CN117175005A

CN117175005A - Lithium ion battery electrolyte containing tri (2-cyanoethyl) phosphate and lithium ion battery

Info

Publication number: CN117175005A
Application number: CN202210581769.1A
Authority: CN
Inventors: 鞠署元; 周景艳; 刘天雷; 盖陆海; 王明华; 王圣贤
Original assignee: Shandong Haike Innovation Research Institute Co Ltd
Current assignee: Shandong Haike Innovation Research Institute Co Ltd
Priority date: 2022-05-26
Filing date: 2022-05-26
Publication date: 2023-12-05

Abstract

The invention provides lithium ion battery electrolyte, which comprises an organic solvent, lithium salt and an additive; the additive comprises a first additive and a second additive; the first additive comprises tris (2-cyanoethyl) phosphate; the second additive includes a cyclic lithium phosphate compound. The invention particularly selects the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate to be compounded as electrolyte additives, and the two additives are synergistic, so that a compact CEI film with a multi-atom structure is formed at the interface between the anode material of the lithium ion battery and the electrolyte, thereby realizing the dual effects of ion directional selection, inhibiting the dissolution of high-valence metal ions and improving the migration rate of lithium ions, and improving the high-voltage performance, the high-temperature performance and the cycle performance of the lithium ion battery.

Description

Lithium ion battery electrolyte containing tri (2-cyanoethyl) phosphate and lithium ion battery

Technical Field

The invention belongs to the technical field of lithium ion battery electrolyte, relates to lithium ion battery electrolyte and a lithium ion battery, and particularly relates to lithium ion battery electrolyte and a lithium ion battery containing tri (2-cyanoethyl) phosphate.

Background

In recent years, lithium ion batteries have been widely used in the fields of digital products, power, energy storage, and the like. With the development of lithium ion battery technology, pursuing higher energy density has become a research hotspot in the industry, and raising the charge cut-off voltage of a battery is one of the key ways to solve the difficult problems in the industry. In high energy density battery systems, the current commercial positive electrode materials are mainly LiNi _x Co _y Mn _(1-x-y) O ₂ And LiCoO ₂ Both are layered structures, and high-valence metal ions are easily dissolved out under a high-voltage environment, so that the battery performance is rapidly deteriorated. The main solutions for alleviating the problem are two, namely, optimizing the structure of the positive electrode material, such as single crystallization, metal ion doping, surface coating, gradient structural design and the like; secondly, the electrolyte formula is optimized, the dissolution of metal ions is inhibited from the angle of the interface between the anode and the electrolyte, and the functionalized electrolyte additive plays a key role in the aspect.

Among many electrolyte additives, cyano groups of nitrile additives have strong electronegativity and strong coordination with transition metal ions, so that the dissolution of metal ions can be inhibited, and meanwhile, H protons are captured preferentially when an oxidation side reaction occurs in the electrolyte, and LiPF is inhibited ₆ And decomposition of FEC. Nitrile additives such as Succinonitrile (SN), adiponitrile (ADN), 1,3, 6-Hexanetrinitrile (HTCN), 1, 2-di (2-cyanoethoxy) ethane (DENE) and the like are applied in batches, and have good effects in improving high voltage, high temperature, cycle performance and the like of batteries. And the large-scale use and comparison of the nitrile additive prove that the performance of the 1,3, 6-hexanetrinitrile is optimal in 4 nitrile additives applied in batches, because 3 cyano groups are contained in a single molecule, so that the coordination effect of the nitrile additive and transition metal ions is stronger. However, there are problems with the use of such nitrile additives, which limit Li ⁺ And is unstable.

Therefore, how to find a more suitable way to solve the above-mentioned problems of the existing nitrile additives has become one of the focus of attention for many researchers and research and development enterprises in the industry.

Disclosure of Invention

In view of this, the present invention provides a lithium ion battery electrolyte and a lithium ion battery, and in particular, a lithium ion battery electrolyte containing tris (2-cyanoethyl) phosphate. The additive containing the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate compound provided by the invention is matched with each other and cooperates with each other to form the CEI film with a framework-pouring structure and a metal ion directional selection effect, so that the cycle performance and the multiplying power performance of the lithium ion battery are improved.

The invention provides lithium ion battery electrolyte, which comprises an organic solvent, lithium salt and an additive;

the additive comprises a first additive and a second additive;

the first additive comprises tris (2-cyanoethyl) phosphate;

the second additive includes a cyclic lithium phosphate compound.

Preferably, the addition amount of the tri (2-cyanoethyl) phosphate accounts for 0.1-5% of the total mass of the electrolyte;

the tri (2-cyanoethyl) phosphate has a structure as shown in formula (I):

preferably, the cyclic lithium phosphate compound comprises lithium difluorobis (oxalato) phosphate and/or lithium tetrafluoro (oxalato) phosphate;

the addition amount of the second additive accounts for 0.01% -3% of the total mass of the electrolyte;

the organic solvent comprises two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, gamma-butyrolactone, propyl propionate and ethyl propionate;

the addition amount of the organic solvent accounts for 50-75% of the total mass of the electrolyte.

