Electrolyte for capturing CO2 to generate film-forming additive and lithium ion battery

Abstract

The invention discloses an electrolyte capable of capturing CO2 to generate a film-forming additive and a lithium ion battery, and belongs to the technical field of lithium ion battery preparation. The electrolyte comprises a carbon dioxide trapping monomer and a catalyst, and the carbon dioxide trapping monomer can trap free CO2 in the lithium battery and generate a cyclic carbonate film-forming additive under the action of the catalyst. The electrolyte provided by the invention can effectively reduce CO2 gas generated by an electrolyte oxidation reaction in the battery and avoid damage to an electrode material and a battery structure, and cyclic carbonate generated by an in-situ reaction of the CO2 trapping monomer and CO2 can preferentially react to form an SEI film, so that the electrochemical performance, the cycle life and the safety of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery preparation, and particularly relates to an electrolyte for capturing CO2 to generate a film-forming additive and a lithium-ion battery. Background Art

[0002] CO2 has a certain solubility in the electrolyte, especially in carbonate solvents (such as ethylene carbonate EC and dimethyl carbonate DMC). After CO2 dissolves, it may form carbonic acid (H2CO3), which then reacts with lithium salts in the electrolyte (such as LiPF6) to form unstable compounds such as Li2CO3 and HF. These by-products may deposit on the electrode surface and form part of the solid electrolyte interface (SEI) film, affecting the interface stability of the battery. Research shows that the presence of CO2 may lead to the thickening and non-uniformity of the SEI film, thereby increasing the internal resistance of the battery and reducing its rate performance (Effect of CO2 on the performance of Li-ion batteries. Journal of Power Sources, 412, 1-8). At the same time, CO2 may have an adverse effect on the cathode material (such as NCM or LFP) and the anode material (such as graphite). On the cathode side, CO2 may react with transition metal ions, resulting in the degradation of the material structure. On the anode side, CO2 may participate in the formation of the SEI film, leading to the instability of the film and the irreversible consumption of lithium ions. In addition, the presence of CO2 may pose a threat to the safety of the battery. Under high voltage or high temperature conditions, CO2 may act together with other gases (such as O2) to trigger the oxidative decomposition of the electrolyte, increasing the risk of thermal runaway. Especially in soft-pack batteries, the accumulation of CO2 may cause the internal pressure of the battery to rise, further triggering mechanical deformation or rupture of the battery. How to improve the impact of carbon dioxide on the battery is an urgent problem to be solved in this field. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides an electrolyte for capturing CO2 to generate a film-forming additive and a lithium-ion battery. The electrolyte of the present invention can effectively reduce the CO2 gas generated by the oxidation reaction of the electrolyte inside the battery, avoid the damage to the electrode material and the battery structure, and the cyclic carbonate formed by the in-situ reaction of the CO2 capture monomer with CO2 can preferentially react to form an SEI film, significantly improving the electrochemical performance, cycle life and safety of the battery.

[0004] The technical solution of the present invention is as follows:

[0005] A first aspect of the present invention protects an electrolyte for a lithium battery, comprising a carbon dioxide (CO2) capture monomer and a catalyst; the carbon dioxide capture monomer can capture free carbon dioxide in the lithium battery and generate a cyclic carbonate film-forming additive under the action of the catalyst.

[0006] Preferably, the structure of the film-forming additive includes at least one of the following formulas I-VI:

[0007]

[0008] Preferably, the carbon dioxide capture monomer includes at least one of the following formulas 1-6:

[0009]

[0010] Preferably, the film-forming additive is formed by the ring-opening reaction of the carbon dioxide capture monomer capturing free carbon dioxide in the lithium battery at -20 to 100 °C under the action of the catalyst; the molar ratio of the catalyst to the carbon dioxide capture monomer is 1:(50-500); and / or, the mass fraction of the carbon dioxide capture monomer in the electrolyte is 1-10%.

[0011] Preferably, the general structural formula of the catalyst is as follows:

[0012]

[0013] Wherein, R is selected from at least one of -OAc, -Cl, -Br, and the like.

[0014] Preferably, the synthesis method of the catalyst is as follows:

[0015] S1: Under nitrogen protection, 4,4',4"-triaminotriphenylmethane is dissolved in solvent I to obtain a 4,4',4"-triaminotriphenylmethane solution, then 2,4-pentanedione is added, and the reaction is carried out under an ice-water bath. After the reaction is completed, recrystallization is carried out, and the solvent is evaporated to dryness to obtain compound B.

