CN113659200A - Electrolyte additive for improving high-temperature performance of lithium battery, electrolyte and electrochemical device - Google Patents
Electrolyte additive for improving high-temperature performance of lithium battery, electrolyte and electrochemical device Download PDFInfo
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- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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Abstract
The application discloses electrolyte additive, electrolyte and electrochemical device for improving high-temperature performance of lithium battery. Wherein the electrolyte additive comprises at least one of a compound I or a compound II selected from the structures shown as follows:
Description
Technical Field
The present disclosure relates to the field of lithium batteries, and more particularly, to an electrolyte additive for improving high temperature performance of a lithium battery, an electrolyte containing the electrolyte additive, and an electrochemical device.
Background
A lithium battery is a type of secondary battery (rechargeable battery) that relies primarily on lithium ions (Li)+) Moving between the positive and negative electrodes to work. During charging of lithium batteries, Li+The lithium ion is extracted from the positive electrode and is inserted into the negative electrode through the electrolyte, so that the negative electrode is in a lithium-rich state, the conversion of electric energy into chemical energy is realized, and the reverse process is just realized.
The lithium battery has the advantages of higher working voltage, high energy density, environmental friendliness and the like, and is widely applied to the aspects of 3C consumer batteries, power batteries, energy storage batteries and the like, for example, the lithium battery is fully applied to the fields of mobile communication equipment such as mobile phones, 5G base stations, two-three-wheeled battery cars, ships, passenger cars, large-scale energy storage power stations and the like, and has wide application prospects in the fields of aerospace, national defense war industry and the like. However, some fields have severe requirements for the performance of lithium batteries, such as high temperature performance, cycle performance, high voltage performance and safety performance, and the electrolyte is one of the key factors determining these performances. In the lithium battery, the electrolyte is the only material in contact with the positive electrode, the negative electrode and the diaphragm, and plays an important role in the specific capacity, the working temperature range, the cycle efficiency, the safety performance and the like of the battery.
Most of the commercial lithium batteries at present adopt carbon materials such as graphite and mesocarbon microbeads (MCMB) or silicon materials such as silicon oxide as battery negative electrodes and LiCoO2、LiMn2O4、NCM、NCA、LiFePO4The materials are used as the anode of the battery, a diaphragm made of materials such as porous polyethylene PE, polypropylene PP and the like is inserted between the anode and the cathode, and finally, a mixed solution containing a non-aqueous organic solvent and electrolyte lithium salt is poured to be used as an electrolyte to complete the manufacture of the lithium battery. Among them, lithium hexafluorophosphate (LiPF) is mostly used as an electrolyte lithium salt of a commercial electrolyte6) However, it is unstable at high temperatures and generally begins to decompose to produce PF at 60 ℃5And the like, which may damage the negative electrode SEI film and affect the positive electrode active material, thus greatly restricting the high temperature performance of the battery.
Research is currently being conducted to seek to improve the high temperature resistance of electrolytes by replacing lithium hexafluorophosphate with other lithium salts, such as lithium tetrafluoroborate (LiBF)4) Lithium bis (oxalato) borate (LiBOB), lithium difluorophosphate (LiF)2PO2) The popularization and application of lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium difluoro (oxalato) borate (LiODFB), lithium difluoro (oxalato) phosphate (LiODFP) and the like in lithium batteries have been reported. However, these lithium salts still suffer from other drawbacks, such as LiBF4Although excellent in high-temperature performance, SEI film formation is not performedStabilizing; LiBOB and LiF2PO2The solubility in a carbonate solvent system is low, and the crystallization risk exists when the temperature is changed; LiFSI is considered to be the most promising replacement for LiPF6The main lithium salt is excellent in high-temperature performance, but the price is high, and the main lithium salt has a corrosion effect on metal aluminum, so that the main lithium salt can damage an aluminum current collector and an aluminum battery shell, and other suitable additives are needed to be matched to prevent aluminum corrosion, which further increases the cost.
