Aza-silane electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an aza-silane electrolyte additive, an electrolyte and a lithium ion battery. The aza-silane electrolyte additive has a structure as shown in a formula I. The invention provides the aza-silane electrolyte additive for the first time, and the unique structure of the additive can effectively eliminate HF in the electrolyte and protect an active material; meanwhile, transition metal manganese ions in the electrolyte can be effectively complexed, manganese deposition is effectively inhibited, and a negative electrode SEI film is protected; various characteristic groups contained in the structure can solve the industrial problem of manganese ion dissolution from multiple angles of positive electrode interface-transition metal dissolution-negative electrode interface, and a membrane structure in a battery cell system is effectively protected, so that the electrochemical performance of the battery is improved, the pain points of materials such as lithium iron manganese phosphate, lithium nickel manganese oxide and lithium-rich manganese are solved, and the service life of the battery is prolonged. And a matched electrolyte is developed.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to an azasilane electrolyte additive, an electrolyte, and a lithium-ion battery. Background Art

[0002] With the continuous popularization of electronic products such as electric vehicles and portable devices, the demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. This type of battery has broad application prospects in the fields of energy storage, aerospace, etc. How to improve the energy density of lithium batteries has become the focus of research by scholars.

[0003] Currently, lithium iron manganese phosphate cathode materials with the same cost and safety level as lithium iron phosphate and the same energy density as high-voltage ternary materials, lithium nickel manganese oxide cathode materials with high energy density and low production cost, and lithium-rich manganese-based cathode materials have received extensive attention and research. However, the above materials all have the disadvantages of poor high-temperature cycle and storage performance, which limits their applications. On the other hand, the corrosion of the electrolyte to the cathode material at high temperature leads to excessive capacity attenuation and the dissolution of transition metal manganese. The dissolved manganese ions will also deposit on the negative electrode, damaging the SEI film at the negative electrode interface and further causing material deterioration.

[0004] The process of the destruction of the electrochemical performance of the battery by transition metals in the electrolyte includes the following steps: manganese dissolution at the positive electrode - manganese dissolution in the electrolyte - manganese deposition at the negative electrode. Because manganese ions dissolve out, a disproportionation reaction will occur on the surface of the positive electrode material to generate divalent manganese, which migrates to the surface of the negative electrode and is reduced for deposition. As a result, the SEI film will be damaged, leading to continuous growth and thickening of the SEI film, problems such as consumption of active lithium, increase in electrode impedance, and gas generation at the negative electrode, and ultimately resulting in continuous attenuation of the battery capacity.

[0005] Generally, there are three strategies to solve the above problem of serious manganese ion dissolution from the perspective of the electrolyte. One is to form an effective CEI film structure on the positive electrode to avoid the corrosion of the electrolyte to the positive electrode material and prevent manganese ions from dissolving out at the source. The second is to form a dense and tough SEI film structure on the negative electrode to reduce the damage to the SEI film caused by manganese deposition on the negative electrode. The third is to capture manganese ions in the solvent to avoid the damage to the SEI film caused by manganese deposition on the negative electrode.

[0006] Most current commercial additives improve in one aspect and it is difficult to completely avoid the dissolution and damage of transition metals. Only when the three levels of manganese ion dissolution - dissolution - deposition at the transition metal manganese work together can the pain points of the industry be solved from the perspective of the electrolyte. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide an azasilane electrolyte additive, an electrolyte, and a lithium-ion battery, which solve the problem of manganese ion dissolution from three aspects.

[0008] To achieve the above object, the present invention provides an azasilane electrolyte additive having the structure shown in Formula I:

[0009]

[0010] Wherein, 0 ≤ n1 ≤ 3; 1 ≤ n2 ≤ 2;

[0011] R 1 and R 2 are independently selected from C1-C6 alkyl groups.

[0012] The above n1 is any integer from 0 to 3, specifically it can be 0, 1, 2 or 3.

