Lithium battery electrolyte and lithium battery
Technical Field
The application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium battery electrolyte and a lithium battery.
Background
The lithium ion battery has the characteristics of high energy density, no memory effect, high working voltage, environmental friendliness and the like, and is widely used as a power supply of a 3C digital product. With the expansion of the market demand of electronic products and the development of power and energy storage devices, power lithium batteries are beginning to be applied to electric tools and electric vehicles, so the requirements of people on lithium batteries are also continuously increased, and it is urgent to develop lithium batteries with lower internal resistance and higher dynamics. At present, the effective method is to reduce the dosage of the film forming additive in the electrolyte based on the existing components, but the storage and the cycle performance of the battery cell are influenced; or resistance-reducing additives, but such additives generally do not have good film-forming ability and need to be used in combination with other film-forming additives, and thus the overall resistance-reducing performance is not satisfactory.
Moreover, the electrolyte widely used in the current lithium ion battery still has many defects, especially under high energy density, the performance of the lithium ion battery is poor, such as larger direct current impedance and poor cycle performance. Therefore, there is a need to develop a new electrolyte for lithium battery and lithium battery, which can effectively reduce impedance and improve battery performance.
Disclosure of Invention
The application provides a lithium battery electrolyte and a lithium battery, which can improve the film forming capacity while optimizing the impedance of the electrolyte, thereby improving the performance of the battery.
One aspect of the present application provides a lithium battery electrolyte including an organic solvent, a lithium salt, and a first additive, wherein the first additive includes a silane phosphate compound selected from at least one of compounds represented by structural formula (1):
wherein, X1, X2 and X3 are respectively selected from substituted or unsubstituted C1~10Alkyl, substituted or unsubstituted C1~10Alkoxy, substituted or unsubstituted C2~10Alkenyl, substituted or unsubstituted C2~10Alkenyloxy, substituted or unsubstituted C2~10Alkynyl, substituted or unsubstituted C2~10Alkynyloxy, a sulfate group; part or all of the hydrogen on the X1, X2 and X3 can be respectively replaced by halogen, nitro, cyano, carboxyl and C1~6Alkyl or C2~6And (3) alkenyl substitution.
In some embodiments of the present application, the silane phosphate compound is selected from the group consisting of
At least one of the compounds shown.
In some embodiments of the present application, the electrolyte further comprises a second additive, the second additive comprising at least one of vinylene carbonate, 1, 3-propane sultone, vinyl vinylene carbonate, 1, 3-propene sultone, and vinyl sulfate.
In some embodiments of the present application, the second additive is contained in the electrolyte in an amount of 0.01% to 20% by mass.
In some embodiments of the present application, the content of the silane phosphate compound in the electrolyte solution is 0.01% to 10% by mass.
In some embodiments of the present application, the organic solvent includes cyclic carbonates and chain carbonates.
In some embodiments of the present application, the cyclic carbonate is selected from at least one of propylene carbonate, ethylene carbonate; the chain carbonate is at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl acetate and propyl acetate.
In some embodiments of the present application, the lithium salt is LiPF6、LiBF4、LiBOB、LiODFB、LiFSI、LiPO2F2One or more of (a).
In some embodiments of the present application, the lithium salt is LiPF6The concentration is 0.8 to 1.5 mol/L.
Another aspect of the present application further provides a lithium battery, including a positive electrode, a negative electrode and an electrolyte, where the electrolyte is the above-mentioned electrolyte.
The application provides a lithium battery electrolyte and lithium cell aims at silane phosphate ester compound's structure is optimized in the first additive, introduces the functional group that has good film forming ability in the structure, can optimize electrolyte impedance improves film forming ability simultaneously to improve battery performance.
Detailed Description
The following description is presented to enable any person skilled in the art to make and use the present disclosure, and is provided in the context of a particular application and its requirements. Various local modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims.
The technical solution of the present invention will be described in detail with reference to examples.
Research shows that in the first charge and discharge process of the liquid lithium ion battery, the electrode material and the electrolyte react on a solid-liquid interface to form a passivation layer covering the surface of the electrode material. This passivation layer is an interfacial layer, which is characterized by a solid electrolyte, is an electronic insulator but is an excellent conductor of lithium ions, and lithium ions can freely intercalate and deintercalate through the passivation layer, so the passivation film is called a "solid electrolyte interfacial film" (SEI film for short).
