Electrolyte, lithium ion battery and electric device

Abstract

This application discloses an electrolyte, a lithium battery, and an electrical device. The electrolyte comprises a solvent, a lithium salt, and additives. The additives include crown ethers, alkali metal nitrates, and cyclic lactones. The alkali metal nitrates include at least one selected from potassium nitrate, rubidium nitrate, and cesium nitrate. The electrolyte can form an inorganic-polymer composite SEI film on the lithium metal surface. The inorganic SEI film layer improves the uniformity of lithium-ion transport and inhibits the formation of lithium dendrites; the polymer portion improves the toughness of the SEI film and reduces the damage to the integrity of the SEI film caused by volume changes. Simultaneously, this solution can improve the fast-charging capability of the electrolyte, enabling high-rate charge and discharge of the lithium metal battery. Therefore, this electrolyte can operate stably for a long time and can withstand lithium metal volume changes.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to electrolytes, lithium-ion batteries and electrical devices. Background Technology

[0002] The energy density of lithium-ion batteries has become a bottleneck limiting further performance improvements in devices such as electric vehicles, drones, and smartphones. The practical capacity of the most widely used graphite anode is nearing its theoretical limit, with limited room for further improvement. Therefore, there is an urgent need to develop new high-capacity anodes. Lithium metal anodes have a theoretical specific capacity as high as 3860 mA / h, an electrochemical potential of -3.04 V, and an extremely high theoretical energy density, which can significantly improve the overall energy density of lithium-ion batteries. However, the cycling stability and safety issues of lithium metal anodes in use severely limit their further application.

[0003] To address the cycling issues of lithium metal anodes, the main approach is to design the electrolyte and use additives to create a uniform and stable SEI structure on the lithium metal surface during cycling, thereby suppressing lithium dendrite formation. The most common method is to use sacrificial additives to form an inorganic SEI layer on the lithium metal surface. However, this method has two problems: first, battery performance rapidly declines after the sacrificial additives are depleted; second, the inorganic SEI is difficult to maintain its integrity under drastic volume changes in lithium metal. During cycling, the exposed lithium metal from the broken SEI continues to react with the electrolyte, accelerating the consumption of electrolyte, additives, and active lithium. Therefore, there is an urgent need to develop an electrolyte that can maintain long-term stability and withstand lithium metal volume changes. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes an electrolyte, a lithium-ion battery, and an electrical device that can operate stably for a long period of time and can withstand changes in the volume of lithium metal.

[0005] A first aspect of this application provides an electrolyte comprising a solvent, a lithium salt, and additives, wherein the additives include crown ethers, alkali metal nitrates, and cyclic lactones, and the alkali metal nitrates include at least one of potassium nitrate, rubidium nitrate, and cesium nitrate.

[0006] The electrolyte according to the first aspect of this application has the following beneficial effects:

[0007] The electrolyte prepared in this application can form an inorganic-polymer composite SEI film on the lithium metal surface. The inorganic SEI film layer improves the uniformity of lithium-ion transport and inhibits the formation of lithium dendrites; the polymer portion enhances the toughness of the SEI film and reduces the damage to its integrity caused by volume changes. Simultaneously, this solution improves the fast-charging capability of the electrolyte, enabling high-rate charge-discharge of lithium metal batteries. Therefore, this electrolyte can operate stably for a long period and is resistant to lithium metal volume changes.

[0008] Specifically, for the combination of the above additives:

[0009] The macrocyclic structure of crown ether molecules contains vacancies, allowing them to form complexes with alkali metal ions of alkali metal nitrates via ion-dipole bonds. When used in combination, the crown ether, acting as an alkali metal coordinating molecule, significantly enhances the solubility of alkali metal nitrates in organic solvents. The resulting crown ether alkali metal complex exhibits excellent catalytic activity for the ring-opening polymerization of cyclic lactones. When all three are combined, the crown ether alkali metal complex is electrostatically adsorbed onto the lithium metal anode surface, catalyzing the ring-opening polymerization of cyclic lactones on the lithium metal surface to form a continuous organic polymer layer. Furthermore, the nitrate ions of the alkali metal nitrate participate in the formation of the solvation shell structure and are preferentially reduced to the inorganic SEI, while the cyclic lactones act sequentially to form the organic polymer SEI layer. Ultimately, this results in an inorganic-polymer layered SEI that can stably exist during long-term cycling, reducing electrolyte and lithium metal anode layer consumption and achieving superior cycling performance.

[0010] In some embodiments of this application, the number of atoms in the ether ring of the crown ether is 12, 15 or 18, and can be referred to as 12-series crown ethers, 15-series crown ethers and 18-series crown ethers respectively.

