CN116632354A - Lithium battery and electrolyte for lithium battery - Google Patents

Lithium battery and electrolyte for lithium battery Download PDF

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CN116632354A
CN116632354A CN202310455319.2A CN202310455319A CN116632354A CN 116632354 A CN116632354 A CN 116632354A CN 202310455319 A CN202310455319 A CN 202310455319A CN 116632354 A CN116632354 A CN 116632354A
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lithium
electrolyte
additive
carbonate
film
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时兰兰
许海萍
付敏
乔跃鹏
苏敏
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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
    • H01M10/056—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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • 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

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Abstract

The application discloses a lithium battery and electrolyte for the lithium battery, and relates to the technical field of lithium battery preparation. In the first charge and discharge process of the liquid lithium ion battery, the electrode material and the electrolyte react on a solid-liquid phase interface, the electrolyte is decomposed to form a passivation layer covering the surface of the electrode material, wherein the passivation layer on the surface of the positive electrode is called as CEI film, the passivation layer on the surface of the negative electrode is called as SEI film, the cyclic silazane compound is rich in rich Si-N groups, ring-opening polymerization can be carried out on the surface of the positive electrode to form a compact and stable CEI film, and meanwhile, the breaking of Si-O bonds is favorable for the film formation of the additive on the negative electrode, so that the stability of the CEI film is improved.

