CN111082139A - Non-aqueous electrolyte and lithium ion battery - Google Patents
Non-aqueous electrolyte and lithium ion battery Download PDFInfo
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Abstract
The invention provides a non-aqueous electrolyte and a lithium ion battery. The non-aqueous electrolyte comprises a solvent, an electrolyte lithium salt and a functional additive, wherein the functional additive comprises 4,4' -dipicolinate diphenyl sulfone, dipyridyl carbonate and lithium difluorophosphate. When the electrolyte is applied to a lithium ion battery with a high-nickel ternary material/graphite system, the impedance of the lithium ion battery can be obviously reduced, the power performance of the lithium ion battery is improved, gas generation in the circulation and storage processes of the lithium ion battery can be obviously inhibited, and the rate performance, the normal-temperature circulation performance, the high-temperature storage performance and the safety performance of the lithium ion battery are obviously improved.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a high-nickel ternary material/graphite system non-aqueous electrolyte for a lithium ion battery and the lithium ion battery.
Background
Lithium Ion Batteries (LIBs) have attracted attention from researchers due to their advantages of high energy density, high power density, long cycle life, and no memory effect. The improvement of the endurance mileage is a concern, and the solution is mainly to improve the energy density of the battery. However, the cathode material is a key factor of the LIB energy density. At present, in order to increase the energy density, Ni-rich oxide (NRO) has become the most promising material for high energy density LIB. However, according to extensive research on NRO, it was found that the surface chemistry is unstable, and under air atmosphere, bulk Li is easily formed on the particle surface2CO3And a passivation film composed of LiOH, which greatly affects the fabrication process of the electrode and the subsequent electrochemical properties. Secondly, the relatively poor structural stability of NRO, particularly NCM811, significantly reduces the cycle performance and high temperature performance of the materialEnergy and rate characteristics, resulting in a large negative impact on the cycle life of the battery. Therefore, it is a great challenge to improve the electrochemical performance of the high nickel ternary material battery.
Generally, a stable Solid Electrolyte Interface (SEI) film can provide better protection for a positive electrode and a negative electrode, so as to ensure that a lithium ion battery has a longer cycle life and a longer storage life, but at the same time, Interface impedance is increased, thereby reducing the power performance of the lithium ion battery. Therefore, how to improve the cycle life and storage life of the lithium ion battery without reducing the power performance of the lithium ion battery becomes one of the difficulties in the current research.
In addition, in order to improve the energy density of the lithium ion battery, the capacity of the anode material needs to be improved, the content of Ni in the ternary material is increased, so that the catalytic performance of the material is enhanced, and the electrolyte is easier to oxidize, which will cause the increase of side reactions and serious gas generation in the process of circulation and storage of the lithium ion battery, so that the cycle life and the storage life of the lithium ion battery are poor, and the safety problem of the lithium ion battery can be caused.
In the prior art, the problem that the protective layer is formed on the surface active point of the positive active material is solved by introducing the positive additive, so that the direct contact between the surface active point of the positive active material and the electrolyte is avoided, and the side reaction is inhibited. However, the use of the positive electrode additive also tends to cause the rate performance of the lithium ion battery to be reduced, thereby affecting the power characteristics of the battery, for example, the common positive electrode film-forming additives, namely Vinylene Carbonate (VC), 1, 3-propane sultone (1,3-PS) and 1, 3-propylene sultone (PES), all reduce the power characteristics of the battery. The existing film forming additive still has the problem of insufficient high-temperature cycle of the lithium ion battery, and the lithium ion battery is easy to swell in high-temperature storage.
Therefore, it is necessary to develop a nonaqueous electrolyte solution suitable for a lithium ion battery using a high nickel ternary material as a positive electrode and a graphite material as a negative electrode.
Disclosure of Invention
The object of the present invention is to solve at least one of the following problems:
(1) how to improve the cycle life and the storage life of the lithium ion battery and not reduce the power performance of the lithium ion battery;
(2) how to improve the energy density of the lithium ion battery and not reduce the safety problem of the lithium ion battery.
