CN115714204A - Electrolyte and lithium ion battery - Google Patents
Electrolyte and lithium ion battery Download PDFInfo
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- CN115714204A CN115714204A CN202211486892.1A CN202211486892A CN115714204A CN 115714204 A CN115714204 A CN 115714204A CN 202211486892 A CN202211486892 A CN 202211486892A CN 115714204 A CN115714204 A CN 115714204A
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Abstract
The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte which comprises lithium salt, a nonaqueous organic solvent and an additive; the additives include a first additive for suppressing gas evolution and a second additive containing boron as shown in the following formula 1;
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte and a lithium ion battery.
Background
CNCN111416153A discloses a high voltage lithium ion battery and electrolyte additive thereof, the high voltage lithium ion Chi Guiqing electrolyte additive provided by the invention is a silicon cyano compound, silicon element is used as a stable group, and through anchoring action, the complete oxidation of a cyano functional group and the cross reduction reaction with a negative electrode are inhibited under high voltage, so that the battery deterioration is avoided, and in addition, the silicon element can also increase the wettability of the electrolyte. The cyano functional group in the silicon cyano compound can eliminate free hydrogen in the electrolyte, reduce water content in the electrolyte, eliminate HF and reduce LiPF 6 The hydrolysis and the destruction of the positive electrode material by HF suppress side reactions between the interface of the positive electrode material and the electrolyte at a high voltage. In addition, the silicon cyano functional group can also form an organic and inorganic interface film containing N at the interface of the anode and the cathode, and the interface film is effectively stabilized through the fixation of silicon elements, so that the electrochemical performance of the high-voltage lithium ion battery is further improved.
In comparative example 4 of the patent, cyclopentyl isocyanate was used instead of the silicon cyano compound used therein, and it was found that cyclopentyl isocyanate had performance inferior to that of the silicon cyano compound; the 100-week cycle retention rate is 75%;
the main purpose of this scheme is: how to realize the effective utilization of cyclopentyl isocyanate in electrolyte and improve the high-temperature performance of the electrolyte.
Disclosure of Invention
The invention aims to provide an electrolyte, which is compounded by a first additive containing isocyanate groups and saturated or unsaturated naphthenic groups and a second additive containing boron; the first additive has the effect of inhibiting gas generation, but has no obvious advantages in the aspects of high-temperature electrochemical performance and normal-temperature electrochemical performance, and the high-temperature electrochemical performance of the second additive can be enhanced by compounding with the boron-containing second additive.
Meanwhile, the invention also discloses a lithium ion battery.
The technical scheme of the invention is as follows:
an electrolyte comprising a lithium salt, a non-aqueous organic solvent, an additive; the additives include a first additive for suppressing gas evolution and a second additive containing boron as shown in the following formula 1;
formula 1
R1-R4 are each independently alkyl, fluoroalkyl; r1 and R2, R3 and R4 are independent or connected to form a ring;
the first additive contains an isocyanate group, a saturated or unsaturated cycloalkyl group;
the weight ratio of the first additive to the second additive is 0.1-5:0.1 to 5;
preferably, the weight ratio of the first additive to the second additive is 1-4:1-4;
more preferably, the weight ratio of the first additive to the second additive is 1 to 3:1-3.
Preferably, the isocyanate group and the saturated or unsaturated cycloalkyl group in the first additive can be directly connected, and an alkyl group can be added between the isocyanate group and the saturated or unsaturated cycloalkyl group; the alkyl group is preferably a C1-C3 alkyl group; the saturated naphthenic base is cyclopentane and cyclohexane; the unsaturated cycloalkyl group is typically a benzene ring;
preferably, R1-R4 are each independently methane, ethane, monofluoromethyl, difluoromethyl, perfluoromethyl, monofluoroethyl or difluoroethyl;
R1-R4 can also be connected to form a ring; specifically, R1, R2, two oxygen atoms, and one boron atom may form a five-membered ring or a six-membered ring;
the formed five-membered ring or six-membered ring can be connected with a substituent group; the substituent group can be C1-C3 alkyl, C1-C3 fluoroalkyl or F; optional substituents are methyl, ethyl, propyl, perfluoromethyl, perfluoroethyl, monofluoromethyl, difluoromethyl, monofluoroethyl, difluoroethyl or F. The number of substituents on a single five-or six-membered ring may be 1 or 2.
