CN112768765A

CN112768765A - High-voltage electrolyte containing sulfate lithium salt additive and lithium ion battery containing electrolyte

Info

Publication number: CN112768765A
Application number: CN201911066506.1A
Authority: CN
Inventors: 曹青青; 周彤; 吴杰; 杨冰; 杜建委
Original assignee: Shanshan Advanced Materials Quzhou Co ltd
Current assignee: Shanshan Advanced Materials Quzhou Co ltd
Priority date: 2019-11-04
Filing date: 2019-11-04
Publication date: 2021-05-07

Abstract

本发明属于锂离子电池技术领域，公开了一种含硫酸酯锂盐添加剂的高电压电解液及含该电解液的锂离子电池。本发明提供的含硫酸酯锂盐添加剂的高电压电解液包含六氟磷酸锂、有机溶剂和添加剂，所述有机溶剂包含链状碳酸酯类、环状碳酸酯类、羧酸酯类中的一种或多种，所述添加剂包含硫酸酯锂盐化合物。所述硫酸酯锂盐化合物耐高温性能好，能够在电极表面形成光滑均匀的薄膜，阻止电极与电解液的进一步氧化分解，减少高温放置后的电池产气膨胀；同时，该膜对锂离子通透性好，能够降低由于成膜造成的阻抗的增加，有效的改善电解液在锂离子电池中的电导率，提高锂离子电池的循环性能。The invention belongs to the technical field of lithium ion batteries, and discloses a high-voltage electrolyte containing a sulfate lithium salt additive and a lithium ion battery containing the electrolyte. The high-voltage electrolyte containing sulfate lithium salt additive provided by the present invention comprises lithium hexafluorophosphate, an organic solvent and an additive, and the organic solvent comprises one or more of chain carbonates, cyclic carbonates and carboxylates The additive comprises a sulfate lithium salt compound. The sulfate lithium salt compound has good high temperature resistance, can form a smooth and uniform film on the surface of the electrode, prevents further oxidative decomposition of the electrode and the electrolyte, and reduces the gas production and expansion of the battery after being placed at high temperature; Good permeability can reduce the increase in impedance caused by film formation, effectively improve the conductivity of the electrolyte in the lithium ion battery, and improve the cycle performance of the lithium ion battery.

Description

High-voltage electrolyte containing sulfate lithium salt additive and lithium ion battery containing electrolyte

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a high-voltage electrolyte containing a sulfate lithium salt additive and a lithium ion battery containing the electrolyte.

Background

In recent years, lithium ion batteries have attracted much attention because they have higher energy densities than other conventional ion batteries. With the rapid development of the application field, people put higher requirements on the energy density, rate capability, applicable temperature, cycle life and safety of the lithium ion battery.

At present, the problems of low oxidation potential, poor wettability with high-compaction positive electrode materials and the like of the conventional carbonate-based high-voltage electrolyte exist, and the practical application of the high-voltage lithium ion battery is severely restricted. The lithium salt is a provider of lithium ions in the electrolyte and is an important component of the electrolyte of the lithium ion battery, but LiPF is the most commonly used lithium salt₆The thermal stability in a non-aqueous solvent is poor, and the stability of a battery system is seriously influenced. LiTFSI has high solubility and conductivity, but severely corrodes the Al current collector at voltages above 3.7V. Therefore, the development of new high voltage electrolyte systems to provide a safe, stable environment is one of the keys to the development of lithium ion batteries.

On the other hand, the application of the film-forming additive inhibits the contact of the electrolyte and the electrode and inhibits the decomposition of the electrolyte by forming a low-resistance stable interface film at the electrode/electrolyte interface. Vinylene Carbonate (VC) is a common SEI film forming additive, and VC forms a layer of compact SEI film through polymerization reaction on the surface of a lithium ion battery cathode, so that electrolyte is prevented from further reductive decomposition on the surface of the cathode, but the VC has poor stability of the SEI film under a high-temperature condition, and the VC has adverse effects on the performance of the lithium ion battery.

Disclosure of Invention

The invention finds that the sulfate ester compound has great development prospect as the additive of the lithium ion battery electrolyte, and in order to overcome the defects of the background technology, the invention provides the high-voltage electrolyte containing the sulfate lithium salt additive. The sulfate lithium salt additive has good high temperature resistance and excellent thermal stability, is easy to form a stable SEI film on the surface of an electrode, has good permeability to lithium ions, and can accelerate the passage of the lithium ions, thereby reducing the impedance increase caused by film formation, and the film can well block the contact between electrolyte and the electrode and inhibit the decomposition of the electrolyte.

