Novel organic additive for improving low temperature resistance and fast charge capacity of lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a novel organic additive for improving the low temperature resistance and fast charge capacity of a lithium ion battery. The electrolyte additive is formed by grafting an ether-containing group and a fluorinated group on the same host molecule, and the ether has relatively low viscosity, so that the wettability of an electrode and the electrolyte can be improved, and the low-temperature performance of the battery is further improved. Meanwhile, the fluorination of the group is an effective way for improving the compatibility of the solvent and the lithium metal anode, an SEI film is formed on the surface of the electrode, the uniform deposition of lithium ions is adjusted, and the fast charging capacity and the low-temperature resistance of the battery are further effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a novel organic additive for improving the low - temperature tolerance and fast - charging ability of lithium - ion batteries. Background Art

[0002] Lithium - ion batteries are widely used in fields such as electric vehicles and mobile phones due to their advantages such as high energy density and long life. With the further development of lithium - ion batteries, higher requirements have been put forward for their safety, charge - discharge performance at high and low temperatures, and fast - charging ability.

[0003] In lithium - ion batteries, interface problems between the electrode and the electrolyte, such as wettability and compatibility, directly determine the electrochemical performance of the battery. Therefore, in the prior art, the interface properties are often changed by adding electrolyte additives. For example, for electrolytes that improve the low - temperature tolerance of lithium - ion batteries, there are generally fluoroethylene carbonate (FEC), dimethyl sulfite (DMS), tris(trimethylsilyl) phosphite (TMSP), 1,3 - propanediol cyclic sulfate (PCS), vinylene carbonate (VC), etc. However, among these additives, the improvement of battery performance by a single active ingredient is limited, and when several components are added together, there may be problems of numerous side reactions between different components. Therefore, in order to better improve the low - temperature tolerance of lithium - ion batteries, a novel electrolyte additive is very necessary. Summary of the Invention

[0004] In order to overcome the above - mentioned technical problems, the present application provides an electrolyte additive with an ether group and a fluorinated group structure, which can improve the low - temperature tolerance and fast - charging ability of the battery.

[0005] To this end, the first technical solution of the present application provides an organic additive, including the following molecular formula:

[0006]

[0007] In the formula, R1 is a fluorinated group, and the structural general formula is - C n H 2n-m+1 F m ;

[0008] R2 is an ether - containing group, and the structural general formula is - C p H 2p+1 O;

[0009] Among them, n, m, p > 0.

[0010] Preferably, in R1, n = 2, m = 3, which is trifluoroethyl; in R2, p = 3, which is methoxyethyl. At this time, the organic additive is methyl ethyl ether trifluoroethyl carbonate.

[0011] The second technical solution of this application discloses an electrolyte, which includes the above-mentioned organic additive, electrolyte solvent, electrolyte additive, and soluble lithium salt.

[0012] Preferably, the soluble lithium salt is lithium hexafluorophosphate.

[0013] Furthermore, the volume ratio of the electrolyte solvent, electrolyte additive, and organic additive is (5 - 7):(2 - 4):(1 - 2).

[0014] The third technical solution of this application discloses an electrochemical device, which includes the above-mentioned organic additive or electrolyte.

[0015] And, the use of the above-mentioned organic additive or electrolyte in improving the low-temperature resistance and fast charging performance of the electrochemical device.

[0016] Preferably, the electrochemical device is a lithium-ion battery.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The organic additive of this application is composed of grafting an ether group-containing group and a fluorinated group on the same main molecule. Among them, the ether has a relatively low viscosity, which can improve the wettability between the electrode and the electrolyte, and further improve the low-temperature performance of the battery. At the same time, fluorination of the group is an effective way to improve the compatibility between the solvent and the lithium metal anode, form a SEI film on the electrode surface, and regulate the uniform deposition of lithium ions, thereby effectively improving the fast charging ability and low-temperature resistance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the rate performance of the lithium metal battery at room temperature;

[0019] Figure 2 is the charge-discharge curve of the lithium metal battery in the first cycle (1 th ) and the 200th cycle (200 th );

[0020] Figure 3 is the charge-discharge curve of the NCM811∥graphite battery at -20 °C in the 5th cycle (5 th ). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present invention.

[0022] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for the sake of convenience in description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the authorization specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: similar reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0023] Unless otherwise specified, the meanings of the scientific and technical terms in this specification are the same as those generally understood by those skilled in the art. However, in case of conflict, the definitions in this specification shall prevail.

