CN115425290A - Low-temperature electrolyte, low-temperature lithium ion battery and preparation method of low-temperature lithium ion battery - Google Patents
Low-temperature electrolyte, low-temperature lithium ion battery and preparation method of low-temperature lithium ion battery Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature lithium ion battery electrolyte, a low-temperature lithium ion battery and a preparation method thereof. The invention provides a low-temperature lithium ion battery electrolyte for improving the low-temperature charge and discharge performance of a lithium ion battery, the low-temperature lithium ion battery and a preparation method thereof.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature lithium ion battery electrolyte, a low-temperature lithium ion battery and a preparation method thereof.
Background
The prior art is as follows:
since the lithium ion battery enters the market, the lithium ion battery is widely applied due to the advantages of long service life, large specific capacity, no memory effect and the like. Particularly in the field of power batteries, under the dual promotion of policies and subsidies, the market breakthrough is increased. However, with the continuous development of the lithium ion battery industry, the problem of poor environmental suitability gradually gains market attention. For example: the lithium ion battery used at low temperature has the problems of low capacity, serious attenuation, poor cycle rate performance, obvious lithium precipitation phenomenon, imbalance of lithium desorption and intercalation and the like. With the continuous expansion of the application field, the restriction caused by the low-temperature performance of the lithium ion battery is more and more obvious: the problem of low-temperature use such as the mileage shrinking in winter and dare not to start warm wind for keeping driving is a big 'pain point' of the owner of the electric automobile, and certain restriction is formed on the development of the electric automobile industry. In high latitude and high altitude areas, the application of lithium ion batteries is limited due to poor low temperature performance.
At present, the main methods for solving the problem of poor low-temperature performance of the lithium ion battery include a heating device, an insulating layer, a low-temperature electrolyte technology and the like. The low-temperature electrolyte technology can effectively improve the low-temperature performance of the lithium ion battery. However, the low-temperature lithium ion electrolyte technology mainly improves the low-temperature discharge performance of the lithium ion battery at present, and the optimization technology research on the low-temperature charge performance of the low-temperature lithium ion battery, especially the lithium ion battery with extremely low temperature (minus 40 ℃ and below), is lacked.
In addition, the main research points in the prior art do not relate to the aspects of improving the low-temperature ionic conductivity of the electrolyte and the low-temperature discharge capacity retention rate of the battery, and do not relate to the aspects of improving the low-temperature charge capacity of the battery. The low-temperature charging, namely the process of lithium intercalation of the negative electrode at low temperature, has the risk of lithium precipitation of the negative electrode, puts higher requirements on the dynamic characteristics of the battery, and the reduction of mass transfer impedance is an important means for improving the lithium intercalation capacity of the battery.
The difficulty and significance of the above technical problems:
therefore, based on the problems, the low-temperature lithium ion battery electrolyte for improving the low-temperature charge and discharge performance of the lithium ion battery, the low-temperature lithium ion battery and the preparation method thereof have important practical values.
Disclosure of Invention
The application aims to solve the technical problems in the prior art and provide a low-temperature lithium ion battery electrolyte for improving the low-temperature charge and discharge performance of a lithium ion battery, the low-temperature lithium ion battery and a preparation method thereof.
The technical scheme adopted by the embodiment of the application to solve the technical problems in the prior art is as follows:
a low-temperature lithium ion battery electrolyte comprises an electrolyte solvent, lithium bis (fluorosulfonyl) imide, lithium difluoro (oxalato) borate, fluoroethylene carbonate, lithium difluoro (phosphates) and ethylene sulfate.
The embodiment of the application can also adopt the following technical scheme:
in the electrolyte of the low-temperature lithium ion battery, the electrolyte solvent accounts for 48.5-85.5% of the electrolyte by mass percent, and comprises the following components by mass percent: 5 to 35 percent of ethylene carbonate, 10 to 30 percent of ethylene glycol propyl ether, 8 to 28 percent of methyl ethyl carbonate and 5 to 20 percent of dimethyl carbonate.
In the low-temperature lithium ion battery electrolyte, further, the lithium bis (fluorosulfonyl) imide component accounts for 3-20% by mass, the lithium difluoro (oxalato) borate component accounts for 1.0-2% by mass, the fluoroethylene carbonate component accounts for 1.0-5% by mass, the lithium difluorophosphate component accounts for 0.5-5% by mass, and the vinyl sulfate component accounts for 0.5-8% by mass.
