Electrolyte, and secondary battery and electric device comprising same

Abstract

The invention provides an electrolyte which comprises a solvent and a lithium supplement additive, the lithium supplement additive is selected from at least one of lithium salt with oxalate, lithium oxide and lithium peroxide, the solvent comprises at least one compound of formula (I), R1 is C1-6 fluoroalkyl, R2 is C1-6 fluoroalkyl, and R3 is C1-6 fluoroalkyl. R2 is a hydrogen atom, a C1-6 alkyl group or a C1-6 fluoroalkyl group; and n represents 1 or 2. And the negative-electrode-free metal lithium secondary battery can realize longer cycle life under higher charging cut-off voltage. # imgabs0 #

Description

Electrolyte, secondary battery containing same, and electrical device Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to an electrolyte, and a secondary battery and an electrical device containing the electrolyte. Background Art

[0002] With the widespread adoption of portable electronics and electric vehicles, the development of secondary batteries with higher energy density has become a research hotspot. Anode-free lithium metal batteries, which eliminate the need for initial anode material, offer the ultimate solution for increasing battery cell energy density. However, due to the initial absence of excess metallic lithium on the anode current collector surface, anode-free lithium metal batteries suffer from poor cycle life. In particular, their long-term cycling capability at high operating voltages above 4.5V remains to be improved.

[0003] In this regard, existing technologies typically employ a positive electrode lithium replenishment strategy, adding an appropriate amount of lithium-rich material to the positive electrode coating. This releases the lithium source after the first cycle, resulting in a loss of cyclability. This strategy then provides excess lithium source on the negative electrode side to compensate for the loss of active lithium. However, this strategy creates a large amount of dead volume and mass within the positive electrode, resulting in a reduction in energy density. It also hinders the maintenance of a good conductive network, compromising both long-term cycling and rate performance.

[0004] Therefore, the art needs a technical solution that can achieve long-cycle high-voltage, high-energy-density, negative-electrode-free lithium metal batteries.

[0005] Summary of the Invention

[0006] The present application has been made in view of the above-mentioned problems, and its object is to provide an electrolyte, and a secondary battery and an electric device containing the electrolyte.

[0007] In order to achieve the above object, the present application provides an electrolyte comprising a solvent and a lithium supplement additive, wherein the lithium supplement additive is selected from at least one of the following: a lithium salt having an oxalate group, lithium oxide, and lithium peroxide, and the solvent comprises at least one compound of formula (I):

[0008]

[0009] wherein R1 is a C1-6 fluoroalkyl group; R2 is a hydrogen atom, a C1-6 alkyl group, or a C1-6 fluoroalkyl group; and n represents 1 or 2. The electrolyte of the present application can enable a negative electrode-free metal lithium secondary battery to achieve a longer cycle life at a higher charge cutoff voltage.

[0010] In any embodiment, the lithium-supplementing additive is selected from at least one of lithium oxalate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxide, and lithium peroxide. Alternatively, the lithium-supplementing additive is selected from at least one of lithium oxalate, lithium bisoxalatoborate, and lithium difluorooxalatoborate. Further selecting the above lithium-supplementing additive facilitates effective lithium-supplementing, thereby further improving the cycle life of the negative-electrode-free lithium metal battery.

[0011] In any embodiment, in formula (I), R1 is a C1-4 fluorinated chain alkyl group, optionally a C1-4 fluorinated straight-chain alkyl group; and / or R2 is a hydrogen atom, a C1-4 chain alkyl group or a C1-4 fluorinated chain alkyl group, optionally a hydrogen atom, a C1-4 straight-chain alkyl group or a C1-4 fluorinated straight-chain alkyl group.

[0012] In any embodiment, the compound of formula (I) is selected from at least one of the following compounds:

[0013]

[0014]

[0015] Optionally, the compound of formula (I) is selected from at least one of I-2, I-11, I-66 and I-68, more preferably I-2 and / or I-66.

