Electrolyte comprising phosphotriester solvent for circulating lithium ion battery and battery comprising same

Abstract

The present invention relates to an electrolyte comprising a phosphotriester solvent for recycling a lithium ion battery and a battery comprising the electrolyte. An electrolyte for a circulating lithium ion battery includes an organic solvent and a lithium salt in the organic solvent. The organic solvent includes a primary solvent component and a secondary solvent component. The primary solvent component includes a phosphotriester having the formula R1O-P (= O) (OR2) (OR3), wherein R1, R2 and R3 are each independently a fluorinated or non-fluorinated organic group selected from the group consisting of hydrocarbyl, heterohydrocarbyl, silyl, siloxy, alkoxysilyl, cyano and alkylcyano. And the lithium salt comprises lithium nitrate (LiNO3). The lithium nitrate is present in the organic solvent at a concentration of 0.5 mol / L or more and 4 mol / L or less. The electrolyte is configured to provide a medium for conducting lithium ions between a negative electrode comprising a lithium-based electroactive negative electrode material and a positive electrode comprising an olivine-type lithium transition metal oxide.

Description

Technical Field

[0001] This disclosure relates to electrolytes for use in cycling lithium-ion battery packs, and more particularly to electrolytes comprising a triphosphate solvent, said electrolyte being formulated to improve the thermal and electrochemical stability of battery packs comprising lithium-based electroactive negative electrode materials. Background Technology

[0002] The information provided in this section is intended to provide a general overview of the background of this disclosure. The work of the currently named inventors described in this section, and the aspects of the specification that may not have been otherwise identified as prior art at the time of filing, are not expressly or impliedly acknowledged as prior art to this disclosure.

[0003] Cyclic lithium-ion battery packs typically include a positive electrode, a negative electrode spaced apart from the positive electrode, and an ion-conducting electrolyte that provides the medium for the conduction of lithium ions between the positive and negative electrodes during the discharge and charging of the battery pack. The electrolyte can be formulated to exhibit certain desired properties, including high ionic conductivity, high dielectric constant (related to the ability to dissolve high salts), good thermal stability, a wide electrochemical stability window, the ability to form a stable ion-conducting solid electrolyte interface on the surfaces of the positive and / or negative electrodes, and good chemical compatibility with other components of the battery pack. Summary of the Invention

[0004] According to one or more embodiments of this disclosure, an electrolyte for a cyclic lithium-ion battery pack comprises an organic solvent and a lithium salt in the organic solvent. The organic solvent comprises a primary solvent component and a secondary solvent component. The primary solvent component comprises a triphosphate having formula (1):

[0005]

[0006] Where R 1 R 2 and R 3 Each of the following is an independently selected fluorinated or non-fluorinated organic group: hydrocarbon group, heterohydrocarbon group, silyl group, siloxy group, alkoxysilyl group, cyano group, and alkylcyano group. The lithium salt includes lithium nitrate (LiNO3). The lithium nitrate is present in the organic solvent at a concentration greater than or equal to 0.5 mol / L and less than or equal to 4 mol / L.

[0007] The LiNO3 may be present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

[0008] The main solvent component may include at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

[0009] The phosphate triester of formula (1) can have a boiling point of 150 degrees Celsius or greater at 1 atmosphere.

[0010] The phosphate triester of formula (1) can have a melting point of less than or equal to -20 degrees Celsius at 1 atmosphere.

[0011] The main solvent component may account for more than or equal to 40% and less than or equal to 80% by volume of the organic solvent.

[0012] The secondary solvent component may include organic carbonates, ethers, or combinations thereof.

[0013] The viscosity of the phosphate triester of formula (1) can be greater than the viscosity of the secondary solvent component.

[0014] The secondary solvent component may comprise propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

[0015] The minor solvent component may account for more than or equal to 20% and less than or equal to 60% by volume of the organic solvent.

[0016] The lithium salt may further comprise at least one secondary lithium salt selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), bis(trifluoromethanesulfonyl)lithiumimide (LiN(CF3SO2)2), bis(fluorosulfonyl)imide lithium (LiN(FSO2)2), lithium tetraphenylborate (LiB(C6H5)4), bis(oxalate-containing)borate (LiB(C2O4)2), and lithium difluoro(oxalate-containing)borate (LiBF2(C2O4)).

[0017] In this case, the at least one secondary lithium salt may be present in the organic solvent at a concentration greater than 0 mol / L and less than or equal to 0.5 mol / L.

[0018] The electrolyte may further comprise at least one additive selected from succinic anhydride (SA), 1,3,2-dioxane-2,2-dioxide (DTD), trimethylsilyl phosphite (TMSPi), trimethylsilyl (TMSi), 1,3-dioxanepentane (DOL), and 1,4-dioxane (DOX). In this case, the at least one additive may constitute more than 0% and less than or equal to 5% by weight of the electrolyte.

