CN105826596B - Preparation method of ionic liquid and secondary battery - Google Patents

Abstract

The invention relates to a preparation method of ionic liquid, in particular to a method for synthesizing quaternary ammonium or quaternary phosphonium compound by one-step method. The method is characterized in that a nitrogen compound or a phosphorus compound, a proton compound and carbonic ester are added into a reactor together to react in one step to synthesize corresponding quaternary ammonium salt or quaternary phosphonium salt ionic liquid, namely, the reaction of the 'one-pot method' relates to the one-step reaction of three reactants. The invention also provides a lithium ion secondary battery containing the ionic liquid prepared by the preparation method. The preparation method of the ionic liquid can widen the selection range of the raw materials for preparing the ionic liquid, thereby widening the types of the synthesized ionic liquid.

Description

Preparation method of ionic liquid and secondary battery

Technical Field

The invention relates to a preparation method of ionic liquid, in particular to a method for synthesizing quaternary ammonium or quaternary phosphonium compound by one-step method.

Background

Ionic liquid (ionic liquid) is a liquid substance completely composed of ions, and is liquid at room temperature or low temperature (-97 ℃ -100 ℃), so it is also called room temperature/low temperature molten salt (room/low temperature molten salt), or liquid is called room temperature/low temperature molten saltOrganic salts (liquid organic salt). The ionic liquids are various, and can be classified into quaternary ammonium salts, quaternary phosphonium salts, nitrogen-containing heterocyclic onium salts and the like according to the difference of organic cations, and the nitrogen-containing heterocyclic ionic liquids include imidazolium salts, pyridinium salts, piperidine salts, pyrrolidine salts and the like. The anions constituting the ionic liquid are of a wide variety, and the inorganic anions include F^-、Cl^-、Br^-、I^-、NO₃ ^-、CO₃ ^2-、PF₆ ^-、BF₄ ^-、C₂O₄ ^2-、SO₄ ^2-、PO₄ ^3-、Al₂Cl₇ ^-Etc., the organic anion includes CH₃COO^-、CF₃SO₃ ^-、C₄H₉SO₃ ^-、CF₃COO^-、N(FSO₂)₂ ^-、N(CF₃SO₂)₂ ^-、N(C₂F₅SO₂)₂ ^-、N(C₄F₉SO₂)₂ ^-、N[(CF₃SO₂)(C₄F₉SO₂)]^-、C(CF₃SO₂)₃ ^-And the like. Theoretically, the ionic liquid can have the species of 10¹⁸There are a plurality of. The structures of the cations and anions of several common imine-type ionic liquids are shown below:

in the 70 s of the 20 th century, american scientist John s.wilks first applied ionic liquids to battery systems. Since the 90 s in the 20 th century, intensive research on the application of ionic liquids to lithium ion secondary batteries has been carried out, and the feasibility and superiority of ionic liquids as electrolyte solvents for lithium ion secondary batteries are increasingly recognized and valued by experts in the industry. Compared with the carbonate organic solvent widely used at present, the ionic liquid is used as the electrolyte solution of the lithium ion secondary batteryThe agent has the advantages that: (1) the liquid temperature range is wide, for example, the electrolyte solvent dimethyl carbonate (DMC) commonly used in lithium ion secondary batteries has a narrow liquid range of 2-90 ℃, the upper liquid limit temperature of most ionic liquids can reach about 300 ℃ (decomposition temperature), even the liquid range of some ionic liquids is as wide as-70-400 ℃, and the use temperature range of the lithium ion secondary batteries is expanded (for example, the liquid range extends to high temperature); (2) the ionic liquid is an ionic substance, has strong capability of dissolving ionic compounds and controllable concentration, and is prepared from several common lithium salts such as LiPF₆、LiBF₄、LiCF₃SO₃、LiN(SO₂CF₃)₂The lithium ion secondary battery can be dissolved in corresponding ionic liquid and can reach higher concentration, and the requirement of the lithium ion secondary battery as a power battery on the concentration of lithium ions in electrolyte can be met; (3) the conductivity is good, and the conductivity of the conductive material can reach 1-10 mS cm under the condition of no lithium salt^-1A rank; (4) the ionic liquid has good stability, the ionic liquid has better thermal stability and chemical stability, the decomposition temperature of most of the ionic liquid is more than 400 ℃, and the chemical stability is realized when the ionic liquid is mixed with the electrode material of the common lithium ion secondary battery such as LiFePO under the common condition₄、LiCoO₂、Li₄Ti₅O₁₂Graphite, etc. do not react chemically; (5) the ionic liquid has no obvious vapor pressure even at the temperature of more than 100 ℃, and when the battery runs in a high-temperature environment, the battery cannot be deformed due to overhigh air pressure, for example, when the ionic liquid is applied to an aluminum plastic film soft package battery, the phenomenon of bulging is not easily caused; (6) the ionic liquid has no flash point and high ignition point, certain ionic liquid is difficult to ignite even if naked fire is used, the currently used carbonate solvent is flammable and explosive, potential safety hazards exist when the ionic liquid is applied to the lithium ion secondary battery, and the ionic liquid is expected to solve the safety problem of the lithium ion secondary battery.

Currently, ionic liquids used as electrolyte solvents in lithium ion secondary batteries have a primary anion of tetrafluoroborate (BF)₄ ^-) Hexafluorophosphate radical (PF)₆ ^-) Triflate (CF)₃SO₃ ^-) Bis (trifluoro benzene)Methylsulfonyl) imide (N (CF)₃SO₂)₂ ^-) And quaternary ammonium salts, piperidine salts, pyrrolidine salts, imidazolium salts, and pyridinium salts. The combination of different cations and anions has great influence on the physical and chemical properties of the ionic liquid electrolyte and directly influences the performance of the lithium ion secondary battery. In recent years, numerous researches show that the ionic liquid with the anion being imine ion has a lower melting point, can be combined with various cations to form molten salt with the melting point lower than zero, widens the selection range of the cations, and enables quaternary ammonium cations, piperidine cations and pyrrolidine cations with higher electrochemical stability to be applied to a lithium ion secondary battery system. For example N-methyl-N-butylpiperidine bis (trifluoromethylsulfonyl) imide [ PP13-TFSI ]]Has a melting point of-18 ℃ and is used for Li/LiCoO₂The battery system has excellent performance, and the specific capacity of the positive electrode can be exerted to 150 mAh.g^-1The coulomb efficiency can reach 100%, and the cycle has no obvious attenuation for tens of weeks (xu jin Qiang, etc.; the journal of chemistry, volume 63, 18 th page 1733); the Zhenghong river research group at Suzhou university finds that N, N, N-trimethyl-N-hexyl di (trifluoromethyl sulfonyl) imide quaternary ammonium salt is applied to a lithium ion secondary battery taking hard carbon as a negative electrode, the battery is normally charged and discharged even at the high temperature of 80 ℃, and the intercalation and deintercalation behaviors of ionic liquid cations are not generated at the hard carbon negative electrode, so that the application prospect of the ionic liquid combined with the hard carbon is considered (RSC adv.,2012,2, 4904) 4912).

The traditional production process of ionic liquid, taking quaternary ammonium salt as an example, is a method for performing alkylation reaction by using tertiary amine and alkyl halide, and the reaction is shown as the following formula:

R₁R₂R₃N+R₄X→[R₁R₂R₃R₄N]⁺X^-(1)

for example, tributylmethylammonium iodide may be prepared by reacting tributyl tertiary amine with methyl iodide:

(C₄H₉)₃N+CH₃I→[(C₄H₉)₃NCH₃]⁺I^-(2)

the quaternary ammonium salts in which at least one methyl group is substituted on the nitrogen can also be prepared by using dimethyl sulfate as the alkylating agent, as shown in the following formula:

R₁R₂R₃N+(CH₃)₂SO₄→[R₁R₂R₃NCH₃]⁺CH₃SO₄ ^-(3)

tertiary amine and dimethyl sulfate are easy to react, and the yield is high, but the dimethyl sulfate is used, but the defects of high toxicity and carcinogenic effect are caused. The greatest disadvantage of the above-mentioned process route is that only certain quaternary ammonium salts can be prepared, for example only the anion Cl, depending on the method of quaternization of the haloalkane^-、Br^-、I^-Quaternary ammonium salts of (a); according to the quaternization of dimethyl sulfate, only the anion which can be prepared is CH₃SO₄ ^-Quaternary ammonium salts of (2). If it is desired to prepare quaternary ammonium salts whose anions are other ions, this can be achieved only by ion exchange reactions, such as those shown by the formulae (4) and (5):

[R₁R₂R₃R₄N]⁺X^-+H⁺A^-→[R₁R₂R₃R₄N]⁺A^-+H⁺X^-(4)

[R₁R₂R₃R₄N]⁺X^-+M⁺A^-→[R₁R₂R₃R₄N]⁺A^-+M⁺X^-(5)

for example, the anion prepared is SO₄ ^2-Quaternary ammonium salt of (2) [ R ]₁R₂R₃R₄P]₂ ²⁺SO₄ ^2-The quaternary ammonium chloride salt is generally synthesized by the formula (1), then the quaternary ammonium chloride salt is reacted with sulfuric acid by the formula (4), hydrochloric acid is removed by utilizing the characteristic of easy volatilization of the hydrochloric acid, and the reaction (4) is balanced and moved to the right, so that the maximum ion exchange is achieved. Also, for example, the anion is BF₄ ^-Quaternary ammonium salt of (2) [ R ]₁R₂R₃R₄P]⁺BF₄ ^-The corresponding quaternary ammonium halide is synthesized by the formula (1) and then the quaternary ammonium halide is reacted with a metal inorganic salt such as NaBF by the formula (5)₄Reacting in organic solvent such as acetone, and precipitating halide ions in the form of precipitate to realize ion exchange by utilizing the characteristic of low solubility of metal halide in organic solvent. Obviously, both the formula (4) and the formula (5) are equilibrium reactions, and both have a phenomenon of incomplete reaction, and the halogen ions inevitably remain in the final product. Even with silver salts such as AgBF₄The reaction (5) can be carried out in an aqueous solution and can be completed, but the cost is too high.

On the one hand, owing to halogen anions such as Cl^-、Br^-、I^-The like has poor stability, is easy to oxidize and releases toxic and corrosive halogen simple substances, and has limited application range; on the other hand, as the research has been advanced and extended, it has been found that when the anion is one of the following (F)^-、NO₃ ^-、CO₃ ^2-、PF₆ ^-、BF₄ ^-、C₂O₄ ^2-、SO₄ ^2-、PO₄ ^3-、Al₂Cl₇ ^-、CH₃COO^-、CF₃SO₃ ^-、C₄H₉SO₃ ^-、CF₃COO^-、N(CF₃SO₂)₂ ^-、N(FSO₂)₂ ^-、N(C₂F₅SO₂)₂ ^-、N(C₄F₉SO₂)₂ ^-、N[(CF₃SO₂)(C₄F₉SO₂)]^-、C(CF₃SO₂)₃ ^-Etc.), quaternary ammonium salts generally possess certain characteristics not possessed by quaternary ammonium halide salts, such as lower melting point, higher conductivity, lower viscosity, strong hydrophobicity, etc., and thus have wider applications. For this reason, it is important to develop a novel method for producing these specific quaternary ammonium salts.

