Lithium metal battery cell, battery device, and electric device

Abstract

The application discloses a lithium metal battery monomer, a battery device and a power utilization device. The lithium metal battery monomer comprises an electrolyte, the electrolyte comprises a lithium salt and a solvent; the LUMO energy of the lithium salt is greater than or equal to -0.8 eV; and the LUMO energy of the solvent is greater than or equal to -0.56 eV. The lithium metal battery monomer provided by the application has improved cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a lithium metal battery cell, battery device, and power supply device. Background Technology

[0002] Batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric car toys, electric toy ships, electric toy airplanes, and power tools.

[0003] In the development of battery cells, improving the cycle performance of battery cells is one of the urgent problems to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a lithium metal battery cell, a battery device, and an electrical device.

[0005] In a first aspect, embodiments of this application provide a lithium metal battery cell, the lithium metal battery cell comprising an electrolyte, the electrolyte comprising a lithium salt and a solvent; the LUMO energy of the lithium salt is greater than or equal to -0.8 eV; the LUMO energy of the solvent is greater than or equal to -0.56 eV.

[0006] According to the embodiments of this application, by limiting the LUMO energy of the lithium salt and solvent to the above range, lithium salts and solvents with high resistance to reduction are selected. This reduces the reactivity of lithium salts and solvents in the electrolyte with the lithium metal anode, reduces side reactions between the lithium metal anode and the electrolyte, and thus reduces the irreversible consumption of active lithium. At the same time, it reduces and thins the SEI film formed by the side reactions. The SEI film can be broken by applying a small current, allowing lithium metal to grow along its lowest energy crystal plane without the restriction of the SEI film. This achieves dendrite-free bulk lithium deposition and improves the coulombic efficiency and cycle performance of the battery cell.

[0007] In some embodiments, the LUMO energy of the lithium salt is from -0.65 eV to 0.8 eV.

[0008] In some embodiments, the LUMO energy of the solvent is -0.5 eV to 0.8 eV.

[0009] In some embodiments, the reduction potential of the lithium salt relative to Li / Li+ is less than or equal to 1V.

[0010] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium pentafluoroethyltrifluoroborate, and lithium tetrafluoroborate.

[0011] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 4 mol / L, based on the total volume of the electrolyte.

[0012] In some embodiments, the concentration of the lithium salt in the electrolyte is 1 mol / L to 3 mol / L, based on the total volume of the electrolyte.

[0013] In some embodiments, the solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, ethylene glycol dipentyl ether, 1,2-dimethoxypropane, and 1,3-dimethoxypropane.

[0014] In some embodiments, the electrolyte further includes an additive having a structure as shown in formula (I):

[0015]

[0016] In Formula 1, R1, R2, R3, R4, R5 and R6 each independently include alkyl, alkoxy, siloxane, aromatic group, aromatic oxy group, alkylthio group, aromatic thio group, hydroxyl group, amino group, cyano group, nitro group, alkenyl group or alkynyl group, and at least one of R1, R2, R3, R4, R5 and R6 contains an oxygen atom.

[0017] In some embodiments, the additive includes one or more of methoxypentamethylcyclotriphosphazene, ethoxypentamethylcyclotriphosphazene, methoxypentoethylcyclotriphosphazene, ethoxypentoethylcyclotriphosphazene, phenoxypentamethylcyclotriphosphazene, phenoxypentoethylcyclotriphosphazene, hexamethoxycyclotriphosphazene, hexaethoxycyclotriphosphazene, and hexaphenoxycyclotriphosphazene.

[0018] In some embodiments, the concentration of the additive in the electrolyte is 0.01 mol / L to 0.8 mol / L, based on the total volume of the electrolyte.

[0019] In some embodiments, the concentration of the additive in the electrolyte is 0.1 mol / L to 0.6 mol / L, based on the total volume of the electrolyte.

[0020] In some embodiments, the SEI membrane breakdown current of the electrolyte is less than or equal to 1 mA / cm. 2 .