Preferably, the first additive is cyclopentyl isocyanate or phenyl isocyanate.
Preferably, R1-R4 are each independently methyl, ethyl, perfluoromethyl;
preferably, the second additive is one of the following compounds:
tetramethoxydiborane, tetraethoxydiborane, tetraperfluoromethoxydiborane, 2- (1,3,2-dioxaborolan-2 yl) 1,3,2-dioxaborolan, difluoro-2- (1,3,2-dioxaborolan-2 yl) 1,3,2-dioxaborolan or neopentyl glycol diborate.
Preferably, the first additive is 0.1 to 5wt% of the total weight of the electrolyte; the second additive is 0.1-5wt% of the total weight of the electrolyte.
Preferably, the first additive is 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 5wt% of the total weight of the hydrolysate;
preferably, it is used in an amount of 0.2wt% to 4wt%;
more preferably, it is used in an amount of 0.5wt% to 3wt%.
The second additive is 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 5wt% of the total weight of the electrolyte;
preferably, it is used in an amount of 0.2wt% to 4wt%;
more preferably, it is used in an amount of 0.5wt% to 3wt%.
In the electrolyte, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium difluorophosphate, lithium difluoro (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium difluoro (oxalato) phosphate and lithium bis (fluorosulfonyl) imide, and the concentration of the lithium salt is 0.5-2M. In general, the concentration of the lithium salt is more commonly 1-1.5M; but higher or lower lithium salt concentrations are also acceptable.
In the electrolyte, the non-aqueous organic solvent is a cyclic organic solvent and/or a chain organic solvent;
the cyclic organic solvent is one or a combination of more of Propylene Carbonate (PC), ethylene Carbonate (EC) and Butylene Carbonate (BC);
the chain-like organic solvent is one or a combination of more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl Propyl Carbonate (MPC), methyl Formate (MF), ethyl Formate (EF), methyl Acetate (MA) and Ethyl Acetate (EA).
As a preferred embodiment of the invention, the invention can also add additional additives as described below, the amount of the additional additives generally not exceeding 10wt% relative to the weight of the electrolyte; preferably 0.01 to 5wt%; more preferably 0.1 to 3wt%; more preferably 0.2 to 2wt%, more preferably 0.3 to 1wt%;
the additional additives may optionally be of the following specific formula:
in order to further improve the electrochemical characteristics in a wide temperature range, it is preferable to further add another additive to the nonaqueous electrolytic solution.
Specific examples of the other additives include the following compounds (a) to (j).
(a) Nitrile
One or more nitriles selected from acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile and sebaconitrile.
Among them, one or two or more selected from succinonitrile, glutaronitrile, adiponitrile and pimelonitrile are more preferable.
(b) Aromatic compound
Aromatic compounds such as cyclohexylbenzene, fluorocyclohexylbenzene compounds (aromatic compounds having a branched alkyl group such as 1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), t-butylbenzene, t-pentylbenzene, 1-fluoro-4-t-butylbenzene, biphenyl, terphenyl (ortho, meta, para), diphenyl ether, fluorobenzene, difluorobenzene (ortho, meta, para), anisole, 2,4-difluoroanisole, partial hydrides of terphenyl (1,2-dicyclohexylbenzene, 2-phenyldicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl).
(c) Isocyanate compounds of other acyclic substituents
One or more isocyanate compounds selected from the group consisting of methyl isocyanate, ethyl isocyanate, butyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate.
(d) Compound containing triple bond
One or more triple bond-containing compounds selected from the group consisting of 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2- (methanesulfonyloxy) propionate, bis (2-propynyl) oxalate, 2-propynyl methyl oxalate, ethyl 2-propynyl oxalate, bis (2-propynyl glutarate), 2-butynyl-1,4-diyldimethanesulfonate, 2-butynyl-1,4-diyldiformate, and 3532 zxf 3532-hexadiynyl-1,6-diyldimethanesulfonate.