[0013] The above n2 is any integer from 1 to 2, specifically it can be 1 or 2.

[0014] The above R 1 and R 2 are independently selected from C1-C6 alkyl groups, more preferably independently selected from C1-C4 alkyl groups, and further preferably independently selected from C1-C3 alkyl groups, specifically it can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

[0015] In the structure of the above azasilane electrolyte additive provided by the present invention, it contains Si-O bonds, which can react with HF in the electrolyte to reduce the destructive effect of HF on the surface of the manganese-based positive electrode, achieving the effect of protecting the positive electrode material; the structure of the azasilane electrolyte additive also contains Si-N bonds, and Si-N can also react with HF and H 2 O in the electrolyte to achieve the purpose of protecting the positive electrode. At the same time, after the Si-N bond reacts with HF, the azasilane ring opens, and the generated chain-like product adheres to the surface of the active material, forming a flexible and strong organic film to avoid the corrosion of the active material by the electrolyte; the structure of the azasilane electrolyte additive also contains an ethylenediamine chain, and the lone pair electrons of the N atom can complex transition metal ions but do not participate in film formation. There are multiple active sites for binding metal ions in the long chain, forming a more stable structure with the transition metal Mn, and can capture transition metal ions in the electrolyte through complexation, significantly slowing down the destruction of the negative electrode surface by the dissolved manganese. The above effects are better than using the additives containing the above several structures alone, and thus solve the problem of manganese ion dissolution from three aspects.

[0016] The present invention provides a preparation method of the above azasilane electrolyte additive, including the following steps:

[0017] S1) The ethylenediamine shown in Formula I-a reacts with trichlorosilane bromide shown in Formula I-b by a substitution reaction to obtain an intermediate;

[0018] S2) The obtained intermediate is subjected to a substitution reaction with an alcohol compound having 1 to 6 carbon atoms to obtain an intermediate represented by Formula I-d;

[0019] S3) The intermediate represented by Formula I-d is subjected to a condensation reaction under the action of pyridine and hexamethyldisilazane to obtain the azasilane electrolyte additive represented by Formula I;

[0020]

[0021] Wherein, 0 ≤ n1 ≤ 3; 1 ≤ n2 ≤ 2;

[0022] R, R 1 、R 2 are independently selected from alkyl groups having 1 to 6 carbon atoms.

[0023] The ranges of the above n1, n2, R 1 、R 2 are the same as those described above.

[0024] The range of the said R is the same as the ranges of R 1 、R 2 described above.

[0025] The molar ratio of the vinylamine represented by Formula I-a to the bromotrichlorosilane represented by Formula I-b is preferably (1 to 1.05):1.

[0026] In some specific embodiments of the present invention, the vinylamine represented by Formula I-a is selected from diethylenetriamine, ethylenediamine, triethylenetetramine or tetraethylenepentamine.

[0027] In some specific embodiments of the present invention, the bromotrichlorosilane represented by Formula I-b is selected from 3-bromopropyltrichlorosilane or 3-bromobutyltrichlorosilane.

[0028] The reaction temperature of the substitution reaction in Step S1) is preferably -20 to 0 °C, and the reaction time is preferably 1 to 3 h.

[0029] Preferably, an acid-binding agent is added to the substitution reaction system.

[0030] The acid-binding agent is preferably triethylamine.

[0031] The molar ratio of the triethylamine to the vinylamine is preferably (5 to 8):1.

[0032] The molar ratio of the intermediate represented by Formula I-c to the alcohol compound having 1 to 6 carbon atoms is preferably 1:(3 to 3.1).

[0033] In some specific embodiments of the present invention, the alcohol compound having 1 to 6 carbon atoms is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol or n-hexanol.

[0034] The reaction temperature of the substitution reaction in step S2) is preferably 0-20°C, and the reaction time is preferably 3-5 h.

[0035] Preferably, pyridine is added to the substitution reaction system.

