Negative electrodes comprising polymer base layers for lithium-metal and lithium-ion electrochemical cells

Abstract

Described herein are lithium-metal negative electrodes, lithium-metal liquid-electrolyte electrochemical cells comprising such electrodes, and methods of fabricating such electrodes. In some examples, a lithium-metal negative electrode comprises a polymer base layer, a current collector layer, and a lithium-metal negative active material layer. The polymer base layer can comprise a high-crystallinity polypropylene homopolymer that may have a melting point of 164-170°C and / or a Viscat softening point of 156-160°C. The current collector is attached to and mechanically supported by the polymer base layer. The negative current collector layer provides a plating surface for the lithium-metal negative active material layer and electronic pathways during charge / discharge. The negative current collector layer is positioned between the polymer base layer and the lithium-metal negative active material layer. The lithium-metal negative active material layer is attached to and supported by the negative current collector layer and the polymer base layer.

Description

Negative Electrodes Comprising Polymer Base Layers for Lithium- Metal and Lithium-Ion Electrochemical CellsCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of US Provisional Patent Application No. 63 / 579,449 (Docket No. CUBRP119P) by David Jorgensen, et al, entitled: "Lithium-Metal Negative Electrodes with Polymer Base Layers", filed on 2023- 08-29, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0001] Lithium-ion (Li-ion or Lil) cells or, more generally, Li-ion batteries are widely used for various applications. For example, Li-ion batteries are used to power devices as small as medical devices or cell phones and as large as electric vehicles or aircraft. The wide adoption of Li-ion batteries across many industries generated many useful designs and knowledge about fabricating Li-ion battery modules and packs. In particular, many concerns involving cycling efficiency, capacity, and safety have been addressed in Li-ion batteries.

[0002] Lithium metal (Li-metal or LiM) cells represent a different battery type and are distinct from Li-ion cells. Specifically, Li-ion cells utilize special negative-electrode active materials (e.g., graphite, silicon) to trap lithium ions when the Li-ion cells are charging. On the other hand, Li-metal cells utilize the direct deposition (e.g., plating) of lithium metal on the negative current collectors without a need for any additional active materials for trapping lithium ions. As such, Li-metal cells tend to have a lower weight and a higher energy density in comparison to Li-ion cells. For example, Li-metal has a specific capacity of 3,860 mAh / g, which is about ten times higher than that of graphite.

[0003] However, Li-metal cells or, more generally, Li-metal batteries are currently not widely adopted at the scale of Li-ion batteries. One limitation involves Li-metal- containing negative electrodes, which can be difficult to manufacture, handle, and operate in Li-metal batteries. For example, Li-metal can be used as standalone structures (e.g., as thick lithium foils) or as layers formed on another substrate. It should be noted that Li-metal has very weak mechanical properties in comparison toother metals. For example, Li-metal tensile strength is only 1.5 MPa, copper's tensile strength is 210 MPa, and aluminum's tensile strength is up to 600 MPa (in the alloy form). Even polymers have tensile strengths that are greater than that of Li-metal, e.g., polypropylene (PP) has a tensile strength of 30-40 MPa, while high-density polyethylene (HDPE) has a tensile strength of 25-30 MPa.

[0004] When Li-metal is provided in a layer formed on another substrate, various properties of this substrate (e.g., the mechanical, weight, electrical, and electrochemical characteristics) determine the properties of the Li-metal-containing negative electrode and that of the resulting Li-metal battery (e.g., energy density). For example, a stronger substrate is desired to ensure that the Li-metal-containing negative electrode can be easily handled / processed. Furthermore, preserving the structural integrity of Li-metal batteries (e.g., operating under pressure) can be important. While metals are stronger than polymers, polymers are much lighter than metals thereby reducing the electrode and battery weight. However, polymers are generally not electronically conductive and can limit the current flow through the negative electrode during the cell's charge and discharge (which can negatively impact the charge / discharge rate characteristics). At least some conductivity may be needed, especially with thin lithium metal layers.

[0005] What is needed are novel electrode structures with polymer base layers for Li- metal-containing negative electrodes.SUMMARY

[0006] Described herein are negative electrodes, lithium-metal and lithium-ion electrochemical cells comprising such electrodes, and methods of fabricating such electrodes. In some examples, a negative electrode comprises a polymer base layer, a current collector layer, and a negative active material layer. The polymer base layer can comprise a high-crystallinity polypropylene homopolymer that may have a melting point of 164-170°C and / or a Vicat softening point of 156-160°C. The current collector is attached to and mechanically supported by the polymer base layer. The negative current collector layer provides a depositing and / or plating surface for the lithium- metal negative active material layer and electronic pathways during charge / discharge. The negative current collector layer is positioned between the polymer base layer and the lithium-metal negative active material layer. The lithium-metal negative activematerial layer is attached to and supported by the negative current collector layer and the polymer base layer.

[0007] Clause 1. A negative battery electrode comprising: a polymer base layer (122) comprising a high-crystallinity polypropylene homopolymer, wherein the high- crystallinity polypropylene homopolymer has a melting point of 164-170°C and a Vicat softening point of 156-160°C; a negative current collector (120) layer (126) attached to and supported by the polymer base layer (122) and a lithium-metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium- metal negative active material layer (112).

[0008] Clause 2. The negative battery electrode of clause 1, wherein: the negative battery electrode is a lithium-metal negative battery electrode (110), and the lithium- metal negative active material layer (112) has a thickness of at least 2 micrometers.

[0009] Clause 3. The negative battery electrode of clause 2, wherein a surface of the lithium-metal negative active material layer (112) facing away from the negativeelectrode current collecting layer (126) is exposed.

[0010] Clause 4. The negative battery electrode of clause 1, wherein the negative battery electrode is a pre-lithiated negative battery electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negative-electrode current collecting layer (126).

[0011] Clause 5. The negative battery electrode of clause 4, wherein the lithium-metal negative active material layer (112) has a thickness of less than 2 micrometers.

[0012] Clause 6. The negative battery electrode of clause 4, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

[0013] Clause 7. The negative battery electrode of clause 1, wherein the high- crystallinity polypropylene homopolymer has a crystallinity of at least 98%.

[0014] Clause 8. The negative battery electrode of clause 1, wherein the polymer base layer (122) has a thickness of 4.5 - 9 micrometers.

[0015] Clause 9. The negative battery electrode of clause 1, wherein the negative current collector (120) layer (126) has a thickness of 0.2 - 1 micrometers.

[0016] Clause 10. The negative battery electrode of clause 1, wherein the lithium- metal negative active material layer (112) has a thickness of 1 - 8 micrometers.

[0017] Clause 11. The negative battery electrode of clause 1, wherein the lithium- metal negative active material layer (112) is thicker than the polymer base layer (122).

[0018] Clause 12. The negative battery electrode of clause 1, wherein the negative current collector (120) layer (126) comprises one or more elements selected from the group consisting of copper, sodium, chromium, and titanium.

[0019] Clause 13. The negative battery electrode of clause 1, wherein the negative current collector (120) layer (126) comprises an alloy or a multi-layered structure comprising at least two or more elements selected from the group consisting of aluminum, cadmium, chromium, cobalt, copper, indium, lithium, manganese, molybdenum, nickel, phosphorous, silicon, silver, sodium, tin, titanium, and zinc.