[0016] S2: Under nitrogen protection, compound B is dissolved in solvent II to obtain a solution of compound B, then a zinc salt is added, and the reaction is carried out at room temperature. After the reaction is completed, filtration is carried out, washing with alcohol is carried out, and the solvent is evaporated to dryness to obtain compound C, which is the catalyst.

[0017] Preferably, in step S1, the concentration of the 4,4',4"-triaminotriphenylmethane solution is 0.5 to 100 mol / L; and / or, the solvent I includes at least one of dichloromethane and tetrahydrofuran; and / or, the molar ratio of 4,4',4"-triaminotriphenylmethane to 2,4-pentanedione is 1:(3 to 50); and / or, the reaction time is 2 to 24 h; in step S2, in the solution of compound B, the concentration of compound B is 0.5 to 10 mol / L; and / or, the solvent II includes at least one of tetrahydrofuran and dichloromethane; and / or, the zinc salt includes at least one of zinc acetate, zinc chloride, zinc bromide, zinc 2,4-dinitrophenolate, and zinc N,N-bis(trimethylsilyl); and / or, the molar ratio of compound B to the zinc salt is 1:(3 to 50); and / or, the reaction time is 2 to 24 h.

[0018] Preferably, the electrolyte further includes a lithium salt, a solvent, and an additive.

[0019] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, and lithium perchlorate; and / or, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and toluene; and / or, the additive includes one or more of fluorinated ethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate; and / or, in the electrolyte, the molar concentration of the lithium salt is 1 to 2 mol / L; and / or, the mass fraction of the additive in the electrolyte is 0.1 to 10%.

[0020] The second aspect of the present invention protects a lithium ion battery, including a positive electrode material, a negative electrode material, and the electrolyte described in the first aspect above; the positive electrode material includes a positive electrode active material; the structural formula of the positive electrode active material is LiNi x Mn y Co z O2, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1; the negative electrode includes a negative electrode active material; the negative electrode active material includes at least one of graphite, silicon-carbon composite, and silicon-oxygen composite.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] By adding a carbon dioxide capture unit and a catalyst to the electrolyte, the present invention can capture carbon dioxide in the electrolyte, effectively reducing the CO2 gas generated by the oxidation reaction of the electrolyte inside the battery, and avoiding damage to the electrode material and the battery structure. At the same time, the captured carbon dioxide can, under the action of the catalyst, react in situ with the carbon dioxide capture monomer to form an epoxy carbonate film-forming additive, which can preferentially react to form a SEI film, significantly improving the electrochemical performance, cycle life and safety of the battery. The present invention not only realizes the capture of carbon dioxide in the electrolyte, but also the generated epoxy carbonate substances can be directly used as film-forming additives, realizing the comprehensive utilization of resources.

[0023] The present invention proposes to use a trinuclear metal zinc catalyst to achieve the catalytic reaction of carbon dioxide and the carbon dioxide capture monomer. This trinuclear metal zinc catalyst has extremely high reaction activity and thermodynamic stability. Even in the later stage of the cycle, it can still rapidly catalyze the ring-opening reaction of the monomer and CO2 to form cyclic carbonate, providing a new catalyst for the rapid catalysis of cyclic carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1H NMR spectrum (600 MHz, Chloroform-d) of the catalyst ligand (Compound B) in Example 1 of the present invention.

[0025] Figure 2 1H NMR spectrum of the film-forming additive in Example 2 of the present invention.

[0026] Figure 3 1H NMR spectrum of the film-forming additive in Example 3 of the present invention.

[0027] Figure 4 1H NMR spectrum of the film-forming additive in Example 4 of the present invention.

[0028] Figure 5 1H NMR spectrum of the film-forming additive in Example 5 of the present invention.

[0029] Figure 6 1H NMR spectrum of the film-forming additive in Example 6 of the present invention.

[0030] Figure 7 1H NMR spectrum of the film-forming additive in Example 7 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be specifically described below in conjunction with the embodiments.

