Lithium hexafluorophosphate fluorine-rich electrolyte and lithium battery

Abstract

The invention provides a lithium hexafluorophosphate fluorine-rich electrolyte and a lithium battery. The electrolyte comprises a lithium salt, an organic solvent and a hydrofluoric acid removal additive, the lithium battery comprises the lithium hexafluorophosphate fluorine-rich electrolyte. According to the lithium hexafluorophosphate fluorine-rich electrolyte, the energy density and the safety of a lithium metal battery can be remarkably improved. After the tri (trimethylsilane) phosphate is added into the lithium hexafluorophosphate fluorine-rich electrolyte, a wide electrochemical window (4.6 V), high-temperature stability (as high as 55 DEG C) and enhanced safety (flame retardance and dendrite growth inhibition) are shown. According to the prepared lithium metal bag type battery (7.2 Ah), a double-sided NCM811 cathode (the mass load is 80.72 g / cm < 2 >) and the low electrolyte amount of 1.23 gAh <-1 > are used, and the energy density of 572 Whkg <-1 > is achieved under the discharge rate of 0.1 C.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage and power batteries, and to a lithium battery electrolyte, and in particular to a lithium hexafluorophosphate fluorine-rich electrolyte and a lithium battery. Background Art

[0002] LiPF6 is the most widely used Li salt in commercial Li battery electrolytes at this stage. It has the advantages of high ionic conductivity, high electrochemical stability, and good aluminum current collector passivation. In addition, LiPF6 has a relatively low cost and is more suitable for large-scale applications. However, LiPF6 has a fatal disadvantage as a Li salt in Li battery electrolytes, that is, LiPF6 is highly sensitive to trace water in the electrolyte and easily reacts with trace water to produce a corrosive acidic byproduct HF. The presence of HF will accelerate the degradation and consumption of the electrolyte during the battery cycle, damage the SEI layer on the electrode surface, and aggravate interfacial side reactions. In addition, HF will accelerate the dissolution of transition metals in the positive electrode material and reduce Li + Therefore, stabilizing LiPF6 in the electrolyte, inhibiting its hydrolysis reaction and reducing the generation of HF are crucial to the study of LiPF6-based electrolytes, but have hardly been analyzed and addressed so far. In addition, the development of energy density exceeding 500Whkg -1 The LMBs remain a key challenge.

[0003] Therefore, it is of great significance to study the lithium hexafluorophosphate fluorine-rich electrolyte system that can effectively eliminate hydrofluoric acid. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a fluorine-rich electrolyte of lithium hexafluorophosphate; another purpose of the present invention is to provide a lithium battery.

[0005] In order to achieve the above-mentioned object, the present invention provides a fluorine-rich lithium hexafluorophosphate electrolyte on the one hand, wherein the electrolyte comprises a lithium salt, an organic solvent and a hydrofluoric acid removal additive.

[0006] Alternatively, the organic solvent comprises fluorocarbonates and fluoroethers.

[0007] Optionally, the fluorocarbonate includes at least one of fluoroethylene carbonate and methyl trifluoroethyl carbonate, and the structural formulas are shown in Formula 1 and Formula 2.

[0008] Formula 1 is:

[0009] Formula 2 is:

[0010] Optionally, the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and the structural formula is shown in Formula 3.

[0011] Formula 3 is:

[0012] Alternatively, the hydrofluoric acid removing additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, trifluoropropyltriethoxysilane and trifluoropropyltrimethoxysilane.

[0013] Optionally, the total volume content of the hydrofluoric acid removing additive in the electrolyte is 1 to 7 vol%.

[0014] Optionally, the volume ratio of the fluoroethylene carbonate, the methyl trifluoroethyl carbonate and the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 0-66.66%:66.66-0%:33.33%.

[0015] Optionally, the lithium salt comprises lithium hexafluorophosphate.

[0016] Optionally, the concentration of the lithium salt in the electrolyte is 1-1.2 mol / L.

[0017] Another aspect of the present invention provides a lithium battery, which includes the above-mentioned lithium hexafluorophosphate fluorine-rich electrolyte.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0019] (1) The present invention uses a combination of fluorocarbonate and fluoroether. The use of these organic solvents can enable the electrolyte to maintain stability and compatibility with the lithium metal negative electrode under high pressure environment, thereby effectively improving the cycle stability, safety and energy density of the battery.

