Electrolyte for thick LFP lithium battery system

Abstract

An electrolyte for a thick LFP-Li battery system is provided. The electrolyte comprises a low-viscosity main salt, at least one lithium-based functional salt and a solvent, wherein the solvent comprises a low-viscosity solvent mixed with a cyclic ether solvent. The low-viscosity main salt comprises at least one of LiTFSI or a lithium salt.

Description

Technical Field

[0001] This disclosure relates to lithium iron phosphate battery systems, and more specifically, to electrolytes used in lithium iron phosphate battery systems. Background Technology

[0002] Rechargeable batteries are known to be used in consumer electronics applications, ranging from small electronic devices such as mobile phones and laptops to larger devices such as vehicles. Compared to older rechargeable batteries such as nickel-metal hydride, nickel-cadmium, or lead-acid batteries, modern rechargeable lithium-ion batteries maintain relatively high energy density. The advantage of rechargeable lithium-ion batteries is that they can be fully or partially charged and discharged multiple times without retaining a memory effect. Furthermore, rechargeable lithium-ion batteries can be used in larger applications, such as electric and hybrid vehicles, because of their high power density, long cycle life, and ability to be formed into various shapes and sizes to efficiently fill the available space in such vehicles.

[0003] Rechargeable lithium-ion batteries utilize an electrolyte to carry or conduct lithium cations (Li+) between the positive and negative electrode active materials. + In LiFePO4 (LFP-Li) type batteries, conventional carbonate electrolytes or high-concentration electrolytes are used. However, problems such as thick electrodes and lithium anodes lead to incompatibility between LFP-Li batteries and carbonate electrolytes or high-concentration electrolytes, resulting in poor electrochemical performance.

[0004] While existing technologies and systems attempt to minimize the drawbacks of using carbonate or high-concentration electrolytes and achieve their specific objectives, a new and improved LFP-Li battery electrolyte remains needed. Therefore, a stable and efficient LFP-Li battery is required. Summary of the Invention

[0005] According to several aspects of this disclosure, an electrolyte for thick LFP-Li battery systems is provided. The electrolyte comprises a low-viscosity main salt, at least one lithium-based functional salt, and a solvent comprising a low-viscosity solvent mixed with a cyclic ether solvent. The low-viscosity main salt comprises at least one of LiTFSI or a lithium salt and has the following structure.

[0006]

[0007] According to another aspect of this disclosure, the electrolyte has a functional group R4 comprising at least one of fluorine (F) atoms or straight-chain C1-C6 fluoroalkyl groups.

[0008] According to another aspect of this disclosure, the electrolyte has a functional group R5 comprising at least one of a fluorine (F) atom or a straight-chain C1-C6 fluoroalkyl group.

[0009] According to another aspect of this disclosure, the electrolyte comprises a low-viscosity primary salt with a concentration of 0.6 M to 2.0 M.

[0010] According to another aspect of this disclosure, the electrolyte comprises a low-viscosity primary salt with a concentration of 0.8M to 1.2M.

[0011] According to another aspect of this disclosure, the electrolyte includes a lithium-based functional salt, which includes at least one of lithium difluoro(oxalate)borate (LiDFOB), LiNO3, lithium perchlorate (LiClO4), LiAlCl4, LiBF4, LiB(C6H5)4, LiAsF6 or lithium bis(oxalate)borate (LiBOB).

[0012] According to another aspect of this disclosure, the electrolyte comprises a lithium-based functional salt at a concentration of 0.05 M to 0.6 M.

[0013] According to another aspect of this disclosure, the electrolyte comprises a lithium-based functional salt at a concentration of 0.1 M to 0.5 M.

[0014] According to another aspect of this disclosure, the electrolyte has a low-viscosity solvent including dimethyl ethylene glycol (DME).

[0015] According to another aspect of this disclosure, the electrolyte has a cyclic ether solvent comprising at least one of 1,3-dioxolane (DOL) or 1,4-dioxane.

