CN113851719B - Multifunctional organosilicon electrolyte suitable for lithium-ion batteries based on ternary cathode materials and its preparation and application - Google Patents

Abstract

The invention discloses a multifunctional organosilicon electrolyte suitable for a lithium ion battery based on a ternary positive electrode material, a preparation method thereof and an application in the lithium ion battery based on a ternary positive electrode material. Multifunctional silicone electrolyte includes basic electrolyte and silicone; basic electrolyte includes ester solvent and lithium salt; silicone is composed of main chain and side chain, and its general structural formula is:

Wherein, the silicon atom is directly connected to the phenyl group, _R1 is hydrogen, _R2 is hydrocarbon group, alkoxyl group, cyano group, hydroxyl group, halogen atom or ester group, _R3 is hydrogen or hydrocarbon group, m≥1. The preparation method comprises: under the protection of an inert gas, dissolving the lithium salt in an ester solvent to prepare a basic electrolyte; under the protection of an inert gas, mixing organic silicon with the basic electrolyte.

Description

Multifunctional organosilicon electrolyte suitable for lithium-ion batteries based on ternary cathode materials and its preparation and application

technical field

The invention relates to the technical field of lithium-ion batteries, in particular to a multifunctional organic silicon electrolyte suitable for lithium-ion batteries based on ternary positive electrode materials and its preparation and application.

Background technique

With the continuous consumption and non-renewable of traditional fossil fuels and the deterioration of the global environment, the need to develop new renewable energy sources is imminent. Lithium-ion batteries have become the most popular among scientists at home and abroad because of their advantages such as high energy density, long cycle life, high charge and discharge efficiency, low self-discharge, no memory effect, wide operating temperature range, high average output voltage, environmental friendliness, safety and reliability, etc. Technicians focus on the direction of research and development. As one of the core and key components of lithium-ion batteries, electrolyte plays an important role in the performance of lithium-ion batteries.

At present, lithium-ion batteries mostly use carbon-based organic electrolytes. These electrolytes have defects such as volatile, flammable, and narrow potential windows, which lead to frequent safety accidents of lithium-ion batteries. Due to its high and low temperature resistance and good chemical stability, organosilicon can be used as an electrolyte solvent or additive to exhibit excellent safety, oxidation resistance, thermal stability, flame retardancy, and film-forming properties. Compared with traditional carbon-based electrolytes, organosilicon electrolytes have the advantages of strong pertinence, simple production process, and can improve the electrochemical performance and safety of lithium-ion batteries, and have attracted attention in lithium-ion batteries in recent years.

The patent specification with the publication number CN107004902A discloses an electrolyte solution of organosilicon compounds containing groups such as alkylene, alkenylene or alkynylene groups, which can work at temperatures up to 250°C and improve stability. The patent specification whose publication number is CN105826599A discloses a kind of organosilicon containing vinyl group, epoxy group, alkyl group with 1-3 carbon atoms, three alkoxy groups, etc. as electrolyte flame retardant additive, and organic solvent, Lithium salts constitute the electrolyte, which can reduce the flammability of the electrolyte, improve its electrochemical and thermal stability, and then improve its safety performance. The patent specification with the publication number CN108878978A discloses an anti-overcharge electrolyte solution with silicone-oxygen bonds as the main chain and four biphenyl organic silicon additives in the main structure of the molecule, which can form cross-linked electrolytes when overcharged. Electrochemical polymers, better battery protection.

Tae J L et al. (ACS Applied Materials &Interfaces.2019; 11(12):11306-16.) used 4-(trimethylsiloxane)-3-penten-2-one (TMSPO) as an electrolyte additive, The Coulombic efficiency and cycle performance of Li/LiNi _0.5 Mn _1.5 O ₄ (LNMO) half cells and graphite/LNMO full cells are improved. Li L L et al. (ElectrochimicaActa, 2011,56(13):4858-4864.) use methylphenylbismethoxydiethoxysilane as a dual-functional additive for lithium-ion battery electrolyte, which can slow down capacity fading, while Play a flame retardant effect. The patent specification with the notification number CN 103401019 B reports that an organic silicon electrolyte additive can prevent corrosion of the steel case of lithium-ion batteries, but the corresponding relationship between the molecular structure of organic silicon and the types of functional groups contained in it and the function of the electrolyte is not yet clear. , to be further explored.

Contents of the invention

Aiming at the problems existing in the lithium-ion battery electrolyte based on the ternary positive electrode material, the present invention provides a multifunctional organosilicon electrolyte suitable for a lithium-ion battery based on the ternary positive electrode material. It is especially suitable for the ternary cathode material LiNi _x Co _y Mn _1-xy O _p , where x, y, and p all represent atomic ratios and x+y< 1, 0.3<x<0.8, 0.2≤y<0.7, 1<p<6.