(e) Compounds containing S = O group
One or more compounds selected from 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxido-1,2-oxathiolan-4-ylacetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, sultones such as ethylene sulfite, hexahydrobenzo [1,3,2] dioxathiolane-2-oxide (also known as 1,2-cyclohexanediol cyclic sulfite), 5-vinyl-hexahydro-3272 zxft 72-benzodioxothiol-2-oxide, cyclic sulfite such as butane-24 zxft 3424-diyl dimethylsulfonate, 3535-butanediothion 353535-dimethylsulfonato ether, divinyl ether (e.g., ethylene-sulfone, divinyl-containing ether, divinyl ether, etc.
As the cyclic S = O group-containing compound, one or more selected from 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propene sultone, 2,2-dioxido-1,2-oxathiolan-4-ylacetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, methylene methane disulfonate, ethylene sulfite, and 4- (methylsulfonylmethyl) -1,3,2-dioxacyclopentane 2-oxide can be suitably cited.
Further, as the linear S = O group-containing compound, one or two or more selected from butane-2,3-diyldimethanesulfonate, butane-1,4-diyldimethanesulfonate, dimethylmethane disulfonate, pentafluorophenyl methanesulfonate, divinylsulfone, and bis (2-vinylsulfonylethyl) ether can be preferably cited.
Among the above cyclic or chain compounds containing an S = O group, one or two or more selected from 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 2,2-dioxido-1,2-oxathiolane-4-yl acetate, 5,5-dimethyl-1,2-oxathiolane-4-one 2,2-dioxide, butane-2,3-diyl disulfonate, pentafluorophenyl methanesulfonate, and divinyl sulfone are more preferable.
(f) Cyclic acetal compound
1,3-dioxolane, 1,3-dioxane, 1,3,5-trioxane and other cyclic acetal compounds. Among them, 1,3-dioxolane and 1,3-dioxane are preferred, and 1,3-dioxane is more preferred.
(g) Phosphorus-containing compound
<xnotran> , , , (5363 zxft 5363- ) , (3242 zxft 3242- ) , (4736 zxft 4736- ) , (8978 zxft 8978- ) 6253 zxft 6253- , (3232 zxft 3232- ) 3238 zxft 3238- , (3262 zxft 3262- ) 3234 zxft 3234- , (3236 zxft 3236- ) 5262 zxft 5262- , (3763 zxft 3763- ) (5754 zxft 5754- ) , (3252 zxft 3252- -2- ) , , , , , , ,2- ( ) ,2- ( ) ,2- ( ) ,2- ( ) ,2- ( ) 2- ,2- ( ) 2- ,2- ( ) ,2- ( ) ,2- ( ) , </xnotran> 2- (diethoxyphosphoryl) acetic acid ethyl ester, 2-propynyl 2- (dimethoxy phosphoryl) acetic acid ester, 2-propynyl 2- (diethoxyphosphoryl) acetic acid ester, methyl pyrophosphate and ethyl pyrophosphate.
Among them, tris (2,2,2-trifluoroethyl) phosphate, tris (1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, methyl 2- (dimethylphosphoryl) acetate, ethyl 2- (dimethylphosphoryl) acetate, methyl 2- (diethylphosphoryl) acetate, ethyl 2- (diethylphosphoryl) acetate, 2-propynyl 2- (dimethylphosphoryl) acetate, 2-propynyl 2- (diethylphosphoryl) acetate, methyl 2- (dimethoxyphosphoryl) acetate, ethyl 2- (dimethoxyphosphoryl) acetate, methyl 2- (diethoxyphosphoryl) acetate, ethyl 2- (diethoxyphosphoryl) acetate, 2-propynyl 2- (dimethoxyphosphoryl) acetate, or 2-propynyl 2- (diethoxyphosphoryl) acetate are preferable, and tris (2,2,2-trifluoroethyl) phosphate, tris (1,1,1,3,3,3-hexafluoropropan-2-propynyl) phosphate, ethyl 2- (diethylphosphoryl) acetate, ethyl 2- (dimethylphosphoryl) acetate, diethyl 2- (dimethoxyphosphoryl) acetate, or 2- (diethoxyphosphoryl) acetate is more preferable.
