High-safety high-voltage halogenated ether-phosphate cosolvent electrolyte and lithium battery

Abstract

The invention provides a high-safety high-voltage halogenated ether-phosphate cosolvent electrolyte and a lithium battery. The electrolyte is composed of a lithium salt, a non-aqueous organic solvent and an additive, the lithium battery is obtained by assembling a positive plate, a negative plate, a diaphragm and the electrolyte. The prepared electrolyte can form a compact and stable interface passivation film on the surfaces of the positive electrode and the negative electrode of the lithium battery, oxygenolysis of the electrolyte is effectively inhibited, and interface side reaction is reduced, so that the electrochemical window and the safety of the battery are improved, and the cycle life of the battery at normal temperature and high temperature is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte and a lithium battery. Background Art

[0002] Lithium batteries dominate the energy storage field due to their high energy density, no memory effect, long cycle life, etc. However, as people's pace of development is getting faster and faster, higher requirements are placed on lithium batteries.

[0003] Electrolyte is an important component of lithium batteries and is called the "blood" of lithium batteries by the industry. At present, lithium battery electrolytes are usually based on organic solvents (such as carbonates) and lithium salts (such as LiPF6). Although they have good performance in terms of conductivity, they still have the following problems: (1) Insufficient safety: the solvent is flammable and has low vapor pressure, which may cause the battery to catch fire or explode; (2) Insufficient temperature adaptability: poor thermal stability, especially at high temperatures, the electrode interface side reactions are aggravated, and it is difficult to form a stable electrode interface, resulting in a low cycle life; (3) Insufficient voltage window: poor oxidation stability, the battery is easy to swell, and it leads to low energy density. In particular, extreme environments such as high temperature will pose a more severe challenge to the safety of lithium batteries, so it is necessary to develop safer electrolyte systems. Solvents play a key role in determining the safety and stability of electrolytes. The construction of a new electrolyte solvation structure by using flame retardant and stable solvents can significantly improve its reliability in extreme environments. Phosphate esters have excellent free radical blocking flame retardant effects. Phosphate esters also have a wide operating temperature range (good thermal stability), a stable electrochemical window, and good solubility in lithium salts, and are considered to be flame retardant solvents with great application prospects. However, due to the growth of molecular chains, the increase of molecular weight, and the increase of viscosity, it may lead to poor compatibility with electrodes (including positive and negative electrodes), low lithium ion conductivity, and poor cycle stability of corresponding lithium batteries. Therefore, it is necessary to find suitable co-solvents / diluents to adjust their solvation structure and improve their electrochemical performance.

[0004] Ether has the following advantages when used as a solvent for lithium battery electrolyte: (1) Good solubility in lithium salts; (2) Good compatibility with lithium metal anode; (3) A relatively uniform and stable SEI can be formed on the surface of the anode, which is beneficial to improving CE. In summary, ether-based electrolytes have shown great potential for application, but ether as an electrolyte solvent (especially in high temperature environments) has the following obvious defects: (1) It is flammable, has a low flash point, low vapor pressure, and the battery is prone to swelling, which poses a serious safety hazard; (2) It usually has poor oxidation stability (<4.0Vvs.Li + / Li), even if the operating voltage window is increased by high concentration or local high concentration electrolyte, the cost will be greatly increased, reducing the cost advantage of practical application; (3) Poor high temperature stability, some ether solvents will produce byproducts during oxidation to corrode the electrode, leading to battery failure, etc. It can be seen that ordinary ethers are not suitable as co-solvents / diluents to build electrolyte systems suitable for high temperature extreme environments with long-chain phosphates. Functionalization of ethers at the molecular level, such as partial replacement of hydrogen with F elements, can effectively improve their oxidation stability and lithium ion conductivity, and due to the strong electron-withdrawing effect of fluorine, the oxidation stability of the electrolyte is significantly improved. Therefore, the combination of long-chain phosphates and halogenated ethers with excellent comprehensive performance will hopefully build a high-safety and high-voltage electrolyte system suitable for lithium batteries in extreme environments such as high temperatures.

[0005] In summary, it is very important and urgent to develop a stable, highly safe and high-voltage resistant lithium battery electrolyte. Summary of the invention

[0006] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte; another purpose of the present invention is to provide a high-safety and high-voltage lithium battery.

[0007] In order to achieve the above objectives, the present invention provides a high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte, which is composed of a lithium salt, a non-aqueous organic solvent and an additive.

[0008] Optionally, the additive includes one or both of 1,3-propane sultone and 1,4-butane sultone.

[0009] Optionally, the content of the additive is less than 5% of the total mass of the electrolyte system;

[0010] Among them, 1% to 2% is preferred.

[0011] Optionally, the lithium salt includes at least one of LiPF6, LiFSI, LiTFSI, LiDFOB, LiBF4 and LiClO4;

[0012] Among them, LiFSI is preferred.

[0013] Optionally, the concentration of the lithium salt in the electrolyte is 0.8 to 3.3 mol / L.

[0014] Among them, 2.8 to 3.0 mol / L is preferred.

