Electrolyte for lithium metal battery containing rare earth phosphate and lithium metal battery

Abstract

The invention belongs to the technical field of lithium metal batteries, and provides a rare earth phosphate-containing electrolyte for a lithium metal battery and the lithium metal battery. The electrolyte comprises the following components in parts by weight: 50-70 parts of an organic solvent, 10-20 parts of electrolyte salt and 5-10 parts of a functional additive, the organic solvent comprises 1-30 parts of a carboxylic ester solvent, 1-30 parts of a carbonic ester solvent and 1-40 parts of an ether solvent, and the electrolyte salt comprises a lithium salt with the concentration of 0.5-2.0 mol / L; the functional additive comprises 1-10 parts of a film-forming additive and 1-5 parts of rare earth phosphate. The electrolyte provided by the invention adopts a mixed solvent system with high ionic conductivity, so that the electrolyte has moderate ionic conductivity and viscosity, the effects of reducing the internal resistance of the battery and prolonging the cycle life are achieved, the lithium metal battery can stably work in a wide temperature interval and under high-rate current, and the service life of the lithium metal battery is prolonged. And the internal short-circuit failure of the battery caused by decomposition is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, and in particular relates to an electrolyte for lithium metal batteries containing rare earth phosphates and a lithium metal battery. Background Art

[0002] In today's society, with the booming development of new industries such as high-end communications, electric vehicles, aerospace, and drones, high energy density energy storage has become an inevitable trend in the development of the battery field. Existing lithium-ion batteries are limited by the theoretical specific capacity of positive and negative electrode materials, and it is difficult to achieve a breakthrough in energy density. In recent years, metallic lithium anodes have received extensive attention from researchers. The specific capacity of metallic lithium is as high as 3860 mAh / g, and the density is only 0.59 g / cm 3 , with a potential as low as -3.04 V, it is the most ideal negative electrode material. Therefore, it is very urgent for power batteries to develop and produce lithium metal battery systems and achieve a leapfrog improvement in battery energy density.

[0003] Lithium metal anodes have attracted widespread attention due to their excellent performance, but applying lithium metal anodes in lithium-ion battery systems is not a simple task. Early commercialization of lithium metal anodes all failed due to safety issues. The main reason is that the non-uniform lithium deposition during charging leads to the continuous growth of lithium dendrites, which eventually pierce the diaphragm and cause a short circuit between the positive and negative electrodes. In addition, the continuous side reactions between the metal lithium anode and the electrolyte during the cycle will lead to a significant decrease in the coulombic efficiency of the battery. The huge volume expansion is another problem faced by the lithium metal anode. During repeated charging and discharging, the deposition of lithium metal on the anode is not a dense structure, but a loose structure with many gaps. The volume of the anode continues to expand, resulting in a rapid decay of the capacity and coulombic efficiency of the lithium metal battery. At present, the commercialization of lithium metal batteries as power batteries is not yet mature. Summary of the invention

[0004] The object of the present invention is to provide an electrolyte for a lithium metal battery and a lithium metal battery containing rare earth phosphate, so that the electrolyte has moderate ionic conductivity and viscosity, thereby reducing the internal resistance of the battery and improving the cycle life, and allowing the lithium metal battery to operate stably in a wide temperature range and at a high rate current without decomposition causing internal short circuit failure of the battery.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A first aspect of the present invention provides an electrolyte for a lithium metal battery containing a rare earth phosphate, which comprises, by weight, 50-70 parts of an organic solvent, 10-20 parts of an electrolyte salt and 5-10 parts of a functional additive; wherein, by weight, the organic solvent comprises 1-30 parts of a carboxylate solvent, 1-30 parts of a carbonate solvent and 1-40 parts of an ether solvent, and the electrolyte salt comprises a lithium salt with a concentration of 0.5-2.0 mol / L; and, by weight, the functional additive comprises 1-10 parts of a film-forming additive and 1-5 parts of a rare earth phosphate.

[0006] Furthermore, the carboxylic acid ester solvent is any one of ethyl acetate, propyl acetate, methyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trifluoroacetate, and ethyl heptafluorobutyrate, or a combination of two or more thereof, but is not limited thereto.

[0007] Further, the carbonate solvent is any one of dimethyl carbonate, ethyl methyl carbonate, dimethyl allyl carbonate, ethylene carbonate, fluoroethylene carbonate, diphenyl carbonate, and propylene carbonate, or a combination of two or more thereof, but is not limited thereto.