(h) Cyclic acid anhydrides
Examples of the acid anhydride include chain carboxylic anhydrides such as acetic anhydride and propionic anhydride, and cyclic anhydrides such as succinic anhydride, maleic anhydride, 2-allylsuccinic anhydride, glutaric anhydride, itaconic anhydride and 3-sulfo-propionic anhydride.
(i) Cyclic phosphazene compounds
Preferable examples of the cyclic phosphazene compound include methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, phenoxy pentafluorocyclotriphosphazene, and ethoxy heptafluorocyclotetraphosphazene.
(j) A fluoro compound;
preferred examples include methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, and propyl fluoroacetate.
Meanwhile, the invention also discloses a lithium ion battery, and the adopted electrolyte is as described in any one of the above.
In the above lithium ion battery, the positive electrode of the lithium ion battery is selected from transition metal oxides of lithium, wherein the transition metal oxide of lithium is LiCoO 2 、LiMn 2 O 4 、LiMnO 2 、Li 2 MnO 4 、LiFePO 4 、Li 1+a Mn 1-x MxO 2 、LiCo 1-x M x O 2 、LiFe 1-x M x PO 4 、Li 2 Mn 1-x O 4 Wherein M is one or more selected from Ni, co, mn, al, cr, mg, zr, mo, V, ti, B and F, and a is more than or equal to 0<0.2，0≤x<And 1, selecting at least one of graphite, a silicon-carbon composite material and lithium titanate as a negative electrode.
In the present invention, the lithium ion battery, as is well known, should comprise a separator and a negative electrode;
the negative electrode is selected from at least one of graphite, silicon-carbon composite material and lithium titanate.
The negative active material in the negative electrode includes at least one of a carbonaceous material, a silicon-carbon material, an alloy material, and a lithium-containing metal composite oxide material, but is not limited thereto, and the negative active material may be selected from various conventionally known materials capable of electrochemically inserting and extracting active ions, which are known in the art and can be used as a negative active material of an electrochemical device;
the method for preparing the negative electrode sheet is a method for preparing a negative electrode sheet that can be used for an electrochemical device, which is well known in the art; the negative electrode active material layer further contains a binder and a solvent. Adding an adhesive and a solvent into the negative active material, adding a thickening agent, a conductive agent, a filling material and the like according to needs to prepare negative slurry, then coating the negative slurry on a negative current collector, drying, pressing to prepare a negative plate, and drying and cold-pressing the negative slurry to form a negative active material layer. Likewise, in the preparation of the anode slurry, a solvent is generally added. The solvent is removed during the drying process. The binder is a binder known in the art that can be used as the negative electrode active material layer, such as, but not limited to, styrene butadiene rubber. The solvent is a solvent known in the art, such as, but not limited to, water, which can be used as the negative electrode active material layer. The thickener is a thickener known in the art that can be used as the anode active material layer, and is, for example, but not limited to, carboxymethyl cellulose. In some embodiments, when the anode active material contains an alloy material, the anode active material layer may be formed using an evaporation method, a sputtering method, a plating method, or the like;
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, inorganic substance.
For example, the barrier film 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.
The invention has the following beneficial effects:
the invention adopts a first additive containing isocyanate group, saturated or unsaturated naphthenic base and a second additive containing boron for compounding; the first additive has the effect of inhibiting gas generation, but has no obvious advantages in the aspects of high-temperature electrochemical performance and normal-temperature electrochemical performance, and the high-temperature electrochemical performance of the second additive can be enhanced by compounding with the boron-containing second additive.
Under high voltage, a first additive represented by cyclopentyl isocyanate can form free radicals through ring opening, and a polymerization reaction is carried out to generate a polymer; the first additive represented by phenyl isocyanate has excellent film-forming characteristics; and since the nitrogen of the first additive contains a lone pair of electrons, a coordinate bond is formed with the transition metal on the surface of the positive electrode. Therefore, the polymer film formed by the first additive can be attached to the surface of the positive electrode to play a role in protection. Boron in the second additive represented by neopentyl glycol diborate contains lone-pair electrons, and can be combined with fluorine ions in hydrofluoric acid to eliminate the hydrofluoric acid, so that the material is protected.