[0020] Clause 14. The negative battery electrode of clause 1, further comprising a carbon-containing layer (124) positioned between the polymer base layer (122) and the negative current collector (120) layer (126), wherein the carbon-containing layer (124) comprises graphene.

[0021] Clause 15. The negative battery electrode of clause 1, wherein the polymer base layer (122) comprises a flame retardant (123) selected from the group consisting of zinc borate, boron phosphate, triphenylphosphate, triphenylphosphine oxide, and ammonium polyphosphate.

[0022] Clause 16. A negative battery electrode comprising: a polymer base layer (122) comprising a polymer base and a flame retardant (123), wherein: the polymer base comprises one or more of polyethylene terephthalate, polypropylene, polycarbonate, polyethylene, polyimide, cellulose, and nylon, and the flame retardant (123) comprises one or more of zinc borate, boron phosphate, triphenylphosphate, triphenylphosphine oxide, and ammonium polyphosphate; a negative current collector (120) layer (126) attached to and supported by the polymer base layer (122), wherein the negative current collector (120) layer (126) is formed from one or more metals; and a lithium- metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that thenegative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112).

[0023] Clause 17. The negative battery electrode of clause 16, wherein: the negative battery electrode is a lithium-metal negative battery electrode (110), and the lithium- metal negative active material layer (112) has a thickness of at least 2 micrometers.

[0024] Clause 18. The negative battery electrode of clause 17, wherein a surface of the lithium-metal negative active material layer (112) facing away from the negativeelectrode current collecting layer (126) is exposed.

[0025] Clause 19. The negative battery electrode of clause 16, wherein the negative battery electrode is a pre-lithiated negative battery electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negative-electrode current collecting layer (126).

[0026] Clause 20. The negative battery electrode of clause 19, wherein the lithium- metal negative active material layer (112) has a thickness of less than 2 micrometers.

[0027] Clause 21. The negative battery electrode of clause 19, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

[0028] Clause 22. The negative battery electrode of clause 16, wherein the flame retardant (123) has a concentration, in the polymer base layer (122), of between 2 - 20% by weight.

[0029] Clause 23. The negative battery electrode of clause 16, wherein the flame retardant (123) is provided in a backbone of a polymer forming the polymer base of the polymer base layer (122).

[0030] Clause 24. A lithium-containing electrochemical cell comprising: a negative electrode comprising a polymer base layer (122), a negative current collector (120) layer (126), and a lithium-metal negative active material layer (112), wherein: the polymer base layer (122) comprises a high-crystallinity polypropylene homopolymer, wherein the high-crystallinity polypropylene homopolymer has a melting point of 164- 170°C and a Vicat softening point of 156-160°C, the negative current collector (120) layer (126) is attached to and supported by the polymer base layer (122), and thelithium-metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112); a positive electrode (130); and a separator (180), positioned between the negative electrode and positive electrode (130).

[0031] Clause 25. The lithium-containing electrochemical cell of clause 24, wherein the lithium-containing electrochemical cell is a LiMLE electrochemical cell (100) such that the lithium-metal negative active material layer (112) directly interfaces with the separator (180).

[0032] Clause 26. The lithium-containing electrochemical cell of clause 24, wherein: the lithium-containing electrochemical cell is a lithium-ion electrochemical cell (101), the negative battery electrode is a pre-lithiated negative electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium- metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negative-electrode current collecting layer (126).

[0033] Clause 27. The lithium-containing electrochemical cell of clause 26, wherein the lithium-metal negative active material layer (112) has a thickness of less than 2 micrometers.

[0034] Clause 28. The lithium-containing electrochemical cell of clause 26, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

[0035] Clause 29. The lithium-containing electrochemical cell of clause 26, wherein the lithium-metal negative active material layer (112) is configured to migrate into the primary negative active material layer (113) upon adding a liquid electrolyte (190) to the lithium-containing electrochemical cell.

[0036] Clause 30. A method (300) of fabricating a negative battery electrode, the method (300) comprising: providing a polymer base layer (122) comprises a high- crystallinity polypropylene homopolymer, wherein the high-crystallinity polypropylene homopolymer has a melting point of 164-170°C and a Vicat softening point of 156- 160°C; depositing a negative current collector (120) layer (126) over the polymer base layer (122) such that the negative current collector (120) layer (126) is attached to andsupported by the polymer base layer (122); and depositing a lithium-metal negative active material layer (112) over the negative current collector (120) layer (126) such that the lithium-metal negative active material layer (112) is attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112).

[0037] Clause 31. The method (300) of clause 30, further comprising depositing a primary negative active material layer (113) over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the negative-electrode current collecting layer (126) and the primary negative active material layer (113).

[0038] Clause 32. The method (300) of clause 30, wherein depositing the primary negative active material layer (113) comprises a solvent-free deposition technique selected from the group consisting of powder deposition, electrostatic deposition, and free-standing film (FSF) deposition.BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The included drawings are for illustrative purposes and serve only to provide examples of possible structures and operations for the disclosed inventive systems, apparatus, and methods for continuous deposition of electrochemically active metals using thermal evaporation. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed implementations.

[0040] FIG. 1A is a schematic block diagram of a lithium-metal liquid-electrolyte electrochemical cell comprising a lithium-metal negative electrode with a polymer base layer, in accordance with some examples.

[0041] FIG. IB is a schematic block diagram of a lithium-ion electrochemical cell comprising a negative electrode with a polymer base layer, a current collector layer, a primary negative active material layer, and a lithium-metal negative active material layer which is operable for prelithiation of the primary negative active material layer, in accordance with some examples.

[0042] FIG. 2 is a schematic cross-sectional view of a negative electrode comprising a polymer base layer positioned between negative current collectors as well as lithium- metal negative active material layers, in accordance with some examples.

[0043] FIG. 3 is a process flowchart corresponding to a method for fabricating a negative electrode in FIG. 1, in accordance with some examples.

[0044] FIG. 4 is a block diagram of an electric vehicle (e.g., aircraft) comprising a battery pack, which in turn comprises one or more lithium-metal liquid-electrolyte electrochemical cells, in accordance with some examples.DETAILED DESCRIPTIONIntroduction

[0045] In the following description, numerous specific details are outlined to provide a thorough understanding of the presented concepts. The presented concepts may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific embodiments, it will be understood that these embodiments are not intended to be limiting.

[0046] Current collectors serve two functions in battery cells, such as lithium-ion batteries (LIBs) and lithium-metal batteries (LMBs). One of these functions is to conduct the electric current between the active material layers (e.g., lithium-metal layers in LMBs) and cell tabs during the charge and discharge. The other function is to mechanically support the active material layers. For example, handling a standalone lithium-metal layer during the fabrication of LMBs is challenging when the thickness of this layer is less than 10-20 micrometers. At the same time, current collectors need to operate in contact with the electrolyte at the potentials of the respective electrodes.