[0019] According to one or more embodiments of this disclosure, a cyclic lithium-ion battery pack includes a negative electrode, a positive electrode spaced apart from the negative electrode, and an electrolyte configured to provide a medium for conducting lithium ions between the negative electrode and the positive electrode. The negative electrode comprises a lithium-based electroactive negative electrode material. The positive electrode comprises an electroactive positive electrode material comprising an olivine-type lithium transition metal oxide represented by the formula LiMePO4, wherein Me is a transition metal selected from Co, Ni, Mn, Fe, Al, and V. The electrolyte comprises an organic solvent and a lithium salt in the organic solvent. The organic solvent comprises a primary solvent component and a secondary solvent component. The primary solvent component comprises a triphosphate having the formula (1):

[0020]

[0021] Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano. The phosphate triester of formula (1) has a boiling point greater than or equal to 150 degrees Celsius at 1 atmosphere. The lithium salt includes lithium nitrate (LiNO3). The lithium nitrate is present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

[0022] The main solvent component may include at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

[0023] The secondary solvent component may comprise propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

[0024] The main solvent component may account for more than or equal to 40% and less than or equal to 50% by volume of the organic solvent.

[0025] The minor solvent component may account for more than or equal to 40% and less than or equal to 50% by volume of the organic solvent.

[0026] The lithium-based electroactive negative electrode material may contain more than 50% lithium.

[0027] The electroactive positive electrode material comprises LiFePO4 (LFP).

[0028] The present invention discloses the following solutions:

[0029] Option 1. An electrolyte for cycling lithium-ion battery packs, the electrolyte comprising:

[0030] An organic solvent comprising a primary solvent component and a secondary solvent component, said primary solvent component comprising a triphosphate having formula (1):

[0031]

[0032] Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano groups; and

[0033] The lithium salt in the organic solvent includes lithium nitrate (LiNO3), which is present in the organic solvent at a concentration greater than or equal to 0.5 mol / L and less than or equal to 4 mol / L.

[0034] Option 2. The electrolyte according to Option 1, wherein the LiNO3 is present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

[0035] Option 3. The electrolyte according to Option 1, wherein the main solvent component comprises at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

[0036] Scheme 4. The electrolyte according to Scheme 1, wherein the triphosphate of formula (1) has a boiling point of greater than or equal to 150 degrees Celsius at 1 atmosphere.

[0037] Scheme 5. The electrolyte according to Scheme 1, wherein the triphosphate of formula (1) has a melting point of less than or equal to -20 degrees Celsius at 1 atmosphere.

[0038] Option 6. The electrolyte according to Option 1, wherein the main solvent component accounts for more than or equal to 40% and less than or equal to 80% by volume of the organic solvent.

[0039] Option 7. The electrolyte according to Option 1, wherein the secondary solvent component comprises an organic carbonate, an ether, or a combination thereof.

[0040] Scheme 8. The electrolyte according to Scheme 7, wherein the viscosity of the triphosphate of formula (1) is greater than the viscosity of the secondary solvent component.

[0041] Option 9. The electrolyte according to Option 1, wherein the secondary solvent component comprises propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

[0042] Option 10. The electrolyte according to Option 1, wherein the minor solvent component accounts for more than or equal to 20% and less than or equal to 60% by volume of the organic solvent.

[0043] Scheme 11. The electrolyte according to Scheme 1, wherein the lithium salt further comprises at least one secondary lithium salt selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), bis(trifluoromethanesulfonyl)lithiumimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalate)borate (LiB(C2O4)2), and lithium difluoro(oxalate)borate (LiBF2(C2O4)).

[0044] Option 12. The electrolyte according to Option 11, wherein the at least one secondary lithium salt is present in the organic solvent at a concentration greater than 0 mol / L and less than or equal to 0.5 mol / L.

[0045] Option 13. The electrolyte according to Option 1, further comprising at least one additive selected from succinic anhydride (SA), 1,3,2-dioxane-2,2-dioxide (DTD), tri(trimethylsilyl) phosphite (TMSPi), trimethylsilyl (TMSi), 1,3-dioxanepentane (DOL), and 1,4-dioxane (DOX), wherein the at least one additive comprises more than 0% and less than or equal to 5% by weight of the electrolyte.

[0046] Option 14. A cyclic lithium-ion battery pack, the battery pack comprising:

[0047] Negative electrode, comprising lithium-based electroactive negative electrode material;

[0048] A positive electrode, spaced apart from the negative electrode and comprising an electroactive positive electrode material, the electroactive positive electrode material comprising an olivine-type lithium transition metal oxide represented by the formula LiMePO4, wherein Me is a transition metal selected from Co, Ni, Mn, Fe, Al, and V; and

[0049] An electrolyte configured to provide a medium for conducting lithium ions between the negative electrode and the positive electrode, the electrolyte comprising:

[0050] An organic solvent comprising a primary solvent component and a secondary solvent component, said primary solvent component comprising a triphosphate having formula (1):

[0051]

[0052] Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano groups, and

[0053] The triphosphate ester of formula (1) has a boiling point of 150 degrees Celsius or greater at 1 atmosphere; and

[0054] The lithium salt in the organic solvent includes lithium nitrate (LiNO3), which is present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

[0055] Option 15. The battery according to Option 14, wherein the main solvent component comprises at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

[0056] Option 16. The battery pack according to Option 15, wherein the secondary solvent component comprises propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

[0057] Option 17. The battery pack according to Option 16, wherein the main solvent component accounts for more than or equal to 40% and less than or equal to 50% by volume of the organic solvent.

