CN111834670A - Lithium-sulfur battery electrolyte and application thereof - Google Patents
Lithium-sulfur battery electrolyte and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium-sulfur battery electrolyte, and particularly discloses a lithium-sulfur battery electrolyte, which comprises conductive lithium salt, a hydrophobic organic solvent and an additive, wherein the additive is at least one of compounds with a structural formula of formula 1:
in the formula 1R1、R2、R3、R4Independently is an alkyl group, wherein at least one substituent is a long-carbon chain alkyl group, and at least one substituent is a short-carbon chain alkyl group; the carbon number of the main chain of the long carbon chain alkyl is not less than 12; the carbon number of the short carbon chain alkyl is not more than 6; the additiveThe content of (A) is 0.1 wt% -10 wt%; x-is a halogen anion; the additive can generate a uniform and compact protective film on the surface of lithium metal in situ, inhibit the growth of lithium dendrites and the generation of dead lithium, and improve the charge-discharge efficiency and the cycling stability of the lithium-sulfur battery.
Description
Technical Field
The invention belongs to the field of lithium-sulfur batteries, and particularly relates to an additive-containing electrolyte for a lithium-sulfur battery and a lithium-sulfur battery using the electrolyte.
Background
In recent years, lithium sulfur batteries have attracted attention from researchers because of their advantages such as high energy density (2500Wh/kg, 2800Wh/L), wide sulfur source as an active material, and low cost, and are considered to be one of the most promising next-generation high energy density energy storage devices. However, since lithium metal is used as the negative electrode, there are the following problems: (1) lithium has high reactivity, can almost react with all substances in the electrolyte, and has complex and unstable products and more side reactions, thereby reducing the charge and discharge efficiency. (2) Interface reaction is uneven, lithium dendrite and dead lithium are easily generated, lithium cycle efficiency is reduced, the growth of the lithium dendrite is easy to puncture a diaphragm, a battery short circuit is caused, and the cycle life of the battery is influenced. (3) The volume expansion and contraction effect generated by the dissolution of lithium deposition can cause the breakage of the SEI film on the surface, which results in the increase of battery impedance and the loss of active lithium. Therefore, a stable protective layer is constructed on the surface of the lithium negative electrode to effectively isolate lithium from electrolyte, and the method is a key technology for successfully applying the lithium-sulfur battery.
Currently, many researchers have made a lot of research on protecting lithium negative electrodes, and mainly focused on the construction and control of a solid electrolyte layer (SEI film) on the surface of lithium metal. One method is to form a film in advance, and to form a relatively stable artificial SEI film on the surface of the negative electrode, so as to reduce the reaction between polysulfide and lithium metal, inhibit the growth of lithium dendrites, reduce the contact between lithium metal and electrolyte, and reduce side reactions. However, the method has the problems of loose contact with the lithium surface, poor uniformity, continuous increase of interface impedance and the like, and has not yet been commercialized. The other method is to form a film on the surface of lithium metal in situ by using an electrolyte additive to form a uniform and compact solid electrolyte protective layer, so as to achieve the purpose of protecting the lithium cathode, wherein the protective layer formed by the method is generally uniform and compact in structure, thin in thickness and small and stable in corresponding impedance.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an additive-containing lithium-sulfur battery electrolyte, aiming at remarkably improving the performance of the electrolyte under a smaller additive amount.
Different types of batteries have different requirements for matching components and materials. For example, for a lithium sulfur battery, it is required that an electrolyte has good wettability to an electrode, can solve a lithium dendrite problem, and can improve cycle performance such as specific capacity and coulombic efficiency. However, the conventional electrolyte for a lithium-sulfur battery has more defects in this respect, and therefore, the present invention provides an electrolyte for a lithium-sulfur battery, comprising a conductive lithium salt, a hydrophobic organic solvent, and an additive: the additive is at least one of compounds with the structural formula of formula 1:
R1、R2、R3、R4independently an alkyl group. Wherein at least one substituent is a long carbon chain alkyl group and at least one substituent is a short carbon chain alkyl group;
the carbon number of the main chain of the long carbon chain alkyl is not less than 12; the carbon number of the short carbon chain alkyl is not more than 6;
x is halogen; the content of the additive is 0.1 wt% -10 wt%.
The invention discovers that the electrolyte added with the compound with the structure shown in the formula 1 can effectively improve the wettability of the electrode of the lithium-sulfur battery, can generate a uniform and compact protective film on the surface of lithium metal in situ, inhibits the growth of lithium dendrite and the generation of dead lithium, and improves the charge-discharge efficiency and the cycle stability of the lithium-sulfur battery.
