Ionic gel electrolyte for battery pack circulating lithium ions and battery pack including same

Abstract

The invention relates to an ionic gel electrolyte for a battery for cycling lithium ions and a battery including the same. A battery pack that circulates lithium ions includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an ionic gel electrolyte. The negative electrode includes particles of an electroactive material comprising silicon. The positive electrode comprises an electroactive positive electrode material. The ionic gel electrolyte includes a polymer matrix, an ionic liquid in the polymer matrix, and a lithium salt in the ionic liquid. The ionic liquid comprises a cation comprising a piperidinium ion and an anion comprising a bis (fluorosulfonyl) imide (FSI).

Description

Technical Field

[0001] The present disclosure relates to an electrolyte for a battery pack for cycling lithium ions, and more particularly to an ion gel electrolyte for a battery pack including a silicon-containing negative electrode. Background Art

[0002] The information provided in this section is intended to generally introduce the background of the present disclosure. To the extent that the work currently attributed to the inventors is described in this section, and aspects of the specification that may not otherwise be determined to be prior art at the time of filing, are not expressly or implicitly admitted to be prior art against the present disclosure.

[0003] Lithium battery packs are used in various electronic devices and, due to their high energy and power density, are promising candidates for meeting the requirements of electric vehicles (including hybrid electric vehicles). A secondary lithium battery pack typically includes a negative electrode, a positive electrode, and an electrolyte that provides a medium for lithium ion conduction between the negative electrode and the positive electrode during discharge and charge of the battery pack. The electrolyte can be formulated to exhibit certain desirable properties, including high ionic conductivity, good thermal stability, a wide electrochemical stability window, the ability to form a stable ion-conductive solid electrolyte interphase on the surface of the positive electrode and / or negative electrode, and chemical compatibility with other components of the battery pack. Summary of the Invention

[0004] According to one or more embodiments of the present disclosure, a battery pack for cycling lithium ions includes a negative electrode, a positive electrode spaced apart from the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an ion gel electrolyte. The negative electrode includes electroactive material particles containing silicon. The positive electrode includes an electroactive positive electrode material. The ion gel electrolyte includes a polymer matrix, an ionic liquid in the polymer matrix, and a lithium salt in the ionic liquid. The ionic liquid includes a cation including a piperidinium ion and an anion including bis(fluorosulfonyl)imide (FSI).

[0005] The polymer matrix may include poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof.

[0006] The polymer matrix may account for greater than or equal to 0.5% and less than or equal to 40% by weight of the ion gel electrolyte.

[0007] The cation may include N-methyl-N-propylpyrrolidinium ([Py 13 + ), 1-propyl-1-methylpiperidinium ([PP 13 + ), 1-butyl-1-methylpiperidinium ([PP 14 + ), 1-methyl-1-ethylpyrrolidinium ([Py 12 + ), 1-propyl-1-methylpyrrolidinium ([Py 13 + ), 1-butyl-1-methylpyrrolidinium (Py 14 + ) or a combination thereof.

[0008] The lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0009] The ionic liquid and the lithium salt may account for greater than or equal to 60% and less than or equal to 99.5% by weight of the ion gel electrolyte.

[0010] The lithium salt may be present in the ionic liquid at a concentration of greater than or equal to 0.6 mole and less than or equal to 4 moles.

[0011] The electroactive material particles of the negative electrode may define open pores extending through the negative electrode, and wherein the ion gel electrolyte may penetrate the open pores defined by the electroactive material particles of the negative electrode.

[0012] The negative electrode may further include a solid electrolyte interphase formed in situ on the surface of the electroactive material particles. The solid electrolyte interphase may include lithium fluoride (LiF), lithium silicate (Li x SiO y ) or a combination thereof. The LiF may account for greater than or equal to 3% and less than or equal to 15% by weight of the solid electrolyte interphase, and the Li x SiO y may account for greater than or equal to 2% and less than or equal to 10% by weight of the solid electrolyte interphase.

[0013] The negative electrode may further include a polymer binder and a conductive material.

[0014] The separator may be a polymer membrane having an open microporous structure with open pores extending therethrough, and the ion gel electrolyte may penetrate the open pores of the polymer membrane.

[0015] ​​​​​​The separator may include solid electrolyte particles that define an opening extending from the negative electrode through the separator to the positive electrode, and the ion gel electrolyte may permeate the opening defined by the solid electrolyte particles.

[0016] The negative electrode may further include solid electrolyte particles.

[0017] According to one or more embodiments of the present disclosure, a battery pack for cycling lithium ions includes a negative electrode, a positive electrode spaced apart from the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an ion gel electrolyte permeating the negative electrode, the positive electrode, and the separator. The negative electrode includes electroactive material particles containing silicon, and the silicon accounts for greater than or equal to 5% by weight of the electroactive material particles. The positive electrode includes an electroactive positive electrode material. The ion gel electrolyte includes a polymer matrix, an ionic liquid in the polymer matrix, and a lithium salt in the ionic liquid. The polymer matrix includes poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The polymer matrix accounts for greater than or equal to 0.5% and less than or equal to 40% by weight of the ion gel electrolyte. The ionic liquid includes N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 -FSI). The lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI).

[0018] The negative electrode may further include a solid electrolyte interphase formed in situ on the surface of the electroactive material particles. The solid electrolyte interphase may include lithium fluoride (LiF), lithium silicate (Li x SiO y ) or a combination thereof.

[0019] According to one or more embodiments of the present disclosure, a method of manufacturing a battery pack for cycling lithium ions includes permeating an opening of a negative electrode with an electrolyte precursor that includes a polymer matrix, an ionic liquid, a lithium salt, and a processing solvent, and then removing the processing solvent from the electrolyte precursor to form an ion gel electrolyte in the opening of the negative electrode. The ionic liquid includes a cation including a piperidinium ion and an anion including bis(fluorosulfonyl)imide (FSI). The lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI). The ion gel electrolyte includes a polymer matrix, an ionic liquid, and a lithium salt. The ionic liquid and the lithium salt are immobilized in the polymer matrix of the ion gel electrolyte.