[0058] Option 18. The battery pack according to Option 17, wherein the secondary solvent component accounts for more than or equal to 40% and less than or equal to 50% by volume of the organic solvent.

[0059] Option 19. The battery pack according to Option 14, wherein the lithium-based electroactive negative electrode material contains more than 50% lithium.

[0060] Option 20. The battery pack according to Option 14, wherein the electroactive positive electrode material comprises LiFePO4 (LFP).

[0061] The further applicability of this disclosure will be apparent from the detailed description, claims, and drawings. The detailed description and specific embodiments are intended to be illustrative only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0062] This disclosure will be more fully understood from the detailed description and the accompanying drawings, in which:

[0063] Figure 1 This is a schematic perspective view of a motor vehicle powered by a battery pack comprising multiple battery modules.

[0064] Figure 2 yes Figure 1 A schematic cross-sectional view of a portion of a battery pack module, which includes multiple cycle lithium-ion electrochemical cells or battery packs.

[0065] Figure 3 This is a schematic cross-sectional view of a cyclic lithium-ion battery pack, which includes a negative electrode, a positive electrode, a porous separator, and a permeable porous separator and is configured to provide an electrolyte for conducting lithium ions between the negative and positive electrodes.

[0066] In the accompanying drawings, reference numerals may be used repeatedly to designate similar and / or identical elements. Detailed Implementation

[0067] The electrolyte of this disclosure is formulated for use in cycling lithium-ion battery packs, particularly those comprising lithium-based electroactive negative electrode materials, to help improve their thermal and electrochemical stability. The electrolyte of this disclosure includes a triphosphate solvent with a relatively high boiling point, which effectively mitigates vaporization in cycling lithium-ion battery packs, even when the battery pack is operated at elevated temperatures, such as above 100°C, optionally above 120°C, or optionally above or equal to 150°C. In contrast, battery packs comprising ethers or organic carbonates as electrolyte solvents (excluding the triphosphate solvent of this disclosure) may experience vaporization when operated at temperatures above about 80°C or above about 120°C due to the relatively low boiling points of ethers and organic carbonate solvents. This can lead to undesirable expansion of the battery pack, electrolyte leakage, and potentially undesirable exposure of battery pack components to air. Furthermore, the triphosphate solvent of this disclosure can effectively solubilize relatively high concentrations of lithium nitrate (LiNO3) compared to ethers and organic carbonate solvents. Including such a high LiNO3 concentration (e.g., greater than 0.5 mol) in the electrolyte of a battery pack that includes a lithium-based electroactive negative electrode material (e.g., a lithium metal negative electrode) can help promote the formation of a uniform and stable nitrogen-containing solid electrolyte interface (SEI) on the lithium-based electroactive negative electrode material during the initial cycling of the battery pack. This can help mitigate the formation of lithium dendrites and improve the cycling stability and capacity retention of the battery pack.

[0068] Figure 1 A motor vehicle 2 is depicted, powered by an electric motor 4, which draws power from a battery pack 6 comprising one or more battery modules 8. The battery modules 8 may be arranged in series and / or parallel and electrically coupled together to meet the capacity and power requirements of the electric motor 4. The vehicle 2 may be a pure electric vehicle and may be powered entirely by the electric motor 4, or the vehicle 2 may be a hybrid electric vehicle and may be powered by both the electric motor 4 and an internal combustion engine (not shown).

[0069] like Figure 2As shown, each battery module 8 includes one or more electrochemical cells or battery packs 10 capable of cycling lithium-ions. In practice, the battery packs 10 in the battery module 8 are typically assembled as a stacked layer, including a negative electrode layer 12, a negative electrode current collector 13, a positive electrode layer 14, a positive electrode current collector 15, and a separator layer 16. Each battery pack 10 is defined by the negative electrode layer 12 and the positive electrode layer 14, which are spaced apart from each other by the separator layer 16. In practice, the separator layer 16 may be permeated with an electrolyte that provides a medium for conducting lithium ions between the negative electrode layer 12 and the positive electrode layer 14, or the separator layer 16 itself may serve as the electrolyte. The negative electrode layer 12 is disposed on and electrically communicated with the negative electrode current collector 13, while the positive electrode layer 14 is disposed on and electrically communicated with the positive electrode current collector 15. Figure 2 As shown, for efficiency, these layers can be stacked such that some negative electrode current collectors 13 and some positive electrode current collectors 15 are double-sided and include a negative electrode layer 12 or a positive electrode layer 14 on each side. In this arrangement, adjacent negative electrode layers 12 and positive electrode layers 14 share a single negative electrode current collector 13 or a positive electrode current collector 15.