Preferably, the lithium salt comprises one or more of lithium hexafluorophosphate, lithium difluorosulfonimide and lithium difluorophosphate;

the addition amount of the lithium salt accounts for 12% -20% of the total mass of the electrolyte;

the additive further comprises a third additive.

Preferably, the third additive comprises one or more of tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) borate, succinonitrile, adiponitrile, 1,3, 6-hexanetrinitrile, 1, 2-bis (2-cyanoethoxy) ethane, 1,2, 3-tris (cyanoethoxy) propane, tris (2-cyanoethyl) borate, tris (2-cyanoethyl) phosphate, tris (2-cyanoethyl) phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, fluorovinyl sulfate, 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propenesulfonic acid, and methane disulfonic acid methylene;

the addition amount of the third additive accounts for 0.1-20% of the total mass of the electrolyte.

Preferably, the tri (2-cyanoethyl) phosphate is obtained by substitution reaction of 3-hydroxy propionitrile and phosphorus oxychloride as raw materials.

Preferably, the preparation method of the tri (2-cyanoethyl) phosphate comprises the following steps:

1) Mixing 3-hydroxy propionitrile and a hydrogen chloride chelating agent to obtain a system solution;

2) Adding phosphorus oxychloride organic solution into the system solution obtained in the step, carrying out low-temperature reaction, adding organic metal alkali under the condition of II-stage reaction temperature after the dripping is completed, and continuing the reaction under the temperature condition to obtain the tri (2-cyanoethyl) phosphate.

Preferably, after the continuous reaction, the method further comprises a purification step;

the purification step comprises one or more of extraction, washing and rotary evaporation;

the extraction comprises organic phase extraction;

the extractant for extraction comprises one or more of toluene, xylene, diethyl ether, methylene chloride, ethyl acetate, chloroform, benzene, trichloroethane and dichloroethane.

The invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode and the electrolyte according to any one of the technical schemes.

Preferably, the positive electrode has a frame-cast CEI film thereon;

the cyclic lithium phosphate provides a framework structure for the CEI film;

the tris (2-cyanoethyl) phosphate is poured into a framework structure formed from cyclic lithium phosphate;

the CEI film has a metal ion orientation selection function;

the CEI film structure contains an organic lithium component.

The invention provides lithium ion battery electrolyte, which comprises an organic solvent, lithium salt and an additive; the additive comprises a first additive and a second additive; the first additive comprises tris (2-cyanoethyl) phosphate; the second additive includes a cyclic lithium phosphate compound. Compared with the prior art, the invention aims at the problems of the prior lithium ion electrolyte additive, in particular to the nitrile additive, and the invention considers that the main chain structure of the 1,3, 6-Hexanetrinitrile (HTCN) is C atom as an example, thus greatly limiting Li ⁺ The conventional nitrile additive does not participate in the positive electrode film formation, so that a protective layer formed at the positive electrode interface is unstable, and therefore, the method starts from the direction of constructing a more stable CEI film, and further obtains electrolyte with more excellent performance, thereby improving the high-voltage performance of the battery.

The invention particularly selects the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate to be compounded as electrolyte additives, and the two additives are synergistic, so that a compact CEI film with a multi-atom structure is formed at the interface between the anode material of the lithium ion battery and the electrolyte, thereby realizing the dual effects of ion directional selection, inhibiting the dissolution of high-valence metal ions and improving the migration rate of lithium ions, and improving the high-voltage performance, the high-temperature performance and the cycle performance of the lithium ion battery.

The lithium ion battery additive containing the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate, which is provided by the invention, is used together, has a good synergistic effect, and can form a specific 'framework-pouring' structure and a CEI film structure with a metal ion directional selection effect when the lithium ion battery is formed or used. Firstly, when the additive is used for forming a film on the positive electrode of a battery, as electronegativity of '-CN' is firstly adsorbed on the interface between electrolyte and the positive electrode, when the additive is charged, annular lithium phosphate is easy to form a film, and plays a role in fixing a tri (2-cyanoethyl) phosphate adsorption layer, namely, the annular lithium phosphate provides a framework structure for a CEI film, and the tri (2-cyanoethyl) phosphate plays a role in pouring; secondly, the CEI film with a framework-pouring structure greatly reduces the usage amount of the annular lithium phosphate, thereby slowing down the negative effect caused by the addition of a large amount of the annular lithium phosphate; the CEI film with a framework-pouring structure has strong directional selectivity on metal ions, and the strong coordination effect of the-CN limits the precipitation of high-valence transition metal ions; and the CEI film structure is rich in organic lithium salt components, and functional groups such as P-O, CN and the like promote lithium ion migration, and the two additives have good effect of inhibiting gas production of the battery, so that the multiplying power, circulation and high-temperature performance of the battery are improved.

Experimental results show that the invention adopts the tri (2-cyanoethyl) phosphate and the annular lithium phosphate, improves the direct current internal resistance of the battery, thereby improving the multiplying power and the cycle performance of the battery, and greatly improves the multiplying power, the cycle, the high-temperature storage and other electrochemical performances of the battery through the synergistic effect of the tri (2-cyanoethyl) phosphate and the annular lithium phosphate.