[0021] Secondly, embodiments of this application provide a battery device, including a lithium metal battery cell according to the first aspect of this application.

[0022] Thirdly, embodiments of this application provide an electrical device, including a lithium metal battery cell according to the first aspect of this application or a battery device according to the second aspect of this application. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0024] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0025] Figure 2 This is an exploded schematic diagram of a battery provided for some embodiments of this application.

[0026] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0027] Figure 4 This is a SEM image of the negative electrode lithium metal deposition in Example 1 of this application.

[0028] Figure 5 This is a SEM image of the lithium metal deposition on the negative electrode in Comparative Example 1 of this application.

[0029] The accompanying drawings are not necessarily drawn to scale.

[0030] The reference numerals in the attached drawings are explained as follows: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Reception space; 6. Battery module; 7. Battery cell. Detailed Implementation

[0031] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0035] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0037] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0038] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0039] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0040] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0041] The battery device mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0042] A single battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. When there are multiple battery cells, they are connected in series, parallel, or mixed connections through a busbar.

[0043] In some embodiments, the battery device may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0044] In some embodiments, the battery device may be a battery pack, which includes a housing and individual battery cells, with the individual battery cells or battery modules housed within the housing.

[0045] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0046] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0047] The technical solutions described in the embodiments of this application are applicable to battery devices and electrical devices that use battery devices.

[0048] Battery devices can be used as the power source for electrical devices or as energy storage units for electrical devices. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), 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.

[0049] Electrical devices can choose the type of battery device according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0050] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0051] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0052] like Figure 1 As shown, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0053] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0054] In some embodiments, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0055] Figure 2 This is a schematic diagram of a battery explosion provided for some embodiments of this application. For example... Figure 2 As shown, the battery device 2 includes a housing 5 and battery cells (not shown), with the battery cells housed within the housing 5.

[0056] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0057] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0058] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0059] In battery device 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells are connected in both series and parallel configurations. Multiple battery cells can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells is housed in housing 5. Alternatively, multiple battery cells can first be connected in series, in parallel, or in a mixed configuration to form battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a mixed configuration to form a whole assembly, which is then housed in housing 5.

[0060] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0061] like Figure 3 As shown, in some embodiments, there are multiple battery cells 7, which are first connected in series, parallel, or mixed to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or mixed to form a whole and housed in a casing.

[0062] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6.

[0063] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a stacked structure, and this application embodiment is not limited in this regard. The electrode assembly generally includes a positive electrode, a negative electrode, and a separator.

[0064] The battery cell provided in this application is a lithium metal battery cell. A lithium metal battery cell uses lithium metal as the negative electrode. Lithium metal has extremely high theoretical specific capacity and the most negative electrode potential (-3.04V vs. standard hydrogen electrode), thus increasing the energy density of the battery cell. However, due to its high reactivity, lithium metal has a low coulombic efficiency, and the uncontrollable side reactions between lithium metal and the electrolyte form an unstable solid electrolyte membrane (SEI membrane). During charge-discharge cycles, repeated rupture and formation of the SEI membrane exacerbate the uneven deposition of lithium metal on the negative electrode surface, leading to the formation of lithium dendrites. This results in the formation of "dead lithium" and irreversible capacity loss. In severe cases, lithium dendrite growth can puncture the separator, causing short circuits within the battery cell and affecting its reliability and cycle life.

[0065] To address these issues, related technologies often employ the construction of a stable SEI film to block contact and side reactions between the electrolyte and the lithium metal anode. This is achieved by selecting electrolyte solvents and lithium salts with low reduction stability and inorganic-rich reduction products, thereby promoting the formation of an inorganic-rich and stable SEI film. However, these methods do not fundamentally reduce the reactivity between the electrolyte and the lithium metal anode. Once the SEI film ruptures during battery cycling, the low-reduction-stability lithium salts and solvents further exacerbate interfacial side reactions and lithium dendrite growth, leading to a rapid deterioration in the electrochemical performance of the battery cell.

