CN115224365A - Graphite cathode system battery electrolyte and lithium ion battery containing same - Google Patents

Graphite cathode system battery electrolyte and lithium ion battery containing same Download PDF

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CN115224365A
CN115224365A CN202211072057.3A CN202211072057A CN115224365A CN 115224365 A CN115224365 A CN 115224365A CN 202211072057 A CN202211072057 A CN 202211072057A CN 115224365 A CN115224365 A CN 115224365A
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electrolyte
carbonate
mass
lithium
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赵小康
冀亚娟
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Eve Energy 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
    • H01M10/0567—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
    • H01M10/052—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
    • H01M10/0568—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
    • H01M10/056—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
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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 a graphite cathode system battery electrolyte and a lithium ion battery containing the same. The electrolyte comprises an organic solvent, lithium salt and an additive, wherein the organic solvent comprises a carbonate compound, the carbonate compound comprises propylene carbonate, and the additive comprises hexafluorobenzene. In the graphite cathode system, the co-intercalation problem of the propylene carbonate in the graphite can be effectively inhibited by adopting the propylene carbonate as a solvent and the hexafluorobenzene as an additive.

Description

Graphite cathode system battery electrolyte and lithium ion battery containing same
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a graphite cathode system battery electrolyte and a lithium ion battery containing the same.
Background
The lithium ion battery has the characteristics of high voltage, long charge-discharge cycle life, large specific energy, environmental friendliness and the like, and is widely applied to the fields of consumer electronics, new energy automobiles, aerospace and the like. With the continuous development of the diversification of the application scenes of the lithium ion battery, people have higher requirements on the low-temperature discharge performance of the ternary-graphite system lithium ion battery with high voltage and large specific energy in the environment of 20 ℃ below zero. The electrolyte is one of four main materials of the lithium ion battery, and in order to meet the requirement of low-temperature discharge performance of the lithium ion battery, the low-temperature lithium ion electrolyte becomes a research hotspot.
Through development for many years, at present, the electrolyte of the commercial power battery consists of three parts, namely an electrolyte, an organic solvent and an additive, wherein the solvent component generally selects a combined solvent formed by cyclic carbonate, linear carbonate and carboxylic ester compounds, and the combined solvent comprises Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl propionate, propyl acetate and other solvents which are matched with one another to meet the requirement of low-temperature discharge performance. Among them, the EC solvent, because of its high dielectric constant, can dissociate more lithium salts, improve conductivity and form a stable SEI film in the formation process, so that the battery has excellent cycle performance, and has now become an indispensable main solvent component of commercial electrolytes. However, since EC is solid at normal temperature, particularly at low temperature, the viscosity of the electrolyte increases, the conductivity decreases, and lithium ions cannot be normally inserted into or removed from the negative electrode, which causes a lithium precipitation phenomenon, and the low-temperature discharge performance deteriorates, affecting the life and safety of the battery. Compared with EC, the Propylene Carbonate (PC) has high dielectric constant and low melting point (-48.8 ℃), does not crystallize in the environment of-20 ℃, and is more favorable for the low-temperature discharge performance of the lithium ion battery. However, PC has a serious co-intercalation problem in the first charge-discharge process of a graphite cathode system, which causes graphite structure damage and influences battery performance.
CN103985905A discloses an electrolyte using propylene carbonate as a main solvent, sulfite is used as an additive of the lithium ion battery electrolyte in the electrolyte, and because sulfite has a higher reduction potential and is higher than the decomposition potential of propylene carbonate, a stable and compact SEI film is formed on the graphite surface before the sulfite decomposes before PC is decomposed in the first charging process, so that PC solvent is effectively inhibited from being jointly inserted into a graphite layer along with lithium ions, the initial discharge capacity and the cycle life of the battery are effectively improved, but side reactions are easily generated by the sulfite, and toxic gases are possibly released.
CN112582671A discloses a propylene carbonate electrolyte and a preparation method and application thereof, wherein the electrolyte further comprises chain carbonate and an isothiocyanate compound, and the propylene carbonate is used as a main solvent and matched with other components with specific content, so that the propylene carbonate is prevented from being embedded into graphite. But does not improve low temperature performance to a large extent.
