WO2018107745A1 - Electrolyte and lithium secondary battery - Google Patents

Abstract

Provided are an electrolyte and a lithium secondary battery. The electrolyte comprises an organic solvent, a lithium salt dissolved in the organic solvent, and an additive. The lithium salt comprises a lithium salt of a nitrogen-containing aromatic heterocycle derivative. The additive comprises a fluorocyclic carbonate and a fluorophosphate salt and/or a cyclic phosphazene compound. The electrolyte of the present invention has a higher storage stability, can significantly improve cycling performance of a lithium secondary battery at normal and high temperatures, and can improve storage performance of the lithium secondary battery at a high temperature. Moreover, the lithium secondary battery has a lower internal resistance.

Description

Electrolyte and lithium secondary battery Technical field

The present invention relates to the field of battery technology, and in particular to an electrolyte and a lithium secondary battery.

Background technique

With the increasing depletion of fossil energy and the increasing pressure of environmental pollution, the automotive industry urgently needs a new type of energy to provide its driving. Lithium-ion secondary batteries stand out because of their high energy density, no memory effect and high working voltage. It makes it the preferred solution for new energy vehicles.

As the automotive industry continues to increase the requirements for cruising range, the energy density requirements for power lithium ion secondary batteries are increasing, with high voltage cathode materials, high nickel cathode materials, high capacity graphite anode materials and silicon carbon anode materials. The introduction of lithium ion secondary batteries requires the following properties: high power performance, long cycle life, and long storage life. Among them, the interaction between the electrolyte and the positive and negative electrodes has a great influence on these properties, especially when using a silicon carbon material, in order to improve the cycle performance, a large amount of fluoroethylene carbonate (FEC) is usually used in the electrolyte. The use of FEC deteriorates the volume expansion ratio of the lithium ion secondary battery after high temperature storage, and cannot meet the requirements of the electric vehicle for the performance reliability of the lithium ion secondary battery. Therefore, it is necessary to provide an electrolyte lithium ion secondary battery having a good overall performance.

Summary of the invention

In view of the problems in the background art, an object of the present invention is to provide an electrolyte and a lithium secondary battery which have high storage stability and can significantly improve the normal temperature and high temperature cycle performance of the lithium secondary battery. And high temperature storage performance, and the lithium secondary battery has a low internal resistance.

In order to achieve the above object, in one aspect of the invention, the invention provides an electrolyte comprising: an organic solvent; a lithium salt, dissolved in an organic solvent; and an additive. The lithium salt includes a nitrogen salt of a nitrogen-containing aromatic heterocyclic derivative. The additive includes: a fluorocyclic carbonate; and a fluorophosphate and/or a cyclophosphazene compound.

In another aspect of the present invention, the present invention provides a lithium secondary battery comprising the present invention The electrolyte described in the aspect.

Compared with the prior art, the beneficial effects of the present invention are:

The electrolyte of the present invention has high storage stability, and can significantly improve the normal temperature and high temperature cycle performance and high temperature storage performance of the lithium secondary battery, and the lithium secondary battery has a low internal resistance.

detailed description

The electrolytic solution and the lithium secondary battery according to the present invention will be described in detail below.

First, the electrolytic solution according to the first aspect of the invention will be explained.

The electrolytic solution according to the first aspect of the invention includes: an organic solvent; a lithium salt, dissolved in an organic solvent; and an additive. The lithium salt includes a nitrogen salt of a nitrogen-containing aromatic heterocyclic derivative. The additive includes: a fluorocyclic carbonate; and a fluorophosphate and/or a cyclophosphazene compound.

