LITHIUM DIFLUOR(OXOLATO)BORATE-BASED LOCALIZED HIGH-CONCENTRATION ELECTROLYTE FOR LITHIUM METAL BATTERIES

Abstract

An electrolyte, a vehicle battery cell comprising the electrolyte, and a method for forming the electrolyte. The electrolyte comprises a solution of lithium difluoro(oxalato)borate, a solvent, and a diluent. The lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent in a molar ratio ranging from 1 to 3, and the diluent in a molar ratio ranging from 1 to 6.

Description

BACKGROUND

[0001] The technology of electric and hybrid vehicles is made possible by the development and use of rechargeable secondary batteries that supply energy to the vehicle's powertrain. Secondary batteries include lithium-ion batteries, which generally comprise a cathode, an anode, a separator, and an electrolyte. The cathode provides the source of lithium ions and determines the battery's capacity and average voltage. The anode stores the lithium ions received from the cathode and releases them when energy is needed. The separator prevents the cathode and anode from coming into contact and short-circuiting the battery, and the electrolyte provides a medium between the cathode and anode through which the lithium ions move.

[0002] Battery performance can be quantified by a number of properties, including energy density, power density, specific energy, specific power, charge and discharge rates, capacity degradation, cycle life, thermal performance, and aging. Of particular interest is the stability of the battery components—that is, the cathode, anode, electrolyte, and current collectors—as the battery ages and undergoes charge / discharge cycles. Highly concentrated electrolytes have relatively higher ion transfer numbers and better thermal stability compared to conventional electrolytes. Highly concentrated electrolytes often contain salt concentrations exceeding 2 molarities (M), whereas traditional electrolytes contain salt concentrations of 1 molarity (M) or less.However, it has been shown that highly concentrated electrolytes have a relatively high viscosity and poor wettability, which can negatively affect battery performance.

[0003] Thus, although current electrolyte chemistries and other battery materials fulfill their purpose, there is a need for new and improved electrolyte chemistries that offer a relatively improved charging speed and other performance characteristics.

[0004] Known electrolytes for lithium battery cells, battery cells as such e.g. for a vehicle and methods for forming an electrolyte for a lithium battery cell are known, for example, from US 2017 / 0 317 385 A1, DE 10 2023 117 108 B3 and US 2024 / 0 282 944 A1. SUMMARY

[0005] According to various aspects, the present disclosure relates to an electrolyte for a lithium battery cell. The electrolyte comprises a solution of lithium difluoro(oxalato)borate, a solvent, and a diluent, wherein the solvent has the following formula: wherein R1 and R2 are individually at least one of a C1- to C4-alkyl and a C1- to C4-fluoroalkyl, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are each a C2- to C3-fluoroalkyl, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen. The lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6.

[0006] In each of the foregoing embodiments, the diluent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. In further embodiments, the diluent is present in a molar ratio in the range of 2 to 4. Alternatively or additionally, the diluent comprises bis(2,2,2-trifluoroethyl) ether. Alternatively or additionally, the diluent comprises tris(2,2,2-trifluoroethyl) orthoformate.

[0007] In embodiments of the foregoing, the solvent is N-methyl-2,2,2-trifluoroacetamide, and the N-methyl-2,2,2-trifluoroacetamide is present in a molar ratio of 2, and the diluent is 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether, and the 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether is present in a molar ratio of 4.

[0008] According to various aspects, the present disclosure relates to a battery cell for a vehicle. The battery cell comprises a cathode electrode, which includes a cathode arranged on a cathode current collector, and an anode electrode, which includes an anode arranged on an anode current collector. The battery cell also includes a separator positioned between the cathode and the anode. Additionally, the battery cell includes an electrolyte that is in contact with the cathode, the anode, and the separator. The electrolyte comprises a solution of lithium difluoro(oxalato)borate, a solvent, and a diluent, the solvent having the following formula: wherein R1 and R2 are individually at least one C1 to C4 alkyl group and one C1 to C4 fluoroalkyl group, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are individually a C2 to C3 fluoroalkyl group, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen. The lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6.

[0009] In embodiments of the foregoing, the cathode current collector comprises aluminium and the anode current collector is copper.