[0070] Figure 3 An electrochemical cell or battery pack 20 for cycling lithium-ion batteries is depicted. The battery pack 20 can generate current during discharge, which can be used to power a load device (e.g., an electric motor 4), and can be charged by connecting to a power source. Similar to... Figure 1 and Figure 2 The battery pack 10 depicted herein, in one aspect, can be used to power the electric motor 4 of the motor vehicle 2. Additionally or alternatively, the battery pack 20 can be used in other transportation applications (e.g., motorcycles, boats, tractors, buses, motorbikes, mobile homes, campervans, tanks, and aircraft), and can be used to power a wide variety of other fixed and / or portable electronic devices, components, and devices used in various other industries and applications, including industrial, residential, and commercial buildings, consumer products, industrial equipment and machinery, agricultural or farm equipment, and heavy machinery (as non-limiting examples).

[0071] Battery pack 20 includes a negative electrode 22, a positive electrode 24, a separator 26, and an electrolyte 28, which provides a medium for conducting lithium ions between the negative electrode 22 and the positive electrode 24. The negative electrode 22 is disposed on the main surface of the negative electrode current collector 30, while the positive electrode 24 is disposed on the main surface of the positive electrode current collector 32. In practice, the negative electrode current collector 30 and the positive electrode current collector 32 are electrically coupled to a power source or load 34 (e.g., a motor 4) via an external circuit 36. The negative electrode 22 and the positive electrode 24 are configured such that an electrochemical potential difference is established between them when the battery pack 20 is at least partially charged. During discharge, the electrochemical potential established between the negative electrode 22 and the positive electrode 24 drives spontaneous reduction and oxidation (redox) reactions within the battery pack 20 and releases lithium ions and electrons from the negative electrode 22. Released lithium ions travel from the negative electrode 22 through the separator 26 and the electrolyte 28 to the positive electrode 24, while electrons travel from the negative electrode 22 to the positive electrode 24 via the external circuit 36, generating an electric current. After the negative electrode 22 has been partially or completely depleted of lithium, the battery pack 20 can be charged by connecting the negative electrode 22 and the positive electrode 24 to a power source 34. This drives a non-spontaneous redox reaction within the battery pack 20 and releases lithium ions and electrons from the positive electrode 24. Repeated discharge and charge cycles of the battery pack 20 are referred to herein as "cycles," with one complete charge event followed by one complete discharge event considered as a complete cycle.

[0072] The negative electrode 22 is configured to store and release lithium ions to facilitate the charging and discharging of the battery pack 20, respectively. The negative electrode 22 may be in the form of a continuous layer of material disposed on the main surface of the negative electrode current collector 30. The negative electrode 22 comprises a lithium-based electrochemically active (electroactive) material and may contain more than 50% lithium, optionally more than or equal to 60% lithium, optionally more than or equal to 70% lithium, optionally more than or equal to 80% lithium, optionally more than or equal to 90% lithium, or optionally more than or equal to 99% lithium by weight. In one aspect, the lithium-based electroactive material of the negative electrode 22 may comprise an alloy of lithium with at least one metallic element selected from aluminum (Al), silver (Ag), silicon (Si), indium (In), and tin (Sn). In another aspect, the negative electrode 22 may be non-porous and may be substantially free of polymer binders. In addition, the negative electrode 22 may be substantially free of carbon, carbon-based materials (e.g., graphite, activated carbon, carbon black and graphene), silicon, transition metal oxides, transition metal phosphides, transition metal sulfides and / or transition metal nitrides.

[0073] The positive electrode 24 is configured to store and release lithium ions during the discharge and charging of the battery pack 20. The positive electrode 24 may be in the form of a continuous porous layer disposed on the main surface of the positive electrode current collector 32. The positive electrode 24 comprises an electrochemically active (electroactive) material (electroactive positive electrode material), a polymer binder, and optionally a conductive material. In some aspects, the electroactive material of the positive electrode 24 may be a granular material, and the particles of the electroactive material of the positive electrode 24 may be mixed with the polymer binder and optionally the conductive material.

[0074] The electroactive material of the positive electrode 24 can store and release lithium ions by undergoing a reversible redox reaction with lithium at a higher electrochemical potential than that of the electrochemically active material of the negative electrode 22, resulting in an electrochemical potential difference between the two electrodes 22. In this aspect, the electroactive material of the positive electrode 24 may comprise an intercalation host material capable of undergoing reversible insertion or intercalation of lithium ions; for example, the electroactive material of the positive electrode 24 may comprise a lithium transition metal oxide. In this aspect, the electroactive material of the positive electrode 24 may comprise an olivine-type lithium transition metal oxide represented by the formula LiMePO4, where Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or combinations thereof). Examples of olivine-type lithium transition metal oxide electroactive positive electrode materials include LiFePO4 (LFP), LiCoPO4, LiMnPO4, LiNiPO4, and combinations thereof. In this aspect, the electroactive material of the positive electrode 24 may comprise LiFePO4. The electroactive material of the positive electrode 24 may account for more than or equal to 80% by weight, or optionally more than or equal to 90%, and less than or equal to 98%, or optionally less than or equal to about 95%.