[0020] (2) The lithium battery LMBs obtained from the lithium hexafluorophosphate fluorine-rich electrolyte capable of effectively eliminating hydrofluoric acid described in the present invention exhibit a wide electrochemical window (4.6V), high temperature stability (up to 55°C) and enhanced LMBs safety (flame retardancy and inhibition of dendrite growth).

[0021] (3) A lithium metal pouch cell (7.2Ah) prepared using the electrolyte of the present invention (double-sided NCM811 cathode, mass loading 80.72 g / cm 2 ), at 1.23gAh -1 At a low electrolyte loading of 572Whkg at a rate of 0.1C -1In a Li||NCM811 coin cell, a 50 μm thick lithium metal anode and a high-loading NCM811 cathode (19.8 mg cm -2 , 3.96mAhcm -2 ), the system supports 160 stable cycles, with a capacity retention rate of 89% at 0.2C charge and 0.5C discharge rates, and provides 164mAhg at 2C discharge rate -1 At an elevated temperature of 55°C, the capacity retention rate was 82% after 100 cycles and 66% after 200 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects and / or features of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0023] Figure 1 The cycle stability and coulombic efficiency of lithium batteries prepared with the electrolytes in Examples 1-4 of the present invention and Comparative Example 1 are shown.

[0024] Figure 2 The cycle stability of the soft-pack battery made with the electrolyte of Example 2 of the present invention is shown. DETAILED DESCRIPTION

[0025] Hereinafter, a lithium hexafluorophosphate fluorine-rich electrolyte and a lithium battery of the present invention will be described in detail in conjunction with exemplary embodiments.

[0026] One of the purposes of the present invention is to solve the problem that the current carbonate-based electrolyte is not resistant to high pressure. The second purpose of the present invention is to solve the problem that the lithium hexafluorophosphate-based electrolyte produces hydrofluoric acid, which helps the commercialization of the battery. The third purpose of the present invention is to break through 500Whkg -1 , reaching 572Whkg -1 The soft-pack energy density represents the international advanced level of high energy density lithium metal soft-pack batteries.

[0027] Exemplary Embodiment 1

[0028] This exemplary embodiment provides a fluorine-rich lithium hexafluorophosphate electrolyte, which includes a lithium salt, an organic solvent, and a hydrofluoric acid-removing additive.

[0029] In this embodiment, the organic solvent includes fluorocarbonate and fluoroether.

[0030] Wherein, the fluorocarbonate comprises at least one of fluoroethylene carbonate and methyl trifluoroethyl carbonate, and the structural formulas are shown in Formula 1 and Formula 2.

[0031] Formula 1 is:

[0032] Formula 2 is:

[0033] The fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and the structural formula is shown in Formula 3, which is:

[0034]

[0035] In this embodiment, the hydrofluoric acid removing additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, trifluoropropyltriethoxysilane and trifluoropropyltrimethoxysilane.

[0036] In this embodiment, the total volume content of the hydrofluoric acid removing additive in the electrolyte is 1-7 vol%, for example, 1 vol%, 2.5 vol%, 3 vol%, 4 vol%, 5 vol% or 7 vol%.

[0037] Among them, hydrofluoric acid additives can improve the safety and cycle stability of the battery, so they can be added according to actual conditions.

[0038] In this embodiment, the volume ratio of the fluoroethylene carbonate, the methyl trifluoroethyl carbonate and the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 0-66.66%:66.66-0%:33.33%, for example, 33.33%:33.33%:33.33%, 0%:66.66%:33.33%, 66.66%:0%:33.33%, etc., wherein 0% means no addition.

[0039] In this embodiment, the volume ratio of the fluoroethylene carbonate, the methyl trifluoroethyl carbonate and the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte is 0-2:0-2:1, i.e., 1:1:1, 1.2:1:1, 2:0:1, 0:2:1, etc.

[0040] In this embodiment, the lithium salt includes lithium hexafluorophosphate.

[0041] In this embodiment, the concentration of the lithium salt in the electrolyte is 1-1.2 mol / L, such as 1 mol / L, 1.05 mol / L, 1.07 mol / L, 1.1 mol / L and 1.2 mol / L.