In the electrolytic solution according to the first aspect of the present invention, the application of the fluorinated cyclic carbonate to the electrolytic solution can effectively improve the cycle performance of the lithium secondary battery, but deteriorates the high-temperature storage gas generation of the lithium secondary battery. The lithium salt of the nitrogen-containing aromatic heterocyclic derivative has high thermal stability, and the oxidation potential thereof is low to form a passivation film on the surface of the positive electrode, thereby inhibiting the decomposition of the electrolyte on the surface of the positive electrode, thereby effectively improving the storage stability of the electrolyte. The high-temperature storage gas generation of the lithium secondary battery is suppressed, but the introduction of the lithium salt of the nitrogen-containing aromatic heterocyclic derivative causes a large increase in internal resistance at a low temperature of the lithium secondary battery. The fluorophosphate can improve the stability of the positive active material and reduce the oxidation activity of the electrolyte, thereby effectively improving the cycle performance of the lithium secondary battery and suppressing the high temperature storage gas production; meanwhile, the fluorophosphate can also reduce the positive electrode electricity. The impedance of the chemical reaction improves the dynamic performance of the positive electrode and reduces the internal resistance of the lithium secondary battery at low temperatures. The decomposition of the cyclophosphazene compound to produce a polyphosphate component can be embedded in the SEI film formed on the surface of the negative electrode, thereby effectively reducing the impedance of the surface of the negative electrode; in addition, the cyclophosphazene compound can also absorb hydrofluoric acid in the electrolyte to reduce hydrofluoric acid. The corrosion of the positive and negative passivation films suppresses the high temperature storage gas production of the lithium secondary battery. When the electrolyte contains both of the above substances, the deterioration of the high-temperature storage gas generating property by the fluorinated cyclic carbonate can be achieved by introducing a lithium salt of a nitrogen-containing aromatic heterocyclic derivative having high heat stability, and a fluorophosphate and/or Or cyclophosphazene compounds to improve, each substance interacts in the film formation process and induces the formation of a stable interface film, thereby significantly improving the cycle performance of the lithium ion secondary battery and inhibiting high temperature storage gas production, while fluorophosphate and / Or a cyclophosphazene compound can also reduce the high internal resistance caused by the lithium salt of the nitrogen-containing aromatic heterocyclic derivative.

In the electrolytic solution according to the first aspect of the invention, the nitrogen-containing aromatic heterocyclic derivative lithium salt may be selected from one of the compounds represented by the following formula 1, formula 2, formula 3, and formula 4 or Several. Wherein R ₁ to R ₁₄ are each independently selected from the group consisting of H, F, a cyano group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an aromatic group having 6 to 12 carbon atoms. One of the groups, the alkyl group, the alkenyl group, and the aryl group may be substituted by one or both of F and a cyano group.

In the electrolytic solution according to the first aspect of the present invention, preferably, R ₂ , R ₃ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R _{14 is} each independently selected from H, a cyano group, an alkyl group having 1 to 10 carbon atoms substituted by a cyano group, an alkenyl group having 2 to 10 carbon atoms substituted by a cyano group, and a carbon substituted by a cyano group. One of aryl groups having 6 to 12 atoms; R ₁ and R ₄ are each independently selected from the group consisting of F, a cyano group, an alkyl group having 1 to 10 carbon atoms substituted by F, and a carbon atom substituted by F. The number of the alkenyl group having 2 to 10 and the aryl group having 6 to 12 carbon atoms substituted by F.

In the electrolytic solution according to the first aspect of the present invention, specifically, the lithium salt of the nitrogen-containing aromatic heterocyclic derivative may be selected from one or more of the following compounds;

In the electrolytic solution according to the first aspect of the invention, the fluorinated cyclic carbonate may be selected from one or more of the compounds represented by the following formula 5. Wherein R ₂₁ , R ₂₂ , R ₂₃ and R ₂₄ are each independently selected from the group consisting of H, F, a fluoroalkyl group having 1 to 20 carbon atoms, a fluoroalkenyl group having 2 to 20 carbon atoms, and a carbon atom. One of 6 to 20 fluoroaryl groups.

In the electrolytic solution according to the first aspect of the present invention, preferably, in Formula 5, R ₂₁ , R ₂₂ , R ₂₃ , and R ₂₄ are each independently selected from H, F, and having 1 to 10 carbon atoms. One of a fluoroalkyl group, a fluoroalkenyl group having 2 to 10 carbon atoms, and a fluoroaryl group having 6 to 10 carbon atoms.

