CN111816920A

CN111816920A - Electrolyte solution and battery

Info

Publication number: CN111816920A
Application number: CN202010897483.5A
Authority: CN
Inventors: 廖波; 李素丽; 王海; 徐延铭; 李俊义
Original assignee: Zhuhai Cosmx Battery Co Ltd
Current assignee: Zhuhai Cosmx Battery Co Ltd
Priority date: 2020-08-31
Filing date: 2020-08-31
Publication date: 2020-10-23
Anticipated expiration: 2040-08-31
Also published as: CN111816920B

Abstract

The invention relates to an electrolyte and a battery. The electrolyte comprises vinyl sulfate and an additive, and the additive has a structure shown in formula (I). According to the electrolyte disclosed by the invention, the additive (I) and the vinyl sulfate are added, so that the thermal stability of the electrolyte is obviously improved, and the increase of the acidity value and the chromatic value of the electrolyte is inhibited. In addition, the additive (I) can complex transition metal ions dissolved out from the positive electrode under the charge-discharge cycle or high pressure, so that the damage of the transition metal ions to the negative electrode is avoided, and the electrolyte can obviously improve the cycle, storage and floating charge performance of the battery. Meanwhile, the electrolyte greatly improves the discharge capacity of the battery at low temperature.

Description

Electrolyte solution and battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte and a battery.

Background

Batteries (such as lithium ion batteries) have high specific energy, excellent cycle performance, and high operating voltage, and thus are widely used in the fields of digital, energy storage, power, military aerospace, and communication equipment. Currently, in order to widen the operating range of the battery, a vinyl sulfate (DTD) is favored as an electrolyte additive, which can significantly reduce the impedance of the battery and improve low-temperature performance and high-temperature performance. However, DTD has poor stability at room temperature, often causing a sharp increase in acidity and chroma of the electrolyte, and thus failing to achieve the effect of DTD, but rather deteriorating the electrochemical performance of the lithium battery.

Therefore, providing an additive capable of improving the stability of the vinyl sulfate in the electrolyte on the premise of ensuring the improvement of the cycle performance, the low-temperature storage performance and the floating charge performance of the battery under high voltage also becomes one of the problems which are always concerned and pursued in the development of the battery industry.

Disclosure of Invention

The invention provides an electrolyte, which can keep the acidity value and the chromatic value of DTD in the electrolyte relatively stable, simultaneously improve the high-temperature performance of the electrolyte, and also improve the cycle, low temperature, storage performance and floating charge performance of a battery under high voltage.

The invention also provides a battery, on the premise of improving the cycle, low temperature, storage performance and floating charge performance under high voltage, the acidity value and chromatic value of the DTD in the electrolyte can be kept relatively stable, and the discharge capacity under low temperature is obviously improved.

The technical scheme provided by the invention is as follows:

in a first aspect, the present invention provides an electrolyte, including vinyl sulfate and an additive, where the additive has a structure of formula (i):

according to the electrolyte disclosed by the invention, the additive (I) and the vinyl sulfate are added, so that the thermal stability of the electrolyte is obviously improved, and the additive (I) can adsorb and complex HF and H in the electrolyte₂And O, simultaneously, the hydrolysis of the vinyl sulfate can be inhibited, so that the thermal stability of the electrolyte is improved, and the increase of the acidity value and the chromatic value of the electrolyte is inhibited. In addition, the additive (I) can complex transition metal ions dissolved out from the positive electrode under the charge-discharge cycle or high pressure, so that the damage of the transition metal ions to the negative electrode is avoided, and the electrolyte can obviously improve the cycle, storage and floating charge performance of the battery. The inventor speculates that the additive can be used as an inducer for forming a film on the interface of the positive electrode and the negative electrode, so that the interface film on the surface of the positive electrode and the negative electrode generates a porous structure, and is beneficial to the transmission of lithium ions, thereby greatly improving the discharge capacity of the battery at low temperature.

And the mass ratio of the vinyl sulfate to the additive (I) is controlled within a certain range, so that the improvement effect is improved. For example, the mass ratio of vinyl sulfate to the additive (I) can be adjusted to about 1:0.01-2, further 1:0.5-1.5, and further 1: 1.

In the present invention, the mass fractions of the vinyl sulfate and the additive (I) can be controlled within a certain range, thereby achieving a better effect. For example, the mass fraction of vinyl sulfate is 0.8 to 1.2%, further such as 1%, based on the mass of the electrolyte; the mass fraction of the additive (I) is 0.01-2%, further such as 1%.

