CN115832436A - Lithium secondary battery electrolyte with high and low temperature performance and lithium secondary battery - Google Patents
Lithium secondary battery electrolyte with high and low temperature performance and lithium secondary battery Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium secondary batteries, and discloses a lithium secondary battery electrolyte with high and low temperature performance and a lithium secondary battery. The electrolyte includes a nonaqueous solvent, a lithium salt, a triphenylphosphine alkenyl compound, and a compound having a carbonyl group. The electrolyte disclosed by the invention has the advantages that the triphenylphosphine alkenyl compound and the compound with carbonyl group act together, wherein the triphenylphosphine alkenyl compound can be reduced in preference to the solvent, and forms a thin and uniform SEI film on the surfaces of the anode and the cathode of the lithium secondary battery through synergistic action with the compound with carbonyl group, the SEI film is complexed with transition metal ions of the anode, the surface of the anode is passivated, metal dissolution is inhibited, the low-temperature rate discharge performance of the battery is improved, and the normal-temperature cycle life and the high-temperature cycle life are prolonged.
Description
Technical Field
The invention belongs to the technical field of lithium secondary batteries, and particularly relates to a lithium secondary battery electrolyte with high and low temperature performances and a lithium secondary battery.
Background
Along with the diversification of requirements on the performance of batteries in the fields of electric vehicles, electric tools, start-stop power supplies, emergency starting power supplies, small and popular products and the like, the performance requirements are different, and lithium ion batteries are gradually developed towards high power and high energy density. In order to meet the requirement of high-current charge and discharge of a high-power battery, high-concentration lithium salt is generally required to be added to improve the concentration of lithium ions, which inevitably results in that the viscosity of an electrolyte system is obviously increased, so that the wettability of the electrolyte is poor, the interfacial impedance is increased, the rate cycle deterioration is serious, especially the low-temperature rate discharge performance, the overall performance of the battery cannot meet the actual market requirement, and the popularization and development of electric vehicles in high-latitude areas are particularly not facilitated. Therefore, there is a need to develop a power type electrolyte that can satisfy both high and low temperature conditions.
KR101337608B1 discloses an electrolyte for a lithium secondary battery, which can form a protective film on the surface of an active material under high pressure by adding a triphenylphosphine alkenyl compound, thereby preventing a side reaction between the active material and the electrolyte and extending the charge/discharge life of the battery. The triphenylphosphine alkenyl compound is only shown to improve the high-temperature storage and cycle performance of a lithium cobaltate battery system, and the effect of the triphenylphosphine alkenyl compound on the aspect of improving the low-temperature rate discharge performance of a lithium secondary battery is not shown.
Patent CN111162316a discloses a nonaqueous electrolytic solution, which comprises lithium salt, organic solvent and functional additive, wherein the functional additive comprises triphenylphosphine derivative. Through the addition of the functional additive triphenylphosphine derivative, the dissolution of metal ions in the positive electrode material can be well inhibited, the positive electrode is protected, the thickness expansion of the lithium battery is effectively reduced, and the capacity retention rate of the secondary lithium battery is improved.
Patent CN110994029a discloses a sulfone-based high voltage electrolyte containing triphenylphosphine additives, which comprises: triphenylphosphine additives, sulfone-based solvents and lithium salts. In the charging and discharging process of the lithium battery containing the electrolyte, a low-impedance and stable protective film can be formed on the surfaces of the lithium-rich manganese-based positive electrode and the graphite negative electrode, the stability of the interface between the positive electrode and the negative electrode and the electrolyte is improved, the cycle stability of the lithium battery under the high-voltage condition is improved, and meanwhile, the compound containing the phosphorus-oxygen double bond can also improve the high-temperature safety performance of the battery.
The above patent art also does not disclose how to improve the effect in terms of low-temperature rate discharge performance of the lithium secondary battery. Therefore, the technical problems to be solved by the application are as follows: how to improve the low-temperature rate discharge performance of the battery while considering the high-temperature performance.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention mainly aims to provide the lithium secondary battery electrolyte with high and low temperature performance. The triphenylphosphine alkenyl compound in the electrolyte can be reduced in preference to the solvent, forms a thin and uniform SEI film on the surface of the negative electrode of the lithium secondary battery through the synergistic effect with the compound with carbonyl, can be complexed with the transition metal ions of the positive electrode, passivates the surface of the positive electrode, inhibits metal dissolution, improves the low-temperature rate discharge performance of ternary and lithium iron batteries, and has normal-temperature and high-temperature cycle life.
Another object of the present invention is to provide a lithium secondary battery comprising the above electrolyte.