[0036] The reaction temperature of the condensation reaction in step S3) is preferably 50-70°C, more preferably 50-60°C; the reaction time is preferably 3-5 h.

[0037] The reaction equation of the above preparation method is as follows:

[0038]

[0039] In the above reaction equation, the ranges of n1, n2, and R are the same as those described above.

[0040] The above reaction is preferably carried out under the protection of an inert gas.

[0041] On the other hand, the present invention provides a lithium-ion electrolyte, including: a non-aqueous solvent, a lithium salt, and the above-mentioned azasilane electrolyte additive.

[0042] The present invention has no special limitation on the type of the non-aqueous solvent, and it can be an organic solvent well-known to those skilled in the art and applicable to lithium-ion electrolytes, preferably including any one or more of carbonate solvents, carboxylate solvents, amine solvents, sulfone solvents, and nitrile solvents.

[0043] The carbonate solvents include but are not limited to one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, butylene carbonate, methyl butyl carbonate, and dibutyl carbonate.

[0044] The carboxylate solvents include but are not limited to one or more of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl propionate.

[0045] The amine solvents include but are not limited to one or more of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide.

[0046] The sulfone solvents include but are not limited to one or more of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, dipropyl sulfone, dimethyl sulfite, diethyl sulfite, and tetramethyl sulfoxide.

[0047] The nitrile solvents include but are not limited to one or more of acetonitrile, succinonitrile, adiponitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, and 1,3,6-hexanetricarbonitrile.

[0048] The content of the non-aqueous solvent in the electrolyte is preferably 70% - 90 wt%.

[0049] The present invention has no special limitation on the lithium salt, and it can be a lithium salt well-known to those skilled in the art and applicable to lithium-ion electrolytes, including but not limited to lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, etc., or one or more of them.

[0050] The concentration of the lithium salt in the electrolyte is preferably 0.5 - 2 M.

[0051] The addition amount of the azasilane electrolyte additive is preferably 0.05 wt% - 3 wt%, more preferably 0.1 wt% - 1 wt%.

[0052] On the other hand, the present invention provides a lithium-ion battery including the above-mentioned lithium-ion electrolyte.

[0053] The present invention has no special limitation on the structure of the above-mentioned lithium-ion battery, and it can be a structure of a lithium-ion battery well-known to those skilled in the art. Preferably, its structure further includes a positive electrode, a negative electrode, and a separator.

[0054] The present invention has no special limitation on the structure of the above-mentioned positive electrode, and it can be a positive electrode applicable to a lithium-ion battery well-known to those skilled in the art. Preferably, the positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the surface of the positive electrode current collector. The material of the positive electrode current collector can be selected from aluminum, titanium, or stainless steel. The positive electrode material layer preferably includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes but is not limited to lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), medium-high nickel ternary materials, and their composite positive electrode materials. The conductive agent includes but is not limited to carbon materials, such as one or more of carbon black, conductive polymers, acetylene black, carbon fibers, carbon nanotubes, and graphite. The binder includes but is not limited to one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene monomer rubber, and styrene-butadiene rubber (SBR).

[0055] The present invention has no special limitation on the structure of the above-mentioned negative electrode, and it can be a negative electrode applicable to a lithium-ion battery well-known to those skilled in the art. Preferably, the negative electrode can include a negative electrode current collector and a negative electrode material layer on the surface of the negative electrode current collector. The material of the negative electrode current collector includes but is not limited to copper, nickel, or stainless steel. The negative electrode material layer includes but is not limited to a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes but is not limited to metallic lithium, lithium-inserted carbon materials, or lithium alloys, etc. The conductive agent and binder used for the negative electrode are the same as those used for the positive electrode.

[0056] The present invention does not particularly limit the material of the above-mentioned separator membrane, and it can be a separator membrane suitable for lithium-ion batteries well-known to those skilled in the art, including but not limited to polypropylene (PP), polyethylene (PE), a composite material of polypropylene (PP) and polyethylene (PE), fiberglass felt, a composite membrane formed by welding or bonding with a wettable polyolefin microporous membrane, etc.