[0066] In view of the above-mentioned technical problems, the lithium metal battery cell provided in this application uses a reduction-resistant electrolyte, which has low reactivity to the lithium metal anode, weak interfacial side reactions, and a thin SEI film formed by the side reactions. When a small current is applied (e.g., less than or equal to 1 mA / cm²), the effect is minimal. 2 This process can break through the SEI film, allowing lithium metal to grow along its lowest energy crystal plane without the restriction of the SEI film, thereby achieving dendrite-free bulk lithium deposition and ultimately obtaining lithium metal battery cells with high coulombic efficiency, long cycle life, and high safety.

[0067] Electrolyte

[0068] The electrolyte consists of a solvent and a lithium salt. The LUMO energy of the lithium salt can be greater than or equal to -0.8 eV, and the LUMO energy of the solvent can be greater than or equal to -0.56 eV.

[0069] In this application, the LUMO energies of lithium salts and solvents are LUMO energies in a solvation environment, that is, the energies of the lowest unoccupied molecular orbitals of lithium salts or solvents in a solvation environment. These energies can be determined by instruments and methods known in the art, such as by photoelectric effect, such as XPS (X-ray diffraction) and UPS (ultraviolet photoelectron spectroscopy), or by cyclic voltammetry (CV). They can also be calculated using quantum chemical methods, such as density functional theory (DFT).

[0070] According to the embodiments of this application, by limiting the LUMO energy of the lithium salt and solvent to the above range, lithium salts and solvents with high resistance to reduction are selected. This reduces the reactivity of lithium salts and solvents in the electrolyte with the lithium metal anode, reduces side reactions between the lithium metal anode and the electrolyte, and thus reduces the irreversible consumption of active lithium. At the same time, it reduces and thins the SEI film formed by the side reactions. The SEI film can be broken by applying a small current, allowing lithium metal to grow along its lowest energy crystal plane without the restriction of the SEI film. This achieves dendrite-free bulk lithium deposition and improves the coulombic efficiency and cycle performance of the battery cell.

[0071] The LUMO energy of lithium salt in a solvated environment can be greater than or equal to -0.8 eV, and can be selected from -0.65 eV to 0.8 eV, for example, it can be -0.8 eV, -0.7 eV, -0.6 eV, -0.5 eV, -0.4 eV, -0.3 eV, -0.2 eV, -0.1 eV, 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, 0.5 eV, 0.6 eV, 0.7 eV, 0.8 eV, 0.9 eV, 1.0 eV, or any range of the above values.

[0072] The LUMO energy of the solvent in the solvation environment can be greater than or equal to -0.56 eV, and can be selected from -0.5 eV to 0.8 eV, for example, it can be -0.5 eV, -0.4 eV, -0.3 eV, -0.2 eV, -0.1 eV, 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, 0.5 eV, 0.6 eV, 0.7 eV, 0.8 eV, or any range of the above values.

[0073] In some embodiments, the reduction potential of the lithium salt relative to Li / Li+ can be less than or equal to 1V, for example, it can be 1V, 0.9V, 0.8V, 0.7V, 0.6V, 0.5V, 0.4V, 0.3V, 0.2V, 0.1V, 0.05V, 0.01V, or any range of the above values.

[0074] In some embodiments, the reduction potential of the solvent relative to Li / Li+ can be less than or equal to 0.1V, for example, it can be 0.10V, 0.09V, 0.08V, 0.07V, 0.06V, 0.05V, 0.04V, 0.03V, 0.02V, 0.01V, or any range of the above values.

[0075] In this application, the reduction potentials of lithium salt and solvent relative to Li / Li+ are well-known in the art and can be measured using methods and instruments known in the art. For example, linear sweep voltammetry (LSV) can be used. An exemplary measurement method is as follows: At 25°C, using an electrochemical workstation, the Li-Ti half-cell containing lithium salt and solvent is scanned from the open-circuit potential to 0V (vs Li / Li+) at a scan rate of 0.1 mV / s. + The potential corresponding to the peak appearance / current-voltage slope abrupt change is the reduction potential, from which the reduction potentials of lithium salt and solvent can be obtained.

