CN116315096A - High-voltage flame-retardant electrolyte, preparation method thereof and lithium ion battery - Google Patents

High-voltage flame-retardant electrolyte, preparation method thereof and lithium ion battery Download PDF

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CN116315096A
CN116315096A CN202310209842.7A CN202310209842A CN116315096A CN 116315096 A CN116315096 A CN 116315096A CN 202310209842 A CN202310209842 A CN 202310209842A CN 116315096 A CN116315096 A CN 116315096A
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carbonate
lithium
retardant electrolyte
electrolyte
additive
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洪波
王梦然
黄泽彧
王麒羽
史晨阳
刘方岩
陈龙
赖延清
张治安
李思敏
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Central South University
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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
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    • 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
    • H01M10/0569—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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Abstract

The invention provides a high-voltage flame-retardant electrolyte, which comprises an additive, a fluorocarbonate solvent and lithium salt, wherein the additive is one or more selected from compounds with a structure shown as the following formula (I) or formula (II):
Figure ZY_1
formula (I); wherein R is 1 、R 2 、R 3 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing compounds;
Figure ZY_2
formula (II); wherein X is 1 、X 2 、X 3 、X 4 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing alkanes. The electrolyte has excellent lithium ion conductivity, high voltage resistance, flame resistance, safety performance and electrochemical performance.

Description

High-voltage flame-retardant electrolyte, preparation method thereof and lithium ion battery
Technical Field
The invention belongs to the field of organic electrolyte of lithium ion batteries, and particularly relates to a high-voltage flame-retardant electrolyte, a preparation method thereof and a lithium ion battery.
Background
With development and utilization of new energy, lithium ion batteries are widely popularized as an energy storage device with excellent performance, and are successfully applied to portable electronic equipment, electric automobiles, hybrid electric automobiles and plug-in hybrid electric automobiles. The lithium ion battery electrolyte is one of core materials in the lithium ion battery, and plays a role of a bridge for transmitting charges between the positive electrode and the negative electrode, and almost participates in all reaction processes occurring in the battery. Currently, there are three main technical routes for the development of electrolytes, liquid electrolytes, polymer electrolytes and solid inorganic electrolytes. Because of the limitations of ionic conductivity and anode-cathode interface compatibility, most of electrolytes used in lithium ion batteries are flammable organic carbonate system electrolytes.
In recent years, safety accidents caused by misuse of lithium ion batteries frequently occur. In general, in the abusive state such as overcharge, overdischarge, short circuit and collision, chemical energy stored in the battery can be quickly converted into heat energy to destroy the solid electrolyte membrane on the surfaces of the positive electrode and the negative electrode in the battery, so that severe chemical reaction occurs between components in the electrolyte and the positive electrode and the negative electrode, and the decomposition of an organic solvent in the electrolyte generates hydroxyl radicals and hydrogen radicals, and the hydroxyl radicals undergo chain reaction to generate a large amount of heat, and the generated heat promotes the reaction between the electrolyte and the lithium-intercalation negative electrode to be aggravated, so that the safety of the battery is finally affected. It is found that the use of the flame-retardant solvent to partially or completely replace the carbonic ester in the electrolyte can make the combustible electrolyte become flame-retardant or non-combustible, reduce the heat release amount and the self-heat release rate of the battery, and improve the thermal stability of the electrolyte. Currently, many nonflammable solvents are being studied including phosphates, fluorosolvents, and phosphazenes.
Wherein, the fluoro solvent contains C-F bond which is more stable than C-H bond structure, which reduces the generation of hydrogen free radical at high temperature. Among them, fluorocarbonates are the most widely used in the battery field. Fluorocarbonates tend to have lower HOMO and LUMO levels than carbonate solvents, and are less resistant to reduction, which exhibit greater oxidation resistance in electrochemistry. However, the CEI film formed by the fluorocarbons alone has single component and is rich in LiF with low ion conductivity, and the performance under high current density is worried, so that the high voltage performance of the fluorocarbons cannot be fully exerted. Patent CN109830752a reports a non-flammable high-voltage lithium ion battery electrolyte based on fluorocarbonate, which has excellent electrochemical performance, high positive electrode capacity retention rate and good cycling stability, but does not regulate the composition of a CEI film, and cannot realize high-current operation of the battery. And by introducing a high-voltage electrolyte additive into the fluoroelectrolyte, the composition of the CEI film is enriched, the ionic conductivity and stability of an interface are improved, the CEI film with good dynamics is obtained, and the electrochemical performance of the CEI film is further improved. CN 114695961a discloses a lithium ion battery additive, which improves the high-temperature and high-pressure cycle performance of a battery by adding a carbamide compound, and the additive is decomposed under high pressure to form a positive electrode protection film, reduces the contact between electrolyte and an electrode, and inhibits the oxidative decomposition and parasitic reaction of the electrolyte, but the decomposition product of the additive has single function, cannot improve the lithium ion conductivity of a positive electrode CEI film, and has no flame retardant function and poor safety performance.