[0047] Referring to negative electrodes in LMBs, a copper foil or a metalized polymer can be used as current collectors. Copper has excellent electronic conductivity (58 x 106S / m), but it is heavy (8.96 g / cm3). For comparison, polypropylene (e.g., a high- crystallinity polypropylene homopolymer) has a density of 0.9 g / cm3(or almost 10 times lighter than copper). As noted above, copper's tensile strength is about 210 MPa, polypropylene's - about 35-50 MPa, and Li-metal's - 1.5 MPa. Even with such a lowtensile strength, Li-metal has been used in standalone structures as long as the thickness of these structures is at least 25-30 micrometers. However, handling thinner Li-metal structures (e.g., foils) is very challenging. At the same time, most of the total thickness (i.e., 25-30 micrometers) is used for the structural support and not used as actual active material (that is removed during the discharge and replated during the charge). Only about 1-8 micrometers of Li-metal layer is needed to support the operation of LiM cells. At the same time, Li-metal is about 3-5 times more expensive than copper and can be at least 10-100 more expensive than most polymers. As such, partially replacing Li-metal with a combination of polymer and non-lithium metal is highly desirable.

[0048] Described herein are negative electrodes comprising polymer base layers, negative current collector layers (containing at least one non-lithium metal), and lithium-metal negative active material layers. In some examples, the polymer base layer comprises or consists essentially of a high-crystallinity polypropylene homopolymer that may have a melting point of 164-170°C and / or a Vicat softening point of 156-160°C. For purposes of this disclosure, the term "consists essentially of" means that the weight ratio of the high-crystallinity polypropylene homopolymer in the negative active material layer is at least 95% or even at least 99%.

[0049] In some examples, the high-crystallinity polypropylene homopolymer may have a crystallinity of at least 96%, at least 98%, or even at least 98.5%. Unlike most conventional polypropylene examples (which have lower crystallinity), the high- crystallinity polypropylene homopolymer has minimal deformation until the polymer base layer melts during a thermal event (e.g., an electric short within the cell). Specifically, the high-crystallinity polypropylene homopolymer holds its shape to high temperatures (e.g., e.g., at least 160°C, defined by Vicat softening points). As such, lithium-metal electrochemical cells (or, more specifically, lithium-metal liquidelectrolyte (LiMLE) electrochemical cells) and / or lithium-ion electrochemical cells, which are fabricated with such lithium-metal negative electrodes, can be operated at higher temperatures, which can be beneficial for many applications (e.g., high- temperature environments, high charge rates associated with self / resistive-heating, high discharge rates associated with self / resistive-heating, etc.). In some examples, electrochemical cells fabricated with such negative electrodes can be operated at temperatures of at least 45°C, at least 60°C, or even at least 75°C (e.g., allowing high- viscosity electrolytes to be used in these cells). As such, negative electrodes can beconfigured to operate at least 45°C, at least 60°C, or even at least 75°C. Considering that the metal components of the electrodes have higher temperature stability, the polymer base layers or, more specifically, the high-crystallinity polypropylene homopolymers forming these bases can be configured to operate at least 45°C, at least 60°C, or even at least 75°C.

[0050] The thickness of the polymer base layer can be 3-10 micrometers or, more specifically, 4.5-9 micrometers. Even with such a small thickness, the polymer base layer can provide sufficient support to other components of the negative electrode. Furthermore, this thickness can help to reduce the overall thickness of the negative electrode (e.g., in comparison with all Li-metal designs). In some examples, the overall thickness of the negative electrode is less than 20 micrometers, less than 15 micrometers, and even less than 10 micrometers.

[0051] This thickness reduction and replacement of lithium with another metal and polymer can significantly reduce the weight of the negative electrode. The following table compares the weight (per unit area) of a conventional 30-micrometer thick Li- metal foil with a novel negative electrode formed from a 5-micrometer thick polypropylene layer, a 0.5-micrometer thick copper layer, and a 3-micrometer Li-metal layer.

[0052] The negative current collector layer (e.g., formed from copper or other similar metals) is attached to and mechanically supported by the polymer base layer and may have a thickness of up to 1 micrometer (e.g., in some applications). Higher-rate applications may use thicker negative current collector layers and / or other materials for these layers (e.g., a combination of a metal layer and a carbon-containing layer).

[0053] The negative current collector layer provides a plating surface and electronic pathway for the negative active material layer and is positioned between the polymerbase layer and the lithium-metal negative active material layer. Even at such low thicknesses, the negative current collector layer can provide sufficient electronic conductivity. For example, the electronic conductivity of copper is almost 6 times greater than that of lithium metal (5.9x107 S / m vs. 1.1x107 S / m). Finally, the lithium- metal negative active material layer is attached to and supported by the negative current collector layer and the polymer base layer.Examples of Lithium-Metal and Lithium-Ion Electrochemical Cells

[0054] FIG. 1A is a schematic block diagram of lithium-metal liquid-electrolyte (LiMLE) electrochemical cell 100 comprising a lithium-metal negative electrode 110 with polymer base layer 122, a negative current collector layer 126, and lithium-metal negative active material layer 112. It should be noted that various aspects of LiMLE electrochemical cells 100 and lithium-metal negative electrodes 110 are applicable to lithium-ion electrochemical cells 101 and pre-lithiated negative electrodes 111 (respectively), which are described below with reference to FIG. IB. A combination of polymer base layer 122 and the negative current collector layer 126 can be referred to as a negative current collector 120. The negative current collector 120 is covered with the lithium-metal negative active material layer 112 to form the lithium-metal negative electrode 110. When polymer base layer 122 is formed from or at least comprises a high-crystallinity polypropylene homopolymer, polymer base layer 122 can be referred to as a polymer base layer. For these examples, a "polymer base layer" and a "base layer" are used interchangeably. It should be noted that other materials (described below) can also be used to form polymer base layer 122.

[0055] In addition to lithium-metal negative electrode 110, LiMLE electrochemical cell 100 comprises positive electrode 130 and separator 180, which is positioned between lithium-metal negative electrode 110 and positive electrode 130 and provides electronic isolation between lithium-metal negative electrode 110 and positive electrode 130. One having ordinary skill in the art would understand that LiMLE electrochemical cell 100 can have any number of positive and negative electrodes arranged in different ways, e.g., stacked, wound, and the like.

[0056] In some examples, LiMLE electrochemical cell 100 also comprises liquid electrolyte 190, which provides ionic transfer between lithium-metal negative electrode 110 and positive electrode 130. For example, liquid electrolyte 190 soaksseparator 180 or, more specifically, the pores of separator 180. Liquid electrolyte 190 should be distinguished from solid and gel electrolytes used in other types of lithium- metal cells. Liquid electrolyte 190 should be distinguished from gel electrolytes, in which polymer matrices are used to retain salts and solvents. Liquid electrolyte 190 described herein are free from polymer components such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), polyvinylchloride (PVC), and polyvinylidene fluoride (PVDF) and have a viscosity of less than l,000cP, less than 500cP, or less than 200cP at the room temperature (e.g., to differentiate the liquid electrolyte 190 from gel electrolytes and solid electrolytes).

[0057] Some examples of liquid electrolyte 190 include, but are not limited to, a mixture of one or more lithium-containing salts 192 and one or more liquid solvents 194. Some examples of lithium-containing salts 192 include, but are not limited to, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)amide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPFg), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium trifluoromethanesulfonate (LiTf), lithium nitrate (LiNOa), and various combinations thereof. In some examples, lithium-containing salts 192 are LiFSI or LiTFSI, e.g., preferably LiFSI. Lithium-containing salts 192 are configured to dissociate into lithium ions and anions. In some examples, the concentration of lithium-containing salts 192 in liquid electrolyte 190 is between 10 mol% and 50 mol% or, more specifically, between 20 mol% and 40 mol%.