[0016] Further selecting the above formula (I) is beneficial to the stable circulation of the electrolyte at a high operating voltage, and is helpful to further improve the cycle life.

[0017] In any embodiment, the concentration of the lithium replenishing additive is 0.1 M to 1 M, optionally 0.3 M to 0.7 M, and more optionally 0.4 M to 0.6 M. Using the lithium replenishing additive concentration within the above range can effectively achieve the lithium replenishment effect without affecting the ion transport performance of the electrolyte, which is more conducive to the long cycle of high-voltage negative electrode-free lithium metal batteries.

[0018] In any embodiment, the solvent comprises at least 50% by weight, optionally at least 70% by weight, more optionally at least 90% by weight of a compound of formula (I), based on the total mass of the solvent. A solvent comprising the compound of formula (I) in such an amount is more conducive to improving the oxidative stability of the electrolyte and improving cycle life.

[0019] In any embodiment, the electrolyte of the present application further comprises an electrolyte salt, wherein the electrolyte salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, and lithium difluorophosphate; alternatively, the electrolyte salt is at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide; more alternatively, the electrolyte salt is lithium bis(fluorosulfonyl)imide. The above electrolyte salt is selected to be well soluble in the solvent and to decompose on the negative electrode surface to form an inorganic fluorine-rich SEI component, which further facilitates the long cycle of the negative electrode-free metal lithium battery.

[0020] In any embodiment, the concentration of the electrolyte salt is 0.5 M to 5 M, optionally 1 M to 3 M, and more optionally 1.5 M to 2.5 M. The electrolyte lithium salt within the above concentration range can provide the electrolyte with ideal ion conductivity and viscosity, and is beneficial to the stability of the electrolyte to the positive and negative electrodes, especially the oxidation resistance of the positive electrode, thereby further promoting the cycle life of the lithium metal secondary battery under high voltage.

[0021] A second aspect of the present application provides a secondary battery comprising the electrolyte of the first aspect of the present application.

[0022] In any embodiment, the secondary battery of the present application further includes a negative electrode plate, which includes a negative electrode current collector and a coating optionally provided on at least one surface of the negative electrode current collector; wherein the coating is selected from the following metal or metal oxide coatings: tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, zinc oxide, aluminum oxide and titanium oxide, optionally silver, gold or titanium oxide.

[0023] In any embodiment, the thickness of the coating is at most 200 nm, optionally at most 100 nm. Such a coating helps the battery achieve good cycle life.

[0024] A third aspect of the present application provides an electrical device comprising a secondary battery selected from any one of claims 9-11.

[0025] The electrolyte of the present application can enable the negative electrode-free liquid metal lithium secondary battery to achieve a longer cycle life at a high operating voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0027] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .

[0028] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0029] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0030] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0031] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0032] Description of reference numerals:

[0033] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0034] Below, the embodiments of the electrolyte, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0040] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0041] With the widespread use of portable electronic products and electric vehicles, the development of secondary batteries with higher energy density has become a research hotspot. Negative electrode-free lithium metal batteries are the ultimate solution to increase the energy density of battery cells because they directly eliminate the initial negative electrode material. However, since there is no excess metallic lithium source on the surface of the negative electrode current collector in the initial state, the cycle life of negative electrode-free lithium metal batteries is poor. Especially at high operating voltages (charge cut-off voltages), especially when increased to 4.5V or above, the long cycle capacity of the battery is poor, making it impossible to further increase the energy density by increasing the operating voltage (e.g., charge cut-off voltage).

[0042] In the prior art, a positive electrode lithium replenishment strategy is usually adopted in negative electrode-free lithium metal batteries to improve their long cycle capability. That is, an appropriate amount of lithium-rich material is added to the positive electrode coating, and the lithium source is released after the first cycle, resulting in loss of cyclability, thereby providing excess lithium source on the negative electrode side to compensate for the loss of active lithium. However, such a strategy creates a large amount of dead volume and dead mass inside the positive electrode, resulting in a decrease in energy density; at the same time, it is not conducive to maintaining a good conductive network, and both long cycle and rate performance will be affected. In summary, the development of a better lithium replenishment method is the key to achieving long cycle of high voltage, high energy density, negative electrode-free lithium metal batteries.