U.S. Pat. No. 4,4892944 describes a process for preparing quaternary ammonium/phosphonium salts using dimethyl carbonate as the alkylating agent. The method is carried out in two steps, wherein tertiary amine/phosphine and dimethyl carbonate react to generate quaternary ammonium/phosphonium methyl carbonate in the first step, quaternary ammonium/phosphonium methyl carbonate reacts with acid to release methanol and carbon dioxide and prepare quaternary ammonium/phosphonium salt, the anion type of the quaternary ammonium/phosphonium salt is determined by the used acid, and the reaction formula is as follows:

R₁R₂R₃N(P)+Me₂CO₃→[R₁R₂R₃N(P)Me]⁺MeCO₃ ^-(6)

[R₁R₂R₃N(P)Me]⁺MeCO₃ ^-+H⁺A^-→[R₁R₂R₃N(P)Me]⁺A^-+MeOH+CO₂(7)

the method is characterized in that the anions of the prepared quaternary ammonium/phosphonium salt are anions of various acids, are not limited by quaternary ammonium/phosphonium reagents, and have a wide anion selection range. However, it is still limited in that the reactant must be a tertiary amine or phosphine that can only be alkylated by dimethyl carbonate to form the corresponding quaternary ammonium/phosphonium salt, ammonia (NH)₃) Primary amine, secondary amine or Phosphine (PH)₃) Primary and secondary phosphines cannot be alkylated by dimethyl carbonate to give quaternary ammonium/phosphonium cations.

Chinese patent (CN200510061094.4, application date 2005.10.10; CN200710008626.7, application date 2007.2.14) discloses a method for preparing quaternary ammonium salt by reacting carbonic diester (ester) and amine (ammonium) salt under the conditions of proper temperature, proper pressure and the like (50-300 ℃, 0.5-50 MPa, 4-12 h), wherein carbonate is used as an alkylating reagent, and hydrogen in amine salt is replaced by methyl in the reaction process to prepare the quaternary ammonium salt. However, the two technical schemes are very different, and the main technical difference is the use of the catalyst. The technical solution of patent CN200510061094.4 requires the use of a catalyst selected from metal compounds, non-metal compounds, mixtures thereof or ionic liquids, so that the product and catalyst components must be present after the reaction is completedThe problem of separation, and it is difficult to ensure high purity of the product; in the technical scheme disclosed by the patent CN200710008626.7, a catalyst is not used, a subsequent complicated separation process is not involved, the operation process is relatively simple, the product purity is greatly improved, and the method is more suitable for application fields with higher requirements on the product purity. However, both synthesis methods are emphasized by starting from amine (ammonia) salts, i.e. the product NH after neutralization of the amine (ammonia) and the acid₄ ⁺L^-、RNH₃ ⁺L^-、R₁R₂NH₂ ⁺L^-、R₁R₂R₃NH⁺L^-As reactants, to synthesize the corresponding quaternary ammonium salt.

Disclosure of Invention

The invention aims to provide a one-step method (namely, a one-pot method) for synthesizing ionic liquid, which can widen the selection range of raw materials required for preparing the ionic liquid and further widen the variety of the synthesized ionic liquid. The specific technical scheme adopted for realizing the first purpose of the invention is as follows: the preparation method of the ionic liquid comprises the steps of synthesizing the ionic liquid by one-step reaction of a nitrogen-containing compound or a phosphorus-containing compound, a proton compound and carbonic ester; the nitrogen-containing compound is selected from ammonia (NH)₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH) and tertiary amines (R)₁R₂R₃N) at least one of; the phosphorus-containing compound is selected from Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH) and tertiary phosphine (R)₁R₂R₃P) at least one of; wherein R is₁、R₂、R₃Each independently selected from hydrogen, alkyl, alkenyl, alkynyl, phenyl or aryl; or R₁、R₂、R₃Each independently at least one organic group selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine and iodine; the R is₁、R₂、R₃Is an independent substituent group(ii) a Or said R₁、R₂、R₃Adjacent groups are combined to form a ring. For example, the nitrogen-containing compound may be sp³Hybridized ammonia or amines, also sp²-hybrid imine compounds. Wherein R is₁、R₂、R₃The structures may be the same or different. As a further preference, the organic group is an alkyl, alkenyl, alkynyl, phenyl or aryl group.

The ionic liquid synthesized by the method is particularly suitable for electrochemical systems with high requirements on the purity of compounds, such as lithium ion secondary batteries, electrochemical supercapacitors and the like, and is also suitable for the fields of green chemical industry, biology, catalysis and the like. According to the method, the raw materials are nontoxic and non-toxic, the raw material selection range is wide, the reaction conditions are mild, the requirements on production equipment are not high, all conventional reaction vessels suitable for liquid phase reaction can be used in principle, and the operations of feeding, mixing, distilling, filtering and the like are simple.

The invention provides a method for preparing quaternary and quaternary phosphonium compound ionic liquid by one-step reaction, which is different from the prior method, the method is 'one-pot method', namely three reactants (amine or phosphine, carbonic ester and proton compound) are added into a reaction kettle together for reaction, and ammonia (NH) gas is used for realizing the reaction₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH), tertiary amine (R)₁R₂R₃N) or Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH), tertiary phosphine (R)₁R₂R₃P) is a route to the corresponding quaternary ammonium or quaternary phosphonium compound from the starting reactants in a single reaction (or in a single reaction). In contrast to the two-step process (US 4892944) in which tertiary phosphine or tertiary amine is used as the starting material, the "one-pot process" in the present invention can be carried out using ammonia (NH)₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH), tertiary amine (R)₁R₂R₃N) or Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH), tertiary phosphine (R)₁R₂R₃P) as starting reactantObviously, the degree of freedom of choice of the reaction materials is larger, and the prepared ionic liquid has various structures and more varieties. For example, the preparation of tetramethylphosphonium tetrafluoroborate, according to the process of the invention, Phosphine (PH)₃) Methyl phosphine, dimethyl phosphine, trimethyl phosphine can be used as starting reactants, while according to US4892944 only trimethyl phosphine can be selected as its actual reactants. Compared with the method for preparing the quaternary ammonium salt by taking the amine (ammonia) salt as the initial reactant in Chinese patents (CN200510061094.4 and CN200710008626.7), the method takes the amine as the initial reactant, and obviously, the reaction steps are simplified. Amine salts are used as reactants, and the quaternary ammonium compound can be prepared by reacting amine with acid to prepare amine salt and then reacting the amine salt with carbonic ester. In the 'one-pot' reaction designed in the method, three reactants (amine, carbonate and proton compound) are added into a reaction kettle together, and the reaction is the reaction of the three reactants, does not relate to amine salt, and does not comprise a first step reaction and a second step reaction.

In the one-step reaction, a nitrogen-containing compound or a phosphorus-containing compound, a proton compound and carbonic ester are added into a reaction kettle; or firstly adding the carbonic ester, the nitrogen-containing compound or the phosphorus-containing compound into the reaction kettle, and then adding the proton compound into the reaction kettle; or adding the proton compound, the nitrogen-containing compound or the phosphorus-containing compound into the reaction kettle, and then adding the carbonic ester into the reaction kettle; or firstly adding the nitrogen-containing compound or the phosphorus-containing compound into the reaction kettle, and then adding the carbonic ester and the proton compound into the reaction kettle.

In one embodiment of the invention, three reactants (A represents a nitrogen-containing compound or a phosphorus-containing compound, B represents carbonic ester, and C represents a proton compound) can be added into a reaction kettle at the same time according to a preset amount to participate in a reaction; or adding A and B into a reaction kettle, and then introducing C at a certain speed; or adding A and C into a reaction kettle, and then introducing B at a certain speed; or adding A into the reaction kettle, and then introducing B and C at a certain speed. As described in the examples, examples 14, 15, 16, 19, 20, 21, 23 and 26 are obtained by adding reactant A and reactant B and then reactant C, and the reaction is started from amine, which is obviously different from the reaction route started from amine salt disclosed in Chinese patent (CN200510061094.4 and CN200710008626.7), and examples 10 and 13 are obviously different from the reaction route started from primary amine and started from tertiary amine or tertiary phosphine disclosed in U.S. Pat. No. 4,4892944. In particular, the differences between the reaction routes disclosed in example 17, example 18, example 22, example 24 and example 25 and the prior art are more apparent and are specifically shown in table 1.

TABLE 1 reaction conditions specific to the examples of the invention

In the table, HTFSI refers to bis (trifluoromethylsulfonyl) imide, and HFSI refers to bis (fluorosulfonyl) imide.

Preferably, the nitrogen-containing compound is selected from at least one of the following structures:

wherein R is₁、R₂、R₃、R₄、R₅、R₆Each independently selected from hydrogen, alkyl, alkenyl, alkynyl, phenyl or aryl; or R₁、R₂、R₃、R₄、R₅、R₆Each independently at least one organic group selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine and iodine; the R is₁、R₂、R₃、R₄、R₅、R₆Is an independent substituent group; or said R₁、R₂、R₃、R₄、R₅、R₆Adjacent groups are combined to form a ring. Wherein R is₁、R₂、R₃、R₄、R₅、R₆The structures may be the same or different. As a further preference, the organic group is an alkyl, alkenyl, alkynyl, phenyl or aryl group.

More preferably, the phosphorus-containing compound is at least one selected from the group consisting of methylphosphine, dimethylphosphine, trimetaphosphine, ethylphosphine, diethylphosphine, triethylphosphine, tripropylphosphine, di-t-butylphosphine, tri-t-butylphosphine, tributylphosphine, tri-n-pentylphosphine, cyclohexylphosphine, dicyclohexylphosphine, tricyclohexylphosphine, trihexylphosphine, trioctylphosphine, phenylphosphine, diphenylphosphine, triphenylphosphine, dimethylphenylphosphine, diethylphenylphosphine, diphenylbutylphosphine, tribenzylphosphine, trimethylolphosphine, 2-chloroethyldiphosphine, and tris (pentafluoroethyl) phosphine.

