CN109411817B - A lithium-ion battery or lithium-sulfur battery electrolyte - Google Patents

Abstract

The invention discloses a lithium-ion battery or lithium-sulfur battery electrolyte, which contains an organic supramolecular additive; the organic supramolecular has an inner-ring pore structure containing electron-deficient spaces. The lithium-ion battery or lithium-sulfur battery electrolyte makes full use of the electron-deficient space of organic supramolecules to capture electron-rich anions in the electrolyte. The migration of lithium ions is limited, the migration number of lithium ions becomes larger, and the rate performance of lithium ion batteries or lithium sulfur batteries can be significantly improved.

Description

A lithium-ion battery or lithium-sulfur battery electrolyte

technical field

The present invention relates to a lithium-ion battery or lithium-sulfur battery electrolyte, in particular to an organic supramolecule with a ring-like pore structure containing electron-deficient spaces as an additive for a lithium-ion battery or a lithium-sulfur battery to effectively enhance the electrical conductivity, The invention improves the lithium ion migration number and improves the battery rate performance; it belongs to the technical field of lithium batteries.

Background technique

Human beings have long relied on the development of traditional fossil energy, and are facing many problems (shortage of resources and environmental pollution). It is urgent to seek new energy that can meet human needs and develop sustainably. Among the new energy sources, lithium batteries have obvious advantages. Lithium batteries have been widely used in our daily life. The rapid development of society now puts forward more requirements for lithium batteries. Many lithium-ion battery companies have turned to ternary cathode materials and silicon carbon anode materials, and many companies have begun to deploy lithium-sulfur batteries and other fields. In lithium-ion batteries, although NCM (811) high-nickel materials and silicon carbon anodes can improve the energy density of the entire battery, charging at high currents still faces great problems. The rapid development of the new energy vehicle industry has put forward higher requirements for the fast charging capability of lithium batteries. The improvement of power performance can be achieved by using positive and negative electrode materials with better rate performance, reducing electrode coating amount, reducing compaction density, and battery structure design. At the same time, the electrolyte has a great influence on the performance of fast-charging lithium-ion batteries. The lithium battery electrolyte plays the role of transporting ions in the battery. Generally composed of lithium salts and organic solvents. Different electrolyte composition, electrolyte conductivity and lithium ion migration number are very different, which will affect the performance of the entire battery. The conductivity of the electrolyte is composed of lithium ions and anions. The closer the migration number t ⁺ of Li ⁺ is, the higher the proportion of Li ⁺ migrated in the electrolyte, and the higher the efficiency of charge transfer between the positive and negative electrodes of the electrolyte. Studies have shown that when the migration number of Li ⁺ is increased to about 0.7, the rate capability of lithium batteries can be significantly improved.

Therefore, the influence of electrolyte properties on the rate performance of batteries is very significant, and the optimization of electrolyte composition and performance is of great significance to improve the rate performance of lithium batteries.

SUMMARY OF THE INVENTION

Aiming at the problems of low electrical conductivity and low lithium ion migration number in the electrolyte of lithium ion batteries or lithium sulfur batteries in the prior art, the purpose of the present invention is to provide an organic superstructure with a ring hole structure containing electron-deficient spaces. Molecules are used as electrolyte additives for lithium-ion batteries or lithium-sulfur batteries. By adding a small amount of organic supramolecules to the electrolyte, the conductivity can be significantly improved, the migration of anions can be limited, the migration number of lithium ions can be increased, and the lithium-ion or lithium-sulfur batteries can be improved. rate performance.

In order to achieve the above technical purpose, the present invention provides a lithium-ion battery or lithium-sulfur battery electrolyte, which contains an organic supramolecular additive; the organic supramolecular has an intracyclic pore structure containing electron-deficient spaces.

The organic supramolecules of the present invention have an intracyclic pore structure containing electron-deficient spaces. Its electron-deficient space can effectively capture electron-rich negative ions in the electrolyte, so that the migration number of negative ions is significantly reduced, and the migration number of lithium ions increases. The electrical conductivity is improved. Therefore, adding organic supramolecules with an intra-ring pore structure containing electron-deficient spaces into the electrolyte can improve the rate performance of lithium-ion batteries or lithium-sulfur batteries.

