Lithium ion battery electrolyte and application thereof

Abstract

The invention relates to the field of lithium ion batteries, and discloses a lithium ion battery electrolyte and application thereof, the electrolyte comprises a lithium salt electrolyte, an organic solvent and an electrolyte additive composition, and the electrolyte additive composition comprises zinc tetraphenylporphyrin, methyl trifluoroethyl carbonate and an acetonitrile dibenzenesulfonimide derivative. According to the improved lithium ion battery electrolyte provided by the invention, the tetraphenylporphyrin zinc, the methyl trifluoroethyl carbonate and the acetonitrile dibenzenesulfonimide derivative are used as electrolyte additives, so that the effects of effectively inhibiting formation and growth of lithium dendrites can be achieved, and an SEI interface layer formed on the surface of an electrode is improved, so that the interface layer is stable and reliable; according to the present invention, the lithium ion battery does not lose efficacy in the charge-discharge process within the expected time, and the lithium can be guided to smoothly and uniformly deposit on the electrode surface during the electrochemical deposition process, such that the process that the lithium tends to form and grow into the dendritic lithium dendrites is substantially inhibited, and the safety of the lithium ion battery is improved.

Description

Technical Field

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

[0002] Compared with traditional secondary batteries, lithium-ion batteries have greater energy density, higher voltage, and longer cycle life. In addition, lithium-ion batteries are environmentally friendly. Therefore, lithium-ion batteries have been widely used in many fields, such as laptops, mobile phones, digital products, and electric vehicles. Therefore, rechargeable lithium-ion batteries have become one of the most promising high-energy secondary rechargeable battery systems. However, the problem of lithium dendrites has also seriously troubled the further development of lithium-ion batteries. Uncontrolled growth of lithium dendrites can quickly reduce battery performance, shorten battery life, and even pierce the diaphragm between electrodes, causing safety problems such as battery short circuit. Therefore, how to effectively inhibit the growth of lithium dendrites under the conditions of high current density, high energy density, and long cycle becomes a key issue.

[0003] An important component of lithium ions is the electrolyte, and the role of the electrolyte is to transfer lithium ions between the positive and negative electrodes of the battery. The electrolyte usually includes a lithium salt electrolyte, an organic solvent, and an additive composition. The additive composition is considered to be the most feasible, economical, and effective method to improve the electrochemical performance of lithium-ion batteries. It introduces electrode reactions that do not participate in the cycle process, but can improve the lithium electrolyte interface and the SEI film of the lithium ion electrode, reduce the side reactions of the lithium interface, reduce the interfacial impedance, and improve the coulombic efficiency, thereby improving the battery's rate performance and cycle life. However, the existing electrolyte additives have limited improvements on the electrochemical performance of the battery, and cannot completely and effectively solve the problem of lithium dendrites, resulting in potential safety hazards in the battery. Summary of the invention

[0004] In order to make the lithium-ion battery have a long cycle life, the present invention provides a lithium-ion battery electrolyte and application thereof.

[0005] To achieve the above object, on the one hand, the present invention provides a lithium ion battery electrolyte, which includes a lithium salt electrolyte, an organic solvent and a lithium ion battery electrolyte additive composition, wherein the electrolyte additive composition includes tetraphenylporphyrin zinc, methyl trifluoroethyl carbonate and an acetonitrile bisbenzenesulfonimide derivative having a structure shown in formula (1);

[0006]

[0007] Among them, R and R 1 Each of them is selected from one of the C1-C5 straight chain alkyl groups;

[0008] The concentrations of the tetraphenylporphyrin zinc, the methyl trifluoroethyl carbonate and the acetonitrile bisbenzenesulfonimide derivative in the lithium ion battery electrolyte are all 0.1-5 mM.

[0009] Preferably, the organic solvent is at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, difluoroethyl acetate, trifluoroethyl acetate, trifluoroethyl methyl carbonate, bistrifluoroethyl carbonate, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether. More preferably, the organic solvent is a combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0010] Preferably, the lithium salt electrolyte is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalatophosphate), and lithium fluorosulfonyl(trifluoromethylsulfonyl)imide.

[0011] Preferably, the molar concentration of the lithium salt electrolyte in the lithium ion battery electrolyte is 0.5-2M.