[0020] The polymer matrix may include poly(vinylidene fluoride - co - hexafluoropropylene) (PVDF - HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride - co - tetrafluoroethylene) (PVDF - TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof, and wherein the cation includes N - methyl - N - propylpyrrolidinium ([Py 13 + )、1 - propyl - 1 - methylpiperidinium ([PP 13 + ), 1 - butyl - 1 - methylpiperidinium ([PP 14 + ), 1 - methyl - 1 - ethylpyrrolidinium ([Py 12 + ), 1 - propyl - 1 - methylpyrrolidinium ([Py 13 + ), 1 - butyl - 1 - methylpyrrolidinium (Py 14 + ), or a combination thereof.

[0021] The method may further include preparing a polymer solution by mixing the polymer matrix and the processing solvent at a temperature greater than or equal to about 55 degrees Celsius and less than or equal to 100 degrees Celsius. The ionic liquid and the lithium salt may be introduced into the polymer solution to form an electrolyte precursor.

[0022] The method may further include, after forming the ion gel electrolyte in the open pores of the negative electrode, assembling the negative electrode into a stack including a positive electrode and a separator to form a battery pack.

[0023] The present invention discloses the following solutions:

[0024] Solution 1. A battery pack for recycling lithium ions, the battery pack comprising:

[0025] A negative electrode including electroactive material particles containing silicon;

[0026] A positive electrode spaced apart from the negative electrode and including an electroactive positive electrode material;

[0027] A separator disposed between the negative electrode and the positive electrode; and

[0028] An ion gel electrolyte comprising:

[0029] A polymer matrix;

[0030] ​​​​​​The ionic liquid in the polymer matrix, the ionic liquid comprising a cation including a piperidinium ion and an anion including bis(fluorosulfonyl)imide (FSI); and

[0031] The lithium salt in the ionic liquid.

[0032] Solution 2. The battery pack according to Solution 1, wherein the polymer matrix comprises poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof.

[0033] Solution 3. The battery pack according to Solution 1, wherein the polymer matrix accounts for greater than or equal to 0.5% and less than or equal to 40% by weight of the ion gel electrolyte.

[0034] Solution 4. The battery pack according to Solution 1, wherein the cation comprises N-methyl-N-propylpyrrolidinium ([Py 13 + ), 1-propyl-1-methylpiperidinium ([PP 13 + ), 1-butyl-1-methylpiperidinium ([PP 14 + ), 1-methyl-1-ethylpyrrolidinium ([Py 12 + ), 1-propyl-1-methylpyrrolidinium ([Py 13 + ), 1-butyl-1-methylpyrrolidinium (Py 14 + ), or a combination thereof.

[0035] Solution 5. The battery pack according to Solution 1, wherein the lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI).

[0036] Solution 6. The battery pack according to Solution 1, wherein the ionic liquid and the lithium salt account for greater than or equal to 60% and less than or equal to 99.5% by weight of the ion gel electrolyte.

[0037] Solution 7. The battery pack according to Solution 1, wherein the lithium salt is present in the ionic liquid at a concentration of greater than or equal to 0.6 mole and less than or equal to 4 moles.

[0038] ​​​​​​Embodiment 8. The battery pack according to Embodiment 1, wherein the electroactive material particles of the negative electrode define an open pore extending through the negative electrode, and wherein the ion gel electrolyte penetrates the open pore defined by the electroactive material particles of the negative electrode.

[0039] Embodiment 9. The battery pack according to Embodiment 1, wherein the negative electrode further comprises a solid electrolyte interphase formed in situ on the surface of the electroactive material particles, and wherein the solid electrolyte interphase comprises lithium fluoride (LiF), lithium silicate (Li x SiO y ) or a combination thereof.

[0040] Embodiment 10. The battery pack according to Embodiment 9, wherein the LiF accounts for greater than or equal to 3% and less than or equal to 15% by weight of the solid electrolyte interphase, and the Li x SiO y accounts for greater than or equal to 2% and less than or equal to 10% by weight of the solid electrolyte interphase.

[0041] Embodiment 11. The battery pack according to Embodiment 1, wherein the negative electrode further comprises a polymer binder and a conductive material.

[0042] Embodiment 12. The battery pack according to Embodiment 1, wherein the separator is a polymer membrane having an open microporous structure, the open microporous structure having an open pore extending therethrough, and wherein the ion gel electrolyte penetrates the open pore of the polymer membrane.

[0043] Embodiment 13. The battery pack according to Embodiment 1, wherein the separator comprises solid electrolyte particles, the solid electrolyte particles defining an open pore extending from the negative electrode through the separator to the positive electrode, and wherein the ion gel electrolyte penetrates the open pore defined by the solid electrolyte particles.

[0044] Embodiment 14. The battery pack according to Embodiment 13, wherein the negative electrode further comprises solid electrolyte particles.

[0045] Embodiment 15. A battery pack for cycling lithium ions, the battery pack comprising:

[0046] A negative electrode comprising electroactive material particles containing silicon, the silicon accounting for greater than or equal to 5% by weight of the electroactive material particles;

[0047] A positive electrode spaced apart from the negative electrode and comprising an electroactive positive electrode material;

[0048] A separator disposed between the negative electrode and the positive electrode; and

[0049] An ion gel electrolyte that penetrates the negative electrode, the positive electrode, and the separator, the ion gel electrolyte comprising:

[0050] A polymer matrix including poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), the polymer matrix accounting for greater than or equal to 0.5% and less than or equal to 40% by weight of the ion gel electrolyte;

[0051] An ionic liquid in the polymer matrix, the ionic liquid including N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 -FSI); and

[0052] A lithium salt in the ionic liquid, the lithium salt including lithium bis(fluorosulfonyl)imide (LiFSI).