A low-temperature lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and the electrolyte of the low-temperature lithium ion battery.
A preparation method of a low-temperature lithium ion battery is used for preparing the low-temperature lithium ion battery.
In the above method for preparing a low-temperature lithium ion battery, further, the method for preparing a low-temperature lithium ion battery comprises the following steps:
the method comprises the following steps: mixing a graphite negative electrode material, a conductive agent, a binder and an NMP solvent, and stirring to obtain negative electrode slurry;
step two: coating the negative electrode slurry on the surface of the current collector, drying, rolling and punching to obtain a negative electrode sheet;
step three: mixing a ternary positive electrode material, a conductive agent, a binder and an NMP solvent, and stirring to obtain positive electrode slurry;
step four: coating the positive electrode slurry on the surface of the current collector, drying, rolling and punching to obtain a positive plate;
step five: and combining the positive plate, the diaphragm and the negative plate by adopting a Z-shaped lamination, putting the positive plate, the diaphragm and the negative plate into a shell, drying, injecting liquid in a vacuum-40 ℃ dew point environment, and packaging to obtain the low-temperature lithium ion battery.
One or more technical schemes provided in the embodiment of the application have at least the following beneficial effects:
1. the electrolyte has the conductivity sigma more than 4mS/cm at 20 ℃, the conductivity sigma more than 1mS/cm at 40 ℃, and the conductivity sigma more than 0.7mS/cm at 50 ℃, namely, the electrolyte has good charge and discharge performance at-40 ℃.
2. In the prior art, the bifluoride sulfimide lithium has a corrosion effect on a current collector and cannot be used as a unique lithium salt, and the solvation lithium salt structure formed by the solvent component inhibits the bifluoride sulfimide lithium from corroding the current collector, so that the bifluoride sulfimide lithium salt with high content is used, and the low-temperature conductivity of the electrolyte is improved.
3. The fluoroethylene carbonate and ethylene glycol propyl ether are used, so that the desolvation process of lithium salt is facilitated, the charge transfer resistance is reduced, the fluoroethylene carbonate can also be used as a film forming additive in the invention, the fluoroethylene carbonate is not a film forming additive commonly used in a graphite system, but a stable thin SEI film with small resistance can be formed, the charge transfer resistance is also facilitated to be reduced, the low-temperature charge and discharge capacity of the battery is improved, and the charge and discharge capacity maintenance of the battery under the condition of extremely low temperature is improved. On one hand, the conductivity of the electrolyte can be improved, on the other hand, the discharge capacity retention rate of the battery at low temperature can be improved, and the charge capacity retention of the battery at low temperature can also be improved.
3. The lithium bis (fluorosulfonyl) imide is used as a lithium salt, the solvent components are 5% -35% of ethylene carbonate, 10% -30% of ethylene glycol propyl ether, 8% -28% of methyl ethyl carbonate and 5% -20% of dimethyl carbonate, the electrolyte additive is lithium difluorooxalato borate, fluoroethylene carbonate, lithium difluorophosphate and vinyl sulfate, and through the design of the lithium salt, the solvent and the film-forming additive of the electrolyte, the desolvation process of the lithium salt on the surface of a negative electrode is facilitated, the SEI film impedance of the surface of the negative electrode is reduced, and the low-temperature conductivity of the electrolyte is improved.
4. At present, the tube lithium bis (fluorosulfonyl) imide has better low-temperature performance, but in the prior art, in order to reduce foil corrosion caused by the lithium bis (fluorosulfonyl) imide, lithium hexafluorophosphate is generally adopted as a lithium salt, or a small amount of lithium bis (fluorosulfonyl) imide is added into the lithium hexafluorophosphate, so that the low-temperature conductivity of the electrolyte is limited. According to the invention, through adjusting the electrolyte formula, in the specific solvent components (the solvent components comprise 5-35% of ethylene carbonate, 10-30% of ethylene glycol propyl ether, 8-28% of ethyl methyl carbonate and 5-20% of dimethyl carbonate) in the electrolyte formula, especially the addition of the ethylene glycol propyl ether ensures that the lithium bis (fluorosulfonyl) imide does not corrode foil materials, so that the scheme can adopt the lithium bis (fluorosulfonyl) imide with high component content as lithium salt, and does not add lithium hexafluorophosphate, and compared with the common electrolyte, the low-temperature conductivity of the electrolyte is obviously improved.
