Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a lithium ion battery electrolyte and a lithium ion battery, the electrolyte comprises an organic solvent, a lithium salt and an electrolyte additive, the electrolyte additive at least comprises one of compounds (1) and (2) shown in the following structure: # imgabs0 #. The lithium ion battery electrolyte provided by the invention adopts the compound (1) or (2) as the electrolyte additive, so that the discharge efficiency and the 100-time cycle capacity retention ratio of the lithium ion battery are obviously improved; the electrolyte additive can be stored for a long time at the room temperature, the electrolyte additive is easier to decompose in the charge-discharge cycle process and forms an SEI film on the surface of a pole piece, the decomposition product contains a large number of heteroatoms such as sulfur, nitrogen, oxygen and fluorine, lithium ions can pass through the SEI film more easily, and therefore the cycle performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a lithium - ion battery electrolyte and a lithium - ion battery. Background Art

[0002] Lithium - ion secondary batteries are the most competitive new - generation batteries, known as "green environmental protection energy", and are the preferred technologies for solving contemporary environmental pollution problems and energy problems. In recent years, great success has been achieved in the field of high - energy batteries for lithium - ion secondary batteries. However, consumers still expect the emergence of batteries with higher comprehensive performance, which depends on the research and development of new electrode materials and electrolyte systems.

[0003] Lithium - ion batteries are particularly attractive due to their high working voltage, high energy density, etc. However, with the increase in usage time, lithium - ion batteries tend to have a capacity decline, and may also be accompanied by safety problems such as gas generation. To solve these problems, various additives have been added to the electrolyte. The additives will undergo redox decomposition in the initial stage of cycling, and can form a solid electrolyte interface film (SEI film) on the surfaces of the positive and negative electrodes, thereby avoiding direct contact between the electrolyte and the electrode surface and inhibiting its decomposition. At the same time, the SEI film can allow ions to pass through freely, thus not affecting the normal cycling of the battery. This ensures that during the long - term cycling of the battery, there is always enough electrolyte in the battery to ensure its normal operation and maintain a sufficiently high capacity.

[0004] Currently, electronic digital products such as smart phones and tablet computers have increasingly high requirements for the energy density of batteries, making it difficult for commercial lithium - ion secondary batteries to meet the requirements. If the charge - discharge performance and cycling performance of lithium - ion batteries can be further improved by improving electrolyte additives, it is still an important research topic at present. Summary of the Invention

[0005] Based on this, the present invention provides a lithium - ion battery electrolyte and a lithium - ion battery. The battery electrolyte additive adopted by the present invention can effectively improve the charge - discharge performance and cycling performance of lithium batteries.

[0006] To achieve the above object, on the one hand, the present invention provides an additive for a battery electrolyte, which comprises an organic solvent, a lithium salt, and an electrolyte additive, wherein the electrolyte additive contains a first additive, and the first additive contains at least one of the following compounds (1) and (2) shown in the following structure:

[0007]

[0008] As a further preferred technical solution of the present invention, relative to 100 parts by weight of the organic solvent, the content of the first additive is 0.1 - 5 parts by weight; the content of the lithium salt is 1 - 20 parts by weight.

[0009] As a further preferred technical solution of the present invention, the organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0010] As a further preferred technical solution of the present invention, the lithium salt is selected from at least one of LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3.

[0011] As a further preferred technical solution of the present invention, the electrolyte further contains a second additive, and the second additive is tris(trifluoroethyl) borate.

[0012] As a further preferred technical solution of the present invention, relative to 100 parts by weight of the organic solvent, the content of the second additive is 0.1 to 5 parts by weight.

[0013] According to another aspect of the present invention, the present invention further provides a lithium ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte is the lithium ion battery electrolyte disclosed in the first aspect above.

[0014] As a further preferred technical solution of the present invention, the active material of the positive electrode is a transition metal oxide.

[0015] As a further preferred technical solution of the present invention, the transition metal oxide is LiNi x Co y Mn z L (1-x-y-z) O2, where L is one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe, and the values of x, y, and z are: 0 ≤ x < 1, 0 < y ≤ 1, 0 ≤ z < 1, and 0 < x + y + z ≤ 1.