In the electrolytic solution according to the first aspect of the present invention, specifically, the fluorinated cyclic carbonate may be selected from one or more of the following compounds;

In the electrolytic solution according to the first aspect of the invention, the fluorophosphate is one or more selected from the group consisting of LiPO ₂ F ₂ (labeled as C1) and LiPOF ₄ (labeled as C2).

In the electrolytic solution according to the first aspect of the invention, the cyclophosphazene compound may be selected from one or more of the compounds represented by the following formula 6. Wherein R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ and R ₃₆ are each independently selected from the group consisting of H, F, Cl, Br, an alkyl group having 1 to 20 carbon atoms, and 2 to 20 carbon atoms. An alkenyl group, an aryl group having 6 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, a halogenated alkenyl group having 2 to 20 carbon atoms, or a halogenated aromatic group having 6 to 20 carbon atoms. a group, an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a halogenated alkoxy group having 1 to 20 carbon atoms, One of a halogenated alkenyloxy group having 2 to 20 carbon atoms and a halogenated aryloxy group having 6 to 20 carbon atoms; and at least one of R ₃₁ , R ₃₃ and R ₃₅ is selected from a carbon atom. The alkoxy group having 1 to 20, the alkenyloxy group having 2 to 20 carbon atoms, the aryloxy group having 6 to 20 carbon atoms, the haloalkoxy group having 1 to 20 carbon atoms, and the number of carbon atoms are One of 2 to 20 haloalkenyloxy groups and 6 to 20 halogenated aryloxy groups, at least two of R ₃₂ , R ₃₄ and R ₃₆ are each independently selected from F and Cl. One of Br.

In the electrolytic solution according to the first aspect of the present invention, preferably, in Formula 6, R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ , and R ₃₆ are each independently selected from H, F, Cl, Br, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, and a carbon number of a halogenated alkenyl group of 2 to 10, a halogenated aryl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, or a carbon atom; One of 6 to 10 aryloxy groups, a halogenated alkoxy group having 1 to 10 carbon atoms, a halogenated alkenyloxy group having 2 to 10 carbon atoms, and a halogenated aryloxy group having 6 to 10 carbon atoms. And at least one of R ₃₂ , R ₃₄ and R ₃₆ is selected from the group consisting of an alkoxy group having 1 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, and a carbon number of 6 to 10; One of an aryloxy group, a halogenated alkoxy group having 1 to 10 carbon atoms, a halogenated alkenyloxy group having 2 to 10 carbon atoms, or a halogenated aryloxy group having 6 to 10 carbon atoms, _31, R _33, R ₃₅ in at least two are each independently selected from F, Cl, Br of Species.

In the electrolytic solution according to the first aspect of the present invention, the cyclophosphazene compound may be selected from one or more of the following compounds;

In the electrolytic solution according to the first aspect of the invention, the concentration of the nitrogen-containing heteroaromatic derivative lithium salt may be from 0.01 M to 0.8 M.

In the electrolytic solution according to the first aspect of the invention, the lithium salt may include only the lithium salt of the nitrogen-containing aromatic heterocyclic derivative. Or in addition to the lithium salt of the nitrogen-containing aromatic heterocyclic derivative, the lithium salt may further include LiPF ₆ , LiBF ₄ , LiN(SO ₂ F) ₂ (abbreviated as LiFSI), LiClO ₄ , LiAsF ₆ , LiB (C ₂ O _{One or more of 4} ) ₂ (abbreviated as LiBOB), LiBF ₂ (C ₂ O ₄ ) (abbreviated as LiDFOB), LiN (SO ₂ RF) ₂ , and LiN (SO ₂ F) (SO ₂ RF). Preferably, the lithium salt may further include one of LiPF ₆ , LiN(SO ₂ F) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ) Kind or several. Further preferably, the lithium salt may further include one or more of LiPF ₆ , LiN(SO ₂ F) ₂ , LiBF ₂ (C ₂ O ₄ ). Wherein RF is represented by C _n F _2n+1 , and n is an integer within 1 to 10. Preferably, RF may be -CF ₃ , -C ₂ F ₅ or -CF ₂ CF ₂ CF ₃ . Wherein, the total concentration of the mixed lithium salt may be from 0.6 M to 1.8 M.