Aiming at the problems, the invention provides a non-aqueous electrolyte, and a new pinacol borate additive, a pyridine ester additive and a fluorophosphate additive are introduced, wherein the additives can enhance the compatibility of a positive electrode and a negative electrode with the electrolyte, improve the interfaces of the positive electrode and the negative electrode with the electrolyte, and endow the electrolyte with excellent comprehensive performance under high pressure, and the electrolyte is particularly suitable for a lithium ion battery taking a high-nickel ternary material as a positive electrode and a graphite material as a negative electrode.
Specifically, the invention adopts the following technical scheme:
in one aspect, the invention provides a nonaqueous electrolyte comprising a solvent, an electrolyte lithium salt, and a functional additive, wherein the functional additive comprises 4,4' -dipicolinate diphenylsulfone, bipyridyl carbonate, and lithium difluorophosphate.
The structure of the 4,4' -dipinacol boric acid ester diphenyl sulfone is as follows:
the structure of the dipyridyl carbonate is as follows:
preferably, the mass percentage of the 4,4' -dipinacol borate diphenyl sulfone in the electrolyte is 0.5-1.5% based on the sum of the mass of the solvent and the electrolyte lithium salt being 100%.
Preferably, the dipyridyl carbonate accounts for 0.5-1.5% by mass of the electrolyte, based on 100% by mass of the sum of the solvent and the electrolyte lithium salt.
Preferably, the mass percentage of the lithium difluorophosphate in the electrolyte is 0.5-1.5% by taking the sum of the mass of the solvent and the electrolyte lithium salt as 100%.
Preferably, the electrolyte further comprises other additives, and the other additives comprise at least one of vinylene carbonate, vinyl vinylene carbonate, fluoroethylene carbonate, 1, 3-propane sultone, 1, 3-propylene sultone and vinyl sulfate.
Preferably, the mass percentage of the other additives in the electrolyte is 1-2% based on 100% of the sum of the mass of the solvent and the electrolyte lithium salt.
Preferably, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.
Further preferably, the solvent is selected from the group consisting of a combination of at least two of Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate EMC), 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.
More preferably, the solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.
Particularly preferably, the solvent comprises 20-40% of ethylene carbonate, 20-50% of ethyl methyl carbonate and 10-40% of dimethyl carbonate by taking the total mass of the solvent as 100%.
Preferably, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorosulfonimide, lithium bis (oxalato) borate, lithium difluorooxalato borate.
Preferably, the concentration of the electrolyte lithium salt is 1.0-1.2 mol/L.
In another aspect, the present invention provides a lithium ion battery comprising the nonaqueous electrolytic solution as described above.
Preferably, the positive active material of the lithium ion battery is highNickel ternary materials, e.g. LiNi0.8Co0.1Mn0.1O2Or LiNi0.8Co0.15Al0.05O2And the like.
Preferably, the negative active material of the lithium ion battery is a graphite material, such as natural graphite or artificial graphite.
The electrolyte is used for the lithium ion battery taking the high-nickel ternary material as the anode and the graphite material as the cathode, can obviously reduce the impedance of the lithium ion battery, improve the power performance of the lithium ion battery, and can obviously inhibit gas generation in the circulation and storage processes of the lithium ion battery, thereby well improving the circulation performance, the high-temperature storage performance and the safety of the lithium ion battery.
In the present invention, when the nomenclature and the structure of the compound are not consistent, the structure of the compound is taken as a standard.
Compared with the prior art, the invention has the following beneficial effects:
(1) in the electrolyte provided by the invention, the HOMO energy level of the functional additive 4,4' -dipinacol borate diphenyl sulfone is higher, the oxidation potential is lower than that of the anode, a thin CEI film can be formed on the anode, C-S bonds connected with benzene rings are easy to break to participate in the formation of the CEI film, and the sulfur-containing component of the film is favorable for ion conductivity, so that the lithium ion intercalation and deintercalation capability is improved; on the other hand, 4' -dipinacol borate diphenyl sulfone can be combined with lithium salt anions in the electrolyte to inhibit solvent decomposition and improve interface impedance.