A multifunctional organosilicon electrolyte suitable for lithium-ion batteries based on ternary cathode materials, including basic electrolyte and organosilicon;

The basic electrolyte includes ester solvent and lithium salt;

The organosilicon is composed of a main chain and a side chain, and its general structural formula is:

Among them, the silicon atom is directly connected to the phenyl group, _R1 is hydrogen, _R2 is hydrocarbon group (including aryl group, etc.), alkoxyl group, cyano group, hydroxyl group, halogen atom or ester group, _R3 is hydrogen or hydrocarbon group, m≥ 1.

The organosilicon electrolyte of the present invention can effectively remove the negative influence of residual moisture in the electrolyte, and the organosilicon can participate in the battery reaction to form a protective film component on the surface of the positive electrode material during the charging and discharging process, thereby increasing the working voltage of the battery and prolonging the battery life. cycle life.

In a preferred example, the organosilicon is nitrogenmethylphenylsilazane, the molecular formula is C ₁₆ H ₂₃ NSi ₂ , and the structural formula is:

The ester solvent is preferably EC (ethylene carbonate), EMC (ethyl methyl carbonate), DEC (diethyl carbonate), PC (propylene carbonate), PP (propyl propionate), EB (ethyl butyrate). ester), BC (butylene carbonate), EA (ethyl acetate), MB (methyl butyrate), DMC (dimethyl carbonate), MP (methyl propionate), ES (ethylene sulfite), A mixture of any two or three of DMS (dimethyl sulfite), FEC (fluoroethylene carbonate), and VC (vinylidene carbonate).

The lithium salt is preferably LiPF ₆ (lithium hexafluorophosphate), LiClO ₄ (anhydrous lithium perchlorate), LiBF ₄ (lithium tetrafluoroborate), LiTF ₃ SI (lithium bis(trifluoromethyl)sulfonylimide), Any of LiFSI (lithium bisfluorosulfonyl imide).

In a preferred example, the volume ratio V of the organosilicon to the basic electrolyte satisfies 0<V≦10%.

In a preferred example, the lithium salt concentration in the basic electrolyte is 1-3 mol/L.

The present invention also provides the preparation method of described multifunctional organosilicon electrolyte, comprising steps:

(1) Under the protection of inert gas, dissolve the lithium salt in the ester solvent to prepare the basic electrolyte;

(2) Under the protection of an inert gas, the organosilicon is mixed with the basic electrolyte to obtain the multifunctional organosilicon electrolyte.

The present invention also provides the application of the multifunctional organosilicon electrolyte in lithium ion batteries based on ternary cathode materials.

Preparation of electrode sheets: Grind the active component (ie the ternary positive electrode material), conductive carbon black and polyvinylidene fluoride into powder and disperse them in a solvent, ultrasonically, stir and mix to obtain a slurry, and then put the The slurry is evenly coated on the surface of the aluminum foil, dried, compacted, and cut into pieces to obtain electrode sheets.

Assembling the battery: taking button-type half-cells as an example, in an argon protective glove box at room temperature, the positive electrode shell, the positive electrode coated with the sample (ie, the electrode sheet obtained above), the electrolyte, the separator, the lithium sheet, the gasket , shrapnel, and negative electrode shells are stacked in sequence, and sealed on a sealing machine to assemble a button half-cell.

Electrochemical performance test: On the electrochemical workstation and charge-discharge equipment, the assembled battery is subjected to cyclic voltammetry test and constant current charge-discharge test to characterize the electrochemical performance of the battery.

In a preferred example, the ternary cathode material is LiNi _x Co _y Mn _1-xy O _p , where x, y, and p all represent atomic ratios and x+y<1, 0.3<x<0.8, 0.2≤y <0.7, 1<p<6.

The principle of the present invention: the organosilicon molecular structure used in the electrolyte is unique, consisting of a main chain and a side chain. silicon-hydrogen bond. This unique molecular structure determines that the organosilicon compound can affect and participate in battery reactions. Among them, the silicon-hydrogen bond is more sensitive to moisture, which can eliminate the residual moisture in the electrolyte and reduce the negative impact of moisture on the electrochemical performance of the battery; at the same time, the silicon-nitrogen bond can be further hydrolyzed into a silicon-oxygen bond to form Stable siloxane, siloxane has a significant effect on broadening the potential window of the electrolyte. The thermal stability of the silicon-benzene bond is good, and the phenyl group has a large steric hindrance effect, which can regulate the reaction rate of the organosilicon compound participating in the battery, and prolong the storage period and service life of the electrolyte, so the long-term performance of the prepared battery excellent.