In the electrolytic solution according to the first aspect of the invention, the content of the fluorinated cyclic carbonate may be 0.01% to 30% of the total weight of the electrolytic solution.

In the electrolytic solution according to the first aspect of the invention, when the additive comprises a fluorinated cyclic carbonate or a mixture comprising a fluorophosphate and a cyclophosphazene compound, the content of the fluorophosphate may be The total weight of the electrolyte is from 0.01% to 2.5%.

In the electrolytic solution according to the first aspect of the invention, when the additive comprises a cyclophosphazene compound or a mixture comprising a cyclophosphazene compound and a fluorophosphate, the content of the cyclophosphazene compound may be 0.01% to 10% of the total weight of the electrolyte.

In the electrolytic solution according to the first aspect of the invention, the additive may further include one or more of a cyclic ester containing a sulfur-oxygen double bond, a cyclic carbonate containing a carbon-carbon unsaturated bond. Specifically, the additive may further include one or more of 1,3-propane sultone (PS), vinyl sulfate (DTD), and vinylene carbonate (VC). The content of 1,3-propane sultone, vinyl sulfate, and vinylene carbonate may be 0.01% to 5% of the total weight of the electrolyte, respectively.

In the electrolytic solution according to the first aspect of the present invention, the specific kind of the organic solvent may be selected according to actual needs, in particular, a non-aqueous organic solvent may be selected, wherein the non-aqueous organic solvent may be any kind, according to actual needs. Make a choice. For example, a compound having 1 to 8 carbon atoms and containing at least one ester group may be optionally used as the organic solvent. Further, the organic solvent may include any kind of carbonate or carboxylate such as a cyclic carbonate, a chain carbonate, a cyclic carboxylate or a chain carboxylate. The organic solvent may also include a halogenated compound of a carbonate. Specifically, the organic solvent may be selected from the group consisting of ethylene carbonate (EC), propylene carbonate, butylene carbonate, pentene carbonate, dimethyl carbonate, diethyl carbonate (EMC), dipropyl carbonate, and carbonic acid. Methyl ethyl ester, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate and ethyl butyrate One or several of them. Of course, it is not limited to the specific compounds mentioned above, but may be a halogenated product of the above specific compounds.

Next, a lithium secondary battery according to a second aspect of the invention, comprising the electrolytic solution according to the first aspect of the invention, is explained.

The lithium secondary battery according to the second aspect of the invention may be a lithium ion secondary battery or a lithium metal secondary battery.

The lithium secondary battery according to the second aspect of the present invention may further include: a positive electrode sheet containing a positive electrode active material, a negative electrode active material negative electrode sheet, a separator, and the like.

In the lithium secondary battery, specific types of the positive electrode active material and the negative electrode active material are Without specific restrictions, you can choose according to your needs. Specifically, the cathode active material may be selected from one or more of lithium cobalt oxide and lithium nickel cobalt manganese oxide ternary materials; the anode active material may be selected from the group consisting of graphite, silicon, silicon oxide, and silicon carbon materials. One or more of the following, wherein the silicon may be selected from one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous structural silicon, and hollow porous silicon, but is not limited to the above The cited silicon. The negative electrode sheet may also use a lithium metal or a lithium metal alloy.

In the lithium secondary battery, the specific kind of the separator is not particularly limited, and any conventional separator material such as polyethylene, polypropylene, polyvinylidene fluoride, and the above polyethylene, polypropylene, or the like may be selected. The multilayer composite film of polyvinylidene fluoride is not limited to the materials mentioned above.