[0043] In order to achieve the purpose of the present invention, the present invention provides an electrolyte for a negative electrode-free metal lithium secondary battery, which can achieve a long cycle life of the battery at a high operating voltage.

[0044] electrolyte

[0045] In one embodiment of the present application, the present application provides an electrolyte comprising a solvent and a lithium supplement additive, wherein the lithium supplement additive is selected from at least one of the following: a lithium salt having an oxalate group, lithium oxide, and lithium peroxide, and the solvent comprises at least one compound of formula (I):

[0046]

[0047] in,

[0048] R1 is C1-6 fluoroalkyl;

[0049] R2 is a hydrogen atom, a C1-6 alkyl group or a C1-6 fluoroalkyl group; and

[0050] n represents 1 or 2.

[0051] The electrolyte of the present application can enable the negative electrode-free metal lithium secondary battery to achieve a longer cycle life at a higher charging cut-off voltage.

[0052] Herein, "negative electrode-free secondary battery" and similar expressions refer to a secondary battery in which the negative electrode sheet only has a metal foil current collector without any negative electrode active material.

[0053] The electrolyte of the present application includes a lithium supplement additive selected from lithium salts with oxalate groups, lithium oxide, and lithium peroxide. Such substances can be oxidatively decomposed at higher operating voltages (higher than 4.3V, for example, 4.6V). Taking lithium salts with oxalate structures as an example, their oxalate groups can be oxidized on the positive electrode side under high-voltage conditions, and the following reactions occur, for example:

[0054]

[0055] At the same time, its lithium ion portion is reduced on the negative electrode side and deposited on the surface of the negative electrode in the form of lithium metal, thereby playing the required lithium replenishment role.

[0056] Including lithium-supplementing additives in the electrolyte avoids the traditional lithium-supplementing method of adding lithium-supplementing powder and corresponding binders during the positive electrode slurry preparation process. The lithium-supplementing additives will not affect the compaction density and internal conductive network structure of the positive electrode after releasing the lithium source, ensuring the stability of the positive electrode throughout the cycle and being more conducive to the long-term stable cycle of the battery.

[0057] In addition, the carbon dioxide released by the decomposition of lithium-supplementing additives may react with the metallic lithium at the negative electrode to form inorganic lithium carbonate components to participate in SEI film formation, thereby promoting a denser lithium metal deposition morphology, improving cycle efficiency, and being more conducive to extending cycle life.

[0058] Without wishing to be bound by any theory, the inventors have discovered that the aforementioned lithium-replenishing additives generally require a relatively high voltage (above 4.5V, for example, 4.6V) to be oxidized and decomposed, achieving the desired lithium-replenishing effect. Increasing the charging voltage can further increase the energy density of lithium metal batteries.

[0059] However, conventional electrolytes (particularly their solvents) often cannot support stable cycling at such high operating voltages. The inventors have discovered that using the compound of formula (I) as a solvent in the electrolyte enables lithium metal batteries (particularly anode-free lithium metal batteries) to cycle stably at high operating voltages, thereby simultaneously improving the energy density and cycle life of lithium metal batteries.

[0060] The compound of formula (I) in this application is an ether with a relatively short carbon chain length and a relatively low fluorine content. The fluorine atom substitution therein is beneficial for improving the oxidative stability of the electrolyte, enabling the battery to cycle stably at a higher cut-off voltage. However, the inventors have found that in the compound of formula (I), the position of the fluorine atom substitution is critical - the fluorine atom substitution cannot be on the carbon adjacent to the oxygen atom. This helps maintain its good solubility for lithium salts (for example, the solubility concentration of lithium bis(fluorosulfonyl)imide (LiFSI) in it should reach 2M or above).