[0012] Preferably, the molar ratio of the tetraphenylporphyrin zinc, the methyl trifluoroethyl carbonate and the acetonitrile bisbenzenesulfonimide derivative is 1:1 to 2:1.

[0013] Preferably, in formula (1), R and R 1 is selected from a C3 or C4 straight chain alkyl group, and R and R 1 same.

[0014] According to another aspect of the present invention, the present invention also provides a use of the above-mentioned lithium ion battery electrolyte in a lithium ion battery.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0016] The formation and growth of lithium dendrites is an extremely complex process, and the influence of electrochemical reactions is not completely clear. Due to various reasons, the surface of the electrode in a lithium-rich state during the electrochemical process, especially during multiple cycles of charge and discharge or overcharge, is very prone to lithium dendrites. Lithium dendrites will cause problems such as battery performance deterioration and safety accidents. Based on this, the present invention provides an improved lithium-ion battery electrolyte, using tetraphenylporphyrin zinc, methyl trifluoroethyl carbonate and acetonitrile bisbenzenesulfonyl imide derivatives as electrolyte additives, and an unexpected effect of inhibiting the formation and growth of lithium dendrites is obtained. Based on a large number of experiments and studies, it is analyzed that the SEI interface layer formed on the electrode surface is improved, so that the interface layer is stable and reliable, and basically will not fail during the charge and discharge process within the expected time. In addition, it can guide the smooth and balanced deposition of lithium on the electrode surface during the electrochemical deposition process, greatly inhibiting the process of its tendency to form and grow into dendritic lithium dendrites, and improving the safety of lithium-ion batteries.

[0017] The materials used in the present invention are all purchased commercially, and the operation is simple, the production cost is low, and it is convenient for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0019] Figure 1 1 and 2 are scanning electron microscope images of the lithium surfaces of Example 1 and Comparative Example 1, wherein a is the lithium sheet sample of the Comparative Example, and b is the lithium sheet sample of Example 1.

[0020] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0022] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0023] Example 1

[0024] The preparation method of the electrolyte provided in this embodiment comprises the following steps:

[0025] Step 1: In a glove box filled with nitrogen or argon, the water and oxygen contents in the glove box are both ≤ 0.1 ppm, ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed evenly to obtain an organic solvent mixture, wherein the volume ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is 1:1:1. Lithium hexafluorophosphate is added to the organic solvent mixture, and the mixture is mixed evenly to obtain a basic electrolyte, wherein the concentration of lithium hexafluorophosphate in the basic electrolyte is 1 mol / L.

[0026] Step 2, in a glove box filled with nitrogen or argon, where the water and oxygen contents in the glove box are both ≤ 0.1 ppm, tetraphenylporphyrin zinc, methyl trifluoroethyl carbonate and the acetonitrile bisbenzenesulfonimide derivative of the structure shown in formula (1) in the additive composition are added to the basic electrolyte, and the mixture is mixed uniformly to obtain an electrolyte;

[0027] In the formula, R and R 1 are selected from methyl.

[0028] The total volume of the electrolyte prepared in this example is 10 ml, wherein the concentrations of tetraphenylporphyrin zinc, methyl trifluoroethyl carbonate and acetonitrile bisbenzenesulfonimide derivative are all 0.5 mM.

[0029] Examples 2-6 and Comparative Examples 1-4

[0030] Compared with Example 1, the difference between Examples 2-6 and Comparative Examples 1-4 is that the formula of the additive composition in the battery electrolyte is different (see Table 1 for the specific formula).

[0031] Test battery assembly:

[0032] (1) Assemble Li / / Li symmetrical cells and mix the electrolytes of Example 1 and Comparative Example 1 at 1 mA cm -2 The current density and 3 mAh cm -2 The lithium-on-lithium deposition stripping test was carried out at a deposition amount of Figure 1 As shown. Figure 1 It can be clearly seen that the surface of the lithium sheet of the electrolyte without additives has a large number of dendrites, while the surface of the lithium sheet with the additive composition is flat and free of dendrites, indicating that the additive composition of the present invention can completely and effectively solve the problem of lithium dendrites. The three-component electrolyte additive composition of the present invention is composed of methyl trifluoroethyl carbonate connecting tetraphenylporphyrin zinc and acetonitrile bisbenzenesulfonimide derivatives through van der Waals bonds to form a three-dimensional network structure, which can prevent the formed SEI film from being destroyed and falling off, and can effectively inhibit the growth of lithium dendrites. At the same time, the three-dimensional network structure can promote the transmission of lithium ions, improve the electrochemical performance of lithium ion batteries, and ensure the safety of lithium batteries.

