Electrolyte containing fluorinated phosphate additive and product containing electrolyte

Abstract

The invention discloses an electrolyte containing a fluorinated phosphate additive and a product containing the electrolyte, and belongs to the technical field of lithium metal secondary batteries, the electrolyte comprises a lithium salt, an organic solvent and the fluorinated phosphate additive; wherein the fluorinated phosphate additive has a structural formula of # imgabs0 #, the fluorinated phosphate additive is used as an optimized electrolyte to be applied to the lithium metal secondary battery, the fluorinated phosphate additive can form a layer of uniform and compact CEI film and SEI film on the surfaces of a positive electrode and a lithium metal negative electrode, and an electrode-electrolyte interface is stabilized, so that side reaction between the positive electrode and the negative electrode and the electrolyte is inhibited, and the service life of the lithium metal secondary battery is prolonged. And meanwhile, due to the flame resistance of the phosphate ester substances, the safety of the battery is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium metal secondary batteries, and in particular relates to an electrolyte containing a fluorinated phosphate additive and a product containing the electrolyte. Background Art

[0002] Due to the limited reserves of traditional fossil energy resources such as oil and coal, the inconvenience of mining and the inevitable environmental pollution caused by their use, some new energy technologies have begun to slowly replace traditional energy, gradually developing and entering people's lives. Among them, new energy secondary batteries are a very important technology, mainly used in electric vehicles and portable electronic products. The most widely used lithium-ion secondary batteries (graphite as the negative electrode) in these fields have an energy density of <200Wh / kg, which is difficult to meet the future long-term battery life requirements. Lithium metal secondary batteries refer to secondary batteries with lithium metal as the negative electrode. Because lithium metal has an extremely high theoretical specific capacity (3860mAh g -1 ) and received widespread attention.

[0003] Although lithium metal secondary batteries have broad application prospects, they still face some basic problems and safety limitations. The main problems they face are the continuous growth of lithium dendrites during the cycle and the side reactions of the metal anode with most electrolytes, which lead to serious degradation of cycle performance. At the same time, since the main body of its electrolyte is mostly flammable organic liquid, there are safety hazards such as combustion and explosion. Given that the formation of lithium dendrites and interfacial reactions are largely affected by the surface characteristics of the lithium metal anode, establishing an effective solid electrolyte interface (SEI) on the lithium surface has become a key method to improve the performance of lithium metal batteries.

[0004] In order to make the lithium metal anode more stable during the cycle and inhibit the growth of dendrites and side reactions, various methods have been proposed, including electrolyte optimization in the electrolyte, solvation regulation of the electrolyte, use of artificial SEI layer, solid electrolyte, assembly of three-dimensional (3D) composite anode to regulate deposition morphology and use of electrolyte additives. Among these methods, the use of electrolyte additives is the simplest and most effective method to control the nucleation and growth behavior of lithium deposition, which has been widely studied.

[0005] Therefore, it is very important to study an electrolyte additive to improve the cycle performance and safety of lithium metal batteries. Summary of the invention

[0006] In view of the above technical problems, the present invention provides an electrolyte containing a fluorinated phosphate additive and a product containing the same.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention:

[0009] An electrolyte containing a fluorinated phosphate ester additive, comprising a lithium salt and an organic solvent, and further comprising a fluorinated phosphate ester additive;

[0010] Wherein, the structural formula of the fluorinated phosphate additive is:

[0011]

[0012] Beneficial effects: In the lithium metal battery prepared by the electrolyte defined in the present invention, during its operation, the fluorinated phosphate additive can preferentially participate in the reaction to form a solid electrolyte film on the surface of the metal negative electrode, inhibiting the growth of lithium dendrites to avoid premature short circuit of the battery and direct reaction of the electrolyte with lithium metal; it can also react on the positive electrode to form a dense and strong positive electrode electrolyte film, thereby avoiding direct contact between the electrolyte and the positive electrode material and preventing capacity decay caused by the dissolution of the positive electrode transition metal; and the fluorinated phosphate additive introduces a large number of fluorine, fluoroalkyl, phosphate and other groups with strong electron-withdrawing ability, which can improve the conductivity of the electrolyte and reduce the combustion ability of the electrolyte. The formed SEI film has good lithium ion transmission ability, thereby effectively reducing the internal resistance of the battery and improving the cycle performance.

