CN113140800A - Preparation method of lithium ion battery electrolyte and secondary battery containing electrolyte - Google Patents

Preparation method of lithium ion battery electrolyte and secondary battery containing electrolyte Download PDF

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CN113140800A
CN113140800A CN202110302028.0A CN202110302028A CN113140800A CN 113140800 A CN113140800 A CN 113140800A CN 202110302028 A CN202110302028 A CN 202110302028A CN 113140800 A CN113140800 A CN 113140800A
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electrolyte
carbonate
negative
lithium
lithium ion
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CN113140800B (en
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宫娇娇
黄建根
高明霞
许梦清
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Wanxiang A123 Systems Asia Co Ltd
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Wanxiang Group Corp
Wanxiang A123 Systems Asia Co Ltd
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    • 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
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/056—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
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0088—Composites
    • H01M2300/0091—Composites in the form of mixtures
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    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract

The invention relates to the technical field of lithium batteries, and discloses a preparation method of an electrolyte of a lithium ion battery and a secondary battery comprising the electrolyte, wherein the secondary battery comprises a lithium salt, a solvent, an additive and the electrolyte; the lithium salt consists of lithium bis (fluorosulfonyl) amide and lithium hexafluorophosphate, and the mass ratio of the lithium salt to the lithium hexafluorophosphate is 1-3: 7-9; the solvent consists of ethylene carbonate EC, dimethyl carbonate DMC and ethyl carbonate EMC; the additive consists of propylene carbonate PC, vinylene carbonate VC and fluoroethylene carbonate FEC; by optimizing the types and the contents of the lithium salt and the additive, the invention improves the conductivity of the electrolyte, reduces the irreversible expansion of the silicon-based negative plate, obviously improves the rate charging performance and the cycle life of the soft package lithium ion battery, further optimizes the driving mileage and the quick charging capability of the electric automobile, and has important technical value for developing new products.

Description

Preparation method of lithium ion battery electrolyte and secondary battery containing electrolyte
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a preparation method of an electrolyte of a lithium ion battery and a secondary battery containing the electrolyte.
Background
Replacement of existing fossil fuel vehicles with lithium ion battery powered electric vehicles is believed to mitigate CO2An effective way to discharge the environmental burden. The high-capacity anode and cathode materials are used, the power transmission characteristic of a battery interface is improved, the energy density and the quick charging capacity of the battery can be effectively increased, the realization of the technical goal depends on the electrolyte to a great extent, and the influence of the electrolyte on the performance of the battery is mainly embodied in three aspects: ionic conductivity of the electrolytic solution, desolvation of lithium ions from the electrolytic solution, and ion diffusion of a solid electrolyte membrane formed on the surface of the negative electrode. The composite cathode composed of silicon carbon and graphite is one of the cathodes widely adopted in the development of the lithium ion battery with high specific energy at present, but the diffusion speed of lithium ions in silicon particles is low, the dynamic performance of the battery is limited, the quick charging capability of the battery is poor, and the cycle service life of the battery is shortened because the volume change of the silicon particles is violent and the breakage and the peeling are easy to occur in the cycle process. These two problems become problems to be solved in the development of an electrolyte of a silicon-carbon system. At present, the research on the electrolyte of a silicon-carbon system in China has been reported, for example, a patent with the application number of CN201910994302.8 discloses a lithium ion battery electrolyte suitable for NCM811 and SiO-C material systems and a preparation method thereof, lithium hexafluorophosphate and lithium difluorophosphate are used as lithium salts, and additives are combined according to a certain proportion to form a solid electrolyte protective film on the surface of an active material, so that the cycle performance of the lithium ion battery is improved. However, the dynamic characteristics of the lithium ion battery are not considered, and the problem of volume expansion of the silicon-based negative electrode is not effectively improved at the same time, so that the method has certain technical limitations.
Disclosure of Invention
In order to solve the technical problems, the invention discloses a preparation method of a lithium ion battery electrolyte and a secondary battery containing the electrolyte.