[0033] (2) The Li / / Li symmetrical cells assembled in Examples 1-6 and Comparative Examples 1-4 according to the above method were subjected to a 1 mA cm -2 The current density and 3 mAh cm -2 The cycle performance test was carried out under the deposition amount.

[0034] The additive composition formulations and battery performance test results of Examples 1-6 and Comparative Examples 1-4 are shown in Table 1.

[0035] Table 1

[0036]

[0037] It can be seen from the test results in Table 1 that the electrolyte using the electrolyte additive composition of the present invention has a significantly improved cycle life for batteries of lithium iron phosphate systems compared to the comparative examples using only no additive or a single additive. Therefore, the three-component electrolyte additive composition of the present invention is indispensable, and the change of any component greatly reduces or even eliminates the effect of inhibiting lithium dendrites, showing that the three have an excellent synergistic effect in inhibiting the formation and growth of lithium dendrites. In addition, when the dosage of the electrolyte additive composition of the present invention (when the molar concentration ratio is 1:1:1) is gradually increased, the cycle life will also gradually increase, but when the molar concentration exceeds 0.5mM, the increase in cycle life is no longer obvious. Among them, Example 1 is the best solution, with relatively less additive dosage and high cycle life.

[0038] Examples 7-10 and Comparative Examples 5-7

[0039] Compared with Example 1, the differences between Examples 7-10 and Comparative Examples 5-7 are that: R and R in the acetonitrile bisbenzenesulfonimide derivatives 1 The corresponding straight-chain alkyl chain lengths are different. The lithium-ion battery performance test methods of Examples 7-10 are the same as those of Example 1.

[0040] Example 1, Example 7-10 Comparative Example 5-7 R and R of the acetonitrile bisbenzenesulfonimide derivatives 1 The corresponding straight-chain alkyl groups and battery performance test results are shown in Table 2.

[0041] Table 2

[0042]

[0043] Note: “ / ” in Table 2 means the corresponding straight-chain alkyl group does not exist, i.e. H.

[0044] It can be seen from the test results in Table 2 that with the increase of the length of the linear alkyl chain, when it is in the range of C1 to C5, the cycle life will gradually increase significantly, and after a large number of experiments, when it is above C5, the increase in cycle life no longer changes significantly. Compared with the comparative example, the present invention uses an acetonitrile-based bisbenzenesulfonimide derivative with bilateral linear alkyl groups, and its effect is significantly better than the case where only one side is a linear alkyl group.

[0045] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A lithium ion battery electrolyte, characterized in that: The invention comprises a lithium salt electrolyte, an organic solvent and an electrolyte additive composition, wherein the electrolyte additive composition comprises zinc tetraphenylporphyrin, methyl trifluoroethyl carbonate and an acetonitrile bisbenzenesulfonimide derivative having a structure shown in formula (1); Among them, R and R 1 One selected from C1 to C5 straight-chain alkyl groups; The concentrations of the tetraphenylporphyrin zinc, the methyl trifluoroethyl carbonate and the acetonitrile bisbenzenesulfonimide derivative in the lithium ion battery electrolyte are all 0.1-5 mM.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, difluoroethyl acetate, trifluoroethyl acetate, trifluoroethyl methyl carbonate, bistrifluoroethyl carbonate, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether.

3. The lithium ion battery electrolyte according to claim 1, characterized in that The lithium salt electrolyte is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorobisoxalatophosphate, and lithium fluorosulfonyl(trifluoromethylsulfonyl)imide.

4. The lithium ion battery electrolyte according to claim 1, characterized in that: The molar concentration of the lithium salt electrolyte in the lithium ion battery electrolyte is 0.5-2M.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: The molar ratio of the tetraphenylporphyrin zinc, the methyl trifluoroethyl carbonate and the acetonitrile bisbenzenesulfonimide derivative is 1:1 to 2:

1.

6. The lithium ion battery electrolyte according to claim 1, characterized in that: In formula (1), R and R 1 is selected from a C3 or C4 straight chain alkyl group, and R and R 1 same.

7. Use of the lithium ion battery electrolyte according to any one of claims 1 to 6 in a lithium ion battery.

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