[0013] Optionally, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethylsulfonylimide, lithium tetrachloroaluminate or lithium hexafluoroarsenate.

[0014] Furthermore, the lithium salt is lithium hexafluorophosphate or lithium bis(trifluoromethylsulfonyl)imide.

[0015] Optionally, the organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide or dimethyl sulfoxide.

[0016] Furthermore, the organic solvent includes a cyclic carbonate and a linear carbonate, and the volume ratio of the two is (3:7)-(1:1);

[0017] Wherein, the cyclic carbonate is any one of ethylene carbonate, propylene carbonate, vinylene carbonate, vinylethylene carbonate or fluoroethylene carbonate;

[0018] The linear carbonate is any one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

[0019] Preferably, the ratio of the lithium salt to the organic solvent is (0.8-1.5) mol:1L;

[0020] The fluorinated phosphate additive accounts for 0.1% to 5% of the volume of the mixed solvent formed by the lithium salt and the organic solvent.

[0021] Preferably, the preparation process of the electrolyte containing the fluorinated phosphate additive is:

[0022] The organic solvent, the lithium salt and the fluorinated phosphate additive are added in this order and stirred evenly to obtain the product.

[0023] The second technical solution of the present invention:

[0024] Application of the above electrolyte containing fluorinated phosphate additive in the preparation of lithium metal batteries.

[0025] The third technical solution of the present invention:

[0026] A lithium metal battery comprises a positive electrode, a negative electrode, a separator (celgard 2400 polypropylene) and an electrolyte containing the above-mentioned fluorinated phosphate additive.

[0027] Preferably, the lithium metal battery is LiNi 0.8 Co 0.1 Mn 0.1 O2 as the positive electrode and lithium metal as the negative electrode of the secondary battery, including LiNi 0.8 Co 0.1 Mn 0.1 O2 / Li button cell or lithium symmetrical button cell.

[0028] Furthermore, the LiNi 0.8 Co 0.1 Mn 0.1 The preparation process of the positive electrode of the O2 / Li button battery is as follows:

[0029] The positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super P, and polyvinylidene fluoride are uniformly dispersed in N,N-dimethylpyrrolidone in a mass ratio of 8:1:1 to prepare a positive electrode slurry;

[0030] The slurry was evenly coated on an aluminum foil with a thickness of 25 μm, placed in a vacuum oven at 110° C. for drying, and rolled and die-cut to form a positive electrode sheet.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The phosphate substances of the present invention are used as additives for lithium metal battery electrolytes. Since they can form a uniform and dense CEI film and SEI film on the surface of the positive electrode and the negative electrode, the electrode-electrolyte interface is stabilized, thereby protecting the positive and negative electrodes from reacting with the electrolyte, thereby improving the battery performance. At the same time, due to the flame retardancy of the phosphate substances, the safety of the battery is also improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 The optimized electrolyte and blank electrolyte obtained in Example 1 of the present invention are used for LiNi 0.8 Co 0.1 Mn 0.1 Cycling performance diagram of O2 / Li button battery;

[0035] Figure 2 The optimized electrolyte and blank electrolyte obtained in Example 2 of the present invention are used for LiNi 0.8 Co 0.1 Mn 0.1 Cycling performance diagram of O2 / Li button battery;

[0036] Figure 3 The cycle performance diagram of the optimized electrolyte and the blank electrolyte obtained in Example 3 of the present invention for lithium symmetric button cells;

[0037] Figure 4 This is a cycle performance diagram of the optimized electrolyte obtained in Example 4 of the present invention and the blank electrolyte used in lithium symmetric button batteries. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] The embodiment of the present invention discloses an electrolyte containing a fluorinated phosphate additive, which comprises a lithium salt, a fluorinated phosphate additive and a non-aqueous organic solvent.

[0044] Among them, the structural formula of the fluorinated phosphate additive is as follows:

[0045]

[0046] In some preferred embodiments, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethylsulfonylimide, lithium tetrachloroaluminate or lithium hexafluoroarsenate.

[0047] In some preferred embodiments, the non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide or dimethyl sulfoxide.