In a preferred solution, the pore size of the intra-ring pore structure of the organic supramolecular is 0.1 nm to 20 nm. The intra-ring pore structure of organic supramolecules has a suitable pore size, which can effectively capture negative ions. If the pore size is too small, it is difficult for negative ions to enter the ring pore, and if the pore size is too large, the negative ions cannot be stably combined by organic supramolecules.

In a preferred solution, the pore structure in the ring containing the electron-deficient space is composed of a cyclic conjugated system. The cyclic conjugated system is a cyclic structure formed by alternating single and double bonds. The conjugated system exhibits electron-deficient body, and the cyclic conjugated system has a large electron free domain, which shows a higher electron-deficient property, which is more conducive to the binding of negative ions.

In a preferred solution, the cyclic conjugated system contains polar substituent groups. The polar substituents are mainly electron-deficient strong polar substituents, such as cyano, nitro, etc., which can improve the binding stability of organic supramolecules to anions.

In a preferred solution, the organic supramolecules have the structure of formula 1. For its synthesis method, please refer to the literature: Lee, S.; Chen, C.-H.; Flood, A.H.Nat.Chem. 2013, 5(8), 704-710.

In a preferred solution, the mass percentage concentration of the organic supramolecular additive in the electrolyte is 0.001-5%; preferably 1-5%. The mass percentage concentration of organic supramolecular additives in the electrolyte is in the range of 0.001 to 5%, which has the effect of improving conductivity, limiting the migration of anions, and increasing the migration number of lithium ions, and the higher the concentration, the more obvious the effect. .

In a preferred solution, the lithium-ion battery or lithium-sulfur battery electrolyte further includes a lithium salt electrolyte and an organic solvent.

In a more preferred solution, the lithium salt electrolyte is a conventional inorganic lithium salt in the field, such as lithium bis(trifluoromethanesulfonyl)imide LiN(SO ₂ CF ₃ ) ₂ , lithium bisfluorosulfonyl imide LiN (SO ₂ F) ₂ , lithium bistrifluorosulfonimide LiN(SO ₂ F ₃ ) ₂ , lithium hexafluorophosphate LiPF ₆ , lithium perchlorate LiClO ₄ , lithium tetrafluoroborate LiBF ₄ , lithium hexafluoroarsenate LiAsF ₆ , Lithium bis-oxalate borate LiBC ₄ O ₈ , lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) and the like.

In a more preferred solution, the solvent is a common organic solvent in the art, such as ethers, sulfones, carbonates (cyclic and chain), carboxylate and the like. Lithium-ion battery electrolytes generally use carbonates (ring and chain), and lithium-sulfur battery electrolytes generally use ethers and sulfones.

Compared with the prior art, the beneficial effects brought by the present invention:

Aiming at the problem of fast charging existing in existing lithium-ion batteries or lithium-sulfur batteries, the technical solution of the present invention uses organic supramolecules with special molecular structure as electrolyte additives to improve this situation for the first time. The organic supramolecules used in the present invention have an intra-ring pore structure containing electron-deficient spaces, which can make full use of this characteristic to capture anions in the electrolyte of lithium-ion batteries or lithium-sulfur batteries, and combine them into macromolecules, thereby promoting the electrolysis of lithium salts. The ionization in the liquid increases the conductivity, and at the same time, the migration number of lithium ions increases, the charge transfer efficiency becomes higher, and the rate performance of the battery is enhanced.

Detailed ways

In order to better explain the present invention and facilitate understanding, the solution and technical effect of the present invention will be described in detail below through specific embodiments. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Comparative Example 1

The following are examples of common lithium-ion battery electrolyte formulations in the prior art:

(1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvent diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1.

(2) Under the condition of room temperature, the lithium salt LiPF ₆ is dissolved in the solvent obtained in step 1, so that the concentration is 1.0 mol/L, and the mixture is uniformly stirred to obtain a common electrolyte.