[0008] Further, the ether solvent is any one or a combination of two or more of tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, isosorbide dimethyl ether, boron trifluoride dimethyl ether, n-propyl ether, diethylene glycol dimethyl ether, and anisole, but is not limited thereto.

[0009] Further, the lithium salt is any one of lithium difluorosulfonyl imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, and lithium bis(trifluoromethylsulfonyl)imide, or a combination of two or more thereof, but is not limited thereto.

[0010] Furthermore, the ionic conductivity of the organic solvent is 1-18 mS / cm.

[0011] Furthermore, the ionic conductivity of the electrolyte for lithium metal batteries is 5-25 mS / cm, the viscosity is 5-15 mPa·s, and can be In a stable state.

[0012] Further, the film-forming additive is any one of lithium difluorooxalatoborate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 3,3,3-trifluoropropylmethyl, 4-propyl ethylene sulfate, dimethyl sulfite, methylene disulfonate, lithium difluorophosphate, and lithium bis(oxalate)borate, or a combination of two or more thereof, but is not limited thereto.

[0013] Furthermore, the rare earth element in the rare earth phosphate is any one or a combination of two or more of lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, dysprosium, holmium, thulium or lutetium, but is not limited thereto.

[0014] A second aspect of the present invention provides a lithium metal battery, comprising the above-mentioned rare earth phosphate-containing lithium metal battery electrolyte.

[0015] Furthermore, the energy density of the lithium metal battery is 400-550 Wh / kg, the internal resistance is less than 15 mΩ, and the number of cycles is greater than 180.

[0016] Beneficial effects of the present invention: 1) The present invention provides an electrolyte for a lithium metal battery. The present invention provides an electrolyte for a lithium metal battery. Inorganic rare earth phosphate is used as an additive for a mixed solvent electrolyte. P element is introduced to react with lithium metal to generate Li3P. Li at the interface of Li3P + The coordination number of solvent molecules in the solvation sheath is the lowest (2.63), and the Li + It is easier to dissolve before diffusing through the solid electrolyte interface (SEI). DFT calculations show that Li3P and Li + The affinity is the strongest, resulting in the Li + The solvation structure is different, which promotes the Li + Rapid desolvation. The inorganic SEI component rich in Li3P is not only beneficial for accelerating Li + The desolvation process can significantly enhance the + The migration speed in SEI greatly improves the rate performance of lithium metal batteries.

[0017] 2) The present invention provides an electrolyte for lithium metal batteries, which uses inorganic rare earth phosphate as an additive for a mixed solvent electrolyte. The unique 4f empty orbitals and 4f orbital electrons of rare earth cations will form complex and diverse coordination structures when interacting with ligands, thereby affecting the solvation structure of lithium ions in the electrolyte, so that the rare earth phosphate has good solubility in the mixed solvent electrolyte and improves the battery stability.

[0018] 3) The electrolyte for lithium metal batteries provided by the present invention adopts a mixed solvent system (carboxylate solvent, carbonate solvent, ether solvent) with high ionic conductivity (1-18 mS / cm), so that the electrolyte has moderate ionic conductivity (5-25 mS / cm) and viscosity (5-15 mPa·s), and has a wide temperature range (-25-50 ) is in a stable state and will not decompose and cause internal short circuit failure of the battery.

[0019] 4) The electrolyte for lithium metal batteries provided by the present invention contains an ether solvent and a film-forming additive in the electrolyte, so that a passivation layer is formed at the interface between the positive and negative electrodes and the electrolyte, which can inhibit the continuous decomposition of the electrolyte solvent and protect the structural stability of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 It is an energy density cycle trend diagram of the soft-pack metal battery prepared by the lithium metal electrolyte configured in Example 1, Example 7, Comparative Example 1 and Comparative Example 9 of the present invention; Figure 2 It is a discharge capacity-voltage diagram of a soft-pack metal battery prepared by lithium metal electrolytes configured in Example 3, Example 6, Comparative Example 2 and Comparative Example 5 of the present invention at a discharge current of 5C; Figure 3 It is an energy density-voltage diagram of a soft-package metal battery prepared by using lithium metal electrolytes configured in Example 4, Example 7, Comparative Example 3 and Comparative Example 9 of the present invention; Figure 4 It is an internal resistance diagram of a soft-pack metal battery prepared by using the lithium metal electrolyte configured in Examples 1-9 and Comparative Examples 1-9 of the present invention; Figure 5 It is a conductivity diagram of soft-pack metal batteries prepared by using lithium metal electrolytes configured in Examples 1-9 and Comparative Examples 1-9 of the present invention; Figure 6 It is a viscosity diagram of soft-pack metal batteries prepared by lithium metal electrolytes configured in Examples 1-9 and Comparative Examples 1-9 of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] A first aspect of the present invention provides an electrolyte for a lithium metal battery containing a rare earth phosphate, which comprises, by weight, 50-70 parts of an organic solvent, 10-20 parts of an electrolyte salt and 5-10 parts of a functional additive; wherein, by weight, the organic solvent comprises 1-30 parts of a carboxylate solvent, 1-30 parts of a carbonate solvent and 1-40 parts of an ether solvent, and the electrolyte salt comprises a lithium salt with a concentration of 0.5-2.0 mol / L; and, by weight, the functional additive comprises 1-10 parts of a film-forming additive and 1-5 parts of a rare earth phosphate.