[0053] Aspect 16. The battery pack according to aspect 15, wherein the negative electrode further includes a solid electrolyte interphase formed in situ on the surface of the electroactive material particles, and wherein the solid electrolyte interphase includes lithium fluoride (LiF), lithium silicate (Li x SiO y ) or a combination thereof.

[0054] Aspect 17. A method of manufacturing a battery pack for cycling lithium ions, the method comprising:

[0055] Penetrating the open pores of a negative electrode with an electrolyte precursor comprising a polymer matrix, an ionic liquid, a lithium salt, and a processing solvent, the ionic liquid comprising a cation including a piperidinium ion and an anion including bis(fluorosulfonyl)imide (FSI), the lithium salt including lithium bis(fluorosulfonyl)imide (LiFSI); then

[0056] Removing the processing solvent from the electrolyte precursor to form an ion gel electrolyte in the open pores of the negative electrode, the ion gel electrolyte comprising a polymer matrix, an ionic liquid, and a lithium salt,

[0057] Wherein the ionic liquid and the lithium salt are immobilized in the polymer matrix of the ion gel electrolyte.

[0058] Scheme 18. The method according to Scheme 17, wherein the polymer matrix comprises poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof, and wherein the cation comprises N-methyl-N-propylpyrrolidinium ([Py 13 + ), 1-propyl-1-methylpiperidinium ([PP 13 + ), 1-butyl-1-methylpiperidinium ([PP 14 + ), 1-methyl-1-ethylpyrrolidinium ([Py 12 + ), 1-propyl-1-methylpyrrolidinium ([Py 13 + ), 1-butyl-1-methylpyrrolidinium (Py 14 + ), or a combination thereof.

[0059] Scheme 19. The method according to Scheme 17, further comprising:

[0060] Preparing a polymer solution by mixing the polymer matrix and the processing solvent at a temperature greater than or equal to about 55 degrees Celsius and less than or equal to 100 degrees Celsius; and

[0061] Introducing the ionic liquid and the lithium salt into the polymer solution to form the electrolyte precursor.

[0062] Scheme 20. The method according to Scheme 17, further comprising:

[0063] After forming the ion gel electrolyte in the pores of the negative electrode, assembling the negative electrode into a stack including a positive electrode and a separator to form the battery pack.

[0064] Further applicable fields of the present disclosure will be apparent from the detailed description, the claims, and the drawings. The detailed description and the specific examples are only intended to illustrate and are not intended to limit the scope of the present disclosure. Brief Description of the Drawings

[0065] The present disclosure is more fully understood from the detailed description and the drawings, wherein:

[0066] Figure 1 ​​​​​​Schematic perspective view of a motor vehicle powered by a battery pack including a plurality of battery pack modules.

[0067] Figure 2 Is Figure 1 Schematic cross-sectional view of a part of one of the battery pack modules, the battery pack module including a plurality of electrochemical cells or battery packs that cycle lithium ions.

[0068] Figure 3 Schematic cross-sectional view of a battery pack that cycles lithium ions, the battery pack including a negative electrode, a positive electrode, a separator in the form of a polymer film, and an ion gel electrolyte that permeates pores in the negative electrode, the positive electrode, and the separator, the negative electrode including electroactive material particles.

[0069] Figure 4 Is Figure 3 Schematic cross-sectional view of one of the electroactive material particles of the negative electrode of, the electroactive material particle having a solid electrolyte interphase formed in situ on its outer surface.

[0070] Figure 5 Schematic cross-sectional view of a battery pack that cycles lithium ions, the battery pack including a negative electrode, a positive electrode, a separator defined by a plurality of solid electrolyte particles, and an ion gel electrolyte that permeates pores in the negative electrode, the positive electrode, and the separator.

[0071] In the drawings, reference numerals may be reused to designate similar and / or identical elements. Detailed Description

[0072] The ion gel electrolyte of the present disclosure includes an ionic liquid immobilized in a polymer matrix and can be used in a battery pack that cycles lithium ions to establish a firm interfacial contact between the electroactive material in the electrode and the ion gel electrolyte, which can improve the electrochemical performance (e.g., rate capability) of the battery pack compared to a battery pack including an ionic liquid electrolyte that does not include a polymer matrix. In addition, the ion gel electrolyte of the present disclosure can more effectively wet the electroactive material in the electrode, thereby increasing the amount of electroactive material that can participate in the electrochemical reactions occurring within the battery pack, which in turn can increase the capacity of the battery pack. Further, when the ion gel electrolyte of the present disclosure is used in combination with a battery pack including a silicon (Si)-containing negative electrode, the ion gel electrolyte can promote the formation of a stable solid electrolyte interphase (SEI) on the surface of the silicon-containing electroactive material in the negative electrode, thereby improving the cycle stability of the battery pack.

[0073] Figure 1Depicts a motor vehicle 2 powered by an electric motor 4 that obtains electrical power from a battery pack 6 including one or more battery pack modules 8. The battery pack modules 8 can be electrically coupled together in series and / or parallel arrangements to meet the capacity and power requirements of the electric motor 4. The vehicle 2 can be a pure electric vehicle and can be powered entirely by the electric motor 4, or the vehicle 2 can be a hybrid vehicle and can be powered by the electric motor 4 and an internal combustion engine (not shown).

[0074] As Figure 2 shown, each battery pack module 8 includes one or more electrochemical cells or battery packs 10 that cycle lithium ions. In practice, the battery packs 10 in the battery pack module 8 are typically assembled as stacked layers, which include a negative electrode layer 12, a negative electrode current collector 13, a positive electrode layer 14, a positive electrode current collector 15, and a separator layer 16. Each battery pack 10 is defined by the negative electrode layer 12 and the positive electrode layer 14, and the negative electrode layer 12 and the positive electrode layer 14 are spaced apart from each other by the separator layer 16. In practice, the separator layer 16 can be permeated with an electrolyte that provides a medium for lithium ion conduction between the negative electrode layer 12 and the positive electrode layer 14, or the separator layer 16 itself can serve as the electrolyte. The negative electrode layer 12 is disposed on the negative electrode current collector 13 and is electrically connected to the negative electrode current collector 13, while the positive electrode layer 14 is disposed on the positive electrode current collector 15 and is electrically connected to the positive electrode current collector 15. As Figure 2 shown, for efficiency, these layers can be stacked such that some of the negative electrode current collectors 13 and some of the positive electrode current collectors 15 are double-sided and include the negative electrode layer 12 or the positive electrode layer 14 on their respective two sides. In this arrangement, adjacent negative electrode layers 12 and positive electrode layers 14 share a single negative electrode current collector 13 or positive electrode current collector 15, respectively.