[0048] In addition, an embodiment of the present invention also discloses a lithium metal battery based on the electrolyte containing the fluorinated phosphate additive. The lithium metal battery includes a positive electrode, a negative electrode, a separator and the electrolyte containing the fluorinated phosphate additive.

[0049] The raw materials used in the embodiments of the present invention are all purchased from the market.

[0050] The technical solution of the present invention is further illustrated by the following embodiments.

[0051] Example 1

[0052] (1) fully mixing cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) at a volume ratio of EC:EMC=1:1 to obtain a basic solvent;

[0053] (2) In a glove box, dissolve the conductive lithium salt LiPF6 in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stir evenly, and obtain a blank electrolyte;

[0054] (3) adding tri(2,2,2-trifluoroethyl)phosphate, whose structural formula is as follows, to the blank electrolyte prepared in step (2) in an amount of 5% of the volume of the blank electrolyte to obtain an optimized electrolyte;

[0055]

[0056] (4) The positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super P, and polyvinylidene fluoride are uniformly dispersed in N,N-dimethylpyrrolidone solvent in a mass ratio of 8:1:1 to prepare positive electrode slurry; the dispersed slurry is uniformly coated on an aluminum foil with a thickness of 25 μm, placed in a vacuum oven at 110°C for drying, and rolled and die-cut to prepare a positive electrode sheet;

[0057] (5) The optimized electrolyte obtained in step (3) of this embodiment and the blank electrolyte obtained in step (2) are respectively used for LiNi 0.8 Co 0.1 Mn 0.1 The cycle performance of O2 / Li button batteries was compared. The results are as follows Figure 1 As shown. Figure 1 It can be seen that the optimized electrolyte prepared by adding tris(2,2,2-trifluoroethyl) phosphate can still have 190 mAh g after 100 cycles at 4.5 V. -1 The capacity retention rate is close to 86%, while the capacity of the blank electrolyte drops rapidly to 35% of the initial capacity after 60 cycles. From the results, it can be seen that the addition of tris (2,2,2-trifluoroethyl) phosphate can improve the performance of lithium metal batteries.

[0058] Example 2

[0059] (1) fully mixing cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent dimethyl carbonate (DMC) at a volume ratio of EC:DMC=1:1 to obtain a base solvent;

[0060] (2) In a glove box, dissolve the conductive lithium salt LiPF6 in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stir evenly, and obtain a blank electrolyte;

[0061] (3) adding tri(2,2,2-trifluoroethyl)phosphite, whose structural formula is as follows, to the blank electrolyte prepared in step (2) in an amount of 2% of the volume of the blank electrolyte to obtain an optimized electrolyte;

[0062]

[0063] (4) The positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super P, and polyvinylidene fluoride are uniformly dispersed in N,N-dimethylpyrrolidone solvent in a mass ratio of 8:1:1 to prepare positive electrode slurry; the dispersed slurry is uniformly coated on an aluminum foil with a thickness of 25 μm, placed in a blast oven at 110°C for drying, and die-cut to prepare positive electrode sheets;

[0064] (5) The optimized electrolyte obtained in step (3) of this embodiment and the blank electrolyte in step (2) are used for LiNi 0.8 Co 0.1 Mn 0.1 The cycle performance of O2 / Li button batteries was compared. The results are as follows Figure 2 As shown. Figure 2 It can be seen that the optimized electrolyte prepared by adding tri(2,2,2-trifluoroethane)phosphite still has 180 mAhg after 120 cycles at 4.5 V. -1 The capacity of the blank electrolyte decreased to 50% of the initial capacity after 50 cycles. The addition of tris(2,2,2-trifluoroethyl)phosphite can improve the performance of lithium metal batteries.

[0065] Example 3

[0066] (1) fully mixing cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent diethyl carbonate (DEC) at a volume ratio of EC:DEC=3:7 to obtain a base solvent;

[0067] (2) In a glove box, dissolve the conductive lithium salt LiTFSI in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, and stir evenly to obtain a blank electrolyte;

[0068] (3) adding methyl bis(2,2,2-trifluoroethyl)phosphonoacetate, whose structural formula is as follows, to the blank electrolyte prepared in step (2) in an amount of 3% of the volume of the blank electrolyte to obtain an optimized electrolyte;

[0069]

[0070] (4) The optimized electrolyte obtained in step (3) of this embodiment and the blank electrolyte in step (2) were used in lithium symmetrical button cells to compare the cycle performance. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the optimized electrolyte prepared by adding methyl bis(2,2,2-trifluoroethyl)phosphonoacetate has a high current density of 1 mA cm -2 , deposition surface capacity 1 mAh cm -2 The cycle time of the blank electrolyte is about 300 hours, which is nearly 200 hours longer than the blank sample, proving its improvement in the cycle capacity of lithium metal batteries.

