CN112563573A

CN112563573A - Electrolyte and lithium battery

Info

Publication number: CN112563573A
Application number: CN202011596802.5A
Authority: CN
Inventors: 秦虎; 陈明凯; 戴建才; 赵世勇
Original assignee: Ningde Guotai Huarong New Material Co ltd
Current assignee: Ningde Guotai Huarong New Material Co ltd
Priority date: 2020-12-29
Filing date: 2020-12-29
Publication date: 2021-03-26
Anticipated expiration: 2040-12-29
Also published as: CN112563573B

Abstract

The invention relates to an electrolyte and a lithium battery, and mainly solves the technical problems of poor cycle performance and poor high-temperature performance of the lithium battery. The invention effectively solves the problem by adding lithium difluorophosphate and an additive S, wherein the structural formula of the additive S is shown in the specification

Wherein R is₁、R₂Independently one of hydrogen, halogen, alkyl or alkoxy with 1-5 carbon atoms substituted or unsubstituted by halogen, R₃Is C_nH_2nOr C_nH_2nO and n are numbers between 0 and 5. The synergistic use of lithium difluorophosphate and the additive S enables the lithium battery to have good cycle performance and good high temperature performance.

Description

Electrolyte and lithium battery

Technical Field

The invention relates to an electrolyte and a lithium battery.

Background

The lithium ion battery is widely applied to the fields of new energy automobiles and energy storage at present due to the advantages of environmental friendliness, high energy density and the like. With the continuous development of new energy vehicles, the new energy vehicles need higher driving mileage and power, and accordingly, the energy density of the lithium ion battery needs to be increased to meet the requirements of the new energy vehicles. In order to improve the energy density of the lithium ion battery, the compacted density of positive and negative electrode materials in the lithium ion battery cell and the surface density of positive and negative electrode plates are further improved; at the same time, the capacity of a single cell is increased to over 50 AH. The design of high compaction of materials in the battery core puts forward the wettability test requirement on the electrolyte, the traditional electrolyte of ferrous phosphate mainly uses Vinylene Carbonate (VC) to improve the cycle performance of lithium iron phosphate, but the surface tension of the electrolyte cannot be improved, so that the wettability of the electrolyte is improved, and the improvement of the wettability of the electrolyte is favorable for improving the production efficiency of the battery.

In the electrolyte, the carbonate compound is used for forming solvated lithium ions and plays a role in transmitting the lithium ions in the lithium ion battery; meanwhile, in the solvent, cyclic carbonate, such as Ethylene Carbonate (EC), Propylene Carbonate (PC) and the like, forms an SEI film on the surface of the lithium ion battery anode material. In order to further improve the components and strength of the SEI film, the electrolyte solution is prepared by adding various additives, such as VC, PS, etc., but the use of PS results in high resistance affecting the performance of the battery.

In the chinese patent cn201610536662.x, a combination mode of Vinylene Carbonate (VC) + Fluorobenzene (FB) + vinyl sulfate (DTD) is adopted to improve the cycle performance and high and low temperature performance of lithium iron phosphate with high energy density, but the additive FB only plays a role in improving the wettability of the electrolyte and cannot play a role in improving the performance of the battery; in addition, after the vinyl sulfate (DTD) is added into the electrolyte, the electrolyte needs low-temperature environment for transportation and storage, and the cost of the electrolyte is greatly increased.

Chinese patent CN201910003270.0 discloses that the electrolyte of a high-energy-density ferrous phosphate lithium battery adopts three additives of Vinylene Carbonate (VC), lithium bis (trifluoromethylsulfonyl) imide (LiTFSi) and vinyl sulfate (DTD) to improve the long-circulating stability and give consideration to the high-low temperature performance; in order to improve the wettability of the electrolyte, a fluoroether additive is added to adjust the impedance of the membrane and enhance the wetting effect of the battery in a high-surface-density and high-voltage entity system, and 4 additives in the electrolyte not only cause the complex formula of the electrolyte but also cause the stricter control of the production process; due to the use of DTD, both low temperature transport and storage of the electrolyte will result in increased costs.