It is still another object of the present invention to provide a method for improving high-temperature performance and low-temperature rate discharge performance of a lithium secondary battery using the above electrolyte.
The purpose of the invention is realized by the following technical scheme:
a lithium secondary battery electrolyte having a high and low temperature performance, the electrolyte comprising:
a non-aqueous solvent;
a lithium salt;
a triphenylphosphine alkenyl compound; and
a compound having a carbonyl group;
the triphenylphosphine alkenyl compound has a general structural formula shown as the following formula I:
wherein R is 1 And R 2 Each independently is H or any one group of C1-C12 alkyl, nitrile group, ester group, carbonyl and phenyl or a combined substituent containing at least two groups.
Further, the compound having a carbonyl group is at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethoxy ethylene carbonate, ethylene carbonate, diethyl pyrocarbonate, 4,4 '-bi-1,3-dioxolane-2,2' -dione, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, and 2-propynyl methylcarbonate.
Further preferably, the triphenylphosphine alkenyl compound comprises at least one of the following structural compounds:
the added triphenylphosphine alkenyl compound can be used as a witting reagent, and can react with active functional groups such as carbonyl and the like in a compound with carbonyl under the catalytic action of a byproduct of electrochemical reaction, namely alkyl lithium, to obtain a compound containing an unsaturated bond and a triphenyl oxyphosphorus compound. The unsaturated double bond compound can be further polymerized to form a flexible SEI film, which is beneficial to improving the structural damage of the electrode active material in the circulating process and improving the circulating stability; the triphenyl oxyphosphorus compounds can participate in film formation, and the introduced heteroatom and large conjugated system can optimize the composition of an interfacial film, improve the ionic conductivity of an SEI film, reduce the internal resistance and improve the power performance of a battery. Meanwhile, the quaternary phosphine alkenyl ions generated in the reaction process can be complexed with the transition metal ions dissolved out of the positive electrode to form stable metal salt, so that on one hand, the decomposition promoting effect of the dissolved out metal ions on the electrolyte can be relieved, on the other hand, the structural stability of the positive electrode can be improved, and the cycle performance of the battery can be improved. Thereby achieving improved properties which are different from or superior to other triphenylphosphine-based compounds (e.g. triphenylphosphine derivatives or triphenylphosphine-based additives as described in the background section).
Further, the addition amount of the triphenylphosphine alkenyl compound is 0.03-0.7% of the mass of the electrolyte; preferably 0.05 to 0.5 percent of the electrolyte mass. When the triphenylphosphine alkenyl compound and the compound having a carbonyl group are added simultaneously within the above range, a stable interfacial film can be formed on the positive and negative electrodes, and a corresponding effect can be produced. Because the addition amount is too small, the formed interface film is too thin and poor in stability, and the effect of protecting the positive electrode and the negative electrode cannot be achieved; however, when the content of the additive is too high, the interface film formed is too thick, which increases the overall resistance of the battery and affects the battery capacity.
Furthermore, the adding amount of the compound with the carbonyl group is 0.1-10% of the mass of the electrolyte.
Further, the nonaqueous solvent accounts for 50% to 92%, more preferably 52% to 90%, and still more preferably 65% to 85% of the total mass of the electrolyte.
Further preferably, the nonaqueous solvent is composed of a cyclic compound and a linear compound; the cyclic compound is selected from at least one of ethylene carbonate, propylene carbonate, gamma-butyrolactone, sulfolane, ethylene trifluoroethoxy carbonate, propylene fluoro carbonate, ethylene trifluoromethyl carbonate and ethylene trifluoroethyl carbonate; the linear compound is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 2,2-difluoroethyl acetate, trifluoroethyl acetate, difluoroethyl acetate, ethyl trifluoroacetate, methyl acetate, propylene glycol methyl ether acetate, 2-methoxy-1-propanol acetate, n-propyl acetate, tris (2-ethylhexyl) trimellitate.
The above description of the non-aqueous solvent does not represent that the above solvent system does not contain other types of solvents, and common solvents such as cyclic carboxylic acid esters, chain carboxylic acid esters, ether compounds and sulfone compounds, which are optional for the electrolyte, can be added;
the specific substance of the cyclic carboxylic ester can be selected from gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, epsilon-caprolactone and the like; it is possible to avoid a decrease in the electrical conductivity, suppress an increase in the negative electrode resistance, and easily achieve a good range of the large-current discharge characteristic of the nonaqueous electrolyte secondary battery.
The chain carboxylic acid ester is preferably a chain carboxylic acid ester having 3 to 7 carbon atoms. Specific examples thereof include: methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, isopropyl isobutyrate, and the like; the chain carboxylic acid ester can suppress increase of the negative electrode resistance and can bring the large current discharge characteristic and cycle characteristic of the nonaqueous electrolyte battery into a good range.