[0057] The test results show that the electrolyte prepared by using the azasilane electrolyte additive provided by the present invention can eliminate HF and H 2 O in the electrolyte, and at the same time can form a film on the surface of the active material, significantly improving the first efficiency, capacity retention rate and cycle stability of the battery cell, and greatly reducing the deposition of transition metal Mn on the negative electrode.

[0058] Compared with the prior art, the present invention provides an azasilane electrolyte additive having the structure shown in Formula I.

[0059] The present invention first proposes an azasilane electrolyte additive. The unique structure of this additive can effectively eliminate HF in the electrolyte and protect the active material; at the same time, it can effectively complex transition metal manganese ions in the electrolyte and effectively inhibit manganese deposition to protect the negative electrode SEI film; the various characteristic groups contained in its structure can solve the industry problem of manganese ion dissolution from multiple perspectives of the positive electrode interface-transition metal dissolution-negative electrode interface, effectively protecting the film structure in the battery cell system, thereby improving the electrochemical performance of the battery, solving the pain points of materials such as lithium iron phosphate manganese, lithium nickel manganese oxide, and lithium-rich manganese, and developing a supporting electrolyte. Detailed Embodiments

[0060] In order to further illustrate the present invention, the following will be described in detail with reference to embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0061] For all raw materials of the present invention, there is no particular limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0062] Example 1

[0063] At -20 °C, 0.105 mol of diethylenetriamine was added to 50 ml of triethylamine, and 0.1 mol of 3-bromopropyltrichlorosilane was slowly added under stirring. The reaction was continued for 2 hours. After the reaction was completed, 50 ml of 1 mol / L aqueous sodium bicarbonate solution was added to wash and extract the organic phase. The intermediate product obtained by distilling the organic phase was added to 50 ml of pyridine, and 0.31 mol of propanol was added at 10 °C under stirring and reacted for 3 h. The temperature was raised to 60 °C, 0.05 mol of hexamethyldisilazane was added and reacted for 4 h. Then the mixed solution was separated and extracted by flash chromatography to obtain compound A, GC-MS (m / z): calcd. for C 13 H 31 O 2 N 3 Si[M +1 + , 289.22, found 289.71.

[0064]

[0065] In a glove box, 30 wt% of EC, 30.5 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until fully dissolved to obtain a mixed salt solution; further, 0.5 wt% of compound A was added to the mixed salt solution, and the resulting mixed solution was used as an electrolyte.

[0066] Preparation of the battery:

[0067] 95 wt% of LiMn 0.4 Fe 0.6 PO 4 , 2.5 wt% of PVDF, and 2.5 wt% of conductive carbon black were taken and mixed and dispersed evenly in N,N-dimethylpyrrolidone to form a slurry, which was evenly coated on aluminum foil;

[0068] The aluminum foil was cut into pieces; 94.8 wt% of artificial graphite, 1.7 wt% of CMC, 1 wt% of SBR, and 2.5 wt% of conductive carbon black were mixed and dispersed evenly in pure water to form a slurry, which was evenly coated on copper foil and roll-pressed and cut into pieces.

[0069] A 2032 coin cell was assembled in the order of negative electrode case - negative electrode sheet - polypropylene separator - positive electrode sheet - gasket - spring piece - positive electrode case.