Disclosure of Invention

The invention aims to solve the technical problem that the lithium battery in the prior art is poor in cycle performance and high-temperature performance, and provides a battery electrolyte and a lithium battery with good cycle performance and high-temperature performance.

In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides an electrolyte, which comprises lithium salt, an organic solvent and an additive, wherein the additive comprises lithium difluorophosphate and an additive S, and the structural formula of the additive S is shown in the specification

Wherein R is₁、R₂Independently one of hydrogen, halogen, alkyl or alkoxy with 1-5 carbon atoms substituted or unsubstituted by halogen, R₃Is C_nH_2nOr C_nH_2nO and n are numbers between 0 and 5.

Because the use of the conventional additives PS and the like can cause high impedance, the lithium difluorophosphate and the additive S are added into the electrolyte, so that the effects of improving SEI film components, reducing impedance and generating low gas are achieved, and the cyclicity and high-temperature storage performance of the lithium battery are further improved.

Preferably, said R is₁、R₂Independently hydrogen or unsubstituted alkyl with 1-5 carbon atoms, R₃Is C_nH_2nAnd n is a number between 0 and 5.

Further preferably, said R₁、R₂Independently hydrogen or unsubstituted alkyl with 1-3 carbon atoms, R₃Is C_nH_2nAnd n is a number between 0 and 3.

In particular, the additive S is S₁And/or S₂Wherein S is₁Has the structural formula

S₂Has the structural formula

In some particular and preferred embodiments of the invention, the additive S is S₁And S₂，S₁And S₂The mass ratio of (A) to (B) is 1: 0.1-5, preferably 1:0.1 to 3, more preferably 1:0.1 to 2.

Preferably, the mass percentage of the lithium difluorophosphate in the electrolyte is 0.01-2%, preferably 0.1-1%, and more preferably 0.3-0.8%.

Preferably, the mass percentage of the additive S in the electrolyte is 0.01-10%, preferably 0.1-5%, and more preferably 0.3-2%.

The lithium salt is at least one of lithium hexafluorophosphate, lithium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonyl) imide, and the concentration of the lithium salt in the electrolyte is 0.5-2 mol/L.

The organic solvent is at least one of ethylene carbonate, diethyl carbonate, propylene carbonate and ethyl methyl carbonate.

Another aspect of the present invention provides a lithium battery including a positive electrode, a negative electrode, and an electrolyte, the lithium battery being the electrolyte as described in any one of the above.

Preferably, the anode is a ternary material, and the charge cut-off voltage of the lithium battery is more than or equal to 4.35g/cm³。

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the electrolyte and the lithium battery have the advantages of good cycle performance and good high-temperature performance.

Drawings

FIG. 1 shows an additive S according to the invention₁The nuclear magnetic resonance hydrogen spectrum of (1);

FIG. 2 shows an additive S according to the invention₂The nuclear magnetic resonance hydrogen spectrum of (1).

Detailed Description

The present invention will be further described with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not mentioned are conventional conditions in the industry. The technical features of the embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

The additives S referred to in the following examples of the invention include S₁And S₂Wherein, in the step (A),

S₁comprises the following steps:

S₂is composed of

Additive S₁And S₂The synthetic technical route is as follows:

(1) additive S₁Synthetic route of (1)

Adding 75g of 1,2,5, 6-hexanetetraol, 350ml of toluene, 150g of triethylamine, 50g of calcium oxide and 6.5g of tetra-n-butyl ammonium bisulfate into a 1000ml reaction bottle, keeping the temperature at 10 ℃, slowly adding 150g of sulfuryl fluoride gas while stirring, reacting for 3 hours, introducing nitrogen for 1.5 hours, filtering to obtain a solid crude product, and obtaining 103.5g of a product by adopting a recrystallization method, wherein the related reaction formula is as follows.

The detection results are shown in FIG. 1.