[0010] In each of the foregoing embodiments, the cathode is at least one of lithium iron phosphate, lithium nickel manganese cobalt oxides, lithium nickel cobalt manganese aluminum oxide and lithium manganese iron phosphate.

[0011] In each of the foregoing embodiments, the anode comprises lithium present in a range of more than 50 percent by weight to 100 percent by weight of the total weight of the anode and is at least one of lithium, lithium aluminum, lithium silver and lithium silicon.

[0012] In each embodiment, the diluent comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. In further embodiments, the diluent is present in a molar ratio in the range of 2 to 4. Additionally or alternatively, the diluent comprises bis(2,2,2-trifluoroethyl) ether. Additionally or alternatively, the diluent comprises tris(2,2,2-trifluoroethyl) orthoformate.

[0013] In embodiments of the foregoing, the solvent is N-methyl-2,2,2-trifluoroacetamide, and the N-methyl-2,2,2-trifluoroacetamide is present in a molar ratio of 2, and the diluent is 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether, and the 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether is present in a molar ratio of 4.

[0014] According to various aspects, the present disclosure relates to a method for forming an electrolyte for a lithium battery cell. The method comprises mixing lithium difluoro(oxalato)borate, a solvent, and a diluent. The solvent has the following formula: wherein R1 and R2 are individually at least one of a C1- to C4-alkyl and a C1- to C4-fluoroalkyl, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are individually a C2- to C3-fluoroalkyl, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen, and wherein the lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. Figure 1 illustrates a vehicle and a powertrain comprising a secondary battery according to the embodiments of the present disclosure. Fig. 2A illustrates a battery according to embodiments of the present disclosure. Fig. 2B illustrates a pouch or prismatic battery cell according to embodiments of the present disclosure. Fig. Figure 2C illustrates a cylindrical battery cell according to embodiments of the present disclosure. Fig. Figure 2D illustrates a button cell according to embodiments of the present disclosure. Fig. Figure 3 illustrates a method for forming a battery cell according to embodiments of the present disclosure. Fig. Figure 4 illustrates a diagram of the formation voltage (V) on the vertical y-axis and the specific capacity (milliampere hours per gram) on the horizontal x-axis for two battery cells during formation. Fig. Figure 5 illustrates the capacity retention percentage on the vertical y-axis as a function of the number of cycles on the horizontal x-axis for two battery cells. DETAILED DESCRIPTION

[0016] The following description is merely exemplary and is not intended to limit the present disclosure, application, or use. Furthermore, there is no intention to be bound by any express or implied theory set forth in the preceding introduction, summary, or subsequent detailed description. It should be understood that in the drawings, corresponding reference numerals denote identical or corresponding parts and features.

[0017] Detailed reference is now made to several embodiments and examples of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and the description to refer to identical or similar parts or steps. The drawings are presented in simplified form and are not to scale.

[0018] The present disclosure relates to an electrolyte for a lithium battery cell, and in particular a localized, highly concentrated electrolyte, a vehicle battery cell comprising the electrolyte, a method for forming the electrolyte, and a method for forming a solid-electrolyte interphase film on the anode electrode. A localized, highly concentrated electrolyte is understood to be an electrolyte comprising salt concentrations exceeding 2 molarity (M). The battery cells include any battery cell platform, such as prismatic, pouch, cylindrical, or button cell batteries. The batteries can be used in electric or hybrid electric vehicles.

[0019] The term "vehicle" as used herein is not limited to motor vehicles. Although the technology presented here is primarily described in the context of electric and hybrid electric vehicles, it is not limited to electric and hybrid electric vehicles.Furthermore, the concepts can be used in a variety of applications, such as in conjunction with components used in motorcycles, mopeds, locomotives, aircraft, watercraft and other vehicles, as well as in other applications that utilize batteries, such as in consumer electronics, power banks for buildings and portable power stations used for powering remote construction sites, for emergency power supplies, as well as in permanent power supply systems assigned to buildings and equipment, such as solar or wind-powered generator systems, power grids and fuel-based power generators such as gasoline, propane, kerosene or diesel generators and Sterling engines.