[0032] Based on the current adverse effects of carbon dioxide on batteries, it is urgent to study how to remove and even further utilize carbon dioxide. Cyclic carbonate additives (VC, VEC, FEC, DFEC, TFPC) are currently the most intensively studied and have ideal effects among organic film-forming additives. For example, after adding 10% of VC to the electrolyte of 1 mol / L LiAsF6 / EC + DMC (1 / 1), Aurbach used a spectroscope to observe the electrode surface and confirmed that VC undergoes a radical polymerization reaction on the surface of the carbon negative electrode to form a lithium polyalkyl carbonate compound, thereby effectively inhibiting the co-insertion reaction of solvent molecules and having no side effects on the positive electrode (Aurbach D, Gamolsky K, Markovsky B, et al. On the use of vinylene carbonate (VC) as an additive to electrolyte solutions for Li-ion batteries. Electrochem. Acta, 2002, 47(9), 1423-1439). Therefore, the present invention proposes that by adding a CO2 capture monomer (epoxyalkane) to the electrolyte, a ring-opening reaction occurs under the action of a catalyst to generate the corresponding cyclic carbonate, which can not only reduce the adverse effects of CO2 on the electrode material and battery structure, but also the product has excellent film-forming properties and participates in the construction of the SEI film to avoid continuous consumption of the electrolyte.

[0033] In a first aspect of the present invention, there is provided an electrolyte for a lithium battery, comprising a carbon dioxide (CO2) capture monomer and a catalyst; the carbon dioxide capture monomer can capture free carbon dioxide in the lithium battery and generate a cyclic carbonate film-forming additive under the action of the catalyst.

[0034] It can be understood that by adding a carbon dioxide capture unit and a catalyst to the electrolyte in the present invention, the carbon dioxide in the electrolyte can be captured, effectively reducing the CO2 gas generated by the oxidation reaction of the electrolyte inside the battery and avoiding damage to the electrode material and battery structure; at the same time, the captured carbon dioxide can react in situ with the carbon dioxide capture monomer under the action of the catalyst to generate an epoxy carbonate film-forming additive, which can preferentially react to form an SEI film, significantly improving the electrochemical performance, cycle life and safety of the battery. The present invention not only realizes the capture of carbon dioxide in the electrolyte, but also the generated epoxy carbonate substances can be directly used as film-forming additives, realizing the comprehensive utilization of resources.

[0035] In some embodiments, the structure of the film-forming additive includes at least one of the following formulas I-VI:

[0036]

[0037] Among the above film-forming additives, I and II are penta-fused six-membered ring structures containing only one carbon-carbon double bond, III and IV are penta-fused six-membered ring structures containing one heteroatom, and V and VI are penta-fused six-membered ring structures containing two heteroatoms. The present invention includes but is not limited to the above structures, and any similar structures that can achieve the effects of the present invention are within the protection scope of the present invention.

[0038] It can be understood that the epoxy carbonate substances of the present invention can preferentially react to form a SEI film.

[0039] In some embodiments, the carbon dioxide capture monomer includes at least one of the following formulas 1-6:

[0040]

[0041] Among the above carbon dioxide capture monomers, structures 1 and 2 are tricyclic six-membered ring structures containing only one carbon-carbon double bond, structures 3 and 4 are tricyclic six-membered ring structures containing one heteroatom, and structures 5 and 6 are tricyclic six-membered ring structures containing two heteroatoms.

[0042] In some embodiments, the film-forming additive is formed by ring-opening reaction of the carbon dioxide capture monomer capturing free carbon dioxide in the lithium battery at -20 to 100 °C under the action of a catalyst.

[0043] In some embodiments, the reaction formula for the reaction of the above carbon dioxide capture monomer with free carbon dioxide in the lithium battery is as follows:

[0044]

[0045]

[0046] In some embodiments, the reaction temperature includes but is not limited to -20 °C, -10 °C, 0 °C, 10 °C, 20 °C, 40 °C, 60 °C, 80 °C, 100 °C.

[0047] In some embodiments, the molar ratio of the catalyst to the carbon dioxide capture monomer is 1:(50-500), including but not limited to 1:50, 1:100, 1:200, 1:400, 1:500.

[0048] In some embodiments, the mass fraction of the carbon dioxide capture monomer in the electrolyte is 1-10%, including but not limited to 1%, 2%, 4%, 6%, 8%, 10%.