[0016] According to another aspect of this disclosure, the electrolyte comprises a cyclic ether solvent having fewer than 6 carbon atoms.

[0017] According to another aspect of this disclosure, the electrolyte comprises a solvent having a low viscosity-to-volume ratio of 50% to 100% (inclusive).

[0018] According to another aspect of this disclosure, the electrolyte comprises a solvent having a low viscosity-to-volume ratio of 50% to 80% (inclusive).

[0019] According to another aspect of this disclosure, the electrolyte comprises a solvent having a volume ratio of less than or equal to 50% cyclic ether solvent.

[0020] According to another aspect of this disclosure, the electrolyte comprises a solvent having a volume ratio of 20% to 50% (including 20% ​​and 50%) of cyclic ether solvent.

[0021] According to several aspects of this disclosure, a thick LFP-Li battery system is provided. The thick LFP-Li battery system includes a battery pack comprising a thick LFP positive electrode, a lithium-based negative electrode, and an electrolyte. The capacity loading of the thick LFP positive electrode is greater than 4 mAh / cm². 2The lithium-based anode has a lithium content of 50% or greater. The electrolyte comprises a low-viscosity main salt, at least one lithium-based functional salt, and a solvent, the solvent comprising a low-viscosity solvent mixed with a cyclic ether solvent. The low-viscosity main salt comprises at least one of LiTFSI or a lithium salt and has the following structure.

[0022]

[0023] According to another aspect of this disclosure, the thick LFP-Li battery system includes a thick LFP positive electrode with an adhesive, the adhesive comprising at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), or styrene-ethylene-butene-styrene copolymer (SEBS).

[0024] According to another aspect of this disclosure, the thick LFP-Li battery system has a lithium-based anode comprising metallic lithium.

[0025] According to another aspect of this disclosure, the thick LFP-Li battery system has a lithium-based anode comprising at least one of a Li-Al alloy, a Li-Ag alloy, or a Li-Si alloy with a lithium content of more than 50% by weight.

[0026] According to several aspects of this disclosure, an electrolyte for a thick LFP-Li battery system is provided. The electrolyte for a thick LFP-Li battery system comprises a low-viscosity main salt, at least one lithium-based functional salt, and a solvent, the solvent comprising a low-viscosity solvent mixed with a cyclic ether solvent. The low-viscosity main salt comprises at least one of LiTFSI or a lithium salt and has the following structure.

[0027]

[0028] Other areas of application of this disclosure will become apparent from the detailed description provided below. It should be understood that the detailed description and specific embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0029] The above-described features and advantages, as well as other features and advantages, of the currently disclosed systems and methods will become apparent when considered in conjunction with the accompanying drawings and the detailed description including the claims and embodiments. Attached Figure Description

[0030] This disclosure will be more fully understood through detailed description and accompanying drawings, in which:

[0031] Figure 1This is a perspective view illustrating an embodiment of a vehicle having a battery cell according to the present disclosure, the battery cell comprising an electrolyte having a low-viscosity primary salt, at least one functional salt, a low-viscosity solvent, and a cyclic ether co-solvent.

[0032] Figure 2 This illustrates the provisions of this disclosure. Figure 1 The diagram shows a perspective view of an embodiment of a battery cell, wherein the battery cell includes a thick LiFePO4 positive electrode, a negative electrode, and an electrolyte having a low-viscosity main salt, at least one functional salt, a low-viscosity solvent, and a cyclic ether co-solvent. Detailed Implementation

[0033] Reference will now be made in detail to several embodiments of the present disclosure illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and description to refer to the same or similar parts or steps. The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or its uses.

