Post-formation electrolyte refill

Abstract

The present disclosure provides "post-formation electrolyte refill". A lithium ion battery cell and a process for its preparation are provided. The method involves first impregnating the anode, cathode, and separator of the cell with a carbonate-based electrolyte to form a lithium fluoride-rich passivation layer. Subsequently, the electrolyte is rinsed and replaced with a soft solvent-based electrolyte. This two-step electrolyte process can help form a more robust initial passivation layer.

Description

Technical Field

[0001] The present disclosure relates to lithium-ion batteries and electrolytes used in lithium-ion batteries. Background Art

[0002] Lithium-ion batteries typically employ carbonate-based electrolytes, which may have limitations. The operating parameters of lithium-ion batteries with conventional carbonate-based electrolytes are generally limited to a voltage ceiling of 4.3 V and a temperature range of -20°C to 50°C. This may be due to an increased incidence of lithium plating at temperatures below -20°C, where the electrolyte exhibits low ionic conductivity and high charge transfer resistance.

[0003] Soft-solvent-based electrolytes can have an extended operating voltage and temperature range. However, the long-term calendar life of the battery at high temperatures (45°C or higher) remains unresolved and can be challenging. This is mainly due to the formation of thin layers of cathode and anode solid / electrolyte interfaces (cathode electrolyte interface and solid electrolyte interface, respectively) within the electrolyte environment. Summary of the Invention

[0004] In one aspect, a method for fabricating a lithium-ion battery cell includes: impregnating an anode, a cathode, and a separator of the cell with a carbonate-based electrolyte to form a lithium fluoride-rich passivation layer between the anode and the separator, thereby providing electron insulation and ion conduction. Subsequently, the carbonate-based electrolyte is rinsed out with a soft-solvent-based electrolyte, thereby leaving the soft-solvent-based electrolyte within the cell.

[0005] The carbonate-based electrolyte can contain various lithium salts dissolved therein, such as lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, and lithium tetrafluoroborate. Additives in the carbonate-based electrolyte can include vinylene carbonate, fluoroethylene carbonate, and similar compounds that enhance battery performance.

[0006] The soft-solvent-based electrolyte includes methyl difluoroacetate, methyl difluoro(sulfonyl)acetate, and can also include a diluent, such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. During the rinsing step, the volume of the soft-solvent-based electrolyte is maintained relative to the total porosity of the electrodes and the separator.

[0007] The method can also involve one or more sealing steps after impregnation and after rinsing. Additionally, the impregnation step can be incorporated into a formation process having at least one charge and discharge cycle, followed by a second cycle to reach different states of charge.

[0008] The lithium-ion battery cell prepared by this method includes a cathode, a current collector, a soft-solvent-based electrolyte, and an anode having a pre-formed passivation layer rich in lithium fluoride. The cathode may include a nickel manganese cobalt oxide material with a specified chemical composition ratio of nickel, manganese, and cobalt of 8:1:1 specifically.

[0009] The battery cell can be designed in a prismatic or cylindrical form. The soft-solvent-based electrolyte within the cell is characterized by a mixture of fluorinated esters and ethers, containing dissolved lithium salts such as lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a flowchart of an assembly process according to one embodiment; and

[0011] Figure 2 is a schematic diagram of a lithium-ion battery cell according to one embodiment. DETAILED DESCRIPTION

[0012] Embodiments are described herein. However, it should be understood that the disclosed embodiments are merely examples and other embodiments may take different and alternative forms. The drawings are not necessarily to scale. Some features may be enlarged or minimized to show details of particular components. Thus, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching one of ordinary skill in the art.

[0013] The various features shown and described in any one of the accompanying drawings can be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. Combinations of the shown features provide representative embodiments for typical applications. However, for a particular application or implementation, various combinations and modifications of the features may be desirable consistent with the teachings of this disclosure.