[0076] It is understood that the concentration of lithium salt in the electrolyte and the solvent environment will affect the reduction potential of lithium salt and solvent. Therefore, the reduction potential of lithium salt and solvent in the embodiments of this application are the reduction potentials obtained by testing under the corresponding electrolyte system environment.

[0077] According to embodiments of this application, by making the lithium salt and solvent have a lower reduction potential (vs Li / Li + This can reduce the reactivity of lithium salts and solvents with lithium metal anodes, reduce side reactions between lithium metal anodes and electrolytes, and thus reduce the consumption of electrolytes and active lithium by side reactions. Excellent results can improve the coulombic efficiency of battery cells and improve the cycle performance of battery cells.

[0078] In some embodiments, the lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiOTF), lithium pentafluoroethyl trifluoroborate (LiFAB), and lithium tetrafluoroborate (LiBF4).

[0079] In some embodiments, based on the total mass of the electrolyte, the concentration of lithium salt in the electrolyte can be between 0.5 mol / L and 4 mol / L, for example, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4.0 mol / L, or any range of the above values; it can be selected as 1 mol / L to 3 mol / L, and more preferably 1.5 mol / L to 2.5 mol / L. A lithium salt concentration within the above range is beneficial for improving the ion transport rate in the electrolyte, while the electrolyte can maintain high stability.

[0080] In some embodiments, the solvent may include one or more of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), ethylene glycol dipropyl ether, ethylene glycol dibutyl ether (EGDE), ethylene glycol dipentyl ether, 1,2-dimethoxypropane, and 1,3-dimethoxypropane.

[0081] In some embodiments, the electrolyte may further include an additive having a structure as shown in formula (I):

[0082]

[0083] In Formula 1, R1, R2, R3, R4, R5 and R6 each independently include alkyl, alkoxy, siloxane, aromatic group, aromatic oxy group, alkylthio group, aromatic thio group, hydroxyl group, amino group, cyano group, nitro group, alkenyl group or alkynyl group, and at least one of R1, R2, R3, R4, R5 and R6 contains an oxygen atom.

[0084] According to the embodiments of this application, an alkoxy-containing cyclotriphosphazene derivative is added to the electrolyte as an additive. This additive has a large steric hindrance, which can coordinate with lithium ions in the electrolyte and thus weaken the interaction between the solvent and lithium ions in the electrolyte. This results in a looser solvation structure, accelerates the desolvation process of lithium ions, promotes the rapid and uniform deposition of lithium ions on the negative electrode surface, and further reduces the formation of lithium dendrites.

[0085] The solvent provided in this application embodiment has high resistance to reduction, but poor oxidation stability when matched with a high-voltage positive electrode. The additive with the above structure has a high HOMO (highest occupied molecular orbital) orbital, which is easy to lose electrons and be oxidized. It can undergo ring-opening and polymerization reactions on the surface of the positive electrode to form a positive electrode interface film (CEI) rich in P and N, thereby reducing the oxidative decomposition of the electrolyte on the positive electrode side and improving the structural stability of the positive electrode active material.

[0086] Furthermore, additives with the above structure are rich in two flame-retardant elements, P and N. Therefore, adding these additives to the electrolyte can improve the flame retardancy of the electrolyte, thereby enhancing the reliability of the battery cells.

[0087] In some embodiments, the additive having the above structure may include one or more of methoxypentamethylcyclotriphosphazene, ethoxypentamethylcyclotriphosphazene, methoxypentoethylcyclotriphosphazene, ethoxypentoethylcyclotriphosphazene, phenoxypentamethylcyclotriphosphazene, phenoxypentoethylcyclotriphosphazene, hexamethoxycyclotriphosphazene, hexaethoxycyclotriphosphazene, and hexaphenoxycyclotriphosphazene.

