Method for producing a solid electrolyte interface layer on the surface of an electrode

Abstract

Method for producing a solid electrolyte interface (SEI) layer on the surface of an electrode, the method comprising: Exposure of the electrode to an electrolyte solution in an electrochemical cell, wherein the electrolyte solution contains an organopolysulfide additive having the formula RS n R' (n ≥ 2) has, wherein R and R' are independently selected from a 3-(trimethoxysilyl)-1-propyl group or a 4-nitrophenyl group, and Applying a voltage or load to the electrochemical cell.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application SN 62 / 079,935, filed November 14, 2014, and U.S. Provisional Application SN 62 / 090,207, filed December 10, 2014. BACKGROUND

[0002] Secondary or rechargeable lithium-ion batteries, or lithium-sulfur batteries, are widely used in many stationary and portable devices, such as those found in the consumer electronics, automotive, and aerospace industries. The lithium class of batteries has gained popularity for several reasons; these include a relatively high energy density, a general lack of memory effect compared to other rechargeable batteries, a relatively low internal resistance, and a low self-discharge rate when not in use. The ability of lithium batteries to undergo repeated energy cycling over their useful life makes them an attractive and reliable power source.Such and comparable electrolytes for a secondary battery / lithium battery as well as secondary batteries / lithium batteries are described, for example, in US 2013 / 0 183 576 A1, US 2014 / 0 170 459 A1 and US 2004 / 0 265 702 A1. SUMMARY

[0003] The present invention is based on the object of providing an improved method for producing a solid electrolyte interface (SEI) layer on the surface of an electrode.

[0004] According to the method for preparing a solid electrolyte interface (SEI) layer on the surface of an electrode, the electrode is exposed to an electrolyte solution in an electrochemical cell. The electrolyte solution comprises an organopolysulfide additive having the formula RS nR' (n ≥ 2), where R and R' are independently selected from a 3-(trimethoxysilyl)-1-propyl group or a 4-nitrophenyl group. A voltage or a load is applied to the electrochemical cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Features of examples of the present disclosure will become clear from the following detailed description and the drawings, in which reference numerals correspond to similar, though perhaps not identical, components. For brevity, reference numerals or features that have a previously described function may or may not be described in connection with other drawings in which they appear. Fig. 1 is a schematic perspective view of an example of a lithium-sulfur battery, showing a discharge state and the formation of an SEI layer on a positive electrode surface. Fig. 2 is a schematic perspective view of an example of a lithium-ion battery showing a state of charge and the formation of an SEI on a negative electrode surface. Fig. Figure 3 is a graph plotting capacity (Ah, Y-axis) vs. cycle count for button cells with graphite working electrodes in a reference electrolyte solution and an example electrolyte solution containing an organopolysulfide additive. Fig. Figure 4 is a graph showing the Coulombic efficiency (Y-axis) vs. cycle number for the button cells with the graphite working electrodes in the comparison electrolyte solution and the example electrolyte solution having an organopolysulfide additive therein. Fig. Figure 5A is a graph plotting Coulombic efficiency (Y-axis) vs. cycle number for coin cells with lithium working electrodes in a comparison electrolyte solution and an example electrolyte solution containing an organopolysulfide additive. Fig. Figure 5B is an exploded view of the circled part of the diagram of Fig. 5A. Fig. 6 is a graph (not according to the invention) illustrating the specific capacity (mAh / g, Y-axis) vs. cycle number for the Li-S electrochemical cells with a comparison electrolyte solution and an example electrolyte solution having an organopolysulfide additive therein. Fig. 7 is a graph (not according to the invention) illustrating the Coulombic efficiency (Y-axis) vs. cycle number for the Li-S electrochemical cells with the comparison electrolyte solution and the example electrolyte solution having an organopolysulfide additive therein. Fig. 8 is a graph (not according to the invention) illustrating the Coulomb efficiency (Y-axis) vs. cycle number for Li-S electrochemical cells with a comparison electrolyte solution and an example electrolyte solution having a fluorinated organopolysulfide additive therein, and Fig. 9 is a graph (not according to the invention) illustrating Coulombic efficiency (Y-axis) vs. cycle number for Li-S electrochemical cells with another comparative electrolyte solution and another example electrolyte solution having a fluorinated organopolysulfide additive therein. DETAILED DESCRIPTION

[0006] Lithium-based batteries generally work by allowing lithium ions to flow reversibly between a negative electrode (sometimes called the anode) and a positive electrode (sometimes called the cathode). The negative and positive electrodes are located on opposite sides of a porous polymer separator impregnated with an electrolyte solution suitable for conducting the lithium ions. During a charge, lithium ions are inserted / intercalated into the negative electrode, and during a discharge, lithium ions are extracted from the negative electrode. Each of the electrodes is also connected to corresponding current collectors, which are connected by an interruptible external circuit that allows an electric current to flow between the negative and positive electrodes. Two examples of lithium-based batteries include the lithium-sulfur battery and the lithium-ion battery.

[0007] Examples of the negative electrode and the positive electrode disclosed herein have a solid electrolyte interface (SEI) layer formed on a surface thereof. This SEI layer is formed from an additive present in the electrolyte solution. Since the additive is present in the electrolyte solution, the SEI layer can be formed during a discharge cycle or a charge cycle of an electrochemical cell. The electrochemical cell, as used herein, may refer to a lithium-sulfur battery, a lithium-ion battery, a lithium-lithium battery, or a symmetric cell or half-cell having a working electrode and a counter / reference electrode.

[0008] In some cases, the deposition process of the SEI layer takes place in situ during the discharge cycle or the charge cycle of the electrochemical cell. Specifically, the SEI layer forms during a reduction process that occurs at the electrode (i.e., electrons move through an external circuit to the electrode). As an example, in a lithium-sulfur battery, the discharge cycle can be used to form the SEI layer on the surface of a sulfur-based positive electrode. As another example, in a lithium-ion battery, the charge cycle can be used to form the SEI layer on the surface of a graphite-based or silicon-based negative electrode.

