An electrolyte for a lithium metal battery containing rare earth phosphate and a lithium metal battery

Abstract

The present invention belongs to the technical field of lithium metal batteries, and provides an electrolyte for a lithium metal battery containing rare earth phosphate and a lithium metal battery. The electrolyte comprises, by weight parts, 50 - 70 parts of an organic solvent, 10 - 20 parts of an 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 carbonate solvent, and 1 - 40 parts of an ether solvent, the electrolyte salt comprises a lithium salt with a 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 present invention adopts a mixed solvent system with high ionic conductivity, so that the electrolyte has moderate ionic conductivity and viscosity, which can reduce the internal resistance of the battery and improve the cycle life, and enables the lithium metal battery to work stably in a wide temperature range and at a high rate of current, avoiding the internal short circuit failure of the battery caused by decomposition.

Description

Technical Field

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

[0002] In today's society, with the booming development of new industries such as high-end communication, 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 the 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, the density is only 0.59 g / cm 3 , and the potential is as low as -3.04 V, which is the most ideal anode material. Therefore, it is very urgent for power batteries to develop and produce a lithium metal battery system to achieve a leapfrog improvement in battery energy density.

[0003] The metallic lithium anode has attracted extensive attention due to its excellent performance. However, applying the metallic lithium anode in a lithium-ion battery system is not an easy task. In the early days, the commercialization of the metallic lithium anode failed due to safety issues. The main reason is that during charging, non-uniform lithium deposition leads to the continuous growth of lithium dendrites, which eventually pierce the separator and cause short circuit between the positive and negative electrodes. In addition, the continuous side reaction between the metallic lithium anode and the electrolyte during cycling will lead to a significant reduction in the Coulombic efficiency of the battery. The huge volume expansion is another problem faced by the metallic lithium anode. During repeated charge and discharge processes, the deposition of metallic lithium on the anode is not a dense structure but a loose structure with many voids, and the volume of the anode continuously expands, resulting in a rapid decay of the capacity and Coulombic efficiency of the lithium metal battery. Currently, the commercialization of lithium metal batteries as power batteries is not yet mature. Summary of the Invention

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

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] In the first aspect of the present invention, an electrolyte for a lithium metal battery containing rare earth phosphate is provided. By weight, it includes 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 includes 1-30 parts of a carboxylic acid ester solvent, 1-30 parts of a carbonate solvent, and 1-40 parts of an ether solvent, and the electrolyte salt includes a lithium salt with a concentration of 0.5-2.0 mol / L; by weight, the functional additive includes 1-10 parts of a film-forming additive and 1-5 parts of rare earth phosphate.

[0007] Further, the carboxylic acid ester solvent is any one or a combination of two or more of ethyl acetate, propyl acetate, methyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trifluoroacetate, ethyl heptafluorobutyrate, etc., but not limited thereto.

[0008] Further, the carbonate solvent is any one or a combination of two or more of dimethyl carbonate, ethyl methyl carbonate, dimethylallyl carbonate, ethylene carbonate, fluorinated ethylene carbonate, diphenyl carbonate, propylene carbonate, etc., but not limited thereto.

[0009] 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, anisole, etc., but not limited thereto.

[0010] Further, the lithium salt is any one or a combination of two or more of lithium difluorosulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium bis(trifluoromethylsulfonyl)imide, etc., but not limited thereto.

[0011] Further, the ionic conductivity of the organic solvent is 1-18 mS / cm.

[0012] Further, the ionic conductivity of the electrolyte for the lithium metal battery is 5-25 mS / cm, the viscosity is 5-15 mPa·s, and it can be in a stable state at -25-50 °C.

[0013] Further, the film-forming additive is any one or a combination of two or more of lithium difluorooxalate borate, vinylene carbonate, ethylene vinylene carbonate, 1,3-propane sultone, 3,3,3-trifluoropropylmethyl sulfite, 4-ethylsulfite ethyl sulfate, dimethyl sulfite, methylene methanedisulfonate, lithium difluorophosphate, lithium bis(oxalato)borate, etc., but not limited thereto.

[0014] Further, 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, lutetium, etc., but not limited thereto.

[0015] In the second aspect of the present invention, a lithium metal battery is provided, which includes the electrolyte for a lithium metal battery containing rare earth phosphate as described above.

[0016] 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 cycling times is greater than 180.