[0075] Figure 3 Depicts an electrochemical cell or battery pack 20 that cycles lithium ions. The battery pack 20 can generate an electric current during discharge, which can be used to power a load device (e.g., the electric motor 4), and can be charged by connecting to a power source. Similar to Figure 1 and 2 the battery pack 10 depicted, in aspects, the battery pack 20 can be used to power the electric motor 4 of the motor vehicle 2. Additionally or alternatively, the battery pack 20 can be used in other transportation applications (e.g., motorcycles, boats, tractors, buses, motorcycles, mobile homes, campers, tanks, and airplanes), and can be used to power a wide variety of other stationary and / or portable electronic devices, components, and devices used in industrial and other applications, including industrial, residential, and commercial buildings, consumer goods, industrial equipment and machinery, agricultural or farm equipment, and heavy machinery (as non-limiting examples).

[0076] The battery pack 20 includes a negative electrode 22, a positive electrode 24, a separator 26, and an ion gel electrolyte 28. The ion gel electrolyte 28 provides a medium for lithium ion conduction between the negative electrode 22 and the positive electrode 24. The negative electrode 22 is disposed on the main surface of a negative electrode current collector 30, while the positive electrode 24 is disposed on the main surface of a positive electrode current collector 32. In practice, the negative electrode current collector 30 and the positive electrode current collector 32 are electrically coupled to a power source or a load 34 (e.g., an electric motor 4) via an external circuit 36. The negative electrode 22 and the positive electrode 24 are formulated to establish an electrochemical potential difference between the negative electrode 22 and the positive electrode 24 when the battery pack 20 is at least partially charged. During discharge of the battery pack 20, the electrochemical potential established between the negative electrode 22 and the positive electrode 24 drives a spontaneous reduction and oxidation (redox) reaction within the battery pack 20 and releases lithium ions and electrons from the negative electrode 22. The released lithium ions travel from the negative electrode 22 through the separator 26 and the electrolyte 28 to the positive electrode 24, while the electrons travel from the negative electrode 22 to the positive electrode 24 via the external circuit 36, which generates an electric current. After the negative electrode 22 has been partially or completely depleted of lithium, the battery pack 20 can be charged by connecting the negative electrode 22 and the positive electrode 24 to a power source 34, which drives a non-spontaneous redox reaction within the battery pack 20 and releases lithium ions and electrons from the positive electrode 24. The repeated discharge and charge of the battery pack 20 may be referred to herein as a "cycle", and a complete charge event followed by a complete discharge event is considered a complete cycle.

[0077] The negative electrode 22 is formulated to store and release lithium ions to facilitate charging and discharging of the battery pack 20, respectively. The negative electrode 22 is disposed on the main surface of the negative electrode current collector 30 and may be in the form of a continuous porous layer having a plurality of openings extending therethrough. The negative electrode 22 includes electrochemically active (electroactive) material particles 38, a polymer binder 40, and an optional conductive material 42. The electrochemically active material particles 38 of the negative electrode 22 may be referred to herein as electroactive negative electrode material particles. The electroactive material particles 38 may be mixed with the polymer binder 40 and the optional conductive material 42 in the negative electrode 22. The negative electrode 22 may have a thickness greater than or equal to 2 micrometers (μm), optionally greater than or equal to 10 μm, optionally greater than or equal to 20 μm, or optionally greater than or equal to 30 μm and less than or equal to 200 μm.

[0078] The electroactive material particles 38 of the negative electrode 22 are made of an electroactive material that is formulated to store and release lithium ions during charging and discharging of the battery pack 20 by undergoing a reversible redox reaction with lithium. Examples of electroactive materials for the negative electrode 22 include silicon, silicon-based materials (e.g., alloys of silicon and lithium, tin, iron, aluminum, and / or cobalt), silicon oxides, silicon-oxide-based materials (such as lithium silicon oxide), lithium, lithium-based materials (e.g., alloys of lithium and silicon, aluminum, indium, and / or tin), carbon-based materials (e.g., graphite, activated carbon, carbon black, hard carbon, soft carbon, and / or graphene), tin oxide, aluminum, indium, zinc, germanium, titanium oxide, lithium titanate, and combinations thereof. The electroactive material particles 38 can account for greater than or equal to about 50% by weight of the negative electrode 22, optionally greater than or equal to about 60%, or optionally greater than or equal to about 70% and less than or equal to about 95%, optionally less than or equal to about 90%, or optionally less than or equal to about 80%.

[0079] At least one of the electroactive materials for forming the electroactive material particles 38 of the negative electrode 22 is silicon. For example, in an embodiment, silicon can account for greater than or equal to 5% by weight of the electroactive material particles 38 of the negative electrode 22, optionally greater than or equal to about 10% and less than or equal to about 90%.

[0080] The polymer binder 40 is electrochemically inactive and can provide structural integrity to the negative electrode 22, e.g., by promoting cohesion between the electroactive material particles 38 and / or by helping the negative electrode 22 adhere to the major surface of the negative electrode current collector 30. Examples of polymers that can be used to form the polymer binder 40 include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene propylene diene monomer (EPDM) rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), nitrile butadiene rubber (NBR), styrene-butadiene rubber (SBR), styrene-ethylene-butene-styrene copolymer (SEBS), polyacrylate, alginate, polyacrylic acid, and combinations thereof. The polymer binder 40 can account for greater than or equal to about 1% by weight of the negative electrode 22, or optionally greater than or equal to about 5% and less than or equal to about 10%.