[0088] In some embodiments, based on the total volume of the electrolyte, the concentration of the additive having the above structure in the electrolyte can be 0.01 mol / L to 0.8 mol / L, for example, it can be 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, or any range of the above values; it can be selected as 0.1 mol / L to 0.6 mol / L, and more preferably 0.2 mol / L to 0.5 mol / L.

[0089] In some embodiments, the SEI membrane breakdown current of the electrolyte can be less than or equal to 1 mA / cm. 2 .

[0090] In this application, the SEI film breakdown current of the electrolyte can be obtained by the constant current step (I-STEP) method, specifically by applying 0.05 mA / cm² to the lithium-lithium symmetric battery. 2 The current was constant for 1 minute, then abruptly changed to 0.1 mA / cm². 2 The device was charged with a constant current for 1 minute, and constant current step tests were performed at the same time intervals as described above, with each current jump increasing by 0.05 mA / cm. 2 The current density applied during a voltage drop is the SEI film breakdown current.

[0091] According to the embodiments of this application, by adjusting the composition of the electrolyte and selecting lithium salts and solvents with high reduction stability, the side reactions between the electrolyte and the lithium metal anode can be reduced. As a result, the SEI film formed by the side reactions is reduced, so a lower current can be applied to break the SEI film and allow lithium metal to grow along its lowest energy crystal plane under the constraint of less SEI film, thereby achieving dendrite-free bulk lithium deposition and improving the cycle performance of the battery cell.

[0092] In some embodiments, the additive may also include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0093] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0094] In the embodiments of this application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte are of a well-known nature in the art and can be detected using equipment and methods known in the art. For example, the concentrations of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed using ion chromatography analysis methods, referring to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis methods.

[0095] In the embodiments of this application, the types and contents of organic components in the electrolyte are as known in the art, and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the implementation of this application, freshly prepared electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0096] For example, to test the composition of an additive in an electrolyte using liquid chromatography-nuclear magnetic resonance (NMR), taking the detection of lithium difluorophosphate and lithium hexafluorophosphate as an example, a 7ml glass bottle is prepared in a nitrogen-filled glove box. 5ml of NMR reagent premix is ​​added to the bottle, and the mixture is left to stand for 24 hours at room temperature (20-25°C) in a nitrogen-filled glove box. This allows the electrolyte in the electrode and separator to diffuse into the NMR premix, thus obtaining the NMR test sample. The NMR premix consists of 100ml of deuterated acetonitrile with 3ml of trifluoromethylbenzene (C7H5F3). This NMR reagent premix is ​​pre-dried using molecular sieve 4A (100ml of NMR reagent premix is ​​added to 15g of freshly opened 4A molecular sieve and dried in a nitrogen-filled glove box at room temperature (20-25°C) for more than 30 days). 19F NMR measurement is performed (NMR: Bruker Avance 400HD).

[0097] [Positive electrode plate]

[0098] In some embodiments, the positive electrode may include a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer including a positive active material.

[0099] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0100] In some embodiments, the positive electrode active material may include one or more of lithium phosphate and layered lithium transition metal oxides.

[0101] Lithium-containing phosphates may include one or more of lithium iron phosphate (LiFePO4), lithium iron phosphate and carbon composites, lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0102] Examples of layered lithium-containing transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds.

[0103] In some embodiments, the layered lithium-containing transition metal oxide may include Ni. The molar amount of Ni may account for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; optionally, the molar amount of Ni may account for more than 80% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; more preferably, the molar amount of Ni may account for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

[0104] The higher the Ni content in layered lithium-containing transition metal oxides, the higher the energy density of the battery cell.

[0105] In some embodiments, layered lithium-containing transition metal oxides may include Li a Ni b Co c M d O e A f Wherein, 0 < a ≤ 1.2; 0.8 ≤ b < 1; 0 < c < 1; 0 < d < 1; b + c + d = 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; A includes, but is not limited to, one or more of N, F, S, and Cl. This can further improve the energy density of individual battery cells.