[0024] The first embodiment of the present application discloses an organic additive having the following structural formula:

[0025]

[0026] In the formula, R1 is a fluorinated group, and the structural general formula is -C n H 2n-m+1 F m ;

[0027] R2 is an ether-containing group, and the structural general formula is -C p H 2p+1 O;

[0028] Wherein, n, m, p > 0.

[0029] Among them, the organic additive can be any one of methyl ethyl ether trifluoroethyl carbonate, ethyl butyl ether trifluorobutyl carbonate, propyl ethyl ether trifluorobutyl carbonate, butyl propyl ether trifluoropropyl carbonate, pentyl methyl ether trifluoroethyl carbonate, and preferably methyl ethyl ether trifluoroethyl carbonate. At this time, n is 2, m is 3, and p is 3.

[0030] Those skilled in the art should know that the above organic additives can be obtained by esterification reaction of the corresponding fluorinated groups and ether-containing groups. For example, methyl ethyl ether trifluoroethyl carbonate can be obtained by the esterification reaction of trifluoroethane and methyl ethyl ether.

[0031] In this structure, ethers have relatively low viscosity, which can improve the wettability between the electrode and the electrolyte, and further enhance the low-temperature performance of the battery. Meanwhile, fluorination of the group is an effective way to improve the compatibility between the solvent and the lithium metal anode, forming a SEI film on the electrode surface to regulate the uniform deposition of lithium ions, thereby effectively improving the fast charging ability of the battery.

[0032] In a further embodiment, an electrolyte is also provided, which includes the above-mentioned organic additive, electrolyte solvent, electrolyte additive, and soluble lithium salt; wherein, the soluble lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoromethanesulfonylimide, and lithium hexafluorophosphate, and the concentration of the salt is 0.5 - 2.0 M; preferably lithium hexafluorophosphate, and the salt concentration is preferably 1 M. The electrolyte solvent is at least one of ethylene carbonate, ethyl methyl carbonate, methyl propionate, and methyl acetate; preferably methyl propionate; the electrolyte additive is at least one of dimethyl sulfite (DMS), vinylene carbonate (VC), ethylene sulfate (DTD), and fluoroethylene carbonate (FEC), and preferably fluoroethylene carbonate. The volume ratio of the electrolyte solvent, electrolyte additive, and organic additive is (5 - 7):(2 - 4):(1 - 2).

[0033] In a further embodiment, the present application also discloses an electrochemical device, including the above-mentioned organic additive or electrolyte. When the electrochemical device is preferably a lithium-ion battery, the positive electrode is a high-nickel NCM material, and the negative electrode active material is lithium metal; the above-mentioned organic additive or the electrolyte containing the above-mentioned organic additive can improve the low-temperature fast charging performance of the electrochemical device.

[0034] The technical effects of the technical solutions of the present application will be described in detail below through specific examples.

[0035] Example 1 Preparation of a lithium-ion battery

[0036] 1. Preparation of the electrolyte: Add the electrolyte solvent, electrolyte additive, and organic additive to the electrolyte containing the soluble lithium salt, and completely dissolve to obtain the electrolyte;

[0037] 2. Preparation of the lithium-ion battery: Use nickel cobalt manganese ternary material as the positive electrode (Ni:Co:Mn = 8:1:1) / (Ni:Co:Mn = 9:0.5:0.5), and metallic lithium as the negative electrode active material (both can be obtained commercially); Stack the above positive electrode, negative electrode, and separator through a layer-by-layer process to prepare a lithium-ion battery. Among them, the area of the separator > the area of the negative electrode > the area of the positive electrode, and the usage amount of the electrolyte is 60 μL - 100 μL to obtain a lithium-ion battery.

[0038] In the above examples, the addition amounts of the electrolyte solvent, electrolyte additive, organic additive, and soluble lithium salt are shown in Table 1.

[0039] Table 1

[0040]

[0041] Experimental Example 1 Electrochemical Experiment

[0042] The batteries prepared in Example 1 and Comparative Examples 1 and 2 were subjected to electrochemical experiments according to the following method.