[0020] Fig. Figure 1 illustrates a vehicle 100 comprising a drive system 120. The drive system 120 generally includes an electric motor 124 and a secondary battery 126 for powering the electric motor 124. Furthermore, in many embodiments, the drive system 120 includes an inverter 128 for converting the DC (direct current) supplied by the battery 126 into AC (alternating current) used by the electric motor 124. The inverter 128 may be enclosed in a power electronics module 130, which includes, for example, transistors and diodes for switching the current from DC to AC and vice versa.

[0021] A controller 132 is connected to the inverter 128 and programmed to control and manage the operation of the electric motor 124 and the associated hardware, including the inverter 128. The electric motor 124 is connected to a gearbox (drive unit) 136 and a drivetrain 138, which transmits the mechanical power and rotation to the wheels 140 of the vehicle 100. The controller 132 comprises one or more processors and a tangible, non-transient memory 134. An internal combustion engine may also be included in the drive system of hybrid electric vehicles.

[0022] Referring again to the electric motor 124, which is powered by the battery 126, the electric motor 124 comprises a stator 142 and a rotor 144 arranged within the stator 142. The stator 142 is the stationary part of the electric motor 124. The stator 142 provides a rotating magnetic field with which the stationary magnetic field of the rotor 144 attempts to align, causing the rotor 144 to rotate in what is known as "motorizing mode." In other applications, the rotating field (as caused by physical rotation) of the rotor 144 generates an electric current in the stator 142—this operating mode is called "generation," and the electric motor 124 used in this way is called a generator. In traction motor vehicle applications, the starting mode provides motion to the vehicle.In generator mode, some of the energy recovered by braking when the vehicle comes to a stop is stored back in the vehicle battery 126.

[0023] It will be on Fig. Reference is made to 2A, which illustrates an example of a secondary battery 126 for operating an electric vehicle 100, as described in Fig. Figure 1 illustrated. As mentioned above, the secondary batteries 126 are rechargeable batteries that can be discharged when a load is applied and recharged when an external power source is applied. Referring to Fig. 2A, Fig. 2B, Fig. 2C and Fig. Figure 2D illustrates a battery 126 connected to a load 148, such as the electric motor 124. Other loads 148, however, include various systems in the vehicle 100, such as air conditioning and infotainment systems. The battery 126 comprises one or more battery cells 150 assembled together. The battery cells 150 can be, for example, bag-shaped, prismatic, cylindrical, or button-shaped battery cells, which are discussed further below. With reference to Fig. 2B to 2D, when a load 148 is applied to the battery 126, Li+ ions move from the anode 158 to the cathode 156 through the separator 160 via the electrolyte 162 in each battery cell 150. Equivalent electrons e- move through the circuit 146 from the cathode 156 to the anode 158 and provide voltage for the load 148. During charging, when an external voltage is applied, the Li+ ions move from the cathode 156 via the electrolyte 162 through the separator 160 to the anode 158 and can be intercalated into the anode 158.

[0024] Each battery cell contains 150 cells, such as those used in Fig. 2B, Fig. 2C and Fig. As illustrated in 2D, the battery cell 150 generally comprises a cathode electrode 151, which includes a cathode current collector 152 and a cathode 156 arranged on the cathode current collector 152, an anode electrode 153, which includes an anode current collector 154, and an anode 158 arranged on the anode current collector 154, a separator 160 positioned between the cathode 156 and the anode 158, and an electrolyte 162. Although the illustrated battery cells 150 comprise an anode 158 (and an anode current collector 154) and a cathode 156 (and a cathode current collector 152), the battery cell 150 can alternatively comprise two or more cathodes 156 (and one or more cathode current collectors 152) and one or more anodes 158 (and one or more anode current collector 154).In further alternative embodiments, the battery cell 150 can comprise one or more cathodes 156 (and one or more cathode current collectors 152) and two or more anodes 158 (and two or more anode current collectors 154). In each of the foregoing designs, one or more separators 160 are nested between the cathodes 156 and the anodes 158 to prevent the cathodes 156 and the anodes 158 from coming into contact.