Therefore, there is a need to develop a solution that can improve the high temperature resistance of lithium batteries and is low in cost.
Disclosure of Invention
Aiming at the defects in the prior art, the application provides the electrolyte additive, the electrolyte and the electrochemical device for improving the high-temperature performance of the lithium battery, wherein the electrolyte additive can relatively improve the capacity retention rate of the lithium battery containing the electrolyte at high temperature, and can also improve the capacity retention rate at higher temperature and under charge-discharge voltage.
In order to achieve the above objects, in a first aspect, the present application provides an electrolyte additive for improving high temperature performance of a lithium battery, the electrolyte additive including at least one of a compound I or a compound II selected from the group consisting of the following structures:
in a second aspect, the present application provides a lithium battery electrolyte comprising an electrolytic lithium salt, an organic solvent and an electrolyte additive according to the above-described first aspect of the present application.
In combination with the second aspect, in one possible embodiment, the concentration of the electrolyte additive in the electrolyte may be 0.5 wt% to 3.0 wt%.
In combination with the second aspect, in one possible embodiment, the electrolyte lithium salt may include lithium hexafluorophosphate (LiPF)6) Lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium bistrifluoromethanesulfonylimide (LiFSI), lithium dioxalate borate (LiBOB), difluorograssesLithium borate acid (LiODFB) and lithium difluorophosphate (LiF)2PO2) At least one of (1).
In combination with the second aspect, in one possible embodiment, the concentration of the electrolytic lithium salt in the electrolytic solution may be 0.8mol/L to 1.2 mol/L.
In combination with the second aspect, in one possible embodiment, the organic solvent may include at least one selected from the group consisting of a carbonate, a carboxylate, and a fluorocarboxylate.
The carbonate may include at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, butylene carbonate, and propyl methyl carbonate.
The carboxylic acid ester may include at least one selected from the group consisting of ethyl formate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, butyl propionate, ethyl butyrate, methyl formate, and ethyl propionate.
The fluorocarboxylic acid ester may include at least one selected from the group consisting of ethylfluorocarboxylate, ethylfluoroacetate, propylfluoroacetate, butylacetate, ethylfluoropropionate, propylfluoropropionate, butylpropionate, ethylfluorobutyrate, and methylfluorocarboxylate.
In combination with the second aspect, in a possible embodiment, the electrolyte may further include a film-forming additive, and the film-forming additive may include at least one selected from fluoroethylene carbonate (FEC), 1, 3-Propane Sultone (PS), 1, 4-Butane Sultone (BS), or Vinylene Carbonate (VC).
In one possible embodiment, the concentration of the film-forming additive in the electrolyte may be 0.2 wt% to 2.5 wt%.
In a third aspect, the present application provides an electrochemical device comprising:
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector;
the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector;
a separator disposed between the positive electrode and the negative electrode; and
an electrolyte, which may be the lithium battery electrolyte according to the third aspect of the present application.
Wherein the electrochemical device may be a lithium battery.
In combination with the third aspect, in one possible embodiment, the positive electrode active material layer may include a positive electrode active material, a binder, and a conductive agent.
The positive active material may include a material selected from lithium cobaltate (LiCoO)2) At least one of nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), lithium iron phosphate, lithium iron manganese phosphate and lithium manganese oxide.
In combination with the third aspect, in one possible embodiment, the negative electrode active material layer may include a negative electrode active material, a binder, and a conductive agent.
The negative active material may include at least one selected from a lithium metal or lithium metal alloy compound, a carbon material, a graphite material, a silicon carbon material, a silicon material, or a silicon oxide material.
The present application also provides an electronic device comprising an electrochemical device according to the third aspect of the present application.