Description

Lithium battery and electrolyte for lithium battery
Technical Field
The application relates to the technical field of lithium battery preparation, in particular to a lithium battery and electrolyte for the lithium battery.
Background
The lithium ion battery has the advantages of high energy density, high working voltage, no memory effect, no pollution and the like, and becomes an important way for relieving the fossil energy crisis and the environmental pollution crisis in the automobile industry; the ternary material gradually becomes a research hot spot due to the advantages of high specific capacity, low cost, excellent safety and the like, and is considered as a lithium ion power battery positive electrode material with great application prospect. But ternary material due to Ni 3+ And Co 3+/4+ The crystal lattice O is separated from the crystal lattice in the high-lithium removal state, especially in the high-temperature cycle and long-cycle life, so that the positive electrode material structure is caused to change phase and even collapse, and the cycle is caused to be poor; in addition, the commercial lithium ion battery electrolyte currently used generally takes the dominant role of a carbonate solvent with high viscosity and high dielectric constant, especially Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate (DMC) and the like, and the dissolution of elemental oxygen and transition metals released from ternary materials can further aggravate the decomposition of the carbonate solvent, especially Ethylene Carbonate (EC) -based electrolyte, under a high-voltage system, so that a series of problems of poor high-temperature performance, serious gas production, potential safety hazard and the like of the lithium ion battery are caused. It is therefore desirable to develop an electrolyte suitable for use in high voltage lithium ion batteries.
CN109346761a discloses a lithium ion battery, lithium ion battery electrolyte and preparation method thereof. The patent effectively improves the high-temperature storage performance and the high-temperature cycle performance of the lithium ion battery by adding a trimethylsilyl iminodiacetonitrile additive with Si-N and C-N functional groups into the battery electrolyte, wherein the dinitrile compound containing Si-N bond and carbon-nitrogen triple bond is used together, but when the nitrile compound is used as the additive, the following components are always present: large gas volume (the main component of the gas is ethylene), temperature sensitivity (high energy consumption in low-temperature preservation), large film forming impedance and the like.
CN108701864a discloses a nonaqueous electrolyte for lithium batteries, which improves the stability of high-temperature storage at 70 ℃ or higher and reduces the storage gas yield by adding a silane compound, a cyclic sulfonic acid compound and a cyclic sulfate compound mixed additive to the electrolyte, but this solution causes unstable factors such as higher impedance, higher acid value of the electrolyte in high-temperature storage, and the removal capacity and low-temperature power performance of water and generated HF are not mentioned, so there is a need for improvement.
Disclosure of Invention
1. Technical problem to be solved by the application
Aiming at the technical problems, the application provides a lithium battery and an electrolyte for the lithium battery, wherein the cyclic silazane compound is rich in rich Si-N groups, ring-opening polymerization can be carried out on the surface of a positive electrode to form a compact and stable CEI film, and meanwhile, the breaking of Si-O bonds is beneficial to the film formation of the additive on a negative electrode, so that the stability of the CEI film is improved.
2. Technical proposal
In order to solve the problems, the technical scheme provided by the application is as follows: the electrolyte for the lithium battery comprises lithium salt, an organic solvent and an additive, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorosulfimide and lithium bis (trifluoromethylsulfonyl) imide, the organic solvent is at least two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, propyl acetate and propyl propionate, the additive comprises an anode film-forming additive, a cathode film-forming additive and a silazane additive, and the silazane additive is a cyclic silazane additive, and has the structural formula:
wherein R1-R8 are one or more of alkyl groups with 1-7 carbon atoms and derivatives thereof.
Optionally, the cyclic silazane compound is selected from one or two of formulas S1 and S2:
optionally, the positive film forming additive is one or more of propane sultone, vinyl sulfate and methane disulfonic acid methylene.
Optionally, the negative electrode film-forming additive comprises one or two of vinylene carbonate and fluoroethylene carbonate.
Optionally, the cyclic silazane-containing compound accounts for 0.01% -10% of the total mass of the electrolyte.
Optionally, the concentration of the lithium salt in the organic solvent is 0.8-1.5 mol/L.
The application also discloses a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm and the electrolyte for the lithium battery, wherein the positive plate comprises a positive active material, a conductive agent, a current collector and a binder, and the negative plate comprises a negative active material, a conductive agent, a current collector and a binder.
Optionally, the positive electrode active material is one or more of lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material and lithium-rich manganese material.
Optionally, the negative electrode active material is one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon carbon and silica.
Optionally, the membrane is any one of a polypropylene membrane, a polyethylene/polypropylene double-layer composite membrane, a polyimide electrostatic spinning membrane, a polypropylene/polyethylene/polypropylene three-layer composite membrane, a ceramic membrane and a PVDF glue coating membrane.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the application has the following beneficial effects:
(1) The electrolyte for the lithium battery provided by the embodiment of the application forms a stable solid electrolyte membrane on the surface of an electrode by adding the multifunctional additive, thereby realizing the purpose of long service life of the lithium ion battery. In the first charge and discharge process of the liquid lithium ion battery, an electrode material reacts with electrolyte on a solid-liquid phase interface, the electrolyte is decomposed to form a passivation layer covering the surface of the electrode material, wherein the passivation layer on the surface of the positive electrode is called as a CEI film, the passivation layer on the surface of the negative electrode is called as an SEI film, the cyclic silazane compound is rich in rich Si-N groups, ring-opening polymerization can be carried out on the surface of the positive electrode to form a compact and stable CEI film, meanwhile, the breaking of Si-O bonds is beneficial to the film formation of the additive on the negative electrode, the stability of the CEI film is improved, and the passivation layer (the positive electrode is the CEI film and the negative electrode is the SEI film) has electronic insulation characteristics, but lithium ions are allowed to be freely embedded and extracted. Meanwhile, the solvent molecules are prevented from passing through, the co-intercalation of the solvent molecules on the electrode is avoided, and the damage to the electrode material caused by the co-intercalation of the solvent molecules is avoided, so that the cycle performance of the electrode is greatly improved, and the Si-N base has excellent adsorption and removal performances on HF and water in the electrolyte, so that the performance of the battery is improved. Meanwhile, the self-sacrificial electrolyte additive such as fluorosulfonic acid group can selectively form a passivation film on the high-reactivity site on the surface of the positive electrode, so that the low-temperature performance of the battery is improved.