The formation of the SEI film has a crucial influence on the performance of the electrode material. On one hand, the formation of the SEI film consumes part of lithium ions, so that the irreversible capacity of the first charge and discharge is increased, and the charge and discharge efficiency of the electrode material is reduced; on the other hand, the SEI film has organic solvent insolubility and can stably exist in an organic electrolyte solution, and solvent molecules cannot pass through the passivation film, so that co-embedding of the solvent molecules can be effectively prevented, damage to an electrode material due to the co-embedding of the solvent molecules is avoided, and the cycle performance and the service life of the electrode are greatly improved. Therefore, developing a lithium battery electrolyte with lower impedance and higher film forming capability becomes a hot spot of lithium battery research. Through intensive research, the inventors of the present application find a functional additive for an electrolyte of a lithium battery, which can improve the film forming ability while optimizing the impedance of the electrolyte, thereby improving the electrochemical performance of the lithium battery.
The embodiment of the application provides a lithium battery electrolyte, which comprises an organic solvent, a lithium salt and a first additive, wherein the first additive comprises a silane phosphate compound, and the silane phosphate compound is at least one selected from compounds shown in a structural formula (1):
wherein, X1, X2 and X3 are respectivelyIs selected from substituted or unsubstituted C1~10Alkyl, substituted or unsubstituted C1~10Alkoxy, substituted or unsubstituted C2~10Alkenyl, substituted or unsubstituted C2~10Alkenyloxy, substituted or unsubstituted C2~10Alkynyl, substituted or unsubstituted C2~10Alkynyloxy, a sulfate group; part or all of the hydrogen on the X1, X2 and X3 can be respectively replaced by halogen, nitro, cyano, carboxyl and C1~6Alkyl or C2~6And (3) alkenyl substitution.
The conventional silane phosphate ester compound has a good resistance-reducing effect, but is not an excellent film-forming additive and cannot improve the film-forming capability of the electrolyte, so that the high-temperature performance of the battery is not obviously improved. The application optimizes the structure of the silane phosphate compound, and substituted or unsubstituted C is introduced into the structure1~10Alkyl, substituted or unsubstituted C1~10Alkoxy, substituted or unsubstituted C2~10Alkenyl, substituted or unsubstituted C2~10Alkenyloxy, substituted or unsubstituted C2~10Alkynyl, substituted or unsubstituted C2~10The functional groups such as alkynyloxy groups and sulfuric acid groups with good film forming capability enable the first additive comprising the silane phosphate compound to optimize the impedance and simultaneously improve the film forming capability of the electrolyte, thereby improving the high-temperature performance of the battery. Among them, groups represented by X1, X2 and X3 have a function of improving the film forming ability of an electrolyte, and trimethylsilyl has a function of reducing the impedance of an electrolyte.
In some embodiments of the present application, the silane phosphate compound is selected from the group consisting of
At least one of the compounds shown.
In some embodiments of the present application, the content of the silane phosphate compound in the electrolyte solution is 0.01% to 10% by mass, such as 1%, 3%, 5%, 7%, 9%, and the like.
In some embodiments of the present application, the content of the silane phosphate compound in the electrolyte solution is 0.5% to 3% by mass, such as 0.5%, 1%, 3%, and the like.
In some embodiments of the present application, the electrolyte further comprises a second additive, the second additive comprising at least one of vinylene carbonate, 1, 3-propane sultone, vinyl vinylene carbonate, 1, 3-propene sultone, and vinyl sulfate. Besides the silane phosphate compound, the electrolyte can be matched with the second additive, and the second additive can play a role in assisting film formation and further optimize the performance of the electrolyte.
In some embodiments of the present application, the second additive is present in the electrolyte in an amount of 0.01% to 20% by mass, for example, 1%, 5%, 10%, 15%, 20%, etc.
In some embodiments of the present application, the second additive is present in the electrolyte in an amount of 0.2% to 5% by mass, for example, 1%, 2%, 3%, 4%, 5%, etc.
In some embodiments of the present application, the organic solvent includes cyclic carbonates and chain carbonates. The organic solvent is an important component of the electrolyte, and has a large influence on the properties of the electrolyte, such as thermal stability, conductivity and viscosity. In particular, different combinations of organic solvents may be selected depending on the desired properties.
In some embodiments of the present application, the concentration ratio of the cyclic carbonate to the chain carbonate may be between 10: 70 and 40: 60 by mass percent. The mass percentage concentration is preferably between 25: 75 and 35: 65, and the electrochemical performance of the electrolyte is improved.
In some embodiments of the present application, the cyclic carbonate is selected from at least one of propylene carbonate, ethylene carbonate; the chain carbonate is at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl acetate and propyl acetate.
In some embodiments of the present application, the organic solvent consists of ethylene carbonate, ethyl methyl carbonate.
In some embodiments of the present application, the organic solvent consists of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate.