The two are compounded with each other, so that an excellent high-temperature performance improvement result is achieved.
Detailed Description
The technical solution of the present invention will be described in further detail with reference to the following embodiments, but the present invention is not limited thereto.
Example 1
1. Preparing an electrolyte: lithium salt LiPF added after mixing by adopting EC and DEC as solvents 6 Adjusting the concentration of lithium salt in the system to be 1.0M; adding a first additive: cyclopentyl isocyanate and second additive: neopentyl glycol diborate; the first additive is 0.2% of the total weight of the electrolyte; the second additive corresponds to 0.2% of the total weight of the electrolyte.
2. Preparing a positive plate: a positive electrode material (LiNi) 0.5 Co 0.2 Mn 0.3 O 2 ) The conductive agent SuperP, the adhesive PVDF and the Carbon Nano Tubes (CNT) are uniformly mixed according to the mass ratio of 95 2 At 8Drying at 5 ℃ and then carrying out cold pressing; and then trimming, cutting into pieces, slitting, drying for 4 hours at 85 ℃ under a vacuum condition after slitting, and welding tabs to prepare the lithium ion battery positive plate meeting the requirements.
3. Preparing a negative plate: preparing graphite, a conductive agent SuperP, a thickening agent CMC and a binding agent SBR (styrene butadiene rubber emulsion) into slurry according to the mass ratio of 95.5.
4. Preparing a lithium ion battery: the positive plate, the negative plate and the diaphragm prepared by the process are manufactured into a lithium ion battery with the thickness of 4.7mm, the width of 55mm and the length of 60mm by a lamination process, the lithium ion battery is baked for 10 hours at the temperature of 75 ℃, and the electrolyte is injected. After standing for 24 hours, the battery was placed in an environment of 45 ℃ and charged to 4.0V at 0.1C (160 mA) with a pressure of 3kg, and then left to stand for 2 days to sufficiently activate the battery, followed by performance test.
Example 2
The same as example 1, except that: cyclopentyl isocyanate is 0.5 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate corresponds to 0.5 percent of the total weight of the electrolyte.
Example 3
The same as example 1, except that: cyclopentyl isocyanate is equivalent to 1 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate accounts for 1 percent of the total weight of the electrolyte.
Example 4
The same as example 1, except that: cyclopentyl isocyanate is 2 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate accounts for 2% of the total weight of the electrolyte.
Example 5
The same as example 1, except that: cyclopentyl isocyanate corresponds to 3 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate accounts for 3% of the total weight of the electrolyte.
Example 6
The same as example 1, except that: cyclopentyl isocyanate is 0.1 percent of the total weight of the electrolyte; the neopentyl glycol diborate accounts for 0.9% of the total weight of the electrolyte.
Example 7
The same as example 1, except that: cyclopentyl isocyanate is 0.3 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate corresponds to 0.7 percent of the total weight of the electrolyte.
Example 8
The same as example 2, except that: cyclopentyl isocyanate is 0.9 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate corresponds to 0.1 percent of the total weight of the electrolyte.
Example 9
The same as example 2, except that: cyclopentyl isocyanate corresponds to 0.7 percent of the total weight of the electrolyte; the weight of the neopentyl glycol diborate corresponds to 0.3 percent of the total weight of the electrolyte.
Example 10
The same as example 2, except that: the first additive is phenyl isocyanate.
Example 11
The same as example 2, except that: the second additive is tetramethoxydiborane.
Example 12
The same as example 2, except that: the second additive is tetraperfluoromethoxydiborane.
Example 13
The same as example 2, except that: adjusting the solvent to PC and DEC; the weight ratio of PC to DEC is 1:1; the total amount of both was the same as in example 2.
Example 14
The same as example 2, except that: the anode material is adjusted to LiCoO 2 。
Comparative example 1
The same as example 2 except that the second additive was not included, the first additive was cyclopentyl isocyanate corresponding to 1% by weight of the total electrolyte.