The additive shown in the formula 1 can obtain a good technical effect under the condition of small addition amount, and mainly benefits from the synergistic cooperation of the long carbon chain, the short carbon chain and the inorganic negative ions in the structure, and on the basis, the precise control on the carbon number of the long carbon chain and the short carbon chain and the control on the addition content are further matched, so that the electrical property of the lithium-sulfur battery can be effectively improved. Researches find that the additive without the carbon numbers of the long carbon chain and the short carbon chain does not obviously improve the performance of the electrolyte, and even possibly reduces the performance of the electrolyte. It has also been found that, in addition to the group control of the compound with the structure of formula 1, it is necessary to control the additive to be in the required range, and the addition amount of the additive is larger than the upper limit or lower than the lower limit, which is not beneficial to the improvement of the electrolyte performance.
The research of the inventor finds that the synergistic coordination of the long carbon chains and the short carbon chains is the key for improving the electrical performance of the additive in the lithium-sulfur battery, however, the research of the inventor finds that the performance of the additive in the lithium-sulfur battery is better when the long carbon chains are more or the total carbon number is more. The research of the invention discovers that R1、R2、R3、R4In the formula (I), one substituent is the long-carbon-chain alkyl, and the rest substituents are the short-carbon-chain alkyl. The additive works better with the preferred synergy of one and three short carbon chains.
The research of the invention finds that under the control of the chain segment number of the long carbon chain and the short carbon chain, the chain segment number of the long carbon chain and the short carbon chain is further matched
The long-carbon chain alkyl group is preferably a straight chain alkyl group having the above carbon number, and more preferably C12～C18A straight chain alkyl group of (1). The research of the invention unexpectedly discovers that in the formula 1, the single long chain segment group is C12～C18The electrical properties of the linear alkyl hydrocarbon group of (2) are more excellent. The number of carbons in the long-carbon chain alkyl groupThe step lifting can reduce the cooperativity between the long carbon chains and the short carbon chains to a certain degree, and influence the performance of the electrolyte to a certain degree.
More preferably, the long carbon paraffin is C16～C18Linear alkanes of (1). The electrolyte has better performance under the preferable long-chain group.
Preferably, the method comprises the following steps: said short-carbon alkanyl radical is C1～C4A straight chain alkyl group of (1). The research of the invention also unexpectedly discovers that the short carbon chain is controlled to be C1～C4When the additive is a linear alkane group, the cooperativity of the additive and a long carbon chain can be improved unexpectedly, and the electrical property of the additive in the electrolyte can be further improved.
More preferably, the short-carbon alkanyl group is C2～C4A straight chain alkyl group of (1). Researches find that the preferable short-chain alkyl and the preferable long-chain alkyl have better synergistic effect and are more beneficial to improving the electrical property of the electrolyte.
According to the invention, X is halogen, and researches show that the X can be further cooperated with the long-chain alkane group and the short-chain alkane group, so that the performance of the electrolyte can be further improved.
Preferably, X-is Cl-or Br-.
In addition to the above-mentioned innovative addition of the compound of formula 1, the addition amount thereof is further controlled within a desired range, whereby the addition effect can be improved.
Preferably, the mass percentage of the additive in the electrolyte is 1 wt% -5 wt%. At the preferable addition amount, the electrical performance of the lithium-sulfur battery can be further improved.
More preferably, the mass percentage of the additive in the electrolyte is 1.5 wt% to 2.5 wt%.
Preferably, the lithium-sulfur battery electrolyte further comprises an auxiliary additive, and the auxiliary additive comprises at least one of lithium nitrate, potassium nitrate, cesium nitrate and lanthanum nitrate.
Preferably, the content of the auxiliary additive is 1-3 wt.%. The auxiliary additive can be cooperated with the additive to unexpectedly improve the circulating coulombic efficiency of the electrolyte.
The organic solvent is a hydrophobic organic solvent suitable for the lithium-sulfur battery.
Preferably, the hydrophobic organic solvent is at least one of polyether compound, carbonate compound, alkyl ester compound, sulfone and sulfoxide compound.
Preferably, the hydrophobic organic solvent is 1, 3-Dioxolane (DOL), 1, 4-Dioxane (DX), ethylene glycol dimethyl ether (DME), and diethylene glycol dimethyl ether (G)2) Trimeric ethylene glycol dimethyl ether (G)3) Tetraglyme (G)4) Tetrahydrofuran (THF), Ethylmethylsulfone (EMS), sulfolane (TMS), Methylisopropylsulfone (MiPS), Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC).
The conductive lithium salt of the present invention may be any known lithium salt known to those skilled in the art.