[0024] Example 1

[0025] Prepare the electrolyte: In a glove box filled with argon, mix 2.4 g of methyl propionate, 1.7 g of dimethyl carbonate, and 4.6 g of ethylene glycol dimethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, slowly add 2 g of lithium bis(difluorosulfonyl)imide with a lithium concentration of 0.9 mol / L, 0.71 g of vinylene carbonate, and 0.36 g of lanthanum phosphate into the organic solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0026] Example 2

[0027] Prepare electrolyte: In a glove box filled with argon, mix 2.7 g of ethyl acetate, 1.4 g of diethyl carbonate, and 4.6 g of tetraethylene glycol dimethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, slowly add 3 g of lithium hexafluorophosphate with a lithium concentration of 1.4 mol / L, 0.89 g of lithium bis(oxaloyl)borate, and 0.5 g of ytterbium phosphate into the organic solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0028] Example 3

[0029] Prepare electrolyte: In a glove box filled with argon, mix 2.7 g of ethyl difluoroacetate, 1.8 g of propylene carbonate, and 4.2 g of anisole to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.2 g of 2.0 mol / L lithium tetrafluoroborate, 0.45 g of lithium difluorophosphate, and 0.77 g of praseodymium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0030] Example 4

[0031] Preparation of electrolyte: In a glove box filled with argon, 1.5 g of ethyl heptafluorobutyrate, 1.83 g of fluoroethylene carbonate, 2.5 g of n-propyl ether and 4.61 g of ethylene glycol dimethyl ether were mixed to obtain a mixed solvent, and the mixed solvent was used as an organic solvent. Then, 2.32 g of lithium hexafluorophosphate with a concentration of 0.9 mol / L, 0.55 g of 3,3,3-trifluoropropylmethyl phosphate and 0.5 g of terbium phosphate were slowly added to the mixed solvent, and the mixture was stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0032] Example 5

[0033] Preparation of electrolyte: In a glove box filled with argon, 1.36 g of propyl acetate, 1.74 g of dimethyl allyl carbonate, 5 g of ethylene glycol diethyl ether and 2.34 g of dimethyl isosorbide were mixed to obtain a mixed solvent, and the mixed solvent was used as an organic solvent. Then, 2 g of lithium nitrate with a concentration of 1.3 mol / L, 0.5 g of 1,3-propane sultone, 0.12 g of lithium bis(oxalate borate) and 0.45 g of lanthanum phosphate were slowly added to the mixed solvent, and the mixture was stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0034] Example 6

[0035] Prepare the electrolyte: in a glove box filled with argon, mix 1.36 g of propyl acetate, 1.55 g of diphenyl carbonate, and 6.66 g of dimethyl isosorbide to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.5 g of 1.5 mol / L lithium hexafluorophosphate, 0.15 g of 1.8 mol / L lithium nitrate, 1.03 g of 4-propyl ethylene sulfate, and 0.2 g of rubidium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0036] Example 7

[0037] Prepare electrolyte: In a glove box filled with argon, mix 1.9 g propyl acetate, 1.81 g dimethyl carbonate, and 9.34 g ethylene glycol dimethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 3 g of 2.0 mol / L lithium hexafluorophosphate, 0.34 g of lithium difluorooxalatoborate, 0.5 g of lutetium phosphate, and 0.78 g of gadolinium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0038] Example 8