(2) The electrolyte for the lithium battery provided by the embodiment of the application provides two cyclic silazane-containing compounds with structural formulas S1 and S2, wherein Si-N bonds and silane bonds are Lewis bases, the electrolyte has excellent removing capability on HF and water, the content of HF in the electrolyte is effectively reduced, and the effect of inhibiting the decomposition of lithium hexafluorophosphate is achieved. In addition, the SEI and CEI films which are compact and have high mechanical strength are generated by decomposition, so that the loss of positive and negative active materials can be effectively inhibited, and the high-temperature stability and low-temperature power of the lithium ion battery are improved.
Detailed Description
For a further understanding of the present application, the present application will be described in detail with reference to examples.
The present application will be described in further detail with reference to specific examples. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting of the application. The first, second, etc. words are provided for convenience in describing the technical scheme of the present application, and have no specific limitation, and are all generic terms, and do not constitute limitation to the technical scheme of the present application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Unless specifically stated or limited otherwise, the terms "mounted," "connected," and "coupled" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art. The technical schemes in the same embodiment and the technical schemes in different embodiments can be arranged and combined to form a new technical scheme without contradiction or conflict, which is within the scope of the application.
The electrolyte for the lithium battery comprises lithium salt, an organic solvent and an additive, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorosulfimide and lithium bis (trifluoromethylsulfonyl) imide, the organic solvent is at least two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, propyl acetate and propyl propionate, the additive comprises an anode film-forming additive, a cathode film-forming additive and a silazane additive, and the silazane additive is a cyclic silazane additive, and has the structural formula:
wherein R1-R8 are one or more of alkyl groups with 1-7 carbon atoms and derivatives thereof, or R1-R8 are one or more of fluorosulfonate groups and derivatives thereof, or R4-R7 are one or more of alkyl groups with 1-3 carbon atoms, and R2 is one or more of alkyl groups or fluorosulfonate groups.
The cyclic silazane compound is selected from one or two of the following formulas S1 and S2:
the concentration of the lithium salt in the organic solvent is 0.8-1.5 mol/L, the positive film-forming additive is one or more of propane sultone, vinyl sulfate, methane disulfonic acid methylene ester and the like, and the negative film-forming additive comprises one or two of vinylene carbonate and fluoroethylene carbonate.
The application also discloses a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm and the electrolyte for the lithium battery, wherein the positive plate comprises a conductive agent, a current collector, a binder and a positive active material for inserting or extracting lithium ions, the negative plate comprises a conductive agent, a current collector, a binder and a negative active material capable of inserting or extracting lithium ions, the positive active material is one or more of lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials and lithium-rich manganese materials, the negative active material is one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon carbon and silica, and the diaphragm is any one of a polypropylene diaphragm, a polyethylene/polypropylene double-layer composite film, a polyimide electrostatic spinning diaphragm, a polypropylene/polyethylene/polypropylene three-layer composite diaphragm, a ceramic diaphragm and a PVDF (polyvinylidene fluoride) adhesive-coated diaphragm.
The electrolyte is prepared by the following method: controlling the water content in the glove box to be not more than 10ppm, fully stirring and uniformly mixing the cyclic carbonate solvent Ethylene Carbonate (EC) and the linear carbonate solvent methyl ethyl carbonate (EMC) according to the proportion of 3:7, and purifying by using a molecular sieve to remove impurities and water;
under the condition of room temperature, adding 1.2mol/L lithium hexafluorophosphate (LiPF 6) into the mixed solvent, stirring while adding, and obtaining the basic electrolyte after uniform mixing.
Specific examples are as follows:
example 1
In this example, the cyclic silazane-containing compound S1 was used, and after all of it was sufficiently and uniformly mixed, an electrolyte containing cyclic silazane-containing compound was obtained, the amount of which added was 0.1% by mass of the total mass fraction of the electrolyte.
Example 2
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S1 is 0.3% of the total mass fraction of the electrolyte.
Example 3
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S1 is 0.5% of the total mass fraction of the electrolyte.
Example 4
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S1 is 0.8% of the total mass fraction of the electrolyte.
Example 5
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S1 is 1.0% of the total mass fraction of the electrolyte.
Example 6
Compared with example 1, the difference of this example is that the cyclic silazane-containing compound S1 is added in an amount of 2.0% by mass of the total electrolyte.
Example 7
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S1 is 3% of the total mass fraction of the electrolyte.
Example 8
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S2 is 0.3% of the total mass fraction of the electrolyte.
Example 9
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S2 is 0.5% of the total mass fraction of the electrolyte.
Example 10
Compared with example 1, the difference of this example is that the added amount of the cyclic silazane-containing compound S2 is 1.0% of the total mass fraction of the electrolyte.
Comparative example 1
The comparative example does not add any cyclic silazane-containing compound as an additive;
comparative example 2
In comparison with example 1, this comparative example did not add any cyclic silazane-containing compound, but the mass fraction was fluoroethylene carbonate (FEC) of 5% of the total mass of the electrolyte.
Comparative example 3
In comparison with example 1, this comparative example did not add any cyclic silazane-containing compound, but the mass fraction was 8% of fluoroethylene carbonate (FEC) based on the total mass of the electrolyte.
The positive electrode active materials of the lithium ion batteries used in examples 1 to 10 and comparative examples 1 to 3 were lini0.8co0.1mn0.1o 2 Graphite soft package battery.
Preparation of positive plate
Dispersing one or more positive electrode active materials, a conductive agent and a binder polyvinylidene fluoride (PVDF) into a proper amount of N-methyl pyrrolidone according to the mass ratio of 96:2:2, and then fully and uniformly stirring the materials according to the pulping step. Uniformly coating the uniformly dispersed positive electrode slurry on an aluminum foil, and baking, rolling, slitting and punching to obtain the positive electrode plate.
Preparation of negative plate
The specific manufacturing process of the negative plate comprises the following steps: one or more negative electrode active materials, a conductive agent, styrene Butadiene Rubber (SBR) and sodium carboxymethylcellulose (CMC) are selected, all raw materials are dispersed into water according to the mass ratio of 97:1:1:1, and the uniformly dispersed negative electrode slurry is prepared according to a pulping process. And uniformly coating the negative electrode slurry on a copper foil, and baking, rolling, slitting and punching to obtain the negative electrode plate.