[0015] Alternatively, the non-aqueous organic solvent comprises a phosphate ester, or a combination of a phosphate ester and a halogenated ether, preferably a combination of tributyl phosphate and a chloroether.

[0016] Alternatively, the phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate and fluorophosphate.

[0017] Alternatively, the halogenated ether includes at least one of fluoroether, chloroether, bromoether and iodoether.

[0018] Optionally, the combined volume ratio of the phosphate ester and the halogenated ether in the non-aqueous organic solvent is 100% to 50%: 0% to 50%;

[0019] Among them, 80% to 70%: 20% to 30% are preferred.

[0020] Another aspect of the present invention provides a high-safety and high-voltage lithium battery, wherein the lithium battery is assembled from a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0021] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0022] (1) The electrolyte of the present invention is a combination of phosphate and halogenated ether, and then a lithium salt of corresponding concentration is added to form a basic electrolyte, and finally 1,3-propane sultone or 1,4-butane sultone additive is added, which can form a dense and stable interfacial passivation film on the surface of the positive and negative electrodes of the lithium battery, effectively inhibit the oxidative decomposition of the electrolyte, and reduce the interfacial side reactions.

[0023] (2) The lithium battery prepared by the electrolyte of the present invention can improve the electrochemical window and safety of the battery and extend the cycle life of the battery at room temperature and high temperature. DETAILED DESCRIPTION

[0024] Hereinafter, a high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte and a lithium battery of the present invention will be described in detail in conjunction with exemplary embodiments.

[0025] Phosphate esters have excellent free radical blocking flame retardant effects. The free radical blocking reaction is as shown in formula (1)-(7):

[0026] PO·+ H· → HPO (1)

[0027] PO· + OH· → HPO2 (2)

[0028] HPO + H· → H2 + PO· (3)

[0029] OH + H2 + PO → H2O + HPO (4)

[0030] HPO2 + H· → H2O + PO (5)

[0031] HPO2 + H· → H2 + PO2 (6)

[0032] HPO2 + OH → H2O + PO2 (7)

[0033] Functionalizing ether at the molecular level, such as partially replacing hydrogen with F, can effectively improve its oxidation stability and lithium ion conductivity, and due to the strong electron-withdrawing effect of fluorine, the oxidation stability of the electrolyte is significantly improved. For another example, after replacing with Cl, when combustion occurs, the electrolyte containing chlorine will react to generate HCl, interfering with the oxidation chain reaction in the flame. The highly active hydrogen and hydroxyl radicals will react with HCl to form free radicals with reduced activity, thereby achieving a flame retardant effect. The chlorine free radical blocks the flame retardant reaction as shown in formulas (8)-(10); and the introduction of chlorine can also reduce the HOMO energy level of the ether molecule, while maintaining a high Li + Solvation ability, and generate an interfacial layer containing LiF and LiCl, to construct a protective layer with synergistic effect. Referring to the advantages of chlorine substitution, it is reasonable to speculate that bromine (Br) and iodine (I) substitution of ether can also produce similar effects.

[0034] M-Cl → M' + Cl· (8)

[0035] H·+Cl·→ HCl (9)

[0036] OH·+HCl→ Cl·+H2O (10)

[0037] Exemplary Embodiment 1

[0038] This exemplary embodiment provides a high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte, which is composed of a lithium salt, a non-aqueous organic solvent, and an additive.

[0039] In this embodiment, the additive includes one or both of 1,3-propane sultone and 1,4-butane sultone.

[0040] The structural formula of 1,3-propane sultone and the structural formula of 1,4-butane sultone are shown in Formula 1 and Formula 2, respectively. Formula 1 and Formula 2 are:

[0041]

[0042] In this embodiment, the content of the additive is less than 5% of the total mass of the electrolyte system, such as 0.5%, 0.8%, 2.5%, 3.6%, 4% and 4.9%;

[0043] Among them, 1% to 2% is preferred.

[0044] In this embodiment, the lithium salt includes at least one of LiPF6, LiFSI, LiTFSI, LiDFOB, LiBF4 and LiClO4;

[0045] Among them, LiFSI is preferred.

[0046] In this embodiment, the concentration of the lithium salt in the electrolyte is 0.8 to 3.3 mol / L, for example, 0.9 mol / L, 1.5 mol / L, 2.3 mol / L, 2.5 mol / L, 2.9 mol / L and 3.2 mol / L;

[0047] Among them, 2.8 to 3.0 mol / L is preferred.

[0048] In this embodiment, the non-aqueous organic solvent includes a phosphate ester, or a combination of a phosphate ester and a halogenated ether, preferably a combination of tributyl phosphate and a chloroether.

[0049] In this embodiment, the phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate and fluorophosphate.

[0050] In this embodiment, the halogenated ether includes at least one of fluoroether, chloroether, bromoether and iodoether.

[0051] In this embodiment, the combined volume ratio of phosphate ester and halogenated ether in the non-aqueous organic solvent is 100%-50%:0%-50% (the volume ratio here is based on the sum of the volume proportions of phosphate ester and halogenated ether being 1).

[0052] Among them, 80% to 70%: 20% to 30% are preferred.