Drawings

FIG. 1 is a nuclear magnetic C spectrum of a first additive tris (2-cyanoethyl) phosphate prepared in accordance with the present invention;

FIG. 2 is a nuclear magnetic H spectrum of the first additive tris (2-cyanoethyl) phosphate prepared in accordance with the present invention;

FIG. 3 is a three electrode LSV test curve for different formulations of electrolytes provided by the present invention.

Detailed Description

For further understanding of the present invention, the technical aspects of the present invention will be clearly and fully described in connection with the following embodiments, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

All the raw materials of the present invention are not particularly limited in their sources, and may be purchased on the market or prepared according to conventional methods well known to those skilled in the art.

All the raw materials of the present invention are not particularly limited in purity, and the present invention preferably employs analytically pure or conventional purity in the field of lithium ion battery electrolytes.

the additive comprises a first additive and a second additive;

the first additive comprises tris (2-cyanoethyl) phosphate;

the second additive includes a cyclic lithium phosphate compound.

In the present invention, the organic solvent preferably includes two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, γ -butyrolactone, propyl propionate and ethyl propionate.

In the present invention, the addition amount of the organic solvent is preferably 50% to 75%, more preferably 55% to 70%, and still more preferably 60% to 65% of the total mass of the electrolyte.

In the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate, lithium difluorosulfonimide and lithium difluorophosphate, more preferably lithium hexafluorophosphate, lithium difluorosulfonimide or lithium difluorophosphate.

In the present invention, the amount of the lithium salt added is preferably 12% to 20%, more preferably 13% to 19%, still more preferably 14% to 18%, and still more preferably 15% to 17% of the total mass of the electrolyte.

In the present invention, the amount of the tri (2-cyanoethyl) phosphate added is preferably 0.1 to 5%, more preferably 0.5 to 4%, still more preferably 1 to 3%, still more preferably 1.5 to 2% of the total mass of the electrolyte.

In the present invention, the tris (2-cyanoethyl) phosphate preferably has a structure represented by formula (I):

in the invention, P-O in the framework structure of the tri (2-cyanoethyl) phosphate improves the lithium ion conductivity, and solves the problem of increased battery impedance caused by the traditional nitrile additive.

In the present invention, the cyclic lithium phosphate compound preferably includes lithium difluorobis (oxalato) phosphate and/or lithium tetrafluoro (oxalato) phosphate, more preferably lithium difluorobis (oxalato) phosphate or lithium tetrafluoro (oxalato) phosphate.

In the present invention, the amount of the second additive added is preferably 0.01% to 3%, more preferably 0.01% to 2%, and still more preferably 0.1% to 1% of the total mass of the electrolyte.

The lithium ion battery electrolyte provided by the invention particularly selects the compound of tri (2-cyanoethyl) phosphate and cyclic lithium phosphate as main components of the additive, wherein the tri (2-cyanoethyl) phosphate has the structural advantage of being similar to that of hexanetrinitrile (HTCN, the nitrile additive with the best commercial application performance currently accepted in industry), the molecular structures of the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate both contain 3 '-CN', compared with the traditional nitrile additive (such as SN, ADN, DENE and the like), the tri (2-cyanoethyl) phosphate has stronger complexing capability with high-valence transition metal ions,

therefore, the inhibition effect on the precipitation of metal ions of the battery under the conditions of high temperature and high voltage is more obvious. The tri (2-cyanoethyl) phosphate has the advantages that compared with HTCN, the tri (2-cyanoethyl) phosphate has a phosphate group as a skeleton structure, and abundant P-O bonds are beneficial to the transfer of lithium ions at the interface between electrolyte and a positive electrode, so that the problem of impedance rise caused by the adsorption effect of the positive electrode surface on nitrile additives is solved.

And the tri (2-cyanoethyl) phosphate and a second additive capable of forming a film at the positive electrode are synergistic to generate a CEI film with ion selectivity, and the (-CN) and high-valence transition metal ions have strong coordination to inhibit the dissolution of metal ions such as cobalt, nickel, manganese and the like; the CEI film structure is rich in organic lithium components, and the functional groups of P-O and CN promote lithium ion migration, so that the cycle and rate performance of the battery are improved.