Therefore, how to prepare the lithium ion battery electrolyte capable of improving low-temperature performance and inhibiting propylene carbonate from being embedded into a graphite cathode is an important research direction in the field.
Disclosure of Invention
The invention aims to provide a lithium ion battery electrolyte with high and low temperature performance and capability of inhibiting propylene carbonate from being embedded into a graphite cathode and a lithium ion battery containing the lithium ion battery electrolyte.
In order to achieve the purpose, the invention adopts the following technical scheme:
one of the purposes of the invention is to provide a graphite cathode system battery electrolyte, which comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a carbonate compound, the carbonate compound comprises propylene carbonate, and the additive comprises hexafluorobenzene.
The invention provides a propylene carbonate-based lithium ion battery electrolyte by adopting an EC-free system, namely propylene carbonate with a lower melting point (-48.8 ℃) as one of main solvents. The problem of co-intercalation of the propylene carbonate in graphite can be effectively solved by adopting the propylene carbonate as a solvent and the hexafluorobenzene as an additive in a graphite cathode system, because the hexafluorobenzene is reduced and decomposed before PC during formation, and an SEI film is formed on the surface of a graphite cathode, so that the damage of the structure of a graphite material caused by the fact that the propylene carbonate and lithium ions are embedded into a graphite layer together is inhibited.
As a preferred embodiment of the present invention, the carbonate compound further comprises any one or a combination of at least two of methyl ethyl carbonate, n-propyl propionate, dimethyl carbonate, carboxylate esters or fluorinated chain carbonate, wherein the combination is exemplified by, but not limited to: a combination of ethyl methyl carbonate and n-propyl propionate, a combination of n-propyl propionate and dimethyl carbonate, a combination of dimethyl carbonate and carboxylic acid esters or a combination of carboxylic acid esters and fluorocarbonic acid esters.
Preferably, the carboxylic acid esters include any one of ethyl acetate, ethyl propionate or propyl propionate or a combination of at least two thereof, wherein typical but non-limiting examples of the combination are: a combination of ethyl acetate and ethyl propionate, a combination of ethyl propionate and propyl propionate, or a combination of ethyl acetate and propyl propionate, and the like.
Preferably, any one or a combination of at least two of the fluorocarbonates trifluoroethyl carbonate, methyl trifluoroethyl carbonate, or fluoroethylene carbonate, wherein typical but non-limiting examples of the combination are: a combination of trifluoroethyl carbonate and methyltrifluoroethyl carbonate, a combination of methyltrifluoroethyl carbonate and fluoroethylene carbonate, a combination of trifluoroethyl carbonate and fluoroethylene carbonate, or the like.
In a preferred embodiment of the present invention, the mass fraction of the propylene carbonate in the electrolytic solution is 20 to 30% based on 100% by mass of the electrolytic solution, and the mass fraction may be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or the like, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned numerical range are also applicable.
Preferably, the total mass fraction of the ethyl methyl carbonate, the carboxylic acid esters and the fluorinated chain carbonates in the electrolyte solution is 40 to 60% based on 100% by mass of the electrolyte solution, wherein the mass fraction may be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% or 60%, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the total mass fraction of the n-propyl propionate and the dimethyl carbonate in the electrolyte is 10 to 20% based on 100% of the electrolyte, wherein the mass fraction may be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferred embodiment of the present invention, the additive further comprises any one or a combination of at least two of fluoroethylene carbonate, ethylene sulfate or vinylene carbonate, wherein typical but non-limiting examples of the combination are: a combination of fluoroethylene carbonate and ethylene sulfate, a combination of ethylene sulfate and vinylene carbonate, or a combination of fluoroethylene carbonate and vinylene carbonate, and the like.
Preferably, the additives include hexafluorobenzene, fluoroethylene carbonate and ethylene sulfate.
According to the invention, under the synergistic effect of hexafluorobenzene, vinylene carbonate and lithium bis (fluorosulfonyl) imide, a compact and low-impedance SEI film containing LiF is generated on the interface of the negative electrode, the lithium ions are rapidly inserted and removed in a low-temperature environment, the electrolyte is stable and free of solvent precipitation, and the low-temperature discharge performance of the battery is effectively improved.