The ether compound is preferably a chain ether having 3 to 10 carbon atoms, and a cyclic ether having 3 to 6 carbon atoms, in which some of the hydrogens are optionally substituted with fluorine; examples of the chain ether having 3 to 10 carbon atoms include: diethyl ether, bis (2-fluoroethyl) ether, bis (2,2-difluoroethyl) ether, bis (2,2,2-trifluoroethyl) ether, ethyl (2-fluoroethyl) ether, ethyl (2,2,2-trifluoroethyl) ether, ethyl (1,1,2,2-tetrafluoroethyl) ether, (2-fluoroethyl) (2,2,2-trifluoroethyl) ether, (2-fluoroethyl) (1,1,2,2-tetrafluoroethyl) ether, (2,2,2-trifluoroethyl) (1,1,2,2-tetrafluoroethyl) ether, ethyl n-propyl ether, ethyl (3-fluoro-n-propyl) ether, ethyl (3,3,3-trifluoro-n-propyl) ether, ethyl (2,2,3,3-tetrafluoro-n-propyl) ether, ethyl (2,2,3,3,3-pentafluoro-n-propyl) ether 2-fluoroethyl-n-propyl ether, (2-fluoroethyl) (3-fluoro-n-propyl) ether, (2-fluoroethyl) (3,3,3-trifluoro-n-propyl) ether, (2-fluoroethyl) (2,2,3,3-tetrafluoro-n-propyl) ether, (2-fluoroethyl) (2,2,3,3,3-pentafluoro-n-propyl) ether, 2,2,2-trifluoroethyl-n-propyl ether, (2,2,2-trifluoroethyl) (3-fluoro-n-propyl) ether, (2,2,2-trifluoroethyl) (3,3,3-trifluoro-n-propyl) ether, (2,2,2-trifluoroethyl) (2,2,3,3-tetrafluoro-n-propyl) ether, (2,2,2-trifluoroethyl) (2,2,3,3,3-pentafluoro-n-propyl) ether, and mixtures thereof, 1,1,2,2 tetrafluoroethyl n-propyl ether, (1,1,2,2 tetrafluoroethyl) (3-fluoro n-propyl) ether, (1,1,2,2 tetrafluoroethyl) (3,3,3-trifluoro n-propyl) ether, (1,1,2,2 tetrafluoroethyl) (2,2,3,3-tetrafluoro n-propyl) ether, (1,1,2,2 tetrafluoroethyl) (2,2,3,3,3-pentafluoro n-propyl) ether, di-n-propyl ether, (n-propyl) (3-fluoro n-propyl) ether, (n-propyl) (3,3,3-trifluoro n-propyl) ether, (n-propyl) (2,2,3,3-tetrafluoro n-propyl) ether, (n-propyl) (2,2,3,3,3-pentafluoro n-propyl) ether, di (3-fluoro n-propyl) ether (3-fluoro-n-propyl) (3,3,3-trifluoro-n-propyl) ether, (3-fluoro-n-propyl) (2,2,3,3-tetrafluoro-n-propyl) ether, (3-fluoro-n-propyl) (2,2,3,3,3-pentafluoro-n-propyl) ether, bis (3,3,3-trifluoro-n-propyl) ether, (3,3,3-trifluoro-n-propyl) (2,2,3,3-tetrafluoro-n-propyl) ether, (3,3,3-trifluoro-n-propyl) (2,2,3,3,3-pentafluoro-n-propyl) ether, bis (2,2,3,3-tetrafluoro-propyl) ether, (2,2,3,3-tetrafluoro-n-propyl) (2,2,3,3,3-pentafluoro-n-propyl) ether, bis (2,2,3,3,3-pentafluoro-n-propyl) ether, bis (n-butyl ether, dimethoxymethane, methoxyethoxymethane, methoxy (2-fluoroethoxy) methane, methoxy (2,2,2-trifluoroethoxy) methane, methoxy (1,1,2,2-tetrafluoroethoxy) methane, diethoxymethane, ethoxy (2-fluoroethoxy) methane, ethoxy (2,2,2-trifluoroethoxy) methane, ethoxy (1,1,2,2-tetrafluoroethoxy) methane, bis (2-fluoroethoxy) methane, (2-fluoroethoxy) (2,2,2-trifluoroethoxy) methane, (2-fluoroethoxy) (1,1,2,2-tetrafluoroethoxy) methane, bis (2,2,2-trifluoroethoxy) methane, (2,2,2-trifluoroethoxy) (1,1,2,2-tetrafluoroethoxy) methane, bis (1,1,2,2-tetrafluoroethoxy) methane, dimethoxyethane, methoxyethoxyethane, methoxy (2-fluoroethoxy) ethane, methoxy (24-trifluoroethoxy) ethane, 3424-trifluoroethoxy) ethane, methoxy (3535 zxft 3272-tetrafluoroethoxy) ethane, bis (ethoxyethoxy) ethane, (3525-ethoxyfluoro-5384-tetrafluoroethoxy) ethane, bis (4925-fluoroethoxy) (3525-ethoxyethoxy) ethane, bis (3525-fluoroethoxy) (3525-ethoxyethoxy) ethane, bis (35fts) (3525-fluoroethoxy) ethane, bis (3523-fluoroethoxy) ethane, bis (ethoxyethoxy) ethane, bis (3-35fts, and the like, (2,2,2-trifluoroethoxy) (1,1,2,2-tetrafluoroethoxy) ethane, bis (1,1,2,2-tetrafluoroethoxy) ethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and the like; examples of the cyclic ether having 3 to 6 carbon atoms include: tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,4-dioxolane, and the like, and fluoro compounds thereof; when the negative electrode active material is a carbonaceous material in the presence of the ether compound as an auxiliary solvent, it is easy to avoid a problem that the ether compound is co-intercalated with lithium ions to cause a decrease in capacity.