[0014] "Soft-solvent"-based electrolytes may extend the operating limits of lithium-ion batteries. The use of fluorinated acetates (such as methyl difluoroacetate and methyl difluoro(sulfonyl)acetate) enables a lithium-ion battery cell composed of nickel manganese cobalt oxide (NMC) with a chemical composition ratio of 8:1:1 of nickel (Ni), manganese (Mn), and cobalt (Co) as the cathode material and graphite as the anode material to operate at a voltage of up to 4.5 V and a temperature as low as -60 °C. The higher electrochemical stability of the soft solvent can reduce battery degradation and extend the battery's voltage range.

[0015] Soft solvents exhibit a well-balanced donor number and dielectric constant, which results in a lower lithium-ion desolvation energy and, consequently, a reduced charge transfer resistance at lower temperatures. Due to the reduced desolvation energy and the formation of a lithium-fluoride (Li-F)-rich interface, lithium plating is inhibited, which can help maintain battery integrity at extreme temperatures.

[0016] The performance parameters of a lithium-ion battery (LiB) can be improved through a dual electrolyte refilling process. The process involves an initial filling with a conventional carbonate-based electrolyte containing specific salts and additives and forming the LiB. The purpose of this initial step can be to establish a Li-F-rich interface that exhibits the necessary thickness for robustness. When operated at elevated temperatures, this initial formation can increase the long-term life and stability of the LiB.

[0017] Once the LiB has been fully formed with the conventional electrolyte, a transition to a second electrolyte occurs. The second electrolyte can consist of a soft solvent, which can include but is not limited to methyl difluoroacetate and methyl difluoro(sulfonyl)acetate. Replacing the first electrolyte with the second electrolyte is to improve the ability of the LiB to function more effectively at higher voltages and lower temperatures. The increased electrochemical stability of the soft solvent and the reduced desolvation energy of lithium ions (Li+) within these solvents contribute to the improved performance.

[0018] In addition, the second electrolyte can incorporate a diluent such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). This combination may not reduce the long-term performance at high temperatures, which is maintained by the Li-F-rich interface formed during the initial electrolyte formation.

[0019] The initial carbonate-based electrolyte is flushed out and replaced with the second soft-solvent-based electrolyte while maintaining the same excess volume relative to the total porosity of the electrodes and separator within the LiB. This can help maintain the designed electrochemical characteristics of the LiB during the electrolyte refilling process.

[0020] Figure 1A flow chart of a lithium-ion battery cell undergoing a dual electrolyte refill process is presented. In box 10, the lithium-ion battery cell is filled with a carbonate-based electrolyte, which can penetrate the jelly roll area. The jelly roll is an internal wound electrode structure of the cell including an anode layer, a cathode layer, and a separator. The cathode may include a nickel-manganese-cobalt oxide material having a chemical composition ratio of nickel, manganese, and cobalt of 8:1:1. The carbonate-based electrolyte promotes the formation of a solid-electrolyte interface (SEI) on the electrode, which is a step including a formation process, and produces a passivation layer rich in lithium fluoride that is electronically insulating and ionically conductive. In some configurations, the formation step may include at least one charge and discharge cycle and a second charge and discharge cycle that reaches a different state of charge than the first cycle. The carbonate-based electrolyte comprises a salt selected from the group consisting of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, and lithium tetrafluoroborate, and may further include an additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3,2-dioxathiapentane-2,3-dioxide, 1,3-propylene glycol cyclic sulfate, and adiponitrile. The battery cell may be a prismatic or cylindrical battery cell.

[0021] After SEI is formed, the cell undergoes a first sealing process in box two 12. This step encapsulates the electrolyte and electrode assembly, which can help maintain the integrity of the formed SEI layer and isolate it from external influences. After initial sealing and formation, in box three 14, the cell is rinsed with a soft solvent-based electrolyte to completely remove the carbonate-based electrolyte, the SEI remains intact, and the internal structure (including the jelly roll) remains unchanged. The rinsing step maintains the same excess volume of electrolyte relative to the total porosity of the electrodes and separators. Soft solvents can include materials such as methyl difluoroacetate and methyl difluoro(sulfonyl)acetate, and can also be mixed with diluents such as TTE. These solvents are selected for their higher electrochemical stability, which can allow the battery to operate at a voltage of up to 4.5V and a temperature as low as -60°C. Box four 16 is the second sealing step and indicates the completion of the battery cell.