[0016] As a further preferred technical solution of the present invention, the active material of the negative electrode is graphite, a Si-containing composite material, or lithium titanate.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0018] The electrolyte of the lithium-ion battery of the present invention uses compound (1) or (2) as an electrolyte additive, which significantly improves the discharge efficiency and the capacity retention rate after 100 charge-discharge cycles of the lithium-ion battery; the electrolyte additive can be stored for a long time at room temperature, and the electrolyte additive is more likely to decompose during the charge-discharge cycle and form a SEI film on the surface of the electrode. Its decomposition products contain a large amount of heteroatoms such as sulfur, nitrogen, oxygen, and fluorine, and lithium ions can more easily pass through the SEI film, thereby improving the cycle performance of the lithium-ion battery. Detailed Embodiments

[0019] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0020] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0021] The electrolyte of the lithium-ion battery of the present invention includes an organic solvent, a lithium salt, and an electrolyte additive, where the electrolyte additive includes at least one of the following compounds (1) and (2) shown in the structure:

[0022]

[0023] The Chinese names of compound (1) and compound (2) are 1-nitro-3,5-bis(trifluoromethylsulfonyl)benzene and 2-methoxy-1-nitro-3,5-bis(trifluoromethylsulfonyl)benzene, respectively, and the corresponding CAS numbers are 57830-56-5 and 75168-98-8, respectively.

[0024] Example 1

[0025] 1) Preparation of electrolyte:

[0026] In an argon glove box, ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 3:7 to obtain an organic solvent. The organic solvent was mixed with lithium hexafluorophosphate to make the lithium salt concentration 1.0 mol / L, and then the electrolyte additive (compound (1)) was added; among them, relative to 100 parts by weight of the organic solvent (ethylene carbonate and diethyl carbonate), the content of the lithium salt (lithium hexafluorophosphate) was 12 parts by weight, and the content of the electrolyte additive was 0.1 part by weight. Stir until all solid substances were completely dissolved to obtain the lithium-ion battery electrolyte.

[0027] 2) Assembly of lithium-ion battery:

[0028] NCM523 (LiNi0.5 Co 0.2 Mn 0.3 (O2), acetylene black and polyvinylidene fluoride are mixed evenly in a weight ratio of 90:5:5 and then pressed onto an aluminum foil to obtain a positive electrode sheet; a graphite sheet is used as the negative electrode sheet; and a conventional PE or PP is used as the ion exchange membrane; a lithium-ion battery electrolyte of this embodiment is used, and a lithium-ion battery is assembled by a conventional method in the art.

[0029] Example 2

[0030] A lithium-ion battery is prepared by the method of Example 1, except that in the electrolyte of this embodiment, relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7), the content of the electrolyte additive (Compound (1)) is 0.5 part by weight.

[0031] Example 3

[0032] A lithium-ion battery is prepared by the method of Example 1, except that in the electrolyte of this embodiment, relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7), the content of the electrolyte additive (Compound (1)) is 1 part by weight.

[0033] Example 4

[0034] A lithium-ion battery is prepared by the method of Example 1, except that in the electrolyte of this embodiment, relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7), the content of the electrolyte additive (Compound (1)) is 3 parts by weight.

[0035] Example 5

[0036] A lithium-ion battery is prepared by the method of Example 1, except that in the electrolyte of this embodiment, relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7), the content of the electrolyte additive (Compound (1)) is 5 parts by weight.

[0037] Example 6

[0038] A lithium-ion battery is prepared by the method of Example 2, except that the electrolyte additive is changed, and the same amount of Compound (2) is used to replace Compound (1).

[0039] Example 7

[0040] The lithium-ion battery was prepared by the method of Example 2, except that the electrolyte in this example further contained a second additive (tris(trifluoroethyl)borate) (CAS No. 659-18-7), and its content was 1 part by weight relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7).

[0041] Example 8

[0042] The lithium-ion battery was prepared by the method of Example 6, except that the electrolyte in this example further contained a second additive (tris(trifluoroethyl)borate) (CAS No. 659-18-7), and its content was 1 part by weight relative to 100 parts by weight of the organic solvent (ethylene carbonate: diethyl carbonate = 3:7).

[0043] Comparative Example 1

[0044] As a control experiment for Example 2, the lithium-ion battery was prepared by the method of Example 2, except that no additives were added to the electrolyte to serve as a blank control group.