[0058] Some examples of liquid solvents 194 but are not limited to, one or more cyclic ethers (e.g., 1,3-dioxane (DOL), 1,4-dioxane (DX), tetrahydrofuran (THF)), one or more linear ethers (e.g., dimethoxyethane (DME), Bis(2-methoxyethyl) ether (G2), triethylene glycol dimethyl ether (G3), or tetraethylene glycol dimethyl ether (G4), Bis(2,2,2-trifluoroethyl)ether (BTFE), ethylal, 1,1,2,2-tetrafluoroethyl 2, 2,3,3- tetrafluoropropyl ether (TFPE)), and a combination thereof. In some examples, the concentration of liquid solvents 194 in liquid electrolyte 190 is between 0 mol% and 60 mol% or, more specifically, between 5 mol% and 50 mol% or even between 10 mol% and 40 mol%. A specific category of liquid solvents 194 is fluoroether diluents, e.g., bis(2,2,2-trifluoroethyl)ether (BTFE), ethylal, and 1,1,2,2-tetrafluoroethyl 2, 2,3,3- tetrafluoropropyl ether (TFPE)), 0-60 mol%. More molecules could be added here.

[0059] Liquid electrolyte 190 can comprise various additives 196, e.g., metal salts(e.g., having bis(trifluoromethanesulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI),hexafluorophosphate (PFg), tetrafluoroborate (BF4), and / or bis(oxalate)borate (BOB) anions), ionic liquids (e.g., propyl-methyl-pyrrolidinium-FSI / TFSI; butyl-methyl- pyrrolidinium-FSI / TFSI; octyl-methyl-pyrrolidinium-FSI / TFSI, and any combination thereof), and the like.

[0060] In some examples, liquid electrolyte 190 comprises ionic liquids in addition to or instead of additives 196. Some examples of ionic liquids include, but are not limited to, l-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMIm)TFSI and 1- methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide (ImuTFSI, or Im 13TFSI - SiOj), n-methyl-n-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PipnTFSI or PipuTFSI -SiOj), n-propyl-n-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (PYR13FSI), n-butyl-n-methylpyrrolidinium bis(fluorosulfonyl) imide (PYR14FSI), trimethylhexyl ammonium bis-(trifluorosulfonyl) imide (TMHATFSI), butyl-trimethyl ammonium bis(trifluoromethanesulfonyl)imide (QATFSI), 3-(2-(2-methoxy ethoxy)ethyl)-l-methylimidazolium TFSI (IMII,IO2OITFSI) and l-(2-methoxyethyl)-3- methylimidazolium TFSI (IMII,2OITFSI). In some examples, the concentration of the ionic liquids in liquid electrolyte 190 is between 0 mol% and 40 mol% or, more specifically, between 5 mol% and 35 mol%, or even between 10 mol% and 30 mol%.

[0061] In some examples, liquid electrolyte 190 can have a viscosity of at least 15 cP or, more specifically, at least 25 cP, at least 50 cP, or even at least 100 cP at room temperature. For example, liquid electrolyte 190 can have a viscosity of 15-500 cP or, more specifically, 20-300 cP or, more specifically, 40-200 cP at room temperature. High viscosity can be driven by specific components needed in liquid electrolyte 190 to enable the functioning of liquid electrolyte 190 in LiMLE electrochemical cell 100. It should be noted that the viscosity changes with temperature. In fact, this characteristic is used to enable the controlled deposition of lithium metal during fast charging (e.g., a charge rate of at least 0.8C or even at least 1C). The viscosity determined the ionic diffusivity (lithium ions) within liquid electrolyte 190. In some examples, liquid electrolyte 190 can have an ionic diffusivity of between IE-13 m2 / sec - IE-10 m2 / sec or, more specifically, 5E-12 m2 / sec - 5E-10 m2 / sec or, even more specifically, IE-12 m2 / sec - IE-11 m2 / sec at room temperature.

[0062] Positive electrode 130 can include positive current collector 140 and positive active material layer 134. Positive current collector 140 comprises at least positive metal layer 144, which may be a standalone layer (e.g., an aluminum foil).Alternatively, positive current collector 140 comprises one or more positive metallayers 144 supported on positive polymer layer 142 (e.g., an aluminum-metalized polymer). Positive active material layer 134 comprises positive active material 136 (e.g., in the form of particles) and binder 137 (e.g., a polymer binder). Some examples of positive active materials 136 include, but are not limited to, lithium nickel manganese cobalt (NMC) oxides, lithium iron phosphate, and the like. Some examples of suitable polymer binders 137 include, but are not limited to, polymer binders (e.g., polyvinylidene-fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxyl methyl cellulose (CMC)). In some examples, positive electrode 130 comprises conductive additive 138 (e.g., carbon black / paracrystalline carbon).

[0063] In some examples, positive electrode 130 single-crystal nickel-manganese- cobalt (NMC)-containing structures, used as positive active material 136. The singlecrystal NMC-containing structures can have a nickel concentration of at least 70% atomic or even at least 80% atomic. Because the bonds within the primary particles are stronger than between primary particles (in polycrystalline materials), single-crystal NMC particles inherently do not have or show intergranular cracking in a way that polycrystalline NMC particles do. Furthermore, single-crystal NMC particles tend to have higher specific capacities due to the greater surface-area-to-volume ratio of the individual particles vs. secondary-particle agglomerates of polycrystalline NMC materials. However, single-crystal NMC particles tend to have slower lithium transport kinetics than polycrystalline materials. As such, increased temperatures during the charge portion of the cycle help with increasing the rate of lithium-ion extraction from single-crystal NMC particles.

[0064] In some examples, single-crystal NMC particles are used with liquid electrolyte 190 comprising one or more imide-containing salts, such as bis(trifluoromethanesulfonyl)imide (TFSI j-containing salts, bis(fluorosulfonyl)imide (FSI j-containing salts, and bis(pentafluoroethanesulfonyl)imide (BETI j-containing salts. These salts can also include various cations, such as lithium (Li+), potassium (K+), sodium (Na+), cesium (Cs+), n-propyl-n-methylpyrrolidinium (Pyrl3+), n-octyl-n- methylpyrrolidinium (Pyrl8+), and 1-methyl-l-pentylpyrrolidinium (Pyrl5+). For example, imide-containing salts can act as a source of lithium ions in lithium-metal salts. In some examples, the liquid electrolyte further comprises one or more of 2,2,2- Trifluoroethyl Ether (TFEE), 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TFPE), one or more phosphites, and one or more phosphates.

[0065] Positive electrode 130, lithium-metal negative electrode 110, separator 180, and liquid electrolyte 190 can be referred to as internal components of lithium-metal electrochemical cell 100. These internal components are sensitive to moisture and other ambient conditions and insulated from the environment by a cell enclosure, such as a metal (e.g., aluminum) case (e.g., for cylindrical or prismatic cells), a pouch laminate, an aluminum-coated polymer (e.g.., polyamide, polyester, polyurethane, and polypropylene). It should be noted that LiMLE electrochemical cell 100 can be heated internally and / or externally. When internal heating is used, the cell enclosure can be thermally insulated to reduce heat dissipation to the environment. Some examples of such thermally insulating features include, but are not limited to, different intercell structures (e.g., thermal-barrier sheet). It should be noted that such structures can also be used for applying cell pressure and / or preventing heat / material propagation during various thermal events. On the other hand, when external heating is used, the cell enclosure can be thermally conductive to promote heat transfer from an externally positioned heater to the cell interior. Some examples of such thermally conductive features include, but are not limited to, intercell heat-conducting structures (e.g., also used for cell cooling during other operations).