(2) Additive S₂Synthetic route of (1)

Adding 75g of 2, 3, 4, 5-hexanetetrol, 350ml of toluene, 100g of triethylamine, 40g of calcium oxide and 5.0g of tetra-n-butyl ammonium bisulfate into a 1000ml reaction bottle, keeping the temperature at 5 ℃, slowly adding 200g of sulfuryl fluoride gas under stirring, reacting for 2 hours, introducing nitrogen for 1 hour, and filtering to obtain a solid crude product. The recrystallization method is adopted to obtain 98.3g of a product, and the related reaction formula is as follows.

The results of the detection are shown in FIG. 2.

Preparing an electrolyte:

BASE electrolyte: in an argon-filled glove box (H)₂Content of O<10ppm), organic solvent diethyl carbonate (EC): propylene Carbonate (PC): ethyl Methyl Carbonate (EMC) was mixed at a mass ratio of 35:5:60, followed by thoroughly drying the lithium salt LiPF₆Dissolved in a mixed organic solvent, LiPF₆The concentration of (2) is 1 mol/L.

Comparative examples 1 to 5

Adding different proportions and different types of conventional additives on the basis of the BASE electrolyte, wherein the conventional additives are as follows: lithium bis (fluorosulfonylimide) (LiFSI), Vinylene Carbonate (VC), 1-3 Propane Sultone (PS), vinyl sulfate (DTD), Methylene Methanedisulfonate (MMDS), 1, 4-Butanesultone (BS), 1,3- (1-propene) sultone (PES), and the components of the electrolytes of comparative examples 1 to 5 are in parts by weight shown in table 1.

TABLE 1 COMPARATIVE EXAMPLES 1 TO 5 ELECTROLYTE COMPONENTS OF PARTS (pbw)

Examples 1 to 10

Adding lithium difluorophosphate and additive S on the basis of BASE electrolyte₁Additive S₂The components and parts by weight of the electrolytes of examples 1 to 10 are shown in Table 2.

TABLE 2 electrolyte Components weight fractions (parts) of examples 1 to 10

	BASE	LiPF₂O₂	S1	S2
					Example 1	100	0.5	0.5
Example 2	100	0.5	1.0
					Example 3	100	0.5	1.5
Example 4	100	0.5		0.5
					Example 5	100	0.5		1.0
Example 6	100	0.5		1.5
					Example 7	100	0.5	0.5	0.5
Example 8	100	0.5	0.5	1.0
					Example 9	100	0.5	1.0	0.1
Example 10	100	0.5	1.0	1.0

Preparation of positive plate

Ternary LiNi as positive electrode active material_1/3Co_1/3Mn_1/3O₂Mixing (NCM), polyvinylidene fluoride (PVDF) as an adhesive and acetylene black as a conductive agent according to a weight ratio of 95:3:2, adding N-methylpyrrolidone (NMP), uniformly stirring to obtain anode slurry, uniformly coating the anode slurry on an aluminum foil of an anode current collector, drying the aluminum foil at room temperature, transferring the dried aluminum foil to a 120 ℃ drying oven for drying, and then cold-pressing and cutting to obtain the anode plate.

Preparation of negative plate

Mixing the negative active material artificial graphite, the binder styrene-butadiene rubber and the conductive agent according to the weight ratio of 97:2:1, adding deionized water, and uniformly stirring to obtain negative slurry; and uniformly coating the negative electrode slurry on a copper foil of a negative current collector, airing the copper foil at room temperature, transferring the copper foil into an oven for drying, and then performing cold pressing and slitting to obtain the negative electrode plate.