More preferably, the protic compound is at least one selected from the group consisting of inorganic oxoacids, organic acids, and aprotic acid-based protic compounds. The proton compound of the present invention refers to a compound which can provide at least one proton and nitrogen-containing compound under certain conditions, including ammonia (NH)₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH), tertiary amine (R)₁R₂R₃N) or with phosphorus-containing compounds including Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH), tertiary phosphine (R)₁R₂R₃P) to which the P element is bonded,

as a further preference, the inorganic oxygen-containing compound is selected from the group consisting of metaaluminic acid (HAlO)₂) Tetrahydroxyaluminum (III) acid (HAl (OH)₄) Arsenic acid (H)₃AsO₄) Meta-arsenous acid (HAsO)₂) Arsenous acid (H)₃AsO₃) Pyroarsenic acid (H)₄As₂O₇) Boric acid (H)₃BO₃) Metaboric acid ((HBO)₂)_n) Tetraboric acid (H)₂B₄O₇) Perboric acid (HBO)₃) Dodecatungstoboric acid (H)₅BW₁₂O₄₀) Bromic acid (HBrO)₃) Bromic acid (HBrO)₂) Hypobromous acid (HBrO), and perbromic acid (HBrO)₄) Ortho carbonic acid (H)₄CO₄)、Peroxydicarbonate (H)₂C₂O₆) Percarbonic acid (H)₂CO₄Or H₂CO₃·H₂O₂) Chloric acid (HClO)₃) Perchloric acid (HClO)₄) Chlorous acid (HClO)₂) Hypochlorous acid (HClO), humic acid (HONC), cyanic acid (HOCN), isocyanic acid (HNCO), iodic acid (HIO)₃) Hypoiodic acid (HIO or IOH), meta-periodic acid (HIO)₄) Periodic acid (H)₅IO₆) Burnt periodic acid (H)₄I₂O₉) Nitric acid (HNO)₃) Nitrous acid (HNO)₂) Phosphoric acid (H)₃PO₄) Orthophosphoric acid (H)₅PO₅) Metaphosphoric acid (HPO)₃) n, phosphorous acid (H)₃PO₃) Pyrophosphorous acid (H)₄P₂O₅) Metaphosphoric acid (HPO)₂) Hypophosphorous acid (H)₃PO₂) Hypophosphorous acid (H)₄P₂O₆) Pyrophosphoric acid (H)₄P₂O₇) Sulfuric acid (H)₂SO₄) Sulfurous acid (H)₂SO₃) Thiosulfuric acid (H)₂S₂O₃) Pyrosulfuric acid (H)₂S₂O₇) Hyposulfuric acid (H)₂SO₂) Polythionic acid (H)₂S_xO₆X is 2 to 6), ortho sulfuric acid (H)₆SO₆) Dithionous acid (H)₂S₂O₄) Peroxymonosulfuric acid (H)₂SO₅) Peroxodisulfuric acid (H)₂S₂O₈) Chlorosulfonic acid (HSO)₃Cl), fluorosulfonic acid (HSO)₃F) Metasilicic acid (H)₂SiO₃Or SiO₂·H₂O), orthosilicic acid (H)₄SiO₄) Di-metasilicic acid (H)₂Si₂O₅Or 2SiO₂·H₂O), trisilicic acid (H)₄Si₃O₈) And pyrosilicic acid (H)₆Si₂O₇Or 2SiO₂·3H₂O) is used.

As a further preference, the inorganic oxygen-free acid is selected from carborane acid (H [ CHB ]₁₁Cl₁₁]) Hydrogen sulfuric acid (H)₂S), peroxycarbonic acid (H)₂CS₄) Thiocarbonic acid (H)₂CS₃) Hydrocyanic acid (HCN), selenocyanate (HSeCN), thiocyanic acid (HSCN), fluoroboric acid (HBF)₄) Fluosilicic acid (H)₂SiF₆) Hexafluorophosphoric acid (HPF)₆) At least one of hydrofluoric acid (HF), hydrochloric acid (HCl), hydrobromic acid (HBr) and hydroiodic acid (HI).

More preferably, the organic acid is at least one selected from the group consisting of oxalic acid, formic acid, acetic acid, propionic acid, succinic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, methanesulfonic acid, mandelic acid, methylsulfuric acid, ethylsulfuric acid, oleic acid, stearic acid, acrylic acid, maleic acid, citric acid, bis (catechol) boric acid, bisoxalatoboric acid, bismalonic acid boric acid, tris (pentafluoroethyl) trifluorophosphoric acid, triethyltrifluorophosphoric acid, tetracyanoboric acid, tartaric acid, malic acid, citric acid, ascorbic acid, benzoic acid, benzenesulfonic acid, p-toluenesulfonic acid, salicylic acid, and caffeic acid.

According to the process of the invention, the above mentioned protic compounds also include acid compounds which are far beyond the usual meaning, which are defined herein as aprotic compounds of the non-acid type, which have active protic hydrogens and which have a high activity for the hydrogen atom due to the very strong electron withdrawing property of the ortho group, i.e. which can release active protons. Still more preferably, the aprotic acid-based compound is an imine compound; the imine compound has a structure as shown in formula 1, formula 2 or formula 3:

formula 1: HN (C)_mF_2m+1SO₂)(C_nF_2n+1SO₂)；

Formula 2: HN (C)_nF_2n+1SO₂)₂；

Formula 3: HN (C)_xF_2xSO₂)₂；

Wherein m is an integer of 0 to 5, n is an integer of 0 to 5, and X is an integer of 1 to 10.

Still more preferably, the imine compound is selected from at least one of the following structural formulae:

more preferably, the aprotic acid-based compound is at least one selected from the group consisting of tris (trifluoromethylsulfonyl) methane, phenol, p-methylphenol, β -naphthol, 2, 4-dichlorophenol and p-aminophenol.

More preferably, the carbonate is at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, methyl phenyl carbonate, diphenyl carbonate and dibenzyl carbonate.

The kind of the protic compound in the present invention has an influence on the yield of the final reaction product. According to one embodiment of the present invention, a strongly acidic acid is advantageous in providing high product yields, for example, hydrochloric acid (HCl), hydrobromic acid (HBr), and hydroiodic acid (HI) in hydrohalic acid are all strong acids, and the yield of the reaction product is also high. In addition, acids of the same type tend to give similar yields of reaction products, inorganic complex acids such as fluoroboric acid (HBF)₄) Hexafluorophosphoric acid (HPF)₆) There is a similar product yield. Of course, the influence of the product yield is manifold and also depends on the structure of the nitrogen-containing compound or phosphorus-containing compound and the structure of the carbonate.

The quaternizing agent and the quaternary phosphonium reagent carbonate in the method of the invention can be represented by RO-CO-OR '(also called alkylating agent), wherein R, R' is independently selected from hydrocarbon-containing alkyl, alkenyl, alkynyl, phenyl OR aryl; or R, R' are each independently an organic group containing at least one element selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine, and iodine. R, R' may be identical or different; r, R' may be independent substituent groups or adjacent groups may be combined to form a ring.

Considering the thermodynamic and kinetic effects of the electron donating/withdrawing effect, the steric hindrance effect and the like of the substituent R, R' on the alkylation reaction, the substituent is preferably at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, phenyl methyl carbonate, diphenyl carbonate and dibenzyl carbonate; dimethyl carbonate, dimethyl carbonate,At least one of ethyl methyl carbonate and diethyl carbonate. In particular, when the carbonate is a cyclic structure, a polyfunctional compound can be obtained by the process of the present invention. For example, by adding ethylene carbonate or propylene carbonate as alkylating agent, it is possible to introduce hydroxyethyl groups (-CH) separately into the end product₂CH₂OH) and 2-hydroxypropyl (-CH)₂CHOHCH₃). Due to the introduction of hydroxyl, the application field of quaternary ammonium salt or quaternary phosphonium salt is expanded (such as enhancing hydrophilicity or water solubility, and can be applied to the field related to water); on the other hand, conditions are provided for "grafting" other functional groups, which may be further functionalized on the basis of hydroxyl groups, for example, by halogenation, etherification, esterification, etc., or by oxidation to carboxylic acids.

Preferably, the temperature of the one-step reaction is controlled to be 100-200 ℃. Preferably, the temperature of the one-step reaction is controlled to be 120-180 ℃. More preferably, the temperature of the one-step reaction is controlled to 140 to 160 ℃.

Preferably, the absolute pressure of the one-step reaction is controlled to be 0.1-3.0 MPa. Further preferably, the absolute pressure of the one-step reaction is controlled to be 0.8 to 2.0 MPa. More preferably, the absolute pressure of the one-step reaction is controlled to be 1.0 to 1.5 MPa. In practice, if the reaction exotherm is significant, it is preferable to slow the rate of addition of one of the reactants, or to allow for a reduction in temperature; if the reaction pressure rises too rapidly, it may also be preferable to slow the rate of feeding one of the reactants.

Preferably, the reaction time of the one-step reaction is controlled to be 0.1-20 hours. More preferably, the reaction time of the one-step reaction is controlled to be 4-15 hours. Preferably, the reaction time of the one-step reaction is controlled to be 9 to 12 hours.

In the synthesis method of the present invention, the reaction may be carried out in a certain solvent or may be carried out without a solvent. The use of a solvent facilitates uniform mixing of the reactants, and in general, facilitates the reaction at lower reaction temperatures or higher yields of product. However, the introduction of the solvent also causes troubles, increases the cost, has a safety hazard, and is recycled. The method of the present invention is not limited to the necessity of a solvent, and the solvent used in the reaction is not particularly limited. In general, if a solvent is selected, the solvent may be at least one selected from the group consisting of alcohols (preferably methanol and ethanol), ethers, ketones (preferably acetone), carbonates (preferably dimethyl carbonate), nitriles, alkanes, halogenated hydrocarbons, and aromatic hydrocarbons. Further, the solvent may be at least one selected from methanol, ethanol, acetone, and dimethyl carbonate.

According to the synthesis method of the present invention, nitrogen-containing compounds such as ammonia (NH)₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH), tertiary amine (R)₁R₂R₃N) or phosphorus-containing compounds, e.g. Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH), tertiary phosphine (R)₁R₂R₃The molar ratio of P) to protic compound depends on the number of protons that the protic compound can provide. For example, with phosphorus-containing compounds, Phosphine (PH) is generated if a molecule of protic compound can donate only one proton₃) Or organic phosphides (including primary phosphanes R)₁PH₂Secondary phosphine R₁R₂PH, tertiary phosphine R₁R₂R₃The molar ratio of P) to protic compound is preferably 1: 1. For example, Phosphine (PH)₃) And hydrofluoric acid (HF) were added to the reactor in a molar ratio of 1: 1. Phosphine (PH) if a molecule of protic compound can provide two or more protons₃) Or organic phosphides (including primary phosphanes R)₁PH₂Secondary phosphine R₁R₂PH, tertiary phosphine R₁R₂R₃The molar ratio of P) to protic compound may be 1:1, 2:1 or 3:1, for example, one molecule of phosphoric acid may provide up to 3 protons, and triethylphosphine and phosphoric acid may be added to the reactor in a molar ratio of 1:1, 2:1 or 3:1, respectively. The molar ratio can be deviated, a certain reactant can be excessive, and the selection of a substance with slight excess is more favorable (low economic cost and environment-friendly) according to the factors of high material cost, low waste recovery difficulty and the like. For the same reason, nitrogen-containing compoundsSuch as ammonia (NH)₃) Primary amine (RNH)₂) Secondary amine (R)₁R₂NH), tertiary amine (R)₁R₂R₃N) or phosphorus-containing compounds, e.g. Phosphine (PH)₃) Primary phosphine (RPH)₂) Secondary phosphine (R)₁R₂PH), tertiary phosphine (R)₁R₂R₃The molar ratio of P) to carbonate depends on the number of hydrogen atoms in the compound. For example, PH₃The molar ratio to the carbonate can be set to 1:4, RPH₂The molar ratio of the polycarbonate to the carbonate can be set to 1:3, R₁R₂The molar ratio of PH to carbonate can be set to 1:2, R₁R₂R₃The molar ratio of P to carbonate can be set to 1: 1. To ensure a high product yield, the amount of carbonate may be in excess. Of course, in order to ensure the completion of the reaction, it is also conceivable that the reactants having a low boiling point and a low cost are slightly excessive and may be removed by washing, distillation under reduced pressure, recrystallization or the like after the completion of the reaction.