[0066] FIG. IB is a schematic block diagram of a lithium-ion electrochemical cell 101, which may have some components that are similar to ones in LiMLE electrochemical cells 100 described above with reference to FIG. 1A. Specifically, a lithium-ion electrochemical cell 101 comprises a positive electrode 130, a separator 180, and a liquid electrolyte 190. Furthermore, a lithium-ion electrochemical cell 101 comprises a negative electrode, which may be referred to as a pre-lithiated negative electrode 111. The key difference between the pre-lithiated negative electrode 111 and the lithium- metal negative electrode 110 (of a LiMLE electrochemical cell 100) is the presence of a primary negative active material layer 113, which is configured to integrate (e.g., intercalate, alloy, etc.) lithium ions / atoms during operation of the lithium-ion electrochemical cell 101. Specifically, when a LiMLE electrochemical cell 100 is charged, the lithium metal is plated as a lithium-metal negative active material layer 112 over the negative-electrode current collector 120. On the other hand, when a lithium-ion electrochemical cell 101 is charged, the lithium metal is distributed in a host material (e.g., graphite, silicon, etc.) without being present as a separate lithium metal layer. The other components of the pre-lithiated negative electrode 111 may be the same as of the lithium-metal negative electrode 110, e.g., a negative-electrodecurrent collector 120 comprising a polymer base layer 122 and one or more negativeelectrode current collecting layers 126.

[0067] It should be noted that FIG. IB is a schematic block diagram of a lithium-ion electrochemical cell 101 at a state when the liquid electrolyte 190 is initially added to the lithium-ion electrochemical cell 101. Specifically, once the liquid electrolyte 190 has been added, the lithium-metal negative active material layer 112 may be redistributed within the lithium-ion electrochemical cell 101 and, more specifically, with the pre-lithiated negative electrode 111 (e.g., driven into the primary negative active material layer 113). In other words, the lithium-metal negative active material layer 112 exists in lithium-ion electrochemical cell 101 only during the electrode fabrication and the initial stages of the cell fabrication. Thereafter, lithium is distributed among various components of the lithium-ion electrochemical cell 101 (e.g., depending on the stage of charge, cycle lifetime, and other factors) and may not form a standalone lithium-metal negative active material layer 112 again.

[0068] This additional lithium (in the form of the initial lithium-metal negative active material layer 112) is used to compensate for various lithium "losses", e.g., lithium trapped in solid electrolyte interphase (SEI) layers. Keeping sufficient amounts of cyclable lithium in the lithium-ion electrochemical cell 101 allows to retain the cell capacity, which is typically determined by the amount and properties of the positive active material 136. In other words, one of the cycle-life degradation mechanisms involves some amounts of lithium getting trapped and no longer being available for cycling. If all initial lithium is provided by the positive active material 136, the positive active material 136 can no longer be fully utilized. Adding a lithium-metal negative active material layer 112 helps to compensate for this lithium trapping and provides sufficient amounts of cyclable lithium, e.g., up to the total capacity of the positive active material 136. This approach may be referred to as prelithiation. However, introducing lithium into the negative electrodes of lithium-ion electrochemical cells is challenging due to the reactive nature of lithium. Specifically, lithium metal reacts with water (e.g., in slurries used to form primary negative active material layers and / or environment).

[0069] Referring to FIG. IB, a lithium-metal negative active material layer 112 may be positioned between the negative-electrode current collector 120 and the primary negative active material layer 113. For example, a lithium-metal negative active material layer 112 may be first deposited (e.g., using physical vapor deposition (PVD))on a negative-electrode current collector 120 with a primary negative active material layer 113 formed thereafter over the lithium-metal negative active material layer 112 (e.g., solvent-free coating techniques). Additional processing details are described below with reference to FIG. 3.

[0070] In some examples, a lithium-metal negative active material layer 112 may have pinholes (e.g., defined by a porosity of at least 5%, at least 10%, or even at least 20%). These pinholes help with adhering the lithium-metal negative active material layer 112 to the negative-electrode current collector 120 and also adhering the primary negative active material layer 113 to the lithium-metal negative active material layer 112. It should be noted that pinholes in a lithium-metal negative active material layer 112 may be less desirable in a LiMLE electrochemical cell 100 since these pinholes increase the surface of the lithium-metal negative active material layer 112 for an SEI layer formation. On the other hand, in lithium-ion electrochemical cells 101, the lithium- metal negative active material layer 112 disappears after introducing the liquid electrolyte 190 (and potentially the initial cycling). In addition to the adhesion improvement, the pinholes help to speed up the redistribution of the lithium-metal negative active material layer 112 (once the liquid electrolyte 190 is introduced) by increasing the electrolyte contact surface. This redistribution of the lithium-metal negative active material layer 112 may be referred to as a localized "charging" of the primary negative active material layer 113 or, more generally, of the pre-lithiated negative electrode 111.

[0071] In some examples, the size / thickness of the lithium-metal negative active material layer 112 may be characterized by the capacity of the active material in the primary negative active material layer 113, e.g., between 10-60% of the negative active material capacity, between 10-40% of this capacity. This capacity is determined by the type and amount of the negative active material in the primary negative active material layer 113. Some examples of the negative active material include, but are not limited to, graphite, silicon, tin oxide, and lithium titanate. Graphite is a layered carbon material with a specific capacity of about 372 mAh / g. Graphite has good electrical conductivity and stable cycling performance. Silicon forms an alloy with lithium and has a theoretical capacity of up to 4,200 mAh / g (with 1,000-2,000 mAh / g being more practical due to significant volume expansion during lithiation leading to mechanical stress and degradation). Silicon can be used in various combinations with graphite (e.g., mixtures, core-shell arrangements) and / or various forms (e.g., oxides). Tin oxide(SnO2) is yet another example that alloys with lithium with a specific capacity of about 782 mAh / g. Lithium titanate (Li4Ti5O12) is a spinel structure that has a lower specific capacity but has stable cycling performance and high safety. In some examples, the thickness of the lithium-metal negative active material layer 112 is less than 2 micrometers, less than 1 micrometer, or even less than 0.5 micrometers. In the same or other examples, the thickness of the primary negative active material layer 113 may be at least 50 micrometers or even at least 75 micrometers.Examples of Negative Electrodes

[0072] FIG. 2 is a schematic cross-sectional view of a negative electrode, which may be a lithium-metal negative electrode 110 or a pre-lithiated negative electrode 111. In some examples, the negative electrode comprises lithium-metal negative electrode 110 comprising polymer base layer 122 positioned between two negative current collector layers 126 as well as lithium-metal negative active material layers 112, in accordance with some examples. Each negative current collector layer 126 is attached to and supported by polymer base layer 122. Furthermore, each lithium-metal negative active material layer 112 is attached to and supported by negative current collector layer 126 (and polymer base layer 122 spaced away from lithium-metal negative active material layer 112 by negative current collector layer 126) such that negative current collector layer 126 is positioned between polymer base layer 122 and lithium-metal negative active material layer 112.