[0049] In some embodiments, the general structural formula of the catalyst is as follows:

[0050]

[0051] Among them, R is selected from at least one of -OAc, -Cl, -Br, and the like.

[0052] It can be understood that the present invention proposes to use a trinuclear metal zinc catalyst to achieve the catalytic reaction of carbon dioxide and a carbon dioxide capture monomer. This trinuclear metal zinc catalyst has extremely high reaction activity and thermodynamic stability. Even in the later stage of the cycle, it can still rapidly catalyze the ring-opening reaction of the monomer and CO2 to form cyclic carbonate, providing a new catalyst for the rapid catalysis of cyclic carbonate.

[0053] In some embodiments, the structure of the catalyst includes at least one of the following structures:

[0054]

[0055] In some embodiments, the synthesis route of the catalyst is as follows:

[0056] In some embodiments, the synthesis method of the catalyst is as follows:

[0057] S1: Under nitrogen protection, 4,4',4"-triaminotriphenylmethane is dissolved in solvent I to obtain a 4,4',4"-triaminotriphenylmethane solution, and then 2,4-pentanedione is added. The reaction is carried out under an ice-water bath. After the reaction is completed, recrystallization is carried out, and the solvent is evaporated to dryness to obtain compound B.

[0058] S2: Under nitrogen protection, compound B is dissolved in solvent II to obtain a solution of compound B, and then a zinc salt is added. The reaction is carried out at room temperature. After the reaction is completed, filtration is carried out, followed by washing with alcohol, and then the solvent is evaporated to dryness to obtain compound C, which is the catalyst.

[0059] In some embodiments, in step S1, the concentration of the 4,4',4"-triaminotriphenylmethane solution is 0.5 - 100 mol / L, including but not limited to 0.5 mol / L, 1 mol / L, 5 mol / L, 10 mol / L, 20 mol / L, 40 mol / L, 60 mol / L, 80 mol / L, 100 mol / L; and / or, the solvent I includes at least one of dichloromethane and tetrahydrofuran; and / or, the molar ratio of 4,4',4"-triaminotriphenylmethane to 2,4-pentanedione is 1:(3 - 50), including but not limited to 1:3, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50; and / or, the reaction time is 2 - 24 h, including but not limited to 2 h, 5 h, 10 h, 15 h, 20 h, 24 h. And / or, the recrystallization is carried out using dichloromethane / ether.

[0060] In the present invention, a solution of 4,4’,4"-triaminotriphenylmethane is prepared, and then 2,4-pentanedione is added. The reaction is carried out under an ice-water bath. Since 2,4-pentanedione is unstable and its α-hydrogen has acidity, it will turn into enol in the solution and then participate in the reaction, as shown in Reaction Scheme (1).

[0061] In some embodiments, in step S2, in the solution of compound B, the concentration of compound B is 0.5 - 10 mol / L, including but not limited to 0.5 mol / L, 1 mol / L, 2 mol / L, 4 mol / L, 6 mol / L, 7 mol / L, 10 mol / L; and / or, the solvent II includes at least one of tetrahydrofuran and dichloromethane; and / or, the zinc salt includes at least one of zinc acetate, zinc chloride, zinc bromide, zinc 2,4-dinitrophenolate, and zinc N,N-bis(trimethylsilyl); and / or, the molar ratio of compound B to the zinc salt is 1:(3 - 50), including but not limited to 1:3, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50; and / or, the reaction time is 2 - 24 h, including but not limited to 2 h, 3 h, 5 h, 10 h, 15 h, 20 h, 24 h.

[0062] In some embodiments, the alcohol washing is performed by washing with methanol 3 - 5 times, including but not limited to 3 times, 4 times, 5 times.

[0063] In some embodiments, the electrolyte further includes a lithium salt, a solvent, and an additive.

[0064] In some embodiments, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, and lithium perchlorate; and / or, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and toluene; and / or, the additive includes one or more of fluoroethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate; and / or, in the electrolyte, the molar concentration of the lithium salt is 1 - 2 mol / L, including but not limited to 1 mol / L, 1.5 mol / L, 2 mol / L; and / or, the mass fraction of the additive in the electrolyte is 0.1 - 10%, including but not limited to 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%.

