Electrolyte, lithium ion battery and electric equipment

Abstract

The invention discloses an electrolyte, a lithium battery and electric equipment. The electrolyte comprises a solvent, a lithium salt and an additive, the additive comprises crown ether, alkali metal nitrate and cyclic lactone, and the alkali metal nitrate comprises at least one of potassium nitrate, rubidium nitrate and cesium nitrate. The electrolyte can form an SEI film with an inorganic-polymer composite structure on the surface of lithium metal, and the inorganic SEI film layer improves the uniformity of lithium ion transmission and inhibits the generation of lithium dendrites; the toughness of the SEI film is improved by the polymer part, and the damage of volume change to the integrity of the SEI film is reduced. Meanwhile, according to the scheme, the fast charging capacity of the electrolyte can be improved, and high-rate charging and discharging of the lithium metal battery can be achieved. Therefore, the electrolyte can stably act for a long time, and can tolerate the volume change of lithium metal.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to electrolytes, lithium-ion batteries and electrical equipment. Background Art

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

[0003] The main solution to the recycling problem of lithium metal negative electrodes is to form a uniform and stable SEI structure on the surface of lithium metal during the cycle through electrolyte design and the use of additives, thereby inhibiting the formation of lithium dendrites. Among them, the most commonly used method is to use sacrificial additives to form an inorganic SEI layer on the surface of lithium metal, but this method has two problems. The first is that the battery performance will rapidly decline after the sacrificial additives are exhausted. The second is that it is difficult for the inorganic SEI to remain intact during the drastic volume changes of lithium metal. During the cycle, the lithium metal exposed by the broken SEI will continue to react with the electrolyte, accelerating the consumption of electrolyte, additives and active lithium. Therefore, it is urgent to develop an electrolyte that can act stably for a long time and can tolerate the volume changes of lithium metal. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes an electrolyte, a lithium ion battery and an electrical device that can function stably for a long time and can tolerate the volume change of lithium metal.

[0005] In a first aspect of the present application, an electrolyte is provided, which includes a solvent, a lithium salt and an additive, wherein the additive includes a crown ether, an alkali metal nitrate and a cyclic lactone, and the alkali metal nitrate includes at least one of potassium nitrate, rubidium nitrate and cesium nitrate.

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

[0007] The electrolyte prepared in this application can form an inorganic-polymer composite structure SEI film on the surface of lithium metal, wherein the inorganic SEI film layer improves the uniformity of lithium ion transmission and inhibits the formation of lithium dendrites; the polymer part improves the toughness of the SEI film and reduces the damage to the integrity of the SEI film caused by volume changes. At the same time, this solution can improve the fast charging ability of the electrolyte and can achieve high-rate charging and discharging of lithium metal batteries. As a result, this electrolyte can act stably for a long time and can tolerate volume changes of lithium metal.

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

[0009] The macrocyclic structure of the crown ether molecule contains holes, which can form a complex with the alkali metal ions of the alkali metal nitrate through ion-dipole bonds. When the two are used together, the crown ether as an alkali metal coordination molecule can significantly improve the solubility of the alkali metal nitrate in organic solvents. The crown ether alkali metal complex formed has an excellent catalytic effect on the ring-opening polymerization of cyclic lactones. When the three are combined together, the crown ether alkali metal complex is adsorbed on the surface of the lithium metal negative electrode by electrostatic force, catalyzing the ring-opening polymerization of cyclic lactones on the lithium metal surface to form a continuous organic polymer layer. In addition, the nitrate of the alkali metal nitrate participates in the formation of the solvation shell structure and can be preferentially reduced to an inorganic SEI, while the cyclic lactone acts later in time to form an organic polymer SEI layer, and finally generates an inorganic-polymer layered SEI that can be stable in long cycles, reducing the consumption of electrolyte and lithium metal negative electrode layers, and obtaining better cycle performance.

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

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

[0012] In some embodiments of the present application, the molar ratio of the crown ether to the 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, 2:1.

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

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

[0015] In some embodiments of the present application, the electrolyte contains at least one of 0.001-0.015 mol / L potassium nitrate, 0.001-0.1 mol / L rubidium nitrate, and 0.001-0.58 mol / L cesium nitrate. 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, 0.01 mol / L, 0.011 mol / L, 0.012 mol / L, 0.013 mol / L, 0.014 mol / L , 0.015mol / L potassium nitrate; and / or, 0.001mol / L, 0.002mol / L, 0.003mol / L, 0.004mol / L, 0.005mol / L, 0.006mol / L, 0.008mol / L, 0.01mol / L, 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, 0.06mol / L, 0.0 8mol / L, 0.1mol / L of rubidium nitrate; and / or, 0.001mol / L, 0.002mol / L, 0.003mol / L, 0.004mol / L, 0.005mol / L, 0.006mol / L, 0.007mol / L, 0.008mol / L, 0.009mol / L, 0.01mol / L, 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, 0.06mol / L, 0.08mol / L, 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.51mol / L, 0.52mol / L, 0.53mol / L, 0.54mol / L, 0.55mol / L, 0.56mol / L, 0.57mol / L, 0.58mol / L of cesium nitrate. For potassium, rubidium and cesium used in alkali metal nitrates, by controlling their concentrations within the above ranges, the actual redox potential of these alkali metal ions can be made lower than that of lithium ions, which can play an electrostatic shielding role in inhibiting the growth of lithium dendrites, slowing down the capacity decline of the battery, and improving the safety performance of the battery.