[0075] The polymer binder of the positive electrode 24 is electrochemically inert and may be included in the positive electrode 24 to provide structural integrity and / or facilitate adhesion of the positive electrode 24 to the main surface of the positive electrode current collector 32. Examples of polymer binders include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), nitrile rubber (NBR), styrene-butadiene rubber (SBR), styrene-ethylene-butene-styrene copolymer (SEBS), polyacrylate, alginate, polyacrylic acid, and combinations thereof. The polymer binder may constitute greater than or equal to 1% by weight of the positive electrode 24, or optionally greater than or equal to 5%, and less than or equal to 20%.

[0076] The optional conductive material of the positive electrode 24 is electrochemically inert and may be included in the positive electrode 24 to provide sufficient conductivity to support electron permeation therefrom. Examples of conductive materials include carbon-based materials, metals (e.g., nickel), and / or conductive polymers. Examples of carbon-based conductive materials include carbon black (CB) (e.g., acetylene black), graphite, graphene (e.g., graphene nanosheets, GNP), graphene oxide, carbon nanotubes (CNTs), and / or carbon fibers (e.g., carbon nanofibers). Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and / or polypyrrole. When included in the positive electrode 24, the optional conductive material may constitute more than 0%, optionally more than or equal to 5%, or optionally more than or equal to 10%, and less than or equal to 30% of the positive electrode 24 by weight.

[0077] The separator 26 physically separates and electrically isolates the negative electrode 22 and the positive electrode 24 from each other while allowing lithium ions to pass through. The separator 26 has an open microporous structure and may contain organic and / or inorganic materials. For example, the separator 26 may contain a polymer. Examples of polymers used for the separator 26 include polyolefins (e.g., polyethylene, PE and / or polypropylene, PP), polyamides (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVDF), poly(vinyl chloride) (PVC), and combinations thereof. In one form, the separator 26 may comprise a polymer laminate, such as a laminate of PE and PP. In another aspect, the separator 26 may comprise a ceramic coating (not shown) disposed on one or both sides thereon. In this case, the ceramic coating may comprise particles of alumina (Al2O3) and / or silica (SiO2).

[0078] Electrolyte 28 is ionicly conductive and configured to provide a medium for lithium-ion conduction between negative electrode 22 and positive electrode 24. Furthermore, electrolyte 28 is formulated to improve the electrochemical performance and cycle life of battery pack 20. For example, by preventing or inhibiting undesirable chemical reactions between components of battery pack 20, which could otherwise lead to a decrease in capacity retention after repeated cycles. Electrolyte 28 contains an organic solvent, a lithium salt, and optional additives.

[0079] The organic solvent in electrolyte 28 comprises a mixture of a primary solvent component and a secondary solvent component. The volume ratio (primary solvent component: secondary solvent component) of the organic solvent may be greater than or equal to 2:3, or optionally greater than or equal to 5:4, and less than or equal to 4:1, or optionally less than or equal to 3:2. The organic solvent may constitute greater than or equal to 80%, or optionally greater than or equal to 85%, and less than or equal to 95%, or optionally less than or equal to 90% by weight of electrolyte 28.

[0080] The primary solvent component is formulated to have a relatively high boiling point to help prevent or suppress vaporization and expansion of the battery pack 20 at high operating temperatures (e.g., temperatures greater than 100°C, optionally greater than 120°C, or optionally greater than 120°C, or optionally greater than or equal to 150°C). Furthermore, the primary solvent component may be formulated to have a low melting point to provide good performance of the battery pack 20 at low operating temperatures. For example, at 1 atmosphere (Atm), the primary solvent component may have a melting point less than or equal to 5°C, optionally less than or equal to -20°C, or optionally less than or equal to -50°C, and a boiling point greater than or equal to 150°C, optionally greater than or equal to 180°C, optionally greater than or equal to 200°C, or optionally greater than or equal to 220°C. In addition, the primary solvent component is formulated to effectively solvate the lithium salt in the electrolyte 28 and to provide thermal stability and flame-retardant properties to the electrolyte 28. The main solvent component may account for more than or equal to 40%, optionally more than or equal to 45%, or optionally more than or equal to 50%, and less than or equal to 80%, optionally less than or equal to 60%, or optionally less than or equal to 55% of the organic solvent by volume.

[0081] The main solvent component comprises a triphosphate having formula (1):

[0082]

[0083] Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano.

[0084] A "hydrocarbon group" is a functional group containing only hydrogen and carbon atoms, including branched or straight-chain, saturated or unsaturated, cyclic, polycyclic, or acyclic groups. Hydrocarbon groups are formed by removing at least one hydrogen atom from a hydrocarbon molecule. Depending on the number of hydrogen atoms removed, hydrocarbon groups can be monovalent (formed by removing one hydrogen atom, also called a hydrocarbon group), divalent (formed by removing two hydrogen atoms, also called a hydrocarbon-like group), and similar. Examples of monovalent hydrocarbon groups include alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, and ynyl. Examples of divalent hydrocarbon groups include alkylene, cycloalkylene, alkenyl, ynylene, and arylene.