[0065] The second aspect of the present invention protects a lithium-ion battery, which includes a positive electrode material, a negative electrode material, and the electrolyte described in the first aspect above; the positive electrode material includes a positive electrode active material; the structural formula of the positive electrode active material is LiNi x Mn y Co zO2, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1; the negative electrode includes a negative electrode active material; the negative electrode active material includes at least one of graphite, silicon-carbon composite, and silicon-oxygen composite.

[0066] The present invention will be further described below through examples and the like.

[0067] Example 1

[0068] A catalyst, its structure (the structure shown by Compound C) and synthesis route are as follows:

[0069]

[0070] The synthesis method of this catalyst is as follows:

[0071] (1) Synthesis of Compound B:

[0072] Under nitrogen protection, dissolve Compound A (4,4,4-triaminotriphenylmethane) in 30 mL of refined dichloromethane, control the concentration of Compound A to be 3 mol / L, and then add 2,4-pentanedione. The molar ratio of Compound A to 2,4-pentanedione is 1:6. React under an ice-water bath for 12 hours. After the reaction, recrystallize with dichloromethane / ether and spin-dry to obtain Compound B (45.2 g). The nuclear magnetic resonance hydrogen spectrum of the obtained Compound B (600 MHz, Chloroform-d) is as Figure 1 shown.

[0073] The hydrogen spectrum data is as follows: 1 H NMR(600MHz,Chloroform-d)δ12.48(d,J=9.0Hz,3H),7.08–7.02(m,13H),5.50(d,J=11.3Hz,1H),5.18(s,3H),3.72(q,J=7.0Hz,3H),2.09(s,9H),2.01(s,9H).

[0074] (2) Synthesis steps of Compound C: Under nitrogen protection, dissolve Compound B in 30 mL of refined tetrahydrofuran, control the concentration of Compound B to be 2 mol / L, and then add zinc acetate. The molar ratio of Compound B to zinc acetate is 1:8. React at room temperature for 24 hours. After the reaction, filter, wash with methanol 3 times, and spin-dry to obtain Compound C (43.3 g), which is the catalyst.

[0075] Example 2

[0076] An electrolyte includes lithium hexafluorophosphate, a solvent, an additive, a CO2 capture monomer, and a catalyst.

[0077] The concentration of lithium hexafluorophosphate in the electrolyte is 1.2 moL / L. -1 The solvent is a mixed solution of EC (ethylene carbonate), EMC (ethyl methyl carbonate), DEC (diethyl carbonate), and TOL (toluene) with a mass ratio of 1:1:3:1; the additive is VC (vinylene carbonate), and the mass fraction of the additive VC is 2%; the CO2 capture monomer is monomer The mass fraction of monomer 1 is 3%; the catalyst is the catalyst prepared in Example 1, that is, compound C; the molar ratio of the catalyst to monomer 1 is 1:500, and this electrolyte is named Electrolyte No. I.

[0078] The electrolyte is obtained by mixing lithium hexafluorophosphate, the solvent, the additive, the CO2 capture monomer, and the catalyst.

[0079] A lithium-ion battery containing the above electrolyte, and its preparation method includes the following steps:

[0080] Prepare a 4.2V LiNi 0.8 Co 0.1 Mn 0.1 O2 / silicon-carbon soft-pack battery; under an argon protection environment, inject the above-prepared Electrolyte No. I into a fully dried 4.2V LiNi 0.8 Co 0.1 Mn 0.1 O2 / silicon-carbon soft-pack battery. After processes such as standing at 45°C, high-temperature fixture formation, and secondary sealing, lithium-ion battery A is obtained.

[0081] In lithium-ion battery A, when the temperature is between -20 and 100°C, monomer 1 in Electrolyte No. I can react with carbon dioxide under the action of the catalyst to produce the following reaction, generating film-forming additive I:

[0082]

[0083] The hydrogen spectrum of film-forming additive I is as Figure 2 shown. 1 H NMR(400MHz,Chloroform-d)δ6.00–5.78(m,1H),5.71(dd,J=10.4,2.6Hz,1H),4.12(q,J=2.7Hz,2H),3.78(dt,J=5.5,3.4Hz,2H),2.13(tt,J=5.7,2.9Hz,2H).

[0084] Example 3

[0085] An electrolyte, whose composition and ratio are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to monomer 2 and is named Electrolyte No. II.