[0011] In some embodiments of this application, the crown ether includes at least one of the following: 15-series crown ethers (such as 15-crown-5, benzo-15-crown-5, 2,3-naphtho-15-crown-5, aza-15-crown-5) and 18-series crown ethers (such as 18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, 4-vinylbenzo-18-crown-6, 4-acrylamidobenzo-18-crown-6, 4'-aminobenzo-18-crown-6, 4'-aminodibenzo-18-crown-6, bis(3,4-dibromobenzo)-18-crown-6, aza-18-crown-6).

[0012] In some embodiments of this application, the molar ratio of crown ether to alkali metal nitrate is (0.5-2):1, for example, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, or 2:1.

[0013] In some embodiments of this application, the cyclic lactone includes at least one of glycolide, lactide, butyrolactone, valproic acid lactone, and caprolactone.

[0014] In some embodiments of this application, the content of cyclic lactones in the electrolyte is 0.05 to 5 wt%, for example, it can be 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0015] In some embodiments of this application, the electrolyte contains at least one of potassium nitrate (0.001–0.015 mol / L), rubidium nitrate (0.001–0.1 mol / L), and cesium nitrate (0.001–0.58 mol / L). For example, the electrolyte may contain 0.001 mol / L, 0.002 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.007 mol / L, 0.008 mol / L, 0.009 mol / L, 0.011 mol / L, 0.012 mol / L, 0.013 mol / L, or 0.014 mol / L. 0.015 mol / L potassium nitrate; and / or, comprising 0.001 mol / L, 0.002 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.008 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.0 Rubidium nitrate at concentrations of 8 mol / L and 0.1 mol / L; and / or, comprising concentrations of 0.001 mol / L, 0.002 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.007 mol / L, 0.008 mol / L, 0.009 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, and 0.04 mol / L. Cesium nitrate concentrations of 0.05 mol / L, 0.06 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, 0.51 mol / L, 0.52 mol / L, 0.53 mol / L, 0.54 mol / L, 0.55 mol / L, 0.56 mol / L, 0.57 mol / L, and 0.58 mol / L. For potassium, rubidium, and cesium used in alkali metal nitrates, controlling their concentrations within the above ranges can lower the actual redox potential of these alkali metal ions compared to lithium ions. This provides electrostatic shielding to inhibit lithium dendrite growth, slow down battery capacity degradation, and improve battery safety.

[0016] In some embodiments of this application, the solvent includes at least one of the following: dimethyl ethylene glycol (DME), dibutyl ethylene glycol (DEGDEM), diethyl ethylene glycol (DEE), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butenyl carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and 1,3-dioxolane.

[0017] In some embodiments of this application, the lithium salt includes at least one of LiPF6, LiAsF6, LiSbF6, LiBF4, lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), LiClO4, lithium 2-trifluoromethyl-4,5-dicyanimidazolium (LiTDI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0018] In some embodiments of this application, the concentration of lithium salt in the electrolyte is 0.01–5 mol / L, for example, it can be 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 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, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or 5 mol / L.

[0019] In some embodiments of this application, the crown ether includes 18-series crown ethers, and the alkali metal nitrate includes at least one of potassium nitrate, rubidium nitrate, and cesium nitrate. The vacancy diameter of the 18-series crown ether is 0.26–0.32 nm, which is similar to the diameters of potassium ions, rubidium ions, and cesium ions (0.266 nm, 0.296 nm, and 0.338 nm, respectively), thus enabling the effective formation of complexes.

[0020] In some embodiments of this application, the crown ether includes a 15-series crown ether, and the alkali metal nitrate includes at least one of potassium nitrate and rubidium nitrate. The vacancy diameter of the 15-series crown ether is smaller than that of the 18-series crown ether, and is similar to the diameter of potassium ions and rubidium ions, thus it can form complexes with the latter two.

[0021] In some embodiments of this application, the crown ether includes a series 12 crown ether, and the alkali metal nitrate includes potassium nitrate. The vacancy diameter of the series 12 crown ether is smaller than that of the series 15 crown ether, and is similar to that of the potassium ion, thus allowing it to form complexes with it.

[0022] A second aspect of this application provides a lithium-ion battery comprising the aforementioned electrolyte.

[0023] In some embodiments of this application, a lithium-ion battery includes a positive electrode, a negative electrode, the aforementioned electrolyte, and a separator. The positive electrode, negative electrode, and separator are processed into a cell by at least one of the following methods: winding, stacking, etc., and then manufactured into a lithium-ion battery.

[0024] In some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, which includes metallic lithium.

[0025] In some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector.

[0026] In some embodiments of this application, the positive current collector is selected from at least one of the following metal materials: metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil or alloy foil of the above metals), metal mesh (such as aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh or alloy mesh of the above metals).

[0027] In some embodiments of this application, the positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel manganese aluminum oxide.

[0028] In some embodiments of this application, the raw materials for the positive electrode active material layer further include at least one of a conductive agent and a binder. The conductive agent includes, but is not limited to, conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, SO, etc.), conductive carbon black (such as Super P, Super S, 350G, acetylene black, Ketjen black, etc.), conductive carbon fiber (such as VGCF, CNT), and graphene. The binder includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, and polyvinyl butyral.