The specific technical scheme of the invention is as follows: a lithium ion battery electrolyte comprises a mixed lithium salt, a solvent and an additive; the method is characterized in that: the mixed lithium salt consists of LiFSA and LiPF6The ratio of the two substances is 1-4.5: 5.5-9; the solvent consists of ethylene carbonate, dimethyl carbonate and ethyl carbonate; the additive consists of propylene carbonate, vinylene carbonate and fluoroethylene carbonate.
The addition of LiFSA can improve the conductivity of the electrolyte, and the addition of a proper amount of vinylene carbonate can effectively reduce the expansion of the negative pole piece; the specific mechanism is as follows: the anionic component of the liquid electrolyte is an important factor that affects the solvating structure, ionic conductivity and viscosity of lithium. The solvation structure of lithium ions plays a decisive role in the redox reaction process of the silicon cathode/electrolyte interface, wherein the lithium ions have a larger solvation number in a LiFSA system, and a [ Li (FSA)3]2 ion cluster is formed, and solvation FSA-anions around the lithium ions simultaneously act as bidentate ligands and monodentate ligands in the ion cluster, namely 1 bidentate ligand and 2 monodentate ligands exist around the lithium ions, so that the Li < + > -O binding length is longer. In the primary charging process, the electronic conductivity of an SEI film formed on the surface of the silicon cathode is low, the initial thickness of the SEI film is low, the SEI film has good growth stability and continuity in the subsequent charging and discharging processes, the transmission impedance of lithium ions is reduced, and the multiplying power performance of the lithium ion battery is improved. Meanwhile, the added vinylene carbonate can form a compact and easily-bent polycarbonate layer on the surface of the silicon particles, and the vinylene carbonate can resist the rapid volume change of silicon without breaking, so that the cycle life of the silicon-based lithium ion battery is prolonged.
Preferably, the total molar concentration of the mixed lithium salt is 0.8 to 1.3 mol/L.
Preferably, the volume ratio of the ethylene carbonate to the dimethyl carbonate to the ethyl carbonate in the solvent is 5-15:20-40: 40-70.
Preferably, the volume contents of fluoroethylene carbonate, vinylene carbonate and propylene carbonate in the additive are respectively 8-15%, 1-5% and 0.5-3% relative to the electrolyte.
Preferably, the preparation method of the electrolyte comprises the following steps: ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate were mixed in a sealed vessel filled with an inert gas, and then a mixed lithium salt composed of LiFSA and LiPF6 was added to the resulting mixed solution, and finally additives were sequentially added: and (3) uniformly stirring fluoroethylene carbonate, vinylene carbonate and propylene carbonate to obtain the lithium ion battery electrolyte.
A secondary battery composed of the electrolyte comprises a positive pole piece, a negative pole piece and the electrolyte; the positive pole piece comprises a positive pole coating and an aluminum foil, wherein the positive pole coating is formed by solidifying a positive pole active substance, a positive pole binder and a positive pole conductive agent; the negative pole piece comprises a negative pole coating and copper foil, wherein the negative pole coating is formed by solidifying a negative pole active substance, a negative pole conductive agent and a negative pole binder.
Preferably, the positive electrode active material is high-nickel layered transition metal oxide, and the mass of the transition metal oxide is 85-95% of that of the positive electrode coating; the positive electrode binder is PVDF, and the mass of the positive electrode binder is 2-7% of that of the positive electrode coating; the positive conductive agent is selected from one or more of carbon black, conductive graphite, carbon nano tubes, Ketjen black or conductive fibers, and the mass of the positive conductive agent is 3-8% of that of the positive coating; the thickness of the aluminum foil is 6-15 microns.
Preferably, the negative electrode active material is a silicon-carbon/graphite composite material, the mass of silicon is 3-9% of the negative electrode coating, and the mass of graphite is 80-95% of the negative electrode coating; the negative conductive agent is one or more of carbon black, conductive graphite, carbon nano tubes, Ketjen black or conductive fibers, and the mass of the negative conductive agent is 0.5-5% of that of the negative coating; the negative binder is one or two of sodium carboxymethylcellulose and styrene butadiene rubber, and the mass of the negative binder is 1.5-6% of that of the negative coating; the thickness of the copper foil is 8-12 microns.