5. The ethylene glycol propyl ether is commonly used as a solvent in the paint industry, is applied to the field of electrochemistry, and is used as an electrolyte solvent, so that the low-temperature viscosity of the electrolyte is reduced, and the low-temperature conductivity of the electrolyte is effectively improved.
6. The invention can generate an SEI film with toughness, and fluoroethylene carbonate is often used in a silicon-carbon cathode system.
7. The electrolyte formula adopted by the invention solves the problem that the foil is corroded by the lithium bis (fluorosulfonyl) imide, can be used as the only lithium salt in the electrolyte, greatly improves the low-temperature conductivity (the conductivity is still above 0.001S/cm at minus 30 ℃), and comprehensively improves the low-temperature performance of the electrolyte by combining the use of low-viscosity mixed solvent components (such as ethylene glycol propyl ether) and low-impedance film-forming additives (such as FEC), so that the battery can be stably charged and discharged at minus 40 ℃.
Detailed Description
The lithium bis-fluorosulfonyl imide for the lithium salt comprises 5-35% of ethylene carbonate, 10-30% of ethylene glycol propyl ether, 8-28% of methyl ethyl carbonate and 5-20% of dimethyl carbonate, and the electrolyte additive is lithium difluoro oxalato borate, fluoroethylene carbonate, lithium difluoro phosphate and ethylene sulfate.
In order to better understand the above technical solutions, the following detailed descriptions will be provided with reference to specific embodiments.
Example 1
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 80% of electrolyte solvent, 10% of lithium bis (fluorosulfonyl) imide, 2% of lithium difluoro (oxalato) borate, 3% of fluoroethylene carbonate, 3% of lithium difluoro (phosphoro) phosphate and 2% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 35% of ethylene carbonate, 30% of ethylene glycol propyl ether, 15% of ethyl methyl carbonate and 20% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 1 was obtained.
Example 2
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 85% of electrolyte solvent, 10% of lithium bis (fluorosulfonyl) imide, 2% of lithium difluoro (oxalato) borate, 1% of fluoroethylene carbonate, 1% of lithium difluoro (phosphoro) phosphate and 1% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 30% of ethylene carbonate, 30% of ethylene glycol propyl ether, 20% of ethyl methyl carbonate and 20% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 2 was obtained.
Example 3
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 80% of electrolyte solvent, 12% of lithium bis (fluorosulfonyl) imide, 2% of lithium difluoro (oxalato) borate, 2% of fluoroethylene carbonate, 2% of lithium difluoro (phosphoro) phosphate and 2% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 30% of ethylene carbonate, 30% of ethylene glycol propyl ether, 20% of methyl ethyl carbonate and 20% of dimethyl carbonate. The electrolyte solvent comprises the following components in percentage by mass: 25% of ethylene carbonate, 30% of ethylene glycol propyl ether, 25% of ethyl methyl carbonate and 20% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 3 was obtained.
Example 4
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 85% of electrolyte solvent, 11% of lithium bis (fluorosulfonyl) imide, 1% of lithium difluoro (oxalato) borate, 1% of fluoroethylene carbonate, 1% of lithium difluoro (phosphoro) phosphate and 1% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 35% of ethylene carbonate, 25% of ethylene glycol propyl ether, 20% of ethyl methyl carbonate and 20% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 4 was obtained.
Example 5
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 80% of electrolyte solvent, 15% of lithium bis (fluorosulfonyl) imide, 1% of lithium difluoro (oxalato) borate, 2% of fluoroethylene carbonate, 1% of lithium difluoro (phosphoro) phosphate and 1% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 30% of ethylene carbonate, 30% of ethylene glycol propyl ether, 25% of ethyl methyl carbonate and 15% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 5 was obtained.
Example 6
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 85% of electrolyte solvent, 15% of lithium bis (fluorosulfonyl) imide, 1% of lithium difluoro (oxalato) borate, 1% of fluoroethylene carbonate, 1% of lithium difluorophosphate and 2% of vinyl sulfate. The electrolyte solvent comprises the following components in percentage by mass: 30% of ethylene carbonate, 30% of ethylene glycol propyl ether, 28% of ethyl methyl carbonate and 12% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Example 6 was obtained.