[0009] In other cases, the deposition process is performed during the formation or manufacturing of the electrode, before it is introduced into the finished battery in which it will be used. In these cases, the deposition process will take place in situ within the electrochemical cell, but the electrochemical cell is not the finished battery. As an example, a half-cell may be used, which includes the electrode to be coated as the working electrode as well as a counter / reference electrode. A discharge process in the half-cell may be used to coat a graphite-based electrode or a silicon-based electrode. As another example, a lithium-lithium battery or a symmetrical cell may be used as the electrochemical cell. In this example, one of the lithium electrodes acts as the working electrode and the other of the lithium electrodes acts as the counter / reference electrode.In these examples, a discharge cycle causes the SEI layer to form on the working lithium electrode.

[0010] Each example of the method disclosed herein involves exposing the electrode to the electrolyte solution in a suitable electrochemical cell and applying a voltage or load to / through the electrochemical cell, causing the additive to form the SEI layer on the electrode surface. The additive is believed to react with the electrode surface. In particular, upon exposure to a working voltage, the additive may self-assemble so that sulfur atoms of the additive align along the electrode surface. A bond may form between atoms of the electrode (e.g., carbon atoms) and the sulfur atoms of the additive. This forms the SEI layer on the electrode surface.

[0011] According to the invention, the additive is an organopolysulfide additive having the formula RS n R' (n ≥ 2), wherein R and R' are independently selected from a 3-(trimethoxysilyl)-1-propyl group or a 4-nitrophenyl group. R and R' can be the same group or different groups. It is understood that the unsaturated chain, the 3-(trimethoxysilyl)-1-propyl group, and the 4-nitrophenyl group will polymerize in situ, and thus some examples of the SEI layer include a polymer layer.

[0012] Not according to the invention, the additive is a fluorinated organopolysulfide additive having the formula RS n R' (n ≥ 2), where R and R' have the general formula C x H y F (2x-y+1)where x is at least one (e.g., in the range of 1 to 100) and y is in the range of 0 to 2x. Some specific examples from which R and R' of the fluorinated organopolysulfide additive can be independently selected include CF3 (x = 1, y = 0), CF2CF3 (x = 2, y = 0), and CH2CF3 (x = 2, y = 2). R and R' can be the same group or a different group. It is understood that each of the R and R' groups will polymerize in situ, and thus, some examples of the SEI layer include a polymer layer.

[0013] The organopolysulfide additive can be added directly to the electrolyte solution in an amount ranging from greater than 0 vol.% to about 50 vol.% of the total vol.% of the electrolyte solution. As specific examples, the organopolysulfide additive can be included in amounts of 0.5 vol.% and 20 vol.%. Examples of the process will be discussed herein with reference to each of the types of electrochemical cells that may be used, as different cells may utilize different electrolyte solutions (each containing the organopolysulfide additive) and / or electrodes. Electrochemical lithium-sulfur cell (lithium-sulfur battery)

[0014] In the lithium-sulfur electrochemical cell or lithium-sulfur battery, the SEI layer forms on the positive electrode surface during the discharge cycle. An example of the lithium-sulfur electrochemical cell 12 during the discharge cycle is shown in Fig. 1 shown.

[0015] The lithium-sulfur electrochemical cell 12 includes the positive electrode 14. The positive electrode 14 comprises any sulfur-based active material that can sufficiently undergo lithium alloying and de-alloying with aluminum or other suitable current collector 16, which functions as the positive terminal of the lithium-sulfur electrochemical cell 12. An example of the sulfur-based active material is a sulfur-carbon composite material. In one example, the weight ratio of S to C in the positive electrode 14 ranges from 1:9 to 8:1.

[0016] The positive electrode 14 may also include a binder material and / or a conductive filler material. The binder material may be used to structurally hold the sulfur-based active material together. Examples of the binder material include 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, polyimide, or any other suitable binder material known to those skilled in the art. Other suitable binders include polyvinyl alcohol (PVA), sodium alginate, or other water-soluble binders.

[0017] The conductive filler material may be a conductive carbon material. The conductive carbon material may be a carbon with a high specific surface area, for example, acetylene black (e.g., SUPER P®, conductive carbon black from TIMCAL). The conductive filler material is included to ensure electron conduction between the sulfur-based active material and the positive-side current collector 16.

[0018] The positive electrode 14 may comprise up to 90 total weight percent (i.e., 90 wt.%) of sulfur-based active material, from about 5 wt.% to about 20 wt.% of conductive filler material, and from about 5 wt.% to about 20 wt.% of binder material. In one example, the positive electrode 14 comprises about 70 wt.% of sulfur-based active material, about 15 wt.% of conductive filler material, and about 15 wt.% of binder material.

[0019] The lithium-sulfur electrochemical cell 12 also includes the negative electrode 18. In this example, the negative electrode 18 comprises an active material, alone or in combination with any of the binder materials and / or conductive filler materials listed above. The active material of the negative electrode 18 of the lithium-sulfur electrochemical cell 12 can be a lithium-, silicon-, graphite-, tin-, or antimony-based material.

[0020] An example of a lithium-based active material is lithium titanate. Lithium foil may also be used, and this example of the negative electrode 18 may not include the binder material or the conductive filler material.

[0021] The silicon-based active material may be any silicon-based lithium host material that can sufficiently undergo lithium alloying and de-alloying with copper or other current collector 20 acting as the negative pole. Examples of the silicon-based active material include crystalline silicon, amorphous silicon, silicon oxide (SiO x ), silicon alloys (Si-Sn), etc. The silicon active material can be in the form of powder, particles, etc., ranging from nanosize to microsize.

[0022] Graphite exhibits favorable lithium intercalation or deintercalation characteristics, is relatively non-reactive, and can store lithium in quantities that produce a relatively high energy density. Commercial forms of graphite that can be used to manufacture the 18' negative electrode are available, for example, from Timcal Graphite & Carbon (Bodio, Switzerland), Lonzo Group (Basel, Switzerland), or Superior Graphite (Chicago, IL).