After the reaction of the present invention is completed, unreacted reactants and solvent may be removed by distillation, distillation under reduced pressure, recrystallization, washing, or the like. Before the reaction is started, the air in the reaction vessel may be preferably replaced with an inert gas atmosphere or may be evacuated by a vacuum pump to avoid adverse effects on the reaction due to air. As is known from the reaction mechanism, one of the by-products of the reaction is CO₂. With the continuous progress of the reaction, CO₂The amount of (A) is increased, which results in a pressure increase in the reaction vessel. Considering safe production and reducing the manufacturing cost of the equipment (the pressure vessel is graded according to the bearing pressure, the higher the pressure, the more the consumable material and the high requirement on air tightness), it can be preferable to slowly add a certain reactant (control the reaction rate) and release CO through an air valve₂So that the pressure in the reaction vessel is stabilized at a certain level. And CO is released while conveying materials₂The method is also beneficial to improving the capacity of the reaction kettle in actual production. As reaction apparatus for the process of the invention, it is in principle possible to use all vessels suitable for liquid-phase reactions as well as pressure vessels. The material of the container is selected according to the physicochemical properties of the reactants, and is preferably selected fromThe method is carried out in a material with acid and alkali resistance, such as a stainless steel (such as 316L stainless steel) pressure vessel or a titanium pressure vessel.

According to an embodiment of the present invention, the cationic structure of the synthesized quaternary ammonium salt may be selected from, but is not limited to, the following structures:

r, R' and R in the structure of the nitrogen-containing compound₁、R₂、R₃、R₄、R₅、R₆Each independently selected from alkyl, alkenyl, alkynyl, phenyl and aryl containing hydrocarbon; or organic groups each independently selected from at least one element selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine, and iodine. R, R' and R₁、R₂、R₃、R₄、R₅、R₆The structures can be the same or different; r, R' and R₁、R₂、R₃、R₄、R₅、R₆Can be independent substituent groups, and can also be adjacent groups combined to form a ring.

According to one embodiment of the present invention, the cationic structure of the synthesized quaternary phosphonium salt may be selected from, but is not limited to, the following structures:

according to one embodiment of the present invention, the anionic structure of the synthesized quaternary ammonium salt or quaternary phosphonium salt may be selected from, but is not limited to, the following structures:

PF₆ ^-，BF₄ ^-，SO₄ ^2-，NO₃ ^-，F^-，Cl^-，Br^-，I^-，PO₄ ^3-，ClO₄ ^-，SiF₆ ^2-，

the second object of the present invention is to provide an electrolyte for a secondary battery, comprising an ionic liquid prepared by any one of the above-described ionic liquid preparation methods.

At present, the main problems facing the application of ionic liquid electrolyte to lithium ion batteries are: 1) the compatibility with carbon-based negative electrode materials such as graphite is poor, reversible polarization cannot be carried out, and ideal lithium insertion/removal performance is difficult to show; 2) the ionic liquid synthesized by the method HAs the problem of halide ion residue, namely, halide ions remain in the ionic liquid, which HAs great influence on the application of the ionic liquid in a secondary battery, and the halide ions can corrode a battery shell, a current collector, a lug and the like, so that the calendar life and the cycle life of the battery are reduced; 3) the wettability of the non-polar and low-porosity commercial PP/PE/PP diaphragm is poor, the performance of the ionic liquid electrolyte is limited, and the lithium secondary battery with deteriorated electrochemical properties cannot be practically applied; 4) when the lithium nickel cobalt manganese composite oxide or the lithium nickel cobalt aluminum composite oxide is used as a positive electrode active material, the lithium nickel cobalt manganese composite oxide or the lithium nickel cobalt aluminum composite oxide has a catalytic oxidation effect on ionic liquid, side reactions in the battery are increased, and the appearance shows swelling or flatulence, so that the cycling stability of the battery is deteriorated; 5) corrosion of aluminum current collectors by Ionic liquid electrolytes, currently commercial electrolytes (carbonates and LiPF)₆System) contains trace HF, and the HF reacts with the alumina on the surface of the aluminum current collector to generate AlF₃The protective film inhibits aluminum from being corroded, however, in the ionic liquid (the anion is bis (trifluoromethyl sulfonyl) imide ion or bis (fluoro sulfonyl) imide ion) electrolyte, under the general condition, an AlF3 protective film is not formed on the surface of the aluminum current collector, and the aluminum current collector is inevitably corroded.

In order to realize the application of the ionic liquid electrolyte on the graphite cathode, Chinese patent (with the patent publication number of CN102138235A) provides a solution, and LiFePO is used as the anode active material₄In ionic liquid electricityThe addition of 1-10% Vinyl Ethylene Carbonate (VEC) to the electrolyte resulted in a battery with good reversible cycling performance, reversing the argument that it is not possible to use ionic liquid electrolytes for graphitic carbon electrodes. However, this solution is limited to the anode being LiFePO₄The scheme is not feasible for active cathode materials with higher oxidation potential, such as lithium nickel cobalt manganese composite oxide or lithium nickel cobalt aluminum composite oxide. In order to improve the compatibility of the ionic liquid electrolyte and the diaphragm, Chinese patent (with the patent publication number of CN102903954A) researches the components, raw materials and characteristics of the ionic liquid electrolyte and the synergistic effect of a specific diaphragm (namely, the substrate of the specific diaphragm is a polar organic polymer, the structure of the specific diaphragm is a porous three-dimensional mesh, and the specific diaphragm has the air permeability of 150-500S/100 CC) so as to exert the respective maximum advantages to improve the high-current performance of the ionic liquid. However, the patent only focuses on matching of the ionic liquid electrolyte and the separator, and does not combine characteristics of a positive electrode, a negative electrode, a current collector and the like, so that a complete solution is provided. In addition, many documents mention the application of ionic liquid electrolytes to lithium ion batteries to improve safety, but few specific requirements are put on the purity of the ionic liquid electrolytes, particularly the residual amount of halogen ions.

In order to solve the above problems, a third object of the present invention is to provide a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolytic solution containing an ionic liquid prepared by the above method for preparing an ionic liquid. The ionic liquid prepared by the method has high purity, does not have the problem of halide ion residue, and greatly prolongs the service life of the secondary battery.

The ionic liquid has residual halide ions, which greatly affects the application of the ionic liquid in secondary batteries. The halide ions corrode the battery shell, the current collector, the electrode lug and the like, the cycle characteristics of the secondary battery are influenced, and the cycle life is shortened. Chinese patent publication No. CN101379653 emphasizes the importance of the purity of the ionic liquid electrolyte and limits the content of halogen ion impurities, but does not indicate how to obtain an ionic liquid completely free of halogen ion impurities. The invention provides a method for synthesizing ionic liquid by one-step reaction by using carbonic ester as an alkylating reagentA method of manufacturing a body. For example, as shown in example 14, 1-methyl-1-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt was synthesized by a one-step method using N-propylpyrrolidine, dimethyl carbonate, and bis (trifluoromethylsulfonyl) imide as reactants. Because halogenated hydrocarbon is not involved in the synthetic route, anion exchange reaction is avoided, and therefore, halogen ions and alkali metal ions are not remained in the synthesized ionic liquid. After formulating into an ionic liquid electrolyte, halide ions (Cl)^-，Br^-，I^-) The content of (B) is not more than 5 ppm.

The cation of the ionic liquid in the present invention is preferably a 1-methyl-1-propylpyrrolidinium ion, 1-methyl-1-butylpyrrolidinium ion, 1-methyl-1-propylpiperidinium ion or 1-methyl-1-butylpiperidinium ion. In addition, it has been found through many experiments that the method for synthesizing ionic liquid by using carbonate as alkylating agent through one-step reaction is preferred, and the yield is higher when the tertiary amine is pyrrolidine or piperidine, for example, in example 14, N-propyl pyrrolidine (500g) and 1000mL dimethyl carbonate are put into a pressure container together, under the protection of nitrogen, bis (trifluoromethyl sulfonyl) imide (1243g) is slowly added, the temperature is kept not to exceed 60 ℃ in the process, after the addition is finished, the reaction is carried out for 20 hours at 150 ℃ and about 1.6MPa, part of gas is released through a vent valve in the reaction process so as not to cause overhigh pressure, low-boiling point substances are removed under reduced pressure after the reaction is finished, products are washed, and after vacuum drying, N-methyl-N-propyl pyrrolidinium bis (trifluoromethyl sulfonyl) imide salt is obtained, and the yield can reach more than 98%. Preferably, the cation of the ionic liquid of the present invention is a pyrrolidinium ion or a piperidinium ion in order to obtain a high-purity and low-cost ionic liquid. Theoretically, the introduction of halogen ions can be completely avoided by using carbonate as an alkylating agent, namely the content of the halogen ions in the ionic liquid electrolyte is zero. However, since starting materials such as pyrrolidine, piperidine and carbonate may be contaminated with halogen ions during the production process, the present invention requires distillation purification of pyrrolidine, piperidine and carbonate before the reaction, and the content of halogen ions in the starting materials is not more than 3 ppm. Currently, electrolyte for lithium secondary battery, carbonate/LiPF₆The water content in the system is reduced from 20ppm to 5ppm years ago. Water (W)The influence of each molecule on the performance of the lithium battery is very serious, one molecule of water at least generates one molecule of HF, and the HF is a main cause of the increase of the internal resistance, the gas generation bulge and the like of the lithium secondary battery. The halogen ion has no harm to the performance of the battery than moisture, so the content of the halogen ion in the ionic liquid electrolyte is required to be less than 5ppm so as to meet the requirement of long service life of the secondary battery.

Preferably, the electrolyte includes a lithium salt and a base component; the base component comprises an ionic liquid; the cation of the ionic liquid is selected from at least one of the following structures:

wherein R is an alkyl group.