As a specific embodiment of the present invention, the method for preparing the additive (i) may comprise the following reaction steps:

the additive (I) is prepared by synthesizing a reactant (II) and a reactant (III). In the present invention, controlling the mass ratio of reactant (II) to reactant (III) to be about 1:0.8 to 1.2, e.g., 1:1, allows for better control of product synthesis while increasing the utilization of the starting materials. Meanwhile, the reaction temperature can be controlled to be 25-60 ℃, such as 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃ and 60 ℃; the reaction time is about 45min-1h, such as 45min, 50min, 55min, 1 h; the reaction pH is greater than 7.0 and may range from 8.0 to 9.0, such as 8.0,8.2,8.5, 9.0. The reactant (ii) and the reactant (iii) in the present invention may be commercially available or may be self-produced, and the present invention is not particularly limited thereto.

The colorimetric value change of the electrolyte is obviously smaller than that of the existing electrolyte. Specifically, after the electrolyte is stored for 12 days to 17 days at the temperature of 53 ℃ to 57 ℃, the chroma value of the electrolyte is changed into 4Hazen to 6Hazen relative to the chroma value before storage. Obviously, the present inventors do not limit other methods to the scope of the present invention, which is within the above range of the present invention, after converting the values obtained by other testing methods.

The change of the acidity value of the electrolyte is obviously smaller than that of the existing electrolyte. After the electrolyte is stored for 12 to 17 days at the temperature of between 53 and 57 ℃, the acidity value of the electrolyte is changed to between 3 and 8ppm relative to the acidity value before storage. Obviously, the present inventors do not limit other methods to the scope of the present invention, which is within the above range of the present invention, after converting the values obtained by other testing methods.

In addition, various additives can be added and mixed to obtain a mixed additive, so that the property of the electrolyte is further improved, and the performance of the battery is improved. For example, additives such as 1,3, 6-Hexanetricarbonitrile (HTCN) and/or lithium difluorophosphate (LiPO) may also be added₂F₂)。

Of course, other additives may be added to improve the performance of the electrolyte and the battery, and are within the scope of the present invention, which is not particularly limited. In the present invention, the other additive may be selected from one or a combination of succinonitrile, adiponitrile, dipropylene glycol ether, 3-methoxypropionitrile, glycerol propane trinitrile, vinylene carbonate, ethylene carbonate, 1, 3-propane sultone, 1, 3-propylene sultone, tris (trimethylsilane) phosphate, tris (trimethylsilane) borate, 2-methyl maleic anhydride, succinic anhydride, tris (triallyl) phosphate and tris (triallyl) phosphate.

Typically, the electrolyte also includes an organic solvent. The organic solvent in the invention comprises a cyclic organic solvent and/or a linear organic solvent, wherein the cyclic organic solvent can be selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, gamma-butyrolactone and gamma-valerolactone; the linear organic solvent may be selected from one or more combinations of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propionate, propyl propionate, and 1,1,2, 3-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether.

The electrolyte of the invention can also comprise lithium salt, and the lithium salt can be selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, lithium difluoro (oxalyl) borate, lithium difluoro (oxalyl) phosphate, lithium tetrafluoro (oxalyl) phosphate, lithium bis (trifluoromethanesulfonyl) imide and lithium bis (oxalyl) borate.

In a second aspect, the invention provides a battery comprising the electrolyte.

The battery of the invention adopts the electrolyte, the circulation, storage and floating charge performance of the battery are obviously improved, the acidity value and chromatic value of the electrolyte can be kept relatively stable, and the discharge capacity at low temperature is also obviously improved.

The positive electrode, negative electrode and separator of the battery used in the present invention are conventional materials in the art, and the inventors do not particularly limit this. For example, the positive electrode active material may be at least one of lithium cobaltate, lithium nickelate, lithium manganate, ternary nickel-cobalt-manganese material, ternary nickel-cobalt-aluminum material, lithium iron phosphate (LFP), lithium nickel manganate, and lithium-rich manganese-based material; the negative active material may be at least one of artificial graphite, hard carbon, and soft carbon.

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.

Drawings

1. FIG. 1 is a GC-MS spectrum of additive (I).

Detailed Description

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

The reactants (II) and (III) in the examples of the present invention were obtained from Santa chemical company, Inc.

Example 1

Example 1 presents an electrolyte and a battery.

(1) Additive and preparation method thereof

Adopting a formula 1, mixing and reacting a reactant (II) and a reactant (III) according to a mass ratio of about 1:1 for about 50min at a temperature of 45 ℃ and a pH value of 9.0 to obtain the additive (I), wherein the additive (I) is shown in the formula (1). And mass spectrometry is performed on the additive (i), as shown in fig. 1, the main peak thereof is at 91, which shows the structural feature of SO2-CN, and meanwhile, the peak at 203 thereof corresponds to the molecular feature of the additive (i).