Comparative example 1
The low-temperature electrolyte of the embodiment comprises the following components in proportion: electrolyte solvent 90%, lithium hexafluorophosphate 11%, lithium difluorooxalato borate 0.1%, fluoroethylene carbonate 0.5%, lithium difluorophosphate 0.5%, and ethylene sulfate 1.9%. The electrolyte solvent comprises the following components in percentage by mass: 50% of ethylene carbonate, 20% of ethyl methyl carbonate and 30% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Comparative example 1 was obtained.
Comparative example 2
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 90% of electrolyte solvent, 15% of lithium hexafluorophosphate, 3% of lithium difluorooxalato borate, 0.2% of fluoroethylene carbonate, 0.3% of lithium difluorophosphate and 1.5% of vinyl sulfate. The electrolyte solvent comprises the following components in percentage by mass: 75% of ethylene carbonate, 10% of ethyl methyl carbonate and 15% of dimethyl carbonate.
And (3) adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Comparative example 2 was obtained.
Comparative example 3
The low-temperature electrolyte of the embodiment comprises the following components in proportion: 88% of electrolyte solvent, 2% of lithium bis (fluorosulfonyl) imide, 5% of lithium difluoro (oxalato) borate, 0.1% of fluoroethylene carbonate, 2% of lithium difluoro (phosphorate) and 2.9% of ethylene sulfate. The electrolyte solvent comprises the following components in percentage by mass: 80% of ethylene carbonate, 10% of ethyl methyl carbonate and 10% of dimethyl carbonate.
And adding the low-temperature electrolyte into graphite serving as a negative electrode and a ternary material serving as a positive electrode to manufacture the soft package lithium ion battery with the capacity of 2 Ah. Comparative example 3 was obtained.
Experiment one
The low-temperature electrolytes prepared in examples 1 to 6 and comparative examples 1 to 3 were measured for electrical conductivity at 20 deg.C, -40 deg.C, -50 deg.C, respectively, and the results of the measurements are shown in Table 1.
TABLE 1 electrolyte conductivity at different temperatures
| Numbering | Conductivity mS/cm at 20 DEG C | Conductivity mS/cm at-40 DEG C | Conductivity mS/cm at-50 DEG C |
| Example 1 | 4.6 | 1.3 | 0.74 |
| Example 2 | 5.1 | 1.5 | 0.77 |
| Example 3 | 4.4 | 1.2 | 0.73 |
| Example 4 | 4.5 | 1.3 | 0.74 |
| Example 5 | 4.5 | 1.2 | 0.74 |
| Example 6 | 4.8 | 1.4 | 0.76 |
| Comparative example 1 | 2.1 | 0.5 | 0.41 |
| Comparative example 2 | 1.9 | 0.4 | 0.33 |
| Comparative example 3 | 2.0 | 0.6 | 0.41 |
According to the test result, compared with the comparative example, the conductivity of the low-temperature lithium ion battery electrolyte prepared by adopting the scheme is greatly improved. In comparative examples 1 and 2, lithium hexafluorophosphate with a high component content was used as a lithium salt, the solvent component contained no ethylene glycol propyl ether, and the low-temperature conductivity of the electrolyte was significantly lower than that of the examples; comparative example 3 adopts lithium bis (fluorosulfonyl) imide with a low content of components as a lithium salt, and the solvent component does not contain ethylene glycol propyl ether, and the low-temperature conductivity of the electrolyte is significantly lower than that of the examples.