[0086] A lithium-ion battery containing the above electrolyte has a preparation method that is basically the same as that of Example 2, except that the CO2 capture monomer in the electrolyte is changed to the CO2 capture monomer of this example, resulting in lithium-ion battery B.

[0087] In lithium-ion battery B, when the temperature is in the range of -20 to 100 °C, monomer 2 in electrolyte II can react with carbon dioxide under the action of a catalyst to undergo the following reaction to form film-forming additive II:

[0088]

[0089] The 1H NMR spectrum of film-forming additive II is as Figure 3 shown. 1 H NMR(400MHz,Chloroform-d)δ6.46–6.30(m,1H),4.67(dt,J=6.7,4.0Hz,1H),4.09–3.91(m,2H),2.10–1.94(m,2H),1.87(p,J=6.0Hz,2H).

[0090] Example 4:

[0091] An electrolyte has a composition and ratio that are basically the same as those of Example 2, except that in this example, the CO2 capture monomer is changed to monomer 3, and it is named electrolyte III.

[0092] A lithium-ion battery containing the above electrolyte has a preparation method that is basically the same as that of Example 2, except that the CO2 capture monomer in the electrolyte is changed to the CO2 capture monomer of this example, resulting in lithium-ion battery C.

[0093] In lithium-ion battery C, when the temperature is in the range of -20 to 100 °C, monomer 3 in electrolyte III can react with carbon dioxide under the action of a catalyst to undergo the following reaction to form film-forming additive III:

[0094]

[0095] The 1H NMR spectrum of film-forming additive III is as Figure 4 shown. 1 H NMR(400MHz,Chloroform-d)δ4.08–3.93(m,2H),3.55(dddd,J=12.6,7.0,5.3,1.4Hz,1H),3.50–3.41(m,1H),3.37(dq,J=3.8,1.8Hz,1H),3.20(td,J=3.2,1.6Hz,1H),2.02(dddd,J=7.0,5.3,3.5,2.2Hz,2H).

[0096] Example 5:

[0097] An electrolyte solution has a composition and ratio that are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to monomer 4 and it is named Electrolyte No. IV.

[0098] A lithium-ion battery containing the above electrolyte solution has a preparation method that is basically the same as that in Example 2, except that the CO2 capture monomer in the electrolyte solution is changed to the CO2 capture monomer of this example, and lithium-ion battery D is obtained.

[0099] In lithium-ion battery D, when the temperature is in the range of -20 to 100 °C, monomer 4 in Electrolyte No. IV can react with carbon dioxide under the action of a catalyst to undergo the following reaction to form film-forming additive IV:

[0100]

[0101] The 1H NMR spectrum of film-forming additive IV is as Figure 5 shown. 1 H NMR(600MHz,Chloroform-d)δ4.99–4.79(m,1H),4.70(tq,J=13.2,8.6Hz,1H),4.20–3.96(m,1H),3.97–3.81(m,1H),3.49(ddt,J=27.0,19.4,7.1Hz,2H),2.28–2.14(m,1H),1.79(q,J=10.3,9.6Hz,1H).

[0102] Example 6:

[0103] An electrolyte solution has a composition and ratio that are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to monomer 5 and it is named Electrolyte No. V.

[0104] A lithium-ion battery containing the above electrolyte solution has a preparation method that is basically the same as that in Example 2, except that the CO2 capture monomer in the electrolyte solution is changed to the CO2 capture monomer of this example, and lithium-ion battery E is obtained.

[0105] In lithium-ion battery E, when the temperature is in the range of -20 to 100 °C, monomer 5 in Electrolyte No. V can react with carbon dioxide under the action of a catalyst to undergo the following reaction to form film-forming additive V:

[0106]

[0107] The 1H NMR spectrum of film-forming additive V is as Figure 6 shown. 11H NMR (600 MHz, Chloroform-d) δ 3.72 (q, J = 7.0 Hz, 2H), 1.25 (t, J = 7.0 Hz, 4H).

[0108] Example 7

[0109] An electrolyte solution, whose composition and ratio are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to monomer 6, and it is named Electrolyte No. VI.

[0110] A lithium-ion battery containing the above electrolyte solution, whose preparation method is basically the same as that in Example 2, except that the CO2 capture monomer in the electrolyte solution is changed to the CO2 capture monomer in this example, and lithium-ion battery F is obtained.