In a preferred embodiment of the present invention, the fluoroethylene carbonate accounts for 5 to 8% by mass of the electrolyte solution based on 100% by mass of the electrolyte solution, wherein the mass fraction may be 5%, 6%, 7%, or 8%, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.
Preferably, the weight fraction of the ethylene sulfate in the electrolyte is 1 to 3% based on 100% by weight of the electrolyte, wherein the weight fraction may be 1%, 2%, 3% or the like, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the vinylene carbonate accounts for 0-3% of the electrolyte solution by mass based on 100% of the electrolyte solution, wherein the mass fraction can be 0%, 1%, 2% or 3%, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the mass fraction of the hexafluorobenzene in the electrolyte is 0.5-2% based on 100% of the electrolyte, wherein the mass fraction may be 0.5%, 1%, 1.5% or 2%, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferred embodiment of the present invention, the lithium salt includes any one of lithium hexafluorophosphate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethylsulfonyl imide, or lithium tetrafluoroborate, or a combination of at least two thereof, wherein the combination is exemplified by, typically but not limited to: a combination of lithium hexafluorophosphate and lithium bis (fluorosulfonyl) imide, a combination of lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide, a combination of lithium bis (trifluoromethylsulfonyl) imide and lithium tetrafluoroborate, or the like.
Preferably, the lithium salt includes lithium hexafluorophosphate and lithium bis-fluorosulfonylimide.
In a preferred embodiment of the present invention, the mass fraction of the lithium hexafluorophosphate in the electrolyte solution is 8 to 14% based on 100% of the electrolyte solution, wherein the mass fraction may be 8%, 9%, 10%, 11%, 12%, 13%, 14% or the like, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable.
Preferably, the mass fraction of the lithium bis (fluorosulfonyl) imide in the electrolyte solution is 1 to 3% based on 100% of the electrolyte solution, wherein the mass fraction may be 1%, 2%, or 3%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the mass fraction of the lithium bistrifluoromethylsulfonyl imide in the electrolyte solution is 0 to 3% based on 100% of the electrolyte solution, wherein the mass fraction may be 0%, 1%, 2%, or 3%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the mass fraction of the lithium tetrafluoroborate in the electrolyte solution is 0 to 3% based on 100% of the electrolyte solution, wherein the mass fraction may be 0%, 1%, 2%, or 3%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
The second purpose of the invention is to provide a lithium ion battery, which comprises the graphite cathode system battery electrolyte as described in the first purpose, and further comprises a positive electrode, a negative electrode and a diaphragm.
In a preferred embodiment of the present invention, the active material of the positive electrode includes any one of NCM523, NCM622, and NCM 811.
The NCM523, the NCM622 or the NCM811 in the invention are nickel-cobalt-manganese ternary positive electrode materials, and the NCM523 has higher specific capacity, lower cost and similar thermal stability, so that the NCM523 becomes a ternary material with the largest market consumption. The 0.1C specific capacity of the NCM622 type multielement material is about 180 mA.h/g, and is higher than that of NCM523 by about 10 mA.h/g. The 0.1C specific capacity of the NCM811 type multi-component material reaches more than 200 mA.h/g, is higher than that of NCM523 by 30 mA.h/g, the nickel content is increased, the cobalt content is reduced, and the NCM811 is expected to get rid of the raw material cost dilemma caused by the shortage of cobalt resources.
In a preferred embodiment of the present invention, the active material of the negative electrode is graphite.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, the propylene carbonate is used as a solvent, and hexafluorobenzene is used as an additive in a graphite cathode system, so that the co-intercalation of the propylene carbonate can be effectively inhibited, and the low-temperature performance of the battery is improved. According to the invention, a technology of solving the compatibility of propylene carbonate and a graphite cathode is adopted, under the mutual synergistic action of a cathode film forming additive, namely ethylene sulfate and lithium bis (fluorosulfonyl) imide, an SEI (solid electrolyte interphase) film which is compact and low in impedance and contains LiF is generated on a cathode interface, the insertion and extraction speed of lithium ions in a low-temperature environment is improved, an electrolyte is stable and is free of solvent precipitation, the low-temperature discharge performance of the battery is effectively improved, the capacitance can reach more than 890mAh at-20 ℃ under 0.05 ℃, and the capacity retention rate can reach more than 77%.