Preferably, the conductive lithium salt is lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), lithium difluorooxalato borate (liddob), lithium difluorobis (oxalato) phosphate (lidbop), lithium dioxalate borate (LiBOB), lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium nitrate (LiNO)3) Lithium perchlorate (LiClO)4) One or more of them.
Preferably, the concentration of the conductive lithium salt in the electrolyte is preferably 0.5-4 mol/L.
The invention also provides an application of the lithium-sulfur battery electrolyte, which is used as the electrolyte for preparing the lithium-sulfur battery.
According to another object of the present invention, there is provided a lithium sulfur battery comprising the electrolyte. The lithium-sulfur battery comprises a positive plate, a negative plate, a diaphragm for separating the positive plate from the negative plate and electrolyte, wherein the electrolyte is the additive-containing lithium-sulfur battery electrolyte.
Preferably, the positive plate comprises a positive current collector and a positive material compounded on the surface of the positive current collector; the positive electrode material is obtained by solidifying slurry of a positive electrode active material, a conductive agent, a binder and a solvent.
The positive active material is one or more of elemental sulfur, sulfur-containing polymer, lithium sulfide and lithium polysulfide.
The negative plate is one of metal lithium foil, a lithium plate, a lithium alloy and a silicon-carbon compound.
A lithium-sulfur battery preferably assembled using the electrolyte, characterized in that: comprises a positive plate, a negative plate, a diaphragm and a shell package; the diaphragm is positioned between the positive plate and the negative plate, and the positive plate, the negative plate, the diaphragm and the electrolyte are sealed in the battery shell package. The positive plate is formed by coating a positive active material, a conductive agent and a binder on a current collector in proportion, wherein the positive active material is one or more of elemental sulfur, a sulfur-containing polymer, lithium sulfide and lithium polysulfide. The negative plate is one of metal lithium foil, a lithium plate, a lithium alloy and a silicon-carbon compound.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the electrolyte additive exists in the electrolyte in a cation form, and a layer of film is formed on the surface of the lithium protrusion which is deposited at the beginning through electrostatic acting force, so that lithium ions are repelled from being deposited on the surface of the lithium protrusion, and are deposited at a smoother position nearby the lithium protrusion, and a layer of smooth and compact SEI film is further formed, so that the growth of lithium dendrites is inhibited, the contact between a lithium cathode and the electrolyte is reduced, the occurrence of side reactions is reduced, the charging and discharging specific capacity of the battery is improved, and the cycling stability of the battery is improved.
In addition, the used electrolyte additive is convenient and easy to obtain, the preparation process of the electrolyte is simple, and the practicability and operability are strong.
According to the technical scheme, the problems of low initial specific capacity and unsatisfactory cycle performance, which are puzzling technicians in the lithium-sulfur battery industry, can be effectively solved, the initial specific capacity can be increased to 1289.3mAh/g from 912.9mAh/g, the retention rate of 100 cycles of charging and discharging under constant current of 0.5C can be increased to 76.9% from the original 65.2%, the average coulomb efficiency is as high as 99.6%, and the effect is remarkable.
Drawings
Fig. 1 shows the cycle curves of the lithium/lithium symmetric battery assembled by the electrolyte provided in example 15 of the present invention and comparative example 7.
Detailed Description
The following examples are intended to illustrate the invention in further detail; and the scope of the claims of the present invention is not limited by the examples.
Example 1
A lithium sulfur battery was prepared as follows:
preparing an electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 1% by mass of the total additive (in formula 1, R)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Preparing a sulfur positive electrode: mixing a sulfur/carbon composite material (the sulfur carrying amount is 65 wt%), acetylene black and PVDF according to a ratio of 70:20:10, adding a proper volume of N-methylpyrrolidone (NMP), placing the mixture in a homogenizer, stirring for 15min, and forming stable and uniform anode slurry at a rotating speed of 15 kr/min. The slurry was coated on carbon-coated aluminum foil with a doctor blade and dried in an oven at 80 ℃ for 8h until the NMP was completely volatilized.
Assembling and testing the lithium-sulfur button cell: and (3) punching the prepared sulfur pole piece into a round pole piece with the diameter of 13mm, and drying in an oven at the temperature of 55 ℃ for 1 h. In argon atmosphere, a metal lithium sheet is taken as a negative electrode, a polypropylene microporous membrane with the model of Celgard2400 is selected as a diaphragm, the using amount of electrolyte is 15 mu L/mg S, and the CR2025 lithium-sulfur battery is sequentially assembled. And (3) standing the prepared battery in a thermostatic chamber at 25 ℃ for 12 hours, and then performing charge-discharge cycle test on a blue test charge-discharge tester under the test conditions of charge-discharge with the magnification of 0.5C, the potential interval of 1.7-2.8V and 100 cycles.