The sulfone compound is selected from dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, tert-butyl methyl sulfone, mono-fluoromethyl sulfone, difluoromethyl sulfone, trifluoromethyl methyl sulfone, mono-fluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl mono-fluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl n-butyl sulfone, trifluoroethyl tert-butyl sulfone, trifluoromethyl n-butyl sulfone, trifluoromethyl tert-butyl sulfone, etc.; under the condition that the sulfone compound exists as an auxiliary solvent, the cycle performance and the cycle retention performance of the battery can be improved, the solution viscosity is reduced, and the electrochemical performance is improved.
Further, the lithium salt is preferably LiPF 6 、LiAsF 6 、LiClO 4 、LiBF 4 、LiB(C 2 O 4 ) 2 、LiBF 2 C 2 O 4 、LiTDI、LiN(SO 2 F) 2 、LiN(SO 2 CF 3 ) 2 、LiPO 2 F 2 、LiPF 2 (C 2 O 4 ) 2 、LiPF 4 C 2 O 4 And lithium perfluorobutylsulfonate.
The lithium salt in the nonaqueous electrolytic solution of the present invention is not particularly limited as long as it is a known lithium salt used for the purpose, and may be used arbitrarily, and specifically, the following lithium salts are exemplified:
LiPF 6 、LiBF 4 、LiClO 4 、LiAlF 4 、LiSbF 6 、LiTaF 6 、LiWF 7 inorganic lithium salts; liWOF 5 Lithium tungstate species;
HCO 2 Li、CH 3 CO 2 Li、CH 2 FCO 2 Li、CHF 2 CO 2 Li、CF 3 CO 2 Li、CF 3 CH 2 CO 2 Li、CF 3 CF 2 CO 2 Li、CF 3 CF 2 CF 2 CO 2 Li、CF 3 CF 2 CF 2 CF 2 CO 2 lithium carboxylates such as Li;
FSO 3 Li、CH 3 SO 3 Li、CH 2 FSO 3 Li、CHF 2 SO 3 Li、CF 3 SO 3 Li、CF 3 CF 2 SO 3 Li、CF 3 CF 2 CF 2 SO 3 Li、CF 3 CF 2 CF 2 CF 2 SO 3 lithium sulfonates such as Li;
LiN(FCO) 2 、LiN(FCO)(FSO 2 )、LiN(FSO 2 ) 2 、LiN(FSO 2 )(CF 3 SO 2 )、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2 cyclic 1,2-perfluoroethane disulfonimide lithium, cyclic 1,3-perfluoropropane disulfonimide lithium, liN (CF) 3 SO 2 )(C 4 F 9 SO 2 ) Lithium imide salts;
LiC(FSO 2 ) 3 、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 lithium methide salts;
lithium oxalato borate salts such as lithium difluorooxalato borate and lithium bis (oxalato) borate;
lithium oxalato phosphate salts such as lithium difluorobis (oxalato) phosphate and lithium tris (oxalato) phosphate;
and LiPF 4 (CF 3 ) 2 、LiPF 4 (C 2 F 5 ) 2 、LiPF 4 (CF 3 SO 2 ) 2 、LiPF 4 (C 2 F 5 SO 2 ) 2 、LiBF 3 CF 3 、LiBF 3 C 2 F 5 、LiBF 3 C 3 F 7 、LiBF 2 (CF 3 ) 2 、LiBF 2 (C 2 F 5 ) 2 、LiBF 2 (CF 3 SO 2 ) 2 、LiBF 2 (C 2 F 5 SO 2 ) 2 Fluorine-containing organic lithium salts; and so on.