[0106] In some embodiments, as an example, layered lithium-containing transition metal oxides may include, but are not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.06 Mn 0.04 O2, LiNi 0.92 Co 0.06 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2N 0.02 One or more of them.

[0107] During the charging and discharging process of a battery cell, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar Li content may change when the positive electrode active material is applied to the battery cell.

[0108] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0109] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0110] In some implementations, the weight percentage of the binder in the positive electrode film layer is greater than or equal to 0.5%, which is beneficial for obtaining good adhesion performance.

[0111] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be made by forming a metal material, such as aluminum, aluminum alloy, copper, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, on the polymer substrate. The polymer substrate may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and other substrates.

[0113] In some embodiments, the thickness of the positive current collector is from 4 μm to 20 μm. It is optionally from 6 μm to 18 μm, and more preferably from 8 μm to 16 μm.

[0114] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0115] [Negative electrode plate]

[0116] In this embodiment of the application, the negative electrode sheet can be lithium metal or an alloy formed by lithium metal and other metal or non-metal elements. These metal or non-metal elements can be one or more of aluminum (Al), tin (Sn), zinc (Zn), silver (Ag), gold (Au), indium (In), boron (B), and silicon (Si).

[0117] The lithium metal battery cell provided in this application embodiment can also be a negative electrode-less lithium metal battery cell, that is, the negative electrode side is only composed of a metal current collector without any active material. The metal current collector includes, but is not limited to, copper foil, titanium foil, and stainless steel foil. Under this condition, all active lithium in the cell cycle is provided by the positive electrode.

[0118] In some embodiments, the negative electrode includes a negative current collector and a conductive coating located on at least one side of the surface of the negative current collector.

[0119] In some embodiments, the conductive coating may include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the conductive coating may also include other additives. For example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0121] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one side of the polymeric material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymeric material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0122] [Isolation Component]

[0123] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0124] In some embodiments, the isolation chamber includes an isolation membrane. This application does not impose any particular limitation on the type of isolation membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0125] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation. The separator may be a single component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be applied to the surface of the separator.

[0126] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0127] Example

[0128] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0129] Example 1

[0130] Positive electrode sheet

[0131] Lithium nickel cobalt manganese oxide (NMC), acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed at a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) solvent was added and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of a positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. The resulting material was then cut into 40mm × 50mm rectangles to serve as the positive electrode sheet, with a positive electrode surface capacity of 3.5 mAh / cm². 2 .

[0132] Negative electrode sheet

[0133] A 50μm lithium foil is rolled onto a 13μm copper foil surface and then cut into rectangular electrodes of 41mm×51mm as negative electrodes.

[0134] Separating membrane

[0135] A polyethylene (PE) film with a thickness of 12μm was selected.

[0136] electrolyte

[0137] Lithium salt LiPF6 and additive ethoxypentamethylcyclotriphosphazene were dispersed in the solvent ethylene glycol dibutyl ether (EGDE) and stirred until homogeneous to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 2 mol / L and the concentration of ethoxypentamethylcyclotriphosphazene was 0.3 mol / L.

[0138] battery cell

[0139] The positive electrode, negative electrode, and separator are stacked in sequence and then injected with electrolyte to obtain a single battery cell.

[0140] Example 2-14

[0141] The preparation method of the battery cell is similar to that in Example 1, except that the composition parameters of the electrolyte are different. For details of the parameter adjustments, please refer to Table 1.

[0142] Comparative Examples 1-2

[0143] The preparation method of the battery cell is similar to that in Example 1, except that the composition parameters of the electrolyte are different. For details of the parameter adjustments, please refer to Table 1.

[0144] Test section

[0145] At 25℃, the battery cells were charged at a constant current rate of 0.1C to 4.3V, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.1C to 2.8V. The discharge capacity of the first cycle was recorded as C0. The above charge-discharge process was repeated until the capacity retention rate of the battery cells reached 80%, and the number of cycles was recorded. Capacity retention rate (%) = Cn / C0 × 100%, where Cn is the discharge capacity of the nth charge-discharge cycle.