The second additive is at least one of annular lithium difluorobis (oxalato) phosphate (LiDFBP) and tetrafluoro (LiTFOP) lithium ion battery electrolyte, and aims to further improve the multiplying power and high-voltage performance of the electrolyte. The annular lithium phosphate participates in the positive electrode film formation in the first charge and discharge process of the battery, and has the advantages of low film formation impedance and good stability, and can inhibit electrolyte decomposition. However, a large amount of cyclic lithium phosphate is added in the electrolyte, which causes two problems, namely, the increase of CEI film thickness and the great increase of battery impedance; secondly, the cyclic lithium phosphate has poor stability and is easy to absorb water, so that the storage stability of the electrolyte is poor. The invention provides a design scheme that tri (2-cyanoethyl) phosphate and cyclic lithium phosphate are respectively used as a first additive and a second additive of electrolyte. The proposal has the advantage that the two additives are used together, and have good synergistic effect. The method has the following specific beneficial effects: firstly, when the positive electrode of the battery forms a film, because electronegativity of '-CN' is firstly adsorbed at the interface between electrolyte and the positive electrode, when the battery is charged, annular lithium phosphate is easy to form a film, and plays a role in fixing a tri (2-cyanoethyl) phosphate adsorption layer, namely, the annular lithium phosphate provides a framework structure for a CEI film, and the tri (2-cyanoethyl) phosphate plays a role in pouring. Secondly, the CEI film with a framework-pouring structure can greatly reduce the using amount of the annular lithium phosphate, thereby slowing down the negative effect caused by the addition of a large amount of the annular lithium phosphate. Thirdly, the CEI film with a framework-pouring structure has strong directional selectivity on metal ions, and the strong coordination effect of the (-CN) limits the precipitation of high-valence transition metal ions; meanwhile, the CEI film structure is rich in organic lithium salt components, functional groups such as P-O and CN promote lithium ion migration, and the two additives have good effect of inhibiting gas production of the battery, so that the multiplying power, circulation and high-temperature performance of the battery are improved. It should be noted that the CEI film is a film layer of the lithium ion battery itself on the positive electrode, and the structure in the present invention is the CEI film or the CEI film containing the above structure.

In the present invention, the additive preferably includes a third additive.

In the present invention, the third additive preferably includes one or more of tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) borate, succinonitrile, adiponitrile, 1,3, 6-hexanetrinitrile, 1, 2-bis (2-cyanoethoxy) ethane, 1,2, 3-tris (cyanoethoxy) propane, tris (2-cyanoethyl) borate, tris (2-cyanoethyl) phosphate, tris (2-cyanoethyl) phosphite, vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, ethylene sulfite, fluoroethylene sulfate, 1, 3-propane sultone, 1, 4-butanesulfonolide, 1, 3-propenesulfonic acid and methane disulfonic acid methylene ester, more preferably tris (trimethylsilane) phosphate, tris (trimethylsilane) phosphite, tris (trimethylsilane) borate, succinonitrile, adiponitrile, 1,3, 6-hexanetrinitrile, 1, 2-bis (2-cyanoethoxy) ethane, 1, 3-cyanoethoxy) phosphite, ethylene carbonate, fluoroethylene carbonate, ethylene propylene carbonate, ethylene-2-bis (2, 3-ethanesulfonate, ethylene-2-trisulfonate, ethylene-propylene carbonate, ethylene-2-bis (2-ethyl) sulfonate, ethylene-4-trisulfonate, ethylene-propylene sulfonate, ethylene-2-bis (2-ethyl) sulfonate, ethylene-2-bis (2-methyl) sulfonate.

In the present invention, the addition amount of the third additive is preferably 0.1% to 20%, more preferably 0.5% to 15%, and still more preferably 1% to 10% of the total mass of the electrolyte.

The invention provides lithium ion battery electrolyte, which comprises an organic solvent, lithium salt and an additive, wherein the electrolyte comprises tris (2-cyanoethyl) phosphate as a first additive, and the structural formula of the electrolyte is as follows; the electrolyte further comprises a cyclic lithium phosphate as a second additive.

Specifically, the first additive and the second additive of the electrolyte together provide a CEI film with a framework-pouring structure, the CEI film has a synergistic effect, and the CEI film with the structure has a metal ion directional selection function.

Specifically, in the electrolyte, the addition amount of the first additive tri (2-cyanoethyl) phosphate accounts for 0.1-5% of the total mass of the electrolyte.

Specifically, in the electrolyte, the second additive is at least one of difluoro bis (oxalato) phosphate (LiDFBP) and tetrafluoro (lithium oxalato) phosphate (LiTFOP), and the addition amount of the second additive accounts for 0.01% -3% of the total mass of the electrolyte.

Specifically, in the electrolyte, the organic solvent is two or more of Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), gamma-butyrolactone (GBL), propyl Propionate (PP) and Ethyl Propionate (EP).

Specifically, in the electrolyte, the addition amount of the organic solvent accounts for 50-75% of the total mass of the electrolyte.

Specifically, in the electrolyte, the lithium salt is lithium hexafluorophosphate (LiPF ₆ ) Lithium bis (fluorosulfonyl imide) (LiLSI), lithium difluorophosphate (LiPO) ₂ F ₂ ) At least one of them.

Specifically, in the electrolyte, the addition amount of the lithium salt accounts for 12-20% of the total mass of the electrolyte.