[0039] Prepare the electrolyte: In a glove box filled with argon, mix 2.5 g of ethyl heptafluorobutyrate, 1.9 g of ethyl methyl carbonate, and 6.04 g of ethylene glycol diethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.42 g of lithium hexafluorophosphate with a concentration of 1.4 mol / L, 0.98 g of methylene methanedisulfonate, and 0.25 g of cerium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0040] Example 9

[0041] Prepare the electrolyte: In a glove box filled with argon, mix 2.88 g of ethyl acetate, 1.74 g of dimethyl carbonate, and 7.56 g of ethylene glycol dimethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.15 g of 1 mol / L lithium hexafluorophosphate, 1.3 g of lithium bis(oxaloyl)borate, and 0.2 g of ytterbium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0042] Comparative Example 1

[0043] Prepare the electrolyte: In a glove box filled with argon, mix 1 g of ethylene carbonate, 5 g of ethyl methyl carbonate, and 2 g of methyl propionate to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 1.0 g of 0.85 mol / L lithium hexafluorophosphate, 0.35 g of lithium bis(oxaloyl)borate, and 0.35 g of neodymium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0044] Comparative Example 2

[0045] Prepare the electrolyte: In a glove box filled with argon, mix 2 g of ethyl propionate, 2 g of hexafluoropropylene oxide, and 4 g of dimethyl isosorbide to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 0.95 g of 1 mol / L lithium hexafluorophosphate, 0.5 g of lithium bis(oxaloyl)borate, and 0.2 g of lanthanum phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0046] Comparative Example 3

[0047] Prepare the electrolyte: In a glove box filled with argon, mix 5 g of dimethyl carbonate and 3 g of ethylene glycol diethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 1.2 g of 0.9 mol / L lithium nitrate, 0.83 g of vinylene carbonate and 0.25 g of ytterbium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0048] Comparative Example 4

[0049] Prepare the electrolyte: In a glove box filled with argon, mix 5.2 g of ethyl methyl carbonate, 2.2 g of propyl propionate, and 2 g of ethylene glycol dimethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 1.35 g of lithium hexafluorophosphate with a concentration of 1.5 mol / L and 0.5 g of vinylene carbonate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0050] Comparative Example 5

[0051] Prepare the electrolyte: In a glove box filled with argon, mix 2.5 g of fluoroethylene carbonate and 6 g of diethyl carbonate to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.0 g of 1 mol / L lithium tetrafluoroborate and 0.4 g of lithium bis(oxalate)borate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0052] Comparative Example 6

[0053] Prepare the electrolyte: In a glove box filled with argon, mix 2.5 g of ethylene carbonate and 6.5 g of ethyl methyl carbonate to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.0 g of 1 mol / L lithium difluorosulfonyl imide, 0.3 g of lithium bis(oxalyl)borate and 0.17 g of praseodymium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0054] Comparative Example 7

[0055] Prepare the electrolyte: In a glove box filled with argon, mix 3 g of dimethyl carbonate and 6 g of diethyl carbonate to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.0 g of lithium hexafluorophosphate with a concentration of 1 mol / L into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0056] Comparative Example 8

[0057] Prepare the electrolyte: In a glove box filled with argon, mix 3 g of ethylene glycol dimethyl ether and 6 g of hexafluoropropylene oxide to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 2.0 g of lithium bistrifluoromethylsulfonyl imide with a concentration of 1 mol / L into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0058] Comparative Example 9

[0059] Prepare the electrolyte: In a glove box filled with argon, mix 4 g of ethyl difluoroacetate and 4 g of ethylene glycol diethyl ether to obtain a mixed solvent, use the mixed solvent as an organic solvent, then slowly add 0.8 g of 2 mol / L lithium nitrate, 0.83 g of vinylene carbonate and 0.25 g of dysprosium phosphate into the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0060] 1. The lithium metal electrolytes prepared in Examples 1-9 and Comparative Examples 1-9 were used as electrolytes to prepare soft-pack lithium metal batteries (nominal capacity 3 Ah): 1) Preparation of positive electrode: Under low dew point conditions (-40 ), LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent (SP), carbon nanotubes (CNT), and adhesive (PVDF) were mixed evenly in a weight ratio of 96.5:1.0:1.0:1.5, and stirred at high speed in vacuum to prepare positive electrode slurry; the slurry was evenly coated on a 12 μm aluminum foil to prepare an electrode; the electrode was placed in a vacuum at 85 Drying under an ambient temperature, and rolling and slitting to obtain a positive electrode sheet; 2) Preparation of negative electrode sheet: In a glove box filled with argon, the lithium strip is punched into a standard shape using a die-cutting machine, the surface is polished and ground, and then rolled flat to obtain the negative electrode sheet; 3) Preparation of battery cells: The prepared positive electrode sheet, negative electrode sheet and a polyethylene separator with a thickness of 19 μm are stacked in sequence to form a square battery cell, and the battery cell is loaded into a soft-pack battery shell (made of aluminum-plastic film), and then the lithium metal electrolyte configured in Examples 1-9 and Comparative Examples 1-9 is injected under a vacuum environment. After packaging, the cells are allowed to stand, formed, degassed, aged and divided into different volumes to obtain soft-pack lithium metal battery cells.