[0045] Comparative Example 2

[0046] As a control experiment for Example 2, the lithium-ion battery was prepared by the method of Example 2, except that the electrolyte additive was changed, and the same amount of compound (3) (1-nitro-3,5-bis(methylsulfonyl)benzene) was used to replace compound (1). The structural formula of compound (3) is as follows:

[0047]

[0048] Comparative Example 3

[0049] As a control experiment for Example 2, the lithium-ion battery was prepared by the method of Example 2, except that the electrolyte additive was changed, and the same amount of compound (4) (1-nitro-3-(trifluoromethyl)sulfonyl)benzene) was used to replace compound (1). The structural formula of compound (4) is as follows:

[0050]

[0051] The prepared lithium-ion batteries were subjected to cycle performance tests and charge-discharge performance tests according to the following method.

[0052] Charge and discharge performance test: The lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-3 were respectively discharged at a constant current of 0.1 mA to 0.005 V at room temperature, and then charged at a constant current of 0.1 mA to 1.5 V. The charging capacity and discharging capacity of the battery were recorded and the charge-discharge efficiency was calculated. Among them, the charge-discharge efficiency (%) = charging capacity / discharging capacity × 100%. The test results are shown in Table 1.

[0053] Cycling performance test: The lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-3 were respectively charged at a constant current and constant voltage of 1C to 4.5 V at room temperature, the charging cut-off current was 0.05 mA, and then discharged at a constant current of 0.5 mA to 2.8 V. The first charging capacity and discharging capacity were recorded. After repeating the charge-discharge cycle 100 times, the discharging capacity of the 100th cycle was recorded and the capacity retention rate after cycling was calculated. Among them, the capacity retention rate after 100 cycles (%) = discharging capacity of the 100th time / first discharging capacity × 100%; the cut-off voltage was 4.5 V. The test results are shown in Table 1. mAh.g -1

[0054] Table 1

[0055]

[0056]

[0057] It can be seen from the data in Table 1 that the lithium batteries containing the electrolyte additives (compound (1) or (2)) of the present invention have excellent charge-discharge performance and cycling performance. Compared with the lithium battery without electrolyte additives in Comparative Example 1, the discharge efficiency and the capacity retention rate after 100 cycles of the lithium-ion battery containing the electrolyte additives of compound (1) or (2) are significantly improved. And compared with Comparative Examples 2 and 3, the discharge efficiency and the capacity retention rate after 100 cycles of the lithium-ion battery are higher. This is because the electrolyte additives (compound (1) and (2)) of the present invention can be stored for a long time at room temperature, are more likely to decompose during the charge-discharge cycle of the lithium-ion battery and form a SEI film on the surface of the electrode. Its decomposition products contain a large number of heteroatoms such as sulfur, nitrogen, oxygen, and fluorine, which helps lithium ions to pass through the SEI film, thereby improving the cycling performance of the lithium-ion battery. Comparing Example 2 with Example 6, compound (2) contains a methoxy group, and the corresponding lithium battery has better cycling performance. Further, by comparing the data in Table 1, it can be found that when the electrolyte additive also contains a second additive (tris(trifluoroethyl)borate), the corresponding lithium battery has better cycling performance. This may be because its decomposition products further contain fluorine, and lithium ions are more likely to pass through the SEI film, further improving the cycling performance of the lithium-ion battery.

[0058] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only illustrative examples, and various changes or modifications can be made to this embodiment without departing from the principles and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive contains a first additive, and the first additive contains at least one of the compounds (1) and (2) shown in the following structures:

2. The additive for battery electrolyte according to claim 1, wherein Relative to 100 parts by weight of the organic solvent, the content of the first additive is 0.1 to 5 parts by weight; the content of the lithium salt is 1 to 20 parts by weight.

3. The additive for battery electrolyte according to claim 1, wherein The organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

4. The additive for battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3.

5. The additive for battery electrolyte according to claim 1, wherein The electrolyte further contains a second additive, and the second additive is tris(trifluoroethyl) borate.

6. The additive for battery electrolyte according to claim 5, wherein, Relative to 100 parts by weight of the organic solvent, the content of the second additive is 0.1 to 5 parts by weight.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the lithium ion battery electrolyte according to any one of claims 1-6.

8. The lithium ion battery according to claim 7, wherein, The active material of the positive electrode is a transition metal oxide.

9. The lithium ion battery according to claim 8, wherein The transition metal oxide is LiNi x Co y Mn z L (1-x-y-z) O2, where L is one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, and the values of x, y, and z are: 0 ≤ x < 1, 0 < y ≤ 1, 0 ≤ z < 1, and 0 < x + y + z ≤ 1.

10. The lithium-ion battery according to claim 7, characterized in that, The active material of the negative electrode is graphite, a Si-containing composite material or lithium titanate.

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