Drawings
FIG. 1 is a graph of 25 ℃ discharge capacity in examples 1 to 3 of the present invention and comparative example 2.
FIG. 2 is a graph showing discharge capacities at-20 ℃ in examples 1 to 3 of the present invention and comparative example 2.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a graphite cathode system battery electrolyte:
the electrolyte comprises the following components in percentage by mass, with the mass of the electrolyte as 100 percent: lithium hexafluorophosphate (LiPF) 6 ) 10%, lithium bis (fluorosulfonyl) imide (LiFSi) 3%, propylene Carbonate (PC) 21%, ethyl Methyl Carbonate (EMC) 45%, n-Propyl Propionate (PP) 12.5%, fluoroethylene carbonate (FEC) 6%, ethylene sulfate (DTD) 1% and Hexafluorobenzene (HFB) 1.5%.
Example 2
The embodiment provides a graphite cathode system battery electrolyte:
the electrolyte comprises the following components in percentage by mass, with the mass of the electrolyte as 100 percent: lithium hexafluorophosphate (LiPF) 6 ) 14%, lithium bis (fluorosulfonyl) imide (LiFSi) 3%, propylene Carbonate (PC) 20%, ethyl Methyl Carbonate (EMC) 40%, n-Propyl Propionate (PP) 10%, fluoroethylene carbonate (FEC) 8%, ethylene sulfate (DTD) 3%, and Hexafluorobenzene (HFB) 2%.
Example 3
The embodiment provides a graphite cathode system battery electrolyte:
the electrolyte comprises the following components in percentage by mass based on 100% of the mass of the electrolyte: lithium hexafluorophosphate (LiPF) 6 ) 8%, lithium bis (fluorosulfonyl) imide (LiFSi) 1%, propylene Carbonate (PC) 25.5%, ethyl Methyl Carbonate (EMC) 39%, n-Propyl Propionate (PP) 20%, fluoroethylene carbonate (FEC) 5%, ethylene sulfate (DTD) 1%, and Hexafluorobenzene (HFB) 0.5%.
Example 4
In this example, the conditions were the same as in example 1 except that the mass fraction of lithium hexafluorophosphate was changed to 13% and lithium difluorosulfonimide was not added.
Example 5
This example was carried out under the same conditions as in example 1 except that 1% by mass of vinylene carbonate (DTD) was replaced with 1% by mass of ethylene sulfate (CV).
Example 6
This example was conducted under the same conditions as example 1 except that the mass fraction of Ethyl Methyl Carbonate (EMC) was replaced with 57.5% and n-Propyl Propionate (PP) was not added.
Example 7
This example was carried out under the same conditions as example 1 except that 6% of fluoroethylene carbonate (FEC) was replaced with 7% and ethylene sulfate (DTD) was not added.
Example 8
This example was carried out under the same conditions as in example 1 except that Hexafluorobenzene (HFB) was replaced with 2.5% for 1.5% and fluoroethylene carbonate (FEC) was replaced with 5% for 6%.
Example 9
This example was carried out under the same conditions as in example 1 except that Hexafluorobenzene (HFB) was replaced with 0.1% at 1.5% and fluoroethylene carbonate (FEC) was replaced with 7.4% at 6%.
Example 10
The embodiment provides a graphite cathode system battery electrolyte:
the electrolyte comprises the following components in percentage by mass based on 100% of the mass of the electrolyte: lithium hexafluorophosphate (LiPF) 6 ) 7 percent; 2% of lithium bis (fluorosulfonyl) imide (LiFSI); lithium tetrafluoroborate (LiBF) 4 ) 2 percent; 25.5 percent of Propylene Carbonate (PC); ethyl Methyl Carbonate (EMC) 55%; fluoroethylene carbonate (FEC) 6%; 1% of ethylene sulfate (DTD); hexafluorobenzene (HFB) 1.5%.