[0025] In embodiments, the battery cell 150 is of Fig. 2B is configured as a pouch-like battery cell or as a prismatic battery cell. In both designs, which have multiple cathodes 156 and multiple anodes 158, separators 160 are provided between the cathodes 156 and the anodes 158. In embodiments, a ribbon-shaped separator 160 can be folded in a Z-shape around each cathode 156 (and the cathode current collector 152) and around each anode 158 (and the anode current collector 154). In a pouch-like cell, tabs 164 are welded to the cathode current collectors 152 and the anode current collectors 154. Alternatively, the flags 164 are integrally formed with the cathode current collectors 152 and the anode current collectors 154 by cutting the flags 164 together with the cathode current collectors 152 and the anode current collectors 154 from a larger sheet of material. Additionally, the cover 166 is provided in the form of a flexible film bag made of aluminum or another material.Prismatic cells, on the other hand, comprise terminals to which the cathode current collectors 152 and anode current collectors 154 are connected, and the cover 166 is formed from a relatively rigid housing, typically in the form of a cuboid. The flags 164 or terminals connected to the cathode current collectors 152 of several battery cells 150 are interconnected, for example by a busbar 168 (see . Fig. 2A) or another electrical connection, and the flags 164 or terminals connected to the anode current collectors 154 of several battery cells 150 are connected to each other, for example by a busbar 169 (see Fig. 2A) or another electrical connection.

[0026] Alternatively, the battery cell 150 from Fig. 2C is configured as a cylindrical battery cell 150. In this design, the cathode current collector 152, the anode current collector 154, the cathode 156, the anode 158, and one or more separators 160 are in the form of long strips rolled into a cylinder or biscuit roll. Like the prismatic cell, the cover 166 is also formed from a relatively rigid housing made of aluminum or another material. Terminals 164 are welded to the cathode current collector 152 and the anode current collector 154. The terminals 164 or clamps connected to the cathode current collectors 152 of several battery cells 150 are connected to each other, for example, by a busbar 168 (see Fig. 2A) or another electrical connection, and the flags 164 or terminals connected to the anode current collectors 154 of several battery cells 150 are connected to each other, for example by a busbar 169 (see Fig. 2A) or another electrical connection.

[0027] In alternative embodiments, the battery cell 150 is packaged in a button cell, as in Fig. Illustrated in 2D. In this construction, the cathode current collector 152, the anode current collector 154, the cathode 156, the anode 158, and one or more separators 160 are in the form of discs, sandwiched together in the button-like packaging that forms the cover 166, which includes a cap 170 and a can 172. A spring washer 174 may be enclosed between the cathode current collector 152 and the cap 170. Before the cap 170 is attached to the can 172, electrolyte 162 is added to the battery cell 150. The cap 170 includes terminals 164 for the anode 158 and cathode 156.

[0028] In the aforementioned various types of battery cells 150, the cathode current collector 152 and the anode current collector 154 are formed from conductive materials. In some embodiments, the cathode current collector 152 is made of aluminum. Alternatively or additionally, the cathode current collector 152 comprises aluminum, such as an aluminum composite film consisting of an aluminum-coated thermoplastic film or an aluminum film coated with conductive carbon. In further alternative embodiments, the cathode current collector comprises titanium. In other embodiments, the anode current collector 154 comprises copper. Alternatively or additionally, the anode current collector 154 may also comprise nickel, stainless steel, and titanium. The current collectors 152 and 154 are illustrated in the form of a film; however, it should be noted that other forms, such as a mesh or foam, can also be used.In embodiments, a film cathode current collector 152 and a film anode current collector 154 are impermeable to gas. The cathode current collector 152 has a thickness in the range of 5 micrometers to 50 micrometers, including all values ​​and ranges therein, such as the range of 5 micrometers to 25 micrometers. The anode current collector 154 has a thickness in the range of 4 micrometers to 50 micrometers, including all values ​​and ranges therein, such as the range of 4 micrometers to 25 micrometers.