The lithium salt may be used alone or in combination of two or more.
Further, the lithium salt accounts for 8-25% of the total mass of the electrolyte. Generally, the concentration of lithium salt suitable in the art is 0.5 to 3M; preferably, the concentration of the lithium salt is 0.8 to 2.5M; preferably, the concentration of the lithium salt is 1 to 2M; preferably, the concentration of the lithium salt is 1 to 1.5M. In practical applications, the amount of lithium salt may be higher, such as up to 35%, which is also a potential possibility.
Further, in the above electrolytic solution, an additive may be contained in addition to the above solvent, lithium salt, triphenylphosphine alkenyl compound and compound having a carbonyl group; the additive includes at least one of vinyl sulfate, propylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, tetraene silane, divinyltetramethyldisilazane, divinyltetramethyldisiloxane, triallylisocyanurate, hexamethylene dinitrate, phenanthroline, p-phenylene diisocyanate, 2,4-toluene diisocyanate, N-phenyl bis (trifluoromethanesulfonyl) imide, vinyl disulfate, phenyl methanesulfonate, bis (allyl sulfate), hydroquinone difluorosulfonate, triallyl phosphate, tripenylpropyl phosphate, 2,4-butane sultone, isocyanoethyl methacrylate, methylene methane disulfonate, tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphate, tris (vinyldimethylsilane) phosphate, dipropyl-2-alkynyl phosphate, ethyl dipropyl-2-alkynyl, 2-trimethoxy (2-allylphenoxy) silane, 1-tetramethylbenzenesulfonylimidazole, pentamethylphenylimidazole, 1-1H-trisfluoroethoxy-2-fluoro-propane sulfonate, trisfluoroethoxy-1H-fluoro-1-fluoro-propane disulfonate, trisulfenpyrronitrile, and 1-fluoro-2-fluoro-propane disulfonate.
The additive accounts for 0.1-10% of the total mass of the electrolyte.
Meanwhile, the invention also discloses a lithium secondary battery containing the electrolyte, and the lithium secondary battery comprises:
a positive electrode;
a negative electrode;
a separator disposed between the positive electrode and the negative electrode; and
the electrolyte for a lithium secondary battery as described above.
Further, the charge cutoff voltage of the lithium secondary battery is not less than 4.2V.
Further, the positive electrode includes, but is not limited to, li 1+a (Ni x Co y M 1-x-y )O 2 、Li(Ni p Mn q Co 2-p-q )O 4 And LiM h (PO 4 ) m One or more of the above; wherein a is more than or equal to 0 and less than or equal to 0.3,0 and less than or equal to 1,0 and less than or equal to 1,0 and more than x + y and less than or equal to 1; p is more than or equal to 0 and less than or equal to 2,0 and less than or equal to q is more than or equal to 2,0 and more than p + q and less than or equal to 2; h is more than 0 and less than 5,0 and less than 5m; m is Fe, ni, co, mn, al or V.
The negative electrode is preferably at least one of graphite, soft carbon, hard carbon, silicon-oxygen compound, and silicon-carbon composite. The negative electrode material may be selected from a variety of conventionally known materials capable of electrochemically intercalating and deintercalating active ions, which are known in the art and may be used as a negative electrode active material for an electrochemical device.
The separator is a separator known in the art that can be used for an electrochemical device and is stable to an electrolyte used, such as, but not limited to, resin, glass fiber, ceramic, etc. For example, the barrier membrane comprises at least one of polyolefin, aramid, polytetrafluoroethylene, polyethersulfone. Preferably, the polyolefin comprises at least one of polyethylene and polypropylene. Preferably, the polyolefin comprises polypropylene. Preferably, the separator is formed by laminating a plurality of layers of materials, for example, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in this order, or an inorganic material separator coated with the above organic material film, or the like.
Finally, the invention also provides a method for improving the high-temperature performance and the low-temperature rate discharge performance of the lithium secondary battery by using the electrolyte; the method comprises the following steps: the electrolyte as described in any of the above is added to a lithium secondary battery.
Compared with the prior art, the invention has the beneficial effects that:
(1) The electrolyte can improve the low-temperature rate discharge performance of the lithium ion battery and improve the normal-temperature and high-temperature rate cycle life through the combined action of the triphenylphosphine alkenyl compound additive and the compound with carbonyl.