(2) In the electrolyte provided by the invention, the functional additive dipyridyl carbonate has two pyridine functional groups directly connected with carbonate functional groups, and the dipyridyl carbonate shows a strong complexing effect in the electrolyte through the common space effect and charge effect of the carbonate functional groups and the two adjacent pyridine functional groups, so that metal ions can be effectively complexed, and lithium salt in the electrolyte can be stabilized; on the other hand, dipyridyl carbonate also exhibits a good film-forming effect, and can form a good passivation film on the surface of the battery negative electrode.
(3) In the electrolyte provided by the invention, the functional additive LiDFP participates in the formation of SEI and CEI films, so that the content of LiF in an interface film is reduced, the interface impedance is further reduced, and the electrochemical performance of the electrolyte is improved.
(4) In the electrolyte provided by the invention, the components of the SEI film and the CEI film are effectively optimized under the synergistic action of the three functional additives, so that the film components have better lithium conductivity and thermal stability, the impedance of the lithium ion battery is obviously reduced, the power performance of the lithium ion battery is improved, and the gas generation in the circulation and storage processes of the lithium ion battery can be obviously inhibited, thereby well improving the circulation performance, high-temperature storage performance and safety performance of the lithium ion battery.
Detailed Description
The composition of the nonaqueous electrolytic solution provided by the present invention will now be described in detail.
According to some embodiments provided herein, a nonaqueous electrolyte includes a solvent, an electrolyte lithium salt, and a functional additive including 4,4' -dipicolinate diphenyl sulfone, bipyridyl carbonate, and lithium difluorophosphate.
In the invention, the 4,4' -dipicolinic acid ester diphenyl sulfone, the dipyridyl carbonate and the lithium difluorophosphate are added into the electrolyte, and the three cooperate with each other, so that the components of the SEI film and the CEI film are effectively optimized, the film components have good lithium conductivity and thermal stability, the battery impedance is reduced, the battery rate capability is improved, and the cycle performance and the high-temperature performance of the battery are improved.
In the invention, because the HOMO energy level of the 4,4' -dipinacol boric acid ester diphenyl sulfone is higher and has lower oxidation potential than that of the anode, a thin CEI film can be formed on the anode, the C-S bond connected with the benzene ring is easy to break to participate in the formation of the CEI film, the sulfur-containing component of the film is beneficial to ion conductivity, and the lithium ion intercalation and deintercalation capability is improved; on the other hand, 4' -dipinacol borate diphenyl sulfone can be combined with lithium salt anions in the electrolyte to inhibit solvent decomposition and improve interface impedance.
According to some embodiments of the present invention, the 4,4' -serendian is 100% of the total mass of the solvent and the electrolyte lithium saltThe mass percentage of the boron alkoxide diphenyl sulfone in the electrolyte is 0.5-1.5%, for example: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%. In the invention, if the addition amount of the 4,4' -dipinacol borate diphenyl sulfone is too small, an effective CEI film cannot be formed on the surface of the high-nickel positive electrode, the battery impedance cannot be effectively reduced, and the cycle performance of the battery is reduced; too much addition will lose more active Li+The formation of the CEI film, in addition, the film is thicker and the resistance is large, which leads to the reduction of the cycle performance of the battery.
In the invention, the functional additive of the carbonic acid dipyridyl ester has two pyridine functional groups directly connected with the carbonic acid ester functional group, and the carbonic acid dipyridyl ester shows stronger complexing effect in the electrolyte through the common space effect and charge effect of the carbonic acid ester functional group and the two adjacent pyridine functional groups, can effectively complex metal ions and can stabilize lithium salt in the electrolyte; on the other hand, the dipyridyl carbonate also shows good film forming effect, and can form a good passivation film on the surface of the battery negative electrode to protect the negative electrode.