It should be noted that the preparation method of the lithium secondary battery provided by the present invention is well known in the art, and the lithium secondary battery provided by the present invention can be produced by the conventional lithium secondary battery preparation method.

The present application is further illustrated below in conjunction with the embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the application. The present invention selects flexible packaging lithium ion secondary batteries for related testing.

The reagents, materials, and instruments used in the examples and comparative examples are commercially available unless otherwise specified.

The lithium ion secondary batteries of Examples 1 to 24 and Comparative Examples 1-6 were each prepared in the following manner.

(1) Preparation of positive electrode sheet

The positive active material lithium nickel cobalt manganese oxide (NCM333), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed at a weight ratio of 98:1:1, and added to the solvent N-methylpyrrolidone (NMP). The mixture was stirred until the system was uniformly transparent by a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on a current collector aluminum foil having a thickness of 12 μm; the aluminum foil was dried at room temperature, transferred to an oven at 120 ° C for 1 hour, and then dried. After cold pressing and slitting, a positive electrode sheet was obtained.

(2) Preparation of negative electrode sheet

The negative active material silicon carbon material, the conductive agent conductive carbon black, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber are mixed at a weight ratio of 97:1:1:1, and added to the solvent. In the ionic water, the negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is uniformly coated to a thickness of 8 μm of the current collector copper foil; the copper foil was air-dried at room temperature, transferred to an oven at 120 ° C for 1 h, and then subjected to cold pressing and slitting to obtain a negative electrode sheet.

(3) Preparation of electrolyte

In the drying room, the EC and EMC which have been subjected to rectification and dehydration purification are uniformly mixed to form an organic solvent, and the sufficiently dried lithium salt is dissolved in the above organic solvent, and then the additive is added to the organic solvent, and the mixture is uniformly mixed to obtain an electrolyte. . Among them, the total concentration of the lithium salt is 1 mol/L, and the weight ratio of EC and EMC is 3:7. In the electrolytic solution, the content of each additive is a weight percentage calculated based on the total weight of the electrolytic solution.

(4) Preparation of lithium ion secondary battery

The cut positive and negative electrodes, and the separator (16 μm thick polypropylene film, model A273, supplied by Celgard) were stacked in order, so that the separator was isolated between the positive and negative plates. Function, and then winding to obtain a bare cell; placing the bare cell in the outer packaging foil, injecting the prepared electrolyte into the dried cell, and vacuum-packing, standing, forming, shaping, etc. A lithium ion secondary battery was obtained.

Table 1 Electrolyte parameters of Comparative Examples 1-6 and Examples 1-24

Next, the performance test of the lithium ion secondary battery will be described.

(1) Lithium ion secondary battery -20 ° C DC discharge resistance test

The lithium ion secondary battery was allowed to stand at 25 ° C for 30 min, then charged to 4.2 V with a constant current of 1 C, then charged at a constant voltage of 4.2 V to a current of ≤ 0.05 C, and allowed to stand for 5 min, and then discharged at a constant current of 1 C. to 2.8V, the recording actual discharge capacity C _0, and then 1C ₀ current lithium ion secondary battery 30min, adjust the state of charge of the lithium ion secondary battery is 50% SOC. The lithium ion secondary battery adjusted in the charged state is transferred to the -20 ° C environment for 2 h or more, so that the internal and external temperatures of the lithium ion secondary battery are uniform, and finally discharged at a constant current of 0.3 C for 10 s, and the voltage difference before and after the discharge is recorded. A DC discharge resistance (DCR) of a lithium ion secondary battery was obtained.

(2) High-temperature storage performance test of lithium ion secondary battery

The lithium ion secondary battery was allowed to stand at 25 ° C for 30 min, then charged to 4.2 V with a constant current of 1 C, then charged at a constant voltage of 4.2 V to a current of ≤ 0.05 C, and allowed to stand for 5 min, and then stored at 60 ° C. After 30 days, the reversible capacity retention rate of the lithium ion secondary battery was measured.