[0070] In order to study the complexing effect of the additive on transition metal manganese, the battery after 200 cycles was disassembled, and the graphite negative electrode of the coin cell was subjected to inductively coupled plasma (ICP) testing to analyze the deposition of transition metal manganese on the negative electrode. The coin cell cycle test was carried out at a constant current of 0.2C and a constant voltage of 4.4V, and then discharged at a constant current of 0.2C to 3V.​

[0071] Example 2

[0072] At 0 °C, 0.10 mol of ethylenediamine was taken and added to 50 ml of triethylamine. Under stirring conditions, 0.1 mol of 3-bromopropyltrichlorosilane was slowly added, and the reaction was continued for 2 hours. After the reaction was completed, 50 ml of 1 mol / L aqueous sodium bicarbonate solution was added to wash and extract the organic phase; the intermediate product obtained by distilling the organic phase was added to 50 ml of pyridine, and 0.3 mol of methanol was added at 20 °C under stirring conditions and reacted for 4 h; the temperature was raised to 50 °C and 0.05 mol of hexamethyldisilazane was added and reacted for 3 h, and then the mixed solution was separated and extracted by flash chromatography to obtain compound B, GC-MS (m / z): calcd. for C 7 H 18 O 2 N 2 Si[M +1 + , 190.11, found 190.64.

[0073]

[0074] In a glove box, 30 wt% of EC, 30 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until completely dissolved to obtain a mixed salt solution; further, 1 wt% of compound B was added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte; after cycling 200 times, the battery was disassembled and the deposition content of Mn on the graphite negative electrode was analyzed. The battery preparation and testing were the same as in Example 1.

[0075] Example 3

[0076] At -10 °C, 0.103 mol of diethylenetriamine was taken and added to 50 ml of triethylamine. Under stirring conditions, 0.1 mol of 3-bromobutyltrichlorosilane was slowly added, and the reaction was continued for 3 hours. After the reaction was completed, 50 ml of 1 mol / L aqueous sodium bicarbonate solution was added to wash and extract the organic phase; the intermediate product obtained by distilling the organic phase was added to 50 ml of pyridine, and 0.31 mol of ethanol was added at 10 °C under stirring conditions and reacted for 5 h; the temperature was raised to 60 °C and 0.05 mol of hexamethyldisilazane was added and reacted for 4 h, and then the mixed solution was separated and extracted by flash chromatography to obtain compound C, GC-MS (m / z): calcd. for C 12 H 29 O 2 N 3 Si[M +1 + , 275.20, found 276.13. ​​

[0077]

[0078] Take 30 wt% EC, 30.95 wt% DMC, and 26 wt% EMC in a glove box and stir evenly to form a mixed solution; add 13 wt% of LiPF 6 Stir well to dissolve to obtain a mixed salt solution; further add 0.05 wt% of Compound C to the mixed salt solution, and use the resulting mixed solution as the electrolyte; after cycling 200 times, disassemble the battery and analyze the deposition content of Mn on the graphite negative electrode. The battery preparation and testing are the same as in Example 1.

[0079] Example 4

[0080] At 0 °C, take 0.104 mol of tetraethylenepentamine and add it to 50 ml of triethylamine. Slowly add 0.1 mol of 3-bromopropyltrichlorosilane under stirring conditions and continue the reaction for 3 hours. After the reaction is completed, add 50 ml of 1 mol / L sodium bicarbonate aqueous solution to wash and extract the organic phase; add the intermediate product obtained by distilling the organic phase to 50 ml of pyridine, and add 0.305 mol of methanol at 20 °C under stirring conditions and react for 5 h; raise the temperature to 70 °C and add 0.05 mol of hexamethyldisilazane and react for 4 h. Then, the mixed solution is separated and extracted by flash chromatography to obtain Compound D, GC-MS (m / z): calcd. for C 13 H 33 O 2 N 5 Si[M +1 + , 319.24, found 319.63.

[0081]

[0082] Take 30 wt% EC, 30.9 wt% DMC, and 26 wt% EMC in a glove box and stir evenly to form a mixed solution; add 13 wt% of LiPF 6 Stir well to dissolve to obtain a mixed salt solution; further add 0.1 wt% of Compound D to the mixed salt solution, and use the resulting mixed solution as the electrolyte; after cycling 200 times, disassemble the battery and analyze the deposition content of Mn on the graphite negative electrode. The battery preparation and testing are the same as in Example 1.