[0085] "Heteroalkyl group" refers to a hydrocarbon group in which at least one carbon atom is replaced by a heteroatom such as nitrogen, oxygen, sulfur, phosphorus, boron, or silicon. Examples of heteroalkyl groups include alkoxy, aryloxy, and ethers (e.g., –CH2OCH3).

[0086] "Silyl" refers to a functional group having the formula –SiR'R"R'", where R', R" and R'" are each independently H, a hydrocarbon group or a heterohydrocarbon group.

[0087] "Silyloxy group" refers to a functional group having the formula –OSiR'R"R'", where R', R" and R'" are each independently H, a hydrocarbon group or a heterohydrocarbon group.

[0088] "Alkoxysilyl" refers to a functional group having the formula -Si(OR)3, where R is H, a hydrocarbon group, a heterohydrocarbon group, or -Si(OR)3.

[0089] "Cyano" refers to a functional group with the formula -C=N.

[0090] "Cyanoalkyl" refers to a functional group having the formula -R'C≡N, where R' is a divalent hydrocarbon group.

[0091] A "fluorinated" organic group is an organic group in which at least one hydrogen atom bonded to a carbon atom is replaced by a fluorine (F) atom. The organic group can be polyfluorinated, in which more than one H atom is replaced by n F atoms, or the organic group can be perfluorinated, in which all H atoms are replaced by F atoms.

[0092] In this respect, R in the phosphate triester of formula (1) 1 R 2 and R 3 It may contain ethyl (–CH2CH3), and the main solvent component may contain tri(ethyl) phosphate (TEP), having a melting point of about -56.5°C and a boiling point of about 215°C at 1 atm.

[0093] In this respect, R in the phosphate triester of formula (1) 1 R 2 and R 3 It may contain trifluoroethyl (–CH2CF3), and the main solvent component may contain tris(2,2,2-trifluoroethyl)) phosphate, having a melting point of about -22°C and a boiling point of about 186°C at 1 atm.

[0094] In this respect, R in the phosphate triester of formula (1) 1 R 2 and R 3 It may contain 2-cyanoethyl (–CH2CH2CN), and the main solvent component may contain tris(2-cyanoethyl) phosphate, having a boiling point of about 162 °C at 1 Atm.

[0095] In this respect, R in the phosphate triester of formula (1) 1 R 2 and R 3 It may contain a trimethylsilyl group (-Si(CH3)3), and the main solvent component may contain trimethylsilyl phosphate, having a melting point of about 4°C and a boiling point of about 228°C at 1 Atm.

[0096] Compared to the primary solvent component, the secondary solvent component has a relatively low viscosity and is included in the electrolyte 28 to provide a suitably low viscosity to the electrolyte 28, which can help enhance the viscosity of lithium-ion (Li-ion) electrolytes. + This diffusion and transport through the electrolyte 28 improves the electrochemical performance of the battery pack 20. Furthermore, the minor solvent component is formulated to provide a wide electrochemical stability window to the electrolyte 28 and can facilitate the formation of a solid electrolyte interface (SEI) on the surface of the negative electrode 22 and a cathode electrolyte interface (CEI) on the surface of the positive electrode 24. This helps prevent or suppress undesirable chemical reactions between the electrolyte 28 and the negative electrode 22, respectively, during cycling of the battery pack 20. The minor solvent component may constitute more than or equal to 20%, optionally more than or equal to 30%, or optionally more than or equal to 40% by volume of the organic solvent, and less than or equal to 60%, optionally less than or equal to 50%, or optionally less than or equal to 40%.

[0097] The secondary solvent component may comprise organic carbonates, ethers, or combinations thereof. For example, the secondary solvent component may comprise cyclic organic carbonates, linear organic carbonates, aliphatic ethers, cyclic ethers, or combinations thereof. Non-limiting examples of cyclic organic carbonates include ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and combinations thereof. Non-limiting examples of linear organic carbonates include diethyl carbonate (DEC), methyl methyl carbonate (EMC), (2,2,2-trifluoroethyl) carbonate (FEMC), di-(2,2,2-trifluoroethyl) carbonate (DFDEC), and combinations thereof. Non-limiting examples of aliphatic ethers include triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether (TEGDME), 1,3-dimethoxypropane (DMP), 1,2-dimethoxyethane (DME), and combinations thereof. Non-limiting examples of cyclic ethers include 1,4-dimethoxybenzene (DMB). In this embodiment, the secondary solvent component may comprise PC or a mixture of FEC and DEC. In an embodiment where the secondary solvent component comprises a mixture of FEC and DEC, the volume ratio of FEC to DEC (FEC:DEC) may be greater than or equal to 1:2 and less than or equal to 1:4; for example, the volume ratio of FEC to DEC in the secondary solvent component may be about 1:3.