[0034] This paper discloses an electrolyte for thick LiFePO4(LFP)-Li (“LFP”) batteries and battery packs by using ether as a component in the electrolyte. This electrolyte exhibits low viscosity and high lithium-ion conductivity, which is advantageous when using thick electrodes to meet a wide charge-discharge rate (C-rate) range. Furthermore, the stripping and electroplating efficiency of the Li anode used in the battery system is significantly improved when using the electrolyte disclosed herein. The electrolyte disclosed herein facilitates the manufacture of thick LFP-Li batteries with improved electrochemical performance.

[0035] Traditional LFP-Li battery systems typically use carbonate or carbonate-based electrolytes. Carbonate electrolytes have relatively low viscosity and high ionic conductivity, which is promising for thick-electrode batteries. However, carbonate electrolytes are porous for deposited lithium. These pores accelerate the reaction between lithium and the carbonate electrolyte, leading to shortened battery life. In some cases, charge and discharge capacities decrease significantly after a short period (e.g., 50 cycles). Furthermore, high-concentration electrolytes stabilize the lithium anode and offer high lithium utilization. However, high-concentration electrolytes also exhibit low ionic conductivity and high viscosity, resulting in poor rate performance. Therefore, thick LFP-Li battery systems require high-performance electrolytes.

[0036] Reference Figure 1This illustration shows a perspective view of a vehicle 10 having a battery pack 12 according to the present disclosure. The battery pack 12 is shown together with the exemplary vehicle 10. The vehicle 10 is an electric vehicle or a hybrid vehicle having wheels 11 driven by an electric motor / inverter 13. The electric motor / inverter 13 receives power from the battery pack 12. Although the vehicle 10 is shown as a passenger road vehicle, it should be understood that the battery pack 12 can be used with a variety of other types of vehicles. For example, the battery pack 12 can be used in marine vehicles such as boats or air vehicles such as drones or passenger planes. Furthermore, the battery pack 12 can be used as a stationary power source separate from and independent of the vehicle. The battery pack 12 includes a housing 14 for supporting a plurality of battery cells 18. In embodiments, the battery pack 12 may have fifty or more battery cells 18.

[0037] Now for reference Figure 2 The perspective view shows a setting according to one aspect of the present disclosure. Figure 1 The battery pack 12 shown contains battery cells 20 (as battery cells 18). Each battery cell 20 has a housing 22 or casing and at least one electrode stack 24, which further includes a thick LFP positive electrode 26, a negative electrode 28, an electrolyte 30, and / or a separator 31. Each battery cell 20 may have tens or hundreds of electrode stacks 24. Each electrode stack 24 is connected to current collectors 32, 34. The electrode stacks are placed in the housing 22, which is filled with electrolyte 30. The current collectors 32, 34 are thin metal plates or foils disposed on the sides of the electrode stacks 24 and / or the housing 22, and typically have a thickness of 5-50 micrometers (μm). The current collectors 32, 34 may be made of copper or aluminum and are attached to the electrode stacks 24 to transmit current to an external circuit (not shown).

[0038] The positive electrode 26 includes a current collector 32 and an active positive electrode material including an olivine-type positive electrode, such as LiFePO4 (LFP) and LiMn. 1-x Fe x PO4 (LMFP). In a specific embodiment, the positive electrode 26 includes an LFP positive electrode 26. The LFP positive electrode 26 uses lithium iron phosphate (LiFePO4) as the positive electrode material. Lithium is a key element for realizing electrochemical reactions within the battery and is the source of positively charged ions moving back and forth between the negative and positive electrodes during charge and discharge cycles. Lithium ions are intercalated into the crystal structure of iron phosphate, providing a stable platform for intercalation and deintercalation during charge and discharge processes. Iron phosphate provides a stable and robust platform for the intercalation and deintercalation of lithium ions during charge and discharge processes. Iron phosphate involves iron ions (Fe... 2+ / Fe 3+ The redox reaction of iron phosphate (FePO4) with lithium cations (Li) is responsible for the movement of electrons, thus generating an electric current. +The cathode and battery are paired to form lithium iron phosphate (LiFePO4). The phosphate structure enhances the stability and safety of LFP batteries, reducing the risk of thermal runaway or combustion. The LFP cathode and battery provide a consistent voltage level throughout discharge, ensuring stable performance in devices such as electric vehicles and portable electronics. These cathodes and batteries can withstand thousands of charge cycles without significant degradation, making them cost-effective and reliable for long-term use. The cathode 26 can be prepared using wet coating processes, dry film processes, dry powder coating processes, etc.