[0083] Example 5

[0084] ​At 0 °C, 0.102 mol of triethylenetetramine was taken and added to 50 ml of triethylamine. Under stirring conditions, 0.1 mol of 3-bromobutyltrichlorosilane was slowly added, and the reaction was continued for 2 hours. After the reaction was completed, 50 ml of 1 mol / L aqueous sodium bicarbonate solution was added to wash and extract the organic phase; the intermediate product obtained by distilling the organic phase was added to 50 ml of pyridine. At 0 °C and under stirring conditions, 0.303 mol of methanol was added and the reaction was carried out for 5 h; the temperature was raised to 60 °C, 0.05 mol of hexamethyldisilazane was added and the reaction was carried out for 4 h. Then the mixed solution was separated and extracted by flash chromatography to obtain compound E, GC-MS (m / z): calcd. for C 12 H 30 O 2 N 4 Si[M +1 + , 290.20, found 290.58.

[0085]

[0086] In the glove box, 30 wt% of EC, 28 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until completely dissolved to obtain a mixed salt solution; further, 3 wt% of compound E was added to the mixed salt solution, and the obtained mixed solution was used as the electrolyte; after cycling 200 times, the battery was disassembled and the deposition content of Mn on the graphite negative electrode was analyzed. The battery preparation and testing were the same as in Example 1.

[0087] Comparative Example 1

[0088] In the glove box, 30 wt% of EC, 31 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until completely dissolved to obtain a mixed salt solution, which was used as the electrolyte; after cycling 200 times, the battery was disassembled and the deposition content of Mn on the graphite negative electrode was analyzed. The battery preparation and testing were the same as in Example 1.

[0089] Comparative Example 2

[0090] In the glove box, 30 wt% of EC, 30 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until completely dissolved to obtain a mixed salt solution; further, 0.5 wt% of diethylenetriamine, 0.25 wt% of hexamethyldisilazane, and 0.25 wt% of tetrapropoxysilane were added to the mixed salt solution, and the obtained mixed solution was used as the electrolyte; after cycling 200 times, the battery was disassembled and the deposition content of Mn on the graphite negative electrode was analyzed. The battery preparation and testing were the same as in Example 1.​

[0091] Comparative Example 3

[0092] At 0 °C, 0.10 mol of pentaethylenehexamine was taken and added to 50 ml of triethylamine. Under stirring conditions, 0.1 mol of 3-bromopropyltrichlorosilane was slowly added, and the reaction was continued for 2 hours. After the reaction was completed, 50 ml of 1 mol / L aqueous sodium bicarbonate solution was added to wash and extract the organic phase; the intermediate product obtained by distilling the organic phase was added to 50 ml of pyridine, and 0.3 mol of methanol was added at 20 °C under stirring conditions and reacted for 4 h; the temperature was raised to 50 °C and 0.05 mol of hexamethyldisilazane was added and reacted for 3 h. Then the mixed solution was separated and extracted by flash chromatography to obtain Compound F, GC-MS (m / z): calcd. for C 15 H 38 O 2 N 6 Si[M +1 + , 362.28, found 362.59.

[0093]

[0094] In a glove box, 30 wt% of EC, 30 wt% of DMC, and 26 wt% of EMC were taken and stirred evenly to form a mixed solution; 13 wt% of LiPF 6 was added to the mixed solution and stirred until completely dissolved to obtain a mixed salt solution; further, 1 wt% of Compound F was added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte; after cycling 200 times, the battery was disassembled and the deposition content of Mn on the graphite negative electrode was analyzed. The battery preparation and testing were the same as in Example 1.

[0095] Table 1 Mn deposition content of the batteries prepared in Examples 1-5 and Comparative Examples 1-3

[0096]

[0097] By comparing Examples 1-5 with Comparative Example 1, it can be found that adding the electrolyte additive of the present invention can eliminate HF and H 2 O in the electrolyte, and at the same time can form a film on the surface of the active material, significantly improving the initial efficiency and capacity retention rate of the battery cell; from the Mn deposition content on the negative electrode, it can be found that the additive of the present invention can effectively inhibit the dissolution of Mn ions and improve the cycle stability of the battery cell.