(2) The triphenylphosphine alkenyl compound additive can be subjected to reduction reaction in preference to a solvent, and a compound with carbonyl can form a flexible, thin and uniform SEI film on the surface of the negative electrode of the lithium secondary battery through synergistic action, and simultaneously passivates the surface of the positive electrode, so that the lithium secondary battery has good low-temperature rate discharge performance and rate cycle life.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
The materials used in the following examples and comparative examples are summarized briefly: succinic Anhydride (SA), fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO) 2 F 2 ) Vinyl sulfate (DTD), 4,4 '-bi-1,3-dioxolane-2,2' -dione (bis EC), tris (dimethylvinylsilyl) phosphate (DMVSP), trifluoroethoxyvinyl carbonate (TFEEC), 2-methylmaleic anhydride (CA), ethylene carbonate (VC), bis-spiro propylene sulfate (TDS), ethylene carbonate (VEC), maleic Anhydride (MA), hexamethylene Diisocyanate (HDI), succinonitrile (SN), tris (trimethylsilyl) borate (TMSB).
Example 1
In this example, ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) were mixed in a glove box at a mass ratio of 3:7, and 85.5g of the mixed solution was taken and added with 12.5g of LiPF in sequence 6 1.5g of vinyl sulfate (DTD) and 0.5g of lithium difluorophosphate (LiPO) 2 F 2 ) 100g of a base electrolyte was prepared. Adding the above compound4 of triphenylphosphine alkenyl compound (0.2 g), succinic Anhydride (SA) (0.3 g) and fluoroethylene carbonate (FEC) (2.0 g) to obtain an electrolyte for a power type lithium secondary battery.
The obtained power type lithium secondary battery electrolyte and the lithium ion battery anode material LiNi 0.33 Co 0.33 Mn 0.33 O 2 And the artificial graphite negative electrode material and the polyethylene film-coated ceramic diaphragm are injected with liquid according to a conventional method and then assembled into the soft-package laminated lithium secondary battery.
Examples 2 to 13 and comparative examples 1 to 13
An electrolyte was prepared according to the composition in table 1 and a laminate lithium secondary battery was assembled by the method of example 1.
TABLE 1 electrolyte compositions of examples and comparative examples
The lithium secondary batteries obtained in the above examples 1 to 13 and comparative examples 1 to 13 were subjected to tests of normal temperature cycle, high temperature cycle and low temperature discharge performance, the test method being:
1. normal temperature cycle performance: the lithium secondary battery is placed at room temperature, is charged to 4.2V at a constant current and a constant voltage of 3C, is then discharged to 2.7V at a constant current of 3C, is cycled for 500 weeks, and the capacity retention rate of the lithium secondary battery is measured.
Capacity retention rate = (500 th discharge capacity/first discharge capacity) × 100%.
2. High temperature cycle performance: and (3) placing the lithium secondary battery in a thermostat with the temperature of 45 ℃, charging the lithium secondary battery to 4.2V by constant current and constant voltage of 3C, then discharging the lithium secondary battery to 2.7V by constant current of 3C, circulating for 500 weeks, and measuring the capacity retention rate of the lithium secondary battery.
Capacity retention rate = (500 th discharge capacity/first discharge capacity) × 100%.
3. Low-temperature storage performance: charging the lithium secondary battery at a constant current of 1C to a voltage of 4.2V at normal temperature, placing the battery in a low-temperature cabinet at the temperature of-20 ℃ for more than 4h, and discharging at 0.2C to 2.7V when the temperature of the battery is reduced to-20 ℃.
And after the discharge is finished, the battery is placed at normal temperature, after the temperature of the battery returns to the normal temperature, the lithium secondary battery is charged to the voltage of 4.2V by using a constant current of 1C, then the battery is placed in a low-temperature cabinet at the temperature of minus 20 ℃ for more than 4 hours, and after the temperature of the battery is reduced to minus 20 ℃, the battery is discharged to the voltage of 2.7V by using 0.5C.
And after the discharge is finished, the battery is placed at normal temperature, after the temperature of the battery returns to the normal temperature, the lithium secondary battery is charged to the voltage of 4.2V by using a 1C constant current, then the battery is placed in a low-temperature cabinet at the temperature of minus 20 ℃ for more than 4h, and after the temperature of the battery is reduced to minus 20 ℃, the battery is discharged to the voltage of 2.7V by using 1C.
The test results are shown in table 2 below:
TABLE 2 test results of cycle performance and Low-temperature Performance of lithium Secondary Battery
As can be seen from the results in Table 2, the lithium ion batteries of examples 1-13 have superior normal and high temperature rate cycle performance and low temperature discharge performance to those of comparative examples 1-13, which shows that the electrolyte additives of examples 1-13 can effectively improve the rate cycle performance and low temperature rate discharge performance of the lithium secondary batteries.