Preferably, the secondary battery is a soft package lithium ion full battery with a laminated structure; the battery capacity of the secondary battery is 5-7 Ah; the thickness of the secondary battery is 5-8 mm.
Compared with the prior art, the invention has the beneficial effects that: according to the invention, by optimizing the types and contents of the lithium salt and the additive, the conductivity of the electrolyte is improved, the irreversible expansion of the silicon-based negative plate is reduced, and the rate charging performance and the cycle life of the soft package lithium ion battery are obviously improved.
Drawings
FIG. 1 is a graph showing the effect of electrolyte composition on conductivity at different temperatures;
FIG. 2 is a graph showing the effect of electrolyte composition on the irreversible expansion of a silicon-based negative plate;
fig. 3 is a graph of cycle life results of 6Ah soft pack lithium ion batteries at room temperature.
Detailed Description
The invention is further described with reference to the following examples; the raw materials and equipment involved in the invention are common raw materials and equipment in the field if not specified; the methods used in the invention are conventional methods in the field if not specified; the reagents used in the invention are all lithium battery grade.
In order to compare the performances of electrolytes with different components, a reference group is added in the invention, conventional LiPF6 is used as lithium salt, the molar concentration is 1.0mol/L, ethylene carbonate, dimethyl carbonate and ethyl carbonate are used as solvent systems, and the volume ratio is 10:20: 70; the volume ratio of fluoroethylene carbonate and propylene carbonate is respectively 8 percent and 4 percent without vinylene carbonate, and the formula is close to that of the conventional electrolyte system. In the present invention, the different electrolyte compositions are labeled (lithium salt anion species) - (vinylene carbonate VC content), for example PF6-VC0, FSA/PF6-2/8-VC1 terms denote the reference group and the components LiFSA, LiPF6 mass ratio 2:8, VC content 1%, while "15-25-60 solvent" denotes the solvent system of ethylene carbonate, dimethyl carbonate, ethyl carbonate volume ratio 15:25: 60.
All materials were dried using molecular sieves during the experiment until the moisture content of the prepared electrolyte was below 12ppm, as determined by karl fischer titration.
The conductivity determination method comprises the following steps: a symmetrical cell containing about 10 ml of electrolyte was immersed in a water bath with a temperature accuracy of ± 0.1 ℃. The ac impedance was measured at 10, 20, 30, 40 and 50 ℃. Before the measurement, the electrolyte was allowed to equilibrate by 30 minutes of immersion at each temperature, with an alternating current frequency ranging from 100 to 5kHz and an amplitude of 5mV, and the conductivity of the electrolyte was calculated from the reciprocal of the impedance obtained.
The specific operation process of the thickness change of the pole piece is as follows: after the electrochemical cell is assembled, the cell is charged and discharged at 25 ℃ with 0.1C multiplying power in the range of 0.01-1.5V, the thickness change of the button cell before and after charging and discharging is recorded, and the irreversible thickness change of the pole piece is selected as a constant value (the irreversible expansion is the thickness of the second cycle lithium pole piece-the thickness of the initial pole piece).
The specific operation process of the battery rate performance and the cycle life is as follows: rate capability: charging to 4.2V at constant current and constant voltage at 25 ℃ and multiplying power of 0.3C, 0.5C, 1.0C, 2.0C and 3.0C respectively, stopping current at 0.05C, standing for 5 minutes, and discharging to 2.8V at 1.0C; cycle life: charging to 4.2V at constant current and constant voltage with 1C rate at 25 deg.C, stopping current at 0.05C, standing for 5 min, discharging to 2.8V at 1.0C, circulating for 500 weeks, and measuring.