The technical scheme that this application provided compares and has following beneficial effect at least in prior art:
the electrolyte additive for improving the high-temperature performance of the lithium battery can relatively improve the high-temperature performance and the high-voltage performance of the lithium battery comprising the electrolyte additive. Compared with the electrolyte without the electrolyte additive, the lithium battery containing the electrolyte can still maintain the capacity retention rate of more than 90% after charging and discharging cycles of up to 500 times at high temperature (60 ℃), and can still maintain the capacity retention rate of more than 92% after charging and discharging cycles of up to 200 times at higher temperature (45 ℃) and higher charging and discharging voltage (3V-4.5V).
Detailed Description
In order to make the present application more clearly understood by those skilled in the art, the present application will be described in further detail with reference to the following examples, but it should be understood that the following examples are only preferred embodiments of the present application, and the scope of the present application is defined by the scope of the claims.
In a first aspect, the present application provides an electrolyte additive for improving high temperature performance of a lithium battery, the electrolyte additive including at least one of a compound I or a compound II selected from the group consisting of the structures shown below:
in the application, the electrolyte additive is added into the electrolyte, so that a lithium battery containing the electrolyte can still maintain the capacity retention rate of more than 90% after charging and discharging cycles of up to 500 times at high temperature (60 ℃), and can still maintain the capacity retention rate of more than 92% after charging and discharging cycles of up to 200 times at higher temperature (45 ℃) and higher charging and discharging voltage (3V-4.5V).
Specifically, the above-mentioned electrolyte additive according to the present application comprises compound I (tris (perfluorophenyl) borate) and/or compound II (tris (p-trifluoromethylphenyl) borate), wherein the relative magnitude of the dissociation energy of the B-O bond and the C-O bond in the molecule is changed so that the dissociation energy of the B-O bond is greater than that of the C-O bond due to the introduction of a perfluoro substituent or a trifluoromethyl substituent on the benzene ring, whereby the chemical bond between the benzene ring and the oxygen atom (i.e., the C-O bond) is easily broken during the charge and discharge of the lithium battery after the additive is added to the electrolyte, and the resulting borate group (B- (O) is formed3-) can participate in the SEI film forming reaction of the negative electrode, and promote the generation of a stable SEI protective film, thereby improving the cycle performance of the corresponding lithium battery at high temperature (60 ℃). In addition, the C-O bond breakage also generates a fluorine-containing substituent which has higher oxidation potential, so that the high-voltage performance of the corresponding lithium battery can be more effectively improved. And, compared to the literature reported tris (perfluorophenyl) boron compound (TPFPB) and LiPF6Reaction to form a strongly active Lewis acid PF5And the like unfavorable for the battery, according to the present applicationThe electrolyte additive does not suffer from this problem.
In a second aspect, the present application provides a lithium battery electrolyte comprising an electrolytic lithium salt, an organic solvent and an electrolyte additive according to the above-described first aspect of the present application.
By adding the electrolyte additive, the prepared electrolyte can promote the generation of a stable negative electrode SEI protective film and has a higher oxidation potential, so that the high-temperature performance and the high-voltage performance of the lithium battery are relatively improved, namely the retention rate of the circulating capacity at a high temperature (60 ℃) is improved, and the retention rate of the circulating capacity at a high temperature (45 ℃) and a high charging and discharging voltage (3V-4.5V) is improved.
Further, in the lithium battery electrolyte according to the present application, the concentration of the electrolyte additive in the electrolyte may be 0.5 wt% to 3.0 wt%, for example, may be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, or other specific values within the range. Within the concentration range, the electrolyte additive can effectively play a role in correspondingly improving the high-temperature performance and the high-voltage performance of the lithium battery. When the concentration is less than 0.5 wt%, it is difficult to exert a due protective effect due to a low content, and when the concentration is more than 3.0 wt%, the generated SEI film may be thick to hinder the exchange of lithium ions between the electrolyte and the electrode, increase the internal resistance of the battery, make it difficult to achieve its effect of improving the high-temperature performance of the battery, and have no advantage in terms of cost. Preferably, the concentration of the electrolyte additive is 1.5 wt%, and at this concentration, the electrolyte additive can exert the optimal effect of improving the high temperature and high voltage performance of the lithium battery.