[0023] The tin-based active material can be any tin-based lithium host material that can undergo sufficient lithium alloying and de-alloying with copper or other current collector 20 acting as the negative pole. Examples of the tin-based active material include metallic tin, tin alloys (e.g., Li-Sn), etc. The tin active material can be in the form of powder, particles, etc., ranging from nano-sized to micro-sized.

[0024] The antimony-based active material can be any antimony-based lithium host material that undergoes sufficient lithium alloying and de-alloying with copper or other current collector 20, which acts as the negative pole. Examples of the antimony-based active material include metallic antimony, antimony alloys (e.g., Fe-Sn, Fe-Sn-C, Cu-Sn, CoSb3), etc. The antimony active material can be in the form of powder, particles, etc., ranging from nanosize to microsize.

[0025] When the negative electrode 18 comprises any of the silicon, graphite, tin, or antimony-based active materials, it is understood that the material may be alloyed with lithium or the negative electrode 18 may be pre-lithiated using a half-cell process or other suitable pre-lithiation process.

[0026] The lithium-sulfur electrochemical cell also includes a porous polymer separator 22 (also referred to herein as porous separator 22) positioned between the positive and negative electrodes 14, 18. The porous polymer separator 22 may be formed, for example, from a polyolefin. The polyolefin may be a homopolymer (derived from a single monomer component) or a heteropolymer (derived from more than one monomer component) and may be either linear or branched. When a heteropolymer derived from two monomer components is used, the polyolefin may adopt any copolymer chain arrangement, including those 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), a blend of PE and PP, or multilayer structured porous films of PE and / or PP. Commercially available porous separators 22 include single-layer polypropylene membranes, for example, CELGARD 2400 and CELGARD 2500 from Celgard, LLC (Charlotte, NC). It should be appreciated that the porous separator 22 can be coated or treated, or uncoated or untreated. For example, the porous separator 22 can be coated or have a surfactant treatment thereon, or not.

[0027] In other examples, the porous separator 22 may be formed from another polymer selected from the group consisting of polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), polyamides (nylon), polyurethanes, polycarbonates, polyesters, polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI), polyamide-imides, 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 (e.g., polydimethylsiloxane (PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), polyphenylenes (e.g., PARMAX™ (Mississippi Polymer Technologies, Inc., Bay Saint Louis, Mississippi)), polyarylene ether ketones, polyperfluorocyclobutanes, polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers and terpolymers, polyvinylidene chloride, polyvinyl fluoride, liquid crystalline polymers (e.g.VECTRAN™ (Hoechst AG, Germany), ZENITE® (DuPont, Wilmington, DE)), polyaramids, polyphenylene oxide, and / or combinations thereof. Another example of a liquid crystalline polymer that may be employed for the porous separator 22 is believed to be poly(p-hydroxybenzoic acid). In yet another example, the porous separator 22 may be selected from a combination of the polyolefin (e.g., PE and / or PP) and one or more of the other polymers listed above.

[0028] The porous separator 22 may be a single layer or may be a multi-layer (e.g., two-layer, three-layer, etc.) laminate produced by a dry or wet process.

[0029] The porous separator 22 acts as an electrical insulator (preventing the occurrence of a short circuit), as a mechanical support and as a barrier to prevent physical contact between the two electrodes 14, 18. The porous separator 22 also ensures the passage of lithium ions (identified by the Li + ) by the electrolyte solution 24 (containing the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention)) which fills its pores.

[0030] The electrolyte solution 24 of the lithium-sulfur electrochemical cell 12 comprises the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention), an ether-based solvent, and a lithium salt dissolved in the ether-based solvent. Examples of the ether-based solvent include 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,2-diethoxyethane, ethoxymethoxyethane, tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether (PEGDME), and mixtures thereof. An example of a mixture includes 1,3-dioxolane and 1,2-dimethoxyethane.Examples of the lithium salt include LiClO4, LiAlCl4, LiIl, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(FSO2)2 (LIFSI), LiN(CF3SO2)2 (LITFSI), LiPF6, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF4(C2O4) (LiFOP), LiNO3, LiPF3(CF3)3, LiSO3CF3 and mixtures thereof. In one example, the concentration of the salt in the electrolyte solution 24 is about 1 mol / L.

[0031] The electrolyte solution 24 for the lithium-sulfur electrochemical cell 12 may also include other additives, for example, LiNO3 (in addition to another lithium salt) and / or a fluorinated ether. If the fluorinated ether is included, it may be bis(2,2,2-trifluoroethyl) ether (F3C-CH2-O-CH2-CF3) and / or propyl 1,1,2,2-tetrafluoroethyl ether (H7C3-O-CF2-CHF2). The concentration of the fluorinated ether in the electrolyte solution 24 ranges from about 0.1 M to about 1 M.

[0032] The lithium-sulfur electrochemical cell 12 also includes an external circuit 28 and a load 30. The application of the load 30 to the lithium-sulfur electrochemical cell 12 closes the external circuit 28 and connects the negative electrode 18 and the positive electrode 14. The closed external circuit 28 allows a working voltage to be applied through the lithium-sulfur electrochemical cell 12. When the negative electrode 18 is lithiated, it contains a sufficiently higher relative amount of alloyed lithium and can generate a beneficial electric current through reversible electrochemical reactions that occur when the external circuit 28 is closed. The working voltage during this discharge cycle is in the range of greater than 0 V and about 3 V. In one example, the working voltage is in the range of about 1.7 V to about 2.7 V. The load 30 is applied for a time sufficient to form the SEI layer 10.In one example, the load 30 is applied for the period of time required for the lithium-sulfur electrochemical cell 12 to discharge (ie, to fall below a working level of lithium in the negative electrode 18).

[0033] During the discharge cycle, the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention) self-assembles and deposits on the exposed surface(s) 15 of the positive electrode 14 to form an example of the SEI layer 10. Without being bound by theory, it is believed that in this example, the sulfur atoms of the additive 26 (according to the invention) or 26' (not according to the invention) bond to carbon atoms in the positive electrode 14. When the organopolysulfide additive 26 (according to the invention) is used and the unsaturated chain comprises the 3-(trimethoxysilyl)-1-propyl group or the 4-nitrophenyl group, polymerization of the functional groups may also occur. When the fluorinated organopolysulfide additive 26' (not according to the invention) is used, polymerization of the R and / or R' functional groups may also occur.In these examples, the SEI layer 10 comprises a polymer layer. The SEI layer 10 may have a thickness of about 10 nm or less.