[0098] ​By comparing Example 1 with Comparative Example 2, it can be found that the additive described in this article solves the disadvantages that the ethyleneamine chain cannot form a film and the silazane-based additive decomposes to produce small molecules, which affects the high-temperature performance, through the coordinated action between various groups. This makes the performance of the battery cell better than that of each functional group used alone, improves the initial efficiency and cycle stability of the battery cell, and further reduces the deposition of transition metal Mn on the negative electrode.

[0099] By comparing Example 2 with Comparative Example 3, it can be found that when n1 > 3, the performance of the battery cell shows a deteriorating trend, which is related to the increase in the film-forming impedance of the battery cell due to the longer ethyleneamine chain.

[0100] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An azosilane electrolyte additive having a structure shown in Formula I: in, 0≤n1≤3; 1≤n2≤2; R1 and R2 are independently selected from C1-C6 alkyl groups.

2. The nitrogen-containing silane electrolyte additive according to claim 1, characterized in that: The R1 and R2 are independently selected from C1-C4 alkyl groups.

3. The method for preparing the azasilane electrolyte additive according to any one of claims 1 to 2, comprising the following steps: S1) the ethyleneamine represented by formula Ⅰ-a undergoes a substitution reaction with bromotrichlorosilane represented by formula Ⅰ-b to obtain an intermediate; S2) subjecting the obtained intermediate to a substitution reaction with a C1-C6 alcohol compound to obtain an intermediate represented by formula I-d; S3) the intermediate represented by formula I-d is subjected to a condensation reaction under the action of pyridine and hexamethyldisilazane to obtain the azasilane electrolyte additive represented by formula I; Among them, 0≤n1≤3; 1≤n2≤2; R, R1, and R2 are independently selected from C1-C6 alkyl groups.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the vinylamine represented by formula I-a to the bromotrichlorosilane represented by formula I-b is (1-1.05):1; The reaction temperature of the substitution reaction in step S1) is -20 to 0°C, and the reaction time is 1 to 3 hours; Adding an acid binding agent to the substitution reaction system; The acid binding agent is triethylamine; the molar ratio of triethylamine to ethyleneamine is (5-8):

1.

5. The preparation method according to claim 3, characterized in that: The molar ratio of the intermediate to the C1-C6 alcohol compound is 1:(3-3.1); The reaction temperature of the substitution reaction in step S2) is 0-20°C and the reaction time is 3-5h; Pyridine is added into the substitution reaction system.

6. The preparation method according to claim 3, characterized in that: The reaction temperature of the condensation reaction in step S3) is 50-70°C, and the reaction time is 3-5h.

7. A lithium ion electrolyte comprising: A non-aqueous solvent, a lithium salt, and the azasilane electrolyte additive according to any one of claims 1 to 2.

8. The lithium ion electrolyte according to claim 7, characterized in that The non-aqueous solvent includes any one or more of carbonate solvents, carboxylate solvents, amine solvents, sulfone solvents, and nitrile solvents; The lithium salt includes one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate); The concentration of the lithium salt is 0.5 to 2M; The addition amount of the azasilane electrolyte additive is 0.05wt% to 3wt%.

9. The lithium ion electrolyte according to claim 8, characterized in that The carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, butylene carbonate, methyl butyl carbonate and dibutyl carbonate; The carboxylate solvent includes one or more of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; The amine solvent includes one or more of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide; The sulfone solvent includes one or more of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, dipropyl sulfone, dimethyl sulfite, diethyl sulfite, and tetramethyl sulfoxide; The nitrile solvent includes one or more of acetonitrile, succinonitrile, adiponitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, and 1,3,6-hexanetrinitrile.

10. A lithium ion battery comprising the lithium ion electrolyte according to any one of claims 7 to 9.

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