[0061] In some embodiments, the lithium-supplementing additive is selected from at least one of lithium oxalate (LO), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOBOB), lithium difluorobis(oxalatophosphate), lithium tetrafluorooxalatophosphate, lithium oxide (Li2O), and lithium peroxide (Li2O2); optionally, the lithium-supplementing additive is selected from at least one of lithium oxalate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate. Further selecting the above lithium-supplementing additive facilitates its effective lithium-supplementing effect, thereby further improving the cycle life of the negative-electrode-free lithium metal battery.

[0062] Regarding the preferred lithium replenishment additives mentioned above, the inventors have found that their solubility in formula (I) varies. For example, LiDFOB generally has good solubility in the compound of formula (I), at least up to a concentration of 1M, while LO and LiBOB are generally slightly soluble or insoluble. However, even in the case of unsatisfactory solubility, preparing them into a uniform suspension for use in battery cell cycling can still achieve an ideal lithium replenishment effect.

[0063] In some embodiments, R1 is C1-4 fluorinated alkyl, optionally C1-4 fluorinated linear alkyl. In some embodiments, R2 is hydrogen, C1-4 alkyl or C1-4 fluorinated alkyl, optionally C1-4 linear alkyl or C1-4 fluorinated linear alkyl.

[0064] In some embodiments, optionally, the number of fluorine atoms substituted in the fluorinated (straight-chain) alkyl group is no more than 3.

[0065] In some embodiments, in formula (I), when n=1, R1 is a C1-3 fluorinated linear alkyl group in which the number of fluorine atoms is no more than 3, and R2 is a hydrogen atom.

[0066] In some embodiments, in formula (I), when n=2, R1 is a C1-4 fluorinated linear alkyl group, and R2 is a hydrogen atom, a C1-4 linear alkyl group, or a C1-4 fluorinated linear alkyl group, wherein R1 and R2 each contain no more than 3 fluorine atoms.

[0067] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0068]

[0069]

[0070]

[0071]

[0072] In some embodiments, the compound of formula (I) is selected from at least one of I-1 to I-16, and I-60 to I-71. In some embodiments, optionally, the compound of formula (I) is selected from at least one of I-2, I-11, I-66 and I-68; more optionally, I-2 and / or I-66.

[0073] Further selecting the above formula (I) is beneficial to the stable circulation of the electrolyte at a high operating voltage, and is helpful to further improve the cycle life.

[0074] In some embodiments, the concentration of the lithium-supplementing additive is 0.1M to 1M, optionally 0.3M to 0.7M, and more optionally 0.4M to 0.6M. Using a lithium-supplementing additive concentration within the above range effectively achieves lithium replenishment without affecting the ion transport properties of the electrolyte, further facilitating the long cycle life of high-voltage, anode-free lithium metal batteries. Furthermore, as mentioned above, gas is generated during the decomposition of the lithium-supplementing additive, so its content needs to be controlled.

[0075] In some embodiments, the solvent comprises at least 50% by weight, optionally at least 70% by weight, and more optionally at least 90% by weight of a compound of formula (I), based on the total mass of the solvent. A solvent containing the compound of formula (I) in such an amount is more conducive to improving the oxidative stability of the electrolyte and improving cycle life.

[0076] In some embodiments, the solvent further comprises at least one other solvent selected from the group consisting of ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene glycol dimethyl ether, butanediol dimethyl ether, dimethoxymethane, diethoxymethane, trimethyl orthoformate, triethyl orthoformate, trimethyl orthocarbonate, triethyl orthocarbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, Ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, acetonitrile, dimethyl sulfoxide, sulfolane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, fluorobenzene, p-difluorobenzene, o-difluorobenzene, m-difluorobenzene, trifluorobenzene, trifluorotoluene, trifluoromethoxybenzene, acetone and perfluoropentanone; optionally, the other solvent is selected from dimethyl carbonate and perfluoropentanone. The above other solvents help improve the lithium metal cycle efficiency and improve the cycle life.