[0034] During the discharge cycle, several other chemical processes also take place in the lithium-sulfur electrochemical cell 12. Examples of these other chemical processes include a lithium (Li + ) dissolution from the surface of the negative electrode 18 and incorporation of the lithium cations into alkali metal polysulfide salts (e.g. Li2S x , e.g. Li2S8, Li2S6, Li2S4, Li2S3, Li2S2 and Li2S) in the positive electrode 14. Thus, polysulfides are formed on the surface of the positive electrode 14 in sequence (sulfur is reduced) while the electrochemical lithium-sulfur cell 12 discharges. The chemical potential difference between the positive electrode 14 and the negative electrode 18 controls electrons (e -) produced by the dissolution of lithium at the negative electrode 18, through the external circuit 28 to the positive electrode 14. The resulting electrical current flowing through the external circuit 28 can be harnessed and directed by the load 30 until the lithium in the negative electrode 18 falls below a working level.

[0035] It is understood that a single discharge cycle will create the SEI layer 10. In subsequent cycles, the SEI layer protects the positive electrode active material (e.g., sulfur-carbon composite material) from coming into contact with the residual electrolyte solution, thus reducing or preventing the occurrence of undesirable internal chemical reactions that can consume the electrolyte solution 24.

[0036] When lithium is used as the negative electrode 18 in the lithium-sulfur electrochemical cell 12, elemental lithium or a compound thereof (e.g., lithium titanate) is used as the negative electrode 18. Due to its high reactivity, the lithium in the negative electrode 18 reacts promptly with the electrolyte solution 24 (i.e., without applying a voltage or a load). This reaction can decompose at least some of the component (other than the additive 26 (according to the invention) or the fluorinated additive 26' (not according to the invention)) in the electrolyte solution 24, and the decomposition product deposits on the exposed surface(s) of the negative electrode 18 to form another SEI layer. (in Fig. 1 not shown). This SEI layer will prevent further contact or reaction between the negative electrode 18 and the electrolyte solution 24. Thus, within the working voltage range, the additive 26 or 26' will react with the positive electrode 14 instead of with the negative electrode 18. Electrochemical lithium-ion cell (lithium-ion battery)

[0037] In the electrochemical lithium-ion cell or battery, the SEI layer forms on the negative electrode surface during the charge cycle. An example of the electrochemical lithium-ion cell 32 during the charge cycle is shown in Fig. 2 shown.

[0038] The lithium-ion electrochemical cell 32 includes the positive electrode 14'. The positive electrode 14' comprises any lithium-based active material that can undergo sufficient lithium insertion and deinsertion, while a lithium or other suitable current collector 16 acts as the positive terminal of the lithium-ion electrochemical cell 32. A common class of known lithium-based active materials suitable for the positive electrode 14' includes lithium transition metal layered oxides. For example, the lithium-based active material can be spinel lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), a manganese nickel oxide spinel [Li(Mn 1,5 Ni 0,5 )O2], a nickel-manganese-cobalt layered oxide (with the general formula xLi2Mn·O3-(1-x)LiMO2, where M consists of Ni, Mn and / or Co in any ratio). A specific example of the nickel-manganese-cobalt layered oxide includes (xLi2MnO3·(1-x)Li(Ni 1 / 3 Mn1 / 3 CO 1 / 3 )O2). Other suitable lithium-based active materials include Li(Ni 1 / 3 Mn 1 / 3 CO 1 / 3 )O2, Li x+y Mn 2-y O4 (LMO, 0 < x < 1 and 0 < y < 0.1) or a lithium iron polyanion oxide, for example, lithium iron phosphate (LiFePO4) or lithium iron fluorophosphate (Li2FePO4F), or a lithium-rich layered structure. Other lithium-based active materials can also be used, for example, LiNi. 1-x Co 1-y M x-y O2 or LiMn 1,5-x Ni 0,5-y M x+y O4 (M consists of Al, Ti, Cr and / or Mg in any ratio), stabilized lithium manganese oxide spinel (Li x Mn 2-y M y O4, where M consists of Al, Ti, Cr and / or Mg in any ratio), lithium nickel cobalt aluminum oxide (e.g. LiNi 0,8 Co0, 15 Al 0,05 O2 or NCA), aluminum-stabilized lithium manganese oxide spinel (e.g. Li x Al 0,05 Mn0,95 O2), lithium vanadium oxide (LiV2O5), Li2MSiO4 (where M consists of Co, Fe, and / or Mn in any ratio), and any other high-energy nickel-manganese-cobalt material (HE-NMC, NMC, or LiNiMnCoO2). By "any ratio," we mean that each element can be present in any amount. Thus, in some examples, M could be Al with or without Cr, Ti, and / or Mg, or any other combination of the listed elements. In another example, anion substitutions can be made in the lattice of any example of the lithium transition metal-based active material to stabilize the crystal structure. For example, an O atom can be replaced by an S atom.

[0039] The positive electrode 14' may also comprise any of the binder materials and / or conductive filler materials described above.

[0040] The lithium-ion electrochemical cell 32 may also include the negative electrode 18'. In this example, the negative electrode 18' comprises an active material, alone or in combination with one of the binder materials and / or conductive filler materials listed above. The negative electrode 18' may comprise any lithium host active material capable of sufficient lithium intercalation and deintercalation while the copper or other current collector 20 functions as the negative terminal of the lithium-ion electrochemical cell 32. Examples of the lithium host active material include graphite, a silicon-based material, a tin-based material, or an antimony-based material. Any of the graphite, silicon-based materials, tin-based materials, or antimony-based materials described above may be used.The negative electrode 18', which is formed from one of these materials, should be lithiated or alloyed with lithium.