[0146] The test results are detailed in Table 1.

[0147] Table 1

[0148]

[0149]

[0150] Figure 4 and Figure 5 The images show the battery cells in Embodiment 1 and Comparative Example 1 of this application at a current density of 0.63 mA / cm². 2 The capacity is 6.3mAh / cm³ 2The SEM images of the lithium deposition morphology under the given conditions (b2 is a magnified view of b1, and c2 is a magnified view of c1) show that the lithium deposition in Example 1 of this application exhibits a dendrite-free morphology and is more uniform and dense. Further combining the data in Table 1, this application's embodiment obtains a high-reduction-stability lithium metal battery electrolyte by adjusting the electrolyte composition design, which can effectively improve the cycle performance of lithium metal battery cells.

[0151] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium metal battery cell, characterized in that, The lithium metal battery cell includes an electrolyte, which includes a lithium salt and a solvent; The LUMO energy of the lithium salt is greater than or equal to -0.8 eV; The solvent has a LUMO energy greater than or equal to -0.56 eV.

2. The lithium metal battery cell according to claim 1, characterized in that, The lithium salt has a LUMO energy of -0.65 eV to 0.8 eV; and / or The solvent has a LUMO energy of -0.5 eV to 0.8 eV.

3. The lithium metal battery cell according to claim 1 or 2, characterized in that, The reduction potential of the lithium salt relative to Li / Li+ is less than or equal to 1V.

4. The lithium metal battery cell according to any one of claims 1-3, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium pentafluoroethyltrifluoroborate, and lithium tetrafluoroborate.

5. The lithium metal battery cell according to any one of claims 1-4, characterized in that, Based on the total volume of the electrolyte, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 4 mol / L.

6. The lithium metal battery cell according to claim 5, characterized in that, Based on the total volume of the electrolyte, the concentration of the lithium salt in the electrolyte is 1 mol / L to 3 mol / L.

7. The lithium metal battery cell according to any one of claims 1-6, characterized in that, The solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, ethylene glycol dipentyl ether, 1,2-dimethoxypropane, and 1,3-dimethoxypropane.

8. The lithium metal battery cell according to any one of claims 1-7, characterized in that, The electrolyte also includes additives having a structure as shown in formula (I): In Formula 1, R1, R2, R3, R4, R5 and R6 each independently include alkyl, alkoxy, siloxane, aromatic group, aromatic oxy group, alkylthio group, aromatic thio group, hydroxyl group, amino group, cyano group, nitro group, alkenyl group or alkynyl group, and at least one of R1, R2, R3, R4, R5 and R6 contains an oxygen atom.

9. The lithium metal battery cell according to claim 8, characterized in that, The additives include one or more of the following: methoxypentamethylcyclotriphosphazene, ethoxypentamethylcyclotriphosphazene, methoxypentoethylcyclotriphosphazene, ethoxypentoethylcyclotriphosphazene, phenoxypentamethylcyclotriphosphazene, phenoxypentoethylcyclotriphosphazene, hexamethoxycyclotriphosphazene, hexaethoxycyclotriphosphazene, and hexaphenoxycyclotriphosphazene.

10. The lithium metal battery cell according to claim 8 or 9, characterized in that, Based on the total volume of the electrolyte, the concentration of the additive in the electrolyte is 0.01 mol / L to 0.8 mol / L.

11. The lithium metal battery cell according to claim 10, characterized in that, Based on the total volume of the electrolyte, the concentration of the additive in the electrolyte is 0.1 mol / L to 0.6 mol / L.

12. The lithium metal battery cell according to any one of claims 1-11, characterized in that, The SEI film breakdown current of the electrolyte in the lithium-lithium symmetric battery is less than or equal to 1 mA / cm. 2 .

13. A battery device, characterized in that, Includes the lithium metal battery cell according to any one of claims 1 to 12.

14. An electrical appliance, characterized in that, Includes the lithium metal battery cell according to any one of claims 1 to 12 or the battery device according to claim 13.

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