Further, in the lithium battery electrolyte according to the present application, the electrolyte lithium salt may include lithium hexafluorophosphate (LiPF)6) Bis (trifluoromethanesulfonyl) amideLithium imide (LiTFSI), lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiODFB) and lithium difluoro (LiF)2PO2) At least one of (1). In the present application, the electrolyte lithium salt may be various electrolyte lithium salts commonly used in lithium battery electrolytes, and those skilled in the art can select the electrolyte lithium salt according to actual needs. The electrolyte additive according to the present invention can be applied to various electrolyte lithium salts, and thus the application range is very wide.
Further, in the lithium battery electrolyte according to the present application, the concentration of the electrolyte lithium salt in the electrolyte may be 0.8mol/L to 1.2mol/L, for example, may be 0.8mol/L, 0.85mol/L, 0.9mol/L, 0.95mol/L, 1.0mol/L, 1.05mol/L, 1.1mol/L, 1.15mol/L, or 1.2mol/L, or other specific values within the range. When the concentration of the electrolyte lithium salt is less than 0.8mol/L, the lithium ion concentration in the electrolyte is generally low, so that the ionic conductivity is too low, resulting in a decrease in the rate capability and cycle performance of the battery. When the concentration of the electrolyte lithium salt is more than 1.2mol/L, the phenomenon that some electrolyte lithium salts are difficult to dissolve or are crystallized during low-temperature storage after dissolution may occur, and too high concentration may cause too high viscosity of the electrolyte, and lithium ion conductivity is reduced, which results in narrow use window and poor wettability of the electrolyte, and affects electrochemical performance of the battery. Preferably, the concentration of the electrolytic lithium salt in the electrolytic solution is 1.0 mol/L.
Further, in the lithium battery electrolyte according to the present application, the organic solvent may include at least one selected from the group consisting of carbonate, carboxylate and fluorocarboxylate. In the present application, the organic solvent may be various organic solvents commonly used in lithium battery electrolytes, and those skilled in the art may select the organic solvent according to actual needs. The electrolyte additive according to the present invention can be applied to various organic solvents, and thus the application range is very wide.
The carbonate may include at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, butylene carbonate, and propyl methyl carbonate.
The carboxylic acid ester may include at least one selected from the group consisting of ethyl formate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, butyl propionate, ethyl butyrate, methyl formate, and ethyl propionate.
The fluorocarboxylic acid ester may include at least one selected from the group consisting of ethylfluorocarboxylate, ethylfluoroacetate, propylfluoroacetate, butylacetate, ethylfluoropropionate, propylfluoropropionate, butylpropionate, ethylfluorobutyrate, and methylfluorocarboxylate.
Further, in the lithium battery electrolyte according to the present application, the electrolyte further includes a film forming additive including at least one of fluoroethylene carbonate (FEC), 1, 3-Propane Sultone (PS), 1, 4-Butane Sultone (BS), or Vinylene Carbonate (VC). The additive is added into the electrolyte, so that the stable SEI film with a compact structure and without impedance increase is formed on the surface of the battery pole piece, and the cycle stability of the lithium battery is further improved.
In the lithium battery electrolyte according to the present application, the concentration of the film-forming additive in the electrolyte may be 0.2 wt% to 2.5 wt%, for example, may be 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, or other specific values within the range. Within the above concentration range, the film-forming additive can make the SEI film-forming property more excellent.
In a third aspect, the present application provides an electrochemical device comprising:
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector;
the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector;
a separator disposed between the positive electrode and the negative electrode; and
an electrolyte, which may be a lithium battery electrolyte according to the second aspect of the present application.
As an alternative solution, the electrochemical device may be a lithium battery, for example, a lithium ion battery, a lithium metal battery, or the like.
As an alternative solution, the positive electrode current collector may be selected from metallic aluminum, but the present application is not limited thereto.