[0041] The lithium-ion electrochemical cell 32 also includes the porous polymer separator 22 positioned between the positive and negative electrodes 14', 18'. Any of the examples of the porous polymer separator 22 described herein can be used in the lithium-ion electrochemical cell 32. In the lithium-ion electrochemical cell 32, the porous separator 22 functions as an electrical insulator (preventing the occurrence of a short circuit), as a mechanical support, and as a barrier to prevent physical contact between the two electrodes 14', 18'. The porous separator 22 also ensures passage of lithium ions (identified by the black dots and by the open circles having a (+) charge) through the electrolyte solution 24' (containing the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention)) that fills its pores.

[0042] The electrolyte solution 24' of the lithium-ion electrochemical cell 32 comprises the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention), an organic solvent, and a lithium salt dissolved in the organic-based solvent. Examples of the organic solvent include cyclic carbonates (ethylene carbonate (EC), propylene carbonate, butylene carbonate, fluoroethylene carbonate), linear carbonates (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)), aliphatic carboxylic acid esters (methyl formate, methyl acetate, methyl propionate), γ-lactones (γ-butyrolactone, γ-valerolactone), chain ethers (1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran), and mixtures thereof. In one example, the electrolyte solution 24' is a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate.Any of the aforementioned salts may be used in the electrolyte solution 24'. In one example, the concentration of the salt in the electrolyte solution 24' is about 1 mol / L. LiNO3 may also be added to the electrolyte solution 24' as another additive in addition to the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention) and the lithium salt. In these cases, the concentration of the lithium salt may be about 0.6 mol / L plus the LiNO3 additive.

[0043] The lithium-ion electrochemical cell 32 also includes the external circuit 28. In this example, an external charger 34 can be connected to the positive and negative electrodes 14', 18' to close the external circuit 28. The charger 34 and the closed external circuit 28 allow a working voltage to be applied through the lithium-ion electrochemical cell 32. The working voltage during this charge cycle ranges from greater than 2 V to about 5 V. In one example, the working voltage ranges from about 2.7 V to about 4.2 V.

[0044] During the charge cycle, the applied voltage extracts intercalated or stored lithium from the positive electrode 14'. The extracted lithium atoms are converted into lithium ions (identified by the black dots and by the open circles, which have a (+) charge) and electrons (e -) when they leave an intercalation host at the positive electrode-electrolyte interface. The potential difference between the positive electrode 14' and the negative electrode 18' controls the electron (e - ) current to the negative electrode 18' through the external circuit 28. At the same time, lithium ions are carried from the electrolyte solution 24' through the porous separator 22 to the negative electrode 18'. The electrons (e - ) and the lithium ions are recombined at the negative electrode 18', thus replenishing them with intercalated lithium for consumption during a next battery discharge cycle.

[0045] The voltage from the external charger 34 is applied for a time sufficient to form the SEI layer 10. In one example, the voltage is applied for a period of time required for the lithium-ion electrochemical cell 32 to charge. In an example using the graphite negative electrode 18' with a current density of 0.1 C, the voltage may be applied for approximately 10 hours.

[0046] During the charging cycle, the organopolysulfide additive 26 (according to the invention) or the fluorinated organopolysulfide additive 26' (not according to the invention) self-assembles and deposits on the exposed surface(s) 17 of the negative electrode 18' to form an example of the SEI layer 10'. Without wishing to be bound by theory, it is believed that in this example, the sulfur atoms of the additive 26 (according to the invention) or the fluorinated additive 26' (not according to the invention) bond to carbon atoms in the graphite negative electrode 18' or to silicon atoms in the silicon negative electrode 18'. When the organopolysulfide additive 26 is used and the unsaturated chain comprises the 3-(trimethoxysilyl)-1-propyl group or the 4-nitrophenyl group, polymerization of the functional groups can also occur.When the non-inventive fluorinated organopolysulfide additive 26' is used, polymerization of the functional groups may also occur. In these examples, the SEI layer 10' comprises a polymer layer. The SEI layer 10' may have a thickness of about 10 nm or less.

[0047] It can be appreciated that a single charging cycle will create the SEI layer 10'. In subsequent cycles, the SEI layer 10' protects the negative electrode active material (e.g., graphite, silicon) from coming into contact with the remaining electrolyte solution 24', thus reducing or preventing the occurrence of undesirable internal chemical reactions that can consume the electrolyte solution 24'.

[0048] As mentioned above, the reaction of the additive(s) according to the invention 26 or the fluorinated additive(s) not according to the invention 26' with the electrode surface takes place in a reducing environment. During the charging process of the lithium-ion battery 32, only the negative electrode 18' has a reducing environment (i.e., electrons flow to the negative electrode 18' from the positive electrode 14' through the external circuit 28). Under these conditions, the additive(s) according to the invention 26 or the fluorinated additive(s) not according to the invention 26' does not react at the surface of the positive electrode 14'. Furthermore, it is assumed that in this particular example, once the lithium-ion battery 32 undergoes a discharge cycle, the reaction cannot take place, even though electrons flow to the positive electrode 14', because the absolute voltage (vs. Li / Li +) of the positive electrode 14' is too high. Electrochemical half-cells

[0049] Instead of being formed in the lithium-ion electrochemical cell 32, the SEI layer can be formed on a graphite electrode or a silicon electrode using a half-cell. In these half-cell examples, the graphite or silicon electrode to be coated is a working electrode (functioning as the cathode in the half-cell), and a voltage is applied across it from a counter / reference electrode (functioning as the anode in the half-cell).

[0050] The graphite working electrode can be formed from graphite and any of the binders and / or conductive fillers described previously. The silicon working electrode can be formed from any of the silicon-based active materials, binders, and / or conductive fillers described previously. The counter / reference electrode is formed from lithium (e.g., lithium foil, lithium titanate, etc.).

[0051] Both the working electrode and the counter / reference electrode are exposed to the electrolyte solution appropriate for the lithium-ion electrochemical cell 32. An external circuit connects the working electrode and the counter / reference electrode. The voltage applied to the Li-graphite or Li-Si half-cell ranges from greater than 0 V to about 2 V. The voltage is applied for a time sufficient to form the SEI layer on the graphite or silicon working electrode. In one example, the voltage is applied for a time required to discharge (i.e., drop below a working level) the lithium metal counter / reference electrode.