[0077] In some embodiments, the solvent consists of a compound of formula (I).

[0078] In some embodiments, the electrolyte of the present application further comprises an electrolyte salt selected from at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, and lithium difluorophosphate. In some embodiments, optionally, the electrolyte salt is at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide; more optionally, the electrolyte salt is lithium bis(fluorosulfonyl)imide. The above electrolyte salts are selected so that they can be well dissolved in the solvent and can decompose on the negative electrode surface to form an inorganic fluorine-rich SEI component, which further facilitates the long cycle of the negative electrode-free metal lithium battery.

[0079] In some embodiments, the concentration of the electrolyte salt is 0.5 M to 5 M, optionally 1 M to 3 M, and more optionally 1.5 M to 2.5 M. The electrolyte lithium salt within the above concentration range can provide the electrolyte with ideal ion conductivity and viscosity, and is beneficial to the stability of the electrolyte to the positive and negative electrodes, especially the oxidation resistance of the positive electrode, thereby further improving the cycle life of the lithium metal secondary battery under high voltage.

[0080] Herein, in the electrolytic solution, the concentration of the electrolyte salt is the concentration of the lithium salt excluding the lithium replenishing additive.

[0081] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0082] Secondary batteries and electrical devices

[0083] A second aspect of the present application provides a secondary battery comprising the electrolyte of the present application.

[0084] In some embodiments, the secondary battery of the present application is a negative electrode-less battery.

[0085] In some embodiments, the secondary battery of the present application further includes a negative electrode plate, comprising a negative electrode current collector and, optionally, a coating disposed on at least one surface of the negative electrode current collector, wherein the coating is selected from the following metal or metal oxide coatings: tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, zinc oxide, aluminum oxide, and titanium oxide, optionally silver, gold, or titanium oxide. The coating helps induce metallic lithium deposition, further improving the battery cycle life. Such a coating cannot be used as an active negative electrode alloy material.

[0086] In some embodiments, the coating is applied to the surface of the current collector by an appropriate method known to those skilled in the art, such as evaporation or magnetron sputtering.

[0087] In some embodiments, the thickness of the coating is at most 200 nm (i.e., 0-200 nm), optionally at most 100 nm. In some embodiments, the thickness of the coating is 25-75 nm, optionally 50 nm. Coatings within this range help the battery achieve good cycle life.

[0088] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, the metal foil may be copper foil, nickel foil, or stainless steel foil. Copper foil is preferred.

[0089] In some embodiments, the charge cutoff voltage of the secondary battery of the present application is greater than 4.3 V, optionally greater than 4.5 V, and optionally 4.6 V. In some embodiments, the cycle voltage range of the secondary battery of the present application is 2.8 V-4.3 V.

[0090] A third aspect of the present application provides an electrical device including the secondary battery of the present application.

[0091] The secondary battery of the present application includes a battery cell form, a battery module form and a battery pack form.

[0092] The battery cells, battery modules, battery packs and electrical devices of the present application are described below with appropriate reference to the accompanying drawings.

[0093] In one embodiment of the present application, a secondary battery is provided.

[0094] Typically, a secondary battery includes a positive electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0095] [Positive electrode]

[0096] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0097] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0098] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0100] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0101] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0103] [Isolation film]

[0104] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0105] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0106] [Outer packaging]

[0107] In some embodiments, a secondary battery may include an outer packaging for encapsulating a positive electrode sheet, a negative electrode sheet, and an electrolyte. For example, the positive electrode sheet, the negative electrode sheet, and the separator may be stacked or wound to form a laminated or wound cell structure, which is encapsulated within the outer packaging. The electrolyte described in the first aspect of this application is used as the electrolyte, which is impregnated within the cell. The number of cells in a secondary battery may be one or more, and can be adjusted based on demand.