In order to achieve the purpose of the invention, the high-voltage electrolyte containing the sulfate lithium salt additive comprises lithium hexafluorophosphate, an organic solvent and an additive, wherein the organic solvent comprises one or more of chain carbonates, cyclic carbonates and carboxylic esters, and the additive comprises a sulfate lithium salt compound shown as a formula (I):

wherein R represents saturated or unsaturated alkane containing 1-10 carbon atoms, halogenated alkane, aromatic hydrocarbon, cyanogen and alkoxy.

Preferably, the lithium sulfate salt compound is a compound represented by the formulae (1) to (6):

more preferably, the lithium sulfate salt compound is a compound represented by the formulae (1) to (3):

further preferably, the addition amount of the sulfate lithium salt compound is 0.1 to 5%, for example, 0.5 to 2% of the total mass of the electrolyte.

Further, the concentration of the lithium salt in the electrolyte is 0.5 to 2M, for example, 1 to 1.5M, in terms of lithium ions.

Further, the additive also comprises one or more additives selected from fluoroethylene carbonate (FEC), Vinylene Carbonate (VC), vinyl sulfate (DTD), 1, 3-propane sultone (1,3-PS), tris (trimethylsilyl) borate (TMSB), ethylene carbonate (VEC), Succinonitrile (SN), Adiponitrile (ADN), Hexanetrinitrile (HTCN) and 1, 2-bis (2-cyanoethoxy) ethane (DENE).

Preferably, the additive also comprises Vinylene Carbonate (VC) with the mass percent of 0.3-0.8%, fluoroethylene carbonate (FEC) with the mass percent of 5-7%, 1, 3-propane sultone (1,3-PS) with the mass percent of 2-3% and Adiponitrile (ADN) with the mass percent of 0.3-0.8% in the electrolyte.

Further, the chain carbonate in the organic solvent is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dipropyl carbonate (DPC); the cyclic carbonate is selected from one or more of Ethylene Carbonate (EC) and Propylene Carbonate (PC); the carboxylic acid ester is selected from one or more of Ethyl Acetate (EA), Ethyl Propionate (EP), Methyl Acetate (MA), propyl acetate (PE), Methyl Propionate (MP), Methyl Butyrate (MB) and Ethyl Butyrate (EB).

Preferably, the organic solvent is Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP).

In another aspect, the present invention also provides a lithium ion battery using the high voltage electrolyte containing the sulfate lithium salt additive of the present invention.

Further, the method for preparing the lithium ion battery comprises injecting the high voltage electrolyte containing the sulfate lithium salt additive into a glove box containing inert gas and fully dried 4.45V LiCoO₂The graphite soft package battery is subjected to the working procedures of laying aside at 45 ℃, forming by a high-temperature clamp and sealing secondarily.

The high-voltage electrolyte containing the sulfate lithium salt additive can effectively inhibit the increase of impedance, improve the conductivity of the lithium ion battery and improve the cycle performance of the lithium ion battery. Compared with the traditional lithium ion battery without the high-voltage electrolyte, the electrolyte contains the sulfate lithium salt, so that the high-temperature resistant effect is good, and the high-temperature cycle performance of the lithium ion battery is excellent; meanwhile, the electrolyte can form a film on the surface of the electrode, the film has good permeability to lithium ions, the increase of impedance caused by film formation is reduced, the conductivity of the electrolyte in the lithium ion battery can be effectively improved, and the low-temperature cycle performance of the lithium ion battery is improved.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples, but the present invention should not be limited to only these examples. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

The indefinite articles "a" and "an" preceding an element or component of the invention are not intended to limit the number requirement (i.e., the number of occurrences) of the element or component. Thus, "a" or "an" should be read to include one or at least one, and the singular form of an element or component also includes the plural unless the number clearly indicates the singular.

Further, 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.

Comparative example 1

The high-voltage electrolyte is prepared by the following method: in a glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP) were mixed in a weight ratio of 25: 10: 30: 35, and then adding lithium hexafluorophosphate to the mixed solvent to dissolve it, to prepare an electrolyte solution having a lithium hexafluorophosphate concentration of 1.2M. Then, 0.5% by mass of propylene carbonate (VC), 6.0% by mass of fluoroethylene carbonate (FEC), 2.5% by mass of 1, 3-propane sultone (1,3-PS), and 2% by mass of Adiponitrile (ADN) in the electrolyte were added to the electrolyte.

The prepared electrolyte was injected into fully dried 4.45V LiCoO₂And (3) carrying out battery performance test on the graphite soft package battery after the working procedures of standing at 45 ℃, high-temperature clamp formation, secondary sealing and the like to obtain the battery used in the comparative example 1.