[0073] As noted above, a combination of polymer base layer 122 and any number (e.g., one or two) of negative current collector layers 126 (present in lithium-metal negative electrode 110) can be referred to as negative current collector 120. Furthermore, any number of lithium-metal negative active material layers 112 can be used. While FIG. 2 illustrates negative current collector 120 supporting two lithium- metal negative active material layers 112, in some examples, lithium-metal negative electrode 110 can include negative current collector 120 without any lithium-metal negative active material layers 112 (at least when the lithium-metal negative electrode 110 is provided for fabrication of LiMLE electrochemical cell 100). These examples may be referred to as an anode-less design of lithium-metal negative electrode 110. In this anode-less design, when LiMLE electrochemical cell 100 is initially charged, lithium-metal negative active material layers 112 are formed (plated) over negative current collector layer 126.

[0074] In some examples, polymer base layer 122 comprises a high-crystallinity polypropylene homopolymer. Specifically, the high-crystallinity polypropylene homopolymer may have a melting point of 164-170°C and a Vicat softening point of 156-160°C. Furthermore, the high-crystallinity polypropylene homopolymer may have a water vapor barrier of less than 0.7 g / m2-d. In the same or other examples, the high- crystallinity polypropylene homopolymer has Young's modulus of greater than 1000 MPa, greater than 1200 MPa, or even greater than 1500 MPa. In some examples, the high-crystallinity polypropylene homopolymer has a penetration energy of less than 5 J / mm, less than 3 J / mm, or even less than 2 J / mm. The following table compares several properties of the high-crystallinity polypropylene homopolymer (Bormod- HD905CF available from Borealis Polyolefine GmbH in Austria).

[0075] Higher temperature stability (e.g., expressed as a higher deflection temperature) enables higher deposition rates of lithium-metal negative active material layers 112 over negative current collector 120 (thereby increasing the production rates). For example, thermal evaporation can be used for this deposition operation, during which the lithium metal condenses and solidifies on negative current collector 120 (thereby releasing heat to the environment during this deposition operation). A portion of this heat is released into and transferred through negative current collector 120 or, more specifically, polymer base layer 122 (that is a part of the negative current collector 120). A higher temperature stability of polymer base layer 122 allows to keep negative current collector 120 at a higher temperature (without damaging polymer base layer 122), in comparison to a base formed from a generic polypropylene, thereby allowing higher lithium-metal deposition rates.

[0076] A lower water vapor barrier value (e.g., 0.65 g / m2-d for Bormod-HD905CF vs. 0.75 g / m2-d for generic polypropylene) ensures that lesser amounts of liquid electrolyte 190 are absorbed by lithium-metal negative active material layer 112. This lower electrolyte absorption helps to extend the cell life (due to less electrolytedepletion and maintaining the ionic conductivity) and lower cell mass (less electrolyte needed).

[0077] The higher Young's modulus value (in comparison to generic polypropylene) ensures that polymer base layer 122 experiences less deformation under stress such as less wrinkling during lithium-metal plating (e.g., during the initial deposition of lithium- metal negative active material layer 112 and later during cycling). As such, a longer cell life is ensured due to less wrinkling of polymer base layer 122. Furthermore, the higher Young's modulus value simplifies web handling (by being less prone to wrinkles) during the fabrication of lithium-metal negative electrode 110. Finally, lower penetration energy (1.8 J / mm vs. 10 J / mm for generic polypropylene) ensures cleaner notching / punching with less susceptibility to burs during the fabrication of lithium- metal negative electrode 110.

[0078] In some examples, the high-crystallinity polypropylene homopolymer has a crystallinity of at least 96%, at least 98%, or even at least 99%. For comparison, generic polypropylene has a crystallinity of 30-60%. Such high levels of crystallinity ensure various functional characteristics of polymer base layer 122 or, more generally, of negative current collector 120 presented above.

[0079] In some examples, polymer base layer 122 has a thickness of 3-8 micrometers, 4.5 - 6 micrometers, or even 4.8 - 5.2 micrometers. Even at such low thicknesses, polymer base layer 122 has sufficient mechanical strength, e.g., for web handling, supporting negative current collector layer 126 and lithium-metal negative active material layer 112, and withstanding stresses associated with plating / de-plating of lithium metal during the operation of LiMLE electrochemical cell 100.

[0080] In some examples, negative current collector layer 126 has a thickness of 0.1 - 2 micrometers, 0.3 - 1 micrometers, or even 0.5 - 0.8 micrometers. The main purpose of negative current collector layer 126 is to conduct the electric current between the lithium-deposition site and an electrode tab, which is usually positioned along one edge of lithium-metal negative electrode 110. The thickness may depend on the rate capabilities of LiMLE electrochemical cell 100, the side of lithium-metal negative electrode 110, the material of negative current collector layer 126, and other characteristics. In some examples, lithium-metal negative active material layer 112 is thicker than polymer base layer 122, e.g., at least 2 times thicker, or even at least 3 times thicker.

[0081] In some examples, negative current collector layer 126 comprises one or more elements selected from the group copper, sodium, and titanium. For example, the entire volume of negative current collector layer 126 can be formed from the same metal. In some examples, negative current collector layer 126 comprises an alloy or a multi-layered structure comprising at least two or more elements selected from the group aluminum, cadmium, chromium, cobalt, copper, indium, lithium, manganese, molybdenum, nickel, phosphorous, silicon, silver, sodium, tin, titanium, and zinc. In more specific examples, negative current collector layers 126 can be formed from a metal base layer (e.g., aluminum, chromium, copper) and a protection layer (e.g., copper, silicon, zinc, magnesium, nickel, molybdenum, tungsten, tantalum, and silver), which forms a surface facing a corresponding lithium-metal negative active material layer 112. For example, aluminum has a better conductivity-to-weight ratio than copper, which can help to increase the gravimetric energy density. Furthermore, aluminum's tensile strength can be up to 600 MPa, while titanium's tensile strength can exceed 1,000 MPa (in some alloys). In the same or other examples, negative current collector layers 126 is a metal foil. However, other structures (e.g., mesh, foam) are within the scope.

[0082] In some examples, lithium-metal negative electrode 110 further comprises carbon-containing layer 124 positioned between polymer base layer 122 and negative current collector layer 126, wherein the carbon-containing layer 124 comprises graphene.

[0083] In some examples, polymer base layer 122 comprises a polymer base and flame retardant 123. One example of the polymer base is a high-crystallinity polypropylene homopolymer that may have a melting point of 164-170°C and / or a Vicat softening point of 156-160°C, described above. Other examples include polyethylene terephthalate, polypropylene, polycarbonate, polyethylene, polyimide, cellulose, and nylon, and

[0084] In some examples, flame retardant 123 is selected from the group consisting of zinc borate, boron phosphate, triphenylphosphate, triphenylphosphine oxide, and ammonium polyphosphate. These materials help to reduce the intensity / energy released (e.g., by increasing the limiting oxygen index [LOI] of polymer base layer 122) during a runaway event while maintaining all other characteristics of polymer base layer 122 needed for the regular cell performance. The effectiveness and temperatureof maximal suppression of flame retardant 123 depend on particle size, concentration, and other characteristics.