[0098] Compared to organic carbonates and / or ethers, the phosphate triesters of formula (1) of this disclosure can effectively solubilize relatively high concentrations of lithium nitrate (LiNO3), and thus allow for the dissolution of relatively high concentrations of LiNO3 in electrolyte 28. For example, the solubility of LiNO3 in phosphate triesters of formula (1) (e.g., TEP) can be greater than or equal to 1 mol / L (mol / L or mole), optionally greater than or equal to 1.5 mol, or optionally greater than or equal to 2 mol. By comparison, the solubility of LiNO3 in organic carbonates (e.g., EC, PC, FEC, DEC, EMC, FEMC and / or DFDEC) and / or ethers (e.g., TEGDME, DMP, DME and / or DMB) can be less than 1 mol, or less than or equal to 0.9 mol.

[0099] The lithium salt is soluble in an organic solvent and is formulated to provide a channel for lithium ions to pass through the electrolyte 28. The lithium salt may constitute greater than or equal to 5% by weight of the electrolyte 28, optionally greater than or equal to about 10%, and less than or equal to 20%, or optionally less than or equal to 15%.

[0100] The lithium salt in electrolyte 28 includes lithium nitrate (LiNO3). During the initial cycling of battery pack 20, lithium nitrate can effectively participate in the formation of a uniform, stable, nitrogen-containing solid electrolyte interface (SEI) on the surface of the lithium-based electroactive material of negative electrode 22. This can help prevent or inhibit the formation of lithium dendrites on negative electrode 22 and improve the cycle stability and capacity retention of battery pack 20. Lithium nitrate may be present in an organic solvent at concentrations greater than or equal to 0.5 mol / L (mol / L or moles), optionally greater than or equal to 0.8 mol, optionally greater than or equal to 1 mol, or optionally greater than or equal to 1.2 mol, and less than or equal to 4 mol, optionally less than or equal to 3 mol, optionally less than or equal to 2.5 mol, optionally less than or equal to 2 mol, optionally less than or equal to 1.8 mol, optionally less than or equal to 1.4 mol, or optionally less than or equal to 1.2 mol.

[0101] In addition to LiNO3, the lithium salt may optionally contain one or more secondary lithium salts. Examples of secondary lithium salts that may optionally be included in electrolyte 28 in combination with LiNO3 include lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2)(LiTFSI), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2)(LiFSI), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalate)borate (LiB(C2O4)2)(LiBOB), lithium difluoro(oxalate)borate (LiBF2(C2O4))(LiDFOB), and combinations thereof. When present, the secondary lithium salt may be contained in an organic solvent at a concentration greater than 0 moles, or optionally greater than or equal to 0.2 moles, and less than or equal to 2 moles, or optionally less than or equal to 0.5 moles.

[0102] Optional additives may be included in the electrolyte 28 to provide certain desirable properties to the electrolyte 28 and / or the battery pack 20. For example, optional additives may be formulated to facilitate the formation of an SEI on the negative electrode 22, the formation of a CEI on the positive electrode 24, the removal of hydrofluoric acid (HF), and / or the prevention or inhibition of the dissolution of transition metal ions from the electrode 24. Examples of additives that may be optionally included in the electrolyte 28 include succinic anhydride (SA), 1,3,2-dioxothiacyclohexane-2,2-dioxide (DTD), tri(trimethylsilyl) phosphite (TMSPi), trimethylsilyl (TMSi), 1,3-dioxolane (DOL), 1,4-dioxane (DOX), and combinations thereof. When present, optional additives may be included in electrolyte 28 in an amount greater than 0% by weight and less than or equal to 5%, optionally less than or equal to 3%, optionally less than or equal to 1%, or optionally less than or equal to 0.5%, or optionally less than or equal to 0.1%.

[0103] The negative electrode current collector 30 and the positive electrode current collector 32 are conductive and electrochemically inert, and respectively provide electrical connections between the external circuit 36 ​​and the negative electrode 22 and the positive electrode 24. In this aspect, the negative electrode current collector 30 and the positive electrode current collector 32 can be made of metal and can be in the form of a non-porous metal foil, a perforated metal foil, a porous metal mesh, or a combination thereof. The negative electrode current collector 30 can be made of copper, nickel, or their alloys, stainless steel, or other suitable conductive materials. The positive electrode current collector 32 can be made of aluminum (Al) or other suitable conductive materials.

[0104] The foregoing description is merely exemplary and is in no way intended to limit this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in various forms. Therefore, although this disclosure includes specific examples, its true scope should not be limited thereto, as other modifications will become apparent upon examination of the drawings, specification, and the following claims. It should be understood that one or more steps within the method may be performed in a different order (or simultaneously) without altering the principles of this disclosure. Furthermore, although the embodiments are described above as having certain features, any one or more features described with respect to any embodiment of this disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if such combination is not explicitly described. In other words, the embodiments are not mutually exclusive, and substitution of one or more embodiments for each other remains within the scope of this disclosure.