[0017] Advantages of the present invention:

[0018] 1) For the electrolyte for a lithium metal battery provided by the present invention, an inorganic rare earth phosphate is used as an additive to the electrolyte of the mixed solvent. P element is introduced to generate Li3P with lithium metal. Among them, the coordination number of the solvent molecules in the solvation sheath at the Li3P interface is the lowest (2.63). The Li with low solvent coordination + is more likely to desolvate before diffusing through the solid electrolyte interface (SEI). DFT calculation shows that the affinity energy between Li3P and Li + is the strongest, resulting in differences in the solvation structure of Li at the interfaces of different components, and promoting the rapid desolvation of Li at the Li3P interface. The inorganic SEI component rich in Li3P is not only beneficial to accelerating the desolvation process of Li + but also can significantly enhance the migration speed of Li + in the SEI, greatly improving the rate performance of the lithium metal battery. + + +

[0019]

[0019] 2) For the electrolyte for a lithium metal battery provided by the present invention, an inorganic rare earth phosphate is used as an additive to the electrolyte of the mixed solvent. 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, making the rare earth phosphate have good solubility in the electrolyte of the mixed solvent and improving the battery stability.

[0020] 3) The electrolyte for a lithium metal battery provided by the present invention adopts a mixed solvent system (carboxylic ester solvents, carbonate solvents, ether solvents) with high ionic conductivity (1 - 18 mS / cm), making the electrolyte have moderate ionic conductivity (5 - 25 mS / cm) and viscosity (5 - 15 mPa·s), and being in a stable state in a wide temperature range (-25 - 50 ), so as not to decompose and cause internal short - circuit failure of the battery.

[0021] 4) The electrolyte for a lithium metal battery 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 electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the drawings.

[0023] Figure 1 It is a graph showing the cyclic trend of the energy density of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Example 1, Example 7, Comparative Example 1, and Comparative Example 9 of the present invention;

[0024] Figure 2 It is the discharge capacity of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Example 3, Example 6, Comparative Example 2, and Comparative Example 5 of the present invention at a 5C discharge current voltage graph;

[0025] Figure 3 It is an energy density-voltage graph of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Example 4, Example 7, Comparative Example 3, and Comparative Example 9 of the present invention;

[0026] Figure 4 It is an internal resistance graph of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Examples 1-9 and Comparative Examples 1-9 of the present invention;

[0027] Figure 5 It is a conductivity graph of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Examples 1-9 and Comparative Examples 1-9 of the present invention;

[0028] Figure 6 It is a viscosity graph of a soft-pack metal battery prepared from the lithium metal electrolytes configured in Examples 1-9 and Comparative Examples 1-9 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0030] In the first aspect of the present invention, an electrolyte for a lithium metal battery containing rare earth phosphate is provided. By weight, it includes 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 includes 1 - 30 parts of a carboxylic acid ester solvent, 1 - 30 parts of a carbonate solvent, and 1 - 40 parts of an ether solvent, and the electrolyte salt includes a lithium salt with a concentration of 0.5 - 2.0 mol / L; by weight, the functional additive includes 1 - 10 parts of a film - forming additive and 1 - 5 parts of rare earth phosphate.

[0031] Example 1

[0032] Prepare the electrolyte: In a glove box filled with argon, 2.4 g of methyl propionate, 1.7 g of dimethyl carbonate, and 4.6 g of ethylene glycol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent. Then, 2 g of lithium bis (difluoromethanesulfonyl) imide with a lithium concentration of 0.9 mol / L, 0.71 g of vinylene carbonate, and 0.36 g of lanthanum phosphate were slowly added to this organic solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0033] Example 2

[0034] Prepare the electrolyte: In a glove box filled with argon, 2.7 g of ethyl acetate, 1.4 g of diethyl carbonate, and 4.6 g of tetraethylene glycol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent. Then, 3 g of lithium hexafluorophosphate with a lithium concentration of 1.4 mol / L, 0.89 g of lithium bis (oxalato) borate, and 0.5 g of ytterbium phosphate were slowly added to this organic solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0035] Example 3

[0036] Prepare the electrolyte: In a glove box filled with argon, 2.7 g of ethyl difluoroacetate, 1.8 g of propylene carbonate, and 4.2 g of anisole were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent. Then, 2.2 g of lithium tetrafluoroborate with a concentration of 2.0 mol / L, 0.45 g of lithium difluorophosphate, and 0.77 g of praseodymium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0037] Example 4

[0038] Preparing the electrolyte: In a glove box filled with argon, 1.5 g of ethyl heptafluorobutyrate, 1.83 g of vinyl fluorocarbonate, 2.5 g of n-propyl ether and 4.61 g of ethylene glycol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 2.32 g of lithium hexafluorophosphate with a concentration of 0.9 mol / L, 0.55 g of 3,3,3-trifluoropropylmethyl sulfoxide and 0.5 g of terbium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0039] Example 5

[0040] Preparing the electrolyte: In a glove box filled with argon, 1.36 g of propyl acetate, 1.74 g of diallyl carbonate, 5 g of ethylene glycol diethyl ether and 2.34 g of isosorbide dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and 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 stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0041] Example 6