[0043] Experimental method steps:

[0044] 1. Materials: A certain amount of lithium hexafluorophosphate (LiPF6) was dissolved in a (methyl propionate / fluoroethylene carbonate) MP / FEC mixed solvent (volume ratio 7:3) and a (methyl propionate / fluoroethylene carbonate / methyl ethyl ether trifluoroethyl carbonate) MP / FEC / CMTE mixed solvent (volume ratios 6.5:3:0.5 and 6:3:1), named M7F3 (Comparative Example 1), M6.5F3C0.5 (Example 1), and M6F3C1 (Comparative Example 2), respectively. All electrolytes were prepared and stored in a glove box filled with argon at room temperature (oxygen < 0.01 ppm, water < 0.01 ppm). The graphite electrode, lithium metal electrode, and NC M811 electrode were stored in a glove box filled with argon. Before use, the electrodes were punched into discs with a diameter of 12 mm.

[0045] 2. Assemble coin cells in a glove box filled with argon, where the water and oxygen content is less than 0.01 ppm. For the coin cells with NCM811 / lithium metal electrodes, 80 μL of electrolyte was added, and a commercial Celgard 2320 membrane was used as the battery separator. For the NCM811 / graphite full cells, 80 μL of electrolyte was added, and a commercial Celgard 2320 membrane was used as the battery separator. All coin cells were cycled on a Neware multi-channel battery cycler.

[0046] Experimental results: As shown in Figure 1 、 2 、3, Figure 1 are the rate performance of the lithium metal batteries of Example 1 and Comparative Examples 1 and 2 at room temperature. By comparing with Comparative Example 1, it can be found that when the additive CMTE is added to the electrolyte, the discharge capacity of the lithium metal battery at high charge and discharge rates is significantly improved, indicating that CMTE as an electrolyte additive has an improvement effect on the rate performance of the lithium metal battery. By comparing with Comparative Example 2, it can be found that when the content of CMTE is increased from 5 v / v% to 10 v / v%, the discharge specific capacity of the lithium metal battery does not increase significantly. However, it still has the technical effects described in this application.

[0047] Figure 2 For the lithium metal battery in the first cycle (1th ) and the 200th cycle (200 th ). By comparing the examples and Comparative Example 1, it can be found that the discharge specific capacity in the first cycle of both is almost the same. However, when the 200th cycle (200 th ) is completed, it can be clearly seen that the discharge specific capacity of the example with CMTE added is higher than that of Comparative Example 1 without the CMTE additive. The former maintains a better capacity during these 200 cycles, indicating that CMTE has a good effect on improving the cycle stability of lithium metal batteries.

[0048] Figure 3 is the charge-discharge curve of the NCM811‖graphite battery at -20°C and the 5th cycle (5 th ). By comparing the experimental examples and Comparative Example 1, it can be found that in a low-temperature environment of -20°C, the lithium-ion battery with CMTE added has a higher capacity, indicating that CMTE has an improvement effect on the low-temperature performance of lithium-ion batteries.

[0049] In summary, under the condition of -20°C, when charging and discharging at a current of 0.2C, the battery can still have a discharge specific capacity of 133.54 mAh g -1 , and can cycle stably, indicating good performance at low temperatures.

[0050] As mentioned above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An organic additive, characterized in that, It includes the following molecular formulas: In the formula, R1 is a fluorinated group, and the structural general formula is -C n H 2n-m+1 F m ; R2 contains an ether group and has a general structural formula of -C p H 2p+1 O; Among them, n, m, p > 0.

2. The organic additive according to claim 1, wherein In R1, n = 2, m = 3, which is trifluoroethyl; in R2, p = 3, which is methoxyethyl. At this time, the organic additive is methyl ethyl ether trifluoroethyl carbonate.

3. An electrolyte, characterized in that, It includes the organic additive, electrolyte solvent, electrolyte additive and soluble lithium salt as described in claim 1 or 2.

4. The electrolyte according to claim 4, characterized in that, The soluble lithium salt is lithium hexafluorophosphate.

5. The electrolyte according to claim 4, wherein The volume ratio of the electrolyte solvent, electrolyte additive to the organic additive is (5 - 7):(2 - 4):(1 - 2).

6. An electrochemical device, characterized in that, The electrochemical device includes the organic additive as described in any one of claims 1 - 2 or the electrolyte as described in any one of claims 3 - 5.

7. Use of the organic additive as described in any one of claims 1 - 2 or the electrolyte as described in any one of claims 3 - 5 in improving the low - temperature resistance and fast - charging performance of an electrochemical device.

8. According to the use described in claim 8, it is characterized in that, The electrochemical device is a lithium - ion battery.

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