According to some embodiments of the present invention, the dipyridyl carbonate is present in the electrolyte in an amount of 0.5 to 1.5% by mass, based on 100% by mass of the sum of the solvent and the electrolyte lithium salt, for example: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%. In the invention, if the addition amount of the dipyridyl carbonate is too small, an effective SEI film cannot be formed on the surface of the graphite cathode, so that the active material is exposed in the electrolyte, and the redox reaction is carried out on the active material and the electrolyte, thereby reducing the cycle performance of the battery; too much addition will consume more active Li+The SEI film is formed so that the loss of battery capacity is large.
In the invention, the functional additive lithium difluorophosphate (LiDFP) can participate in the formation of SEI and CEI films at the same time, so that the content of LiF in the interfacial film is reduced, the interfacial resistance is further reduced, and the electrochemical performance of the electrolyte is improved.
According to some embodiments of the present invention, the lithium difluorophosphate accounts for 0.5 to 1.5% by mass of the electrolyte solution, based on 100% by mass of the sum of the mass of the solvent and the electrolyte lithium salt, for example: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%. The addition of a proper amount of lithium difluorophosphate can effectively reduce the internal resistance of the battery and improve the cycle performance of the battery, and if the addition amount of the lithium difluorophosphate is insufficient, a complete SEI (solid electrolyte interphase) film and a complete CEI (CEI) film cannot be formed; since the amount of lithium difluorophosphate dissolved in the electrolyte is limited, if the amount of lithium difluorophosphate is too large, the lithium difluorophosphate cannot be completely dissolved and functions, and the cost of the electrolyte is increased.
According to the invention, 4' -dipicolinic acid ester diphenyl sulfone, dipyridyl carbonate and lithium difluorophosphate are specially selected to be matched, so that the impedance of the lithium ion battery can be obviously reduced, the power performance of the lithium ion battery is improved, and gas generation in the cycle and storage processes of the lithium ion battery can be obviously inhibited, thereby the cycle performance, the high-temperature storage performance and the safety of the lithium ion battery are well improved. If the 4,4' -dipinacol borate diphenyl sulfone is replaced by other pinacolol borate compounds with the structure close to that of the pinacolol borate compounds, the synergistic effect can not be generated to improve the high-temperature performance of the lithium battery, particularly the cycle performance of the lithium battery taking a high-nickel ternary material as a positive electrode and a graphite material as a negative electrode and reduce gas generation.
In addition, other additives can be added into the electrolyte according to actual needs.
Preferably, the other additive includes at least one of Vinylene Carbonate (VC), vinyl vinylene carbonate (VEC), fluoroethylene carbonate (FEC), 1, 3-propane sultone (1,3-PS), 1, 3-propene sultone (PES), and vinyl sulfate (DTD).
In some embodiments, the other additives include one or both of Vinylene Carbonate (VC), vinyl vinylene carbonate (VEC), fluoroethylene carbonate (FEC), 1, 3-propane sultone (1,3-PS), 1, 3-propene sultone (PES), and vinyl sulfate (DTD).
In addition to the other additives listed above, other additives commonly used in the art to achieve the same or equivalent technical effects may also be used in the present invention.
According to some embodiments of the present invention, the mass percentage of the other additives in the electrolyte is 1 to 2% based on 100% of the total mass of the solvent and the electrolyte lithium salt, for example: 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%.
In the invention, the mass fraction of the solvent is 80-90% based on 100% of the sum of the mass of the solvent and the electrolyte lithium salt.
The specific type of the solvent can be selected according to actual requirements. In particular, nonaqueous organic solvents are selected. The non-aqueous organic solvent may include a carbonate (e.g., cyclic carbonate or chain carbonate), a carboxylate (e.g., cyclic carboxylate or chain carboxylate), a halogenated carbonate, and the like.
Specifically, the solvent is selected from at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate EMC), 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.
Preferably, the solvent is selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate EMC), 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and a combination of at least two of ethyl butyrate.
More preferably, the solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.