Beneficial effects of the present invention:

1. Compared with the prior art, most of the electrolytes on the market do not contain organosilicon compounds. The electrolyte of the present invention uses organosilicon compounds with special structures as functional components, which can eliminate moisture, increase working voltage, and prolong battery life. Multiple functions of cycle performance;

2. Most of the electrolytes on the market can achieve multiple functions by adding a variety of different functional components. The formula is complex and the formula ratio is difficult to control. The organosilicon compound used in the present invention is a single compound, which overcomes the complexity of the formula ratio and is difficult to control. The disadvantages are convenient for industrialized mass production.

3. The electrolyte solution of the present invention is especially suitable for LiNi _x Co _y Mn _1-xy O _p (x, y, p all represent atomic ratio and x+y<1, 0.3<x<0.8, 0.2≤y<0.7, 1<p<6) as the representative cathode material, which provides a new screening strategy and optimization scheme for the cathode material electrolyte.

Description of drawings

Fig. 1 is the charge-discharge curve diagram of positive electrode material LiNi _0.6 Co _0.2 Mn _{0.2 O} in comparative example 1 basic electrolyte;

Fig. 2 is the charge-discharge curve diagram _of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O in the organosilicon electrolyte of embodiment 1;

Fig. 3 is the charge-discharge curve diagram of positive electrode material LiNi _0.6 Co _0.2 Mn _{0.2 O} in embodiment 2 organosilicon electrolyte;

Fig. 4 is positive electrode material LiNi _0.6 Co _0.2 Mn _{0.2 O} The cyclic voltammetry curve in comparative example 1 basic electrolyte;

Fig. 5 is the cyclic voltammetry graph of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the organosilicon electrolyte of embodiment 1;

Fig. 6 is the cyclic voltammetry curve graph of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the organosilicon electrolyte of embodiment 2;

Fig. 7 is the number of cycles-charge-discharge specific capacity diagram of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the basic electrolyte of Comparative Example 1;

Fig. 8 is the number of cycles-charge-discharge specific capacity diagram of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the organosilicon electrolyte of Example 1;

Fig. 9 is a cycle number-charge-discharge specific capacity diagram of positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the organosilicon electrolyte of Example 2;

Fig. 10 is a comparison chart of the number of cycles-charge-discharge specific capacity of the positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in the basic electrolyte of Comparative Example 1 and the organosilicon electrolyte of Example 2.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods not indicated in the following examples are generally in accordance with conventional conditions, or in accordance with the conditions suggested by the manufacturer. Unless otherwise specified, the materials used in the examples and comparative examples can be purchased commercially.

Example 1

Organosilicon electrolyte matching cathode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is applied to the steps of preparing lithium-ion batteries:

1) Preparation of organosilicon electrolyte:

1-1) In an argon-protected glove box, mix ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) with a volume ratio of 1:1:1 as a solvent to LiPF ₆ is configured as a solute into a 1mol L ^-1 solution as the basic electrolyte;

1-2) In an argon-protected glove box at room temperature, uniformly mix nitrogenmethylphenylsilazane and basic electrolyte at a volume ratio of 1:100 to obtain an organosilicon electrolyte, which is ready for use.

Nitromethylphenylsilazane, the molecular formula is C ₁₆ H ₂₃ NSi ₂ , and the structural formula is:

2) Preparation of positive electrode sheet: In an argon-protected glove box, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , conductive carbon black, and polyvinylidene fluoride were mixed and ground into powder according to the mass ratio of 7:2:1, and dispersed in In the solvent N-methylpyrrolidone, ultrasonic for 1 hour and stirred for 3 hours at room temperature, the powder is mixed evenly in the solvent to make a slurry, and the slurry is evenly coated on the cleaned metal aluminum foil, and transferred out of the glove box. Quickly put into 80°C vacuum oven for 24 hours. The dried positive electrode sheet was compacted with 10MPa on a tablet press, quickly transferred to the glove box, and the positive electrode sheet was cut into small discs with a diameter of 16mm with cutting pliers to obtain a loading capacity of 1-2 mg·cm ^-2 the positive plate.

3) Assembling button-type half-cells: In an argon-protected glove box, stack the batteries in the order of positive electrode case, positive electrode sheet, electrolyte, diaphragm, lithium sheet, gasket, shrapnel, and negative electrode case, and put them into the seal Machine sealing. The electrolyte is the silicone electrolyte prepared in step 1-2), the dosage is 120 μL, the separator is Celgare 2400 porous PP membrane, and the battery case model is CR2016.

Charge and discharge test: Use charge and discharge equipment to detect the charge and discharge curve of the battery at a current density of 50mA·g ^-1 , and the results are shown in Figure 2 and Figure 8 . After testing, the first charge-discharge specific capacity of the half-cell composed of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is 138mAh·g ^-1 , after 10 cycles, the charge-discharge specific capacity is still stable at about 135mAh·g ^-1 .