[0108] In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into the electrode assembly through a winding process or a lamination process. The outer packaging can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0109] In some embodiments, the outer packaging of the secondary battery may be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. This application has no particular restrictions on the shape of the secondary battery, which may be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 of a square structure as an example.

[0110] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0111] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0112] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0113] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0114] In some embodiments, the above-mentioned battery cells or battery modules can also be assembled into a battery pack. The number of battery cells or battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0115] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0116] In addition, the present application also provides an electric device, which includes at least one of the battery cells, battery modules and battery packs provided in the present application. The battery cells, battery modules or battery packs can be used as the power source of the electric device, and can also be used as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0117] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0118] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0119] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0120] Example

[0121] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0122] Example 1

[0123] 1. Preparation of Electrolyte

[0124] Take 1.87g of LiFSI and 0.36g of LiDFOB, add them to 5ml of I-2 solvent, and stir thoroughly to form a colorless and transparent electrolyte with a concentration of 2M-LiFSI and 0.5M-LiDFOB, which is used for subsequent performance testing and battery cell cycling.

[0125] 2. Preparation of negative electrode-free liquid metal lithium secondary batteries

[0126] (1) Positive electrode preparation: The positive electrode active material lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), conductive agent acetylene black, binder PVDF were mixed in a mass ratio of 98:1:1, solvent N-methylpyrrolidone (NMP) was added and stirred until the system became uniform to obtain a positive electrode slurry (solid content of 70%); the positive electrode slurry was heated at about 25 mg / cm 2 The positive electrode sheet was evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. It was then cut into 40mm*50mm rectangles as positive electrode sheets. The positive electrode surface capacity was 3.5mAh / cm 2 .

[0127] (2) Isolation film: Use a polyethylene porous film and cut it into a 45mm*55mm rectangle for later use.

[0128] (3) Negative electrode preparation: 12 μm thick copper foil was selected and cut into a 41 mm * 51 mm rectangle as the negative electrode sheet.

[0129] (4) Battery assembly: Take a cut positive electrode sheet and match it with two cut negative electrode sheets, use the above-mentioned separator to isolate the positive and negative electrodes in the middle, and wrap them in an aluminum-plastic film bag to form a laminated dry cell. Inject 0.3g of the above-mentioned electrolyte, and vacuum heat-press the aluminum-plastic film bag to obtain a laminated battery (rated capacity of 140mAh). After the laminated battery is left to stand at room temperature for at least 6 hours, the cycle test can be started.

[0130] 3. Room temperature long cycle test of negative electrode-free liquid lithium metal secondary battery

[0131] Take the battery prepared as above, at an ambient temperature of 25°C, use a constant current charge of 0.2C rate (i.e. 28mA) to reach a cut-off voltage of 4.6V, then use a constant voltage charge of 4.6V until the current decays to 0.1C (i.e. 14mA), and then discharge to 2.8V at a rate of 1C (i.e. 140mA), which is one charge and discharge cycle (i.e., the cycle voltage range is 2.8V-4.6V). Carry out the charge and discharge cycle in this way, and test the discharge capacity of each cycle. When the discharge capacity of a certain number of cycles decays to 80% of the discharge capacity of the first cycle, the battery life is considered to be terminated, and the number of cycles at this time is the cycle life. The test results are shown in Table 1 below.

[0132] Examples 2-5

[0133] The preparation and testing methods of Examples 2-5 are similar to those of Example 1, except that different lithium supplement additives are used. Details and test results are shown in Table 1.

[0134] During the preparation of the electrolyte in the embodiment, if it is found that the electrolyte cannot be completely dissolved to form a transparent solution, a magnet is first added to stir the electrolyte at a high speed of 100 rpm overnight, and then the glass bottle container containing the above electrolyte is placed in an ultrasonic instrument (Fisher Scientific FS110D) and 37 kHz ultrasonic waves are used to fully break up and disperse the undissolved lithium salt in the electrolyte to form a uniform suspension. After the suspension is allowed to stand for 10 hours, there is still no obvious stratification. The suspension electrolyte prepared above is used to make and test the same battery cells as in Example 1.