[0111] In lithium-ion battery F, when the temperature is between -20 and 100 °C, monomer 6 in Electrolyte No. VI can react with carbon dioxide under the action of a catalyst to undergo the following reaction to generate film-forming additive VI:

[0112]

[0113] The 1H NMR spectrum of film-forming additive VI is as Figure 7 shown. 1 1H NMR (600 MHz, Chloroform-d) δ 6.88 (d, J = 7.9 Hz, 2H), 6.59 (d, J = 7.9 Hz, 2H), 3.56 (s, 2H).

[0114] Example 8

[0115] An electrolyte solution, whose composition and ratio are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to a 1:1 molar ratio mixture of monomer 1 and monomer 3, and it is named Electrolyte No. VII.

[0116] A lithium-ion battery containing the above electrolyte solution, whose preparation method is basically the same as that in Example 2, except that the CO2 capture monomer in the electrolyte solution is changed to the CO2 capture monomer in this example, and lithium-ion battery G is obtained.

[0117] Example 9

[0118] An electrolyte solution, whose composition and ratio are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is changed to a 1:1 molar ratio mixture of monomer 2 and monomer 4, and it is named Electrolyte No. VIII.

[0119] A lithium-ion battery containing the above electrolyte solution, whose preparation method is basically the same as that in Example 2, except that the CO2 capture monomer in the electrolyte solution is changed to the CO2 capture monomer in this example, and lithium-ion battery H is obtained.

[0120] Comparative Example 1

[0121] An electrolyte solution, whose composition and proportion are basically the same as those in Example 2, except that in this example, the CO2 capture monomer is not added, and it is named Electrolyte No. IX.

[0122] A lithium-ion battery containing the above electrolyte solution, whose preparation method is basically the same as that in Example 2, except that the CO2 capture monomer is not added to the electrolyte solution, and the lithium-ion battery I is obtained.

[0123] Comparative Example 2

[0124] An electrolyte solution, whose composition and proportion are basically the same as those in Example 2, except that in this example, the CO2 capture monomer and the catalyst are not added, and a film-forming additive I is added, and it is named Electrolyte No. 10.

[0125] A lithium-ion battery containing the above electrolyte solution, whose preparation method is basically the same as that in Example 2, except that Electrolyte No. 10 is added to the electrolyte solution, and the lithium-ion battery J is obtained.

[0126] Test Example:

[0127] The performance of the batteries in each example and comparative example was tested respectively, and the gas generation results of each battery were quantitatively analyzed. The analysis results are shown in Table 1.

[0128] Among them, the test methods for the battery capacity retention rate and the swelling rate are as follows:

[0129] Under the condition of 45 °C, the above lithium-ion battery was charged to 4.2 V at a constant current of 3C and a constant voltage, with a cut-off current of 0.05C, and then discharged to 2.5 V under the condition of a constant current of 4C. After 800 charge-discharge cycles, the capacity retention rate and the swelling rate after the 800th cycle were calculated:

[0130]

[0131] The test method for the CO2 content after gas production is as follows: after the batteries of the embodiment and the comparative example have been cycled for 800 cycles, the generated gas is detected in real time by using an in-situ differential electrochemical mass spectrometer. After the battery discharge is completed, the CO2 is quantitatively analyzed. Since the CO2 content is relatively low, it is characterized by the relative proportion of CO2. Specifically, the content of carbon dioxide measured in comparative example 1 after the above-mentioned cycle is used as a benchmark to calculate the percentage of the CO2 content of the battery of the embodiment or comparative example to be tested after the above-mentioned cycle to the CO2 content in the battery of comparative example 1 after the cycle. The calculation formula is shown in the following formula (13). For example, the relative amount of CO2 after gas production in embodiment 2 is the ratio of the amount of CO2 measured by the battery of embodiment 2 after 800 cycles to the amount of CO2 measured by the battery of comparative example 1 after 800 cycles, and then multiplied by 100% to obtain the percentage content. Among them, the amount of CO2 in the battery to be tested and the amount of CO2 in comparative example 1 are both the amounts of carbon dioxide in the battery measured after the above-mentioned cycles.

[0132]

[0133] The test results of the relative content of CO2 after gas generation obtained by the batteries of the embodiment and the comparative example are shown in Table 1.