[0085] In some examples, flame retardant 123 has a concentration, in polymer base layer 112, of between 1 - 30% by weight, between 2 - 20% by weight, or between 5 - 10% by weight. For example, insufficient amounts of flame retardant 123 would mean insufficient thermal runaway (TR) suppression (due to the insufficient increase of the LOI in polymer base layer 122). On the other hand, excessive amounts of flame retardant 123 would unnecessarily decrease the cell-specific energy (by increasing the weight of polymer base layer 122). Also, to accommodate a composite material, polymer base layer 122 may need to be thicker (e.g., at least 5 micrometers or even at least 8 micrometers) to meet the target mechanical properties for polymer base layer 122. The maximum thickness / mass of polymer base layer 122 can limit the flame retardant content.

[0086] In some examples, flame retardant 123 is provided in a backbone of a polymer forming the polymer base of polymer base layer 122. Specifically, this example refers to a composite polymer material being synthesized with flame-retardant additives thereby integrating the two materials together at a chemical level.

[0087] In some examples, lithium-metal negative active material layer 112 has a thickness of less than 40 micrometers, less than 20 micrometers, less than 10 micrometers, or even less than 5 micrometers. When a negative battery electrode is a lithium-metal negative electrode 110, the thickness of the lithium-metal negative active material layer 112 may be at least 2 micrometers or even at least 3 micrometers, e.g., 2-10 micrometers or 3-5 micrometers. It should be noted that the mechanical support is provided by the polymer base layer 122 while the electrical conductivity is provided by the negative-electrode current collecting layer 126. When a negative battery electrode is a pre-lithiated negative electrode 111, the thickness of the lithium-metal negative active material layer 112 may be less than 2 micrometers, less than 1 micrometer, or even less than 0.5 micrometers, e.g., 0.1-2 micrometers or 0.5-2 micrometers. In these examples, the lithium-metal negative active material layer 112 is dissipated and this amount of lithium (originally provided on the lithium-metal negative active material layer 112) is used to compensate for lithium losses in the lithium-ion electrochemical cell 101.

[0088] It should be noted that the addition of negative current collector 120 helps to keep the thickness of the lithium-metal layer small. For example, a thickness of less than 20 micrometers is difficult to achieve with freestanding lithium. As such, lithium- metal cells with negative electrodes formed by freestanding lithium foils / layers require substantially more lithium than lithium-metal cells with negative electrodes formed by a combination of a current collector and a lithium-metal layer (to achieve the same cell capacity). Lower amounts of lithium are highly desirable from the safety perspective as less lithium ejecta (e.g., molten lithium ejecta) needs to be contained when the cell goes into a thermal runaway. It should be noted that lithium-metal negative electrode 110 forms a solid electrolyte interphase (SEI) layer when exposed to liquid electrolyte 190 at operating potentials. Furthermore, a naturally-forming SEI layer can be supplemented with or partially / fully replaced with an artificial SEI layer (e.g., formed on the surface of lithium-metal negative electrode 110 before contacting liquid electrolyte 190). In either case, an SEI layer (natural and / or artificial) can interfere with the lithium-ion migration in and out of lithium-metal negative electrode 110. Raising the temperature before charging, helps to improve the ionic conductivity of such SEI layers.

[0089] When a negative electrode is a lithium-metal negative electrode 110, the lithium-metal negative active material layers 112 are exposed. Specifically, the surface of each lithium-metal negative active material layer 112 (that faces away from the corresponding negative-electrode current collecting layer 126) is exposed. When a negative electrode is a pre-lithiated negative electrode 111, the pre-lithiated negative electrode 111 also comprises one or two primary negative active material layers 113, positioned over the corresponding lithium-metal negative active material layers 112. Specifically, each lithium-metal negative active material layer 112 is positioned between a corresponding primary negative active material layer 113 and a corresponding negative-electrode current collecting layer 126. Various aspects of the primary negative active material layer 113 are described above.Methods for Fabricating Negative Electrodes

[0090] FIG. 3 is a process flowchart corresponding to method 300 for fabricating lithium-metal negative electrode 110 in FIG. 2, in accordance with some examples. In some examples, method 300 commences with (block 310) providing polymer baselayer 122, various examples of which are described above. Specifically, in some examples, polymer base layer 122 comprises a high-crystallinity polypropylene homopolymer with a melting point of 164-170°C and a Vicat softening point of 156- 160°C. In the same or other examples, polymer base layer 122 comprises flame retardant 123. Polymer base layer 122 can be provided in a roll form.

[0091] Method 300 may proceed with (block 320) depositing negative current collector layer 126 over polymer base layer 122 such that negative current collector layer 126 is attached to and supported by the polymer base layer 122. Various examples of negative current collector layer 126 are described above. Various deposition techniques can be used for this operation, e.g., magnetron sputtering PVD, e-beam evaporation PVD, thermal evaporation PVD, HIPIMS, electroplating, thermal plasma spraying, suspension plasma spraying, and cold spraying, or a combination of these techniques. Various examples of negative current collector layer 126 are described above with reference to FIG. 2.

[0092] Method 300 may proceed with (block 330) depositing one or more lithium- metal negative active material layers (e.g., lithium-metal negative active material layer 112). Various deposition techniques can be used for this operation, e.g., thermal evaporation PVD, lamination, or electroplating. This operation is optional. In some examples, the initial lithium-metal negative active material layer 112 may be formed during the initial charge of the battery fabricated with the anodeless-version of lithium- metal negative electrode 110.

[0093] Method 300 may proceed with (block 340) depositing a primary negative active material layer 113. As noted above with reference to FIG. 1A, the primary negative active material layer 113 is deposited over the lithium-metal negative active material layer 112. The deposition technique may be solvent-free to avoid any reaction between the lithium-metal negative active material layer 112 and water (e.g., in a slurry used in a conventional deposition). Some examples of solvent-free deposition techniques include, but are not limited to, powder deposition, electro-static deposition, and free-standing film (FSF) deposition coupled with lamination. For example, in an FSF method, a lithium-metal negative active material layer 112 may be deposited on an adhesive layer comprising conductive material (e.g., carbon black) and / or an adhesive material (e.g., polymethyl methacrylate (PMMA)).Application Examples

[0053] Llithium-metal liquid-electrolyte electrochemical cell 100 / or a lithium-ion electrochemical cell 101 described herein, can be used for various applications, such as ground-based vehicles, boats, aircraft, and spacecraft. For example, aircraft and / or spacecraft use Li-metal batteries as such batteries have significantly higher gravimetric energy density than, e.g., Li-ion batteries. Both aircraft and spacecraft applications require lower mass cells, as additional mass leads to lower payload capacity. For these applications to utilize the maximum amount of their designed capacity, the energy system must be the lowest mass possible. In addition, safety is paramount in both of these applications, as onboard fires while in flight could be mission-critical and cause catastrophic failure of the system. In this scenario, occupants or personnel using the system are not able to simply depart from aircraft and / or spacecraft (e.g., in comparison to ground-based vehicles). FIG. 4 is a block diagram of an electric vehicle 400 (e.g., aircraft) comprising battery pack 420, which in turn comprises one or more lithium electrochemical cells such as lithium-metal liquid-electrolyte electrochemical cell 100 / or a lithium-ion electrochemical cell 101. Electric vehicle 400 also comprises battery management system 410, electrically and communicatively coupled to battery pack 420.Conclusion

[0054] Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing processes, systems, and apparatuses. Accordingly, the present embodiments are to be considered illustrative and not restrictive.

