the electrolyte solution consists of: Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), LiPF6, or combinations thereof; a solvent mixture of dimethoxyethane (DME) and 1,3-dioxolane (DIOX); a lithium salt additive selected from the group consisting of LiBF2(C2O4) (LiODFB), LiPF6, LiB(C2O4)2 or combinations thereof, wherein the amount of the lithium salt additive is approximately 0.1 wt% to approximately 10 wt% of the total wt% of the electrolyte solution; and optional LiNO3; and If LiPF6 is present, the electrolyte solution also consists of a Lewis base. [10] Silicon-sulfur battery according to the definition in claim 9, wherein the LiPF6 is the lithium salt additive and wherein the Lewis base is selected from a group consisting of dimethylacetamide (DMAc) and tributylamine (TBA). [11] Silicon-sulfur battery according to the definition in claim 10, wherein the amount of Lewis base is approximately 0.1 wt% to approximately 5 wt% of the total wt% of the electrolyte solution. [12] Prelithiation set, comprising: a negative electrode containing a silicon-based active material; and an electrolyte solution for prelithiation of the negative electrode, the electrolyte solution comprising a lithium salt dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC) in a volume:volume ratio ranging from 10:1 to 1:10.

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