In summary, the current small regulation and control of CEI film of the fluorocarbonate-based electrolyte limits the high-voltage advantage of the fluorocarbonate-based electrolyte, and it is necessary to develop a fluorocarbonate-based electrolyte with excellent film forming performance.
Disclosure of Invention
In order to solve the problems, the invention provides a high-voltage flame-retardant electrolyte, a preparation method thereof and a lithium ion battery.
Aiming at the technical problems, the following solution is provided:
one of the purposes of the invention is to provide a high-voltage flame-retardant electrolyte, which comprises a high-voltage electrolyte additive, a fluorocarbonate solvent and lithium salt.
In the above electrolyte, the high-voltage electrolyte additive is selected from one or more of compounds having a structure represented by the following formula (i) or formula (ii):
Figure SMS_1
formula (I);
wherein R is 1 、R 2 、R 3 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing compounds;
Figure SMS_2
formula (II);
wherein X is 1 、X 2 、X 3 、X 4 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing alkanes.
Preferably, in formula (I), the R 1 、R 2 、R 3 Each independently selected from alkyl groups having 1 to 5 carbon atoms, alkoxy groups, and fluorine-containing compounds; in the formula (2), the X 1 、X 2 、X 3 、X 4 Each independently selected from alkyl groups having 1 to 5 carbon atoms, alkoxy groups, and fluorine-containing alkanes.
Including but not limited to additive 1:
Figure SMS_3
additive 2: />
Figure SMS_4
Additive 3: />
Figure SMS_5
Additive 4: />
Figure SMS_6
Additive 5:
Figure SMS_7
additive 6: />
Figure SMS_8
。
Preferably, the mass percentage of the additive in the electrolyte is 0.01-2%, and more preferably 0.8-1.2%;
preferably, the fluorinated carbonate solvent includes fluorinated cyclic carbonate and fluorinated chain carbonate, and more preferably, the volume ratio of fluorinated cyclic carbonate to fluorinated chain carbonate is 1-5:5-9, and still more preferably, 3-4: 6-7.
Preferably, the fluorinated cyclic carbonate is at least one of fluoroethylene carbonate (FEC), bis-fluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC), and more preferably fluoroethylene carbonate.
Preferably, the fluorinated chain carbonate is at least one of trifluoroethyl methyl carbonate (FEMC), ditrifluoroethyl carbonate (DFDEC), fluoroethyl methyl carbonate (AFEMC), methyl Trifluoroacetate (TFMA), ethyl Trifluoroacetate (TFEA), ethyl Difluoroacetate (DFEA), and methyl Difluoroacetate (DFMA), and more preferably, trifluoroethyl methyl carbonate.
Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (oxalato) borate, and lithium difluorooxalato borate, and more preferably lithium hexafluorophosphate.
Preferably, the lithium salt concentration is 0.5 to 1.5mol/L, more preferably 0.8 to 1mol/L.
The second object of the present invention is to provide a method for preparing the high-voltage flame-retardant electrolyte, which comprises the following steps:
s1, uniformly mixing fluorinated cyclic carbonate and fluorinated chain carbonate according to a volume ratio to obtain a mixed solution A;
s2, adding the lithium salt into the mixed solution A according to the molar concentration, and uniformly mixing to obtain a mixed solution B;
and S3, adding the additive into the mixed solution B according to the mass ratio, and uniformly mixing to obtain the additive.
A third object of the present invention is to provide a lithium ion battery comprising the above high voltage flame retardant electrolyte.