Specifically, the electrolyte further comprises a third additive, wherein the third additive comprises at least one of tris (trimethylsilane) phosphate (TMSP), tris (trimethylsilane) phosphite (TMSP), tris (trimethylsilane) borate (TMSB), succinonitrile (SN), adiponitrile (ADN), 1,3, 6-Hexanetrinitrile (HTCN), 1, 2-bis (2-cyanoethoxy) ethane (DENE), 1,2, 3-tris (cyanoethoxy) propane, tris (2-cyanoethyl) borate, tris (2-cyanoethyl) phosphate, tris (2-cyanoethyl) phosphite, vinylene Carbonate (VC), fluoroethylene carbonate (FEC), ethylene carbonate (VEC), ethylene sulfate (DTD), ethylene Sulfite (ES) or fluoroethylene sulfate, 1, 3-Propane Sultone (PS), 1, 4-Butane Sultone (BS), 1, 3-propylene sulfonic acid (PST) and methane disulfonic acid methylene (DS), and the mass percent of the third additive accounts for 0.1% -20% of the total electrolyte.

Specifically, in the electrolyte, the synthesis path of the first additive tri (2-cyanoethyl) phosphate is prepared by taking 3-hydroxy propionitrile and phosphorus oxychloride as raw materials and carrying out substitution reaction. Namely, the tri (2-cyanoethyl) phosphate is obtained by taking 3-hydroxy propionitrile and phosphorus oxychloride as raw materials, preferably through substitution reaction.

In the present invention, the preparation method of the tris (2-cyanoethyl) phosphate preferably comprises the steps of:

2) Adding phosphorus oxychloride organic solution into the system solution obtained in the step, carrying out low-temperature reaction, adding organic metal alkali under the condition of II-stage reaction temperature after the dripping is completed, and continuing the reaction under the temperature condition to obtain tris (2-cyanoethyl) phosphate;

firstly, mixing 3-hydroxy propionitrile and a hydrogen chloride chelating agent to obtain a system solution.

In the present invention, the hydrogen chloride chelating agent preferably includes one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine, and pyridine, more preferably pyridine, triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, or n-butylamine.

In the present invention, the molar ratio of the hydrogen chloride chelating agent to phosphorus oxychloride is preferably (3 to 6): 1, more preferably (3.5 to 5.5): 1, more preferably (4 to 5): 1.

in the present invention, the molar ratio of 3-hydroxypropionitrile to phosphorus oxychloride is preferably (3 to 10): 1, more preferably (4 to 9): 1, more preferably (5 to 8): 1, more preferably (6 to 7): 1.

adding phosphorus oxychloride organic solution into the system solution obtained in the steps, performing low-temperature dropwise addition reaction, adding organic metal alkali under the condition of II-stage temperature after dropwise addition, and continuously reacting to obtain the tri (2-cyanoethyl) phosphate.

In the present invention, the organic solvent in the phosphorus oxychloride organic solution preferably includes one or more of benzene, toluene, xylene, n-hexane, methylene chloride, dichloroethane, trichloroethane, acetonitrile, ethyl acetate, petroleum ether, diethyl ether and t-methyl butyl ether, more preferably toluene, xylene, ethyl acetate, diethyl ether, t-methyl butyl ether, methylene chloride or dichloroethane.

In the present invention, the temperature of the low temperature reaction is preferably-40 to 10 ℃, more preferably-30 to 5 ℃, and still more preferably-20 to 0 ℃.

In the present invention, the volume ratio of the organic solvent to phosphorus oxychloride is preferably (1 to 10): 1, more preferably (3 to 8): 1, more preferably (5 to 6): 1.

in the present invention, the mode of adding the phosphorus oxychloride organic solution preferably includes dropwise addition.

In the present invention, the rate of the dropping is preferably 5 to 20ml/h, more preferably 8 to 17ml/h, and still more preferably 11 to 14ml/h.

In the present invention, the organic metal alkali in the organic metal alkali solution preferably includes one or more of sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, potassium tert-butoxide, n-butyllithium and lithium diisopropylamide, more preferably sodium hydrogen, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, potassium tert-butoxide, n-butyllithium or lithium diisopropylamide.

In the present invention, the molar ratio of the organometallic base to the phosphorus oxychloride is 1: (10 to 20), more preferably 1: (12 to 18), more preferably 1: (14-16).

In the present invention, the temperature of the stage II reaction is preferably 50 to 100 ℃, more preferably 60 to 80 ℃, still more preferably 65 to 78 ℃.

In the present invention, the time for continuing the reaction is preferably 0.5 to 20 hours, more preferably 8 to 17 hours, and still more preferably 11 to 15 hours.

In the present invention, the purification step is preferably included after the reaction is continued.

In the present invention, the purification step preferably includes one or more steps of extraction, washing and rotary evaporation, more preferably a plurality of steps of extraction, washing and rotary evaporation.

In the present invention, the extraction preferably comprises organic phase extraction.

In the present invention, the extractant for extraction preferably includes one or more of xylene, toluene, n-hexane, methylene chloride, ethyl acetate, chloroform, benzene, trichloroethane and dichloroethane, more preferably methylene chloride, n-hexane, chloroform, xylene, ethyl acetate, diethyl ether, benzene or dichloroethane.

In the present invention, the organic phase preferably includes one or more of dichloromethane, dichloroethane, benzene, toluene, octane, petroleum ether, triacontane, octacosane, carbon tetrachloride, ethane and cyclohexane, more preferably dichloromethane, dichloroethane, benzene, toluene, octane, petroleum ether, octacosane, carbon disulfide, carbon tetrachloride, ethane or cyclohexane.

