CN115377486A - Electrolyte for improving low-temperature performance and reducing gas generation of lithium ion battery and preparation method thereof - Google Patents
Electrolyte for improving low-temperature performance and reducing gas generation of lithium ion battery and preparation method thereof Download PDFInfo
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- CN115377486A CN115377486A CN202211083331.7A CN202211083331A CN115377486A CN 115377486 A CN115377486 A CN 115377486A CN 202211083331 A CN202211083331 A CN 202211083331A CN 115377486 A CN115377486 A CN 115377486A
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- 239000003792 electrolyte Substances 0.000 title claims abstract description 85
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 35
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 35
- 238000002360 preparation method Methods 0.000 title claims description 17
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 claims abstract description 54
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims abstract description 41
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 41
- 239000010439 graphite Substances 0.000 claims abstract description 41
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 29
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims description 22
- 238000002156 mixing Methods 0.000 claims description 10
- -1 lithium hexafluorophosphate Chemical group 0.000 claims description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 7
- 239000001301 oxygen Substances 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 7
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 6
- 239000012300 argon atmosphere Substances 0.000 claims description 6
- 229910052744 lithium Inorganic materials 0.000 claims description 6
- 239000002131 composite material Substances 0.000 claims 1
- 239000000654 additive Substances 0.000 abstract description 6
- 230000000996 additive effect Effects 0.000 abstract description 6
- 230000000877 morphologic effect Effects 0.000 abstract description 3
- 239000007784 solid electrolyte Substances 0.000 abstract description 3
- 238000007614 solvation Methods 0.000 abstract description 3
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 abstract 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 20
- 230000000052 comparative effect Effects 0.000 description 12
- 229910013870 LiPF 6 Inorganic materials 0.000 description 9
- 239000008151 electrolyte solution Substances 0.000 description 9
- 239000007789 gas Substances 0.000 description 9
- 239000002904 solvent Substances 0.000 description 9
- 230000006399 behavior Effects 0.000 description 8
- 238000012360 testing method Methods 0.000 description 8
- 229910000572 Lithium Nickel Cobalt Manganese Oxide (NCM) Inorganic materials 0.000 description 6
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 6
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 6
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 6
- 229910013872 LiPF Inorganic materials 0.000 description 5
- 101150058243 Lipf gene Proteins 0.000 description 5
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- FBDMTTNVIIVBKI-UHFFFAOYSA-N [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] Chemical compound [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] FBDMTTNVIIVBKI-UHFFFAOYSA-N 0.000 description 3
- 230000001351 cycling effect Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 238000002161 passivation Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- 230000008014 freezing Effects 0.000 description 2
- 238000007710 freezing Methods 0.000 description 2
- 239000007770 graphite material Substances 0.000 description 2
- 238000009830 intercalation Methods 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910021382 natural graphite Inorganic materials 0.000 description 2
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 241001521809 Acoma Species 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910017246 Ni0.8Co0.1Mn0.1 Inorganic materials 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 229940125753 fibrate Drugs 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 1
- LXCFILQKKLGQFO-UHFFFAOYSA-N methylparaben Chemical compound COC(=O)C1=CC=C(O)C=C1 LXCFILQKKLGQFO-UHFFFAOYSA-N 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 238000000643 oven drying Methods 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides an electrolyte, which comprises propylene carbonate, N-methyl pyrrolidone and lithium salt. The invention utilizes the high donor number property of the N-methyl pyrrolidone as an additive, successfully inhibits the behavior of propylene carbonate co-embedding into graphite by adjusting the solvation structure of the lithium ion battery electrolyte and the characteristics of a solid electrolyte interface film, and maintains the original morphological structure of the graphite electrode after the graphite electrode is circulated in the electrolyte. The novel electrolyte has better low-temperature performance than a commercial vinyl carbonate-based electrolyte, and gas evolution behavior of the battery in the electrolyte is also suppressed.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to an electrolyte, a preparation method thereof and a lithium ion battery.
Background
Lithium ion batteries have received widespread attention from people because of their high energy density, long cycle life, small size, portability, and other features, and have been widely used in the fields of consumer electronics and electric vehicles. The main components of the lithium ion battery comprise a positive electrode, a negative electrode, a diaphragm and electrolyte.