[0039] The positive electrode 26 may include an adhesive or a combination of adhesives. The adhesive is used to secure the positive electrode material within the battery cell in a compact and stable form. Some examples of adhesives that may be included in the positive electrode 26 include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), styrene-ethylene-butene-styrene copolymer (SEBS), etc. In one case, the capacity loading of the positive electrode 26 is higher than 4 mAh / cm³. 2 .

[0040] Still referencing Figure 2 The negative electrode 28 includes a negative current collector 34 and a negative active material layer. The negative active material layer contains metallic lithium or a lithium alloy. For example, the negative electrode 14 may include lithium aluminum (Li-Al), lithium silver (Li-Ag), and / or lithium silicon (Li-Si). The lithium content is equal to or greater than 50% by weight.

[0041] refer to Figure 2 The battery pack 12 includes an electrolyte 30. The electrolyte 30 includes a low-viscosity main salt, at least one functional salt, a low-viscosity solvent, and a cyclic ether solvent. The electrolyte 30 transports charged ions between the negative electrode 28 and the thick LFP positive electrode 26.

[0042] The low-viscosity main salt of electrolyte 30 includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or a lithium salt having the structure shown below, wherein R4 includes at least one of a fluorine (F) atom or a straight-chain C1-C6 fluoroalkyl group, and wherein R5 includes at least one of a fluorine (F) atom or a straight-chain C1-C6 fluoroalkyl group.

[0043]

[0044] Additionally, the concentration of the low-viscosity primary salt can be from about 0.6 mol / L (M) to about 2.0 M. In one embodiment, the concentration of the low-viscosity primary salt comprising LiTFSI is preferably from about 0.8 M to about 1.2 M. It should be understood that the concentration of the low-viscosity primary salt may include other concentrations and ranges disclosed herein. In this document, the term “about” is known to those skilled in the art. Alternatively, the term “about” may be understood to mean adding or subtracting 0.1 M.

[0045] Functional salts promote the formation of the solid electrolyte interphase (SEI) and the positive electrode electrolyte interphase (CEI). Functional salts may include at least one of lithium difluoro(oxalate)borate (LiDFOB), LiNO3, lithium perchlorate (LiClO4), LiAlCl4, LiBF4, LiB(C6H5)4, LiAsF6, or lithium bis(oxalate)borate (LiBOB). The concentration of the functional salt may be from about 0.05 M to about 0.6 M. Preferably, the concentration of the functional salt may be from about 0.1 M to about 0.5 M. In one embodiment, electrolyte 30 has a variety of functional salts, including LiDFOB at a concentration of about 0.2 M and LiNO3 at a concentration of about 0.3 M. Those skilled in the art will understand that functional salts may include other salts or combinations of salts having concentrations other than those listed herein. In the context of functional salts, the term "about" is known to those skilled in the art. Alternatively, the term "about" may be understood to mean adding or subtracting 0.01 M.

[0046] The electrolyte 30 used in the thick LFP-Li battery cell 20 includes a low-viscosity solvent. The low-viscosity solvent includes dimethyl glycol ether (DME). The concentration of dimethyl glycol ether (DME) can be from about 50% to about 100% of the total solvent volume. The total solvent includes both low-viscosity solvents and cyclic ether solvents. More preferably, the concentration of dimethyl glycol ether (DME) is from about 50% to about 80% of the total solvent volume. Those skilled in the art will understand that the low-viscosity solvent may include other solvents having concentrations different from those listed herein. In the context of low-viscosity solvents, the term "about" is known to those skilled in the art. Alternatively, the term "about" can be understood to mean a total solvent volume ratio plus or minus 1%.