Comparative example 2
The electrolyte is substantially the same as example 2, except that the first additive is not included, the second additive is neopentyl glycol diborate, and the neopentyl glycol diborate corresponds to 1% of the total weight of the electrolyte.
Comparative example 3
The same as example 2, except that no additive was added.
Comparative example 4
The procedure is substantially the same as in example 13, except that no additive is added.
Comparative example 5
The same as example 14, except that no additive was added.
Performance testing
Test item 1: high temperature Performance test
The lithium ion batteries in examples 1 to 14 and comparative examples 1 to 5 were subjected to high-temperature cycle performance and high-temperature storage performance tests in the following manner;
high temperature cycle performance: at 45 ℃, the lithium ion battery is charged to a voltage of 4.4V at a constant current of 1.0C, then the lithium ion battery is discharged to a voltage of 3.0V at a constant current of 1.0C, 200 times of cyclic charge and discharge tests are carried out, and the discharge capacity of the 200 th cycle is detected.
Capacity retention rate = (200 th discharge capacity/1 st discharge capacity) × 100%
High temperature storage performance: at normal temperature, charging the lithium ion battery at a constant current of 1C to a voltage of 4.4V and at a constant voltage of 4.4V to a current of 0.05C, and recording the thickness of the lithium ion battery as H in the test 0 (ii) a Then placing the mixture into a 60 ℃ oven for storage for 14 days, taking the mixture out, testing the thickness, and recording the thickness as H 1 (ii) a Taking out the lithium ion battery, cooling to room temperature, discharging to 3.0V at 1C, and recording the discharge capacity; and then charging the discharged lithium ion battery to a voltage of 4.4V by a constant current of 1C, charging to a current of 0.05C by a constant voltage of 4.4V, discharging to 3.0V by 1C, and recording the capacity in the 10 th week as the recovery capacity after 10 weeks of circulation.
High-temperature storage capacity retention ratio = (discharge capacity after storage/discharge capacity before storage) × 100%;
high-temperature storage capacity recovery rate = (recovery capacity after storage/discharge capacity before storage) × 100%;
high temperature storage expansion rate = (H) 1 /H 0 )×100％。
Test item 2: normal temperature performance test
The lithium ion batteries in examples 1 to 14 and comparative examples 1 to 5 were subjected to a normal temperature cycle performance test in the following manner;
at 25 ℃, the lithium ion battery is charged to a voltage of 4.4V at a constant current of 1.0C, then the lithium ion battery is discharged to a voltage of 3.0V at a constant current of 1.0C, 200 times of cyclic charge and discharge tests are carried out, and the discharge capacity of the 200 th cycle is detected.
Capacity retention rate = (200 th discharge capacity/1 st discharge capacity) × 100%.
The test results are shown in table 1 below:
TABLE 1 test results for lithium ion batteries
Under high voltage, a first additive represented by cyclopentyl isocyanate can form free radicals through ring opening, and a polymerization reaction is carried out to generate a polymer; the first additive represented by phenyl isocyanate has excellent film-forming characteristics; and since the nitrogen of the first additive contains a lone pair of electrons, a coordinate bond is formed with the transition metal on the surface of the positive electrode. Therefore, the polymer film formed by the first additive can be attached to the surface of the positive electrode to play a role in protection. Boron in the second additive represented by neopentyl glycol diborate contains lone-pair electrons, and can be combined with fluorine ions in hydrofluoric acid to eliminate the hydrofluoric acid, so that the material is protected.
By comparison of examples 1-9, example 2 was found to work best when the cyclopentyl isocyanate was 0.5% and the neopentyl glycol diborate was 0.5%. When the contents of cyclopentyl isocyanate and neopentyl glycol diborate are simultaneously reduced to 0.2% or increased by more than 0.5%, the overall performance of the battery is deteriorated. When the overall additive content is 1%, it was found that the performance was best when the ratio of the two was 1:1. Less than 0.5% of cyclopentyl isocyanate, the interfacial film is too sparse to protect. Less than 0.5% neopentyl glycol diborate is insufficient for hydrofluoric acid elimination. Above 0.5% cyclopentyl isocyanate, the interfacial film is too dense, resulting in an increase in impedance. Above 0.5% neopentyl glycol diborate acts to eliminate hydrofluoric acid, but excessive amounts of neopentyl glycol diborate can cause adhesion at the positive electrode, resulting in an interface film that is too dense.