Lithium currently in commercial useThe negative electrode material of the ion battery is mainly graphite material, such as natural graphite, modified natural graphite, artificial graphite and the like. The lithium ion battery electrolyte generally consists of lithium salt, an organic solvent and an additive, and plays a role in conducting anions and cations between a positive electrode and a negative electrode. The most developed and widely used electrolyte is an Ethylene Carbonate (EC) -based electrolyte, and the essential component of such an electrolyte is EC, and on the basis of EC, linear carbonates with high dielectric constants, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Methyl Carbonate (EMC), etc., are added to reduce the viscosity of the electrolyte and improve the solubility of the lithium salt in the electrolyte. A commonly used lithium salt is lithium hexafluorophosphate (LiPF) 6 )。
The freezing point of EC is 37 deg.C, and the electrolyte is solid at room temperature, so the lithium ion battery composed of EC-based electrolyte has lower conductivity at low temperature and poorer low-temperature performance. Propylene Carbonate (PC) has a similar structure to EC, has only one more methyl group than EC, and has a lower freezing point (-48 ℃) than EC, and good low-temperature performance. But at present, PC is only used as an additive to improve the low-temperature performance of the battery and cannot be used as a main solvent. The reason is that the negative electrode of the current commercial lithium ion battery is mainly made of graphite materials, and the surface of the graphite electrode cannot be effectively passivated by PC, so that a PC solvent is embedded into the graphite electrode, the structure of the graphite electrode is damaged, and the battery cannot be normally charged and discharged.
Therefore, it is of great importance to develop a new method capable of suppressing the intercalation of PC into the graphite electrode, and a new electrolyte.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide an electrolyte, which can effectively reduce the generation of battery gas and has good low-temperature discharge performance.
The invention provides an electrolyte, which comprises propylene carbonate, N-methyl pyrrolidone and lithium salt.
Preferably, the volume ratio of the propylene carbonate to the N-methylpyrrolidone is 6.
Preferably, the lithium salt is lithium hexafluorophosphate.
Preferably, the volume percentage of the propylene carbonate in the electrolyte is 50-66.7%; the concentration of the lithium salt is 0.8-1.2M.
The invention provides a preparation method of electrolyte, which comprises the following steps:
mixing propylene carbonate, N-methyl pyrrolidone and lithium salt to obtain the product.
Preferably, the volume ratio of the propylene carbonate to the N-methyl pyrrolidone is 6.
Preferably, the mixing is carried out in an argon atmosphere glove box having both a moisture and oxygen content of less than 0.1 ppm.
Preferably, the mixing temperature is 10 to 30 ℃.
The invention provides a lithium ion battery, comprising: the electrolyte solution according to any one of the above technical schemes or the electrolyte solution prepared by the preparation method according to any one of the above technical schemes.
Preferably, the negative electrode of the lithium ion battery is graphite, and the reference electrode is a lithium sheet.
Compared with the prior art, the invention provides an electrolyte, which comprises propylene carbonate, N-methyl pyrrolidone and lithium salt. The invention utilizes the high donor number property of N-methyl pyrrolidone as an additive, and successfully enables the behavior of PC co-embedded into graphite to be inhibited and the original morphological structure of the graphite electrode of the lithium ion battery to be maintained after the graphite electrode is circulated in the electrolyte of the invention by adjusting the solvation structure of the lithium ion battery electrolyte and the characteristics of a solid electrolyte interface film. The new electrolyte has better low temperature performance than commercial EC-based electrolytes, while the gassing behavior of the battery is suppressed.
Drawings
FIG. 1 is a schematic diagram of the low temperature discharge process of a lithium ion battery in a commercial electrolyte and an electrolyte developed by the present invention;
FIG. 2 is a constant current charge and discharge curve of a graphite electrode of a lithium ion battery in different embodiments;
FIG. 3 discharge curves at-30 ℃ for lithium ion batteries using commercial electrolytes and electrolytes developed in accordance with the present invention;
FIG. 4 gas evolution behavior of lithium-graphite batteries (a) 1MLiPF6in PC (b) 1MLiPF6in PC/NMP, inset is the corresponding voltage curve;
FIG. 5 is an electron microscope characterization of a graphite electrode of a lithium ion battery after cycling in an electrolyte developed by the present invention.
Detailed Description
The invention provides an electrolyte, a preparation method thereof and a lithium ion battery, and a person skilled in the art can use the contents for reference and appropriately improve process parameters to realize the purpose. It is specifically noted that all such substitutions and modifications will be apparent to those skilled in the art, and are intended to be within the scope of the present invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.
The invention provides an electrolyte, which comprises propylene carbonate, N-methyl pyrrolidone and lithium salt.
In a preferred embodiment of the present invention, the volume ratio of propylene carbonate to N-methylpyrrolidone is 6.