[0071] Example 4

[0072] (1) fully mixing cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent diethyl carbonate (DEC) at a volume ratio of EC:DEC=3:7 to obtain a base solvent;

[0073] (2) In a glove box, dissolve the conductive lithium salt LiPF6 in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stir evenly, and obtain a blank electrolyte;

[0074] (3) adding bis(2,2,2-trifluoroethyl)phosphite, whose structural formula is as follows, to the blank electrolyte prepared in step (2) in an amount of 3% of the volume of the blank electrolyte to obtain an optimized electrolyte;

[0075]

[0076] (4) The optimized electrolyte obtained in step (3) of this embodiment and the blank electrolyte in step (2) were used in lithium symmetrical button cells to compare the cycle performance. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the voltage of the optimized electrolyte prepared by adding bis(2,2,2-trifluoroethyl)phosphite is smaller than that of the blank electrolyte, which proves its ability to reduce the internal resistance of the battery. At the same time, its current density is 1mA·cm -2 , deposition surface capacity 1 mAh cm -2In the case of the test sample, the cycle time can reach about 550 hours, while that of the blank sample is only about 300 hours. The improvement in the cycle performance of lithium metal is still very obvious.

[0077] The time taken for the electrolytes of Examples 1-4 to self-extinguish after penetrating the paper and burning was verified below. The specific effect data are shown in Table 1.

[0078] Table 1

[0079]

[0080] Comparative Example 1

[0081] On the basis of Example 4, the amount of the fluorinated phosphate additive was changed so that the amount of bis(2,2,2-trifluoroethyl)phosphite was 10% of the volume of the blank electrolyte.

[0082] The optimized electrolyte prepared in this comparative example has a current density of 1 mA cm -2 In this case, the cycle time can reach about 310h.

[0083] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An electrolyte containing a fluorinated phosphate additive, comprising a lithium salt and an organic solvent, characterized in that: Also included are fluorinated phosphate ester additives; Wherein, the structural formula of the fluorinated phosphate additive is:

2. The electrolyte containing a fluorinated phosphate additive according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethylsulfonylimide, lithium tetrachloroaluminate or lithium hexafluoroarsenate.

3. The electrolyte containing a fluorinated phosphate additive according to claim 2, characterized in that: The lithium salt is lithium hexafluorophosphate or lithium bis(trifluoromethylsulfonyl)imide.

4. The electrolyte containing a fluorinated phosphate additive according to claim 1, characterized in that: The organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide or dimethyl sulfoxide.

5. The electrolyte containing a fluorinated phosphate additive according to claim 4, characterized in that: The organic solvent includes a cyclic carbonate and a linear carbonate, and the volume ratio of the two is (3:7)-(1:1); Wherein, the cyclic carbonate is any one of ethylene carbonate, propylene carbonate, vinylene carbonate, vinylethylene carbonate or fluoroethylene carbonate; The linear carbonate is any one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

6. The electrolyte containing a fluorinated phosphate additive according to claim 1, characterized in that: The ratio of the lithium salt to the organic solvent is (0.8-1.5) mol: 1L; The fluorinated phosphate additive accounts for 0.1% to 5% of the volume of the mixed solvent formed by the lithium salt and the organic solvent.

7. Use of the electrolyte containing the fluorinated phosphate additive according to any one of claims 1 to 6 in the preparation of a lithium metal battery.

8. A lithium metal battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte containing a fluorinated phosphate additive as claimed in any one of claims 1 to 6.

9. A lithium metal battery according to claim 8, characterized in that: The lithium metal battery is LiNi 0.8 Co 0.1 Mn 0.1 A secondary battery with O2 as the positive electrode and lithium metal as the negative electrode.

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