Example 1
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA with the total molar concentration of 1mol/L and LiPF6 mixed lithium salt (the mass ratio of the two substances is 2:8) are slowly added into the mixed solution, and finally, the additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are 1.5% and 2.5%, and the mass ratio of the binder is 4%. The materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: the high-nickel layered transition metal oxide is selected, the mass ratio is 90%, PVDF is used as a binder, the addition amount is 5%, carbon black is used as a conductive agent, the mass ratio is 5%, the materials are uniformly mixed in a ball mill and then coated on an aluminum foil with the thickness of 12 microns, the prepared electrolyte is injected to assemble a soft package lithium ion full battery, the battery adopts a laminated structure, the actual capacity is 6Ah, the thickness of the battery is 6.5mm, and the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
Example 2
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA with the total molar concentration of 1mol/L and LiPF6 mixed lithium salt (the mass ratio of the two substances is 3:7) are slowly added into the mixed solution, and finally, the additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are respectively 1.5% and 2.5%, and the mass ratio of the binder is 4%; the materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: selecting high-nickel layered transition metal oxide with the mass ratio of 90%, PVDF as a binder and the addition of 5%, selecting carbon black as a conductive agent with the mass ratio of 5%, uniformly mixing the materials in a ball mill, coating the materials on an aluminum foil with the thickness of 12 microns, injecting the prepared electrolyte to assemble a soft package lithium ion full battery, wherein the battery adopts a laminated structure, the actual capacity is 6Ah, and the thickness of the battery is 6.5 mm; the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
Example 3
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA with the total molar concentration of 1mol/L and LiPF6 mixed lithium salt (the mass ratio of the two substances is 4.5:5.5) are slowly added into the mixed solution, and finally, the following additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are 1.5% and 2.5%, and the mass ratio of the binder is 4%. The materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: the high-nickel layered transition metal oxide is selected, the mass ratio is 90%, PVDF is used as a binder, the addition amount is 5%, carbon black is used as a conductive agent, the mass ratio is 5%, the materials are uniformly mixed in a ball mill and then coated on an aluminum foil with the thickness of 12 microns, the prepared electrolyte is injected to assemble a soft package lithium ion full battery, the battery adopts a laminated structure, the actual capacity is 6Ah, the thickness of the battery is 6.5mm, and the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
Example 4
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA + LiPF6 mixed lithium salt with the total molar concentration of 1mol/L (the mass ratio of the two substances is 2:8) is slowly added into the mixed solution, and finally, the additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte, vinylene carbonate accounting for 2% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are 1.5% and 2.5%, and the mass ratio of the binder is 4%. The materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: the high-nickel layered transition metal oxide is selected, the mass ratio is 90%, PVDF is used as a binder, the addition amount is 5%, carbon black is used as a conductive agent, the mass ratio is 5%, the materials are uniformly mixed in a ball mill and then coated on an aluminum foil with the thickness of 12 microns, the prepared electrolyte is injected to assemble a soft package lithium ion full battery, the battery adopts a laminated structure, the actual capacity is 6Ah, the thickness of the battery is 6.5mm, and the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
Example 5
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA + LiPF6 mixed lithium salt with the total molar concentration of 1mol/L (the mass ratio of the two substances is 4.5:5.5) is slowly added into the mixed solution, and finally, the following additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte, vinylene carbonate accounting for 2% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are 1.5% and 2.5%, and the mass ratio of the binder is 4%. The materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: the high-nickel layered transition metal oxide is selected, the mass ratio is 90%, PVDF is used as a binder, the addition amount is 5%, carbon black is used as a conductive agent, the mass ratio is 5%, the materials are uniformly mixed in a ball mill and then coated on an aluminum foil with the thickness of 12 microns, the prepared electrolyte is injected to assemble a soft package lithium ion full battery, the battery adopts a laminated structure, the actual capacity is 6Ah, the thickness of the battery is 6.5mm, and the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
Example 6
A preparation method of lithium ion battery electrolyte and a secondary battery containing the electrolyte comprise the following steps: in a glove box filled with argon, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed according to the volume ratio of 15:25:60, then LiFSA + LiPF6 mixed lithium salt with the total molar concentration of 1mol/L (the mass ratio of the two substances is 4.5:5.5) is slowly added into the mixed solution, and finally, the following additives are sequentially added: fluoroethylene carbonate accounting for 8% of the total volume of the electrolyte, vinylene carbonate accounting for 4% of the total volume of the electrolyte and propylene carbonate accounting for 4% of the total volume of the electrolyte are uniformly stirred to obtain the electrolyte of the lithium ion battery.