Example 11
The embodiment provides a graphite cathode system battery electrolyte:
the electrolyte comprises the following components in percentage by mass, with the mass of the electrolyte as 100 percent: lithium hexafluorophosphate (LiPF) 6 ) 10.5 percent; 2% of lithium bis (fluorosulfonyl) imide (LiFSI); 25% of Propylene Carbonate (PC); ethyl Methyl Carbonate (EMC) 55%; fluoroethylene carbonate (FEC) 6%; hexafluorobenzene (HFB) 1.5%.
Comparative example 1
The comparative example was conducted under the same conditions as in example 1 except that Hexafluorobenzene (HFB) was not added and the mass fraction of the electrolyte was changed to 6% for 7.5% for fluoroethylene carbonate (FEC).
Comparative example 2
This comparative example provides a commercial lithium ion battery EC-based B99 electrolyte.
The electrolytes in examples 1 to 11 and comparative examples 1 to 2 were assembled into a ternary ion battery, and a room temperature capacity test and a cycle performance test were performed, and the test results are shown in table 1, wherein "/" represents that the battery is too much to perform a test. The discharge capacity at 25 ℃ of examples 1 to 3 and comparative example 2 of the present invention is shown in FIG. 1, and the discharge capacity at-20 ℃ is shown in FIG. 2.
The positive electrode of the battery is NCM811, the negative electrode of the battery is graphite, and the battery is a 396389 soft package battery.
(1) The method comprises the following steps of (1) calibrating the normal-temperature capacity of a 4.2V ternary lithium ion battery:
charging the 1C constant current and voltage to 4.2V, discharging the 1C constant current and voltage to 2.75V at the cut-off current of 0.05C and 1C constant current, and circulating for 3 weeks to obtain an average value;
(2) And (3) low-temperature discharge testing:
charging to 4.2V at constant temperature under constant current and constant voltage of 1C, stopping current of 0.05C to make the battery in full charge state, and then discharging to 2.2V under constant current of 1C at-20 ℃.
TABLE 1
Figure BDA0003829345550000091
Figure BDA0003829345550000101
The table can show that the example 1 can be used as the optimal scheme of the first table, the viscosity of the electrolyte can be effectively reduced when the PP content in the example 3 is 20%, although the additive content is slightly less than that in the example 1, the low-temperature performance is influenced because the side reaction is increased due to the higher additive content unlike that in the example 2, and the low-temperature discharge capacity retention rate reaches 72.11%.
Comparing examples 1, 4 and 10, it can be seen that in examples 4 and 10, liPF is caused 6 And LiBF 4 The dissociation property is much less than LiFSI, so that more lithium ions can not be dissociated at low temperature to satisfy the electric transmission, and the low-temperature discharge capacity retention rate is only about 63 percent and is much lower than 77.89 percent of the embodiment 1.
In example 1, compared with example 5, it is seen that in example 5, VC is used as a negative electrode film forming additive as compared with DTD, but the film forming resistance is large, which is not favorable for the low temperature performance of lithium ion transport in SEI film in low temperature environment.
Compared with the embodiment 1, the embodiment 6 and the embodiment 11 do not contain PP, so that the low-temperature performance is reduced, and the reduction is mainly caused by that the PP has low melting point and low viscosity, the fluidity of the electrolyte is effectively improved in the environment of-20 ℃, and the conductivity of the electrolyte is increased.
The comparison of examples 1, 7 and 11 shows that the low temperature performance is somewhat impaired compared to example 1 from examples 7 and 11 which do not contain DTD and example 2 which contains a higher amount of DTD.
As is clear from comparison between example 1 and example 8, in example 8, the resulting SEI film layer is too thick and unstable due to the excessive HFB content, resulting in a decrease in low-temperature performance.
As can be seen from the comparison of examples 1 and 9 with comparative examples 1-2, the HFB additive content in examples 9 and comparative examples 1-2 is too low to be 0.5%, resulting in severe gassing of the cells, which was not tested, while the remaining examples contained a certain amount of HFB. The reason is that hexafluorobenzene is reduced and decomposed before PC during formation, an SEI film is formed on the surface of the graphite cathode, and the damage to the graphite material structure caused by the fact that propylene carbonate and lithium ions are co-inserted into a graphite layer can be effectively inhibited.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. The graphite cathode system battery electrolyte is characterized by comprising an organic solvent, lithium salt and an additive, wherein the organic solvent comprises a carbonate compound, the carbonate compound comprises propylene carbonate, and the additive comprises hexafluorobenzene.