[0081] Optional conductive material 42 is electrochemically inert and can provide good electrical conductivity to the negative electrode 22. Examples of conductive materials for optional conductive material 42 that can be used to form negative electrode 22 include carbon-based materials, metals (e.g., nickel), and / or conductive polymers. Examples of carbon-based conductive materials include carbon black (CB) (e.g., acetylene black), graphite, graphene (e.g., graphene nanosheets, GNP), graphene oxide, carbon nanotubes (CNT), and / or carbon fibers (e.g., carbon nanofibers). Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and / or polypyrrole. When included in negative electrode 22, optional conductive material 42 can account for greater than 0% by weight of negative electrode 22, optionally greater than or equal to about 1%, or optionally greater than or equal to about 5% and less than or equal to about 10%.

[0082] Positive electrode 24 is configured to store and release lithium ions during discharge and charge of battery pack 20. Positive electrode 24 can be in the form of a continuous porous layer disposed on a major surface of positive electrode current collector 32 and can include a plurality of open pores extending therethrough. Positive electrode 24 includes an electroactive material (electroactive positive electrode material), a polymeric binder, and an optional conductive material. The electroactive material of positive electrode 24 can be a particulate material, and the particles of the electroactive material of positive electrode 24 can be mixed with the polymeric binder and the optional conductive material. The same polymeric binder and / or conductive material disclosed above for negative electrode 22 can be used in positive electrode 24 in substantially the same amounts.

[0083] The electroactive material of positive electrode 24 can store and release lithium ions by undergoing a reversible redox reaction with lithium at a higher electrochemical potential than the electrochemically active material of negative electrode 22, such that there is an electrochemical potential difference between negative electrode 22 and positive electrode 24. The electroactive material of positive electrode 24 can include a material capable of lithium intercalation and deintercalation or a material capable of a conversion reaction with lithium. In aspects where the electroactive material of positive electrode 24 includes an intercalation host material capable of undergoing reversible insertion or intercalation of lithium ions, the electroactive material of positive electrode 24 can include lithium transition metal oxides. For example, the electroactive material of positive electrode 24 can include layered lithium transition metal oxides represented by the formula LiMeO2 and / or Li2MeO3, the formula Li 1+x Me 1-xA layered lithium-rich transition metal oxide represented by O2 (where 0 < x ≤ 0.33), a monoclinic lithium transition metal oxide represented by the formula Li3Me2(PO4)3, a spinel-type lithium transition metal oxide represented by the formula LiMe2O4, a lithiophilite or a combination thereof represented by one or both of the following formulas LiMeSO4F or LiMePO4F, where Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or a combination thereof). In aspects where the electroactive material of the positive electrode 24 includes a conversion material, the electroactive material of the positive electrode 24 can include sulfur, selenium, tellurium, iodine, halides (e.g., fluorides or chlorides), sulfides, selenides, tellurides, iodides, phosphides, nitrides, oxides, oxysulfides, oxyfluorides, sulfur fluorides, sulfur-oxyfluorides, or lithium and / or its metal compounds (e.g., compounds of iron, manganese, nickel, copper, and / or cobalt).

[0084] The separator 26 physically separates and electrically isolates the negative electrode 22 and the positive electrode 24 from each other while allowing lithium ions to pass through. The separator 26 has an open microporous structure including a plurality of openings and can include organic and / or inorganic materials. The separator 26 can have a thickness greater than or equal to about 5 micrometers (μm), optionally greater than or equal to about 10 μm, or optionally greater than or equal to about 20 μm and less than or equal to about 200 μm, optionally less than or equal to about 100 μm, or optionally less than or equal to about 50 μm.

[0085] As Figure 3 shown, in some embodiments, the separator 26 can be in the form of a polymer membrane. In embodiments where the separator 26 is in the form of a polymer membrane, the separator 26 can include polyolefins (e.g., polyethylene, PE, and / or polypropylene, PP), polyamides (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVDF), poly(vinyl chloride) (PVC), or a combination thereof. As Figure 5 shown, in some embodiments, the separator 26 can be defined by a plurality of solid electrolyte particles 44. The solid electrolyte particles 44 include an inorganic solid electrolyte material that is formulated to conduct solid-state lithium ions by diffusing through its lattice. Examples of inorganic solid electrolyte materials include oxide-based, sulfide-based, and phosphate-based materials. In some embodiments, the separator 26 can include a polymer membrane and a plurality of solid electrolyte particles 44 (not shown). As Figure 5 shown, in embodiments where the separator 26 is defined by a plurality of solid electrolyte particles 44, the negative electrode 22 and / or the positive electrode 24 can further include a plurality of solid electrolyte particles 44. In this case, the solid electrolyte particles 44 can account for greater than 0% by weight, optionally greater than or equal to 20% and less than or equal to 30% of the negative electrode 22 and / or the positive electrode 24.

[0086] The ionic gel electrolyte 28 is ionically conductive and provides a medium for the conduction of lithium ions through the negative electrode 22, the positive electrode 24, and the separator 26 and between the negative electrode 22 and the positive electrode 24. The ionic gel electrolyte 28 can penetrate the open pores of the negative electrode 22, the positive electrode 24, and the separator 26 and wet their surfaces. The ionic gel electrolyte 28 includes a polymer matrix, an ionic liquid immobilized in the polymer matrix, and a lithium salt in the ionic liquid. Compared with an ionic liquid electrolyte (including an ionic liquid and a lithium salt but not including a polymer matrix), the ionic gel electrolyte 28 (including an ionic liquid, a lithium salt, and a polymer matrix) can wet the electroactive material particles 38 of the negative electrode 22 more thoroughly and effectively, thereby increasing the amount of electroactive material particles 38 that can participate in the electrochemical reactions occurring within the battery pack 20 during the operation of the battery pack 20. Therefore, compared with an ionic liquid electrolyte that does not include a polymer matrix, the ionic gel electrolyte 28 (including an ionic liquid, a lithium salt, and a polymer matrix) can provide improved rate performance and increased capacity for the battery pack 20.