And assembling the obtained positive plate, negative plate and diaphragm to obtain a snack, packaging the battery core, injecting electrolyte, sealing again, and performing the procedures of formation, capacity division and the like to obtain the lithium ion battery.
Lithium ion battery performance test
The electrolytes of examples 1 to 10 and comparative examples 1 to 3 and lithium ion batteries were tested and compared for performance differences using the following methods:
(1) And (3) high-temperature storage and gas production test:
after the batteries obtained in comparative examples 1 to 2 and examples 1 to 17 were charged to a full state at normal temperature in a constant current and constant voltage manner, the batteries were stored at a constant temperature of 75 ℃ for 15 days, the volumes of the batteries before and after storage were recorded, and the volume expansion ratio was calculated as follows:
cell volume expansion (%) = (V2-V1)/V1 x 100%;
wherein, V1: storing the volume of the battery before storing the battery, and mL;
v2: battery volume, mL after storage.
(2) 60 ℃ high-temperature storage performance test
And (3) charging the lithium ion battery to 4.25V at room temperature by using a 1C constant current and constant voltage, stopping the current at 0.05C, discharging to 2.8V by using a 1C constant current, recording the discharge capacity C0 of the lithium ion battery at the moment, charging to 4.25V by using a 1C constant current and constant voltage, stopping the current at 0.05C, storing in a 60 ℃ constant temperature box for 30 days after full charge, and then testing the holding capacity Cn of the battery by using a standard charge-discharge flow of the battery.
Capacity retention = Cn/c0 x 100% after 30 days storage at 60 ℃ for lithium ion batteries
Wherein n is the storage days of the lithium ion battery at 60 ℃.
45 ℃ high temperature cycle performance test
And 1C is charged to 4.25V at constant current and constant voltage, the cut-off current is 0.05C, then 1C is discharged to 2.8V at constant current, the cycle is carried out for 800 circles, and the cycle capacity retention percentage is tested. The calculation formula is as follows:
the capacity retention (%) = (discharge capacity of the nth cycle/first discharge capacity) ×100% after n cycles of the lithium ion battery;
wherein n is the cycle number of the lithium ion battery.
Power performance test of lithium ion battery
The power performance of a lithium ion battery is characterized by detecting its Direct Current Internal Resistance (DCIR) at 50% SOC at 25 ℃, where SOC identifies the state of charge.
Low temperature power test: charging the lithium ion battery to 4.25V at 25 ℃ with a constant current of 1C, charging to a current of less than or equal to 0.05C at a constant voltage, standing for 5min, discharging to 2.8V with a constant current of 1C, recording the discharge capacity of the lithium ion battery, and adjusting the charge state of the lithium ion battery to 50% SOC as required with the discharge capacity of 100% SOC. Then, the discharge was continued at-10℃for 30 seconds at a current of 1℃respectively, and the voltage difference before and after the discharge was calculated, and the DCIR was calculated by dividing it by the current.
The results of the above performance tests are shown in table 1:
table 1: lithium ion battery electrical performance test results:
comparing the results shown in Table 1, the following correlation results can be obtained: the volume expansion rate of the battery is reduced after the battery is stored at the high temperature of 75 ℃ for 15 days, the capacity recovery rate is obviously improved after the battery is stored at the high temperature of 60 ℃ for 30 days, and the capacity retention rate is obviously improved after the battery is cycled for 500 circles at 45 ℃.
In comparative example 1, when the additive is not applicable, the battery cycle performance, the power performance and the high-temperature storage performance are all poor, mainly because no additive is reduced to form a film at the positive and negative electrodes, resulting in poor performance in all aspects of the battery.
In comparative examples 2 to 3, the performance of the lithium ion battery was significantly improved after the FEC additive was used, but the volume expansion rate at 60 ℃ was deteriorated, and the battery performance was adversely affected as the FEC content was continuously increased.
The reason for this phenomenon is mainly because FEC can be reduced to form a film at the negative electrode, and the stability of the SEI film is improved, thereby improving the performance of the battery, but excessive FEC may cause an increase in polarization of the battery, causing a problem of deterioration in the battery performance. In addition, FEC does not have the ability to remove HF and moisture from the electrolyte and itself may undergo decomposition reaction, resulting in serious gas generation during high temperature storage of the battery.
In examples 1 to 4, when the amount of the cyclic silicon nitrogen-containing compound S1[ N, N-bis (fluorosulfonate-based dimethylsilyl) -tetramethyl-cyclodisilazane ] added was gradually increased, both the high-temperature cycle performance and the high-temperature storage performance of the battery were remarkably improved, and the low-temperature power and the gas production were also remarkably improved. This is mainly because the cyclic silicon nitrogen compound S1 can undergo ring-opening polymerization on the surface of the positive electrode to form a dense and stable CEI film, and at the same time, the cleavage of the si—o bond is favorable for the film formation of the additive on the negative electrode, increasing the stability of the CEI film, and the si—n group has excellent adsorption and removal properties for HF and moisture in the electrolyte, thereby improving the performance of the battery.
In examples 5-7, further increases in the amount of N, N-bis (fluorosulfonate-based dimethylsilyl) -tetramethyl-cyclodisilazane additive have a more pronounced negative effect on the performance of the battery. The reason for this phenomenon is mainly because excessive additives excessively grow on the positive and negative electrode surfaces of the battery, causing thickening of the CEI or SEI layer, increasing the internal resistance of the battery, and thus deteriorating the cycle and storage performance of the battery. In addition, excessive additives decompose themselves, which can also result in increased gas production during high temperature storage.
In examples 8 to 10, when the fluorinated cyclic silicon nitrogen compound S2 (1-fluorosulfonate-based dimethylsilyl-3-trimethylsilyl-2, 4-tetramethyl-1, 3-cyclodisilazane) was added, the low temperature performance of the battery was significantly improved, and the cycle performance, high temperature storage and gas production performance were all superimposed, mainly because the electrolyte additive with the self-sacrifice type fluorosulfonate group was able to selectively form a passivation film at the site with high reactivity on the surface of the positive electrode, improving the low temperature performance of the battery. However, as the content of such additives increases, more passivation films are formed by decomposition, and more passivation films also result in higher impedance of the battery, resulting in a loss of power density.
The present application and its embodiments have been described in detail by way of illustration, and not limitation, so that those skilled in the art should not be informed by the teachings of the present application to devise structural arrangements and examples similar to those described herein without departing from the spirit of the application.