The prepared electrolyte is assembled into a single-chip symmetrical battery, and the pole piece comprises the following components: the silicon-carbon/graphite composite material comprises 4% of silicon by mass and 89% of graphite by mass, carbon nano tubes are selected as a conductive agent, the mass ratio is 3%, sodium carboxymethylcellulose and styrene butadiene rubber are selected as binders, the mass fractions of the two binders are 1.5% and 2.5%, and the mass ratio of the binder is 4%. The materials are uniformly mixed in a ball mill, then uniformly coated on a copper foil with the thickness of 8 microns, dried and punched, and then two pole pieces are taken and injected with the prepared electrolyte to assemble the symmetrical battery. After the cell was left to stand at room temperature for 12 hours, the electrolyte conductivity was measured using electrochemical impedance technology in combination with a frequency response meter and a potentiostat.
The obtained negative plate is used as a working electrode, a lithium plate is used as a counter electrode, a proper amount of electrolyte is added to assemble an electrochemical cell, the thickness change of the negative plate in the electrolyte with different components is measured by using an in-situ electrochemical dilatometer, the mechanical relaxation in the material can be eliminated by an electrochemical in-situ dilatometry method, and the measurement precision is high.
Finally, the manufacturing method of the cathode pole piece is as follows: the high-nickel layered transition metal oxide is selected, the mass ratio is 90%, PVDF is used as a binder, the addition amount is 5%, carbon black is used as a conductive agent, the mass ratio is 5%, the materials are uniformly mixed in a ball mill and then coated on an aluminum foil with the thickness of 12 microns, the prepared electrolyte is injected to assemble a soft package lithium ion full battery, the battery adopts a laminated structure, the actual capacity is 6Ah, the thickness of the battery is 6.5mm, and the working voltage range is 2.8-4.2V. After the battery assembly is finished, the battery is activated by charging and discharging for 3 weeks at a low current of 0.1C, and then the normal-temperature rate performance and the cycle performance of the battery are measured.
By the embodiment of the invention, the results are as follows:
as shown in fig. 1, the conductivity results of the electrolytes with different components show that, compared with the reference group PF6-VC0(15-25-60), when the total concentration of 1mol/L is maintained, the conductivity at different temperatures is obviously increased after a certain amount of LiFSA is added to the lithium salt, and the conductivity is also increased as the ratio of LiFSA is increased from 2 to 4.5, which indicates that the addition of LiFSA can improve the conductivity of the electrolyte, and the data in fig. 1 can show that the conductivity is not obviously affected after the addition of VC.
As shown in fig. 2, the irreversible expansion of the negative electrode plate in different electrolytes measured by an electrochemical in-situ expansion method is not significantly reduced compared with a reference group PF6-VC0, when the electrolyte is FSA/PF6-4.5/5.5-VC0(15-25-60), the irreversible expansion of the negative electrode plate is reduced from 4.5 micrometers to about 3.5 micrometers under the same conditions after 2% of VC is added, and the irreversible expansion is reduced to 3 micrometers after the VC content is increased to 4%, which indicates that the addition of a proper amount of VC can effectively reduce the expansion of the negative electrode plate.
As shown in fig. 3, which is a result of cycle life of a 6Ah soft package lithium ion battery at room temperature, the cycle performance of the FSA/PF6-2/8-VC4(15-25-60) group is the best, the capacity retention rate is not significantly reduced after 95 cycles, the cycle performance of the reference group is the worst under the same test conditions, and the capacity retention rate is only about 90% after 95 cycles.