As an alternative solution, the positive electrode active material layer may include a positive electrode active material, a binder, and a conductive agent.
As an alternative embodiment of the present invention, the positive active material may include a material selected from lithium cobaltate (LiCoO)2) The lithium battery may include at least one of nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), lithium iron phosphate, lithium iron manganese phosphate, and lithium manganese oxide, but the present application is not limited thereto.
As an alternative solution, the negative electrode current collector may be selected from metallic copper, but the present application is not limited thereto.
As an alternative aspect of the present application, the negative electrode active material layer may include a negative electrode active material, a binder, and a conductive agent.
As an alternative aspect of the present application, the negative electrode active material may include at least one selected from a lithium metal or lithium metal alloy compound, a carbon material, a graphite material, a silicon carbon material, a silicon material, or a silicon oxygen material, but the present application is not limited thereto.
As an alternative solution, the binder that may be used for the positive electrode active material layer and the negative electrode active material layer may include at least one selected from among polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PTFE), Styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), Polyacrylonitrile (PAN), and polyacrylate, independently of each other, but the present application is not limited thereto.
As an alternative solution of the present application, the conductive agent that may be used for the positive electrode active material layer and the negative electrode active material layer may include at least one selected from carbon black, conductive graphite, Carbon Nanotube (CNT), carbon fiber (VGCF), graphene, Acetylene Black (AB), and Ketjen Black (KB) independently of each other, but the present application is not limited thereto.
The present application also provides an electronic device comprising an electrochemical device according to the third aspect of the present application.
The electrolyte additive for improving the high-temperature performance of the lithium battery can relatively improve the high-temperature performance and the high-voltage performance of the lithium battery comprising the electrolyte additive. Compared with the electrolyte without the electrolyte additive, the lithium battery containing the electrolyte can still maintain the capacity retention rate of more than 90% after charging and discharging cycles of up to 500 times at high temperature (60 ℃), and can still maintain the capacity retention rate of more than 92% after charging and discharging cycles of up to 200 times at higher temperature (45 ℃) and higher charging and discharging voltage (3V-4.5V).
The technical solution of the present application is exemplarily described below by specific embodiments:
each of the compounds used herein is commercially available or ordered and commercially available to one skilled in the art as desired.
< example >
Example 1
The weight ratio of the raw materials is 1: 1: 1 a mixed solvent of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) as an organic solvent of an electrolyte for a lithium battery, to which LiPF is added6Lithium salt, Vinylene Carbonate (VC) and fluoroethylene carbonate (FEC), and an electrolyte additive (compound I) according to the present application, such that the concentration of the electrolyte lithium salt is 1.0mol/L, the concentration of vinylene carbonate is 2 wt%, the concentration of fluoroethylene carbonate is 1 wt%, and the concentration of compound I is 0.5 wt%, thereby obtaining a lithium battery electrolyte.
Example 2
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the concentration of the electrolyte additive (compound I) according to the present application was 1.5 wt%.
Example 3
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the concentration of the electrolyte additive (compound I) according to the present application was 3.0 wt%.
Example 4
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the electrolyte additive according to the present application (compound II) was used instead of compound I, and the concentration of compound II was 0.5 wt%.
Example 5
A lithium battery electrolyte was prepared in the same manner as in example 4, except that the concentration of the electrolyte additive (compound II) according to the present application was 1.5 wt%.
Example 6
A lithium battery electrolyte was prepared in the same manner as in example 4, except that the concentration of the electrolyte additive (compound II) according to the present application was 3.0 wt%.
Comparative example 1
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the electrolyte additive (compound I or compound II) of the present application was not added.
Comparative example 2
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the concentration of the electrolyte additive (compound I) according to the present application was 0.3 wt%.
Comparative example 3
A lithium battery electrolyte was prepared in the same manner as in example 1, except that the concentration of the electrolyte additive (compound I) according to the present application was 3.5 wt%.