Preferably, the cation of the ionic liquid is pyrrolidinium ion or piperidinium ion, and on one hand, the five-membered heterocyclic ring and the six-membered heterocyclic ring have stable structures and are beneficial to prolonging the service life of the secondary battery; on the other hand, different from common quaternary ammonium ions, two substituents on the N atom are combined to form a ring, so that the steric hindrance between the four substituents is reduced, the mutual winding between substituted alkyl groups is reduced, the reduction of the viscosity of the ionic liquid is facilitated, and the high-current charge and discharge performance of the ionic liquid electrolyte is improved.

Preferably, the cation is at least one of a 1-methyl-1-propylpyrrolidinium ion, a 1-methyl-1-butylpyrrolidinium ion, a 1-methyl-1-propylpiperidinium ion, and a 1-methyl-1-butylpiperidinium ion.

Preferably, the negative electrode active material has a lithium deintercalation potential of not less than 0.25V (for Li/Li)⁺)。

Preferably, the negative active material is a silicon carbon material or a silicon alloy material; the silicon-carbon material is coated with

The carbon contained is not graphite.

Preferably, the silicon alloy material is at least one of a silicon copper-based material and a silicon tin-based material.

Preferably, the negative active material is a titanium-based oxide.

Preferably, the titanium-based oxide is lithium titanium oxide.

Preferably, the content of the halogen ions in the electrolyte is less than or equal to 5 ppm.

Preferably, the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis (catechol) borate, lithium bismalonate borate, lithium bisoxalate borate, lithium tris (catechol) phosphate, lithium tris (perfluoroethyl) trifluorophosphate, lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide and lithium difluorosulfonimide.

Preferably, the lithium salt is selected from at least one of a first lithium salt and at least one of a second lithium salt; the first lithium salt comprises lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide and lithium difluorosulfonimide; the second lithium salt includes lithium hexafluorophosphate and lithium tetrafluoroborate. More preferably, the mass of the first lithium salt accounts for 0.5-30% of the total mass of the electrolyte; the mass of the second lithium salt accounts for 0.5-30% of the total mass of the electrolyte.

Preferably, the molar ratio of the first lithium salt to the second lithium salt is 1:19 to 19: 1. More preferably, the molar ratio of the first lithium salt to the second lithium salt is 1:9 to 9: 1. More preferably, the molar ratio of the first lithium salt to the second lithium salt is 3:7 to 7: 3.

On the one hand, the use of the mixed lithium salt can adjust the physical properties of the ionic liquid electrolyte, for example, the melting point is reduced, and the use temperature range is widened; on the other hand, the second lithium salt, lithium hexafluorophosphate or lithium tetrafluoroborate, may be hydrolyzed in the presence of trace amounts of water to produce trace amounts of HF, HF and Al on the surface of the aluminum current collector₂O₃React to generate AlF₃Thereby protecting the current collector from corrosion. Since the industrial production process of lithium hexafluorophosphate is mature, the production scale is large, and the cost has been reduced to the limit, it is preferable to use lithium hexafluorophosphate in the composition of the mixed lithium salt, and a larger amount of lithium hexafluorophosphate is used as much as possible. However, in many cases, the use of a larger amount of lithium hexafluorophosphate may result in ionizationThe physicochemical properties of the sub-liquid electrolyte are changed. For example, crystallization occurs at low temperatures. The amount of lithium hexafluorophosphate is closely related to the anion structure of the ionic liquid. If the anion is bis (trifluoromethylsulfonyl) imide, the amount of lithium hexafluorophosphate used may be increased as appropriate; if the anion is triflate, lithium hexafluorophosphate is used in as small an amount as possible, preferably lithium tetrafluoroborate is used. Of course, in order to adjust the physicochemical and electrochemical properties of the ionic liquid electrolyte, a third lithium salt may be added, and the third lithium salt may function as an electrolyte or an additive. For example, a small amount of lithium salt such as LiBOB and LiODBF is added into the ionic liquid electrolyte, so that an SEI film with special performance can be formed on the surface of the silicon-based negative electrode.

Preferably, the base component further comprises an organic solvent; the organic solvent is at least one of carbonates, carboxylic acid esters, sulfurous acid esters, sulfonic acid esters, sulfones, ethers, organic silicon, nitriles and fluoro phosphazenes. More preferably, the organic solvent is at least one of propylene methyl carbonate, propylene ethyl carbonate, phenol methyl carbonate, ethylene carbonate, halogenated ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, vinylene carbonate, ethylene sulfite, propylene sulfite, butylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, ethyl methyl sulfoxide, 1, 3-propanesulfonate, 1, 4-butanesultone, dioxolane, dimethoxypropane, ethoxypentafluorophosphazene, phenoxypentafluorophosphazene, adiponitrile, and succinonitrile.

Preferably, the base component further comprises a film-forming agent, wherein the film-forming agent is sulfur dioxide, ethylene sulfite (VS), Vinylene Carbonate (VC), sulfite, sulfoxide, sulfonate, halogenated organic ester, organic unsaturated compound containing vinylidene, organic boride and Li₂CO₃And LiBOB.

Preferably, the base component further comprises a functional additive; the functional additive is at least one of an overcharge-preventing additive, a flame-retardant additive, a conductive additive and a high-pressure-resistant additive. More preferably, the functional additive is at least one of biphenyl (DP), cyclohexylbenzene, aryladamantane, naphthalene derivatives, polyparaphenylene, trimethyl phosphate (TMP), triphenyl phosphate (TPP), tris (2, 2,2 trifluoroethyl) phosphite, p-dinitrogen (hetero) benzene, tris (pentafluorophenyl) boron, ethoxypentafluorophosphononitrile, phenoxypentafluorophosphononitrile, adiponitrile, and succinonitrile.

Preferably, the base component comprises 70-100 wt% of ionic liquid, 0-30 wt% of organic solvent, 0-10 wt% of film forming agent and 0-10 wt% of functional additive.

Preferably, the positive electrode active material is at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium manganese nickel composite oxide, lithium phosphorus oxide, lithium cobalt oxide, and lithium manganese composite oxide. The lithium manganese nickel composite oxide has a spinel structure, and the lithium phosphorus oxide has an olivine structure.

The positive electrode active material included in the secondary battery of the present invention is not particularly limited, and may be at least one of a lithium nickel cobalt manganese composite oxide, a lithium nickel cobalt aluminum composite oxide, a spinel-type lithium manganese nickel composite oxide, a lithium phosphorus oxide having an olivine structure, a lithium cobalt oxide, and a lithium manganese composite oxide. Materials that can improve the operating voltage of the battery and have high electrochemical stability, such as lithium nickel cobalt manganese complex oxide NCM (333), lithium nickel cobalt manganese complex oxide NCM (442), lithium nickel cobalt manganese complex oxide NCM (523), and the like, are preferred.

Preferably, the diaphragm is at least one of a polyethylene terephthalate diaphragm, a polyacrylonitrile diaphragm and a polyvinylidene fluoride diaphragm. The ionic liquid is a polar substance, and a polar diaphragm is selected, so that the electrolyte can be favorably used for fully wetting the diaphragm.

Preferably, the average pore diameter of the diaphragm is 1-25 μm; the porosity of the diaphragm is 50-85%. The porosity of the diaphragm is high, the holding capacity of the diaphragm to the electrolyte is large, and the diaphragm is very suitable for the ionic liquid electrolyte with high viscosity.

Drawings

FIG. 1a is a charging curve of a secondary battery prepared in example 14 of the present invention;

FIG. 1b is a discharge curve of a secondary battery prepared in example 14 of the present invention;

fig. 2 is a cycle life curve of a secondary battery prepared in example 14 of the present invention;

fig. 3 is a discharge curve of a secondary battery prepared in example 15 of the present invention;

fig. 4 is a discharge curve of a secondary battery prepared in example 16 of the present invention;

fig. 5a is a charging curve of a secondary battery prepared in example 17 of the present invention;

fig. 5b is a discharge curve of a secondary battery prepared in example 17 of the present invention;

fig. 6a is a charging curve of a secondary battery prepared in example 18 of the present invention;

fig. 6b is a discharge curve of a secondary battery prepared in example 18 of the present invention;

fig. 7a is a charging curve of a secondary battery prepared in example 19 of the present invention;

fig. 7b is a discharge curve of the secondary battery prepared in example 19 of the present invention;

fig. 8a is a charging curve of a secondary battery prepared in example 20 of the present invention;

fig. 8b is a discharge curve of the secondary battery prepared in example 20 of the present invention;

fig. 9a is a charging curve of a secondary battery prepared in comparative example 1 of the present invention;

fig. 9b is a discharge curve of a secondary battery prepared in comparative example 1 of the present invention;

fig. 10a is a charging curve of a secondary battery prepared in comparative example 2 of the present invention;

fig. 10b is a discharge curve of a secondary battery prepared in comparative example 2 of the present invention;

fig. 11 is a cycle life curve of a secondary battery prepared in comparative example 3 of the present invention;

FIG. 12 SEM images of three types of membranes, namely PVDF, PET and PP/PE/PP, used in the examples of the present invention.

Detailed Description

The following specific examples describe the present invention in detail, however, the present invention is not limited to the following examples.

The structure of the lithium ion secondary battery is not limited, and the lithium ion secondary battery can be cylindrical, square or button type, flexible package or steel shell or aluminum shell. In the embodiment of the invention, a button type lithium ion secondary battery (CR2025) and a flexible package lithium ion battery are adopted. The positive electrode active material of the battery is not limited, and may be at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, spinel-type lithium manganese nickel composite oxide, lithium phosphorus oxide having an olivine structure, lithium cobalt oxide, and lithium manganese composite oxide. The negative electrode active material has a lithium deintercalation potential of not less than 0.25V (for Li/Li)⁺) The material may be selected from materials other than carbon materials such as graphite (natural graphite or artificial graphite), such as lithium titanate, elemental silicon, carbon-silicon composite materials, silicon-copper composite materials, silicon-tin composite materials, and the like.

Example 1:

triethylamine (606g) was placed in a pressure vessel with 1000mL of dimethyl carbonate and blanketed with nitrogen. Introducing concentrated sulfuric acid (300g, 98%) under the condition of temperature reduction, heating to 200 deg.C after adding sulfuric acid, and if the reaction pressure exceeds 3.0MPa, releasing gas through valve to make the pressure in the reactor not rise any more. The reaction time was 0.2 hour. After the reaction was completed and cooled to room temperature, low boilers were removed under reduced pressure and the product was washed to give N-methyl-N-triethylammonium sulfate (950 g).

Example 2:

N-N-propylpyrrolidine (500g) was placed in a pressure vessel along with 1000mL of dimethyl carbonate. Bis (trifluoromethylsulfonyl) imide (1234g) was added slowly under nitrogen, during which time the temperature was kept at 60 ℃ or below. After the addition, the reaction is carried out for 20 hours at 150 ℃ and about 1.6MPa, and part of gas is released through a release valve during the reaction process so as to avoid overhigh pressure. After completion of the reaction, the low boilers were removed under reduced pressure and the product was washed to give N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (1675 g).