Compared with the prior art, the invention has the following beneficial effects:
the invention adds special additive into the high-voltage electrolyte, and the additive is oxidized to generate Li with high lithium ion conductivity 3 N, liF generated by oxidation with the fluorocarbonate solvent can form a crystal boundary, the lithium ion conductivity of a LiF-rich interface is improved, and cyano (-CN) in the additive has the effect of inhibiting the dissolution of transition metal under high voltage, so that the interface stability is improved. The electrolyte provided by the invention can obtain a solid electrolyte membrane (CEI membrane) with high stability, low impedance and strong protection effect, so that the high-pressure resistance of the electrolyte in practical application is improved, and meanwhile, the electrolyte has both safety performance and electrochemical performance by matching with the flame retardant property of the fluorocarbonate solvent. The lithium ion battery containing the electrolyte has stable long-cycle capacity and excellent intrinsic safety.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flame retardant property of the high voltage flame retardant electrolyte prepared in example 1, wherein (a) is an ignition picture and (b) is a picture 5s after ignition;
FIG. 2 is a flame retardant property of the conventional carbonate electrolyte prepared in comparative example 1, wherein (a) is an ignition picture and (b) is a picture 5s after ignition;
FIG. 3 is the cycle performance of the button cell prepared in example 1;
FIG. 4 is a microstructure of the electrode after cycling of the button cell prepared in example 1;
FIG. 5 is a microstructure of the electrode after cycling of the button cell prepared in comparative example 1;
table 1 shows the electrochemical impedance after 3 cycles of the button cells prepared in example 1, comparative example 2, and comparative example 3.
Detailed Description
The invention will be described more fully hereinafter with reference to the accompanying drawings and preferred embodiments in order to facilitate an understanding of the invention, but the scope of the invention is not limited to the following specific embodiments.
Example 1
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml trifluoroethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 1:
Figure SMS_9
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 182.2 mAh/g, and after 500 circles of cycle test, the discharge capacity still remains 170.8 mAh/g.
Example 2
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml trifluoroethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 2:
Figure SMS_10
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive and negative electrodes: weighing 1 gram of lithium cobaltate anode material, 1:1:1 of conductive agent and PVDF (polyvinylidene fluoride) in mass ratio, adding a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP (N-methyl pyrrolidone) as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5 x 5cm by using a die for later use; weighing 1 gram of graphite anode material, conductive agent and PVDF according to the mass ratio of 8:1:1, adding into a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on copper foil, placing into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets of 5 x 5cm for later use by using a die.
The soft-package dry battery cell is manufactured by taking high-voltage lithium cobalt oxide as an anode, graphite as a cathode and a microporous polyethylene film as a diaphragm. And (5) drying the dry battery cell in an oven at 80-85 ℃ for 24 hours, and then transferring the dry battery cell into a glove box for standby. And (3) injecting the high-voltage flame-retardant electrolyte into the dried dry battery cell, standing for 24 hours, pre-charging, forming once, sealing, and forming twice to obtain the experimental battery of the embodiment 2. In the charge-discharge interval of 2.75-4.4V, a charge-discharge test is carried out with a constant current of 200 mA, the discharge capacity of the first circle reaches 219 mAh, after 100 circles of cycle test, the discharge capacity still has 217 mAh, and the capacity retention rate is 99.09%.
Example 3
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.8 ml trifluoro ethylene carbonate and 1.2 ml trifluoro ethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) of lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 3:
Figure SMS_11
and 0.04g (2 wt%) of additive 2: />
Figure SMS_12
And uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive and negative electrodes: weighing 1 gram of lithium cobaltate anode material, 1:1:1 of conductive agent and PVDF (polyvinylidene fluoride) in mass ratio, adding a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP (N-methyl pyrrolidone) as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5 x 5cm by using a die for later use; weighing 1 gram of graphite anode material, conductive agent and PVDF according to the mass ratio of 8:1:1, adding into a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on copper foil, placing into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets of 5 x 5cm for later use by using a die.
The soft-package dry battery cell is manufactured by taking high-voltage lithium cobalt oxide as an anode, graphite as a cathode and a microporous polyethylene film as a diaphragm. And (5) drying the dry battery cell in an oven at 80-85 ℃ for 24 hours, and then transferring the dry battery cell into a glove box for standby. And (3) injecting the high-voltage flame-retardant electrolyte into the dried dry battery cell, standing for 24 hours, pre-charging, forming once, sealing, and forming twice to obtain the experimental battery of the embodiment 3. In the charge-discharge interval of 2.75-4.4V, a charge-discharge test is carried out with a constant current of 200 mA, the discharge capacity of the first circle reaches 215 mAh, and after 100 circles of cycle test, the discharge capacity still has 212 mAh, and the capacity retention rate is 98.60%.