In some preferred embodiments of the invention, the volume ratio of propylene carbonate to N-methylpyrrolidone is 6.
In some preferred embodiments of the present invention, the volume ratio of propylene carbonate to N-methylpyrrolidone is 1.
In some preferred embodiments of the invention, the volume ratio of propylene carbonate to N-methylpyrrolidone is 6.
The lithium salts of the present invention include, but are not limited to, lithium hexafluorophosphate.
According to the invention, the volume percentage of the propylene carbonate accounts for 50-66.7% of the electrolyte; the concentration of the lithium salt is 0.8-1.2M.
The invention provides a preparation method of electrolyte, which comprises the following steps:
mixing propylene carbonate, N-methyl pyrrolidone and lithium salt to obtain the product.
In an argon atmosphere glove box with the moisture content and the oxygen content both less than 0.1ppm, uniformly mixing propylene carbonate and N-methyl pyrrolidone; the volume ratio of the propylene carbonate to the N-methyl pyrrolidone is 6-1.
And slowly adding lithium salt, controlling the temperature of the electrolyte not to exceed 30 ℃ in the process of adding the lithium salt, and shaking up the electrolyte to obtain the electrolyte taking the propylene carbonate as a main solvent after the lithium salt is completely dissolved. The mixing temperature is 10-30 ℃.
The invention provides a lithium ion battery, comprising: the electrolyte solution according to any one of the above technical aspects or the electrolyte solution prepared by the preparation method according to any one of the above technical aspects.
The negative electrode of the lithium ion battery is graphite, and the reference electrode is a lithium sheet.
The invention develops the electrolyte taking PC as the main solvent by introducing a new additive, so that the electrolyte is in graphite-Li [ Ni ] 0.8 Co 0.1 Mn 0.1 ]O 2 (NCM 811) full cell exhibiting excellent discharge performance at low temperature and suppressing gas evolution of electrolyte
The invention provides an electrolyte, which comprises propylene carbonate, N-methyl pyrrolidone and lithium salt. The invention utilizes the high donor number property of the N-methyl pyrrolidone as an additive, successfully inhibits the action of PC co-embedding into graphite by adjusting the solvation structure of the lithium ion battery electrolyte and the characteristics of a solid electrolyte interface film, and maintains the original morphological structure of the lithium ion battery graphite electrode after the lithium ion battery graphite electrode is circulated in the electrolyte. The new electrolyte has better low temperature performance than commercial EC-based electrolytes, while the gassing behavior of the battery is suppressed.
In order to further illustrate the present invention, the following describes an electrolyte, a preparation method thereof and a lithium ion battery in detail with reference to examples.
Example 1 preparation of an electrolyte solution comprising propylene carbonate as a main solvent
Argon gas with water content and oxygen content less than 0.1ppmIn an atmosphere glove box, a volume of propylene carbonate (PC, battery grade, multi chemistry) and N-methyl pyrrolidone (NMP, battery grade, multi chemistry) was mixed well from 6:1 to 1:9 optimization of the optimal volume ratio, then slowly adding 0.456g lithium hexafluorophosphate (LiPF) 6 Battery grade, multi-chemistry), the temperature of the electrolyte is controlled not to exceed 30 ℃ in the process of adding the lithium salt, the electrolyte taking propylene carbonate as a main solvent is obtained after the lithium salt is completely dissolved and shaken up, and the name of the electrolyte is 1M LiPF 6 in PC/NMP。
Comparative example 1 preparation of propylene carbonate electrolyte solution
In an argon atmosphere glove box having a moisture and oxygen content of less than 0.1ppm, 0.159g of lithium hexafluorophosphate (LiPF) 6 Battery grade, multi-chemistry) is slowly added into 1ml of propylene carbonate (PC, battery grade, multi-chemistry), the temperature of the electrolyte is controlled not to exceed 30 ℃ in the process of adding lithium salt, and the electrolyte obtained after the lithium salt is completely dissolved is shaken up is named as 1MLiPF 6 inPC。
Comparative example 2 preparation of N-methylpyrrolidone electrolyte solution
In an argon atmosphere glove box having a moisture and oxygen content of less than 0.1ppm, 0.159g of lithium hexafluorophosphate (LiPF) 6 Battery grade, multi-chemistry) is slowly added into 1ml of N-methyl pyrrolidone (NMP, battery grade, multi-chemistry), the temperature of the electrolyte is controlled not to exceed 30 ℃ in the process of adding lithium salt, and the electrolyte obtained after the lithium salt is completely dissolved and shaken up is named as 1MLiPF 6 inNMP。
Comparative example 3 preparation of ethylene carbonate-based electrolyte solution