TABLE 1 comparison of battery double charging Performance for different electrolyte formulations
Figure BDA0002986694880000081
Table 1 shows the result of a test on the rate charging performance of the soft package lithium ion full battery, a certain amount of LiFSA is added on the basis of a reference group, the rate charging capacity of FSA/PF6-2/8-VC0(15-25-60) is improved, the rate charging performance of the battery is the best as the LiFSA content is increased to 4.5%, particularly, the capacity retention rate is improved by 2.3% when the battery is charged at high rates of 2.0C and 3.0C, and the rate charging performance of the battery is not obviously influenced by adding VC.
The results prove that compared with the conventional electrolyte system, the electrolyte disclosed by the invention can be obviously improved in cycle life and rate capability by adding a certain amount of LiFSA and VC, further optimizes the driving mileage and quick charging capability of the electric automobile, and has important technical value for developing new products.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modifications, alterations, and equivalent structural changes made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims (9)

1. A lithium ion battery electrolyte comprises a mixed lithium salt, a solvent and an additive; the method is characterized in that: the mixed lithium salt consists of LiFSA and LiPF6The ratio of the two substances is 1-4.5: 5.5-9; the solvent consists of ethylene carbonate, dimethyl carbonate and ethyl carbonate; the additive consists of propylene carbonate, vinylene carbonate and fluoroethylene carbonate.
2. The lithium ion battery electrolyte of claim 1 wherein the total molar concentration of the mixed lithium salts is 0.8 to 1.3 mol/L.
3. The lithium ion battery electrolyte of claim 1, wherein the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl carbonate in the solvent is 5-15:20-40: 40-70.
4. The lithium ion battery electrolyte of claim 1, wherein the additive comprises 8-15%, 1-5%, and 0.5-3% by volume of fluoroethylene carbonate, vinylene carbonate, and propylene carbonate, respectively, with respect to the electrolyte.
5. The lithium ion battery electrolyte as claimed in any of claims 1 to 4, wherein the preparation method comprises the following steps: ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate were mixed in a sealed vessel filled with an inert gas, and then a solution of LiFSA and LiPF was added to the resulting mixture6And finally, sequentially adding additives: and (3) uniformly stirring fluoroethylene carbonate, vinylene carbonate and propylene carbonate to obtain the lithium ion battery electrolyte.
6. A secondary battery comprising the electrolyte of any one of claims 1 to 5, comprising a positive electrode tab, a negative electrode tab and the electrolyte; the positive pole piece comprises a positive pole coating and an aluminum foil, wherein the positive pole coating is formed by solidifying a positive pole active substance, a positive pole binder and a positive pole conductive agent; the negative pole piece comprises a negative pole coating and copper foil, wherein the negative pole coating is formed by solidifying a negative pole active substance, a negative pole conductive agent and a negative pole binder.
7. The secondary battery according to claim 6, wherein the positive electrode active material is a transition metal oxide having a high nickel content, and the mass of the transition metal oxide is 85-95% of that of the positive electrode coating; the positive electrode binder is PVDF, and the mass of the positive electrode binder is 2-7% of that of the positive electrode coating; the positive conductive agent is selected from one or more of carbon black, conductive graphite, carbon nano tubes, Ketjen black or conductive fibers, and the mass of the positive conductive agent is 3-8% of that of the positive coating; the thickness of the aluminum foil is 6-15 microns.
8. The secondary battery according to claim 6, wherein the negative active material is a silicon carbon/graphite composite material, the mass of silicon is 3-9% of the negative coating, and the mass of graphite is 80-95% of the negative coating; the negative conductive agent is one or more of carbon black, conductive graphite, carbon nano tubes, Ketjen black or conductive fibers, and the mass of the negative conductive agent is 0.5-5% of that of the negative coating; the negative binder is one or two of sodium carboxymethylcellulose and styrene butadiene rubber, and the mass of the negative binder is 1.5-6% of that of the negative coating; the thickness of the copper foil is 8-12 microns.
9. The secondary battery according to claim 6, wherein the secondary battery is a laminate-structured pouch lithium-ion full battery; the battery capacity of the secondary battery is 5-7 Ah; the thickness of the secondary battery is 5-8 mm.
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