The invention relates to a complete and refined integral preparation process, which better ensures the structure of tri (2-cyanoethyl) phosphate and improves the purity and yield of products, and the preparation method of the tri (2-cyanoethyl) phosphate comprises the following steps:

1) Adding a mixture of 3-hydroxypropionitrile and a hydrogen chloride chelating agent to the addition three-necked flask;

2) Dropwise adding a mixed solution of phosphorus oxychloride and an organic dilution solvent into the step 1) at a low temperature;

3) Adding a certain proportion of organic metal alkali into the mixed solution obtained after the reaction in the step 2) to the temperature of 50-100 ℃ for continuous reaction for 0.5-20 h;

4) Filtering, extracting and separating the reaction in the step 3), and carrying out reduced pressure distillation on the tri (2-cyanoethyl) phosphate mixed solution to obtain a tri (2-cyanoethyl) phosphate crude product;

5) Adding the crude reaction product obtained in the step 4) into ice water for dissolution, adding an organic solvent, fully stirring, separating an organic phase (the product of the tri (2-cyanoethyl) phosphate compound is extracted into the organic phase) by using a separating funnel, washing the organic phase with ice water for 3-4 times, and removing the organic solvent by rotary evaporation to obtain the pure tri (2-cyanoethyl) phosphate.

In the method for preparing the compound of the embodiment, 3-hydroxy propionitrile is contacted with phosphorus oxychloride, and OH containing cyano groups and Cl in the phosphorus oxychloride undergo substitution reaction to obtain tri (2-cyanoethyl) phosphate and the compound of the embodiment:

according to the embodiment of the invention, in order to obtain the compound of the embodiment, phosphorus oxychloride is dropwise added into 3-hydroxy propionitrile, and excessive 3-hydroxy propionitrile can provide sufficient reaction raw materials for a reaction system relative to phosphorus oxychloride, so that more tri (2-cyanoethyl) phosphate is generated, and the yield of the product compound can be further improved.

According to the embodiment of the invention, in order to obtain the compound of the embodiment, the organic solution dilutes phosphorus oxychloride, and the reaction rate is controlled, so that the reaction is more sufficient, and the yield of the product compound can be further improved.

According to an embodiment of the present invention, in order to obtain the compound of the above embodiment, a low temperature reaction is selected, and since the reaction is exothermic, a temperature of-40℃to 10℃is selected, preferably a temperature of-20℃to-5 ℃.

According to an embodiment of the present invention, in order to obtain the compound of the above embodiment, the organic base is selected to be a hydrogen chloride chelating agent, and the organic base is triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine, and pyridine, and the molar ratio of the hydrogen chloride chelating agent to phosphorus oxychloride is 3:1 to 6:1, preferably 3:1 to 4:1, so that the yield of the product compound can be further improved.

According to the embodiment of the present invention, in order to obtain the compound of the above embodiment, the phosphorus oxychloride in the step (2) and the step (3) is diluted with an organic diluent solvent and the dropping reaction rate is controlled, and the yield of the product compound can be further improved.

According to the embodiment of the invention, in order to obtain the compound of the embodiment, the organic metal base is dropwise added in the step (4), so that the conversion of the di (2-cyanoethyl) phosphoric acid to the target product is facilitated, and the yield of the product compound can be further improved.

According to the embodiment of the invention, in order to obtain the compound of the embodiment, the compound is reacted at 50-100 ℃ after the completion of the dropwise addition reaction, so that conditions are provided for overcoming the trisubstituted steric hindrance reaction, and the yield of the product compound is improved.

The invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and the electrolyte in any one of the technical schemes.

In the present invention, the positive electrode is preferably a CEI film having a frame-casting structure.

In the present invention, the cyclic lithium phosphate preferably provides a framework structure for the CEI film.

In the present invention, the tris (2-cyanoethyl) phosphate is poured into a framework structure formed from cyclic lithium phosphate. In particular, the casting is preferably intercalation, i.e. tris (2-cyanoethyl) phosphate is intercalated in a membrane layer frame structure formed from cyclic lithium phosphate.

In the present invention, the CEI film preferably has a metal ion orientation selection function.

In the present invention, the CEI film structure preferably contains an organolithium component.

The invention provides a lithium ion battery electrolyte containing tri (2-cyanoethyl) phosphate and a lithium ion battery. The invention particularly selects the tri (2-cyanoethyl) phosphate and the cyclic lithium phosphate to be compounded as electrolyte additives, and the two additives are synergistic, so that a compact CEI film with a multi-atom structure is formed at the interface between the anode material of the lithium ion battery and the electrolyte, thereby realizing the dual effects of ion directional selection, inhibiting the dissolution of high-valence metal ions and improving the migration rate of lithium ions, and improving the high-voltage performance, the high-temperature performance and the cycle performance of the lithium ion battery.