In an argon atmosphere glove box with moisture and oxygen content less than 0.1ppm, ethylene carbonate (EC, battery grade, multi-chemistry) was first melted to a liquid by heating, after which 0.5ml ethylene carbonate and 0.5ml dimethyl carbonate (DMC, battery grade, multi-chemistry) were mixed well, and then 0.159g lithium hexafluorophosphate (LiPF) was slowly added 6 Battery grade, multi-chemistry), the temperature of the electrolyte is controlled not to exceed 30 ℃ in the process of adding the lithium salt, after the lithium salt is completely dissolved, a commercialized ethylene carbonate-based electrolyte is obtained after shaking up, and the name of the ethylene carbonate-based electrolyte is 1M LiPF 6 in EC/DMC。
EXAMPLES electrode preparation and testing
Preparing a graphite cathode:
according to the mass ratio of 8:1:1 weighing graphite powder (Tianjin fibrate), acetylene black conductive powder (Switzerland Temmin) and a binder polyvinylidene fluoride (PVDF, france Acoma), mixing the three materials, and adding a certain amount of N-methyl pyrrolidone (NMP, doxono chemical) to form uniform slurry. The slurry was then uniformly coated on a copper foil using a maker. After complete NMP evaporation at room temperature, the pole pieces were transferred to a 50 ℃ forced air Oven, dried overnight and cut into 12mm diameter discs, then dried overnight at 80 ℃ using a catch Oven drying tube and transferred to a glove box for use. The active loading was about 1.7mg/cm2.
Preparation of the positive electrode:
Li[Ni0.8Co0.1Mn0.1]O 2 (NCM 811, nipagin and new materials) the process for making the positive electrode was similar to that of the graphite negative electrode, with the only difference being that the NCM811 positive electrode required vacuum drying at 110 ℃ overnight. The loading of active material is about 3.3mg/cm2.
Performance test
Graphite is used as a working electrode, a lithium sheet is used as a reference electrode, a CR2032 button cell is assembled, and a charge-discharge test is carried out on a battery charge-discharge instrument (CT 2001A, wuhan's blue electricity), wherein the voltage cut-off range is 2.5-0.005V, and the charge-discharge current is 18.6mA/g graphite.
The results are shown in the figures, wherein fig. 1 is a schematic diagram of the low temperature discharge process of a lithium ion battery in a commercial electrolyte and an electrolyte developed by the present invention;
FIG. 2 is a constant current charge and discharge curve of a graphite electrode of a lithium ion battery in different embodiments; in 1M LiPF 6 in PC (comparative example 1) and 1M LiPF 6 In the NMP (comparative example 2) system, the solvent co-intercalates into the graphite electrode and continues to decompose on the electrode surface; in 1M LiPF 6 in PC/NMP System (inventive example 1) and 1M LiPF 6 in the in EC/DMC system (comparative example 3 according to the invention), lithium ions can be inserted reversibly into the graphite).
As can be seen from the figure, as the discharging process progresses, the voltage of the battery gradually decreases, and the specific capacity gradually increases; however, the electrochemical behaviors of different electrolytes on the graphite electrode are different, and for 1MLiPF6inPC (comparative example 1) electrolyte, a very long platform appears at 0.9V in a discharge curve, which means that PC is continuously decomposed on the surface of the electrode and cannot form an effective passivation film, so that PC is co-embedded into graphite, and the graphite electrode is damaged; the electrochemical behavior of the electrolyte of 1MLiPF6inNMP (comparative example 2) on the surface of a graphite electrode is similar to that of PC, and a very long platform also appears on a discharge curve at 0.5V along with the reduction of voltage, which means that NMP is continuously decomposed on the surface of the electrode and an effective passivation film cannot be formed, so that NMP is co-embedded into the graphite, and the graphite electrode is also damaged;
however, in the 1MLiPF6inPC/NMP electrolyte (example 1 of the present invention), as the discharge proceeds, a very small plateau appears in the discharge curve at 0.8V, and then the voltage continues to drop, which means that an effective passivation film is formed on the electrode surface after the solvent is decomposed, and this film can inhibit the co-intercalation of the solvent, and when the voltage reaches below 0.2V, 3 plateaus appear, which means that the lithium ions can intercalate the graphite; the charging process and the discharging process are reversed. The charge and discharge processes of the battery in example 1 are similar to those of the existing commercial system (comparative example 3), which illustrates that the lithium ion battery electrolyte developed by the present invention can be applied to the existing battery system.