[0061] 2. The performance of the lithium metal electrolyte prepared in Examples 1-9 and Comparative Examples 1-9 and the prepared soft-package metal battery cells were tested respectively, and the testing method was as follows: 1) Energy density detection: at 25 Under the conditions, the soft-pack lithium metal battery cells prepared by Examples 1-9 and Comparative Examples 1-9 were charged to 4.3 V at a constant current and constant voltage of 0.2 C, with a cut-off current of 0.05 C; then left for 10 minutes; and then discharged to 3.0 V at a constant current of 0.5 C, and the discharge energy under the conditions was recorded. The energy density (Wh / kg) of the battery cell was obtained by dividing the discharge energy (Wh) by the mass (kg) of the battery cell; 2) Ratio test: at 25 Under the conditions, the soft-pack lithium metal battery cells prepared by Examples 1-9 and Comparative Examples 1-9 were charged to 4.3 V at 0.2 C constant current and constant voltage, with a cut-off current of 0.05 C; then left for 10 minutes; and then discharged to 3.0 V at 5 C constant current, and the percentage obtained by dividing the discharge capacity under this condition by the nominal capacity was recorded; 3) Cyclic capacity test: at 25 Under the conditions, the soft-pack lithium metal battery cells prepared by Examples 1-9 and Comparative Examples 1-9 were charged to 4.3 V at 0.2 C constant current and constant voltage, with a cut-off current of 0.05 C; then left for 10 minutes; and then discharged to 3.0 V at 0.5 C constant current, and the number of cycles when the capacity decayed to 80% of the nominal capacity was recorded; 4) Discharge test at different temperatures: Under the conditions, the soft-pack lithium metal battery cells prepared by Examples 1-9 and Comparative Examples 1-9 were charged to 4.3 V at 0.2 C constant current and constant voltage, with a cut-off current of 0.05 C; then placed in a high and low temperature test cabinet, set different temperatures (stand at this temperature for 2 h), and discharged to 3.0 V at 0.5 C constant current (the cut-off voltage was reduced to 2.0 V at low temperatures to ensure that the battery cells can be discharged normally), and the battery cells were recorded at -25 , -15 , 0 , 25 , 50 The discharge capacity under the condition of 25 60% of the time is considered to be able to work; 5) Internal resistance detection: at 25 Under the conditions, the soft-pack lithium metal batteries prepared in Examples 1-9 and Comparative Examples 1-9 were tested for internal resistance using an internal resistance meter, and the internal resistance data were recorded; 6) Conductivity test: at 25 Under the conditions, the lithium metal battery electrolytes prepared by Examples 1-9 and Comparative Examples 1-9 were tested for conductivity using conductivity, and the internal resistance data were recorded; 7) Viscosity test: at 25 Under the conditions, the viscosity of the lithium metal battery electrolytes prepared in Examples 1-9 and Comparative Examples 1-9 was tested using a viscosity tester, and the internal resistance data was recorded.

[0062] The above results are shown in Table 1 and Figure 1-6 As shown: Table 1

[0063] From Table 1 and Figure 1-6 It can be seen that the electrolyte for lithium metal battery provided by the present invention uses inorganic rare earth phosphate as an additive for mixed solvent electrolyte, introduces P element and lithium metal to generate Li3P, wherein Li + The coordination number of solvent molecules in the solvation sheath is the lowest (2.63), and the Li + It is easier to dissolve before diffusing through the solid electrolyte interface (SEI). DFT calculations show that Li3P and Li + The affinity is the strongest, resulting in the Li + The solvation structure is different, which promotes the Li + Rapid desolvation. The inorganic SEI component rich in Li3P is not only beneficial for accelerating Li + The desolvation process can significantly enhance the +The migration speed in SEI greatly improves the rate performance of lithium metal batteries.