(3) Test the conductivity and lithium ion migration number of the electrolyte. The lithium ion migration number was 0.4. The conductivity was 12.45 mS/cm.

Comparative Example 2

The following are examples of common lithium-sulfur battery electrolyte formulations in the prior art:

(1) The solvent ethylene glycol dimethyl ether DME and the solvent 1,3 dioxolane are mixed according to the volume ratio of 1:1.

(2) under room temperature condition, lithium salt bis-trifluoromethylsulfonimide lithium LiTFSI is dissolved in the solvent obtained in step 1, so that concentration is 1.0mol/L, stir to obtain common electrolyte.

(3) Test the conductivity and lithium ion migration number of the electrolyte. The lithium ion migration number was 0.4. The conductivity was 12.47 mS/cm.

The following Examples 1 to 4 illustrate the addition of supramolecular additives to the common lithium-ion battery electrolyte or lithium-sulfur battery electrolyte formulations in the prior art.

Example 1

(1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvent diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1.

(2) At room temperature, the lithium salt LiPF ₆ is dissolved in the solvent obtained in step 1, so that the concentration is 1.0 mol/L, and the mixture is stirred evenly, and at the same time, supramolecular CS is added as an additive.

(3) The mass percentage of the supramolecular CS in the lithium battery electrolyte is 0.1 wt %.

(4) Test the conductivity and lithium ion migration number of the electrolyte. The lithium ion migration number was 0.44. The conductivity was higher than that in Comparative Example 1, at 13.21 mS/cm.

Example 2

(1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvent diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1.

(2) At room temperature, the lithium salt LiPF ₆ is dissolved in the solvent obtained in step 1, so that the concentration is 1.0 mol/L, and the mixture is stirred evenly, and at the same time, supramolecular CS is added as an additive.

(3) The mass percentage of supramolecular CS in the electrolyte is 2 wt %.

(4) Test the conductivity and lithium ion migration number of the electrolyte. The lithium ion migration number was 0.6. The conductivity was higher than that in Comparative Example 1, at 15 mS/cm.

Example 3

(1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvent diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1.

(2) At room temperature, the lithium salt LiPF ₆ is dissolved in the solvent obtained in step 1, so that the concentration is 1.0 mol/L, and the mixture is stirred evenly, and at the same time, supramolecular CS is added as an additive.

(3) The mass percentage of supramolecular CS in the electrolyte is 5 wt %.

(4) Test the conductivity and lithium ion migration number of the electrolyte. The conductivity was higher than that in Comparative Example 1. The lithium ion migration number was 0.7. The conductivity was higher than that in Comparative Example 1, at 16 mS/cm.

Example 4

(4) The solvent ethylene glycol dimethyl ether DME and the solvent 1,3 dioxolane are mixed according to the volume ratio of 1:1.

(5) Under room temperature conditions, the lithium salt bistrifluoromethylsulfonimide lithium LiTFSI is dissolved in the solvent obtained in step 1, so that the concentration is 1.0 mol/L, stirred evenly, and added supramolecular CS as an additive simultaneously.

(6) The mass percentage of supramolecular CS in the electrolyte is 4 wt %.

(7) Test the conductivity and lithium ion migration number of the electrolyte. The conductivity was higher than that in Comparative Example 2. The lithium ion migration number was 0.65. The conductivity was higher than that in Comparative Example 1, at 15.32 mS/cm.

Table 1 Comparative Examples 1-2 and Examples 1-4 Electrolyte Composition Table

Claims (1)

1. A lithium sulfur battery electrolyte characterized by: comprising an organic supramolecular additive, a lithium salt electrolyte and an organic solvent;

the organic supramolecules have the structure of formula 1:

the mass percentage concentration of the organic supermolecule additive in the electrolyte is 0.001-5%;

the lithium salt electrolyte comprises at least one of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis (oxalato) borate and lithium trifluoromethanesulfonate;

the organic solvent comprises at least one of ethers and sulfones.