[0087] The polymer matrix is formulated to provide flexibility to the ionic gel electrolyte 28 and the ability to establish firm interfacial contact with the electroactive material of the negative electrode 22 and the positive electrode 24 (i.e., with the electroactive material particles 38 in the negative electrode 22). The polymer matrix can include poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof. The polymer matrix can account for greater than or equal to 0.5% by weight of the ionic gel electrolyte 28, optionally greater than or equal to 3% and less than or equal to 40%, optionally less than or equal to 10%. In an embodiment, the polymer matrix can account for about 5% by weight of the ionic gel electrolyte 28.

[0088] The ionic liquid penetrates the polymer matrix and is formulated to provide the ionic gel electrolyte 28 with high ionic conductivity, nonflammability, low volatility, and good electrochemical and thermal stability. The ionic liquid includes a cation and an anion. The cation of the ionic liquid includes a piperidinium ion. In an embodiment, the cation of the ionic liquid can include N-methyl-N-propylpyrrolidinium ([Py 13 + ), 1-propyl-1-methylpiperidinium ([PP 13 + ), 1-butyl-1-methylpiperidinium ([PP 14 + ), 1-methyl-1-ethylpyrrolidinium ([Py 12 ​​​​+ ) 1-propyl-1-methylpyrrolidinium ([Py 13 )] + ) 1-butyl-1-methylpyrrolidinium (Py 14 )] + ) or a combination thereof. The anion of the ionic liquid includes bis(fluorosulfonyl)imide (N(SO2F)2 - )(FSI - ). The ionic liquid may account for greater than or equal to 40% by weight, optionally greater than or equal to 50%, optionally greater than or equal to 60%, optionally greater than or equal to 70%, and less than or equal to 92% of the ion gel electrolyte 28. In an embodiment, the ionic liquid may account for about 83.4% by weight of the ion gel electrolyte 28.

[0089] The lithium salt is formulated to provide an ion gel electrolyte 28 with good ionic conductivity, for example, by creating a lithium ion transport channel therethrough. The lithium salt may include lithium imide. In an embodiment, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiFSI). When dissolved in the ionic liquid, LiFSI dissociates to form Li + cations and N(SO2F)2 - anions. The lithium salt may be present in the ionic liquid at a concentration greater than or equal to 0.6 moles and less than or equal to 4 moles, optionally less than or equal to 2 moles. In an embodiment, the lithium salt may be present in the ionic liquid at a concentration of about 1 mole. In an embodiment, the lithium salt may account for greater than or equal to 7% by weight, optionally greater than or equal to 10%, and less than or equal to 21.5%, or optionally less than or equal to 15% of the ion gel electrolyte 28. In an embodiment, the lithium salt may account for about 11.6% by weight of the ion gel electrolyte 28.

[0090] In combination, the ionic liquid and the lithium salt may account for greater than or equal to 60% by weight, optionally greater than or equal to 80%, and less than or equal to 99.5%, optionally less than or equal to 98% of the ion gel electrolyte 28. In an embodiment, the ionic liquid and the lithium salt may account for about 95% by weight of the ion gel electrolyte 28.

[0091] Now referring to Figure 4 , N(SO2F)2 in the ion gel electrolyte 28 -The anions are formulated to participate in the in-situ formation of a solid electrolyte interphase 46 on the surface 48 of each electroactive material particle 38 of the negative electrode 22 during the initial and / or repeated cycling of the battery pack 20. The solid electrolyte interphase 46 is electrically insulating and ion-conductive and, when present, is configured to help prevent undesirable chemical reactions from occurring between the ionic gel electrolyte 28 and the electroactive material particles 38 of the negative electrode 22 during cycling of the battery pack 20. During the formation of the solid electrolyte interphase 46, N(SO2F)2 in the ionic gel electrolyte 28 - anions can react with silicon and lithium in the electroactive material particles 38 of the negative electrode 22 and decompose to form inorganic compounds such as lithium fluoride (LiF), lithium silicate (Li x SiO y ), lithium silicide (Li x Si), and combinations thereof. N(SO2CF3)2 - The inorganic decomposition products of the anions can deposit on the surface 48 of the electroactive material particles 38 and form the solid electrolyte interphase 46. Accordingly, the solid electrolyte interface 46 can include lithium fluoride (LiF), lithium silicate (Li x SiO y ), lithium silicide (Li x Si), and combinations thereof. In an embodiment, LiF can account for greater than or equal to 3% and less than or equal to 15% by weight of the solid electrolyte interphase 46, and Li x SiO y can account for greater than or equal to 2% and less than or equal to 10% by weight of the solid electrolyte interphase 46. For example, in an embodiment, LiF can account for about 6% by weight of the solid electrolyte interphase 46, and Li x SiO y can account for about 5% by weight of the solid electrolyte interphase 46.

[0092] In an embodiment, the ionic gel electrolyte 28 can be substantially free of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and can be substantially free of bis(trifluoromethanesulfonyl)imide N(SO2CF3)2 - anions. Without being bound by theory, it is believed that when silicon is used as the electroactive negative electrode material and N(SO2CF3)2 - anions are included in the electrolyte of a battery pack (such as battery pack 20) that cycles lithium ions, N(SO2CF3)2 - anions can decompose on the surface of the electroactive negative electrode material and form organic compounds (e.g., SO2CF3 - and NSO2CF3 2- ), as compared to where N(SO2F)2 -Compared to a battery pack in which anions are included in an electrolyte (such as ionic gel electrolyte 28), this can result in the formation of a relatively thick and unstable solid electrolyte interphase on the surface of the electroactive positive electrode material. The formation of a relatively thick and unstable solid electrolyte interphase containing organic compounds on the surface of the electroactive negative electrode material can lead to rapid capacity fade.