[0047] The electrolyte 30 for the thick LFP-Li battery cell 20 comprises a cyclic ether solvent (or co-solvent). The cyclic ether solvent comprises a cyclic ether having fewer than 6 carbon atoms. For example, the cyclic ether solvent may comprise 1,4-dioxane (4 carbon atoms) and / or 1,3-dioxolane (DOL) (3 carbon atoms). The cyclic ether solvent may comprise one or more cyclic ethers in a concentration ranging from about 0% to about 50% of the total solvent volume. Preferably, the solvent has a volume ratio of 20% to 50% (inclusive) of the cyclic ether solvent. In one embodiment, the cyclic ether solvent comprises a 1:1 ratio of DME to DOL. Those skilled in the art will understand that the cyclic ether solvent may include other cyclic ethers having concentrations different from those listed herein. In the context of cyclic ether solvents, the term "about" is known to those skilled in the art. Alternatively, the term "about" may be understood to mean a total solvent volume ratio plus or minus 1%.

[0048] Cyclic ethers form a polymer coating on the lithium surface of the negative electrode 28 through the reaction of cyclic ethers with lithium metal. 1,4-Dioxacyclohexane and / or 1,3-dioxolane (DOL) are polymerized via a ring-opening reaction, subsequently forming a ring-opening product chain.

[0049] The electrolyte 30 disclosed herein is superior to prior art carbonate electrolytes and battery packs using carbonate electrolytes. Electrolyte 30 has low viscosity and high Li-ion conductivity, which is advantageous when using thick electrodes (i.e., thick LFP cathode 26) to meet a wide C-rate range application. Furthermore, when using the electrolyte 30 disclosed herein, the stripping and electroplating efficiency of the Li anode 28 used in the battery pack is significantly improved. The electrolyte disclosed herein enables thick LFP-Li batteries to have improved electrochemical performance.

[0050] This description is merely illustrative in nature and is in no way intended to limit the scope of this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in many forms. Therefore, while this disclosure includes specific embodiments, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, description, and appended claims.

Claims

1. An electrolyte for a thick LFP-Li battery system, comprising: Low viscosity primary salt with the following structure The main salt includes at least one of LiTFSI or lithium salt; At least one lithium-based functional salt; and Solvents, including low-viscosity solvents that are mixed with cyclic ether solvents.

2. The electrolyte according to claim 1, wherein, R4 includes at least one of a fluorine (F) atom or a straight-chain C1-C6 fluoroalkyl group.

3. The electrolyte according to claim 1, wherein, R5 includes at least one of a fluorine (F) atom or a straight-chain C1-C6 fluoroalkyl group.

4. The electrolyte according to claim 1, wherein, The concentration of the low-viscosity primary salt is from 0.6 M to 2.0 M.

5. The electrolyte according to claim 4, wherein, The concentration of the low-viscosity primary salt is 0.8M to 1.2M.

6. The electrolyte according to claim 1, wherein, The lithium-based functional salt includes at least one of lithium difluoro(oxalate)borate (LiDFOB), LiNO3, lithium perchlorate (LiClO4), LiAlCl4, LiBF4, LiB(C6H5)4, LiAsF6, or lithium bis(oxalate)borate (LiBOB).

7. The electrolyte according to claim 1, wherein, The concentration of the lithium-based functional salt is from 0.05 M to 0.6 M.

8. The electrolyte according to claim 7, wherein, The concentration of the lithium-based functional salt is from 0.1 M to 0.5 M.

9. The electrolyte according to claim 1, wherein, The low-viscosity solvent includes dimethyl ethylene glycol (DME).

10. The electrolyte according to claim 1, wherein, The cyclic ether solvent includes at least one of 1,3-dioxolane (DOL) or 1,4-dioxane.

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