2. The electrolyte according to claim 1, wherein the carbonate compound further comprises any one or a combination of at least two of ethyl methyl carbonate, n-propyl propionate, dimethyl carbonate, carboxylic acid esters, or fluorinated chain carbonates;
preferably, the carboxylic acid esters include any one of ethyl acetate, ethyl propionate or propyl propionate or a combination of at least two thereof;
preferably, the fluorinated chain carbonates include any one of trifluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, or methyl hexafluoroisopropyl carbonate, or a combination of at least two thereof.
3. The electrolyte of claim 2, wherein the propylene carbonate accounts for 20-30% of the electrolyte by mass based on 100% of the electrolyte by mass;
preferably, the total mass of the methyl ethyl carbonate, the carboxylic acid esters and the fluorinated chain carbonates accounts for 40-60% of the mass of the electrolyte, based on 100% of the mass of the electrolyte;
preferably, the total mass of the n-propyl propionate and the dimethyl carbonate accounts for 10-20% of the electrolyte by taking the mass of the electrolyte as 100%.
4. The electrolyte of any one of claims 1-3, wherein the additive further comprises any one of fluoroethylene carbonate, ethylene sulfate, or vinylene carbonate, or a combination of at least two thereof;
preferably, the additives include hexafluorobenzene, fluoroethylene carbonate and vinylene carbonate.
5. The electrolyte according to claim 4, wherein the fluoroethylene carbonate accounts for 5 to 8% by mass of the electrolyte, based on 100% by mass of the electrolyte;
preferably, the weight percentage of the ethylene sulfate in the electrolyte is 1-3% based on 100% of the electrolyte;
preferably, the vinylene carbonate accounts for 0-3% of the electrolyte by mass based on 100% of the electrolyte by mass;
preferably, the mass fraction of the hexafluorobenzene in the electrolyte is 0.5-2% by mass based on 100% by mass of the electrolyte.
6. The electrolyte of any one of claims 1-5, wherein the lithium salt comprises any one of lithium hexafluorophosphate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethylsulfonyl imide, or lithium tetrafluoroborate, or a combination of at least two thereof;
preferably, the lithium salt includes lithium hexafluorophosphate and lithium bis-fluorosulfonylimide.
7. The electrolyte of claim 6, wherein the lithium hexafluorophosphate accounts for 8 to 14% by mass of the electrolyte based on 100% of the electrolyte;
preferably, the mass fraction of the lithium bis (fluorosulfonyl) imide in the electrolyte is 1-3% based on 100% of the electrolyte;
preferably, the lithium bis (trifluoromethyl) sulfonyl imide accounts for 0-3% of the electrolyte by taking the electrolyte as 100%;
preferably, the mass fraction of the lithium tetrafluoroborate in the electrolyte is 0-3% based on 100% of the electrolyte.
8. A lithium ion battery comprising the graphite negative electrode system battery electrolyte according to any one of claims 1 to 7, and further comprising a positive electrode, a negative electrode and a separator.
9. The lithium ion battery of claim 8, wherein the active material of the positive electrode comprises any one of NCM523, NCM622, or NCM 811.
10. The lithium ion battery according to claim 8 or 9, wherein the active material of the negative electrode is graphite.
CN202211072057.3A 2022-09-02 2022-09-02 Graphite cathode system battery electrolyte and lithium ion battery containing same Pending CN115224365A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116565324A (en) * 2023-07-05 2023-08-08 华中科技大学 Lithium ion battery electrolyte and lithium ion battery comprising same

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116565324A (en) * 2023-07-05 2023-08-08 华中科技大学 Lithium ion battery electrolyte and lithium ion battery comprising same
CN116565324B (en) * 2023-07-05 2023-10-20 华中科技大学 Lithium ion battery electrolyte and lithium ion battery comprising same

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