[0053] Exemplary Embodiment 2

[0054] This exemplary embodiment provides a high-safety and high-voltage lithium battery, which is assembled from a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described in exemplary embodiment 1.

[0055] In order to better understand the above exemplary embodiments, further description is given below with reference to specific examples.

[0056] Example 1

[0057] Electrolyte preparation:

[0058] The electrolyte was prepared in a glove box with a water content and an oxygen content of less than 0.1 ppm. First, tributyl phosphate and dichlorotriethyl ether were mixed and stirred evenly at a volume ratio of 7:3, and then a certain amount of bis(fluorosulfonyl)imide lithium salt was added to the mixture and stirred until it was clear to obtain a solution with a concentration of 3 mol / L, and finally a high-safety and high-voltage lithium battery electrolyte was prepared.

[0059] Lithium battery assembly:

[0060] The CR2032 button cell was assembled in a glove box with water and oxygen contents less than 0.1 ppm, in the order of positive electrode shell, positive electrode sheet, diaphragm, negative electrode sheet, gasket, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2, conductive agent (acetylene black), and binder (PVDF) are dissolved in solvent NMP in a mass ratio of 8:1:1 and stirred for 10 hours to obtain a positive electrode slurry, which is then evenly coated on the positive electrode collector aluminum foil and dried to obtain a positive electrode sheet; the separator is polypropylene; and the negative electrode sheet is lithium metal.

[0061] Example 2

[0062] The difference from Example 1 is that the additive 1,3-propane sultone is finally added to the electrolyte, with a mass proportion of 1%.

[0063] Example 3

[0064] The difference from Example 1 is that the additive 1,3-propane sultone is finally added to the electrolyte, accounting for 2% by weight.

[0065] Example 4

[0066] The difference from Example 1 is that the additive 1,3-propane sultone is finally added to the electrolyte, accounting for 3% by weight.

[0067] Example 5

[0068] The difference from Example 1 is that the additive 1,3-propane sultone is finally added to the electrolyte, with a mass proportion of 5%.

[0069] Example 6

[0070] The difference from Example 1 is that the additive 1,4-butanesultone is finally added to the electrolyte, with a mass proportion of 1%.

[0071] Example 7

[0072] The difference from Example 1 is that the additive 1,4-butanesultone is finally added to the electrolyte, with a mass proportion of 2%.

[0073] Example 8

[0074] The difference from Example 1 is that the additive 1,4-butanesultone is finally added to the electrolyte, accounting for 3% by weight.

[0075] Example 9

[0076] The difference from Example 1 is that the additive 1,4-butanesultone is finally added to the electrolyte, with a mass proportion of 5%.

[0077] Example 10

[0078] The difference from Example 1 is that 1,3-propane sultone additive and 1,4-butane sultone additive are finally added to the electrolyte, with the mass proportions being 1% and 1% respectively.

[0079] Example 11

[0080] The difference from Example 1 is that 1,3-propane sultone additive and 1,4-butane sultone additive are finally added to the electrolyte, with the mass proportions being 2% and 2% respectively.

[0081] Example 12

[0082] The difference from Example 1 is that 1,3-propane sultone additive and 1,4-butane sultone additive are finally added to the electrolyte, with the mass proportions being 2% and 3% respectively.

[0083] The lithium batteries prepared in Examples 1 to 12 above were tested at room temperature, high temperature and high voltage. The test results are shown in Table 1.

[0084] Table 1 Electrochemical performance of lithium batteries prepared with high safety and high voltage halogenated ether-phosphate co-solvent electrolyte

[0085]

[0086]

[0087] As can be seen from Table 1, the halogenated ether-phosphate co-solvent electrolyte effectively improves the room temperature, high temperature and high voltage cycle performance of the lithium battery, indicating that the electrolyte can improve the interface stability and safety of the battery.

[0088] Although the present invention has been described above in conjunction with exemplary embodiments, it will be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte, characterized in that: The electrolyte consists of lithium salt, non-aqueous organic solvent and additives.

2. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 1, characterized in that: The additive includes one or both of 1,3-propane sultone and 1,4-butane sultone.

3. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 1, characterized in that: The content of the additive is less than 5% of the total mass of the electrolyte system.

4. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 1, characterized in that: The lithium salt includes at least one of LiPF6, LiFSI, LiTFSI, LiDFOB, LiBF4 and LiClO4.

5. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 1, characterized in that: The concentration of the lithium salt in the electrolyte is 0.8 to 3.3 mol / L.

6. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent includes a phosphate ester, or a combination of a phosphate ester and a halogenated ether.

7. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 6, characterized in that: The phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate and fluorophosphate.

8. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 6, characterized in that: The halogenated ether includes at least one of fluoroether, chloroether, bromoether and iodoether.

9. The high-safety and high-voltage halogenated ether-phosphate co-solvent electrolyte according to claim 6, characterized in that: The volume ratio of the phosphoric acid ester to the halogenated ether is 100% to 50%: 0% to 50%.

10. A high-safety high-voltage lithium battery, characterized in that: The lithium battery is assembled from a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9.

Images