[0029] The cathode 156 includes a source of lithium ions (Li). +) and can reversibly store or intercalate lithium ions, which determines, for example, the battery's capacity and average voltage. In embodiments, the cathode material comprises lithium iron phosphate, which has an olivine-like structure. Additionally or alternatively, the cathode material, lithium manganese iron phosphate, which also has an olivine-like structure, comprises lithium cobalt oxide, lithium nickel manganese oxides, lithium nickel manganese cobalt oxides, lithium nickel cobalt aluminum oxides, and lithium nickel cobalt manganese aluminum oxide. In embodiments, the lithium nickel manganese cobalt oxides have the formula LiNi a Mn b Co c O2, where the sum of a, b, c is 1, such as LiNi 0,33 Mn 0,33 Co 0,33 O2 (NMC111), LiNi 0,5 Mn 0,3 Co 0,2 O2 (NMC 523), LiNi 0,6 Mn 0,2 Co 0,2 O2 (NMC 622), Li-Ni 0,7 Mn 0,2 Co 0,1 O2 (NMC 721), LiNi 0,75 Mn 0,25O2 (NM75), and LiNi 0,8 Mn 0,1 Co 0,1 O2 (NMC 811). It should be noted that lithium manganese oxide, Li2Mn2O4, is a spinel-like cathode.

[0030] In embodiments, the cathode material is deposited on the cathode current collector 152 with a density ranging from 1.5 milliampere-hours per square centimeter to 5.5 milliampere-hours per square centimeter, including all values ​​and ranges therein, such as from 1.7 milliampere-hours per square centimeter to 3.5 milliampere-hours per square centimeter. The cathode material comprises particles with a particle size (largest linear cross-section, measured by optical microscopy) ranging from 5 nanometers to 50 micrometers, including all values ​​and ranges therein. Furthermore, the olivine cathode particles are coated with carbon particles. The carbon particles are present in a range of 0.9 to 4 percent by weight of the total weight of the cathode particles.

[0031] The cathode electrode 151, which includes both the cathode current collector 152 and the cathode 156, has a thickness in the range of 10 micrometers to 500 micrometers, including all values ​​and ranges therein, when the cathode material is formed on one side of the cathode current collector 152. When the cathode material is formed on both sides of the cathode current collector 152, the cathode electrode 151 has a thickness in the range of 30 micrometers to 1050 micrometers, including all values ​​and ranges therein, for a double-sided cathode electrode, for example, in the range of 205 micrometers to 500 micrometers.

[0032] The anode 158 comprises materials capable of reversible incorporation or intercalation of lithium ions at a lower electrochemical potential than that of the cathode 156, such that an electrochemical potential difference exists between the anode 158 and cathode 156. In some embodiments, the anode material comprises lithium comprising more than 50% by weight of the total anode weight, including all values ​​and ranges from 51% by weight to 100% by weight. In other embodiments, the anode material is lithium. In additional or alternative embodiments, the anode material comprises at least one of lithium-aluminum, lithium-silver, and lithium-silicon.

[0033] In embodiments, the anode 158 has a thickness in the range of 10 micrometers to 550 micrometers, including all values ​​and ranges therein. The anode 158 is applied to the anode current collector 154 and forms a coating on the anode current collector 154, using a deposition method such as a slurry-based process, a hot rolling process, extrusion, or additive manufacturing. The combined anode 158 and the anode current collector 154 provide the anode electrode 153.

[0034] The separator 160 is a porous material formed from an electrically insulating material and prevents the cathode 156 and anode 158 from coming into contact and potentially short-circuiting the circuit. The separator 160 is sandwiched between the cathode 156 and anode 158 or at least partially enclosed within them, allowing the lithium ions and electrolyte 162 to pass through the pores of the separator 160. The separator 160 can comprise one or more components of a composite material, a polymeric material, or a nonwoven fabric. In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyamide, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride. Additionally, the separator 160 can be filled, i.e., it can comprise one or more fillers dispersed therein, the one or more fillers comprising materials such as glass fibers, nonwovens, or woven fabrics.In additional or alternative embodiments, the separator 160 can comprise at least one thermally stable, porous polymer coating and a ceramic coating, such as an aluminum oxide coating. The coating is arranged on one or more surfaces of a porous polymer film, the polymer film being selected from at least one of polyethylene and polypropylene. The separator 160 can comprise one or more layers, each layer being formed from one or more of the aforementioned materials. The separator 160 can be in the form of a film or a mesh, such as a woven mesh or a slotted film. In embodiments, the separator 160 has a thickness in the range of 4 micrometers to 25 micrometers, including all values ​​and ranges therein.