Specifically, the method comprises the following steps:
1. from examples 1 to 13 and comparative examples 1 to 4, it can be seen that: neither addition of the triphenylphosphine alkenyl compound additive nor the compound having a carbonyl group, or use of the triphenylphosphine alkenyl compound additive alone, or use of the compound having a carbonyl group alone, can achieve satisfactory electrochemical effects. The single use of the triphenylphosphine alkenyl compound additive can improve the low-temperature performance to a certain extent, but can affect the high-temperature performance; the use of the compound having a carbonyl group alone improves high-temperature performance but reduces low-temperature performance; the combination of the triphenylphosphine alkenyl compound and the compound with carbonyl can simultaneously improve high-temperature performance and low-temperature performance, the improvement effect of high-temperature cycle performance is more obvious than that of a single compound with carbonyl, and the improvement effect of low-temperature discharge performance is more obvious than that of a single triphenylphosphine alkenyl compound, so that the combination of the triphenylphosphine alkenyl compound and the compound with carbonyl achieves good synergistic effect.
2. From examples 1 to 13 and comparative examples 5 to 8, it can be seen that: when used in combination with a compound having a carbonyl group, a triphenylphosphine alkenyl compound having an excessively high or excessively low content does not achieve a satisfactory electrochemical effect. It can be seen from the results of comparing examples 1 to 4 with comparative examples 5 to 6 that when the content of triphenylphosphine alkenyl compound 4 was reduced to 0.01% or increased to 1.5%, both cycle performance and low-temperature discharge performance of the lithium secondary battery were significantly reduced. When the content of the triphenylphosphine alkenyl compound 4 is within the range of 0.05-0.7 percent, a satisfactory electrochemical effect can be achieved. It can be seen from the results of comparing examples 5 to 8 with comparative examples 7 to 8 that when the content of triphenylphosphine alkenyl compound 5 was reduced to 0.01% or increased to 1.5%, both cycle performance and low-temperature discharge performance of the lithium secondary battery were significantly reduced. When the content of the triphenylphosphine alkenyl compound 5 is within the range of 0.1-0.7%, a satisfactory electrochemical effect can be achieved.
3. From examples 1 to 13 and comparative examples 9 to 10, it can be seen that: the compound having a carbonyl group used in combination with the triphenylphosphine alkenyl compound has too high (20.3%) or too low (0.06%) of a content to achieve a satisfactory electrochemical effect, and the cycle performance and low-temperature discharge performance of the lithium secondary battery are both reduced to some extent. When the addition amount of the compound with carbonyl is 0.1-10% of the mass of the electrolyte, a satisfactory electrochemical effect can be achieved.
4. From examples 1 to 13 and comparative example 11, it can be seen that: the functional group linked to the triphenylphosphine alkenyl group is peculiar, and a non-limited structure cannot achieve a satisfactory electrochemical effect.
5. As can be seen from examples 1 to 13 and comparative examples 12 to 13, when the additives of comparative examples 12 and 13 are used in combination with the triphenylphosphine alkenyl compound, satisfactory electrochemical effects cannot be achieved.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A lithium secondary battery electrolyte compatible with high and low temperature performance, the electrolyte comprising:
a non-aqueous solvent;
a lithium salt;
a triphenylphosphine alkenyl compound; and
a compound having a carbonyl group;
the triphenylphosphine alkenyl compound has a structural general formula shown in the following formula I:
wherein R is 1 And R 2 Each independently is H or any one group of C1-C12 alkyl, nitrile group, ester group, carbonyl and phenyl or a combined substituent containing at least two groups.
2. The electrolyte solution for a lithium secondary battery compatible with high and low temperature performance according to claim 1, wherein the triphenylphosphine alkenyl compound comprises at least one of the following structural compounds:
3. the electrolyte for lithium secondary batteries compatible with high and low temperature performance according to claim 1 or 2, wherein the triphenylphosphine alkenyl compound is added in an amount of 0.03-0.7%, preferably 0.05-0.5% by mass of the electrolyte.
4. The electrolyte for lithium secondary batteries compatible with high and low temperature performance according to claim 1, wherein the compound having a carbonyl group is at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethoxy ethylene carbonate, ethylene carbonate, diethylpyrocarbonate, 4,4 '-bi-1,3-dioxolan-2,2' -dione, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, and 2-propynyl methylcarbonate.
5. The electrolyte solution for a lithium secondary battery having both high and low temperature performance according to claim 1 or 4, wherein the amount of the compound having a carbonyl group added is 0.1% to 10% by mass of the electrolyte solution.