Electrochemical workstation CV test: using an electrochemical workstation, the test potential window is 2.0-4.2V, and the scan rate is 0.05mV·s ^-1 , as shown in Figure 5, its stable working voltage is 2.0-3.75V. The 2.0-3.5V of the electrolyte widens its electrochemical working window.

Comparative example 1

The only difference from Example 1 is that there is no step 1-2), the basic electrolyte is used in step 3) instead of the organosilicon electrolyte, and the rest of the steps and conditions are the same.

Charge and discharge test: Use charge and discharge equipment to detect the charge and discharge curve of the battery at a current density of 50 mA g ^-1 , and the results are shown in Figure 1 and Figure 7 . After testing, the first charge-discharge specific capacity of the half-cell composed of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is 135mAh·g ^-1 , after 25 cycles, its charge-discharge specific capacity rapidly decays to 20mAh·g ^-1 , poor electrochemical stability.

Electrochemical workstation CV test: using an electrochemical workstation, the test potential window is 2.0-4.2V, and the scan rate is 0.05mV·s ^-1 , as shown in Figure 4, its stable working voltage is 2.0-3.5V.

Example 2

The difference from Example 1 is only that the volume ratio of organosilicon and basic electrolyte in step 1-2) is 2:100, and the rest of the steps and conditions are the same.

Charge and discharge test: Use charge and discharge equipment to detect the charge and discharge curve of the battery at a current density of 50mA·g ^-1 , and the results are shown in Figure 3 and Figure 9 . After testing, the first charge-discharge specific capacity of the half-cell composed of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is 143mAh·g ^-1 . From the second cycle, the specific capacity is relatively stable. After 10 cycles, the charge-discharge The specific capacity is still stable at about 140mAh·g ^-1 .

Electrochemical workstation CV test: using an electrochemical workstation, the test window is 2.0-4.2V, and the scan rate is 0.05mV·s ^-1 , as shown in Figure 6, its stable working voltage is 2.0-3.7V. Liquid 2.0 ~ 3.5V, widened its electrochemical working window.

Comparing positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in comparative example 1 basic electrolyte and embodiment 2 organosilicon electrolyte cycle number-charge-discharge specific capacity (Fig. 10, table 1), it can be seen that the electrode material is in The cycle performance in the silicone electrolyte is significantly improved.

Table 1 Comparison of cycle performance of ternary cathode materials in basic electrolyte and organosilicon electrolyte

In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (8)

1. A multifunctional organosilicon electrolyte suitable for lithium-ion batteries based on ternary cathode materials, characterized in that it comprises basic electrolyte and organosilicon; The basic electrolyte includes ester solvent and lithium salt; The organosilicon is composed of a main chain and a side chain, and its general structural formula is: Wherein, the silicon atom is directly connected to the phenyl group, _R1 is hydrogen, _R2 is hydrocarbon group, alkoxyl group, cyano group, hydroxyl group, halogen atom or ester group, _R3 is hydrogen or hydrocarbon group, m≥1. 2. The multifunctional organosilicon electrolyte according to claim 1, wherein the organosilicon is nitrogenmethylphenylsilazane, the molecular formula is C ₁₆ H ₂₃ NSi ₂ , and the structural formula is: 3. The multifunctional organosilicon electrolyte according to claim 1, wherein the ester solvent is EC, EMC, DEC, PC, PP, EB, BC, EA, MB, DMC, MP, ES, A mixture of any two or three of DMS, FEC, and VC. 4 . The multifunctional organosilicon electrolyte according to claim 1 , wherein the lithium salt is any one of LiPF ₆ , LiClO ₄ , LiBF ₄ , LiTFSI, and LiFSI. 5 . The multifunctional organosilicon electrolyte according to claim 1 , wherein the volume ratio V of the organosilicon to the base electrolyte satisfies 0<V≦10%. 6 . The multifunctional organosilicon electrolyte according to claim 1 , wherein the lithium salt concentration in the basic electrolyte is 1˜3 mol/L. 7. The method for preparing the multifunctional organosilicon electrolyte according to any one of claims 1 to 6, characterized in that it comprises the steps of: (1) Under the protection of inert gas, dissolve the lithium salt in the ester solvent to prepare the basic electrolyte; (2) Under the protection of an inert gas, the organosilicon is mixed with the basic electrolyte to obtain the multifunctional organosilicon electrolyte. 8. The application of the multifunctional organosilicon electrolyte according to any one of claims 1 to 6 in a lithium-ion battery based on a ternary positive electrode material, wherein the ternary positive electrode material is LiNi _x Co _y Mn _1-xy O _p , where x, y, and p all represent atomic ratios and x+y<1, 0.3<x<0.8, 0.2≤y<0.7, 1<p<6.

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