[0035] The electrolyte 162 provides a fluid medium through which lithium ions migrate between the cathode 156 and the anode 158 and permeate the separator 160. The electrolyte 162 generally comprises a lithium salt dissolved in a solvent that includes a diluent. In some embodiments, the electrolyte is a localized, highly concentrated electrolyte comprising more than 1.0 molarity (M) of lithium salt, for example, more than 2 molarity (M). The lithium salt comprises lithium difluoro(oxalato)borate (LiDFOB). The lithium difluoro(oxalato)borate is present in the solvent at a concentration (moles of salt per liter of solvent) of more than 1.0 molarity (M) up to 4.0 M, including all values ​​and ranges therein, such as 1.2 M, 2.0 M to 4.0 M, etc.

[0036] As mentioned, the lithium difluoro(oxalato)borate is combined with a solvent. In some embodiments, the solvent has the following formula: where R1 and R2 are individually at least one of C1 to C4 alkyl and C1 to C4 fluoroalkyl. The reference to C1, C2, C3, C4, etc., refers to the number of carbons present in a particular group, e.g., alkyl or fluoroalkyl; C1 indicates that one carbon is present, C2 indicates that two carbons are present, etc. In embodiments, the solvent comprises N-methyl-2,2,2-trifluoroacetamide (NMTFA). In alternative embodiments, the solvent comprises a derivative of a secondary amide function, such as N-methylacetamide or N-methylpropionamide. Without being bound to any particular theory, it is assumed that the polar functional groups, i.e., the amide groups in the solvent molecules, function similarly to a Lewis base and increase the solubility of the lithium difluoro(oxalato)borate, which functions similarly to a Lewis acid.

[0037] The electrolyte 162 also includes a diluent. The addition of the diluent reduces the viscosity of the electrolyte and improves the surface wettability of the electrolyte with the cathode 156. The diluent described herein is also understood to improve the performance of the battery cells during formation, i.e., during the initial charging and discharging process of a battery cell, in order to activate the materials contained therein. In embodiments, formation takes place at temperatures in the range of 21°C to 50°C, including all values ​​and ranges therein. Alternatively, formation can also take place at temperatures above 50°C up to 80°C, including all values ​​and ranges therein.The addition of the diluent described herein increases the specific charge and discharge capacity as well as the Coulomb efficiency compared to a battery cell comprising an electrolyte that does not include the diluents described herein. In embodiments, the specific charge capacities of the battery cells formed using the salts, solvents, and diluents described herein are in the range of 100 milliampere-hours per gram to 300 milliampere-hours per gram, including all values ​​and ranges therein, and the specific discharge capacities are in the range of 100 milliampere-hours per gram to 300 milliampere-hours per gram, including all values ​​and ranges therein. Furthermore, the Coulomb efficiency is greater than 90%, including all values ​​and ranges therein, such as in the range of 90% to 98%.

[0038] The diluent comprises at least one fluorinated ether and one fluorinated orthoester. The fluorinated ether has the following formula: where R3 and R4 are individually C2- to C3-fluoroalkyl groups. In embodiments, the fluorinated ether comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). Additionally or alternatively, in embodiments, the fluorinated ether also comprises bis(2,2,2-trifluoroethyl) ether (BTFE). The fluorinated orthoester has the following formula: wherein R5, R6 and R7 are individually C1 to C2 fluoroalkyl, and R8 is hydrogen, In embodiments the fluorinated orthoester comprises tris(2,2,2-trifluoroethyl) orthoformate (TFEO).

[0039] The electrolyte is clear and transparent. In some embodiments, the electrolyte comprises lithium difluoro(oxalato)borate in a molar ratio of 1, the solvent is present in a molar ratio ranging from 1 to 5 (including all values ​​and ranges therein), and the diluent is present in a molar ratio ranging from 1 to 6 (including all values ​​and ranges therein). In other embodiments, the electrolyte comprises lithium difluoro(oxalato)borate in a molar ratio of 1, the solvent is present in a molar ratio of 2, and the diluent is present in a molar ratio ranging from 2 to 4.In further embodiments, the electrolyte 162 comprises lithium difluoro(oxalato)borate in a molar ratio of 1, N-methyl-2,2,2-trifluoroacetamide is present in a molar ratio of 2, and 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether is present in a molar ratio of 4.

