A lithium metal battery electrolyte and its application and lithium metal battery

Abstract

The present invention discloses a lithium metal battery electrolyte, its application and a lithium metal battery. The lithium metal battery electrolyte comprises LiTFSI, an organic solvent and a deionized water additive. The present invention uses deionized water as a lithium metal battery electrolyte additive, effectively inhibits the corrosion of LiTFSI on the positive electrode Al current collector at high potential, ensures the normal cycle of the battery, and improves the electrochemical performance of the battery; the present invention realizes the application of conventional low-concentration LiTFSI electrolyte to lithium metal batteries by simply adding a small amount of cheap and easily available deionized water additive, reduces the preparation cost of LiTFSI salt electrolyte, simplifies the process, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a lithium metal battery electrolyte and an application thereof and a lithium metal battery. Background Art

[0002] Lithium-ion batteries are widely used in all aspects of modern life as important energy storage devices. However, the limitations of energy density and cycle life still cannot meet the needs of equipment such as electric vehicles. Lithium metal batteries are considered to be one of the most promising next-generation high-energy density storage devices because they directly use metallic lithium as the negative electrode. As the "blood" of lithium metal batteries, the electrolyte plays an important role in conducting ions between the positive and negative electrodes, greatly affecting the battery's cycle performance and safety performance. The electrolyte is generally composed of lithium salts, organic solvents and necessary additives. Lithium hexafluorophosphate (LiPF 6 ) has the advantages of high ion conductivity and good solubility, and is a commonly used lithium salt in lithium metal battery electrolyte. However, its thermal and chemical stability are poor, and it easily absorbs water to generate acidic substances such as HF, which leads to rapid attenuation of battery performance.

[0003] The conductivity, thermal stability and electrochemical stability of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) are significantly better than those of LiPF 6 , and is stable to water. However, when LiTFSI is used in the electrolyte at a conventional low concentration (such as about 1 mol / L), it will seriously corrode the positive electrode Al current collector under high potential, limiting its application as an electrolyte lithium salt. Currently, the main methods to improve the electrolyte are to increase the concentration of LiTFSI in the electrolyte (such as increasing the concentration to greater than 4 mol / L) or add lithium difluorooxalatoborate (LiDFOB), lithium hexafluorophosphate (LiPF 6 ) can preferentially form a film on the positive electrode Al current collector to solve the problem of Al corrosion. However, these methods will increase the preparation cost of the electrolyte and the operation is more complicated. Summary of the invention

[0004] The purpose of the present invention is to provide a lithium metal battery electrolyte and its application and a lithium metal battery. By adding deionized water as an additive to the electrolyte containing conventional low-concentration LiTFSI, the electrochemical corrosion of LiTFSI on the positive electrode Al current collector at high potential in the lithium metal battery can be effectively inhibited to ensure the normal cycle of the battery.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive.

[0007] According to the above scheme, the concentration of the deionized water in the electrolyte is 0.02-0.6 mol / L, preferably 0.028-0.11 mol / L.

[0008] According to the above scheme, the concentration of lithium salt LiTFSI in the electrolyte is 0.6-1.6 mol / L.

[0009] According to the above scheme, the organic solvent in the electrolyte is one or more of ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and propylene carbonate (PC); preferably, the organic solvent is ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC) in a volume ratio of 1:3-3:1.

[0010] Provided is a use of the lithium metal battery electrolyte in a lithium metal battery whose positive electrode contains an Al current collector.

[0011] A lithium metal battery is provided, comprising:

[0012] A negative electrode, wherein the negative electrode is metallic lithium;

[0013] A positive electrode, the positive electrode comprising an Al current collector and a positive electrode film coated on the Al current collector and comprising a positive electrode active material, a positive electrode conductor and a positive electrode binder;

[0014] The separator, located between the positive and negative electrodes;

[0015] Also included is the above-mentioned lithium metal battery electrolyte, including LiTFSI, an organic solvent and a deionized water additive.

[0016] According to the above scheme, the positive electrode active material is a material with an average output voltage of more than 4V. Preferably, the positive electrode active material is layered lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), spinel lithium manganese oxide (LiMn 2 O 4 ), spinel lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ).

[0017] According to the above scheme, the positive electrode conductive agent is conductive carbon black, and the positive electrode binder is polyvinylidene fluoride.

[0018] According to the above scheme, the separator is a glass fiber membrane, a polyethylene microporous membrane, a polypropylene microporous membrane or an ethylene-propylene copolymer microporous membrane.

[0019] According to the above scheme, the lithium metal battery can be assembled into a button battery, a soft pack battery or a cylindrical battery.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention provides a lithium metal battery electrolyte, wherein the lithium salt is conventional low-concentration LiTFSI and deionized water is an additive; in a lithium metal battery containing a low-concentration LiTFSI electrolyte, the addition of deionized water can effectively inhibit the electrochemical corrosion of the Al current collector of the positive electrode of the lithium metal battery, and enable normal battery cycles; at 2C (1C = 180mAg -1 ) rate, electrolytes with different water contents can effectively improve battery performance.