[0093] In addition, in an embodiment, the ionic gel electrolyte 28 can be substantially free of non-aqueous aprotic organic solvents. Non-limiting examples of non-aqueous aprotic organic solvents that can be excluded from the composition of the ionic gel electrolyte 28 include cyclic carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC)); linear carbonates (e.g., dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)); aliphatic carboxylic acid esters (e.g., methyl formate, methyl acetate, methyl propionate); lactones (e.g., γ-butyrolactone, γ-valerolactone, and / or δ-valerolactone); nitriles (e.g., succinonitrile, glutaronitrile, and / or adiponitrile); sulfones (e.g., tetramethylene sulfone, ethyl methyl sulfone, vinyl sulfone, benzene sulfone, 4-fluorobenzene sulfone, benzyl sulfone, and / or sulfolane); aliphatic ethers (e.g., triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dimethoxypropane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and / or ethoxymethoxyethane); cyclic ethers (e.g., 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane); phosphate esters (e.g., triethyl phosphate and / or trimethyl phosphate); and combinations thereof.

[0094] The negative electrode current collector 30 and the positive electrode current collector 32 are conductive and provide electrical connections between the external circuit 36 and the negative electrode 22 and the positive electrode 24, respectively. In an aspect, the negative electrode current collector 30 and the positive electrode current collector 32 can be made of metal and can be in the form of a non-porous metal foil, a perforated metal foil, a porous metal mesh, or a combination thereof. The negative electrode current collector 30 can be made of copper, nickel, or an alloy thereof, stainless steel, or other suitable conductive materials. The positive electrode current collector 32 can be made of aluminum (Al) or other suitable conductive materials.

[0095] Method

[0096] The ionic gel electrolyte 28 can be manufactured by preparing an electrolyte precursor that includes a polymer matrix, an ionic liquid, a lithium salt, and a processing solvent. The polymer matrix, the ionic liquid, and the lithium salt can have substantially the same composition as the polymer matrix, the ionic liquid, and the lithium salt included in the ionic gel electrolyte 28 and can be present in the electrolyte precursor in substantially the same proportions.

[0097] The processing solvent may include an organic solvent having a low vapor pressure such that the processing solvent can be easily removed from the precursor electrolyte by evaporation at a temperature of less than or equal to 100 degrees Celsius (°C). Examples of the processing solvent include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), tetrahydrofuran (THF), ethyl acetate, dimethyl sulfoxide, acetonitrile (ACN), N-methyl-2-pyrrolidone (NMP), dimethoxyethane, dioxolane, acetone, N,N-dimethylformamide (DMF), alcohols (e.g., ethanol, methanol, and / or isopropanol), and combinations thereof. The processing solvent may account for greater than or equal to 15% and less than or equal to 85% by weight of the precursor electrolyte.

[0098] In an embodiment, the precursor electrolyte can be prepared by mixing a polymer matrix and a processing solvent together to form a polymer solution, and separately mixing an ionic liquid and a lithium salt together to form an ionic liquid mixture. Then, the ionic liquid mixture can be introduced into the polymer solution to form the precursor electrolyte. In an embodiment, the polymer matrix and the processing solvent can be mixed together at a temperature of greater than or equal to about 55 °C and less than or equal to 100 °C to form the polymer solution.

[0099] During the assembly of the battery pack 20, the precursor electrolyte can be introduced into the openings of the negative electrode 22, the positive electrode 24, and / or the separator 26, and then the processing solvent can be removed from the precursor electrolyte to form an ion gel electrolyte 28 in the openings of the negative electrode 22, the positive electrode 24, and / or the separator 26. The processing solvent can be removed from the precursor electrolyte, for example, at a temperature of greater than or equal to 10 °C and less than or equal to 100 °C (e.g., ambient temperature, about 25 °C) for a time of greater than or equal to 30 minutes and less than or equal to 24 hours. In an embodiment, the ion gel electrolyte 28 can be formed separately in the openings of each of the negative electrode 22, the positive electrode 24, and / or the separator 26, and then the negative electrode 22, the positive electrode 24, and the separator 26 can be assembled in the form of the battery pack 20.

[0100] In an embodiment, the precursor electrolyte can be introduced into the openings of the negative electrode 22, the positive electrode 24, and / or the separator 26 by depositing the precursor electrolyte on the negative electrode 22, the positive electrode 24, and / or the separator 26 such that the precursor electrolyte penetrates into the openings of the negative electrode 22, the positive electrode 24, and / or the separator 26. The precursor electrolyte can be deposited on the negative electrode 22, the positive electrode 24, and / or the separator 26, for example, by drop coating, dip coating, spraying, blade coating, or a combination thereof.

[0101] In an embodiment, the negative electrode 22 can be formed on a substrate, a precursor electrolyte can be introduced into the open pores of the negative electrode 22, and then the processing solvent can be removed from the precursor electrolyte to form an ion gel electrolyte 28 in the open pores in the negative electrode 22. In an embodiment, the substrate can have substantially the same composition as the negative electrode current collector 30, and after the ion gel electrolyte 28 is formed in the open pores of the negative electrode 22, the negative electrode 22 and the substrate can be assembled into the battery pack 20, where the substrate is the negative electrode current collector 30.

[0102] In some embodiments, the negative electrode 22, the positive electrode 24, and / or the separator 26 can be formed or disposed on a release film, the ion gel electrolyte 28 can be formed in the open pores of the negative electrode 22, the positive electrode 24, and / or the separator 26, and then the negative electrode 22, the positive electrode 24, and / or the separator 26 can be removed from the release film and assembled into the battery pack 20.