By comparing example 2 with examples 10, 11 and 12, it was found that cyclopentyl isonitrile acid ester has better performance than phenyl isocyanate, which may be the result of more stable interfacial film; it was found that the diborane tetraperfluoromethoxy performs better than the diborane bismuthate due to its elimination of hydrofluoric acid.
By comparing example 2 with comparative examples 1,2, and 3, it was found that the use of cyclopentyl isonitrile acid ester and neopentyl glycol diborate alone improved cell performance, but with a different emphasis on reducing swelling and a higher emphasis on improving cycle performance and high temperature retention and recovery. When the two are used together, a better synergistic effect can be generated.
By comparing examples 13, 14 with comparative examples 4, 5, it was found that the combination of cyclopentylisocyanate and neopentyl glycol diborate worked even when the solvent and cathode materials were changed.
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 modifications are intended to be included in the scope of the present invention.
Claims (9)
1. An electrolyte, comprising a lithium salt, a non-aqueous organic solvent, an additive; the additives include a first additive for suppressing gas evolution and a second additive containing boron as shown in the following formula 1;
R1-R4 are each independently alkyl, fluoroalkyl; r1 and R2, R3 and R4 are independent or connected to form a ring;
the first additive contains an isocyanate group, a saturated or unsaturated cycloalkyl group;
the weight ratio of the first additive to the second additive is 0.1-5:0.1-5.
2. The electrolyte of claim 1, wherein the first additive is cyclopentyl isocyanate or phenyl isocyanate.
3. The electrolyte of claim 1, wherein R1-R4 are each independently methyl, ethyl, or perfluoromethyl.
4. The electrolyte of claim 2, wherein the second additive is one of the following compounds:
tetramethoxydiborane, tetraethoxydiborane, tetraperfluoromethoxydiborane, 2- (1,3,2-dioxaborolan-2 yl) 1,3,2-dioxaborolan, difluoro-2- (1,3,2-dioxaborolan-2 yl) 1,3,2-dioxaborolan or neopentyl glycol diborate.
5. The electrolyte of claim 1, wherein the first additive is 0.1 to 5wt% based on the total weight of the electrolyte; the second additive is 0.1-5wt% of the total weight of the electrolyte.
6. The electrolyte of claim 1, wherein the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium difluorophosphate, lithium difluoro (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium difluoro (oxalato) phosphate, and lithium bis (fluorosulfonylimide), and the concentration of the lithium salt is 0.5-2M.
7. The electrolyte according to claim 1, wherein the non-aqueous organic solvent is a cyclic organic solvent and/or a chain organic solvent;
the cyclic organic solvent is one or a combination of more of propylene carbonate, ethylene carbonate and butylene carbonate;
the chain organic solvent is one or a combination of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate and ethyl acetate.
8. A lithium ion battery, characterized in that an electrolyte is used according to any of claims 1-7.
9. The lithium ion battery of claim 8, wherein the positive electrode of the lithium ion battery is selected from lithium-containing transition metal oxides, wherein the lithium-containing transition metal oxide is LiCoO 2 、LiMn 2 O 4 、LiMnO 2 、Li 2 MnO 4 、LiFePO 4 、Li 1+a Mn 1-x MxO 2 、LiCo 1-x M x O 2 、LiFe 1-x M x PO 4 、Li 2 Mn 1-x O 4 Wherein M is one or more selected from Ni, co, mn, al, cr, mg, zr, mo, V, ti, B and F, and a is more than or equal to 0<0.2，0≤x<1; the negative electrode is selected from at least one of graphite, silicon-carbon composite material and lithium titanate.
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| CN117638083B (en) * | 2024-01-24 | 2024-04-30 | 宁德新能源科技有限公司 | Lithium ion battery and electronic device |
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