[0042] Among them, the lithium hexafluorophosphate fluorine-rich electrolyte described in this embodiment can effectively eliminate hydrofluoric acid.

[0043] Exemplary Embodiment 2

[0044] This exemplary embodiment provides a lithium battery, which includes the lithium hexafluorophosphate fluorine-rich electrolyte described in exemplary embodiment 1.

[0045] In this embodiment, the preparation of the lithium battery is carried out in a glove box filled with argon gas, and the water content and oxygen content are controlled to be less than or equal to 0.1 ppm.

[0046] In order to better understand the above exemplary embodiments of the present invention, they are further described below in conjunction with specific examples.

[0047] Example 1

[0048] In a glove box with an argon atmosphere in which the water content and oxygen content were both less than or equal to 0.1 ppm, a fluorine-rich electrolyte was first prepared by dissolving 1.2 mol / L LiPF6 in a co-solvent consisting of fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), with the volume ratio of the three solvents being 1:1:1. Then, 1 vol% tris(trimethylsilyl) phosphate (TMSPa) was added and stirred evenly to obtain a fluorine-rich lithium hexafluorophosphate electrolyte that can effectively eliminate hydrofluoric acid.

[0049] Example 2

[0050] In a glove box with an argon atmosphere in which the water content and oxygen content were both less than or equal to 0.1 ppm, a fluorine-rich electrolyte was first prepared by dissolving 1.2 mol / L LiPF6 into a co-solvent consisting of FEC, FEMC and TTE in a volume ratio of 1:1:1. Then 3 vol% tris(trimethylsilyl) phosphate (TMSPa) was added and stirred evenly to obtain a lithium hexafluorophosphate fluorine-rich electrolyte that can effectively eliminate hydrofluoric acid.

[0051] Example 3

[0052] In a glove box with an argon atmosphere in which the water content and oxygen content were both less than or equal to 0.1 ppm, a fluorine-rich electrolyte was first prepared by dissolving 1.2 mol / L LiPF6 into a co-solvent consisting of FEC, FEMC and TTE in a volume ratio of 1:1:1. Then 5 vol% tris(trimethylsilyl) phosphate (TMSPa) was added and stirred evenly to obtain a lithium hexafluorophosphate fluorine-rich electrolyte that can effectively eliminate hydrofluoric acid.

[0053] Example 4

[0054] In a glove box with an argon atmosphere in which the water content and oxygen content were both less than or equal to 0.1 ppm, a fluorine-rich electrolyte was first prepared by dissolving 1.2 mol / L LiPF6 into a co-solvent consisting of FEC, FEMC and TTE in a volume ratio of 1:1:1. Then 7 vol% tris(trimethylsilyl) phosphate (TMSPa) was added and stirred evenly to obtain a lithium hexafluorophosphate fluorine-rich electrolyte that can effectively eliminate hydrofluoric acid.

[0055] Comparative Example 1

[0056] In a glove box with an argon atmosphere where the water content and oxygen content were both less than or equal to 0.1 ppm, a fluorine-rich electrolyte was first prepared by dissolving 1.2 mol / L LiPF6 into a co-solvent consisting of FEC, FEMC and TTE in a volume ratio of 1:1:1. After stirring evenly, a lithium battery electrolyte was obtained.

[0057] Preparation of lithium battery:

[0058] All battery preparations were carried out in a glove box filled with argon gas, and the water and oxygen contents were controlled to be less than or equal to 0.1 ppm. The button cell used was CR-2032 model, purchased from Clude Technology Co., Ltd. The Li||NMC811 button cell used a single-sided 3.96 mAh cm -2 The loaded NMC811 positive electrode, a single-sided 50μm thick lithium metal negative electrode and a polypropylene separator (PP, thickness 25μm); the Li||Cu battery is composed of a 25μm thick Cu foil, a 600μm thick lithium metal sheet and a PP separator; the Li||stainless steel battery is composed of a 1mm thick stainless steel gasket, a 600μm thick lithium metal sheet PP separator; the Li||Li symmetric battery is composed of two 600μm thick Li metal electrodes and a PP separator. The electrolyte dosage of all button cells is 70μL. The soft pack battery uses a double-sided 20μm thick Li metal negative electrode, a double-sided NMC811 positive electrode (8.2mAhcm-2) and a PE separator. The negative electrode size is 4.5×5.8cm, the positive electrode size is 4.3×5.6cm, and the stacking assembly (MSK-111A, Hefei Kejing Materials Technology Co., Ltd.) is adopted. The electrolyte dosage is 2.1g / Ah.