In some embodiments of the present application, the organic solvent consists of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate.
In some embodiments of the present application, the lithium salt is LiPF6、LiBF4、LiBOB、LiODFB、LiFSI、LiPO2F2One or more of (a). In a lithium battery, a lithium salt is mainly used to supply lithium ions, making the basic operation of the lithium battery possible.
In some embodiments of the present application, the lithium salt is LiPF6The concentration is 0.8 to 1.5mol/L, for example, 0.8mol/L, 1mol/L, 1.2mol/L, etc. Increasing the concentration of lithium hexafluorophosphate can increase the density of the ionophore, which is helpful for increasing the interface reaction frequency, but when the concentration is too high, the phenomena of obvious reduction of ion conductivity and viscosity increase are caused, the overall resistance of the battery is increased, and the mobility of lithium ions is reduced.
Example 1
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, and slowly adding 1mol/L lithium salt LiPF into the organic solvents6Then, a silane phosphate compound represented by the structural formula (2) in an amount of 0.5% by weight of the total mass of the electrolyte and vinylene carbonate in an amount of 0.5% by weight were added to prepare an electrolyte 1.
Example 2
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, and slowly adding 1mol/L lithium salt LiPO into the organic solvents2F2Then, a silane phosphate compound represented by the structural formula (2) accounting for 1% of the total mass of the electrolyte and vinylene carbonate accounting for 0.5% of the total mass of the electrolyte are added to prepare an electrolyte 2.
Example 3
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 40: 30: 20, and slowly adding 1mol/L lithium salt LiPO into the organic solvents2F2Then, a silane phosphate compound represented by the structural formula (2) in an amount of 3% by mass of the total electrolyte and vinylene carbonate in an amount of 0.5% by mass of the total electrolyte were added to prepare an electrolyte 3.
Example 4
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 40: 30: 20, and slowly adding 0.8mol/L lithium salt LiPO into the organic solvents2F2And then adding a silane phosphate compound shown in a structural formula (3) accounting for 0.5% of the total mass of the electrolyte and LiFSI accounting for 1% of the total mass of the electrolyte to prepare the electrolyte 4.
Example 5
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, and slowly adding 0.8mol/L lithium salt LiPF into the organic solvents6And then adding a silane phosphate compound represented by a structural formula (3) accounting for 1% of the total mass of the electrolyte and 1% of LiFSI to prepare the electrolyte 5.
Example 6
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, and slowly adding 0.8mol/L lithium salt LiPO into the organic solvents2F2And then adding a silane phosphate compound represented by a structural formula (3) accounting for 3% of the total mass of the electrolyte and LiFSI accounting for 1% of the total mass of the electrolyte to prepare the electrolyte 6.
Example 7
Uniformly mixing organic solvents of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, slowly adding 1.2mol/L lithium salt LiBOB into the organic solvents, and then adding a silane phosphate compound shown in a structural formula (4) accounting for 0.5% of the total mass of the electrolyte and 1, 3-propylene sultone according to the proportion of 1% to prepare the electrolyte 7.
Example 8
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, and slowly adding 1.2mol/L lithium salt LiPF into the organic solvents6Then adding a silane phosphate compound represented by a structural formula (4) accounting for 1% of the total mass of the electrolyte and 1, 3-propylene sultone accounting for 1% of the total mass of the electrolyte to prepare an electrolyte 8.
Example 9
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 40: 30: 20, and slowly adding 1.2mol/L lithium salt LiPF into the organic solvents6Then adding a silane phosphate compound represented by a structural formula (4) accounting for 3% of the total mass of the electrolyte and 1, 3-propylene sultone accounting for 1% of the total mass of the electrolyte to prepare an electrolyte 9.
Example 10
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 40: 30: 20, and slowly adding 1.2mol/L lithium salt LiPF into the organic solvents6Then adding a silane phosphate compound represented by a structural formula (5) accounting for 0.5 percent of the total mass of the electrolyte and 0.5 percent of LiBF4The electrolytic solution 10 was prepared.
Example 11
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, slowly adding 1.2mol/L lithium salt LiODFB into the organic solvents, and then adding 1% of silane phosphate compound shown in a structural formula (5) and 0.5% of LiBF according to the total mass of the electrolyte4An electrolytic solution 11 was prepared.
Example 12
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, and slowly adding 1.2mol/L lithium salt LiPF into the organic solvents6Then adding a silane phosphate compound represented by a structural formula (5) accounting for 3% of the total mass of the electrolyte and 0.5% of LiBF4An electrolytic solution 12 was prepared.