[0016] In some embodiments of the present application, the solvent includes at least one of ethylene glycol dimethyl ether DME, diethylene glycol butyl ether DEGDEM, ethylene glycol diethyl ether (DEE), ethylene carbonate EC, diethyl carbonate DEC, dimethyl carbonate DMC, ethyl methyl carbonate EMC, propylene carbonate PC, butylene 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 the present application, the lithium salt includes at least one of LiPF6, LiAsF6, LiSbF6, LiBF4, lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), LiClO4, 2-trifluoromethyl-4,5-dicyanoimidazole lithium (LiTDI), bis(fluorosulfonyl)imide lithium salt (LiFSI), and bis(trifluoromethanesulfonyl)imide lithium (LiTFSI).

[0018] In some embodiments of the present application, the concentration of lithium salt in the electrolyte is 0.01 to 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 the present 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 hole diameter of the 18 series crown ethers is 0.26 to 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), and thus can effectively form a complex.

[0020] In some embodiments of the present 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 hole 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, so it can form a complex with the latter two.

[0021] In some embodiments of the present application, the crown ether includes 12 series crown ethers, and the alkali metal nitrate includes potassium nitrate. The hole diameter of the 12 series crown ethers is smaller than that of the 15 series crown ethers, and is close to the diameter of potassium ions, so a complex can be formed therewith.

[0022] In a second aspect of the present application, a lithium-ion battery is provided. The lithium-ion battery comprises the aforementioned electrolyte.

[0023] In some embodiments of the present application, the lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, the aforementioned electrolyte and a separator. The positive electrode sheet, the negative electrode sheet and the separator are wound, laminated or the like to obtain a battery cell and manufacture a lithium-ion battery.

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

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

[0026] In some embodiments of the present application, the positive electrode current collector is selected from at least one of metal materials including 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 the present application, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material 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 the present application, the raw material of the positive electrode active material layer also includes 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, etc. The binder includes but is not limited to at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, polyvinyl butyral, etc.

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

[0030] In some embodiments of the present application, the separator comprises a polymer separator, and the polymer separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, and multilayer composite films thereof.

[0031] According to a third aspect of the present application, there is provided an electrical device, the electrical device comprising the aforementioned lithium-ion battery.

[0032] Among them, electrical equipment refers to any equipment that can use electrical energy and convert it into mechanical energy, thermal energy, light energy or other one or more forms of energy, such as electric motors, electric heat engines, electric light sources, etc. Among them, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can be mobile phones, laptops, drones, sweeping robots, electronic 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 the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the concept of the present application and the technical effects produced in combination with the embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present application.

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

[0036] In the description of this application, "several" means more than one, "many" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, "above", "below", "within", etc. are understood to include the number itself, and "about" means within the range of ±20%, 10%, 8%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.2%, 0.1%, etc. of the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0037] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0038] The present application is described below in conjunction with specific embodiments.

[0039] Example 1

[0040] This embodiment provides an electrolyte, and the composition of the electrolyte is as follows:

[0041] Organic solvent: 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] The lithium salt and additives are dissolved in the 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, which is different from the embodiment 1 in that the additive composition is 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, which is different from the embodiment 1 in that the composition of the additive is 0.01 mol / L potassium nitrate, 0.01 mol / L 15-crown-5 and 1 wt % of lactide.

[0049] Embodiments 4 to 10

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

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

[0052]

[0053]

[0054] Performance Testing

[0055] The lithium copper composite tape with a lithium layer thickness of 20 μm was used as the negative electrode, and NCA (LiNi 0.8 Co 0.15 Al 0.05 O2) as the positive electrode, the electrolyte of the embodiment or the comparative example is used to assemble a lithium metal battery with a surface capacity of 3 mAh / cm 2 Under 25℃ environment, the battery 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 rate during the cycle. The comparative electrolyte is also referred to Table 1, and the test results are shown in Table 2.

[0056] 100-cycle capacity retention rate = 100th-cycle discharge capacity / 1st-cycle discharge capacity × 100%.

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

[0058]

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

[0060] The present application is described in detail above in conjunction with the embodiments, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. An electrolyte, characterized in that The electrolyte includes a solvent, a lithium salt and an additive, wherein the additive includes a crown ether, an alkali metal nitrate and a cyclic lactone, and the alkali metal nitrate includes at least one of potassium nitrate, rubidium nitrate and cesium nitrate.

2. The electrolyte according to claim 1, characterized in that The ether ring of the crown ether contains 12, 15 or 18 atoms.

3. The electrolyte according to claim 2, characterized in that The crown ether includes 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, dicyclohexane-18-crown-6, 4-vinylbenzo-18-crown-6, 4-acrylamidobenzo-18-crown-6, 4'-aminobenzo-18-crown-6, 4'-aminodibenzo-18-crown-6, di(3,4-dibromobenzo)-18-crown-6, and aza-18-crown-6.

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

1.

5. The electrolyte according to claim 1, characterized in that The cyclic lactone includes at least one of glycolide, lactide, butyrolactone, valerolactone and caprolactone.

6. The electrolyte according to claim 1 or 5, characterized in that The content of the cyclic lactone in the electrolyte is 0.05 to 5 wt %.

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

8. A lithium-ion battery, characterized in that The electrolyte comprising the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that: The negative electrode active material of the lithium ion battery includes metallic lithium.

10. Electrical equipment, characterized in that: A lithium ion battery comprising any one of claims 8 to 9.

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