Experiment two
The lithium ion batteries prepared in examples 1 to 6 and comparative examples 1 to 3 were tested according to the following test protocols:
1) Standing for 4h at 25 ℃;
2) Discharging to 2.8V at constant current of 1 Ah;
3) Standing for 0.5h;
4) Charging to 4.2V at a constant current of 1Ah and charging to 100mAh at a constant voltage of 4.2V;
5) Standing for 10min;
6) Standing at-40 ℃ for 8h;
7) Discharging at constant current of 1Ah to 2.8V to obtain the discharge capacity retention rate at-40 ℃;
8) Standing for 4h at 25 ℃;
9) Discharging to 2.8V at constant current of 1 Ah;
10 ) standing for 10min;
11 Standing at-40 ℃ for 8h;
12 0.4Ah constant current charging to 4.2V,4.2V constant voltage charging to 100mAh, obtaining a-40 ℃ charge capacity retention rate;
13 ) standing at 25 ℃ for 4h;
14 Constant current discharge of 0.5C to 1.5V
TABLE 2 Low temperature Charge-discharge Capacity conservation Rate
| Number of | Discharge capacity at-40 ℃ to ensureRetention rate | Retention ratio of charging capacity at-40 DEG C |
| Example 1 | 72％ | 60％ |
| Example 2 | 75％ | 61％ |
| Example 3 | 70％ | 54％ |
| Example 4 | 70％ | 55％ |
| Example 5 | 71％ | 55％ |
| Example 6 | 73％ | 58％ |
| Comparative example 1 | 32％ | 20％ |
| Comparative example 2 | 28％ | 15％ |
| Comparative example 3 | 30％ | 20％ |
The test results are shown in table 2, and it can be seen from the test results that the low-temperature discharge capacity and the low-temperature charge capacity retention rate of the low-temperature lithium ion battery prepared by the scheme are greatly improved compared with those of the comparative example. In comparative examples 1 and 2, lithium hexafluorophosphate with high component content is used as a lithium salt, and a solvent component does not contain ethylene glycol propyl ether, so that the low-temperature charge and discharge capacity of the corresponding lithium ion battery is obviously lower than that of the examples; in the comparative example 3, the low-component content lithium bis (fluorosulfonyl) imide is adopted as the lithium salt, and the solvent component does not contain ethylene glycol propyl ether, so that the low-temperature charge and discharge capacity of the corresponding lithium ion battery is obviously lower than that of the example.
In summary, the invention provides a low-temperature lithium ion battery electrolyte for improving the low-temperature charge and discharge performance of a lithium ion battery, a low-temperature lithium ion battery and a preparation method thereof.
The present invention has been described in detail with reference to the above examples, but the description is only for the preferred examples of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.
Claims (6)
1. The electrolyte of the low-temperature lithium ion battery is characterized in that: the low-temperature lithium ion battery electrolyte comprises an electrolyte solvent, lithium bis (fluorosulfonyl) imide, lithium difluoro (oxalato) borate, fluoroethylene carbonate, lithium difluoro (phosphonato) phosphate and ethylene sulfate.
2. The low temperature lithium ion battery electrolyte of claim 1, wherein: the electrolyte solvent accounts for 48.5-85.5% of the mass percent of the electrolyte, and comprises the following components in percentage by mass: 5 to 35 percent of ethylene carbonate, 10 to 30 percent of ethylene glycol propyl ether, 8 to 28 percent of methyl ethyl carbonate and 5 to 20 percent of dimethyl carbonate.
3. The low temperature lithium ion battery electrolyte of claim 1, wherein: the lithium bis (fluorosulfonyl) imide component accounts for 3% -20% by mass, the lithium difluoro (oxalato) borate component accounts for 1.0% -2% by mass, the fluoroethylene carbonate component accounts for 1.0% -5% by mass, the lithium difluoro (phosphoro) phosphate component accounts for 0.5% -5% by mass, and the vinyl sulfate component accounts for 0.5% -8% by mass.
4. A low temperature lithium ion battery, characterized in that: the low-temperature lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and the low-temperature lithium ion battery electrolyte as claimed in any one of claims 1 to 3.
5. A preparation method of a low-temperature lithium ion battery is characterized by comprising the following steps: the preparation method of the low-temperature lithium ion battery is used for preparing the low-temperature lithium ion battery in claim 4.
6. The method for preparing a low-temperature lithium ion battery according to claim 5, wherein the method comprises the following steps: the preparation method of the low-temperature lithium ion battery comprises the following steps:
the method comprises the following steps: mixing a graphite negative electrode material, a conductive agent, a binder and an NMP solvent, and stirring to obtain negative electrode slurry;
step two: coating the negative electrode slurry on the surface of the current collector, drying, rolling and punching to obtain a negative electrode sheet;
step three: mixing a ternary positive electrode material, a conductive agent, a binder and an NMP solvent, and stirring to obtain positive electrode slurry;
step four: coating the positive electrode slurry on the surface of the current collector, drying, rolling and punching to obtain a positive plate;
step five: and combining the positive plate, the diaphragm and the negative plate by adopting a Z-shaped lamination, putting the positive plate, the diaphragm and the negative plate into a shell, drying the shell, injecting liquid into a vacuum-40 ℃ dew point environment, and packaging to obtain the low-temperature lithium ion battery.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116417570A (en) * | 2023-06-12 | 2023-07-11 | 蔚来电池科技(安徽)有限公司 | Secondary battery and device |
| CN116417570B (en) * | 2023-06-12 | 2023-08-22 | 蔚来电池科技(安徽)有限公司 | Secondary battery and device |
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