Example 4
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate, 0.7 ml fluoroethyl methyl carbonate and 0.7 ml bis-trifluoroethyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.03 g (1.5 wt%) additive 4:
Figure SMS_13
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive and negative electrodes: weighing 1 gram of lithium cobaltate anode material, 1:1:1 of conductive agent and PVDF (polyvinylidene fluoride) in mass ratio, adding a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP (N-methyl pyrrolidone) as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for later use; weighing 1 gram of graphite anode material, conductive agent and PVDF according to the mass ratio of 8:1:1, adding into a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on copper foil, placing into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for standby.
The soft-package dry battery cell is manufactured by taking high-voltage lithium cobalt oxide as an anode, graphite as a cathode and a microporous polyethylene film as a diaphragm. And (5) drying the dry battery cell in an oven at 80-85 ℃ for 24 hours, and then transferring the dry battery cell into a glove box for standby. And (3) injecting the high-voltage flame-retardant electrolyte into the dried dry battery cell, standing for 24 hours, pre-charging, forming once, sealing, and forming twice to obtain the experimental battery of the embodiment 4. In the charge-discharge interval of 2.75-4.4V, a charge-discharge test is carried out with a constant current of 200 mA, the discharge capacity of the first circle reaches 214 mAh, and after 100 circles of cycle test, the discharge capacity still has 201 mAh, and the capacity retention rate is 93.92%.
Example 5
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate, 0.7 ml trifluoroethyl methyl carbonate and 0.7 ml bis trifluoroethyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.03 g (1.5 wt%) of additive 5:
Figure SMS_14
and 0.03 g (1.5 wt%) additive 6: />
Figure SMS_15
And uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive and negative electrodes: weighing 1 gram of lithium cobaltate anode material, 1:1:1 of conductive agent and PVDF (polyvinylidene fluoride) in mass ratio, adding a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP (N-methyl pyrrolidone) as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for later use; weighing 1 gram of graphite anode material, conductive agent and PVDF according to the mass ratio of 8:1:1, adding into a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on copper foil, placing into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for standby.
The soft-package dry battery cell is manufactured by taking high-voltage lithium cobalt oxide as an anode, graphite as a cathode and a microporous polyethylene film as a diaphragm. And (5) drying the dry battery cell in an oven at 80-85 ℃ for 24 hours, and then transferring the dry battery cell into a glove box for standby. And (3) injecting the high-voltage flame-retardant electrolyte into the dried dry battery cell, standing for 24 hours, pre-charging, forming once, sealing, and forming twice to obtain the experimental battery of the embodiment 4. In the charge-discharge interval of 2.75-4.4V, a charge-discharge test is carried out with a constant current of 200 mA, the discharge capacity of the first circle reaches 201 mAh, and after 100 circles of cycle test, the discharge capacity is still 198 mAh, and the capacity retention rate is 98.51%.
Example 6
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate, 0.7 ml trifluoroethyl methyl carbonate and 0.7 ml bis trifluoroethyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.03 g (1.5 wt%) additive 6:
Figure SMS_16
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive and negative electrodes: weighing 1 gram of lithium cobaltate anode material, 1:1:1 of conductive agent and PVDF (polyvinylidene fluoride) in mass ratio, adding a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP (N-methyl pyrrolidone) as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for later use; weighing 1 gram of graphite anode material, conductive agent and PVDF according to the mass ratio of 8:1:1, adding into a mortar, grinding to be uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on copper foil, placing into an 80 ℃ oven for baking for 10 hours, and finally cutting into anode sheets with the length of 5cm by using a die for standby.
The soft-package dry battery cell is manufactured by taking high-voltage lithium cobalt oxide as an anode, graphite as a cathode and a microporous polyethylene film as a diaphragm. And (5) drying the dry battery cell in an oven at 80-85 ℃ for 24 hours, and then transferring the dry battery cell into a glove box for standby. And (3) injecting the high-voltage flame-retardant electrolyte into the dried dry battery cell, standing for 24 hours, pre-charging, forming once, sealing, and forming twice to obtain the experimental battery of the embodiment 4. In the charge-discharge interval of 2.75-4.4V, a charge-discharge test is carried out with a constant current of 200 mA, the discharge capacity of the first circle reaches 201 mAh, and after 100 circles of cycle test, the discharge capacity is still 198 mAh, and the capacity retention rate is 98.51%.