Example 1

The high-voltage electrolyte is prepared by the following method: in a glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP) were mixed in a weight ratio of 25: 10: 30: 35, and then adding lithium hexafluorophosphate to the mixed solvent to dissolve it, to prepare an electrolyte solution having a lithium hexafluorophosphate concentration of 1.2M. Then, 0.5% of propylene carbonate (VC), 6.0% of fluoroethylene carbonate (FEC), 2.5% of 1, 3-propane sultone (1,3-PS) and 2% of Adiponitrile (ADN) in percentage by mass in the electrolyte are added into the electrolyte; then adding a sulfate lithium salt compound (1) accounting for 0.1 percent of the mass of the electrolyte into the solution.

The prepared high voltage electrolyte containing lithium sulfate salt additive is injected into the fully dried 4.45V LiCoO₂The graphite soft package battery is subjected to battery performance test after the procedures of laying aside at 45 ℃, forming by a high-temperature clamp, sealing secondarily and the like。

In the present invention, other comparative examples and preparation methods of examples refer to comparative example 1 and example 1, and table 1 is a table of electrolyte formulations of each example and comparative example.

TABLE 1 electrolyte formulations for the examples and comparative examples

Lithium ion battery performance testing

1. High temperature cycle performance

Under the condition of high temperature (45 ℃), the lithium ion battery is charged to 4.45V under the constant current and constant voltage of 1C, and then is discharged to 3.0V under the constant current of 1C. After 300 cycles of charge and discharge, the capacity retention rate after the 300 th cycle was calculated as:

2. high temperature storage Properties

The lithium ion battery was subjected to primary 1C/1C charging and discharging (discharge capacity is designated DC) at room temperature (25 ℃ C.)₀) Then charging the battery to 4.45V under the condition of 1C constant current and constant voltage; the lithium ion battery is stored in a high-temperature box at 60 ℃ for 7 days, and after being taken out, 1C discharge (the discharge capacity is recorded as DC) is carried out at normal temperature₁) (ii) a Then, 1C/1C charging and discharging (discharge capacity is designated as DC) were carried out under ambient conditions₂) Calculating the capacity retention rate and the capacity recovery rate of the lithium ion battery by using the following formulas:

3. low temperature cycle performance

The lithium ion battery is charged to 4.45V at a constant current and a constant voltage of 0.25 ℃ under the condition of low temperature (10 ℃), and then discharged to 3.0V under the condition of a constant current of 0.5 ℃. After 50 cycles of charge and discharge, the capacity retention rate after the 50 th cycle was calculated as:

the results of the battery performance tests of the above-described specific examples and comparative examples are shown in table 2.

Table 2 results of cell performance test of each specific example and comparative example

As can be seen from the data above, in comparative example 1, lithium hexafluorophosphate was applied to high voltage 4.45V LiCoO₂When the graphite is used for a soft package battery, LiF and PF are easily generated by decomposition due to poor thermal stability of lithium hexafluorophosphate₅PF produced by the aggravation of the reaction at high temperature₅The acid is very strong, so that cyclic carbonate in the solution can generate a ring-opening reaction to decompose partial linear carbonate, and can react with trace water to generate hydrofluoric acid, further corrode electrode materials, rapidly reduce battery capacity, and seriously affect the performance of the battery at high temperature.

When a lithium sulfate compound is added as an additive, the oxidation potential of the lithium sulfate compound is lower than that of the solvent, and the lithium sulfate compound can be oxidized preferentially to the electrolyte, so that a dense interfacial film is formed on the surface of the electrode, and the interfacial film is not easily decomposed at high temperature, and the contact between the electrode and the electrolyte can be effectively prevented, and the further decomposition of the electrolyte at high temperature can be inhibited. The interfacial film has good permeability to lithium ions, and can make lithium ions rapidly pass through the interfacial film, thereby reducing the impedance caused by film formation.

When the sulfate lithium salt is added into a nitrile group, the compound is shown as the formula (1), and test results show that the addition of the nitrile group is beneficial to forming a polymer film on the surface of the positive electrode of the battery, can better complex transition metal ions, better prevent side reactions from occurring, and further improve the high-temperature performance of the battery, but the low-temperature cycle performance of the battery is reduced due to the increase of film forming impedance; when the fluorine element is added into the sulfate lithium salt, the compounds are shown as the formula (2) and the formula (3), and the test result shows that the wettability of the electrolyte to the electrode is improved due to the addition of the fluorine element, the impedance of the battery is reduced, and the low-temperature cycle performance of the battery is improved to a certain extent. When the content of the lithium sulfate salt is higher, the impedance of the battery can be increased to a certain extent, and the low-temperature cycle performance of the battery is reduced, and particularly when the mass percentage of the additive reaches more than 2.0%, the low-temperature cycle performance of the battery can be obviously reduced.