(3) Cyclic performance test of lithium ion secondary battery

Lithium-ion secondary batteries were charged to 4.2V at a constant current of 1C at 25 ° C and 45 ° C, respectively, and then charged at a constant voltage of 4.2 V until the current was 0.05 C, and then discharged with a constant current of 1 C to 2.8 V. In the secondary cycle, the lithium ion secondary battery was subjected to a plurality of cycles in accordance with the above conditions until the discharge capacity after the cycle was ≤ 80% of the discharge capacity of the first cycle, and the number of cycles of the lithium ion secondary battery was recorded.

(4) Lithium ion secondary battery high temperature storage gas production performance test

The lithium ion secondary battery was charged to 4.2 V at a constant current of 1 C at 25 ° C, and then charged at a constant voltage of 4.2 V until the current was 0.05 C, so that it was in a fully charged state of 4.2 V, and then the lithium ion secondary battery was placed. It was kept in a high-temperature furnace at 70 ° C for 10 days, and the volume expansion ratio of the lithium ion secondary battery after 10 days of storage was recorded, and the volume expansion ratio of the lithium ion secondary battery = (post-storage volume / pre-storage volume - 1) × 100%.

Table 2 Performance test results of Comparative Examples 1-6 and Examples 1-24

As can be seen from Table 2, Examples 1-24 of the present invention have a higher number of cycles and a higher reversible capacity retention rate after high temperature storage, a volume expansion ratio after high temperature storage, and an internal resistance at a low temperature. Both are lower.

In Comparative Examples 1-6, the introduction of the additive B1 in the electrolytic solution can remarkably improve the cycle performance of the lithium ion secondary battery, but the high-temperature storage gas production is remarkably deteriorated. The introduction of lithium salt A3 significantly improves the high temperature storage gas production of lithium ion secondary batteries, which is due to the high thermal stability of lithium salt A3, and its low oxidation potential can oxidize on the surface of the positive electrode to form a passivation film, inhibiting the electrolyte in The decomposition of the surface of the positive electrode can effectively suppress the high-temperature storage gas generation of the lithium ion secondary battery, but the introduction of the lithium salt A3 causes the DCR of the lithium ion secondary battery to be greatly increased.

The additive C1 is introduced in the embodiment 1, which can improve the stability of the positive electrode active material and reduce the oxidation activity of the electrolyte, thereby effectively increasing the number of cycles of the lithium ion secondary battery and suppressing the high temperature storage gas generation of the lithium ion secondary battery. At the same time, the additive C1 can also reduce the impedance of the positive electrode electrochemical reaction and improve the dynamic performance of the positive electrode, so the DCR of the lithium ion secondary battery is significantly reduced.

In the second embodiment, the additive D2 is introduced, which can absorb the hydrofluoric acid in the electrolyte, reduce the corrosion of the positive and negative passivation films of the hydrofluoric acid, effectively inhibit the high temperature storage gas production of the lithium ion secondary battery, and simultaneously decompose the additive D2. The polyphosphate component can be embedded in the SEI film formed on the surface of the negative electrode, thereby effectively reducing the impedance of the surface of the negative electrode, so that the number of cycles of the lithium ion secondary battery and the reversible capacity retention rate after high temperature storage are also improved.

In Example 3, the additives C1 and D2 were simultaneously introduced, the number of cycles of the lithium ion secondary battery, the reversible capacity retention rate after high-temperature storage were greatly improved, and the volume expansion ratio after high-temperature storage was also significantly suppressed, and the DCR was still at a low level. s level. This is because the additive B1 can significantly improve the cycle performance of the lithium ion secondary battery, and is used as a main film-forming agent, and the deterioration of the high-temperature storage gas production performance brought about by the introduction of the lithium salt A3 and the additive having high heat stability. C1 and/or D2 are improved, and each substance interacts in the film formation process and induces formation of a stable interface film, thereby significantly improving the cycle performance of the lithium ion secondary battery and suppressing high temperature storage gas generation. At the same time, the additives C1 and/or D2 can also lower the high DCR brought about by the lithium salt A3.