[0052] During the discharge cycle, the organopolysulfide additive (according to the invention) or the fluorinated organopolysulfide additive (not according to the invention) self-assembles and deposits on the exposed surface(s) of the graphite or silicon working electrode, forming an example of the SEI layer. Without being bound by theory, it is believed that in this example, the sulfur atoms of the additive bond to carbon atoms in the graphite working electrode or to silicon atoms in the silicon working electrode. When the organopolysulfide additive (according to the invention) is used and the unsaturated chain comprises the 3-(trimethoxysilyl)-1-propyl group or the 4-nitrophenyl group, polymerization of the functional groups may also occur. When the fluorinated organopolysulfide additive (not according to the invention) is used, polymerization of the functional groups may also occur.In these examples, the SEI layer comprises a polymer layer. The SEI layer may have a thickness of about 10 nm or less.

[0053] During this example of a discharge cycle, other chemical processes also take place in the half-cell. For example, lithium ions are dissolved (or deplated) from the lithium metal counter / reference electrode and are alloyed with the graphite or silicon through an electroformation reaction with the electrolyte solution (which can conduct the lithium ions). In particular, the lithium ions can alloy with the graphite active material or the silicon-based active material, thereby lithiating the graphite working electrode or the silicon working electrode.

[0054] Once the SEI layer has been fully formed, the lithiated graphite or silicon working electrode that has the SEI layer formed on it can be rinsed to remove any residual electrolyte solution. These coated electrodes can be used as negative electrodes in lithium-sulfur or lithium-ion batteries. Electrochemical lithium-lithium cells (lithium-lithium batteries)

[0055] The SEI layer can be formed on a lithium electrode in a cell comprising both a lithium working electrode (functioning as the cathode) and a lithium counter electrode (functioning as the anode), separated by a separator. In these examples, a voltage is applied across the counter / reference electrode.

[0056] Both the lithium working electrode and the lithium counter / reference electrode can be formed / shaped from lithium (e.g., lithium foil, lithium titanate, etc.). Both the lithium working electrode and the lithium counter / reference electrode are also exposed to the electrolyte solution comprising the organopolysulfide additive (according to the invention) or the fluorinated organopolysulfide additive (not according to the invention). In this example, either the electrolyte solution used in the lithium-sulfur electrochemical cell 12 or the electrolyte solution used in the lithium-ion electrochemical cell 32 can be used.

[0057] Due to their high reactivity, the lithium electrodes in the Li-Li cell react instantaneously with the electrolyte solution (i.e., without the application of any voltage or load). A lower potential can be applied to the lithium working electrode to force the reaction between the working electrode and the additive to occur. In one example, the discharge cycle is applied with a specific current passing through the Li-Li cell (e.g., 1 mA). In an example Li-Li cell, the voltage of the Li working electrode is approximately -10 mV (-0.01 V) (indicating that the voltage depends on the additive used), which provides enough energy to force the reaction to occur at the working electrode surface. This process deposits a certain amount of Li metal at the working electrode.In one example, the voltage can be switched so that the charge is then directed directly back to the counter electrode (which has a cutoff voltage of +2 V). It can be appreciated that since the working electrode in this example is already Li, the removal of the extra deposited Li is not necessary for the electrode to be used as the negative electrode in the lithium-sulfur battery 12 or the lithium-ion battery 32.

[0058] During the discharge cycle, the organopolysulfide additive (according to the invention) or the fluorinated organopolysulfide additive (not according to the invention) self-assembles and deposits on the exposed surface(s) of the lithium working electrode, forming an example of the SEI layer. Without being bound by theory, it is believed that in this example, the sulfur atoms of the additive bond to lithium atoms in the lithium working electrode. When the organopolysulfide additive (according to the invention) is used and it comprises the unsaturated chain, the 3-(trimethoxysilyl)-1-propyl group, or the 4-nitrophenyl group, polymerization of the functional groups may also occur. When the fluorinated organopolysulfide additive (not according to the invention) is used, polymerization of the functional groups may also occur. In these examples, the SEI layer comprises a polymer layer.The SEI layer can have a thickness of about 10 nm or less.

[0059] During this example of the discharge cycle, other chemical processes also occur in the Li-Li cell. For example, lithium ions are leached (or deplated) from the lithium metal counter / reference electrode and plated onto the lithium working electrode through an electroformation reaction with the electrolyte solution (which can conduct the lithium ions).

[0060] Once the formation of the SEI layer is complete, the lithium working electrode that has the SEI layer formed on it can be rinsed to remove any remaining electrolyte solution. This coated electrode can be used as a negative electrode in the lithium-sulfur battery 12 or the lithium-ion battery 32.

[0061] The examples of the SEI layer 10, 10' disclosed herein have several advantages. First, the SEI layer 10, 10' protects the positive electrode active material (e.g., sulfur-carbon composite material) or the negative electrode active material (e.g., lithium, silicon, or graphite) from coming into contact with the electrolyte solution in the battery. Theoretically, this SEI layer covers the electrode surface and blocks electrons from diffusing out of the electrode, which would otherwise inevitably consume the electrolyte through electrochemical reduction. As such, the SEI layer 10, 10' reduces or prevents the occurrence of undesirable internal chemical reactions and thus reduces or prevents self-discharge. Self-discharge occurs when internal chemical reactions occur in the battery, even when no connection is established between the positive and negative electrodes.These reactions can reduce the battery's stored charge. Second, the SEI layer is also ionically conductive, allowing lithium ions to move through the layer. Third, because the SEI layer is an organic-based protective layer, it exhibits greater flexibility compared to ceramic or other rigid electrode coating layers. Overall, the SEI layer should contribute to good battery cycling.