Example 2
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 3
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M) are mixed and added with 5 percent of additive (R) in the formula 1 in the total mass1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 4
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is dodecyl radical, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 5
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is octadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 6
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is behenyl radical, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 7
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Br-), and the electrolyte is fully and uniformly stirred to obtain the electrolyte of the lithium-sulfur battery.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 8
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is hexadecyl, R2、R3、R4All are ethyl, and X-is Br-), and the mixture is fully and uniformly stirred to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 9
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is hexadecyl, R2、R3、R4All are n-butyl, and X-is Br-), and the electrolyte is fully and uniformly stirred to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 10
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1、R2Is octadecyl, R3、R4All are methyl, and X-is Br-), and the electrolyte is fully and uniformly stirred to obtain the electrolyte of the lithium-sulfur battery.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 11
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1、R2、R3Is hexadecyl, R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 12
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 is mixed with LiTFSI (1.0M), andadding 2% of additive (in formula 1, R)1Is hexadecyl, R2、R3、R4Are all n-butyl, X-is Br-) and 2 percent of lithium nitrate, and the electrolyte of the lithium-sulfur battery is obtained after the materials are fully and uniformly stirred.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 13
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and 0.1% of additive (R in formula 1) in total mass is added1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 14
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and 10% by mass of an additive (R in the formula 1)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Example 15
Preparing electrolyte: same as in example 1.
Lithium/lithium symmetrical button cell assembly test: in argon atmosphere, metal lithium sheets are used as a positive electrode and a negative electrode, a polypropylene microporous membrane with the model of Celgard2400 is selected as a diaphragm, the using amount of electrolyte is 15 mu L/mg S, and the CR2025 lithium-sulfur battery is assembled in sequence. After the prepared battery is placed in a thermostatic chamber at 25 ℃ and is kept stand for 12 hours, a charging and discharging circulation test is carried out on a blue test charging and discharging tester under the conditions of constant current and 2mA charging and discharging, and the circulation is carried out for 100 circles (see figure 1).
Comparative example 1
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 2
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1、R2、R3、R4N-butyl and X-Cl-) tetrabutylammonium chloride are fully and uniformly stirred to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 3
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1、R2、R3、R4Dodecyl, and Br-) tetradodecyl ammonium bromide are fully and uniformly stirred to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 4
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), 2% by mass of the total additive (in formula 1, R)1Is decaalkyl, R2、R3、R4Methyl and Br-) dodecyl trimethyl ammonium chloride are fully and uniformly stirred to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 5
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and 0.05% of the total mass of additives (R in formula 1)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 6
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and 20% by mass of an additive (R in the formula 1)1Is hexadecyl, R2、R3、R4All are methyl, and X-is Cl-), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
Sulfur positive electrode preparation and lithium sulfur button cell assembly testing were the same as in example 1.
Comparative example 7
Preparing electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm), the organic solvent is ethylene glycol dimethyl ether (DME) according to volume ratio: 1, 3-Dioxolane (DOL) ═ 1: 1 and LiTFSI (1.0M), and fully and uniformly stirring to obtain the lithium-sulfur battery electrolyte.
The lithium/lithium symmetrical button cell assembly test was the same as example 15.
TABLE 1 test results of examples 1-14 and comparative examples 1-6
As can be seen from table 1, the cell without the additive provided by the present invention (comparative example 1) had a relatively low coulombic efficiency and a relatively fast cell capacity fade; the electrolyte added with the additive provided by the invention improves the capacity, circulation and coulombic efficiency of the battery to different degrees. Compared with the comparative ratio 1, the electrolyte additive provided by the invention can promote the surface of the lithium cathode to form a flat and compact SEI film, so that the growth of lithium dendrites is inhibited, the contact between the lithium cathode and the electrolyte is reduced, the occurrence of side reactions is reduced, the charging and discharging specific capacity of the battery is improved, and the cycling stability of the battery is improved.
The electrolyte can be obtained from the embodiments 1 to 3 and the embodiments 13 and 14, the electrochemical properties of the electrolyte are different when different amounts of the cetyltrimethylammonium chloride are added, when the addition amount is 1 to 5 wt%, the effect is obvious, and the property of 2 wt% is the best; when the addition amount is 0.1 wt% and 10 wt%, there is an effect, but the effect is not significant. Therefore, the amount of addition is optimized to 1 to 5 wt%. However, if the amount of the additive added to the electrolyte was too small (comparative example 5), the effect was almost the same as that of the blank control (comparative example 1), and the additive failed to function; if the amount is too large (comparative example 6), the viscosity of the electrolyte increases, the lithium ion transport efficiency decreases, and the specific capacity and coulombic efficiency decrease.