Battery testing

(1) High temperature cycle performance test of lithium ion secondary battery

Charging the lithium ion secondary battery at 55 ℃ with a constant current of 1C until the voltage is 4.35V, then charging at a constant voltage until the current is 0.05C, and then discharging at a constant current of 1C until the voltage is 2.75V, wherein the process is a charge-discharge cycle process, and the discharge capacity of the lithium ion secondary battery is the discharge capacity Q of the first cycle₁. The lithium ion secondary battery is subjected to 1000-cycle charge/discharge tests according to the method, and the discharge capacity Q of the 600 th cycle is detected₂. Capacity retention rate Q₂/Q₁*100％

(2) High temperature storage performance test of lithium ion secondary battery

The lithium ion secondary battery was charged at a constant current of 0.2C to 100% SOC at 25 deg.C, and the thickness of the lithium ion secondary battery was measured and recorded as h₀(ii) a Then the lithium ion secondary battery is placed into a constant temperature box with the temperature of 60 ℃, is taken out after being stored for 30 days, and the thickness of the lithium ion secondary battery is tested and recorded as h₁The battery takes 1C constant current discharge capacity as Q₃. At 25 deg.C, the battery is circulated for three weeks at 0.2C constant current, the fourth battery is charged at 1C constant current to 4.35V, then charged at constant voltage to 0.05C current, and then charged at constant voltageDischarging 1C at constant current to voltage of 2.75V and discharge capacity of Q₄. Thickness expansion rate [ (h) of lithium ion secondary battery after 30 days of storage at 60 ℃₁-h₀)/h₀]100% and capacity protection rate Q₃/Q₁100% and capacity recovery rate Q₄/Q₁100%, 3 lithium ion secondary batteries were tested per group and averaged.

Lithium ion batteries were prepared using the electrolytes of the comparative examples and the positive electrode sheet and the negative electrode sheet prepared by the above methods, and battery tests were performed, and the electrochemical properties of the relevant lithium ion batteries were as shown in table 3.

TABLE 3

Since the use of the conventional additive PS or the like causes high impedance, the present invention adds lithium difluorophosphate, additive S to the electrolyte₁And S₂The effects of improving SEI film components, reducing impedance and low gas generation are achieved, and the cyclicity and the high-temperature storage performance are further improved.

The present invention has been described in detail in order to enable those skilled in the art to understand the invention and to practice it, and it is not intended to limit the scope of the invention, and all equivalent changes and modifications made according to the spirit of the present invention should be covered by the present invention.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent and an additive, wherein: the additive comprises lithium difluorophosphate and an additive S, wherein the structural formula of the additive S is shown in the specification

Wherein，R₁、R₂Independently one of hydrogen, halogen, alkyl or alkoxy with 1-5 carbon atoms substituted or unsubstituted by halogen, R₃Is C_nH_2nOr C_nH_2nO and n are numbers between 0 and 5.

2. An electrolyte as claimed in claim 1, wherein: the R is₁、R₂Independently hydrogen or unsubstituted alkyl with 1-5 carbon atoms, R₃Is C_nH_2nAnd n is a number between 0 and 5.

3. An electrolyte as claimed in claim 2, wherein: the additive S is S₁And/or S₂Wherein S is₁Has the structural formula

S₂Has the structural formula

4. An electrolyte as claimed in claim 3, wherein: the additive S is S₁And S₂，S₁And S₂The mass ratio of (A) to (B) is 1: 0.1-5.

5. An electrolyte as claimed in claim 1, wherein: the mass percentage of the lithium difluorophosphate in the electrolyte is 0.01-2%, and the mass percentage of the additive S in the electrolyte is 0.01-10%.

6. An electrolyte as claimed in claim 5, wherein: the mass percentage of the lithium difluorophosphate in the electrolyte is 0.1-1%, and the mass percentage of the additive S in the electrolyte is 0.1-5%.

7. An electrolyte as claimed in claim 1, wherein: the lithium salt is at least one of lithium hexafluorophosphate, lithium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonyl) imide, and the concentration of the lithium salt in the electrolyte is 0.5-2 mol/L.

8. An electrolyte as claimed in claim 1, wherein: the organic solvent is at least one of ethylene carbonate, diethyl carbonate, propylene carbonate and ethyl methyl carbonate.

9. A lithium battery comprises a positive electrode, a negative electrode and electrolyte, and is characterized in that: the electrolyte solution according to any one of claims 1 to 8.

10. A lithium battery as claimed in claim 9, characterized in that: the anode is a ternary material, and the charge cut-off voltage of the lithium battery is more than or equal to 4.35g/cm³。