According to some embodiments of the invention, the solvent has a composition, based on 100% of the total mass of the solvent: 20-40% (e.g., 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%) ethylene carbonate, 20-50% (e.g., 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, or 50%) ethyl methyl carbonate, and 10-40% (e.g., 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%) dimethyl carbonate.
According to some embodiments of the invention, the electrolyte lithium salt may be selected from lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Inorganic lithium salt, LiPF6-n(CF3)n(0<n<6 integer), etc., lithium salts of perfluoro-substituted complex phosphates, lithium salts of boric acids such as lithium tris-catechol phosphates, lithium bis (oxalato) borate (LiBOB), lithium bis (oxalato) borate (LiDFOB), etc., and LiN [ (FSO)2C6F4)(CF3SO2)]Lithium trifluoromethanesulfonate (LiSO)3CF3) Lithium salts of sulfimide such as lithium bistrifluoromethylsulfimide (LiTFSI), and LiCH (SO)2CF3)2The polyfluoroalkyl-based lithium salt such as (LiTFSM) may be used alone or in combination of two or more, and is not limited to the above-mentioned lithium salts, and other lithium salts which are generally used in the art and can achieve similar effects may be used in the present invention.
According to some embodiments of the invention, the electrolyte lithium salt is selected from lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) And lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (oxalato) borate (LiBOB), and lithium difluoro (oxalato) borate (LiODFB).
Preferably, the concentration of the electrolyte lithium salt in the electrolyte is 1.0-1.2 mol/L, such as 1.0mol/L, 1.02mol/L, 1.05mol/L, 1.08mol/L, 1.1mol/L, 1.12mol/L, 1.14mol/L, 1.15mol/L, 1.18mol/L or 1.2 mol/L.
Specifically, the concentration of the electrolyte lithium salt refers to the concentration of lithium ions in the solvent.
According to some embodiments of the invention, the method of preparing a lithium ion battery electrolyte as described above, comprises the steps of:
s1: adding electrolyte lithium salt into a solvent, and stirring to completely dissolve the lithium salt to obtain a lithium salt solution;
s2: and adding a functional additive and optionally other additives into the lithium salt solution, and uniformly mixing to obtain the lithium ion battery electrolyte.
Preferably, the solvent is purified. The purification refers to the operations of impurity removal and water removal of the solvent, and preferably the purification is carried out by a molecular sieve and activated carbon. The molecular sieve can adopt
The model is,
Type or
And (4) molding.
According to some embodiments of the invention, the temperature at which the electrolytic lithium salt is dissolved in the organic solvent is 10 to 20 ℃.
The selection and the dosage of the electrolyte lithium salt, the solvent, the functional additive and other additives are the same as those of the lithium ion battery electrolyte.
In another aspect, the present invention provides a lithium ion battery comprising the nonaqueous electrolytic solution as described above.
The cathode comprises a cathode current collector and a cathode diaphragm on the surface of the cathode current collector, the cathode diaphragm comprises a cathode active substance, a conductive agent and a binder, and the cathode diaphragm comprises a cathode active substance, a conductive agent and a binder.
Preferably, the positive active material of the lithium ion battery is a high nickel ternary material, such as: LiNi0.8Co0.1Mn0.1O2Or LiNi0.8Co0.15Al0.05O2。
Preferably, the negative active material of the lithium ion battery is a graphite material, such as natural graphite or artificial graphite.
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The lithium ion batteries of comparative examples 1 to 6 and examples 1 to 6 were each prepared as follows.
(1) Preparing an electrolyte:
in a glove box with less than 10ppm moisture, the organic solvent is mixed as Ethylene Carbonate (EC): ethyl Methyl Carbonate (EMC): uniformly mixing dimethyl carbonate (DEC) in a mass ratio of 1:1:1, drying, removing water and impurities, adding electrolyte lithium salt LiPF6Preparing a 1mol/L solution, fully stirring and uniformly mixing, and adding a functional additive and other additives as shown in table 1, wherein the content of the functional additive and the other additives is the mass percentage content of the functional additive and the other additives in the electrolyte respectively, wherein the mass sum of the solvent and the electrolyte lithium salt is 100%.