[0105] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a” and “the” used herein are intended to include the plural forms as well. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of a designated feature, element, composition, step, integer, operation, and / or component, but do not exclude the presence or inclusion of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. Although the open-ended terms “comprising,” “including,” and “having” should be understood as non-limiting terms used to describe and claim protection for the various embodiments described herein, in some respects these terms can be understood as more restrictive and binding terms such as “consisting of” or “substantially consisting of.” Therefore, for any given embodiment enumerating compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps, this disclosure also expressly includes embodiments consisting of or substantially consisting of these enumerated compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps. In the case of “consisting of…”, the alternative embodiment does not include any additional compositions, materials, components, elements, ingredients, features, integers, operating and / or method steps. In the case of “essentially composed of…”, such an embodiment does not include any additional compositions, materials, components, elements, ingredients, features, integers, operating and / or method steps that substantially affect the essential and novel features, but may include any compositions, materials, components, elements, ingredients, features, integers, operating and / or method steps that do not substantially affect the essential and novel features.

[0106] The phrase “at least one of A, B and C” as used in this article should be interpreted as referring to the logic of using non-exclusive OR (A or B or C), and should not be interpreted as referring to “at least one of A, at least one of B and at least one of C”.

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

[0108] As used herein, the term "metal" can refer to a pure elemental metal, or an alloy of an elemental metal and one or more other metallic or nonmetallic elements (referred to as "alloying" elements). Alloying elements can be selected to impart desirable properties to the alloy that are not present in the base metallic elements.

Claims

1. An electrolyte for use in a cyclic lithium-ion battery pack, the electrolyte comprising: Organic solvents, comprising: The main solvent component comprises a triphosphate having formula (1): Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano groups, and The triphosphate ester of formula (1) has a boiling point of 150 degrees Celsius or greater at 1 atmosphere, and Secondary solvent components, comprising organic carbonates, ethers, or combinations thereof; and The lithium salt in the organic solvent includes lithium nitrate (LiNO3). The lithium nitrate is present in the organic solvent at a concentration greater than or equal to 0.5 mol / L and less than or equal to 4 mol / L, and Optionally, the LiNO3 is present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

2. The electrolyte according to claim 1, wherein the main solvent component comprises at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

3. The electrolyte of claim 1, wherein the primary solvent component comprises, by volume, 40% or more and 80% or less of the organic solvent, and wherein the secondary solvent component comprises, by volume, 20% or more and 60% or less of the organic solvent.

4. The electrolyte according to claim 1, wherein The viscosity of the triphosphate in formula (1) is greater than that of the minor solvent component. Optionally, the phosphate triester of formula (1) has a melting point of less than or equal to -20 degrees Celsius at 1 atmosphere, and Optionally, the secondary solvent component comprises propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

5. The electrolyte according to claim 1, wherein the lithium salt further comprises a compound selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and bis(trifluoromethanesulfonyl) salts. The organic solvent contains at least one secondary lithium salt of lithium imide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalate)borate (LiB(C2O4)2), and lithium difluoro(oxalate)borate (LiBF2(C2O4)), wherein the at least one secondary lithium salt is present in the organic solvent at a concentration greater than 0 mol / L and less than or equal to 0.5 mol / L.

6. The electrolyte according to claim 1, further comprising at least one additive selected from succinic anhydride (SA), 1,3,2-dioxane-2,2-dioxide (DTD), tri(trimethylsilyl) phosphite (TMSPi), trimethylsilyl (TMSi), 1,3-dioxanepentane (DOL), and 1,4-dioxane (DOX), wherein the at least one additive comprises more than 0% and less than or equal to 5% by weight of the electrolyte.

7. A cyclic lithium-ion battery pack, the battery pack comprising: A negative electrode comprising a lithium-based electroactive negative electrode material, wherein the lithium-based electroactive negative electrode material comprises more than 50% lithium; A positive electrode, spaced apart from the negative electrode and comprising an electroactive positive electrode material, the electroactive positive electrode material comprising an olivine-type lithium transition metal oxide represented by the formula LiMePO4, wherein Me is a transition metal selected from Co, Ni, Mn, Fe, Al, and V, optionally wherein the electroactive positive electrode material comprises LiFePO4; and An electrolyte configured to provide a medium for conducting lithium ions between the negative electrode and the positive electrode, the electrolyte comprising: Organic solvents, comprising: The main solvent component comprises a triphosphate having formula (1): Where R 1 R 2 and R 3 Each is independently a fluorinated or non-fluorinated organic group selected from hydrocarbon, heterohydrocarbon, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano groups, and The triphosphate ester of formula (1) has a boiling point of 150 degrees Celsius or greater at 1 atmosphere, and Secondary solvent components, comprising organic carbonates, ethers, or combinations thereof; and The lithium salt in the organic solvent includes lithium nitrate (LiNO3), which is present in the organic solvent at a concentration greater than or equal to 0.8 mol / L and less than or equal to 2 mol / L.

8. The battery pack according to claim 7, wherein the main solvent component comprises at least one triphosphate selected from tri(ethyl) phosphate (TEP), tri(2,2,2-trifluoroethyl) phosphate, tri(2-cyanoethyl) phosphate and tri(trimethylsilyl) phosphate.

9. The battery pack of claim 7, wherein the secondary solvent component comprises propylene carbonate (PC) or a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

10. The battery pack of claim 7, wherein the primary solvent component comprises, by volume, 40% or more and 50% or less of the organic solvent, and wherein the secondary solvent component comprises, by volume, 40% or more and 50% or less of the organic solvent.

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