When PS, DTD, and VC are further introduced into the electrolyte, the overall performance of the lithium ion secondary battery is further improved.

Claims (11)

1. An electrolyte comprising:

   Organic solvents;

   a lithium salt dissolved in an organic solvent;

   additive;

   It is characterized in that

   The lithium salt includes a nitrogen salt of a nitrogen-containing aromatic heterocyclic derivative;

   The additive includes:

   Fluorinated cyclic carbonate;

   Fluorophosphate and/or cyclophosphazene compounds.
2. The electrolytic solution according to claim 1, wherein the nitrogen-containing heteroaromatic derivative lithium salt is one or more selected from the group consisting of the compounds represented by the following formula 1, formula 2, formula 3, and formula 4; Species

   

   among them,

   R ₁ to R ₁₄ are each independently selected from the group consisting of H, F, a cyano group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an aryl group having 6 to 12 carbon atoms. One type, the alkyl group, the alkenyl group, and the aryl group may be substituted by one or both of F and a cyano group.
3. The electrolyte according to claim 2, wherein said nitrogen-containing aromatic heterocyclic derivative The lithium salt is selected from one or more of the following compounds;

   
4. The electrolyte according to claim 1, wherein the fluorinated cyclic carbonate is one or more selected from the group consisting of compounds represented by the following formula 5;

   

   among them,

   R ₂₁ , R ₂₂ , R ₂₃ and R ₂₄ are each independently selected from H, F, a fluoroalkyl group having 1 to 20 carbon atoms, a fluoroalkenyl group having 2 to 20 carbon atoms, and a carbon number of One of 6 to 20 fluoroaryl groups.
5. The electrolyte according to claim 4, wherein the fluorocyclic carbonate is selected from one or more of the following compounds;

   
6. The electrolyte according to claim 1, wherein the fluorophosphate is one or more selected from the group consisting of LiPO ₂ F ₂ and LiPOF ₄ .
7. The electrolyte according to claim 1, wherein the cyclophosphazene compound is one or more selected from the group consisting of compounds represented by the following formula 6;

   

   among them,

   R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ and R ₃₆ are each independently selected from the group consisting of H, F, Cl, Br, an alkyl group having 1 to 20 carbon atoms, and an alkene having 2 to 20 carbon atoms. a group, an aryl group having 6 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, a halogenated alkenyl group having 2 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms, An alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a halogenated alkoxy group having 1 to 20 carbon atoms, or a carbon atom One of a halogenated alkenyloxy group having 2 to 20 carbon atoms and a halogenated aryloxy group having 6 to 20 carbon atoms;

   Further, at least one of R ₃₂ , R ₃₄ and R ₃₆ is selected from an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, and an aryloxy group having 6 to 20 carbon atoms. One of a group, a halogenated alkoxy group having 1 to 20 carbon atoms, a halogenated alkenyloxy group having 2 to 20 carbon atoms, or a halogenated aryloxy group having 6 to 20 carbon atoms, in R ₃₁ , At least two of R ₃₃ and R ₃₅ are each independently selected from one of F, Cl, and Br.
8. The electrolyte according to claim 7, wherein said cyclophosphazene compound is selected from the group consisting of One or more of the following compounds;

   

   
9. The electrolyte according to claim 1, wherein

   The concentration of the nitrogen-containing aromatic heterocyclic derivative lithium salt is 0.01M to 0.8M;

   The content of the fluorinated cyclic carbonate is 0.01% to 30% of the total weight of the electrolyte;

   The content of the fluorophosphate is 0.01% to 2.5% of the total weight of the electrolyte;

   The content of the cyclophosphazene compound is 0.01% to 10% of the total weight of the electrolyte.
10. The electrolyte according to any one of claims 1 to 9, wherein the additive further comprises one or more of 1,3-propane sultone, vinyl sulfate, and vinylene carbonate. .
11. A lithium secondary battery comprising the electrolytic solution according to any one of claims 1 to 10.