6. The electrolyte for lithium secondary batteries compatible with high and low temperature performances according to claim 1, wherein the non-aqueous solvent accounts for 50-92%, preferably 52-90%, and more preferably 65-85% of the total mass of the electrolyte;
the non-aqueous solvent is composed of a cyclic compound and a linear compound;
the cyclic compound is selected from at least one of ethylene carbonate, propylene carbonate, gamma-butyrolactone, sulfolane, ethylene trifluoroethoxy carbonate, propylene fluoro carbonate, ethylene trifluoromethyl carbonate and ethylene trifluoroethyl carbonate;
the linear compound is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 2,2-difluoroethyl acetate, trifluoroethyl acetate, difluoroethyl acetate, ethyl trifluoroacetate, methyl acetate, propylene glycol methyl ether acetate, 2-methoxy-1-propanol acetate, n-propyl acetate, tris (2-ethylhexyl) trimellitate.
7. The electrolyte for a lithium secondary battery having both high and low temperature characteristics as claimed in claim 1, wherein the lithium salt is LiPF 6 、LiAsF 6 、LiClO 4 、LiBF 4 、LiB(C 2 O 4 ) 2 、LiBF 2 C 2 O 4 、LiTDI、LiN(SO 2 F) 2 、LiN(SO 2 CF 3 ) 2 、LiPO 2 F 2 、LiPF 2 (C 2 O 4 ) 2 、LiPF 4 C 2 O 4 And lithium perfluorobutylsulfonate;
the lithium salt accounts for 8-25% of the total mass of the electrolyte.
8. The electrolyte for a lithium secondary battery having both high and low temperature performance according to claim 1, further comprising an additive;
the additive comprises at least one of vinyl sulfate, propylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, tetraene silane, divinyltetramethyldisilazane, divinyltetramethyldisiloxane, triallyl isocyanurate, hexamethylene dinitrate, phenanthroline, p-phenylene diisocyanate, 2,4-toluene diisocyanate, N-phenyl bis (trifluoromethanesulfonyl) imide, vinyl disulfate, phenyl methanesulfonate, bis (allyl sulfate), hydroquinone difluorosulfonate, triallyl phosphate, tripenylpropyl phosphate, 2,4-butane sultone, isocyanoethyl methacrylate, methylene methane disulfonate, tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphate, tris (vinyldimethylsilane) phosphate, dipropyl-2-alkynyl phosphate, ethyl dipropyl-2-alkynyl, (2-allylphenoxy) trimethylsilyl phosphate, 1-tetramethylidenesulfonylimidazole, pentamethylphenylimidazole, 1H-ethoxyphenyl propane sulfonate, 1H-trisfluoroethoxyl-1-fluoro-2-fluoro-propane sulfonate, 1-fluoro-2-fluoro-propane sulfonate;
the additive accounts for 0.1-10% of the total mass of the electrolyte.
9. A lithium secondary battery, characterized in that the lithium secondary battery comprises:
a positive electrode;
a negative electrode;
a separator disposed between the positive electrode and the negative electrode; and
the electrolyte for a lithium secondary battery according to any one of claims 1 to 8.
10. The power lithium secondary battery according to claim 9, wherein the positive electrode is Li 1+a (Ni x Co y M 1-x-y )O 2 、Li(Ni p Mn q Co 2-p-q )O 4 And LiM h (PO 4 ) m One or more of the above;
wherein a is more than or equal to 0 and less than or equal to 0.3,0 and less than or equal to 1,0 and less than or equal to 1,0 and more than or equal to x + y and less than or equal to 1; p is more than or equal to 0 and less than or equal to 2,0 and less than or equal to q 2,0 and p + q is more than or equal to 2; h is more than 0 and less than 5,0 and less than 5m; m is Fe, ni, co, mn, al or V;
the negative electrode is at least one of graphite, soft carbon, hard carbon, silicon-oxygen compound and silicon-carbon compound;
the diaphragm is at least one of resin, glass fiber and ceramic membrane.
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| CN116742124A (en) * | 2023-06-14 | 2023-09-12 | 广州天赐高新材料股份有限公司 | Novel use of nitrogen-containing compound, electrolyte additive composition and battery electrolyte |
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| CN116742124A (en) * | 2023-06-14 | 2023-09-12 | 广州天赐高新材料股份有限公司 | Novel use of nitrogen-containing compound, electrolyte additive composition and battery electrolyte |
| CN116742124B (en) * | 2023-06-14 | 2024-02-09 | 广州天赐高新材料股份有限公司 | Novel use of nitrogen-containing compound, electrolyte additive composition and battery electrolyte |
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