[0029] In some embodiments of this application, the positive electrode active material layer comprises 70-99 wt% positive electrode active material, 0.5-6 wt% conductive agent and 0.5-20 wt% binder.

[0030] In some embodiments of this application, the diaphragm comprises a polymer diaphragm, which includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, and their multilayer composite membranes.

[0031] A third aspect of this application provides an electrical device that includes the aforementioned lithium-ion battery.

[0032] Electrical equipment refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other forms of energy, such as electric motors, electric heaters, and electric light sources. This includes mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can be mobile phones, laptops, drones, robot vacuum cleaners, e-cigarettes, etc.; electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0033] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0034] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0035] The embodiments of this application are described in detail below. The described embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0036] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number, and "approximately" means within the range of ±20%, 10%, 8%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.2%, 0.1%, etc. of the stated number. The use of "first" and "second" is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0037] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] The present application will be described below with reference to specific embodiments.

[0039] Example 1

[0040] This embodiment provides an electrolyte with the following composition:

[0041] Organic solvents: ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 1:1:1;

[0042] Lithium salt: 1 mol / L LiPF6;

[0043] Additives: 0.2 mol / L cesium nitrate, 0.2 mol / L 18-crown-6 and 1 wt% lactide.

[0044] Lithium salts and additives are dissolved in a well-mixed organic solvent according to the proportions and their respective final concentrations to prepare an electrolyte.

[0045] Example 2

[0046] This embodiment provides an electrolyte that differs from that in Example 1 in that the additives consist of 0.1 mol / L rubidium nitrate, 0.1 mol / L 18-crown-6, and 1 wt% lactide.

[0047] Example 3

[0048] This embodiment provides an electrolyte that differs from that in Example 1 in that the additives consist of 0.01 mol / L potassium nitrate, 0.01 mol / L 15-crown-5, and 1 wt% lactide.

[0049] Examples 4-10

[0050] Examples 4-10 provide an electrolyte that differs from Example 1 in that the composition of the additives is different, as detailed in Table 1.

[0051] Table 1. Additive composition of some examples and comparative examples

[0052]

[0053]

[0054] Performance testing

[0055] Using a lithium-copper composite strip with a lithium layer thickness of 20 μm as the negative electrode, and NCA (LiNi) as the negative electrode... 0.8 Co 0.15 Al 0.05 Using O2 as the positive electrode, lithium metal battery cladding cells were assembled using the electrolyte from the examples or comparative examples, with an areal capacity of 3 mAh / cm². 2 At 25°C, the electrolyte was cycled at a charge / discharge rate of 0.5 / 1C (charging mode: 0.5C CC to 4.25V, CV to 0.02C; discharging mode: 1C DC to 3.0V) to examine the capacity retention during cycling. The electrolyte for the comparative example is also referenced in Table 1, and the test results are shown in Table 2.

[0056] 100-week capacity retention = discharge capacity in week 100 / discharge capacity in week 1 × 100%.

[0057] Table 2. Performance test results of the examples and comparative examples

[0058]

[0059] As can be seen from the above results, compared with Example 1, the capacity retention rates of Comparative Examples 1 to 7 all showed significant decreases to varying degrees when one or more components were omitted.

[0060] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. Furthermore, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises a solvent, a lithium salt, and additives, wherein the additives include crown ethers, alkali metal nitrates, and cyclic lactones, and the alkali metal nitrates include at least one of potassium nitrate, rubidium nitrate, and cesium nitrate. The crown ether has 12, 15 or 18 atoms in its ether ring; The cyclic lactones include at least one of glycolide, lactide, butyrolactone, valproic acid lactone, and caprolactone. The content of the cyclic lactone in the electrolyte is 0.05~5 wt%.

2. The electrolyte according to claim 1, characterized in that, The crown ether comprises at least one of 15-crown-5, benzo-15-crown-5, 2,3-naphtho-15-crown-5, aza-15-crown-5, 18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, 4-vinylbenzo-18-crown-6, 4-acrylamidobenzo-18-crown-6, 4'-aminobenzo-18-crown-6, 4'-aminodibenzo-18-crown-6, bis(3,4-dibromobenzo)-18-crown-6, and aza-18-crown-6.

3. The electrolyte according to claim 1, characterized in that, The molar ratio of the crown ether to the alkali metal nitrate is (0.5~2):

1.

4. The electrolyte according to claim 1, characterized in that, The electrolyte contains at least one of potassium nitrate at 0.001~0.015 mol / L, rubidium nitrate at 0.001~0.1 mol / L, and cesium nitrate at 0.001~0.58 mol / L.

5. A lithium-ion battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 4.

6. The lithium-ion battery according to claim 5, characterized in that, The negative electrode active material of the lithium-ion battery includes metallic lithium.

7. Electrical equipment, characterized in that, Including the lithium-ion battery as described in any one of claims 5 to 6.

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