[0062] To further illustrate the present disclosure, examples are provided herein. It should be understood that these examples are provided for illustrative purposes and are not intended to limit the scope of the present disclosure. EXAMPLE 1

[0063] A reference electrolyte was prepared with 1 M LiPF6 in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (1:1:1 v / v). An example electrolyte was prepared with 1 M LiPF6 in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (1:1:1) and 0.5 vol% R-S2-R (where R is 3-(trimethoxysilyl-1-propyl)).

[0064] A reference button cell (1) was prepared with a graphite electrode as working electrode, Li metal as counter electrode and the reference electrolyte solution.

[0065] An example button cell (2) was prepared with a graphite electrode as the working electrode, Li metal as the counter electrode and the example electrolyte solution.

[0066] The comparison and example button cells 1 and 2 were tested with a cut-off voltage of between 0.05 V and 1.5 V vs. Li / Li + cycled. The discharge capacity results are in Fig. 3 shown. In Fig. 3, the Y-axis, marked with “C”, represents the capacity (Ah) and the X-axis, marked with “#”, represents the cycle number. As shown in Fig. 3, after several cycles, the discharge capacity of the example button cell 2 with the organopolysulfide additive was higher than the discharge capacity of the comparison button cell 1. Thus, the example button cell 2 with the organopolysulfide additive exhibited improved stability.

[0067] The results for the Coulomb efficiency are in Fig. 4 shown. In Fig. 4, the Y-axis, labeled CE, represents the Coulomb efficiency (numbers multiplied by 100 to obtain the percentage) and the X-axis, labeled “#”, represents the cycle number. As in Fig. As shown in Figure 4, throughout the cycles, the Coulombic efficiency of the example button cell 2 with the organopolysulfide additive was as good as or slightly higher than the Coulombic efficiency of the comparison button cell 1.

[0068] These results demonstrate that the organopolysulfide additive improves the performance of the electrochemical cell by forming an SEI layer during discharge. EXAMPLE 2

[0069] A reference electrolyte was prepared with 1 M LiTFSI in 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v). A first example electrolyte was prepared with 0.4 M LiTFSI / 0.6 M LiNO3 in 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v) and 20 vol% Me-S2-Me (where Me is a methyl group). A second example electrolyte was prepared with 0.4 M LiTFSI / 0.6 M LiNO3 in 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v) and 0.5 vol% R-S2-R (where R is 3-(trimethoxysilyl-1-propyl)).

[0070] A reference button cell (3) was prepared with Li metal as working electrode, Li metal as counter electrode and the reference electrolyte solution.

[0071] An example button cell (4) was prepared with Li metal as working electrode, Li metal as counter electrode and the first example electrolyte solution.

[0072] Another example button cell (5) was prepared with Li metal as working electrode, Li metal as counter electrode and the second example electrolyte solution.

[0073] The control button cell and the two example button cells, 3, 4 and 5, were charged with a constant current at a cut-off voltage of between -1 V and 2 V vs. Li / Li + The results for the Coulomb efficiency are shown in Fig. 5A. In Fig. 5A, the Y-axis, labeled CE, represents the Coulomb efficiency (numbers multiplied by 100 to obtain the percentage) and the X-axis, labeled “#”, represents the cycle number. As in Fig. As shown in Figure 5A, the Coulombic efficiency of Example Button Cells 4 and 5, each prepared with an example of the organopolysulfide additive, was higher than the Coulombic efficiency of Comparative Button Cell 3. Fig. Figure 5B shows the Coulombic efficiency between 0.95 and 0.99 for Example Button Cells 4 and 5. Both examples showed high efficiency, however Example Button Cell 5, which included a polymerizing additive, showed improved stability.

[0074] These results demonstrate that the organopolysulfide additive improves the performance of the electrochemical cell by forming an SEI layer during discharge. REFERENCE EXAMPLE 3

[0075] A reference electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v), 0.6 M LiNO3, and 0.4 M LiTFSI. An example electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v), 0.6 M LiNO3, 0.5 M LiTFSI, and 0.5 vol% R-S2-R (where R is a methyl group).

[0076] The comparison electrolyte and the example electrolyte were used in respective Li-S batteries (i.e., comparison Li-S battery 6 and example Li-S battery 7), which included a Li-metal negative electrode and a sulfur-carbon composite positive electrode.

[0077] A load was connected to initiate a discharge cycle.

[0078] The results of the specific discharge capacity are in Fig. 6 shown. In Fig. 6, the Y-axis, marked with “SC”, represents the specific capacity (mAh / g) and the X-axis, marked with “#”, represents the cycle number. As shown in Fig. As shown in Figure 6, the specific discharge capacity of the example Li-S battery 7 with the organopolysulfide additive was higher than the specific discharge capacity of the comparative Li-S battery 6. Thus, the example Li-S battery 7 with the organopolysulfide additive exhibited improved stability.

[0079] The results for the Coulomb efficiency are in Fig. 7 shown. In Fig. 7, the Y-axis, labeled CE, represents the Coulomb efficiency and the X-axis, labeled “#”, represents the cycle number. As in Fig. As shown in Figure 7, the Coulombic efficiency of the example Li-S battery 7 with the organopolysulfide additive was stable throughout the cycles and did not exhibit overcharging, which was exhibited by the comparison Li-S battery 6. REFERENCE EXAMPLE 4

[0080] A reference electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v) and 1 M LiTFSI. An example electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v), 0.6 M LiNO3, 0.4 M LITFSI, and 1 vol% CF3S2CF3.

[0081] The comparison electrolyte and the example electrolyte were used in respective Li-S batteries (i.e., example Li-S battery 8 and comparison Li-S battery 9) comprising a Li-metal negative electrode and a sulfur-carbon composite positive electrode.

[0082] A load was connected to initiate a discharge cycle.

[0083] The results for the Coulomb efficiency are in Fig. 8 shown. In Fig. 8, the Y-axis, labeled CE, represents the Coulomb efficiency (multiply by 100 to get the percentage) and the X-axis, labeled “#”, represents the cycle number. As in Fig. As shown in Figure 8, the Coulombic efficiency of the example Li-S battery 8 with the fluorinated organopolysulfide additive was more stable than the comparative Li-S battery 9 and showed no overcharge. REFERENCE EXAMPLE 5

[0084] A reference electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v), 0.6 M LiNO3, and 0.4 M LiTFSI. An example electrolyte was prepared with 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v), 0.6 M LiNO3, 0.4 M LiTFSI, and 1 vol% CF3S2CF3.