Example 3:

putting N-N-propyl pyrrolidine (500g), 500g dimethyl carbonate and 500mL methanol in a pressure container, heating to 120 ℃, adding bis (trifluoromethyl sulfonyl) imine (1236g) according to a certain flow, and keeping the temperature in the reaction container at 120-130 ℃ in the process. The continuous feeding time is 12 hours, after the bis (trifluoromethylsulfonyl) imide material is conveyed according to the set amount, the temperature is increased to 150 ℃ to continue the reaction for 2 hours. In the reaction process, if the reaction pressure exceeds 2.6Mpa, the pressure in the kettle is kept not to rise through valve deflation. After the reaction was completed and cooled to room temperature, the low boilers were removed under reduced pressure and the product was washed to give N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (1704 g).

Example 4:

N-N-butylpyrrolidine (500g) was placed in a pressure vessel under nitrogen, the temperature was maintained at 60 ℃ and a mixture of trifluoromethanesulfonic acid (585g) and 1000mL of dimethyl carbonate was slowly added. After the addition is finished, the reaction is carried out for 15 hours at 140 ℃ and about 1.5MPa, and part of gas is released through a release valve during the reaction process so as to avoid overhigh pressure. After completion of the reaction, low boilers were removed under reduced pressure to give N-methyl-N-N-butylpyrrolidinium trifluoromethanesulfonate (1006 g).

Example 5:

N-Ethylimidazole (298g) was placed in a pressure vessel and a solution of tetrafluoroboric acid in methanol (682g, 40%) was slowly added, during which time the temperature was kept at room temperature. After the addition, 600mL of dimethyl carbonate was added, and the whole process was protected with nitrogen. The temperature is raised to 180 ℃ and the reaction is carried out for 3 hours under the pressure of about 1.5MPa, and part of gas is released through a vent valve during the reaction process so as to avoid overhigh pressure. After completion of the reaction, low-boiling substances were removed under reduced pressure to obtain 1-methyl-3-ethylimidazolium tetrafluoroborate (574 g).

Example 6:

bis (trifluoromethylsulfonyl) imide (125g) was placed in a pressure vessel under nitrogen blanket and tri-n-butylphosphine (89g) and 150mL dimethyl carbonate were added slowly, maintaining the temperature at no more than room temperature during this time. After the completion of the addition, the temperature was raised to 180 ℃ and the reaction was carried out at about 1.5MPa for 5 hours, after which the low-boiling substance was removed under reduced pressure to obtain methyltri-n-butylphosphonium bis (trifluoromethylsulfonyl) imide salt (214 g).

Example 7:

triphenylphosphine (115g), 150mL dimethyl carbonate and bis (trifluoromethylsulfonyl) imide (125g) were placed together in a pressure vessel under nitrogen, the temperature was raised to 180 ℃ and the reaction was carried out at about 1.5MPa for 4 hours, and after completion of the reaction, the low-boiling point material was removed under reduced pressure to obtain methyltriphenylphosphonium bis (trifluoromethylsulfonyl) imide salt (240 g).

Example 8:

triphenylphosphine (115g) and bis (trifluoromethylsulfonyl) imide (125g) were placed in a pressure vessel under nitrogen, and 150mL diethyl carbonate was added. After the addition was completed, the temperature was raised to 180 ℃ and the reaction was carried out at about 2.5MPa for 5 hours, after which the low-boiling substance was removed under reduced pressure to obtain ethyltriphenylphosphonium bis (trifluoromethylsulfonyl) imide salt (236 g).

Example 9:

bis (trifluoromethylsulfonyl) imide (152g) was placed in a pressure vessel under nitrogen blanket and diphenylphosphine (100g) and 150mL diethyl carbonate were added slowly. After the completion of the addition, the temperature was elevated to 180 ℃ and the reaction was carried out at about 2.0MPa for 5 hours, after which the low-boiling substance was removed under reduced pressure to obtain diethyldiphenylphosphonium bis (trifluoromethylsulfonyl) imide salt (262 g).

Example 10:

under the protection of nitrogen, n-octylamine (100g) and 250mL dimethyl carbonate were placed in a pressure vessel, concentrated sulfuric acid (39g, 98%) was slowly added, and the temperature was controlled not to exceed 60 ℃. After the addition was completed, the temperature was raised to 180 ℃ and the reaction was carried out at about 0.5MPa for 8 hours, after which the low boilers were removed under reduced pressure to obtain trimethyloctylammonium sulfate (159 g).

Example 11:

under the protection of nitrogen, dioctylamine (1200g) and 2000mL dimethyl carbonate are placed in a pressure vessel, hydrogen chloride gas (180g) is slowly introduced, the temperature in the reaction process is kept to be not more than 60 ℃, after the addition is finished, the temperature is raised to 160 ℃, the reaction is carried out for 20 hours under the pressure of about 0.2MPa, and after the reaction is finished, low-boiling-point substances are removed under reduced pressure to obtain dimethyl dioctylammonium hydrochloride (1070 g).

Example 12:

tributylphosphine (100g), ethylene carbonate (100g) and an ethanol solution of hydrogen chloride (55g, 33%) were placed together in a pressure vessel under argon protection, the temperature was raised to 160 ℃, and the reaction was carried out at about 1.5MPa for 3 hours, after the completion of the reaction, the low-boiling substances were removed under reduced pressure to obtain 2-hydroxyethyl tributylphosphonium hydrochloride (138 g).

Example 13:

putting n-hexylamine (300g) and 500g dimethyl carbonate into a pressure vessel, heating to 120 ℃, then adding bis (fluorosulfonyl) imide (538g) according to a certain flow rate, heating to 160 ℃, and continuing to react for 3 hours. In the reaction process, if the reaction pressure exceeds 1.6Mpa, the pressure in the kettle is kept not to rise through valve deflation. After the reaction was completed and cooled to room temperature, the low boilers were removed under reduced pressure and the product was washed to give trimethyl-n-hexylammonium bis (fluorosulfonyl) imide salt (753 g).

Example 14:

synthesis of ionic liquid: N-N-propylpyrrolidine (500g) was placed in a pressure vessel along with 1000mL of dimethyl carbonate. Bis (trifluoromethylsulfonyl) imide (1243g) was added slowly under nitrogen, during which time the temperature was kept at 60 ℃ or below. After the addition, the reaction is carried out for 20 hours at 150 ℃ and about 1.6MPa, and part of gas is released through a release valve during the reaction process so as to avoid overhigh pressure. And after the reaction is finished, removing low-boiling-point substances under reduced pressure, washing the product, and drying in vacuum to obtain the N-methyl-N-propyl pyrrolidinium bis (trifluoromethylsulfonyl) imide salt.

Preparing an ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pr)_{1, 3}TFSI) and Propylene Carbonate (PC) are mixed into a homogeneous solution according to the mass ratio of 85:15, and LiPF is added₆And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) in a molar ratio of 1:7, and dissolving to form a 0.8mol/L (M/L) electrolyte solution. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the positive electrode material isNi-Co-Mn ternary (523), the cathode material is lithium titanate Li₄Ti₅O₁₂(LTO)), a conductive agent (conductive carbon black) and a binder (PVDF) are uniformly mixed according to a certain mass ratio, a solvent N-methyl pyrrolidone is added, the mixture is further uniformly mixed to prepare slurry with the solid content of 60%, then the slurry is coated on an Al foil current collector, and the slurry is dried, rolled and die-cut into pole pieces. The diaphragm is made of polyethylene glycol terephthalate (PET) diaphragm with average pore diameter>1 μm, porosity>65 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: under the environment temperature of 25 ℃, the flexible package battery is charged and discharged in the voltage range of 1.0V-2.8V, the constant current charging rate is 0.2C, the constant current discharging rate is 0.2C, and the capacity exertion capacity of the flexible package battery is examined, which is shown in figure 1a and figure 1 b. The flexible package battery is charged and discharged in a voltage range of 2.0V-2.8V at the ambient temperature of 45 ℃, the charge and discharge multiplying power is 0.2C, and the cycle stability is examined, which is shown in figure 2.

Example 15:

the ionic liquid was synthesized as in example 14.

Preparing an ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pr)_{1, 3}TFSI) Propylene Carbonate (PC), fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC) are mixed into a homogeneous solution according to the mass ratio of 85:10:3:2, and then LiPF is added₆And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) in a molar ratio of 4:4, and forming a 0.8M/L electrolyte solution after dissolution. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking an active electrode material (the positive electrode material is Nickel Cobalt Aluminum (NCA), Ni: Co: Al is 80:15:5, the negative electrode material is a silicon carbon composite material), a conductive agent (conductive carbon black) and a binder (PVDF) to be uniformly mixed according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece, wherein the PET diaphragm is selected as the diaphragm, the average pore diameter is larger than 1 mu m, the porosity is larger than 65%, and the soft package battery is assembled in a drying room with strictly controlled humidity, and the design capacity is 5 Ah.

And (3) testing the battery performance: the flexible package battery is charged and discharged in a voltage range of 2.5V-4.1V at the ambient temperature of 25 ℃, the constant current charging rate is 0.1C, the constant current discharging rate is 0.1C, and the discharging performance of the flexible package battery is examined, and the figure 3 is shown.

Example 16:

synthesis of an ionic liquid and preparation of an ionic liquid electrolyte the same as in example 14, except that sultone (1,3-PS) was used in place of Vinylene Carbonate (VC) in the preparation of an ionic liquid electrolyte.

Assembly of nonaqueous electrolyte secondary battery: respectively taking an active electrode material (the positive electrode material is nickel-cobalt-manganese ternary (523), the negative electrode material is a silicon-copper composite material), a conductive agent (conductive carbon black) and a binder (PVDF) to be uniformly mixed according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form the pole piece. The diaphragm is made of PET diaphragm, the average pore diameter is larger than 1 μm, and the porosity is larger than 65%. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 4 Ah.

And (3) testing the battery performance: the flexible package battery is charged and discharged in a voltage range of 2.5V-4.1V at the ambient temperature of 25 ℃, the constant current charging rate is 0.1C, the constant current discharging rate is 0.1C, and the discharging performance of the flexible package battery is examined, and the figure 4 is shown.

Example 17:

synthesis of ionic liquid: putting N-N-propyl pyrrolidine (500g), dimethyl carbonate (500g) and methanol (500 mL) into a pressure container, heating to 120 ℃, adding bis (trifluoromethyl sulfonyl) imide (1243g) according to a certain flow, and keeping the temperature in the reaction container to be 120-130 ℃ in the process. The continuous feeding time is 12 hours, after the bis (trifluoromethylsulfonyl) imide material is conveyed according to the set amount, the temperature is increased to 150 ℃ to continue the reaction for 2 hours. In the reaction process, if the reaction pressure exceeds 2.6Mpa, the pressure in the kettle is kept not to rise through valve deflation. After the reaction was completed and the temperature was reduced to room temperature, the low boilers were removed under reduced pressure and the product was washed to give N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt.