[0135] During the preparation of the electrolytes in the following embodiments, if the lithium supplement additive cannot be dissolved and a suspension needs to be prepared, the above operation is followed.

[0136] Examples 6-8

[0137] The preparation and testing methods of Examples 6-8 are similar to those of Example 1, except that the solvents of formula (I) are different. Details and test results are shown in Table 1.

[0138] Examples 9-14

[0139] The preparation and testing methods of Examples 9-14 are similar to those of Example 1, except that the concentrations of the lithium supplement additives are different. Details and test results are shown in Table 1.

[0140] Examples 15-17

[0141] The preparation and testing methods of Examples 15-17 are similar to those of Example 1, except that the solvent contains other solvents in addition to the solvent of formula (I) of the present invention. Details and test results are shown in Table 1.

[0142] Comparative Example 1

[0143] The preparation and testing methods of Comparative Example 1 are similar to those of Example 1, except that no lithium supplement additive is added. Details and test results are shown in Table 1.

[0144] Comparative Example 2

[0145] The preparation and testing methods of Comparative Example 2 are similar to those of Example 1, except that the solvent is ethylene glycol dimethyl ether (DME). Details and test results are shown in Table 1.

[0146] Comparative Example 3

[0147] The preparation and testing methods of Comparative Example 3 are similar to those of Example 1, except that the solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (denoted as "EC-DEC" in the table below). Details and test results are shown in Table 1.

[0148] Comparative Example 4

[0149] The preparation and testing methods of Comparative Example 4 are similar to those of Example 1, except that the secondary battery is cycled in a cycle voltage range of 2.8V-4.3V. The test results are shown in Table 1.

[0150] Comparative Example 5

[0151] The preparation and testing methods of Comparative Example 4 are similar to those of Example 1, except that the secondary battery is cycled in a cycle voltage range of 2.8V-4.3V. The test results are shown in Table 1.

[0152]

[0153]

[0154] As can be seen from Table 1, the combination of the lithium-supplementing additive of the present invention and the solvent of formula (I) can significantly improve the cycle life of a negative electrode-free secondary battery. The inventors also found that even if the lithium-supplementing additive of the present invention cannot dissolve well, as long as it can be well dispersed in the electrolyte in the form of a suspension (as described above, the suspension still shows no obvious stratification after standing for 10 hours), it does not affect the performance of its lithium-supplementing function. At the same time, the concentration of the lithium-supplementing additive should be controlled in the range of 0.05M-1.5M, preferably 0.1-1M, which can effectively improve the cycle life and the electrolyte has good ion transport capacity.

[0155] The above examples illustrate that the combination of the solvent of formula (I) of the present invention and the lithium supplement additive greatly improves the positive electrode cycle stability of the battery cell at an ultra-high voltage of 4.6V, and such a high operating voltage is also conducive to the oxidative decomposition of the lithium supplement additive to play a lithium supplement role, thereby further extending the cycle life of the negative electrode-free lithium metal secondary battery. As can be seen from Comparative Examples 4-5, the lithium supplement additive does not significantly improve the cycle life of the negative electrode-free lithium metal secondary battery at a lower voltage (e.g., 4.3V). The lithium supplement additive of the present application can only effectively play a role at a higher operating voltage, and a higher operating voltage is conducive to further improving the energy density.

[0156] Examples 18-25

[0157] The preparation and testing methods of Examples 18-25 are similar to those of Example 1, except that the electrolyte salt concentrations are different. Details and test results are shown in Table 2. If the lithium supplement additive cannot be dissolved, the treatment method is the same as in Example 2.

[0158] Examples 26-27

[0159] The preparation and testing methods of Examples 26-27 are similar to those of Example 1, except for the electrolyte salt. Details and test results are shown in Table 2.