For further explanation of the present invention, the lithium ion battery electrolyte and the lithium ion battery provided by the present invention are described in detail below with reference to examples, but it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation and specific operation procedures are given only for further explanation of the features and advantages of the present invention, and not limitation of the claims of the present invention, and the scope of protection of the present invention is not limited to the examples described below.

The reagents used in the following examples of the present invention are all commercially available.

Preparation and purification examples

The synthetic route for tris (2-cyanoethyl) phosphate is as follows:

(1) Adding a mixed solution of 0.4mol of anhydrous 3-hydroxy propionitrile and 0.3mol of triethylamine into a three-neck flask, and controlling the reaction temperature below 0 ℃;

(2) Mixing 0.1mol of phosphorus oxychloride 15.33g with 100ml of xylene, and placing the mixture in a constant pressure dropping funnel;

(3) Dropwise adding the mixed solution obtained in the step (2) into the mixed solution obtained in the step (1), and controlling the dropwise adding rate to be 10ml/h;

(4) After the dripping is completed, the temperature is raised to 60 ℃, 0.68g of sodium ethoxide is added, and the reaction is carried out for 5 hours;

(5) Adding 100ml of dimethylbenzene into the reacted solution for extraction, filtering out triethylamine hydrochloride, and distilling the filtrate under reduced pressure to obtain a crude product;

(6) Adding the crude reaction product into ice water for dissolution, adding dimethylbenzene for full stirring, separating an organic phase (the product of the tri (2-cyanoethyl) phosphate compound is extracted into the organic phase) by using a separating funnel, washing the organic phase with ice water for 3-4 times, and removing the dimethylbenzene by rotary evaporation to obtain pure tri (2-cyanoethyl) phosphate, wherein the yield is 70.5%, the product content is 97.16% and the chlorine content is 0.32ppm by using a gas chromatograph.

The nuclear magnetic H spectrum and the C spectrum of the target product are shown in figures 1 and 2, and are matched with the calculated result of ChemDraw software on the nuclear magnetic of the tri (2-cyanoethyl) phosphate.

Referring to fig. 1, fig. 1 is a nuclear magnetic C spectrum of the first additive tris (2-cyanoethyl) phosphate prepared according to the present invention.

Referring to fig. 2, fig. 2 is a nuclear magnetic H-spectrum of the first additive tris (2-cyanoethyl) phosphate prepared in accordance with the present invention.

Examples

(1) Preparation of electrolyte: in a glove box filled with argon, the corresponding solvents were uniformly mixed according to a predetermined ratio and continuously stirred, and predetermined amounts of electrolyte lithium salt and additives were slowly added to the mixed solvents to obtain examples 1 to 8 and comparative examples 1 to 6, and the electrolyte formulations are shown in table 1.

(2) LSV test: the LSV curve of the electrolyte of comparative example 1, example 3, example 7 was tested using a three electrode test method.

(3) Preparing a positive electrode plate: polyvinylidene fluoride (PVDF), a conductive agent and lithium cobaltate are mixed according to the mass ratio of 1.2 percent: 1%:97.8 percent of the aluminum foil current collector is added into N-methyl pyrrolidone (NMP) in sequence, fully stirred and uniformly mixed, the slurry is coated on the aluminum foil current collector, and the positive electrode plate is prepared by drying, cold pressing and punching.

(4) Preparing a negative electrode plate: sodium carboxymethylcellulose (CMC), styrene butadiene rubber emulsion (SBR), a conductive agent and graphite are mixed according to the mass ratio of 1.2 percent: 2%:1%:96.8 percent of the mixture is added into deionized water in sequence, fully stirred and uniformly mixed, the slurry is coated on a copper foil current collector, and the negative pole piece is prepared by drying, cold pressing and punching.

(5) Preparation of a lithium battery: and (3) stacking the diaphragm, the positive electrode plate and the negative electrode plate in a Z shape to obtain a bare cell to be injected with liquid, packaging the bare cell with an aluminum plastic film to obtain the battery cell to be injected with liquid, baking the battery cell, and injecting electrolyte according to the addition amount of 2g/Ah to obtain the lithium ion battery with nominal capacity of 5Ah to be tested.

(6) Testing of lithium ion batteries:

DCR test: charging the battery to 4.0V at constant current and constant voltage, and standing for 6 hours to test the direct current internal resistance of the battery;

and (3) testing the rate discharge performance: charging 0.2C to 4.5V, discharging 0.2C, 0.5C, 1C and 5C to 3.0V, and calculating the ratio of discharge capacity to 0.2C discharge capacity under different multiplying powers;

and (3) multiplying power charging performance test: discharging 0.2C to 3.0V, charging 0.2C, 0.5C, 1C and 5C to 4.5V, and calculating the ratio of the cross current charging capacity to the total charging capacity under different multiplying power charging;

and (3) testing the cycle performance: testing capacity retention rate of 1C under different cycle times of charge and discharge at different temperatures, wherein the charge and discharge cut-off voltage is 3.0V-4.2V;

high temperature storage performance test: the fully charged battery was stored at 60 ℃ for 7 days, and the capacity retention rate and the capacity recovery rate were tested.