Comparative example 1
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, and slowly adding 1mol/L lithium salt LiPF into the organic solvents6Then vinylene carbonate accounting for 0.5 percent of the total mass of the electrolyte is added to prepare the electrolyte 13.
Comparative example 2
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, and slowly adding 0.8mol/L lithium salt LiPF into the organic solvents6And then adding LiFSI accounting for 1% of the total mass of the electrolyte to prepare the electrolyte 14.
Comparative example 3
Uniformly mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 30: 50: 20, and slowly adding 1.2mol/L lithium salt LiPO into the organic solvents2F2Then adding 1, 3-propylene sultone accounting for 1 percent of the total mass of the electrolyte to prepare the electrolyte 15.
Comparative example 4
Uniformly mixing organic solvents ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 30: 70, and slowly adding 1.2mol/L lithium salt LiPF into the organic solvents6Then adding LiBF accounting for 0.5 percent of the total mass of the electrolyte4An electrolytic solution 16 was prepared.
According to the lithium battery electrolyte, the structure of the silane phosphate compound in the first additive is optimized, a functional group with good film forming capability is introduced into the structure, the impedance of the electrolyte can be optimized, and the film forming capability is improved, so that the performance of a battery is improved.
The embodiment of the application also provides a lithium battery, which comprises a positive electrode, a negative electrode and electrolyte, wherein the electrolyte is any one of the electrolytes described in the embodiments of the application.
In some embodiments of the present application, the method of preparing the positive electrode is: in a homogenizing device, N-methyl pyrrolidone is used as a solvent, lithium cobaltate, acetylene black and polyvinylidene fluoride are uniformly mixed according to the mass ratio of 96: 2 to form anode slurry, the anode slurry is coated on an aluminum foil of 12 microns, and an anode sheet is obtained after drying and cold pressing.
In some embodiments of the present application, the method of preparing the negative electrode is: in a homogenizing device, deionized water is used as a solvent, artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethylcellulose are uniformly mixed according to the mass ratio of 94.5: 2: 1 to form negative electrode slurry, the negative electrode slurry is coated on a copper foil of 8 microns, and the negative electrode sheet is obtained after drying and cold pressing.
In some embodiments of the present application, a method of making the battery comprises: stacking the positive plate, the PE isolating film and the negative plate in sequence to enable the PE isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a bare cell; and placing the bare cell in an aluminum-plastic film shell, injecting the prepared electrolyte into the dried battery, and performing vacuum packaging, standing, formation, shaping and other processes to complete the preparation of the lithium ion battery.
The inventors also performed several experiments to test the performance of the lithium ion batteries described in the examples of the present application. The cell used for the test was made as described above.
Test 1: cycle test at ambient temperature 25 deg.C
And (3) respectively placing the prepared batteries at the normal temperature of 25 ℃, charging to 4.2V at a constant current and a constant voltage of 1C, then discharging to 3V at a constant current of 1C, performing charge-discharge cycle test, circulating for 300 times, and recording cycle data.
And (3) testing 2: high temperature 45 ℃ cycle test
And (3) respectively placing the prepared batteries at the normal temperature of 45 ℃, charging to 4.2V at a constant current and a constant voltage of 1C, then discharging to 3V at a constant current of 1C, performing charge-discharge cycle test, circulating for 300 times, and recording cycle data.
Table 1 shows the charge-discharge cycle test results of the batteries using different electrolytes.
TABLE 1
Referring to table 1, the test results of the battery 1, the battery 2, the battery 3 and the comparative battery 1 are compared to show that the electrolyte using the silane phosphate compound as an additive can improve the capacity retention rate of the battery at 25 ℃ and 45 ℃, i.e., improve the cycle characteristics of the battery.
According to the lithium battery, the structure of the silane phosphate compound in the first additive is optimized, and the functional group with good film forming capability is introduced into the structure, so that the film forming capability can be improved while the impedance of the electrolyte is optimized, and the performance of the battery is improved.
In conclusion, upon reading the present detailed disclosure, those skilled in the art will appreciate that the foregoing detailed disclosure can be presented by way of example only, and not limitation. Those skilled in the art will appreciate that the present application is intended to cover various reasonable variations, adaptations, and modifications of the embodiments described herein, although not explicitly described herein. Such alterations, improvements, and modifications are intended to be suggested by this disclosure, and are within the spirit and scope of the exemplary embodiments of this disclosure.
It is to be understood that the term "and/or" as used herein includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be further understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, a first element in some embodiments may be termed a second element in other embodiments without departing from the teachings of the present invention. The same reference numerals or the same reference identifiers denote the same elements throughout the specification.