Claims

CLAIMS1. A negative battery electrode comprising: a polymer base layer (122) comprising a high-crystallinity polypropylene homopolymer, wherein the high-crystallinity polypropylene homopolymer has a melting point of 164-170°C and a Vicat softening point of 156-160°C; a negative current collector (120) layer (126) attached to and supported by the polymer base layer (122) and a lithium-metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112).

2. The negative battery electrode of claim 1, wherein: the negative battery electrode is a lithium-metal negative battery electrode (110), and the lithium-metal negative active material layer (112) has a thickness of at least 2 micrometers.

3. The negative battery electrode of claim 2, wherein a surface of the lithium-metal negative active material layer (112) facing away from the negative-electrode current collecting layer (126) is exposed.

4. The negative battery electrode of claim 1, wherein the negative battery electrode is a pre-lithiated negative battery electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negativeelectrode current collecting layer (126).

5. The negative battery electrode of claim 4, wherein the lithium-metal negative active material layer (112) has a thickness of less than 2 micrometers.

6. The negative battery electrode of claim 4, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

7. The negative battery electrode of claim 1, wherein the high-crystallinity polypropylene homopolymer has a crystallinity of at least 98%.

8. The negative battery electrode of claim 1, wherein the polymer base layer (122) has a thickness of 4.5 - 9 micrometers.

9. The negative battery electrode of claim 1, wherein the negative current collector (120) layer (126) has a thickness of 0.2 - 1 micrometers.

10. The negative battery electrode of claim 1, wherein the lithium-metal negative active material layer (112) has a thickness of 1 - 8 micrometers.

11. The negative battery electrode of claim 1, wherein the lithium-metal negative active material layer (112) is thicker than the polymer base layer (122).

12. The negative battery electrode of claim 1, wherein the negative current collector (120) layer (126) comprises one or more elements selected from the group consisting of copper, sodium, chromium, and titanium.

13. The negative battery electrode of claim 1, wherein the negative current collector (120) layer (126) comprises an alloy or a multi-layered structure comprising at least two or more elements selected from the group consisting of aluminum, cadmium, chromium, cobalt, copper, indium, lithium, manganese, molybdenum, nickel, phosphorous, silicon, silver, sodium, tin, titanium, and zinc.

14. The negative battery electrode of claim 1, further comprising a carbon-containing layer (124) positioned between the polymer base layer (122) and the negative current collector (120) layer (126), wherein the carbon-containing layer (124) comprises graphene.

15. The negative battery electrode of claim 1, wherein the polymer base layer (122) comprises a flame retardant (123) selected from the group consisting of zinc borate, boron phosphate, triphenylphosphate, triphenylphosphine oxide, and ammonium polyphosphate.

16. A negative battery electrode comprising: a polymer base layer (122) comprising a polymer base and a flame retardant (123), wherein: the polymer base comprises one or more of polyethylene terephthalate, polypropylene, polycarbonate, polyethylene, polyimide, cellulose, and nylon, and the flame retardant (123) comprises one or more of zinc borate, boron phosphate, triphenylphosphate, triphenylphosphine oxide, and ammonium polyphosphate; a negative current collector (120) layer (126) attached to and supported by the polymer base layer (122), wherein the negative current collector (120) layer (126) is formed from one or more metals; and a lithium-metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112).

17. The negative battery electrode of claim 16, wherein: the negative battery electrode is a lithium-metal negative battery electrode (110), and the lithium-metal negative active material layer (112) has a thickness of at least 2 micrometers.

18. The negative battery electrode of claim 17, wherein a surface of the lithium-metal negative active material layer (112) facing away from the negative-electrode current collecting layer (126) is exposed.

19. The negative battery electrode of claim 16, wherein the negative battery electrode is a pre-lithiated negative battery electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium-metal negative activematerial layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negativeelectrode current collecting layer (126).

20. The negative battery electrode of claim 19, wherein the lithium-metal negative active material layer (112) has a thickness of less than 2 micrometers.

21. The negative battery electrode of claim 19, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

22. The negative battery electrode of claim 16, wherein the flame retardant (123) has a concentration, in the polymer base layer (122), of between 2 - 20% by weight.

23. The negative battery electrode of claim 16, wherein the flame retardant (123) is provided in a backbone of a polymer forming the polymer base of the polymer base layer (122).

24. A lithium-containing electrochemical cell comprising: a negative electrode comprising a polymer base layer (122), a negative current collector (120) layer (126), and a lithium-metal negative active material layer (112), wherein: the polymer base layer (122) comprises a high-crystallinity polypropylene homopolymer, wherein the high-crystallinity polypropylene homopolymer has a melting point of 164-170°C and a Vicat softening point of 156-160°C, the negative current collector (120) layer (126) is attached to and supported by the polymer base layer (122), and the lithium-metal negative active material layer (112) attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112); a positive electrode (130); anda separator (180), positioned between the negative electrode and positive electrode (130).

25. The lithium-containing electrochemical cell of claim 24, wherein the lithium- containing electrochemical cell is a LiMLE electrochemical cell (100) such that the lithium-metal negative active material layer (112) directly interfaces the separator (180).

26. The lithium-containing electrochemical cell of claim 24, wherein: the lithium-containing electrochemical cell is a lithium-ion electrochemical cell (101), the negative battery electrode is a pre-lithiated negative electrode (111) further comprising a primary negative active material layer (113) positioned over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the primary negative active material layer (113) and the negative-electrode current collecting layer (126).

27. The lithium-containing electrochemical cell of claim 26, wherein the lithium-metal negative active material layer (112) has a thickness of less than 2 micrometers.

28. The lithium-containing electrochemical cell of claim 26, wherein the primary negative active material layer (113) comprises one or more materials selected from the group consisting of carbon, silicon, tin, and lithium titanate.

29. The lithium-containing electrochemical cell of claim 26, wherein the lithium-metal negative active material layer (112) is configured to migrate into the primary negative active material layer (113) upon adding a liquid electrolyte (190) to the lithium- containing electrochemical cell.

30. A method (300) of fabricating a negative battery electrode, the method (300) comprising: providing a polymer base layer (122) comprises a high-crystallinity polypropylene homopolymer, wherein the high-crystallinity polypropylene homopolymer has a melting point of 164-170°C and a Vicat softening point of 156- 160°C;depositing a negative current collector (120) layer (126) over the polymer base layer (122) such that the negative current collector (120) layer (126) is attached to and supported by the polymer base layer (122); and depositing a lithium-metal negative active material layer (112) over the negative current collector (120) layer (126) such that the lithium-metal negative active material layer (112) is attached to and supported by the negative current collector (120) layer (126) and the polymer base layer (122) such that the negative current collector (120) layer (126) is positioned between the polymer base layer (122) and the lithium-metal negative active material layer (112).

31. The method (300) of claim 30, further comprising depositing a primary negative active material layer (113) over the lithium-metal negative active material layer (112) such that the lithium-metal negative active material layer (112) is positioned between the negative-electrode current collecting layer (126) and the primary negative active material layer (113).

32. The method (300) of claim 30, wherein depositing the primary negative active material layer (113) comprises a solvent-free deposition technique selected from the group consisting of powder deposition, electro-static deposition, and free-standing film (FSF) deposition.

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