[0064] The present invention provides an electrolyte for lithium metal batteries, which uses inorganic rare earth phosphate as an additive for a mixed solvent electrolyte. The unique 4f orbital electrons and 4f empty orbitals of rare earth cations form complex and diverse coordination structures when interacting with ligands, thereby affecting the solvation structure of lithium ions in the electrolyte, so that the rare earth phosphate has good solubility in the mixed solvent electrolyte, thereby improving battery stability.

[0065] The present invention provides an electrolyte for lithium metal batteries, which uses a mixed solvent system (carboxylate solvent, carbonate solvent, ether solvent) with high ionic conductivity (1-18 mS / cm) as an organic solvent, so that the obtained electrolyte has moderate ionic conductivity (5-25 mS / cm) and viscosity (5-15 mPa·s), and has a wide temperature range (-25-50 ) is in a stable state and will not decompose and cause internal short circuit failure of the battery.

[0066] The electrolyte for a lithium metal battery provided by the present invention contains a film-forming additive and an ether solvent in the electrolyte, so that a passivation layer is formed at the interface between the positive and negative electrodes and the electrolyte, which can inhibit the continuous decomposition of the electrolyte solvent and protect the structural stability of the electrodes; in addition, the electrolyte for a lithium metal battery provided by the present invention has excellent electrochemical performance in the selection of the solvent system (carboxylic acid ester solvents, carbonate solvents, ether solvents) and various functional additives in the electrolyte, including an energy density of 400-550 Wh / kg, an internal resistance of less than 15mΩ, and a cycle number of more than 180.

[0067] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0068] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An electrolyte for a lithium metal battery containing a rare earth phosphate, characterized in that: In parts by weight, it includes 50-70 parts of organic solvent, 10-20 parts of electrolyte salt and 5-10 parts of functional additives; wherein, in parts by weight, the organic solvent includes 1-30 parts of carboxylate solvent, 1-30 parts of carbonate solvent and 1-40 parts of ether solvent, and the electrolyte salt includes a lithium salt with a concentration of 0.5-2.0 mol / L; in parts by weight, the functional additive includes 1-10 parts of film-forming additive and 1-5 parts of rare earth phosphate.

2. The electrolyte for lithium metal batteries containing rare earth phosphate according to claim 1, characterized in that: The carboxylic acid ester solvent is any one of ethyl acetate, propyl acetate, methyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trifluoroacetate, and ethyl heptafluorobutyrate, or a combination of two or more thereof.

3. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The carbonate solvent is any one of dimethyl carbonate, ethyl methyl carbonate, dimethyl allyl carbonate, ethylene carbonate, fluoroethylene carbonate, diphenyl carbonate, and propylene carbonate, or a combination of two or more thereof.

4. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The ether solvent is any one of tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, isosorbide dimethyl ether, boron trifluoride dimethyl ether, n-propyl ether, diethylene glycol dimethyl ether, and anisole, or a combination of two or more thereof.

5. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The lithium salt is any one of lithium difluorosulfonyl imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, and lithium bis(trifluoromethylsulfonyl)imide, or a combination of two or more thereof.

6. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The ionic conductivity of the organic solvent is 1-18 mS / cm.

7. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The lithium metal battery electrolyte has an ion conductivity of 5-25 mS / cm and a viscosity of 5-15 mPa·s, and can be In a stable state.

8. The electrolyte for lithium metal battery containing rare earth phosphate according to claim 1, characterized in that: The film-forming additive is any one of lithium difluorooxalatoborate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 3,3,3-trifluoropropylmethyl ethylene, 4-propyl ethylene sulfate, dimethyl sulfite, methylene methanedisulfonate, lithium difluorophosphate, and lithium bis(oxalate)borate, or a combination of two or more thereof; And / or, the rare earth element in the rare earth phosphate is any one of lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, dysprosium, holmium, thulium or lutetium, or a combination of two or more thereof.

9. A lithium metal battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte comprises the rare earth phosphate-containing lithium metal battery electrolyte according to any one of claims 1 to 8.

10. A lithium metal battery according to claim 9, characterized in that: The energy density of the lithium metal battery is 400-550 Wh / kg, the internal resistance is less than 15 mΩ, and the number of cycles is greater than 180.

Images