Comparative example 4
A lithium battery electrolyte was prepared in the same manner as in example 4, except that the concentration of the electrolyte additive (compound II) according to the present application was 0.2 wt%.
Comparative example 5
A lithium battery electrolyte was prepared in the same manner as in example 4, except that the concentration of the electrolyte additive (compound II) according to the present application was 3.5 wt%.
< test examples >
1. Retention of cycle capacity at high temperature
Preparing a plurality of lithium ion batteries, wherein the positive electrode adopts a lithium iron phosphate pole piece, the negative electrode adopts a graphite pole piece, the diaphragm adopts a PP isolating membrane with the diameter of 16 microns, the electrolyte prepared in the embodiments 1 to 6 and the electrolyte prepared in the comparative examples 1 to 5 are respectively filled, and the lithium ion batteries are packaged to prepare the corresponding lithium ion batteries. The capacity retention (%) of the lithium ion battery after 500 cycles at high temperature (60 ℃) was tested at a charging voltage of 3.65V and a discharging voltage of 2.5V, respectively, and at a charging and discharging rate of 1C/1C. That is, the capacity of the lithium ion battery in the first charge-discharge cycle at a high temperature (60 ℃) was set to 1, and thereafter, the charge-discharge cycle was continued under the same conditions, and the ratio of the cycle capacity of the lithium ion battery at 500 cycles to the first cycle capacity (1) was measured as the cycle capacity retention (%) at a high temperature (60 ℃). The results are shown in table 1 below.
[ Table 1]
| Retention ratio of circulating Capacity (%) | |
| Example 1 | 91.4％ |
| Example 2 | 93.5％ |
| Example 3 | 91.7％ |
| Example 4 | 90.2％ |
| Example 5 | 92.3％ |
| Example 6 | 91.2％ |
| Comparative example 1 | 86.0％ |
| Comparative example 2 | 87.3％ |
| Comparative example 3 | 86.5％ |
| Comparative example 4 | 86.8％ |
| Comparative example 5 | 86.2％ |
As shown in table 1, compared with comparative example 1 in which the electrolyte additive according to the present application is not added, the lithium ion batteries added with the electrolyte additives of examples 1 to 6 of the present application all effectively slow down the decrease of the cycle capacity after a plurality of charge and discharge cycles, and advantageously improve the high temperature performance of the batteries. The best improved performance is exhibited especially when the electrolyte additives (compound I and compound II) are both at a concentration of 1.5 wt% (examples 2 and 5). In addition, comparative examples 2 to 5 used electrolytes having the electrolyte additive content out of the suitable concentration range (0.5 wt% to 3.0 wt%) of the present application, and it was seen that the cycle capacity was significantly lower than that of the corresponding examples.
2. Cycle capacity retention ratio at higher temperature and higher charge-discharge voltage
Further, a plurality of lithium ion batteries were prepared, in which the positive electrode was an NCM ternary material electrode sheet, the negative electrode was a graphite electrode sheet, and the separator was a PP separator of 16 μm, and the electrolytes according to the present application prepared in examples 2 and 5 and the electrolyte prepared in comparative example 1 were separately injected and packaged, thereby preparing corresponding lithium ion batteries. The capacity retention (%) of the lithium ion battery after cycling 200 times at a higher temperature (45 ℃) was tested at a charging voltage of 4.5V and a discharging voltage of 3.0V, respectively, at a charging and discharging rate of 1C. That is, the capacity of the lithium ion battery in the first charge-discharge cycle at a high temperature (45 ℃) was set to 1, and then the charge-discharge cycle was continued under the same conditions, and the ratio of the cycle capacity of the lithium ion battery in 200 cycles to the first cycle capacity (1) was measured as the cycle capacity retention (%) at a high temperature (45 ℃). The results are shown in table 2 below.