Table 2, table 3 provides performance testing of the different example and comparative batteries.

TABLE 1

TABLE 2

TABLE 3 Table 3

Analysis of results:

FIG. 1 and FIG. 2 provide nuclear magnetic spectra of tris (2-cyanoethyl) phosphate, which prove that the scheme of the synthetic route of the patent is feasible, and the purity of the product can reach more than 99%. Fig. 3 provides LSV curves for the electrolytes of comparative example 1, example 3 and example 7, confirming that the electrolytes of the formulations employing the first additive and the second additive undergo significant oxidation reaction at about 4.5V, corresponding to the film formation potential during the first charge of the battery, thereby greatly improving the antioxidant potential of the electrolyte, and confirming the feasibility of constructing the CEI film of the "frame-casting" structure using the scheme of this patent.

In conjunction with table 2, table 3 analysis of battery test results:

comparison of the test results of comparative examples 1,4, 3 and 5 and comparison of the test results of examples 7 and 6 shows that the same addition amount of tri (2-cyanoethyl) phosphate substituted HTCN can greatly reduce the direct current internal resistance of the battery, and the overall performance of the battery is also greatly improved, thereby proving the effectiveness of the phosphate skeleton structure for improving the electrochemical performance of the nitrile additive.

Comparative example 2, comparative example 3 and test results of examples 1 to 8 show that, when only the second additive, namely, cyclic lithium phosphate, was added, the battery showed a direct current internal resistance and rate performance comparable to those of the example battery, but the high-temperature storage performance and cycle performance of the battery were severely deteriorated.

From a combination of the test results of comparative example 1 and examples 1 to 8, it can be seen that the comparative example added only the first additive tris (2-cyanoethyl) phosphate, and the overall performance of the battery was significantly reduced as compared with the examples. By combining the overall test effects of the batteries of the examples and the comparative examples, it can be found that the overall performance of the battery is optimal when the addition amount of the first additive tri (2-cyanoethyl) phosphate is between 2% and 3% and the addition amount of the second additive cyclic lithium phosphate is 1%. It is difficult to achieve the synergistic effect of the co-use of the first and second additives with the single addition of either additive, which also demonstrates from the battery performance testing end the effectiveness of constructing a "frame-cast" CEI film to promote overall performance enhancement of the battery.

The foregoing has outlined rather broadly the principles and embodiments of the present invention in order that the detailed description of the invention that follows may be better understood, and in order that the present invention may be practiced by anyone skilled in the art, including in any regard to the manufacture and use of the devices or systems, and in order that the present invention may be carried out in any combination. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims. The scope of the patent protection is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. The lithium ion battery electrolyte is characterized by comprising an organic solvent, lithium salt and an additive;

the additive comprises a first additive and a second additive;

the first additive comprises tris (2-cyanoethyl) phosphate;

the second additive includes a cyclic lithium phosphate compound.

2. The lithium ion battery electrolyte according to claim 1, wherein the addition amount of the tri (2-cyanoethyl) phosphate is 0.1-5% of the total mass of the electrolyte;

the tri (2-cyanoethyl) phosphate has a structure as shown in formula (I):

3. the lithium ion battery electrolyte of claim 1, wherein the cyclic lithium phosphate compound comprises lithium difluorobis (oxalato) phosphate and/or lithium tetrafluorooxalato phosphate;

4. The lithium ion battery electrolyte of claim 1, wherein the lithium salt comprises one or more of lithium hexafluorophosphate, lithium bis-fluorosulfonyl imide, and lithium difluorophosphate;

the additive further comprises a third additive.

5. The lithium ion battery electrolyte of claim 4, wherein the third additive comprises one or more of tris (trimethylsilane) phosphate, tris (trimethylsilane) phosphite, tris (trimethylsilane) borate, succinonitrile, adiponitrile, 1,3, 6-hexanetrinitrile, 1, 2-bis (2-cyanoethoxy) ethane, 1,2, 3-tris (cyanoethoxy) propane, tris (2-cyanoethyl) borate, tris (2-cyanoethyl) phosphate, tris (2-cyanoethyl) phosphite, vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, vinyl fluorosulfate, 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propene sulfonic acid, and methane disulfonic acid methylene;

6. The lithium ion battery electrolyte according to claim 1, wherein the tri (2-cyanoethyl) phosphate is obtained by substitution reaction of 3-hydroxypropionitrile and phosphorus oxychloride as raw materials.

7. The lithium ion battery electrolyte according to claim 6, wherein the preparation method of the tri (2-cyanoethyl) phosphate comprises the following steps:

8. The lithium ion battery electrolyte according to claim 7, further comprising a purification step after the continuing reaction;

the extraction comprises organic phase extraction;

9. A lithium ion battery comprising a positive electrode, a negative electrode and the electrolyte of any one of claims 1 to 8.

10. The lithium ion battery of claim 1, wherein the positive electrode has a frame-cast CEI film thereon;

the cyclic lithium phosphate provides a framework structure for the CEI film;

the CEI film has a metal ion orientation selection function;

the CEI film structure contains an organic lithium component.