[0040] The present electrolyte 162, which includes the diluent, has a viscosity in the range of 0.4 centipoise to 1 centipoise, measured at room temperature (i.e., 21°C to 23°C), whereas the viscosity of an electrolyte without the diluent is in the range of 1.2 centipoise to 5 centipoise, measured at room temperature. Furthermore, the electrolyte 162 exhibits high stability with respect to lithium and relatively uniform lithium deposition properties when forming a solid-electrolyte intermediate film on the anode 158.

[0041] The electrolyte 162 is formed by mixing lithium salt, solvent, and diluent. In embodiments, the mixing takes place at room temperature under an inert atmosphere, such as nitrogen or argon. The electrolyte 162 can then be added to a battery cell 150, including one of the battery cells 150 which is in Fig. 2B to 2D are illustrated. Fig. Figure 3 illustrates a general method 300 for forming a battery cell 150 comprising the electrolyte 162. In block 302, the cathode current collector 152 with the cathode 156, the anode current collector 154 with the anode 158, and the separator 160 are assembled in a cover 166, 170, 172 to obtain a battery cell 150. In embodiments, the cathode 156 is deposited onto the cathode current collector 152 and the anode 158 is deposited onto the anode current collector 154 before the battery cell 150 is assembled. In block 304, the electrolyte 162 is added to the battery cell 150. In block 306, the battery cell 150 is sealed. In further embodiments, the battery cell 150 is coupled to a circuit in block 308 and undergoes formation.In some embodiments, battery formation occurs at temperatures below 50 degrees Celsius, for example in the range of 20 to 50 degrees Celsius, or alternatively at elevated temperatures of 51 to 80 degrees Celsius. As mentioned above, during battery formation, films of solid electrolyte intermediate phases, such as lithium fluoride, lithium oxide, and organic lithium salts, form on the anode, creating cathode-electrolyte intermediate phases, and structural changes occur in the cathode and anode materials. However, the corrosion of the cathode current collector is made more difficult, if not completely prevented, by the addition of electrolyte 162.

[0042] Fig. Figure 4 illustrates a diagram showing the voltage (V) on the vertical y-axis and the specific capacity (milliampere-hours per gram) on the horizontal x-axis for two battery cells during their formation. The first battery cell (represented by line A) was formed using a lithium iron phosphate cathode, a lithium anode, an aluminum cathode current collector, a copper anode current collector, and an electrolyte comprising lithium difluoro(oxalato)borate present in a molar ratio of 1 and N-methyl-2,2,2-trifluoroacetamide solvent present in a molar ratio of 2.The second battery cell (represented by line A) was formed using a lithium iron phosphate cathode, a lithium anode, an aluminum cathode current collector, a copper anode current collector, and an electrolyte comprising lithium difluoro(oxalato)borate present in a molar ratio of 1, N-methyl-2,2,2-trifluoroacetamide solvent present in a molar ratio of 2, and 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether as a diluent present in a molar ratio of 4. Formation was carried out at a temperature of 25 degrees Celsius and a charge and discharge rate of 0.1°C (10 hours).

[0043] As can be seen, the electrolyte containing the diluent (B) had a significantly higher specific capacity than the electrolyte without the diluent (A). The electrolyte containing the diluent had a specific charge capacity of 159.5 milliampere-hours per gram and a specific discharge capacity of 154.8 milliampere-hours per gram. The Columb efficiency was determined to be 97.1 percent. The electrolyte without the diluent had a specific charge capacity of 134.6 milliampere-hours per gram and a specific discharge capacity of 90.2 milliampere-hours per gram. The Columb efficiency was determined to be 67.0 percent.

[0044] Fig.Figure 5 illustrates the capacity retention percentage on the vertical y-axis as a function of the number of cycles on the horizontal x-axis for the two battery cells described above. The battery cell without the diluent, represented by line A, loses capacity before it has completed five charge and discharge cycles. The battery cell represented by line B, which includes the diluent, retains over 90 percent of its capacity for at least 30 charge and discharge cycles. Additionally, no aluminum corrosion was observed at the cathode after cycling.