[0085] The comparison electrolyte and the example electrolyte were used in respective Li-S batteries (i.e., example Li-S battery 10 and comparison Li-S battery 11) comprising a Li-metal negative electrode and a sulfur-carbon composite positive electrode.

[0086] A load was connected to initiate a discharge cycle.

[0087] The results of the Coulomb efficiency are in Fig. 9 shown. In Fig. 9, the Y-axis, labeled CE, represents the Coulomb efficiency (multiply by 100 to get the percentage) and the X-axis, labeled “#”, represents the cycle number. As in Fig. As illustrated in Figure 9, throughout the cycles, the Coulombic efficiency of the example Li-S battery 10 with the fluorinated organopolysulfide additive was more stable than that of the comparative Li-S battery 11 and showed no overcharge.

[0088] It should be understood that the ranges stated herein include the stated range and any value or sub-range within the stated range. For example, a range of greater than 0 vol% to 50 vol% should be interpreted to include not only the explicitly stated limits of greater than 0 vol% to about 50 vol%, but also to include individual values, for example, 0.75 vol%, 15 vol%, 32 vol%, 49.5 vol%, etc., and sub-ranges, for example, from about 0.25 vol% to about 35 vol%, from about 2 vol% to about 25 vol%, etc. Furthermore, when "about" is used to describe a value, it is meant to include minor variations (up to + / - 5%) from the stated value.

[0089] Reference in the specification to "an example," "another example," "another example," "an example," etc., means that a particular element (e.g., feature, structure, and / or characteristic) 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 any example may be combined in any suitable manner across the various examples, unless the context clearly dictates otherwise.

[0090] In describing and claiming the examples disclosed herein, the singular forms “a,” “an,” and “the” include plurals unless the context clearly dictates otherwise.

[0091] While various examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is not to be considered limiting.

Claims

[1] A method for producing a solid electrolyte interface (SEI) layer on the surface of an electrode, the method comprising: Exposing the electrode to an electrolyte solution in an electrochemical cell, wherein the electrolyte solution contains an organopolysulfide additive having the formula RS n R' (n ≥ 2), wherein R and R' are independently selected from a 3-(trimethoxysilyl)-1-propyl group or a 4-nitrophenyl group, and Applying a voltage or a load to the electrochemical cell. [2] The method of claim 1, wherein: the electrochemical cell is a lithium-sulfur battery; Applying the load initiates a discharge cycle of the lithium-sulfur battery and Applying the load causes the organopolysulfide additive to react to form the SEI layer. [3] The method of claim 2, wherein: the electrode of the lithium-sulfur battery is a positive electrode made of sulfur-carbon composite material; the lithium-sulfur battery further comprises a lithium negative electrode; the working voltage through the load ranges from greater than 0 V to about 3 V and The electrolyte solution also includes: a solvent selected from the group consisting of 1,3-dioxolane, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-diethoxyethane, ethoxymethoxyethane, tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether (PEGDME) and mixtures thereof, and a lithium salt selected from the group consisting of lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2 or LiTFSI), LiNO3, LiPF6, LiBF4, LiI1, LiBr, LiSCN, LiClO4, LiAICI4, LiB(C2O4)2 (LiBOB), LiB(C6H5)4, LiBF2(C2O4) (LiODFB), LiN(SO2F)2 (LiFSI), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF4(C2O4) (LiFOP), LiPF3(CF3)3, LiSO3CF3, LiCF3SO3, Li-AsF6 and mixtures thereof. [4] The method of claim 3, wherein the electrolyte solution further comprises a fluorinated ether selected from the group consisting of bis(2,2,2-trifluoroethyl) ether (F3C-CH2-O-CH2-CF3) and propyl 1,1,2,2-tetrafluoroethyl ether (H7C3-O-CF2-CHF2). [5] The method of claim 1, wherein: the electrochemical cell is a lithium-ion battery; applying the voltage initiates a charging cycle of the lithium-ion battery; applying the voltage causes the organopolysulfide additive to react to form the SEI layer; the electrode is a graphite negative electrode or a silicon negative electrode of the lithium-ion battery; the lithium-ion battery also comprises a lithium-based positive electrode and the applied voltage ranges from greater than 2 V to about 5 V. [6] The method of claim 5, wherein the electrolyte solution further comprises: a solvent selected from the group consisting of ethylene carbonate, dimethyl carbonate, diethyl carbonate and a mixture of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and a lithium salt selected from the group consisting of lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2 or LiTFSI), LiNO3, LiPF6, LiBF4, LiI1, LiBr, LiSCN, LiClO4, LiAlCl4, LiB(C2O4)2 (LiBOB), LiB(C6H5)4, LiBF2(C2O4) (LiODFB), LiN(SO2F)2 (LiFSI), LiPF3(C2F5)3 (LiFAP), LiPF4(CF3)2, LiPF4(C2O4) (LiFOP), LiPF3(CF3)3, LiSO3CF3, LiCF3SO3, LiAsF6 and mixtures thereof. [7] The method of claim 1, wherein: the electrode is a graphite working electrode or a silicon working electrode; the electrochemical cell is a half-cell comprising a lithium reference / counter electrode; the applied voltage ranges from higher than 0 V to about 2 V and the method further comprises incorporating the electrode having the solid electrolyte interface (SEI) layer thereon into a lithium-ion battery. [8] The method of claim 1, wherein the electrolyte solution comprises the organopolysulfide in an amount ranging from greater than 0 vol% to about 50 vol% of the total vol% of the electrolyte solution. [9] The method of claim 1, wherein: the electrode is a silicon working electrode; the electrochemical cell is a half-cell comprising a lithium reference / counter electrode and the applied voltage forces a reaction between the lithium working electrode and the organopolysulfide to form the SEI layer.

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