[0103] The foregoing description is only exemplary and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Thus, although the disclosure includes specific examples, the true scope of the disclosure should not be so limited because other modifications will become apparent after study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be implemented in a different order (or concurrently) without altering the principles of the disclosure. Further, although the embodiments are described above as having certain features, any one or more of the features described with respect to any one embodiment of the disclosure can be implemented in and / or combined with any other embodiment, even if not explicitly described in that combination. In other words, the embodiments are not mutually exclusive, and permutations of one or more embodiments are still within the scope of the disclosure. Any method steps, methods, and operations described herein should not be construed as necessarily requiring them to be performed in the order discussed or illustrated, unless explicitly designated as an order of performance. It should also be understood that, unless otherwise specified, additional or alternative steps may be used.

[0104] The phrase “at least one of A, B, and C” as used herein should be construed to mean a logical (A or B or C) using a non-exclusive logical OR and should not be construed to mean “at least one of A, at least one of B, and at least one of C”. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0105] The terms used herein are for the purpose of describing exemplary embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" used herein are also intended to include the plural forms. The terms "comprising", "including", and "having" are inclusive and thus specify the presence of the stated features, elements, compositions, steps, integers, operations, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or their combinations. Although the open-ended terms "comprising", "including", and "having" should be understood as non-limiting terms for describing and claiming the various embodiments described herein, in some instances these terms may alternatively be understood as more restrictive and limiting terms, such as "consisting of" or "consisting essentially of". Thus, for any given embodiment that lists a composition, material, component, element, ingredient, feature, integer, operation, and / or method step, the present disclosure also expressly includes embodiments consisting of or consisting essentially of these listed composition, material, component, element, ingredient, feature, integer, operation, and / or method step. In the case of "consisting of", the alternative embodiment does not include any additional composition, material, component, element, ingredient, feature, integer, operation, and / or method step, and in the case of "consisting essentially of", such an embodiment does not include any additional composition, material, component, element, ingredient, feature, integer, operation, and / or method step that materially affects the basic and novel features, but may include any composition, material, component, element, ingredient, feature, integer, operation, and / or method step that does not materially affect the basic and novel features in the embodiment.

[0106] Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers, and / or sections, these steps, elements, components, regions, layers, and / or sections should not be limited by these terms unless otherwise indicated. These terms are only used to distinguish one step, element, component, region, layer, or section from another. Ordinal terms such as "first", "second", etc. do not imply an order or sequence when used herein unless the context clearly indicates. Thus, the first step, element, component, region, layer, or section discussed below may be referred to as the second step, element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0107] Unless otherwise specified, the terms "composition" and "material" as used herein are used interchangeably to generally refer to a substance that contains at least a preferred chemical component, element or compound but may also contain additional elements, compounds or substances, including trace impurities. A "X-based" composition or material generally refers to a composition or material in which "X" is the single largest component of the composition or material by weight percentage (%). This can include compositions or materials having greater than 50 wt% X, and can also include compositions or materials having less than 50 wt% X, as long as X is the single largest component of the composition or material based on its total weight. When a composition or material is referred to as "substantially free of" a substance, the composition or material may contain less than 5%, optionally less than 3%, optionally less than 1% or optionally less than 0.1% by weight of the substance.

Claims

1. A battery pack with a cyclic lithium ion, the battery pack comprising: A negative electrode comprising electroactive material particles containing silicon; A positive electrode spaced apart from the negative electrode and comprising an electroactive positive electrode material; A separator disposed between the negative electrode and the positive electrode; And An ionic gel electrolyte comprising: A polymer matrix comprising poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), or a combination thereof; An ionic liquid in the polymer matrix, the ionic liquid comprising a cation comprising a piperidinium ion and an anion comprising bis(fluorosulfonyl)imide (FSI); and A lithium salt in the ionic liquid.

2. The battery pack according to claim 1, wherein the polymer matrix accounts for greater than or equal to 0.5% and less than or equal to 40% by weight of the ionic gel electrolyte.

3. The battery pack according to claim 1, wherein the cation includes N-methyl-N-propylpyrrolidinium ([Py 13 + ), 1-propyl-1-methylpiperidinium ([PP 13 + ), 1-butyl-1-methylpiperidinium ([PP 14 + ), 1-methyl-1-ethylpyrrolidinium ([Py 12 + ), 1-propyl-1-methylpyrrolidinium ([Py 13 + ), 1-butyl-1-methylpyrrolidinium (Py 14 + ) or a combination thereof.​​​​​​ 4. The battery pack according to claim 1, wherein the lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), and wherein the lithium salt is present in the ionic liquid at a concentration greater than or equal to 0.6 mole and less than or equal to 4 moles.

5. The battery pack according to claim 1, wherein the ionic liquid and the lithium salt account for greater than or equal to 60% and less than or equal to 99.5% by weight of the ionic gel electrolyte.

6. The battery pack according to claim 1, wherein the electroactive material particles of the negative electrode define an open pore extending through the negative electrode, and wherein the ionic gel electrolyte penetrates the open pore defined by the electroactive material particles of the negative electrode.

7. The battery pack according to claim 1, wherein the negative electrode further comprises a solid electrolyte interphase formed in situ on the surface of the electroactive material particles, and wherein the solid electrolyte interphase comprises lithium fluoride (LiF), lithium silicate (Li x SiO y ) or a combination thereof.

8. The battery pack according to claim 7, wherein the LiF accounts for greater than or equal to 3% and less than or equal to 15% by weight of the solid electrolyte interphase, and the Li x SiO y accounts for greater than or equal to 2% and less than or equal to 10% by weight of the solid electrolyte interphase.

9. The battery pack according to claim 1, wherein the separator is a polymer membrane having an open microporous structure with open pores extending therethrough, and wherein the ionic gel electrolyte penetrates the open pores of the polymer membrane.

10. The battery pack according to claim 1, wherein the separator comprises solid electrolyte particles, the solid electrolyte particles define an open pore extending from the negative electrode through the separator to the positive electrode, and wherein the ionic gel electrolyte penetrates the open pore defined by the solid electrolyte particles, and wherein the negative electrode further comprises solid electrolyte particles.

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