FIG. 3 is a discharge curve at-30 ℃ for a lithium ion battery using a commercial electrolyte and an electrolyte developed in accordance with the present invention;
FIG. 3 is a discharge curve at-30 ℃ of a lithium ion battery using the electrolytes prepared in example 1 and comparative example 3; the test was carried out by using graphite as the negative electrode of the cell and lithium nickel cobalt manganese oxide (LiNi) 0.8 Co 0.1 Mn 0.1 O 2 ) And (4) preparing a battery anode to assemble a CR2032 button battery. First, at room temperature, the battery was placed on a charge/discharge instrument (CT 2001A, wuhan blue) to perform a charge test with a cut-off voltage of 4.2V and a charge current of 20mA/g Lithium nickel cobalt manganese oxide . After the charging is finished, a discharge test is carried out at the temperature of minus 30 ℃, the cut-off voltage is 2V, and the discharge current is 20mA/g Lithium nickel cobalt manganese oxide . As can be seen from FIG. 3, the 1M LiPF6in EC/DMC electrolyte used in comparative example 3 hardly discharged at-30 ℃ and the discharge capacity was 8.7mAh g -1 The electrolyte of example 1 of the present invention had a specific discharge capacity of 125.9mAh g at-30 ℃ -1 14 times that of the commercial electrolyte.
FIG. 4 gas evolution behavior of lithium-graphite batteries (a) 1M LiPF 6 in PC (comparative example 1) (b) 1M LiPF 6 in PC/NMP (example 1), the inset is the corresponding voltage curve; FIG. 4 is a graph of gas evolution for lithium-graphite batteries using different electrolytes, as can be seen in FIG. a, using 1M LiPF 6 When the PC electrolyte is in, the voltage is gradually reduced along with the progress of the discharging process, propylene is generated in the battery, the amount of the propylene is more and more, and the generation of the propylene is caused by the decomposition of propylene carbonate; in sharp contrast, 1MLiPF was used 6 in PC/NMP electrolyte, the voltage gradually decreases along with the progress of the discharge process, although propylene is generated in the battery, the amount of propylene is relatively small, and when the voltage reaches 0.5V, the amount of propylene begins to decrease (figure 4 b), which shows that the gas generation behavior of the electrolyte is inhibited after the addition of NMP. In conclusion, the electrolyte can effectively reduce the generation of gas in the battery.
FIG. 5 is an electron microscope representation of a graphite electrode of a lithium ion battery after cycling in an electrolyte solution developed in accordance with the present invention; in 1MLiPF 6 in the in PC/NMP (inventive example 1) system, the graphite electrode maintains the original spherical structure after cycling
The test is carried out by using graphite as working electrode and lithium sheet as reference electrode, assembling into CR2032 button cell, and carrying out charge-discharge test on battery charge-discharge instrument (CT 2001A, wuhan blue electricity) with voltage cut-off range of 2.5-0.005V and charge-discharge current of 18.6mA/g Graphite . After the test, the graphite electrode was removed from the cell and characterized by a scanning electron microscope.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. An electrolyte is characterized by comprising propylene carbonate, N-methyl pyrrolidone and lithium salt.
2. The electrolyte according to claim 1, wherein the volume ratio of propylene carbonate to N-methylpyrrolidone is from 6 to 1.
3. The electrolyte of claim 1, wherein the lithium salt is lithium hexafluorophosphate.
4. The electrolyte of claim 1, wherein the propylene carbonate accounts for 50-66.7% of the electrolyte by volume; the concentration of the lithium salt is 0.8-1.2M.
5. The preparation method of the electrolyte is characterized by comprising the following steps:
and mixing the propylene carbonate, the N-methyl pyrrolidone and the lithium salt to obtain the composite material.
6. The preparation method according to claim 5, wherein the volume ratio of the propylene carbonate to the N-methylpyrrolidone is 6.
7. The method of claim 5, wherein the mixing is performed in an argon atmosphere glove box having a moisture and oxygen content of less than 0.1 ppm.
8. The method according to claim 5, wherein the mixing temperature is 10 to 30 ℃.
9. A lithium ion battery, comprising: the electrolyte according to any one of claims 1 to 4 or the electrolyte prepared by the method according to any one of claims 5 to 8.
10. The lithium ion battery of claim 9, wherein the negative electrode of the lithium ion battery is graphite and the reference electrode is a lithium sheet.
Priority Applications (1)
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