Preparing an ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pr)_{1, 3}TFSI) and Ethylene Carbonate (EC) are mixed into a homogeneous solution according to the mass ratio of 90:10, and then LiPF is added₆And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) with the molar ratio of 1:7, and forming 0.8M/L electrolyte solution after dissolving. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the anode material is nickel-cobalt-manganese ternary (523), and the cathode material is lithium titanate Li₄Ti₅O₁₂) Uniformly mixing a conductive agent (conductive carbon black) and a binder (PVDF) according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece. The diaphragm is PET diaphragm with average pore diameter>1 μm, porosity>65 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: at an ambient temperature of 25 ℃, the flexible package battery is charged and discharged in a voltage range of 1.0V to 2.8V, the constant current charging rate is 0.2C, and the constant current discharging rate is 0.2C, and the charging and discharging capacity of the flexible package battery is examined, see fig. 5a and 5 b.

Example 18:

synthesis of ionic liquid: N-N-butylpyrrolidine (500g) was placed in a pressure vessel under nitrogen, the temperature was maintained at 60 ℃ and a mixture of trifluoromethanesulfonic acid (663g) and 1000mL of dimethyl carbonate was slowly added. After the addition is finished, the reaction is carried out for 15 hours at 140 ℃ and about 1.5MPa, and part of gas is released through a release valve during the reaction process so as to avoid overhigh pressure. After the reaction is finished, the low-boiling point substances are removed under reduced pressure to obtain the N-methyl-N-N-butyl pyrrolidinium trifluoromethanesulfonate.

Preparing an ionic liquid electrolyte: N-methyl-N-butylpyrrolidinium trifluoromethanesulfonate (Pr)_1,4OTf) and Propylene Carbonate (PC) are mixed into a homogeneous solution according to the mass ratio of 70:30, and then LiBF is added₄And lithium trifluoromethanesulfonate (LiOTf), the molar ratio of which is 9:1, and the two lithium salts are dissolved to form a 1.0M/L electrolyte solution. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the anode material is nickel-cobalt-manganese ternary (523), and the cathode material is lithium titanate Li₄Ti₅O₁₂) Uniformly mixing a conductive agent (conductive carbon black) and a binder (PVDF) according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece. The diaphragm is PET diaphragm with average pore diameter>1 μm, porosity>65 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: at an ambient temperature of 25 ℃, the flexible package battery is charged and discharged in a voltage range of 1.0V to 2.8V, the constant current charging rate is 0.2C, and the constant current discharging rate is 0.2C, and the charging and discharging capacity of the flexible package battery is examined, see fig. 6a and fig. 6 b.

Example 19

Synthesis of ionic liquid: putting N-N-butyl piperidine and dimethyl carbonate into a pressure container according to the molar ratio of 1:3, heating to 120 ℃, adding bis (fluorosulfonyl) imide (the molar ratio of the N-N-butyl piperidine to the bis (fluorosulfonyl) imide is 1:1) according to a certain flow, heating to 160 ℃, and continuing to react for 3 hours. In the reaction process, if the reaction pressure exceeds 1.6Mpa, the pressure in the kettle is kept not to rise through valve deflation. After the reaction is finished and the temperature is reduced to room temperature, the low-boiling point substances are removed under reduced pressure, the product is washed, and the N-methyl-N-N-butyl piperidinium bis (fluorosulfonyl) imide salt (Py) is obtained after vacuum drying_1,4FSI)。

Preparing an ionic liquid electrolyte:N-methyl-N-N-butylpiperidinium bis (fluorosulfonyl) imide salt (Py)_1,4FSI) and then LiPF is added₆And lithium bis (fluorosulfonyl) imide (LiFSI) in a molar ratio of 1:9, and dissolving the two lithium salts to form a 1.0M/L electrolyte. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the anode material is nickel-cobalt-manganese ternary (523), and the cathode material is lithium titanate Li₄Ti₅O₁₂) Uniformly mixing a conductive agent (conductive carbon black) and a binder (PVDF) according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece. The diaphragm is PET diaphragm with average pore diameter>1 μm, porosity>65 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: at an ambient temperature of 25 ℃, the flexible package battery is charged and discharged in a voltage range of 1.0V to 2.8V, the constant current charging rate is 0.5C, and the constant current discharging rate is 0.5C, and the charging and discharging capacity of the flexible package battery is examined, see fig. 7a and 7 b.

Example 20

The ionic liquid was synthesized as in example 19.

Preparing an ionic liquid electrolyte: N-methyl-N-N-butylpiperidinium bis (fluorosulfonyl) imide salt (Py)_1,4FSI) and Propylene Carbonate (PC) in a mass ratio of 95:5, and then adding LiPF₆And lithium bis (fluorosulfonyl) imide (LiFSI) in a molar ratio of 1:9, and dissolving the two lithium salts to form a 1.0M/L electrolyte. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the anode material is nickel-cobalt-manganese ternary (523), and the cathode material is lithium titanate Li₄Ti₅O₁₂) A conductive agent (conductive carbon black),Uniformly mixing a binder (PVDF) according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece. The membrane is polyvinylidene fluoride (PVDF) membrane with average pore diameter>1 μ 1, porosity>60 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: at an ambient temperature of 45 ℃, the flexible package battery is charged and discharged in a voltage range of 1.0V to 2.8V, the constant current charging rate is 1C, the constant current discharging rate is 1C, and the charging and discharging capacity of the flexible package battery is examined, and refer to fig. 8a and 8 b.

Comparative example 1

The ionic liquid was synthesized as in example 14.

Preparing an ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pr)_{1, 3}TFSI), Propylene Carbonate (PC) and Vinylene Carbonate (VC) are mixed into a homogeneous solution according to the mass ratio of 85:10:5, and LiPF is added₆And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) with the molar ratio of 1:7, and forming 0.8M/L electrolyte solution after dissolving. The detection and analysis by ion chromatography and ICP means shows that the electrolyte contains halide ions (Cl)^-，Br^-，I^-) Is less than 5 ppm.

Assembly of nonaqueous electrolyte secondary battery: respectively taking an active electrode material (the positive electrode material is nickel-cobalt-manganese ternary (523), the negative electrode material is graphite), a conductive agent (conductive carbon black) and a binder (PVDF) to be uniformly mixed according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to obtain the pole piece. The diaphragm is made of PET diaphragm, the average pore diameter is larger than 1 μm, and the porosity is larger than 65%. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 10 Ah.

And (3) testing the battery performance: the flexible package battery is charged and discharged in a voltage range of 3.0V-4.2V at an ambient temperature of 45 ℃, the constant current charging rate is 0.2C, the constant current discharging rate is 0.2C, and the charging and discharging performance of the flexible package battery is examined, and the flexible package battery is shown in figure 9a and figure 9 b.

Comparative example 2

The ionic liquid synthesis and ionic liquid electrolyte formulation were the same as in example 20.

Assembly of nonaqueous electrolyte secondary battery: respectively taking active electrode materials (the anode material is nickel-cobalt-manganese ternary (523), and the cathode material is lithium titanate Li₄Ti₅O₁₂) Uniformly mixing a conductive agent (conductive carbon black) and a binder (PVDF) according to a certain mass ratio, adding a solvent N-methyl pyrrolidone, further uniformly mixing to prepare slurry with the solid content of 60%, then coating the slurry on an Al foil current collector, drying, rolling and punching to form a pole piece. The diaphragm is a PP/PE/PP diaphragm with average pore diameter<1 μm, porosity<50 percent. The flexible package battery is assembled in a drying room with strictly controlled humidity, and the designed capacity is 5 Ah.

And (3) testing the battery performance: the flexible package battery is charged and discharged in a voltage range of 1.0V-2.8V at an ambient temperature of 25 ℃, the constant current charging rate is 0.2C, the constant current discharging rate is 0.2C, and the charging and discharging performance of the flexible package battery is examined, which is shown in figure 10a and figure 10 b.

Comparative example 3

Synthesis of ionic liquid: n-methylpyrrolidine (500g) was substituted with 1000mL of bromopropane, and then bis (trifluoromethylsulfonyl) imide potassium salt (1243g) was added thereto for anion exchange reaction while keeping the temperature at 60 ℃ or less. After the reaction is finished, the low-boiling point substances are removed by decompression, the product is washed, and the N-methyl-N-propyl pyrrolidinium bis (trifluoromethyl sulfonyl) imide salt (Pr) is obtained after vacuum drying_1,3TFSI)。

Preparing an ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pr)_{1, 3}TFSI) and Propylene Carbonate (PC) are mixed into a homogeneous solution according to the mass ratio of 85:15, and LiPF is added₆And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) with the molar ratio of 1:7, and forming 0.8M/L electrolyte solution after dissolving. The results of detection and analysis by means of ion chromatography and ICP show that the content of alkali metal as impurity in the electrolyte is more than that of the impurity300ppm, the content of halide ions is more than 300 ppm.

And (3) testing the battery performance: at an ambient temperature of 25 ℃, the flexible package battery is charged and discharged in a voltage range of 1.0V to 2.8V, the constant current charging rate is 0.2C, the constant current discharging rate is 0.2C, and the capacity exertion capacity of the flexible package battery is examined, see fig. 11.

Table 2 compositions of nonaqueous electrolyte secondary batteries in examples 14 to 20 of the present invention and comparative examples 1 to 3

In table 1, E represents an ionic liquid in the electrolyte base component, F represents an organic solvent in the electrolyte base component, and G and H represent functional additives or film-forming agents in the electrolyte base component. From table 1, it can be seen that the present invention has designed three groups of comparative examples, comparative example 1, comparative example 2 and comparative example 3; among them, comparative example 1 mainly verifies the influence of using a graphite negative electrode; comparative example 2 demonstrates mainly the effect of using a non-polar membrane and comparative example 3 demonstrates mainly the effect of an ionic liquid prepared by anion exchange technology (halide >300 ppm).