[0160] Table 2

[0161]

[0162]

[0163] As can be seen from the above examples, electrolyte salts such as lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide are beneficial for achieving a good cycle life at room temperature. Furthermore, an electrolyte salt concentration between 0.5M and 5M exhibits a relatively ideal cycle life.

[0164] Examples 28-32

[0165] In Example 28, the negative electrode copper foil current collector was first subjected to 50 nm thick Ag evaporation, and then a negative electrode-free lithium metal battery was assembled. Other tests were similar to those in Example 1. The preparation and testing methods of Examples 29-31 were similar to those of Example 23, with details shown in Table 1. In Example 32, the negative electrode copper foil current collector was first subjected to 50 nm thick TiO2 magnetron sputtering, and then a negative electrode-free lithium metal battery was assembled. Other tests were the same as those in Example 1.

[0166]

[0167] As can be seen from the above, metal coating (especially gold or silver coating) is more conducive to further improving the cycle life. The coating thickness is at most 200nm, preferably 50-200nm, and the performance is good within this range.

[0168] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte comprising a solvent and a lithium supplement additive, wherein the lithium supplement additive is selected from at least one of the following: a lithium salt having an oxalate group, lithium oxide and lithium peroxide, and the solvent comprises at least one compound of formula (I): in, R1 is C1-6 fluoroalkyl; R2 is a hydrogen atom, a C1-6 alkyl group or a C1-6 fluoroalkyl group; and n represents 1 or 2.

2. The electrolyte according to claim 1, wherein the lithium supplement additive is selected from at least one of lithium oxalate, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxide and lithium peroxide; optionally, the lithium supplement additive is selected from at least one of lithium oxalate, lithium dioxalatoborate and lithium difluorooxalatoborate.

3. The electrolyte according to claim 1 or 2, wherein R1 is a C1-4 fluorinated chain alkyl group, optionally a C1-4 fluorinated straight chain alkyl group; and / or R2 is a hydrogen atom, a C1-4 chain alkyl group or a C1-4 fluorinated chain alkyl group, and may alternatively be a hydrogen atom, a C1-4 straight chain alkyl group or a C1-4 fluorinated straight chain alkyl group.

4. The electrolyte according to any one of claims 1 to 3, wherein the compound of formula (I) is selected from at least one of the following compounds: Optionally, the compound of formula (I) is selected from at least one of I-2, I-11, I-66 and I-68, more preferably I-2 and / or I-66. 5 . The electrolyte according to claim 1 , wherein the concentration of the lithium supplement additive is 0.1M to 1M, optionally 0.3M to 0.7M, and more optionally 0.4M to 0.6M.

6. The electrolyte according to any one of claims 1 to 5, wherein the solvent comprises at least 50 wt %, optionally at least 70 wt %, more optionally at least 90 wt % of the compound of formula (I), based on the total mass of the solvent.

7. The electrolyte according to any one of claims 1 to 6, further comprising an electrolyte salt, wherein the electrolyte salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate and lithium difluorophosphate; optionally, the electrolyte salt is at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide; more optionally, the electrolyte salt is lithium bis(fluorosulfonyl)imide.

8. The electrolyte according to claim 7, wherein the concentration of the electrolyte salt is 0.5M to 5M, alternatively 1M to 3M, more alternatively 1.5M to 2.5M. 9 . A secondary battery comprising the electrolyte according to claim 1 .

10. The secondary battery according to claim 9, further comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a coating optionally disposed on at least one surface of the negative electrode current collector; wherein the coating is selected from the following metal or metal oxide coatings: tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, zinc oxide, aluminum oxide and titanium oxide, optionally silver, gold or titanium oxide.

11. The secondary battery according to claim 9 or 10, wherein the thickness of the plating layer is at most 200 nm, optionally at most 100 nm.

12. An electrical device comprising a secondary battery selected from any one of claims 9 to 11.

Images