(2) Preparing a positive plate:
the positive active material LiNi ternary material0.8Co0.1Mn0.1O2Adding a solvent N-methyl pyrrolidone into acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to a mass ratio of 95:3:2, and stirring the mixture under the action of a vacuum stirrer until the system is stable and uniform to obtain anode slurry; and coating the slurry on an Al foil of the positive current collector, and drying, cold pressing, slitting and flaking to obtain the positive plate.
(3) Preparing a negative plate:
stirring a negative active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR) and a thickening agent sodium carboxymethyl cellulose (CMC) in a deionized water solvent system according to a mass ratio of 96:2:1.2:0.8 under the action of a vacuum stirrer until the system is stable and uniform to obtain a negative slurry, coating the negative slurry on a negative current collector Cu foil, and drying, cold pressing, slitting and tabletting to obtain a negative plate.
(4) Preparing a lithium ion battery:
and winding the positive plate, the negative plate and the diaphragm to obtain a battery core, putting the battery core into the punched aluminum-plastic film, injecting electrolyte, sequentially sealing, standing, carrying out hot cold pressing, forming, exhausting, testing capacity and other processes to obtain the lithium ion battery.
Performance testing
Evaluation of cycle performance at normal temperature: and at 25 ℃, the formed lithium ion battery is subjected to constant current charging to 4.2V at a rate of 1C, the cutoff current is 0.05C, and then the lithium ion battery is subjected to constant current discharging to 2.75V at the rate of 1C, wherein the constant current charging is the first cycle, and the obtained discharge capacity is the first discharge capacity. After N cycles of charge/discharge, the capacity retention rate after the Nth cycle was calculated to evaluate the normal temperature cycle performance.
The calculation formula of the capacity retention rate at 25 ℃ for 1C circulation N times is as follows:
the nth cycle capacity retention (%) was (nth cycle discharge capacity/first cycle discharge capacity) × 100%.
Evaluation of high-temperature cycle performance: the test temperature is 45 ℃, and the cycle performance of the rest processes is evaluated at the same normal temperature.
The calculation formula of the capacity retention rate at 45 ℃ for 1C circulation N times is as follows:
the nth cycle capacity retention (%) was (nth cycle discharge capacity/first cycle discharge capacity) × 100%.
60 ℃ high-temperature storage performance test: the formed battery is charged to 4.2V at constant current and constant voltage of 1C at normal temperature, the cut-off current is 0.01C, then the 1C constant current is used for discharging to 2.75V, the initial discharge capacity of the battery is measured, then the 1C constant current and constant voltage are used for charging to 4.2V, the cut-off current is 0.01C, the initial thickness of the battery is measured, then the battery is stored for N days at the temperature of 60 ℃, the thickness of the battery is measured, then the 1C constant current is used for discharging to 2.75V, the retention capacity of the battery is measured, then the 1C constant current and constant voltage are used for charging to 4.2V, the cut-off current is 0.01C, then the 1C constant current is used for discharging to 2.75V. The calculation formulas of the capacity retention rate and the capacity recovery rate are as follows:
battery capacity retention (%) — retention capacity/initial capacity × 100%;
battery capacity recovery (%) — recovery capacity/initial capacity × 100%;
the battery thickness swelling ratio (%) (thickness after N days-initial thickness)/initial thickness × 100%.
The results of the above performance tests are detailed in table 1.
In table 1:
a is 4,4' -dipinacol boric acid ester diphenyl sulfone with the structure of
B is dipyridyl carbonate with the structure
C is 2-fluoropyridine-4-boric acid pinacol ester with the structure of
TABLE 1 electrolyte additive composition and assembled lithium ion battery Performance
It can be seen from the test results of examples 1 to 6 and comparative examples 1 to 5 in table 1 that the combined functional additive 4,4' -dipicolinic acid ester diphenyl sulfone provided by the invention, bipyridyl carbonate and lithium difluorophosphate are added to the non-aqueous electrolyte, and the three can be matched to act on an electrode interface of a lithium ion battery, so that the interface impedance of a positive electrode CEI film and a negative electrode SEI film of the lithium ion battery is remarkably reduced, the power performance of the lithium ion battery is improved, the gas generation in the cycle and storage processes of the high-nickel lithium ion battery can be remarkably improved, and the cycle performance, the high-temperature storage performance and the safety performance of the high-nickel lithium ion battery are well improved.