Example 7
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml trifluoroethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.574 and g (1 mol/L) lithium bistrifluoromethylsulfonyl imide into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 1:
Figure SMS_17
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 181.3 mAh/g, and the discharge capacity still remains 167.1 mAh/g after 500 circles of cycle test.
Example 8
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml ethyl trifluoroacetate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 1:
Figure SMS_18
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 179.8 mAh/g, and after 500 circles of cycle test, the discharge capacity still remains 165.3 mAh/g.
Example 9
A lithium ion battery high-voltage flame-retardant electrolyte comprises the following steps:
(1) Uniformly stirring 0.6 ml trifluoro propylene carbonate and 1.4 ml trifluoro ethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of additive 1:
Figure SMS_19
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 183.4 mAh/g, and after 500 circles of cycle test, the discharge capacity still remains 162.2 mAh/g.
Comparative example 1
A conventional carbonate electrolyte for a lithium ion battery is prepared by the following steps:
(1) Uniformly stirring 0.6 ml ethylene carbonate, 0.7 ml methyl ethyl carbonate and 0.7 ml diethyl carbonate by magnetic force to obtain a mixed solution A;
(2) And adding 0.304g (1 mol/L) lithium hexafluorophosphate into the mixed solution A, and magnetically stirring uniformly to obtain the conventional carbonate electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 181.5 mAh/g, and the discharge capacity is 60.3 mAh/g after 500 circles of cycle test.
Comparative example 2
The lithium ion battery flame-retardant electrolyte comprises the following preparation steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml trifluoroethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.574 and g (1 mol/L) lithium bistrifluoromethylsulfonyl imide into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 180.3 mAh/g, and the discharge capacity is 140.1 mAh/g after 500 circles of cycle test.
Comparative example 3
The lithium ion battery flame-retardant electrolyte comprises the following preparation steps:
(1) Uniformly stirring 0.6 ml fluoroethylene carbonate and 1.4 ml trifluoroethyl methyl carbonate by magnetic force to obtain a mixed solution A;
(2) Adding 0.574 and g (1 mol/L) lithium bistrifluoromethylsulfonyl imide into the mixed solution A, and magnetically stirring uniformly to obtain a mixed solution B;
(3) To mixture B was added 0.02g (1 wt%) of 1,3, 6-hexanetrinitrile additive:
Figure SMS_20
and uniformly mixing to obtain the high-voltage flame-retardant electrolyte.
Preparation of positive electrode: weighing 1 gram of lithium cobaltate anode material, 1 gram of conductive agent and 1 gram of PVDF according to the mass ratio of 8:1:1, adding a mortar, grinding until the mixture is uniformly dispersed, adding 100 drops of NMP as a dispersing agent, uniformly coating the mixed slurry on an aluminum foil, putting the aluminum foil into an 80 ℃ oven for baking for 10h, and finally cutting into anode plates with the radius of 5 mm by using a die for later use;
the button half cell is manufactured by taking lithium cobaltate as an anode, a lithium sheet as a cathode and a microporous polyethylene film as a diaphragm. In the charge-discharge interval of 2.75-4.5V, the charge-discharge test is carried out at a constant multiplying power of 1C, the discharge gram capacity of the first circle reaches 183.5 mAh/g, and the discharge capacity is 152.8 mAh/g after 500 circles of cycle test.
FIG. 1 is a graph showing the flame retardant properties of the high voltage flame retardant electrolyte prepared in example 1, wherein (a) is an ignition picture, (b) is a picture 5 seconds after ignition, which shows that the electrolyte cannot burn when exposed to an open flame, and FIG. 2 is a graph showing the flame retardant properties of the conventional carbonate electrolyte prepared in comparative example 1, wherein (a) is an ignition picture, (b) is a picture 5 seconds after ignition, which shows that the electrolyte can burn when exposed to a flame, indicating that the high voltage flame retardant electrolyte prepared in example 1 hasHas excellent flame retardant property. Fig. 3 shows the cycle performance of the button cell prepared in example 1, and the capacity retention rate after 500 cycles is up to 88% or more, indicating that the present invention has excellent high-voltage electrochemical stability. Fig. 4 shows the microscopic morphology of the electrode after 500 circles of the button cell cycle prepared in example 1, the lithium cobaltate particles are complete, and fig. 5 shows the microscopic morphology of the electrode after 500 circles of the button cell cycle prepared in comparative example 1, the lithium cobaltate particles are broken, which shows that the CEI film derived from the high-voltage flame-retardant electrolyte prepared in example 1 has good protection effect on the lithium cobaltate particles. Table 1 shows the impedances after 3 cycles of the button cells prepared in example 1, comparative example 2 and comparative example 3, and the membrane resistance R of example 1 is shown in Table 1 f 12.0Ω, film resistance R of comparative example 2 f 40.5 omega, showing that the addition of the additive effectively improves the lithium ion conductivity of the solid electrolyte membrane, comparative example 3 membrane resistance R f 39.9Ω, indicating that commercial nitrile additives cannot effectively enhance the lithium ion conductivity of the CEI film; it can be seen that the present additive is effective in enhancing the lithium ion conductivity of CEI films relative to commercial nitrile additives, presumably because the additives of the present invention are oxidized to form Li of high lithium ion conductivity 3 And N, the LiF generated by oxidation with the fluorocarbonate solvent can form a crystal boundary, so that the lithium ion conductivity of the LiF-rich interface is improved.