(2) Electrolyte solution

Adopting a mixed solvent of ethylene carbonate and diethyl carbonate with the mass ratio of 3:7, and adding LiPF₆And fully stirring to obtain the reference electrolyte. Wherein, based on the mass of the electrolyte, LiPF₆Is 12 percent. Then adding 0.01 percent of additive (I) and 1 percent of ethylene sulfate (DTD) by mass.

(3) Preparation of the Battery

Preparing a positive pole piece: dispersing a positive active material lithium cobaltate, a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF) in a proper amount of N-methyl pyrrolidone (NMP) solvent according to a mass ratio of 96:2:2, fully stirring and mixing to form uniform positive slurry, uniformly coating the positive slurry on a positive current collector aluminum foil, and drying, rolling and cutting to obtain a positive pole piece.

Preparing a negative pole piece: dispersing a negative active material graphite, a conductive agent acetylene black, a binder sodium carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) in a proper amount of deionized water according to a mass ratio of 95:2:2:1, fully stirring and mixing to form uniform negative slurry, uniformly coating the negative slurry on a negative current collector copper foil, and drying, rolling and slitting to obtain a negative pole piece.

And sequentially stacking the positive pole piece, the diaphragm and the negative pole piece to enable the diaphragm to be positioned between the positive pole piece and the negative pole piece to play a role in isolation, then winding to obtain a bare cell, placing the bare cell in an outer packaging shell, drying, injecting the electrolyte, and then performing vacuum packaging, standing, formation, shaping and other processes to obtain the battery with the rated capacity of 2 Ah.

Examples 2-7 and comparative examples 1-5 additives were prepared using the method shown in example 1, and electrolytes and batteries were prepared according to the specific components and ratios of the additives shown in table 1.

TABLE 1 additive composition in electrolytes of examples and comparative examples

	DTD	Additive (I)	Other additives
				Example 1	1％	0.01％	-
Example 2	1％	0.2％	-
				Example 3	1％	0.5％	-
Example 4	1％	1％	-
				Example 5	1％	2％	-
Example 6	1％	0.5％	1％HTCN
				Example 7	1％	1％	1％LiPO₂F₂
Comparative example 1	1％	-	-
				Comparative example 2	1％	3％	-
Comparative example 3	1％	-	1％HTCN
				Comparative example 4	1％	-	1％LiPO₂F₂
Comparative example 5	-	-	-

The examples and comparative examples were tested and the results are shown in tables 2 and 3.

1. Electrolyte storage colorimetric value and acidity value test

The electrolytes of the above examples and comparative examples were sampled to test the colorimetric value and the acidity value, and then placed in aluminum bottles, respectively, and sealed, and the aluminum bottles were vacuum-sealed with aluminum plastic films, and then placed in a thermostat at a set temperature of 55 ℃ to store for 15 days, and then sampled to test the colorimetric value and the acidity value of the electrolytes. The colorimetric value determination method adopts a platinum-cobalt colorimetric method, and the colorimetric value unit is Hazen. The acidity value was measured by potentiometric titration (Karl-Fisher 798GPT Titrino, Vanton Switzerland), and the acidity value was measured in ppm in HF, and the measurement results are shown in Table 2.

TABLE 2 test results of chroma and acidity values of examples and comparative examples

2. High temperature cycle test

The battery is placed at 45 ℃, a 1C current is used for carrying out charge-discharge circulation in a charge-discharge voltage interval of 3-4.5V, the initial capacity is recorded as Q1, the capacity selected from the cycle to 500 weeks is recorded as Q2, and the capacity retention rate of the battery after 500 weeks of high-temperature circulation is calculated according to the following formula: the cycle capacity retention ratio is Q2/Q1 × 100%.

3. High temperature storage test

At normal temperature, 1C multiplying power of the battery is charged to 4.5V, then 1C is discharged to 3V, the discharge capacity is recorded as Q3, then the battery is charged to 4.5V by 1C multiplying power of the battery, the thickness of the battery is recorded as T1, then the battery is placed in a constant temperature box at 60 ℃ for storage for 30 days, and the thickness of the battery after storage is recorded as T2. The cell was discharged to 3V at 1C at ambient temperature and the discharge capacity Q4 was recorded. The high-temperature storage capacity retention rate and the thickness expansion rate of the battery are calculated by the following formulas: capacity retention rate is Q4/Q3 multiplied by 100%; thickness expansion ratio ((T2-T1)/T1). times.100%

4. High temperature float charge test

After the battery was charged to 4.5V at 1C at normal temperature, the thickness T3 of the battery was measured, and then the battery was placed in a 45 ℃ incubator at a constant voltage of 4.5V for 15 days to measure the thickness T4 of the battery. The battery thickness expansion rate was calculated from the following formula: thickness expansion ratio ((T4-T3)/T3). times.100%

5. Low temperature discharge test

The method comprises the following steps of cycling the battery for 3-4.5 times at a current of 1C at normal temperature, recording the discharge capacity as Q5, fully charging the battery 1C, placing the battery at a temperature of-20 ℃, discharging at a current of 0.5C, recording the discharge capacity Q6, and calculating the low-temperature discharge capacity retention rate of the battery according to the following formula: the retention ratio of the discharge capacity at low temperature was Q6/Q5X 100%.