[0134] Table 1 Lithium ion battery performance test and gas production test results of each embodiment

[0135]

[0136] It can be seen from Table 1 that the lithium batteries of Examples 2-9 have good high-temperature cycle performance and gas production inhibition effects. Comparison of Example 2 and Comparative Example 2 shows that the CO2 capture monomer has a good capture effect on CO2. Comparison of Example 2 and Example 4 shows that the double-bond substituted CO2 capture monomer is better than the oxygen-substituted monomer. This may be because the double bond has a stronger electron-withdrawing effect, which is more conducive to alkoxy ring opening. Comparison of Example 9 and Examples 3 and 5 shows that the effect of the mixture of the two monomers is stronger than that of a single monomer. This may be because when the film-forming additive is formed, the SEI film formed by the interaction of multiple components is more stable, which has a better effect on improving battery performance.

[0137] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. An electrolyte for a lithium battery, characterized in that: Including carbon dioxide capture monomers and catalysts; The carbon dioxide capture monomer can capture free carbon dioxide in the lithium battery and generate a cyclic carbonate film-forming additive under the action of a catalyst.

2. The electrolyte according to claim 1, characterized in that The structure of the film-forming additive comprises at least one of the following formulas I-VI:

3. The electrolyte according to claim 1, characterized in that The carbon dioxide capture monomer includes at least one of the following formulas 1-6:

4. The electrolyte according to claim 1, characterized in that The film-forming additive is generated by using a carbon dioxide capture monomer to capture free carbon dioxide in a lithium battery, and undergoing a ring-opening reaction under the action of a catalyst at -20 to 100°C; The molar ratio of the catalyst to the carbon dioxide capture monomer is 1:(50-500); and / or, The mass fraction of the carbon dioxide capture monomer in the electrolyte is 1 to 10%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The general structural formula of the catalyst is as follows: wherein R is selected from -OAc, -Cl, -Br, At least one of .

6. The electrolyte according to claim 5, characterized in that The synthesis method of the catalyst is: S1: Under nitrogen protection, 4,4',4"-triaminotriphenylmethane was dissolved in solvent I to obtain a 4,4',4"-triaminotriphenylmethane solution, and then 2,4-pentanedione was added to react in an ice-water bath. After the reaction was completed, the mixture was recrystallized and dried to obtain compound B; S2: Under nitrogen protection, compound B is dissolved in solvent II to obtain a solution of compound B, and then zinc salt is added to react at room temperature. After the reaction is completed, the solution is filtered, washed with alcohol, and dried to obtain compound C, which is the catalyst.

7. The electrolyte according to claim 6, characterized in that In step S1, the concentration of the 4,4',4"-triaminotriphenylmethane solution is 0.5-100 mol / L; and / or, the solvent I comprises at least one of dichloromethane and tetrahydrofuran; and / or, the molar ratio of the 4,4',4"-triaminotriphenylmethane to the 2,4-pentanedione is 1:(3-50); and / or, the reaction time is 2-24 h; In step S2, in the solution of compound B, the concentration of compound B is 0.5-10 mol / L; and / or, the solvent II includes at least one of tetrahydrofuran and dichloromethane; and / or, the zinc salt includes at least one of zinc acetate, zinc chloride, zinc bromide, 2,4-dinitrophenol zinc, and N,N-bis(trimethylsilyl)zinc; and / or, the molar ratio of compound B to the zinc salt is 1:(3-50); and / or, the reaction time is 2-24 h.

8. The electrolyte according to claim 1, characterized in that The electrolyte also includes lithium salt, solvent and additives.

9. The electrolyte according to claim 1, characterized in that The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium perchlorate; and / or, The solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and toluene; and / or, The additive includes one or more of fluoroethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate; and / or, In the electrolyte, the molar concentration of the lithium salt is 1 to 2 mol / L; and / or, The mass fraction of the additive in the electrolyte is 0.1-10%.

10. A lithium ion battery, characterized in that: Comprising a positive electrode material, a negative electrode material, and the electrolyte according to any one of claims 1 to 9; The positive electrode material includes a positive electrode active material; The structural formula of the positive electrode active material is LiNi x Mn y Co z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1; The negative electrode includes a negative electrode active material; The negative electrode active material includes at least one of graphite, a silicon-carbon composite, and a silicon-oxygen composite.

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