When the negative electrode contains the active material having a potential of lithium deintercalation potential of not less than 0.25V (for Li/Li) as compared with example 14, example 15, example 16, example 17, example 18, example 19, example 20, and comparative example 1, it can be seen that⁺) When the ionic liquid and the prepared electrolyte solution are used as the materials, the normal charge and discharge of the battery can be realized, and the rated capacity can be exerted at the ambient temperature of 25 ℃. When the active material of the negative electrode is graphite (potential for deintercalating lithium is less than 0.25V (for Li/Li)⁺) In time), the battery is charged or discharged abnormally, the rated capacity cannot be discharged, the battery bulges, and the negative pole piece is found after the battery is disassembledThe active material coating layer is peeled off and peeled off from the current collector. It is thus demonstrated that when the positive electrode active material in the secondary battery is a lithium nickel cobalt manganese composite oxide or a lithium nickel cobalt composite oxide, the negative electrode active material is preferably selected from one of lithium titanate, elemental silicon, a carbon silicon composite material, a silicon copper composite material, a silicon tin composite material, and the like, and an ionic liquid electrolyte may be used. If the graphite material is used, the intercalation potential of the ionic liquid cations is higher than that of the lithium ions, namely, the ionic liquid cations are inserted into the graphite layer before the lithium ions during charging, so that the channels for inserting the lithium ions are blocked, and even the graphite layer is expanded, so that the graphite layer is stripped. This phenomenon cannot be suppressed even by adding a film-forming agent such as VC.

Claims (39)

1. The preparation method of the ionic liquid is characterized by comprising the following steps: synthesizing ionic liquid by one-step reaction of a nitrogen-containing compound or a phosphorus-containing compound, a proton compound and carbonic ester; the temperature of the one-step reaction is controlled to be 100-200 ℃; controlling the absolute pressure of the one-step reaction to be 0.1-0.8 Mpa; the nitrogen-containing compound is selected from ammonia (NH)₃) RNH, primary amines₂(ii) a secondary amine R₁R₂NH and tertiary amines R₁R₂R₃At least one of N; the phosphorus-containing compound is selected from Phosphine (PH)₃) Primary phosphine RPH₂Secondary phosphine R₁R₂PH and tertiary phosphine R₁R₂R₃At least one of P; wherein R is₁、R₂、R₃Each independently is selected from alkyl, alkenyl, alkynyl or aryl; or R₁、R₂、R₃Each independently at least one organic group selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine and iodine; the R is₁、R₂、R₃Is an independent substituent group; or said R₁、R₂、R₃Adjacent groups are combined to form a ring; the proton compound is at least one of inorganic oxygen acid, inorganic oxygen-free acid and organic acid; the inorganic oxoacid is selected from perchloric acid (HClO)₄) Iodic acid (HIO)₃) Periodic acid (H)₅IO₆) Phosphorous acid (H)₃PO₃) Pyrophosphoric acid (H)₄P₂O₇) And sulfuric acid (H)₂SO₄) At least one of (1); the inorganic oxygen-free acid is selected from carborane acid H (CHB)₁₁Cl₁₁) At least one of thiocyanic acid (HSCN), hydrochloric acid (HCl), hydrobromic acid (HBr) and hydroiodic acid (HI); the organic acid is at least one selected from oxalic acid, trifluoroacetic acid and salicylic acid.

2. A process for the preparation of an ionic liquid according to claim 1, wherein: the R is₁、R₂、R₃Each independently selected from phenyl.

3. A process for the preparation of an ionic liquid according to claim 1, wherein: the nitrogen-containing compound is selected from at least one of the following structures:

(ii) a Wherein R is₁、R₂、R₃、R₄、R₅、R₆Each independently is selected from hydrogen, alkyl, alkenyl, alkynyl or aryl; or R₁、R₂、R₃、R₄、R₅、R₆Each independently at least one organic group selected from boron, silicon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine and iodine; the R is₁、R₂、R₃、R₄、R₅、R₆Is an independent substituent group; or said R₁、R₂、R₃、R₄、R₅、R₆Adjacent groups are combined to form a ring.

4. A process for the preparation of an ionic liquid according to claim 3, wherein: the R is₁、R₂、R₃、R₄、R₅、R₆Each independently selected from phenyl.

5. A process for the preparation of an ionic liquid according to claim 1, wherein: the phosphorus-containing compound is at least one selected from the group consisting of methylphosphine, dimethylphosphine, trimetaphosphine, ethylphosphine, diethylphosphine, triethylphosphine, tripropylphosphine, di-tert-butylphosphine, tri-tert-butylphosphine, tributylphosphine, tri-n-pentylphosphine, cyclohexylphosphine, dicyclohexylphosphine, tricyclohexylphosphine, trihexylphosphine, trioctylphosphine, phenylphosphine, diphenylphosphine, triphenylphosphine, dimethylphenylphosphine, diethylphenylphosphine, diphenylbutylphosphine, tribenzylphosphine, trimethylolphosphine, 2-chloroethyldiphosphine, and tris (pentafluoroethyl) phosphine.

6. A process for the preparation of an ionic liquid according to claim 1, wherein: the carbonate is at least one selected from dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, phenyl methyl carbonate, diphenyl carbonate and dibenzyl carbonate.

7. The method for preparing an ionic liquid according to claim 6, wherein: the carbonate is at least one selected from dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

8. A process for the preparation of an ionic liquid according to claim 1, wherein: the temperature of the one-step reaction is controlled to be 120-180 ℃.

9. A process for the preparation of an ionic liquid according to claim 8, wherein: the temperature of the one-step reaction is controlled to be 140-160 ℃.

10. A process for the preparation of an ionic liquid according to claim 1, wherein: the reaction time of the one-step reaction is controlled to be 0.1-20 hours.

11. A process for the preparation of an ionic liquid according to claim 10, wherein: the reaction time of the one-step reaction is controlled to be 4-15 hours.

12. A process for the preparation of an ionic liquid according to claim 11, wherein: the reaction time of the one-step reaction is controlled to be 9-12 hours.

13. An electrolyte for a secondary battery comprising the ionic liquid produced by the method for producing an ionic liquid according to any one of claims 1 to 12.

14. The secondary battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, and is characterized in that: the electrolyte comprises an ionic liquid prepared by the method for preparing an ionic liquid according to any one of claims 1 to 12.

15. The secondary battery according to claim 14, wherein: the electrolyte includes a lithium salt and a base component; the base component comprises an ionic liquid; the cation of the ionic liquid is selected from at least one of the following structures:

wherein R is an alkyl group.

16. The secondary battery according to claim 15, wherein: the cation is at least one of 1-methyl-1-propyl pyrrolidinium ion, 1-methyl-1-butyl pyrrolidinium ion, 1-methyl-1-propyl piperidinium ion and 1-methyl-1-butyl piperidinium ion.

17. The secondary battery according to claim 14, wherein: the negative electrode active material in the negative electrode has a lithium deintercalation potential with respect to Li/Li⁺Not less than 0.25V.

18. The secondary battery according to claim 17, wherein: the negative active material is a silicon-carbon material or a silicon alloy material; the carbon contained in the silicon carbon material is not graphite.

19. The secondary battery according to claim 18, wherein: the silicon alloy material is at least one of a silicon copper-based material and a silicon tin-based material.

20. The secondary battery according to claim 17, wherein: the negative active material is a titanium-based oxide.

21. The secondary battery according to claim 20, wherein: the titanium-based oxide is a lithium titanium oxide.

22. The secondary battery according to claim 14, wherein: the content of halogen ions in the electrolyte is less than or equal to 5 ppm.

23. The secondary battery according to claim 15, wherein: the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis (catechol) borate, lithium dimalonate borate, lithium bis (oxalato) borate, lithium tris (catechol) phosphate, lithium tris (perfluoroethyl) trifluorophosphate, lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide and lithium difluorosulfonimide.

24. The secondary battery according to claim 23, wherein: the lithium salt is selected from at least one of a first lithium salt and at least one of a second lithium salt; the first lithium salt comprises lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide and lithium difluorosulfonimide; the second lithium salt includes lithium hexafluorophosphate and lithium tetrafluoroborate.

25. The secondary battery according to claim 24, wherein: the mass of the first lithium salt accounts for 0.5-30% of the total mass of the electrolyte; the mass of the second lithium salt accounts for 0.5-30% of the total mass of the electrolyte.

26. The secondary battery according to claim 24, wherein: the molar ratio of the first lithium salt to the second lithium salt is 1: 19-19: 1.

27. The secondary battery according to claim 26, wherein: the molar ratio of the first lithium salt to the second lithium salt is 1: 9-9: 1.

28. The secondary battery according to claim 27, wherein: the molar ratio of the first lithium salt to the second lithium salt is 3:7 to 7: 3.

29. The secondary battery according to claim 15, wherein: the base component further comprises an organic solvent; the organic solvent is at least one of carbonates, carboxylic acid esters, sulfurous acid esters, sulfonic acid esters, sulfones, ethers, organic silicon, nitriles and fluoro phosphazenes.

30. The secondary battery of claim 29, wherein: the organic solvent is at least one of methyl propylene carbonate, ethyl propylene carbonate, methyl phenol carbonate, ethylene carbonate, halogenated ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, vinylene carbonate, ethylene sulfite, propylene sulfite, butylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, ethyl methyl sulfoxide, 1, 3-propanesulfonate, 1, 4-butanesultone, dioxolane, dimethoxypropane, ethoxypentafluorophosphazene, phenoxypentafluorophosphazene, adiponitrile and succinonitrile.

31. The secondary battery according to claim 15, wherein: the base component further comprises a film-forming agent; the film-forming agent is sulfur dioxide, sulfite, sulfoxide, sulfonate, halogenated organic ester, unsaturated organic compound containing vinylidene, organic boride and Li₂CO₃At least one of them.

32. The secondary battery according to claim 31, wherein: the unsaturated organic compound containing vinylidene is Vinylene Carbonate (VC); the organic boride is LiBOB.

33. The secondary battery according to claim 31, wherein: the sulfite is ethylene sulfite.

34. The secondary battery according to claim 15, wherein: the base component further comprises a functional additive; the functional additive is at least one of an overcharge-preventing additive, a flame-retardant additive, a conductive additive and a high-pressure-resistant additive.

35. The secondary battery of claim 34, wherein: the functional additive is at least one of biphenyl (DP), cyclohexylbenzene, aryl adamantane, naphthalene derivatives, polyphenyl, trimethyl phosphate (TMP), triphenyl phosphate (TPP), tris (2, 2,2 trifluoroethyl) phosphite, p-diazene, p-diazabenzene, tris (pentafluorinated phenyl) boron, ethoxy pentafluorophosphazene, phenoxy pentafluorophosphazene, adiponitrile and succinonitrile.

36. The secondary battery of claim 34, wherein: the base component comprises 70-100 wt% of ionic liquid, 0-30 wt% of organic solvent, 0-10 wt% of film forming agent and 0-10 wt% of functional additive.

37. The secondary battery according to claim 14, wherein: the positive active material in the positive electrode is selected from at least one of lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium manganese nickel composite oxide, lithium phosphorus oxide, lithium cobalt oxide and lithium manganese composite oxide.

38. The secondary battery according to claim 14, wherein: the diaphragm is at least one of a polyethylene glycol terephthalate diaphragm, a polyacrylonitrile diaphragm and a polyvinylidene fluoride diaphragm.

39. The secondary battery according to claim 14, wherein: the average pore diameter of the diaphragm is 1-25 mu m; the porosity of the diaphragm is 50-85%.

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