[0042] Preparing the electrolyte: In a glove box filled with argon, 1.36 g of propyl acetate, 1.55 g of diphenyl carbonate and 6.66 g of isosorbide dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 2.5 g of lithium hexafluorophosphate with a concentration of 1.5 mol / L, 0.15 g of lithium nitrate with a concentration of 1.8 mol / L, 1.03 g of 4-ethylsulfonylsulfite and 0.2 g of rubidium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0043] Example 7

[0044] Preparing the electrolyte: In a glove box filled with argon, 1.9 g of propyl acetate, 1.81 g of dimethyl carbonate and 9.34 g of ethylene glycol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 3 g of lithium hexafluorophosphate with a concentration of 2.0 mol / L, 0.34 g of lithium difluoro(oxalato)borate, 0.5 g of lutetium phosphate and 0.78 g of gadolinium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0045] Example 8

[0046] Preparing the electrolyte: In a glove box filled with argon, 2.5 g of ethyl heptafluorobutyrate, 1.9 g of ethyl methyl carbonate, and 6.04 g of ethylene glycol diethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 2.42 g of lithium hexafluorophosphate with a concentration of 1.4 mol / L, 0.98 g of methylene methanesulfonate, and 0.25 g of cerium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0047] Example 9

[0048] Preparing the electrolyte: In a glove box filled with argon, 2.88 g of ethyl acetate, 1.74 g of dimethyl carbonate, and 7.56 g of ethylene glycol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 2.15 g of lithium hexafluorophosphate with a concentration of 1 mol / L, 1.3 g of lithium bis(oxalato)borate, and 0.2 g of ytterbium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0049] Comparative Example 1

[0050] Preparing the electrolyte: In a glove box filled with argon, 1 g of ethylene carbonate, 5 g of ethyl methyl carbonate, and 2 g of methyl propionate were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 1.0 g of lithium hexafluorophosphate with a concentration of 0.85 mol / L, 0.35 g of lithium bis(oxalato)borate, and 0.35 g of neodymium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0051] Comparative Example 2

[0052] Preparing the electrolyte: In a glove box filled with argon, 2 g of ethyl propionate, 2 g of hexafluoropropylene oxide, and 4 g of isosorbitol dimethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 0.95 g of lithium hexafluorophosphate with a concentration of 1 mol / L, 0.5 g of lithium bis(oxalato)borate, and 0.2 g of lanthanum phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0053] Comparative Example 3

[0054] Preparing the electrolyte: In a glove box filled with argon, 5 g of dimethyl carbonate and 3 g of ethylene glycol diethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent, and then 1.2 g of lithium nitrate with a concentration of 0.9 mol / L, 0.83 g of vinylene carbonate, and 0.25 g of ytterbium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0055] Comparative Example 4

[0056] Prepare 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 this mixed solvent as the organic solvent, and then slowly add 1.35 g of lithium hexafluorophosphate with a concentration of 1.5 mol / L and 0.5 g of vinylene carbonate to the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0057] Comparative Example 5

[0058] Prepare 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 this mixed solvent as the organic solvent, and then slowly add 2.0 g of lithium tetrafluoroborate with a concentration of 1 mol / L and 0.4 g of lithium bis(oxalato)borate to the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0059] Comparative Example 6

[0060] Prepare 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 this mixed solvent as the organic solvent, and then slowly add 2.0 g of lithium difluoromethanesulfonimide with a concentration of 1 mol / L, 0.3 g of lithium bis(oxalato)borate, and 0.17 g of praseodymium phosphate to the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0061] Comparative Example 7

[0062] Prepare 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 this mixed solvent as the organic solvent, and then slowly add 2.0 g of lithium hexafluorophosphate with a concentration of 1 mol / L to the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0063] Comparative Example 8

[0064] Prepare 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 this mixed solvent as the organic solvent, and then slowly add 2.0 g of lithium bis(trifluoromethanesulfonyl)imide with a concentration of 1 mol / L to the mixed solvent, and stir evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0065] Comparative Example 9

[0066] Preparing the electrolyte: In a glove box filled with argon, 4 g of ethyl difluoroacetate and 4 g of ethylene glycol diethyl ether were mixed to obtain a mixed solvent. This mixed solvent was used as the organic solvent. Then, 0.8 g of lithium nitrate with a concentration of 2 mol / L, 0.83 g of vinylene carbonate, and 0.25 g of dysprosium phosphate were slowly added to the mixed solvent and stirred evenly on a magnetic stirrer to obtain a lithium metal electrolyte.