[0022] 2. The present invention can realize the application of conventional low-concentration LiTFSI electrolyte (such as 0.6-1.6 mol / L) in lithium metal batteries by simply adding a small amount of cheap and readily available deionized water additive, thereby reducing the preparation cost of LiTFSI salt-containing electrolyte, simplifying the process, and having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the first cycle charging curve of the lithium metal battery obtained in Comparative Example 1.

[0024] Figure 2 It is a comparison curve of the cycle performance of the lithium metal batteries obtained in Examples 1-5.

[0025] Figure 3 It is the aluminum foil after constant voltage charging in the experimental design of the electrolyte corrosion resistance test on Al foil.

[0026] Figure 4 This is the aluminum foil after constant voltage charging in the control example. DETAILED DESCRIPTION

[0027] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0028] Comparative Example 1

[0029] A lithium metal battery is provided, and the preparation method thereof is as follows:

[0030] LiNi 0.8 Co 0.1 Mn 0.1 O 2Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added and stirred evenly before coating on Al foil. The solvent was dried in a vacuum drying oven at 110°C and cut into discs with a diameter of 12 mm as the positive electrode. Lithium bistrifluoromethylsulfonyl imide (LiTFSI) was dissolved in a mixed solvent of ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC) (volume ratio = 3:1) to obtain an electrolyte (the concentration of LiTFSI in the electrolyte was 1 mol / L). The battery was assembled using glass fiber as a separator and a lithium sheet as a negative electrode.

[0031] The battery was tested for charge and discharge cycles at a 2C rate, and the electrochemical window was 3.0-4.4V. The test results showed that the battery could not reach 4.4V during the first cycle of charging, resulting in severe overcharging. Due to the severe corrosion of LiTFSI on the positive electrode Al current collector, the battery could not undergo normal charge and discharge cycles.

[0032] Example 1

[0033] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.11 mol / L.

[0034] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0035] LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil, and the solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.11 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled using glass fiber as a separator and a lithium sheet as a negative electrode.

[0036] The battery was tested for charge and discharge cycles at a 2C rate, with an electrochemical window of 3.0-4.4 V. The test results showed that the battery was able to cycle normally, with an 80% capacity retention rate after 250 cycles and an average coulombic efficiency of up to 99.91%.

[0037] This embodiment uses deionized water as an electrolyte additive, which effectively inhibits the corrosion of LiTFSI in the electrolyte on the positive electrode Al current collector, allowing the battery to circulate normally. The deionized water used in this method is cheap and easy to obtain, and the electrolyte preparation method is simple and fast. Compared with the battery in comparative example 1 in which the electrolyte does not contain deionized water, the battery performance is significantly improved, showing obvious advantages.

[0038] Example 2

[0039] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.028 mol / L.

[0040] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0041] LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil. The solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.028 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as a separator and lithium sheet as a negative electrode. The battery was charged and discharged at a rate of 2C. The test results showed that the battery could still maintain a capacity retention rate of 78% after 150 cycles, and the average coulombic efficiency was as high as 99.83%.

[0042] Example 3

[0043] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.056 mol / L.

[0044] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0045] LiNi 0.8 Co 0.1 Mn 0.1 O2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil. The solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.056 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as a diaphragm and lithium sheet as a negative electrode. The battery was charged and discharged at a rate of 2C. The test results showed that the battery could still maintain a capacity retention rate of 78% after 300 cycles, and the average coulombic efficiency was as high as 99.92%.

[0046] Example 4

[0047] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.28 mol / L.

[0048] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0049] LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil. The solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.28 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as the diaphragm and lithium sheet as the negative electrode. The battery was charged and discharged at a rate of 2C. The test results show that the battery can be stably cycled normally.

[0050] Example 5

[0051] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.55 mol / L.

[0052] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0053] LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil. The solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.55 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as the diaphragm and lithium sheet as the negative electrode. The battery was charged and discharged at a rate of 2C. The test results show that the battery can be stably cycled normally.

[0054] Example 6

[0055] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.11 mol / L.

[0056] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0057] LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly before coating on Al foil. The solvent was dried in a vacuum drying oven at 110°C and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.11 mol / L, and the concentration of LiTFSI was 1 mol / L). A polypropylene microporous membrane was used as a separator, and a lithium sheet was used as a negative electrode to assemble a battery for charge and discharge tests.

[0058] Example 7

[0059] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.056 mol / L.

[0060] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0061] LiMn 2 O 4 Conductive carbon black and polyvinylidene fluoride were mixed and ground in a mass ratio of 8:1:1, and then coated on Al foil after adding appropriate amount of NMP and stirring evenly. The solvent was dried in a vacuum drying oven at 110°C and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.056 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as the separator and lithium sheet as the negative electrode for charge and discharge tests.

[0062] Example 8

[0063] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.11 mol / L.