[0022] Figure 2It is a schematic diagram of a lithium-ion battery cell 18, and the lithium-ion battery cell includes an anode 20 and a cathode 22 having a SEI layer 24. The anode and the cathode are separated by a separator 26, and the cell 18 has a soft solvent-based electrolyte 28. The SEI layer 24 is formed during the initial electrolyte filling and formation process and is a passivation layer rich in lithium fluoride, which is both electronically insulating and ionically conductive. The soft solvent-based electrolyte 28 is introduced after the formation of the SEI layer 24 and is selected for its electrochemical stability. The electrolyte 28 may include a mixture of compounds such as methyl difluoroacetate, and may also be combined with a diluent (such as TTE), which is selected for its low-temperature fluidity and compatibility with the SEI layer 24.

[0023] The algorithms, methods, or processes disclosed or proposed herein may be delivered to or implemented by a computer, a controller, or a processing device, which may include any dedicated electronic control unit or programmable electronic control unit. Similarly, the algorithms, methods, or processes may be stored in many forms as data and instructions executable by a computer or a controller, including but not limited to information permanently stored on a non-writable storage medium such as a read-only memory device and information changeably stored on a writable storage medium such as an optical disc, a random access memory device, or other magnetic and optical media. The algorithms, methods, or processes may also be implemented as software-executable objects. Alternatively, suitable hardware components (such as application-specific integrated circuits, field-programmable gate arrays, state machines, or other hardware components or devices) or a combination of firmware, hardware, and software components may be used to embody the algorithms, methods, or processes in whole or in part.

[0024] Although the exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the disclosed materials.

[0025] As previously described, the features of various embodiments can be combined to form additional embodiments of the present disclosure that may not be explicitly described or illustrated. Although various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve the desired overall system attributes, depending on the particular application and implementation. These attributes can include, but are not limited to: strength, durability, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. Thus, embodiments that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are within the scope of the present disclosure and may be desirable for a particular application.

[0026] According to the present invention, a method includes: impregnating an anode, a cathode, and a separator of a lithium-ion battery cell with a carbonate-based electrolyte such that an electronically insulating and ionically conductive lithium fluoride-rich passivation layer is formed between the anode and the separator; and rinsing the lithium-ion battery cell of the carbonate-based electrolyte with a soft-solvent-based electrolyte such that the soft-solvent-based electrolyte remains in the lithium-ion battery cell.

[0027] In one aspect of the present invention, the carbonate-based electrolyte includes a salt selected from the group consisting of: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, and lithium tetrafluoroborate.

[0028] In one aspect of the present invention, the carbonate-based electrolyte further includes an additive selected from the group consisting of: vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3,2-dioxathiolane-2,3-dioxide, 1,3-propanediol cyclic sulfate, and adiponitrile.

[0029] In one aspect of the present invention, the soft-solvent-based electrolyte includes methyl difluoroacetate and methyl difluoro(sulfonyl)acetate.

[0030] In one aspect of the present invention, the soft-solvent-based electrolyte further includes a diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0031] In one aspect of the present invention, the rinsing maintains the same electrolyte excess volume with respect to the total porosity of the anode, the cathode, and the separator.

[0032] In one aspect of the present invention, the method includes sealing the lithium-ion battery cell after the impregnation.

[0033] In one aspect of the present invention, the method includes sealing the lithium-ion battery cell after the rinsing.

[0034] In one aspect of the present invention, the soaking includes a forming process that includes at least one charge and discharge cycle.

[0035] In one aspect of the present invention, the forming process further includes a second charge and discharge cycle that reaches a state of charge different from the first charge and discharge cycle.

[0036] According to the present invention, there is provided a lithium-ion battery cell having: a cathode; an anode having an electronically insulating and ionically conductive lithium fluoride-rich passivation layer formed from a carbonate-based electrolyte; and a soft solvent-based electrolyte that soaks the cathode and the anode.