In summary, for the high voltage electrolyte of the present invention, the following conclusions can be drawn by comparing the experimental data of the examples and the comparative examples:

1. the sulfate lithium salt is used as an electrolyte additive, has a certain effect on improving the low-temperature performance and the high-temperature performance of the electrolyte, and particularly can well improve the high-temperature cycle performance of the electrolyte;

2. the sulfate lithium salt is not easy to decompose at high temperature, and is formed into a film on the surface of an electrode preferentially, so that the contact between an electrolyte and the electrode is inhibited, and the excellent high-temperature performance is shown;

3. the lithium sulfate salt is used as an additive in the electrolyte, and the formed electrode/electrolyte interface film has good permeability to lithium ions and can well pass through the lithium ions, so that the impedance caused by film formation is reduced, the decomposition of the electrolyte can be inhibited, and the good low-temperature performance is shown;

4. when the lithium sulfate salt is used as an additive in an electrolyte, the dosage of the lithium sulfate salt needs to be controlled within a proper concentration range, and when the content is too low, the performance of the lithium sulfate salt is influenced and the function of the lithium sulfate salt cannot be shown; when the content is too high, the film forming resistance is increased, and the cycle performance of the battery is influenced;

5. among the lithium sulfate salts of the present invention, the compounds represented by the formulae (1), (2) and (3) are excellent in effect, and are more suitable for use as additives in an electrolytic solution.

It will be understood by those skilled in the art that the foregoing is only a partial example of the present invention and is not intended to limit the invention, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. a high-voltage electrolyte containing sulfuric ester lithium salt additive, it is characterized in that, described high-voltage electrolyte containing sulfuric ester lithium salt additive comprises lithium hexafluorophosphate, organic solvent and additive, and described organic solvent comprises chain carbonate One or more of carboxylate, cyclic carbonate, and carboxylate, and the additive comprises a sulfate lithium salt compound represented by formula (I):

Wherein, R represents a saturated or unsaturated alkane, halogenated alkane, aromatic hydrocarbon, cyano, and alkoxy containing 1-10 carbon atoms.

2. The high-voltage electrolyte containing sulfate lithium salt additive according to claim 1, wherein the sulfate lithium salt compound is a compound represented by formula (1)-(6):

3. The high-voltage electrolyte containing sulfate lithium salt additive according to claim 1 or 2, wherein the sulfate lithium salt compound is a compound represented by formula (1)-(3):

Preferably, the added amount of the sulfate lithium salt compound accounts for 0.1-5% of the total mass of the electrolyte, for example, 0.5-2%.

4. The high-voltage electrolyte containing sulfate lithium salt additive according to claim 1, characterized in that, in terms of lithium ions, the concentration of the lithium salt in the electrolyte is 0.5-2M, such as 1-1.5M .

5. the high-voltage electrolyte containing sulfate lithium salt additive according to claim 1, is characterized in that, in described additive, also comprises and is selected from fluoro ethylene carbonate, vinylene carbonate, vinyl sulfate, 1, 3-Propane sultone, tris(trimethylsilyl)borate, ethylene ethylene carbonate, succinonitrile, adiponitrile, hexanetrinitrile, 1,2-bis(2-cyanoethoxy) ) one or more additives in ethane.

6. The high-voltage electrolyte solution containing sulfate lithium salt additive according to claim 1 or 5, characterized in that, the mass percentage of vinylene carbonate contained in the electrolyte solution is 0.3-0.8% in the additive. , 5-7% by mass of fluoroethylene carbonate, 2-3% by mass of 1,3-propane sultone and 0.3-0.8% by mass of adiponitrile.

7. The high-voltage electrolyte containing sulfate lithium salt additive according to claim 1, wherein the chain carbonate in the organic solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , one or more in dipropyl carbonate; Described cyclic carbonate is selected from one or more in ethylene carbonate, propylene carbonate; Described carboxylate is selected from ethyl acetate, ethyl propionate One or more of ester, methyl acetate, propyl acetate, methyl propionate, methyl butyrate, and ethyl butyrate.

8. The high-voltage electrolyte containing sulfate lithium salt additive according to claim 1 or 7, wherein the organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl propionate.

9 . A lithium ion battery, characterized in that, the lithium ion battery uses the high-voltage electrolyte containing the sulfate lithium salt additive according to any one of claims 1 to 8 .

10 . The high-voltage electrolyte containing sulfate lithium salt additive according to claim 9 , wherein the preparation method of the lithium ion battery comprises adding the high-voltage electrolyte containing sulfate lithium salt additive in a solution containing 10 . In the glove box of inert gas, it was injected into the fully dried 4.45V LiCoO ₂ graphite soft pack battery, which was put on hold at 45°C, formed into a high-temperature fixture and sealed twice.