[ Table 2]
| Retention ratio of circulating Capacity (%) | |
| Example 2 | 93.6％ |
| Example 5 | 92.7％ |
| Comparative example1 | 83.5％ |
| Comparative example 2 | 87.2％ |
| Comparative example 3 | 92.7％ |
| Comparative example 4 | 86.5％ |
| Comparative example 5 | 92.1％ |
As shown in the above table 2, high voltage performance at the optimum concentration of the electrolyte additive according to the present application was measured, respectively. Compared with comparative example 1 without the electrolyte additive, after multiple charge-discharge cycles, the lithium ion battery added with the electrolyte additives of the embodiment 2 (compound I) and the embodiment 5 (compound II) effectively slows down the reduction of the cycle capacity in 200 charge-discharge cycles at higher temperature (45 ℃) and higher charge-discharge voltage (3V-4.5V), and advantageously improves the high-voltage performance of the battery. In addition, comparative examples 2 and 4 employ electrolytes having the electrolyte additive content lower than the suitable concentration range (0.5 wt% to 3.0 wt%) of the present application, and it can be seen that examples having a cycle capacity significantly lower than the corresponding optimum concentration are shown, while comparative examples 3 and 5 exhibit a relatively excellent cycle capacity retention rate at a relatively high charge and discharge pressure, but exhibit a poor cycle capacity retention rate at a high temperature (60 ℃) and a relatively low charge and discharge voltage (a charge voltage of 3.65V and a discharge voltage of 2.5V) compared to the examples due to the increase in internal resistance of the battery by the electrolyte additive having a higher content (3.5 wt%).
The above-described embodiments of the present application are only examples of the present application and should not be construed as limiting the present application, and those skilled in the art can make modifications without inventive contribution as required after reading the present specification, however, any modifications, equivalents, improvements, etc. within the spirit and principle of the present application should be included in the scope of the present application.
Claims (9)
1. An electrolyte additive for improving the high-temperature performance of a lithium battery, which is characterized by comprising at least one of a compound I or a compound II selected from the following structures:
2. a lithium battery electrolyte, characterized in that it comprises an electrolytic lithium salt, an organic solvent and the electrolyte additive according to claim 1.
3. The lithium battery electrolyte of claim 2 wherein the concentration of the electrolyte additive in the electrolyte is between 0.5 wt% and 3.0 wt%.
4. The lithium battery electrolyte of claim 2 wherein the electrolyte lithium salt comprises at least one selected from the group consisting of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonimide, lithium bistrifluorosulfonimide, lithium dioxalate borate, lithium difluorooxalate borate, and lithium difluorophosphate.
5. The lithium battery electrolyte of claim 2 wherein the concentration of the electrolyte lithium salt in the electrolyte is 0.8mol/L to 1.2 mol/L.
6. The lithium battery electrolyte as claimed in claim 2 wherein the organic solvent comprises at least one selected from the group consisting of carbonates, carboxylates, and fluorocarboxylates, wherein
The carbonate comprises at least one selected from dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, butylene carbonate or methyl propyl carbonate;
the carboxylic ester comprises at least one selected from ethyl formate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, butyl propionate, ethyl butyrate, methyl formate or ethyl propionate; and
the fluorocarboxylic acid ester includes at least one selected from the group consisting of ethylfluorocarboxylate, ethylfluoroacetate, propylfluoroacetate, butylacetate, ethylfluoropropionate, propylfluoropropionate, butylpropionate, ethylfluorobutyrate, and methylfluorocarboxylate.
7. The lithium battery electrolyte of claim 2, further comprising a film forming additive comprising at least one selected from fluoroethylene carbonate, 1, 3-propane sultone, 1, 4-butane sultone, or vinylene carbonate.
8. The lithium battery electrolyte of claim 7 wherein the concentration of the film forming additive in the lithium battery electrolyte is between 0.2 wt% and 2.5 wt%.
9. An electrochemical device, comprising:
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector;
the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector;
a separator disposed between the positive electrode and the negative electrode; and
an electrolyte for a lithium battery according to any one of claims 2 to 8,
wherein the electrochemical device is a lithium battery.
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