[0045] The electrolytes, battery cells, secondary batteries, and manufacturing processes described herein offer a number of advantages. These advantages include, for example, retaining the benefits of localized, highly concentrated electrolytes, including reduced viscosity, improved wettability, relatively high stability with respect to lithium, and relatively uniform lithium plating when forming a solid-electrolyte interphase film that provides a passivation layer on the anode electrode. The advantages also include reducing, if not completely eliminating, the corrosion of aluminum in cathode current collectors that occurs in electrolytes lacking the diluents described herein. These advantages further include the ability to incorporate higher concentrations of lithium difluoro(oxalato)borate into the electrolyte solution.

[0046] As used herein, the term "controller" and related terms such as microcontroller, control module, module, controller, control unit, processor, and similar terms refer to one or more combinations of application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), electronic circuits, central processing units (CPUs), e.g., microprocessors, and associated non-volatile memory components in the form of storage and memory devices (read-only, programmable read-only, direct-access, disk-based, etc.). The controller 132 may also consist of multiple controllers that are in electrical communication with each other. The controller 132 may be connected to other systems and / or controllers of the vehicle 100, enabling the controller 132 to access data, such as speed, acceleration, braking, and steering angle of the vehicle 100.

[0047] A processor can be any custom or commercially available processor, central processing unit (CPU), graphics processing unit (GPU), auxiliary processor among several processors assigned to controller 132, semi-composite semiconductor-based microprocessor (in the form of a microchip or chipset), macroprocessor, a combination thereof, or generally a device for executing instructions.

[0048] The tangible, non-transient memory 134 can include volatile and non-volatile memory, such as read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM). A KAM is persistent or non-volatile memory that can be used to store various operating variables while the processor is powered off. The tangible, non-transient memory 134 can be implemented using a number of memory devices, such as PROMs (programmable read-only memory), EPROMs (erasable PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combined memory devices capable of storing data, some of which represents executable instructions used by the controller 132 to control various systems of the vehicle 100.

Claims

[1] Electrolyte for a lithium battery cell, wherein the electrolyte comprises: a solution of lithium difluoro(oxalato)borate, a solvent and a diluent, where The solvent has the following formula: wherein R1 and R2 individually contain at least one of a C1 to C4 alkyl group and a C1 to C4 fluoroalkyl, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are individually a C2- to C3-fluoroalkyl, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen, and wherein the lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6. [2] Electrolyte for the lithium battery cell according to claim 1, wherein the diluent is 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether. [3] Electrolyte for the lithium battery cell according to claim 2, wherein the diluent is present in a molar ratio in the range of 2 to 4. [4] Electrolyte for the lithium battery cell according to claim 1, wherein the diluent is bis(2,2,2-trifluoroethyl) ether. [5] Electrolyte for the lithium battery cell according to claim 1, wherein the diluent is tris(2,2,2-trifluoroethyl)orthoformate. [6] Battery cell for a vehicle, comprising: a cathode electrode comprising a cathode arranged on a cathode current collector; a cathode electrode comprising an anode arranged on an anode current collector; a separator positioned between the cathode and the anode; and an electrolyte that is in contact with the cathode, the anode and the separator, wherein the electrolyte comprises: a solution of lithium difluoro(oxalato)borate, a solvent and a diluent, where The solvent has the following formula: wherein R1 and R2 are individually at least one C1 to C4 alkyl group and one C1 to C4 fluoroalkyl group, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are individually a C2 to C3 fluoroalkyl group, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen, and wherein the lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6. [7] Method for forming an electrolyte for a lithium battery cell, comprising: Mixing lithium difluoro(oxalato)borate, a solvent and a diluent, where The solvent has the following formula: wherein R1 and R2 individually contain at least one of a C1 to C4 alkyl group and a C1 to C4 fluoroalkyl, wherein the solvent is N-methyl-2,2,2-trifluoroacetamide and wherein the solvent is present in a molar ratio of 2, and the diluent is at least one of i) a fluorinated ether having the following formula: where R3 and R4 are individually a C2- to C3-fluoroalkyl, and ii) a fluorinated orthoester having the following formula: where R5, R6 and R7 are individually C1 to C2 fluoroalkyls, and R8 is hydrogen, and wherein the lithium difluoro(oxalato)borate is present in a molar ratio of 1, the solvent is present in a molar ratio in the range of 1 to 3, and the diluent is present in a molar ratio in the range of 1 to 6.

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