From the test results of comparative example 6, it can be seen that the use of other pinacol borate additive C in combination with dipyridyl carbonate and lithium difluorophosphate also improved the battery performance to some extent, but the effect was inferior compared to example 1.
The data are combined to show that when the electrolyte provided by the application is applied to a lithium ion battery, particularly a lithium ion battery of a high-nickel ternary material/graphite system, the high-pressure resistance of the lithium ion battery is improved, and the rate capability, normal-temperature cycle, high-temperature cycle and high-temperature storage performance of the lithium ion battery are also obviously improved.
The present invention is described in terms of the nonaqueous battery electrolyte and the lithium ion battery according to the present invention by the above examples, but the present invention is not limited to the above examples, that is, the present invention is not meant to be implemented by relying on the above examples. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (12)
1. A non-aqueous electrolyte, characterized in that the electrolyte comprises a solvent, an electrolyte lithium salt and a functional additive, wherein the functional additive comprises 4,4' -dipicolinate diphenyl sulfone, bipyridyl carbonate and lithium difluorophosphate.
2. The nonaqueous electrolytic solution of claim 1, wherein the 4,4' -dipinacol borate diphenyl sulfone is contained in the electrolytic solution in an amount of 0.5 to 1.5% by mass based on 100% by mass of the sum of the solvent and the electrolyte lithium salt.
3. The nonaqueous electrolytic solution of claim 1, wherein the dipyridyl carbonate is contained in the electrolytic solution in an amount of 0.5 to 1.5% by mass based on 100% by mass of the sum of the solvent and the electrolyte lithium salt.
4. The nonaqueous electrolytic solution of claim 1, wherein the lithium difluorophosphate is contained in the electrolytic solution in an amount of 0.5 to 1.5% by mass based on 100% by mass of the sum of the solvent and the electrolyte lithium salt.
5. The nonaqueous electrolytic solution of claim 1, wherein the electrolytic solution further comprises other additives, and the other additives comprise at least one of vinylene carbonate, vinyl vinylene carbonate, fluoroethylene carbonate, 1, 3-propane sultone, 1, 3-propene sultone, and vinyl sulfate.
6. The nonaqueous electrolytic solution of claim 5, wherein the other additive is contained in the electrolytic solution in an amount of 1 to 2% by mass based on 100% by mass of the sum of the solvent and the electrolyte lithium salt.
7. The nonaqueous electrolytic solution of any one of claims 1 to 6, wherein the solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.
8. The nonaqueous electrolytic solution of claim 7, wherein the solvent comprises 20 to 40% of ethylene carbonate, 20 to 50% of ethyl methyl carbonate, and 10 to 40% of dimethyl carbonate, based on 100% by mass of the total solvent.
9. The nonaqueous electrolytic solution of any one of claims 1 to 6, wherein the electrolyte lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorosulfonimide, lithium bis (oxalato) borate and lithium difluorooxalato borate.
10. The nonaqueous electrolytic solution of claim 9, wherein a concentration of the electrolyte lithium salt is 1.0 to 1.2 mol/L.
11. A lithium ion battery comprising the nonaqueous electrolytic solution according to any one of claims 1 to 10.
12. Lithium ion battery according to claim 11, characterized in that the positive active substance of the lithium ion battery is a high nickel ternary material, preferably LiNi0.8Co0.1Mn0.1O2Or LiNi0.8Co0.15Al0.05O2(ii) a Optionally, the negative active material of the lithium ion battery is a graphite material, preferably natural graphite or artificial graphite.
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