[0064] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0065] LiMn 2 O 4 Conductive carbon black and polyvinylidene fluoride were mixed and ground in a mass ratio of 8:1:1, and then coated on Al foil after being stirred evenly with an appropriate amount of NMP. The solvent was dried in a vacuum drying oven at 110°C and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.11 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as the separator and lithium sheet as the negative electrode for charge and discharge tests.

[0066] Example 9

[0067] Provided is a lithium metal battery electrolyte, comprising LiTFSI, an organic solvent and a deionized water additive, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.28 mol / L.

[0068] Provided is a lithium metal battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned lithium metal battery electrolyte, and the preparation method thereof is as follows:

[0069] LiMn 2 O 4 Conductive carbon black and polyvinylidene fluoride were mixed and ground evenly in a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred evenly, and then coated on Al foil. The solvent was dried in a vacuum drying oven at 110°C, and cut into discs with a diameter of 12 mm as the positive electrode. LiTFSI was dissolved in a mixed solvent of EMC and FEC (volume ratio = 3:1), and an appropriate amount of deionized water was added to obtain an electrolyte (the concentration of deionized water in the electrolyte was 0.28 mol / L, and the concentration of LiTFSI was 1 mol / L). The battery was assembled with glass fiber as the separator and lithium sheet as the negative electrode for charge and discharge tests.

[0070] Experimental design of corrosion resistance test of Al foil by electrolyte

[0071] Al foil was used directly as the positive electrode to assemble a lithium metal battery to explore the inhibitory effect of deionized water on the corrosion of Al current collector by LiTFSI salt. The positive electrode of the lithium metal battery is Al foil, the negative electrode is lithium sheet, the separator is glass fiber, and the electrolyte includes LiTFSI, organic solvent and deionized water additives, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), the concentration of LiTFSI in the electrolyte is 1 mol / L, and the concentration of deionized water in the electrolyte is 0.056 mol / L. Starting from 4V, the battery was charged at a constant voltage for four hours at intervals of 0.05V, and the charging was stopped at 4.6V.

[0072] Figure 3 This is the Al foil after the test. As can be seen from the figure, the Al foil is very intact and there are no obvious holes, indicating that the addition of deionized water effectively inhibits the corrosion of LiTFSI on the Al foil. Therefore, the electrolyte containing deionized water can support the normal cycle of lithium metal batteries.

[0073] Comparison example

[0074] Lithium metal batteries were assembled using Al foil directly as the positive electrode to explore the corrosion of Al by LiTFSI salt in the electrolyte. The positive electrode of the lithium metal battery is Al foil, the negative electrode is lithium sheet, the separator is glass fiber, and the electrolyte includes LiTFSI and organic solvent, wherein the organic solvent is a mixed solvent of EMC and FEC (volume ratio = 3:1), and the concentration of LiTFSI in the electrolyte is 1 mol / L. Starting from 4V, the battery was charged at a constant voltage of 0.05V for four hours, and the charging was stopped at 4.6V.

[0075] Figure 4 This is the Al foil after the test. As can be seen from the figure, many obvious holes appeared on the Al foil and it became brittle, indicating that the LiTFSI in the electrolyte will cause serious corrosion to the Al foil during the charging process, resulting in the lithium metal battery assembled using the electrolyte with Al foil as the current collector unable to work properly.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A lithium metal battery electrolyte, characterized in that: The electrolyte includes LiTFSI, an organic solvent and a deionized water additive; wherein: the concentration of the lithium salt LiTFSI in the electrolyte is 0.6-1.6 mol / L; the concentration of the deionized water in the electrolyte is 0.02-0.6 mol / L.

2. The electrolyte according to claim 1, characterized in that The concentration of the deionized water in the electrolyte is 0.028-0.11 mol / L.

3. The electrolyte according to claim 1, characterized in that The organic solvent in the electrolyte is one or more of ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate and propylene carbonate.

4. Use of the electrolyte according to any one of claims 1 to 3 in a lithium metal battery having an Al current collector at the positive electrode.

5. A lithium metal battery comprising: A negative electrode, wherein the negative electrode is metallic lithium; A positive electrode, the positive electrode comprising an Al current collector and a positive electrode film coated on the Al current collector and comprising a positive electrode active material, a positive electrode conductor and a positive electrode binder; The separator is located between the positive electrode and the negative electrode; it is characterized in that It also includes the lithium metal battery electrolyte according to any one of claims 1 to 3.

6. The lithium metal battery according to claim 5, characterized in that The positive electrode active material is a material with an average output voltage of more than 4 V.

7. The lithium metal battery according to claim 6, characterized in that The positive electrode active material is layered lithium nickel cobalt manganese oxide, spinel lithium manganese oxide or spinel lithium nickel manganese oxide.

8. The lithium metal battery according to claim 5, characterized in that The positive electrode conductive agent is conductive carbon black, the positive electrode binder is polyvinylidene fluoride; the separator is a glass fiber membrane, a polyethylene microporous membrane, a polypropylene microporous membrane or an ethylene-propylene copolymer microporous membrane.

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