Claims (10)

1. The electrolyte for the lithium battery is characterized by comprising lithium salt, an organic solvent and an additive, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorosulfimide and lithium bis (trifluoromethylsulfonyl) imide, the organic solvent is at least two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, propyl acetate and propyl propionate, the additive comprises an anode film-forming additive, a cathode film-forming additive and a silazane additive, and the silazane additive is a cyclic silazane additive, and has the structural formula:
wherein R1-R8 are one or more of alkyl groups with 1-7 carbon atoms and derivatives thereof.
2. The electrolyte for lithium battery according to claim 1, wherein the cyclic silazane compound is selected from one or both of formulas S1 and S2:
3. the electrolyte for lithium battery according to claim 1, wherein the positive electrode film-forming additive is one or more of propane sultone, vinyl sulfate, and methylene methane disulfonate.
4. The electrolyte for a lithium battery according to claim 1, wherein the negative electrode film-forming additive comprises one or both of vinylene carbonate and fluoroethylene carbonate.
5. The electrolyte for lithium battery according to claim 1, wherein the cyclic silazane-containing compound accounts for 0.01% -10% of the total mass of the electrolyte.
6. The electrolyte for lithium battery according to claim 1, wherein the concentration of the lithium salt in the organic solvent is 0.8 to 1.5mol/L.
7. A lithium ion battery, comprising a positive plate, a negative plate, a diaphragm and the electrolyte for the lithium battery according to any one of claims 1 to 6, wherein the positive plate comprises a positive active material, a conductive agent, a current collector and a binder, and the negative plate comprises a negative active material, a conductive agent, a current collector and a binder.
8. The lithium ion battery of claim 7, wherein the positive electrode active material is one or more of lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium-rich manganese material.
9. The lithium ion battery of claim 7, wherein the negative electrode active material is one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon carbon, and silicon oxygen.
10. The lithium ion battery of claim 7, wherein the membrane is any one of a polypropylene membrane, a polyethylene/polypropylene double layer composite membrane, a polyimide electrospun membrane, a polypropylene/polyethylene/polypropylene three layer composite membrane, a ceramic membrane, and a PVDF rubberized membrane.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117454670A (en) * 2023-12-22 2024-01-26 浙江大学 Electrochemical model-based lithium battery aging state prediction method and device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117454670A (en) * 2023-12-22 2024-01-26 浙江大学 Electrochemical model-based lithium battery aging state prediction method and device
CN117454670B (en) * 2023-12-22 2024-04-12 浙江大学 Electrochemical model-based lithium battery aging state prediction method and device

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