[0037] According to an embodiment, the soft solvent-based electrolyte includes methyl difluoroacetate and methyl difluoro(sulfonyl)acetate.

[0038] According to an embodiment, the soft solvent-based electrolyte further includes a diluent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0039] According to an embodiment, the carbonate-based electrolyte further includes an additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3,2-dioxathiolane-2,3-dioxide, 1,3-propanediol cyclic sulfate, and adiponitrile.

[0040] According to an embodiment, the carbonate-based electrolyte further includes an additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3,2-dioxathiolane-2,3-dioxide, 1,3-propanediol cyclic sulfate, and adiponitrile.

[0041] According to an embodiment, the cathode includes a nickel manganese cobalt oxide material with a chemical composition ratio of nickel, manganese, and cobalt of 8:1:1.

[0042] According to an embodiment, the cell is a prismatic cell.

[0043] According to an embodiment, the cell is a cylindrical cell.

[0044] According to the present invention, there is provided a lithium-ion battery cell having: a cathode; an anode having a lithium fluoride-rich passivation layer formed by a carbonate-based electrolyte; a separator between the cathode and the anode; and a soft solvent-based electrolyte in which a lithium salt is dissolved in a solvent mixture including a fluorinated ester and an ether, thereby soaking the cathode and the anode.

[0045] According to an embodiment, the lithium salt is selected from the group consisting of: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate.

Claims

1. A method comprising: impregnating an anode, cathode and separator of a lithium-ion battery cell with a carbonate-based electrolyte such that an electronically insulating and ionically conductive lithium fluoride-rich passivation layer forms between the anode and the separator; as well as The lithium ion battery cell of the carbonate-based electrolyte is flushed with a soft solvent-based electrolyte so that the soft solvent-based electrolyte remains in the lithium ion battery cell.

2. The method of claim 1, wherein the carbonate-based electrolyte comprises a salt selected from the group consisting of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, and lithium tetrafluoroborate.

3. The method of claim 1, wherein the carbonate-based electrolyte further comprises an additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3,2-dioxasulfane-2,3-dioxide, 1,3-propylene glycol cyclic sulfate, and adiponitrile.

4. The method of claim 1, wherein the soft solvent-based electrolyte comprises methyl difluoroacetate and methyl difluoro(sulfonyl)acetate.

5. The method of claim 1, wherein the soft solvent-based electrolyte further comprises a diluent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

6. The method of claim 1, wherein the flushing maintains the same excess volume of electrolyte relative to the total porosity of the anode, the cathode, and the separator.

7. The method of claim 1 further comprising sealing said lithium ion battery cell after said soaking.

8. The method of claim 7, further comprising sealing the lithium-ion battery cell after said flushing.

9. The method of claim 1, wherein the soaking comprises a formation process, the formation process comprising at least one charge and discharge cycle.

10. The method of claim 9, wherein the forming process further comprises a second charge and discharge cycle to a different state of charge than the first charge and discharge cycle.

11. A lithium ion battery cell, comprising: cathode; an anode having an electronically insulating and ionically conductive lithium fluoride-rich passivation layer formed from a carbonate-based electrolyte; as well as A soft solvent-based electrolyte impregnates the cathode and the anode.

12. The lithium ion battery cell of claim 11, wherein the soft solvent-based electrolyte comprises methyl difluoroacetate and methyl difluoro(sulfonyl)acetate.

13. The lithium-ion battery cell of claim 11, wherein the soft solvent-based electrolyte further comprises a diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

14. A lithium ion battery cell, comprising: cathode; an anode having a lithium fluoride-rich passivation layer generated from a carbonate-based electrolyte; a separator between the cathode and the anode; as well as A soft solvent-based electrolyte in which a lithium salt is dissolved in a solvent mixture including a fluorinated ester and an ether, thereby impregnating the cathode and the anode.

15. The lithium ion battery cell of claim 14, wherein the lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate.

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