By comparing example 2 with comparative example 2, it can be seen that the long and short chain synergistic additives can improve the electrochemical performance of the battery without the short chain having a significant effect.
The cycle performance of the battery can be obtained by comparing examples 2, 4, 5, 6 and comparative example 4: the carbon number of the carbon chain of the single long chain is in the range of C12-C18, the specific capacity and the coulombic efficiency are increased along with the increase of the length of the long chain, the carbon number is lower than 12 or higher than 18, and the electrical performance is reduced; by comparing example 2 with example 7, the anion is Cl ion or Br ion, and the cycle performance of the battery is similar.
Through comparison among examples 7, 8 and 9, the long chain length is constant, and the specific capacity of the battery is increased along with the increase of the short chain length, but the specific capacity of examples 10 and 11 is obviously lower than that of other examples, which shows that the increase of the number of the long chains is not beneficial to the cycle performance of the battery, and the additive of the long chain with one carbon number and three short chains has good electrochemical performance, i.e. the long chain and the short chains have synergistic effect. Comparing example 9 with example 12, it can be seen that adding lithium nitrate to the electrolyte as an additive can increase the average coulombic efficiency to 99.6%, i.e., the two can act synergistically, significantly improving the cycling stability of the battery.
As can be seen from fig. 1, example 15 has a smaller overpotential and thus better cycle performance, is more stable, and has better compatibility with lithium than comparative example 7, which indicates that the additive has a significant effect on protecting a lithium negative electrode, inhibiting the growth of lithium dendrites, and the generation of dead lithium.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A lithium-sulfur battery electrolyte comprising a conductive lithium salt, a hydrophobic organic solvent, and an additive: characterized in that the additive is at least one of compounds with a structural formula 1
R1、R2、R3、R4Independently is an alkyl group; wherein at least one substituent is a long-chain alkyl group and at least one substituent is a short-chain alkyl group
The carbon number of the main chain of the long carbon chain alkyl is not less than 12; the carbon number of the short carbon chain alkyl is not more than 6;
x-is a halogen anion;
the content of the additive is 0.1 wt% -10 wt%.
2. The lithium sulfur battery electrolyte of claim 1 wherein: r1、R2、R3、R4In the formula (I), one substituent is the long-carbon-chain alkyl, and the rest substituents are the short-carbon-chain alkyl.
3. The lithium sulfur battery electrolyte of claim 1 or 2 wherein: said long carbon chain alkyl is C12～C18A straight chain alkyl group of (1).
4. The lithium sulfur battery electrolyte as defined in any one of claims 1 to 3, wherein: said short-carbon alkanyl radical is C1～C4A straight chain alkyl group of (1).
5. The lithium sulfur battery electrolyte as defined in any one of claims 1 to 4, wherein: the mass percentage of the additive in the electrolyte is 1 wt% -5 wt%.
6. The lithium sulfur battery electrolyte as defined in any one of claims 1 to 5, wherein: the additive also comprises an auxiliary additive, wherein the auxiliary additive comprises at least one of lithium nitrate, potassium nitrate, cesium nitrate and lanthanum nitrate;
preferably, the content of the auxiliary additive is 1-3 wt%.
7. The lithium sulfur battery electrolyte of claim 1 wherein: the hydrophobic organic solvent is at least one of polyether compounds, carbonate compounds, alkyl ester compounds, sulfone and sulfoxide compounds;
preferably, the hydrophobic organic solvent is a mixture of one or more of 1, 3-dioxolane, 1, 4-dioxane, ethylene glycol dimethyl ether, trimeric ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl sulfone, sulfolane, methyl isopropyl sulfone, ethylene carbonate, dimethyl carbonate and diethyl carbonate.
8. The lithium sulfur battery electrolyte of claim 1 wherein: the conductive lithium salt is one or more of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium trifluoromethanesulfonate, lithium difluorooxalato borate, lithium difluorobis (oxalato) phosphate, lithium dioxalate borate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate and lithium perchlorate;
the concentration of the conductive lithium salt in the electrolyte is 0.5-4 mol/L.
9. Use of the lithium sulphur battery electrolyte according to any of claims 1 to 8, wherein: used as an electrolyte for preparing a lithium-sulfur battery.
10. The utility model provides a lithium sulfur battery, by positive plate, negative pole piece, be used for positive plate and negative pole piece separated diaphragm and electrolyte, its characterized in that: the electrolyte comprises the electrolyte as claimed in any one of claims 1 to 8.
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