[0059] Test Case

[0060] The electrochemical cycle test of Li||NMC811, Li||Cu and Li||Li button cells was carried out using a BTS-5V10mA constant current charge and discharge instrument (Shenzhen Xinweier Electronics Co., Ltd.). Unless otherwise specified, all batteries were tested in a 30°C constant temperature box (Shenzhen Xinweier Electronics Co., Ltd.). For Li||NMC811 button cells, the charge and discharge voltage ranges were 2.7-4.4V, 2.7-4.5V and 2.7-4.6V, respectively. All batteries first underwent three C / 10 formation cycles, and then the batteries were charged at C / 5 and discharged at C / 2. For Li||Cu batteries, each cycle was charged at 0.5mAcm on Cu foil. -2 The current density of Li deposition is 1 mAh cm -2 , and then completely stripped, and so on. The deposition current of Li||Li symmetric cell is 1mAcm -2 , deposition capacity is 1mAcm -2 . The linear sweep voltammetry test and (LSV) electrochemical impedance spectroscopy (EIS) test of the battery were performed using a CHI760D electrochemical workstation. The battery rate test was performed in a Li||NMC811 battery. All batteries were charged at a rate of C / 10 and then discharged at different rates. The LSV test was performed in a Li||stainless steel battery. The test voltage range was from the battery open circuit voltage to 6.0V, and the scan rate was 0.1mVs -1 After 100 cycles, the Li||NMC811 button cell was used for EIS test, with a voltage of 5mV and a test frequency of 0.01-100kHZ. The charge and discharge test of the soft pack battery was carried out using a BT-4008Tn-5V6A-S1 constant current charge and discharge instrument (Shenzhen Xinweier Electronics Co., Ltd.). After three formation cycles at a C / 20 rate, the battery was charged and discharged at a C / 10 rate.

[0061] Results and Discussion

[0062] Figure 1 The cycle stability and coulombic efficiency of lithium batteries prepared with the electrolytes in Examples 1-4 and Comparative Example 1 show that the cycle performance of Examples 1-4 is more stable than that of Comparative Example 1, and Example 2 is the most stable.

[0063] Figure 2 The cycle stability of the soft-pack battery made with the electrolyte of Example 2 of the present invention is shown, from which it can be seen that the soft-pack battery made with the electrolyte of Example 2 achieves high energy density and cycle stability.

[0064] Although the present invention has been described above in conjunction with the exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A fluorine-rich lithium hexafluorophosphate electrolyte, characterized in that: The electrolyte includes a lithium salt, an organic solvent and a hydrofluoric acid removing additive.

2. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that The organic solvents include fluorocarbonates and fluoroethers.

3. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 2, characterized in that: The fluorocarbonate comprises at least one of fluoroethylene carbonate and methyl trifluoroethyl carbonate, and the structural formulas are shown in Formula 1 and Formula 2. Formula 1 is: Formula 2 is:

4. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 2, characterized in that: The fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and its structural formula is shown in Formula 3. Formula 3 is:

5. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that: The hydrofluoric acid removing additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, trifluoropropyltriethoxysilane and trifluoropropyltrimethoxysilane.

6. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that: The total volume content of the hydrofluoric acid removing additive in the electrolyte is 1 to 7 vol%.

7. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that: The organic solvent includes fluoroethylene carbonate, methyl trifluoroethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 0-66.66%:66.66-0%:33.33% in the electrolyte.

8. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that The lithium salt includes lithium hexafluorophosphate.

9. The fluorine-rich lithium hexafluorophosphate electrolyte according to claim 1, characterized in that: The concentration of the lithium salt in the electrolyte is 1 to 1.2 mol / L.

10. A lithium battery, characterized in that: The lithium battery comprises the lithium hexafluorophosphate fluorine-rich electrolyte according to any one of claims 1 to 9.

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