Table 3 test results of the batteries in examples and comparative examples

As can be seen from Table 2, after the electrolyte of the embodiment of the present invention is stored in the incubator at 55 ℃ for 15 days, the change of the colorimetric value and the acidity value is significantly much smaller than that of the electrolyte of each proportion, which shows that the colorimetric value and the acidity value can be kept stable for a certain time after the additive of the present invention is added into the electrolyte.

As can be seen from table 3, the results of the high temperature cycle test, the high temperature storage test, the high temperature float charge test and the low temperature discharge test of the battery according to the example of the present invention are significantly improved compared to the results of the comparative example, which shows that the cycle, storage and float charge performance of the battery can be significantly improved and the discharge capacity of the battery at low temperature can also be improved after the additive according to the present invention is added.

In summary, the electrolyte of the present invention significantly improves the thermal stability of the electrolyte by adding the additive (i) and the vinyl sulfate, because the additive (i) can adsorb and complex HF and H in the electrolyte₂And O, simultaneously, the hydrolysis of the vinyl sulfate can be inhibited, so that the thermal stability of the electrolyte is improved, and the increase of the acidity value and the chromatic value of the electrolyte is inhibited. In addition, the additive (I) can complex transition metal ions dissolved out from the positive electrode under the charge-discharge cycle or high pressure, so that the damage of the transition metal ions to the negative electrode is avoided, and the electrolyte can obviously improve the cycle, storage and floating charge performance of the battery. The inventor speculates that the additive can be used as an inducer for forming a film on the interface of the positive electrode and the negative electrode, so that the interface film on the surface of the positive electrode and the negative electrode generates a porous structure, and is beneficial to the transmission of lithium ions, thereby greatly improving the discharge capacity of the battery at low temperature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. An electrolyte, comprising vinyl sulfate and an additive, wherein the additive has a structure of formula (I):

2. the electrolyte according to claim 1, wherein the mass ratio of the vinyl sulfate to the additive (I) is 1: 0.01-2.

3. The electrolyte according to claim 1 or 2, wherein the mass fraction of vinyl sulfate is 0.8-1.2% based on the mass of the electrolyte; the mass fraction of the additive (I) is 0.01-2%.

4. The electrolyte as claimed in any one of claims 1 to 3, wherein the electrolyte has a colorimetric value change of 4Hazen to 6Hazen from the colorimetric value before storage after storage at a temperature of 53 ℃ to 57 ℃ for 12 days to 17 days.

5. The electrolyte according to any one of claims 1 to 4, wherein the electrolyte has a change in acidity value of from 3ppm to 8ppm after storage at a temperature of from 53 ℃ to 57 ℃ for from 12 days to 17 days, relative to the acidity value before storage.

6. The electrolyte of any one of claims 1 to 5, further comprising the following additives: 1,3, 6-hexanetricarbonitrile and/or lithium difluorophosphate.

7. The electrolyte as claimed in any one of claims 1 to 6, further comprising one or a combination of several of the following additives: succinonitrile, adiponitrile, dipropylene glycol ether, 3-methoxypropionitrile, glycerol propane dinitrile, vinylene carbonate, vinyl ethylene carbonate, 1, 3-propane sultone, 1, 3-propene sultone, tris (trimethylsilane) phosphate, tris (trimethylsilane) borate, 2-methyl maleic anhydride, succinic anhydride, tris (triallyl) phosphate and tris (triallyl) phosphate.

8. The electrolyte as claimed in any one of claims 1 to 6, further comprising a cyclic organic solvent selected from one or more combinations of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, γ -butyrolactone and γ -valerolactone, and/or a linear organic solvent; the linear organic solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propionate, propyl propionate and 1,1,2, 3-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether; and/or the presence of a gas in the gas,

and lithium salt selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, lithium difluoro oxalato borate, lithium difluoro bis (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium bis (trifluoromethanesulfonyl) imide and lithium bis (oxalato borate.

9. A battery comprising the electrolyte of any one of claims 1-8.