[0067] I. Using the lithium metal electrolytes prepared in Examples 1-9 and Comparative Examples 1-9 as electrolytes respectively to prepare soft-pack lithium metal cells (nominal capacity 3 Ah):

[0068] 1) Preparation of the positive electrode sheet: Under low dew point conditions (-40 ), in an NMP solvent, LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent (SP), carbon nanotubes (CNT), and binder (PVDF) were mixed evenly according to a weight ratio of 96.5:1.0:1.0:1.5, and a positive electrode slurry was made by high-speed vacuum stirring; the slurry was evenly coated on a 12 μm aluminum foil to prepare an electrode sheet; the electrode sheet was dried in a vacuum at 85 environment and then cut into sheets by rolling to obtain the positive electrode sheet;

[0069] 2) Preparation of the negative electrode sheet: In a glove box filled with argon, lithium strips were punched into standard shapes with a die cutter, their surfaces were polished and ground, and then rolled flat to obtain the negative electrode sheet;

[0070] 3) Preparation of the cell: The prepared positive electrode sheet, negative electrode sheet, and a polyethylene separator with a thickness of 19 μm were laminated in sequence to form a square cell, and this cell was placed into a soft-pack battery case (made of aluminum-plastic film). Then, the lithium metal electrolytes prepared in Examples 1-9 and Comparative Examples 1-9 were injected in a vacuum environment. After encapsulation, it was left standing, formed, degassed, aged, and capacitanced to finally obtain soft-pack lithium metal cells respectively.

[0071] II. Performance testing was carried out on the lithium metal electrolytes prepared in Examples 1-9 and Comparative Examples 1-9 and the obtained soft-pack metal cells respectively. The testing methods are as follows:

[0072] 1) Energy density testing: At 25 conditions, the soft-pack lithium metal cells prepared in Examples 1-9 and Comparative Examples 1-9 were charged at a constant current of 0.2 C and a constant voltage to 4.3 V, with a cut-off current of 0.05 C; then left standing for 10 minutes; and then discharged at a constant current of 0.5 C to 3.0 V. The discharge energy under this condition was recorded, and the energy density (Wh / kg) of the cell was obtained by dividing the discharge energy (Wh) by the cell mass (kg);

[0073] 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;

[0074] 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;

[0075] 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;

[0076] 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;

[0077] 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;

[0078] 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.

[0079] The above results are shown in Table 1 and Figure 1-6 As shown:

[0080] Table 1

[0081]

[0082] 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.

[0083] 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.

[0084] 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.

[0085] An electrolyte for a lithium metal battery provided by the present invention contains a film-forming additive and an ether solvent in the electrolyte, enabling a passivation layer to form at the interfaces of 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. Additionally, for the selection of the solvent system (carboxylic ester solvent, carbonate solvent, ether solvent) and various functional additives in the electrolyte of the lithium metal battery provided by the present invention, as well as the amounts added, the battery achieves excellent electrochemical performance, including an energy density of 400 - 550 Wh / kg, an internal resistance of less than 15 mΩ, and a cycle life of more than 180 cycles for the lithium metal battery.

[0086] In addition, the inventors of this case also referred to the foregoing embodiments and conducted tests using other raw materials, process operations, and process conditions described in this specification, and all obtained relatively ideal results.

[0087] It should be noted that in this text, relational terms such as first and second 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 term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0088] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and 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 rare earth phosphate, characterized in that, By weight, it includes 50 - 70 parts of organic solvent, 10 - 20 parts of electrolyte salt, and 5 - 10 parts of functional additive; wherein, by weight, the organic solvent includes 1 - 30 parts of carboxylic ester 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; by weight, the functional additive includes 1 - 10 parts of film-forming additive and 1 - 5 parts of rare earth phosphate; 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.

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

3. The electrolyte for a lithium metal battery containing rare earth phosphate according to claim 1, wherein, The carbonate solvent is any one or a combination of two or more of dimethyl carbonate, ethyl methyl carbonate, dimethylallyl carbonate, ethylene carbonate, fluoroethylene carbonate, diphenyl carbonate, propylene carbonate.

4. An electrolyte for a lithium metal battery containing rare earth phosphate according to claim 1, characterized in that, 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, anisole.

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

6. The electrolyte for a 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. An electrolyte for a lithium metal battery containing rare earth phosphate according to claim 1, characterized in that, The ionic conductivity of the electrolyte for the lithium metal battery is 5 - 25 mS / cm, the viscosity is 5 - 15 mPa·s, and it can be in a stable state at -25 - 50 °C.

8. An electrolyte for a lithium metal battery containing rare earth phosphate according to claim 1, characterized in that, The film-forming additive is any one or a combination of two or more of lithium difluoro(oxalato)borate, vinylene carbonate, ethylene vinylene carbonate, 1,3-propane sultone, ethyl 4-propylsulfite, dimethyl sulfite, methylene methanedisulfonate, lithium difluorophosphate, lithium bis(oxalato)borate.

9. A lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte, characterized in that, The electrolyte includes the electrolyte for the lithium metal battery containing rare earth phosphate according to any one of claims 1 - 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 charge-discharge cycles is greater than 180.

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