TABLE 1
Rf Rct
Example 1 12.0 Ω 83.2 Ω
Comparative example 1 27.6 Ω 123.9 Ω
Comparative example 2 40.5 Ω 110.3 Ω
Comparative example 3 39.9 Ω 108.4 Ω
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims (10)

1. A high voltage flame retardant electrolyte, comprising an additive, a fluorocarbonate solvent and a lithium salt, wherein the additive has one or more selected from the compounds with the structures shown in the following formula (I) or formula (II):
Figure QLYQS_1
formula (I);
wherein R is 1 、R 2 、R 3 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing compounds;
Figure QLYQS_2
formula (II);
wherein X is 1 、X 2 、X 3 、X 4 Each independently selected from alkyl groups having 1 to 10 carbon atoms, alkoxy groups, and fluorine-containing alkanes.
2. The high voltage flame retardant electrolyte of claim 1, wherein the fluorocarbonate solvent comprises a fluorocyclic carbonate and a fluorochain carbonate.
3. The high-voltage flame-retardant electrolyte according to claim 1 or 2, wherein the mass percentage of the additive in the electrolyte is 0.01-2%.
4. The high-voltage flame-retardant electrolyte according to claim 2, wherein the volume ratio of the fluorinated cyclic carbonate to the fluorinated chain carbonate is 1-5:5-9.
5. The high voltage flame retardant electrolyte of claim 2 wherein the fluorinated cyclic carbonate is at least one of fluoroethylene carbonate, bis-fluoroethylene carbonate, and tri-fluoroethylene carbonate;
the fluoro chain carbonate is at least one of trifluoroethyl methyl carbonate, bis-trifluoroethyl carbonate, fluoroethyl methyl carbonate, methyl trifluoroacetate, ethyl difluoroacetate and methyl difluoroacetate.
6. The high voltage flame retardant electrolyte of claim 1 or 2, wherein the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethylsulfonyl imide, lithium bis-oxalato borate, and lithium difluoro-oxalato borate.
7. The high-voltage flame-retardant electrolyte according to claim 1 or 2, wherein the lithium salt concentration is 0.5-1.5 mol/L.
8. The high voltage flame retardant electrolyte according to claim 1 or 2, wherein in the formula (i), R 1 、R 2 、R 3 Each independently selected from alkyl groups having 1 to 5 carbon atoms, alkoxy groups, and fluorine-containing compounds;
in the formula (II), X 1 、X 2 、X 3 、X 4 Each independently selected from alkyl groups having 1 to 5 carbon atoms, alkoxy groups, and fluorine-containing alkanes.
9. The method for preparing a high voltage flame retardant electrolyte according to any one of claims 2-8, comprising the steps of:
s1, uniformly mixing the fluorinated cyclic carbonate and the fluorinated chain carbonate according to a volume ratio to obtain a mixed solution A;
s2, adding the lithium salt into the mixed solution A according to the molar concentration, and uniformly mixing to obtain a mixed solution B;
and S3, adding the additive into the mixed solution B according to the mass ratio, and uniformly mixing to obtain the additive.
10. A lithium ion battery comprising the high voltage flame retardant electrolyte of any one of claims 1-9.
CN202310209842.7A 2023-03-07 2023-03-07 High-voltage flame-retardant electrolyte, preparation method thereof and lithium ion battery Pending CN116315096A (en)

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