CN118472394B - Electrolyte and secondary battery - Google Patents

Abstract

The application discloses an electrolyte and a secondary battery with the same, wherein the electrolyte comprises an additive, the additive accounts for 0.1 to 3 weight percent of the electrolyte, and the additive comprises a compound shown in a formula 1;Formula 1, wherein R ₁, R ₂, and R ₃ are each independently selected from substituted or unsubstituted C ₆ to C ₂₀ aryl, substituted or unsubstituted C ₁ to C ₁₀ alkyl, substituted or unsubstituted C ₁ to C ₁₀ alkoxy, substituted or unsubstituted C ₂ to C ₆ alkenyl, substituted or unsubstituted C ₃ to C ₂₀ heterocyclyl, halogen. The electrolyte in the application is beneficial to prolonging the service life of the secondary battery.

Description

Electrolyte and secondary battery

Technical Field

The present application relates to the field of batteries, and in particular to an electrolyte and a secondary battery.

Background Art

At present, electrochemical devices (e.g., lithium metal batteries) have been widely used in new energy electric vehicles, electronic products such as cameras, digital cameras, and 3C products due to their high energy density, high operating voltage, long life, and green environmental protection.

Lithium metal batteries generally include a positive electrode, a negative electrode, a separator and an electrolyte. In the related art, the electrolyte of lithium metal batteries has problems such as low conductivity, difficulty in ion movement, and high cost, which limits the further improvement of its performance and practical application. In addition, the electrolyte used for lithium metal batteries is generally a high-concentration or locally high-concentration electrolyte (for example, the concentration of lithium salt is above 1 mol/L), which has low conductivity and difficulty in ion movement, resulting in safety hazards such as overheating and even combustion inside the lithium metal battery with this electrolyte.

Summary of the invention

In view of this, the present application provides an electrolyte and a secondary battery. The secondary battery having the electrolyte has a longer lifespan.

In a first aspect, an embodiment of the present application provides an electrolyte for a secondary battery, characterized in that the electrolyte includes an additive, the additive accounts for 0.1 wt% to 3 wt% of the electrolyte, and the additive includes a compound shown in Formula 1;

Formula 1,

Wherein, R ₁ , R ₂ and R ₃ are each independently selected from substituted or unsubstituted C ₆ to C ₂₀ aryl, substituted or unsubstituted C ₁ to C ₁₀ alkyl, substituted or unsubstituted C ₁ to C ₁₀ alkoxy, substituted or unsubstituted C ₂ to C ₆ alkenyl, substituted or unsubstituted C ₃ to C ₂₀ heterocyclyl, and halogen.

In some embodiments of the present application, R ₁ , R ₂ and R ₃ are each independently selected from substituted or unsubstituted C ₆ to C ₁₂ aryl, substituted or unsubstituted C ₁ to C ₆ alkyl, substituted or unsubstituted C ₁ to C ₆ alkoxy, and halogen.

In some embodiments of the present application, the additive is selected from at least one of triphenyl phosphine, tri-p-phenyl phosphine, diphenyl methoxy phosphine, tri(1-naphthyl) phosphine, tri-m-phenyl phosphine, dimethyl phenyl phosphine, diphenyl phosphine chloride, and diethyl phenyl phosphine.

In some embodiments of the present application, the additive is selected from at least one of triphenylphosphine, tri(1-naphthyl)phosphine and diphenylphosphine chloride.

In some embodiments of the present application, the additive accounts for 0.5 wt % to 2 wt % of the electrolyte.

In some embodiments of the present application, the electrolyte further includes a lithium salt and a solvent, and the concentration of the lithium salt in the electrolyte is 0.01 mol/L to 0.3 mol/L; or

Calculated by mass percentage, the electrolyte includes: 1 wt % to 6 wt % of lithium salt; 93 wt % to 98 % of solvent; and 0.1 wt % to 3 wt % of additives.

In some embodiments of the present application, the lithium salt is selected from one or more of lithium difluorooxalatoborate, lithium difluorophosphate, lithium nitrate, lithium dioxalatoborate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide).

In some embodiments of the present application, the solvent is selected from cyclic ethers and/or esters; or,

The solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3-dioxolane, dioxane, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate.

In a second aspect of the present application, a secondary battery is provided, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte.

In some embodiments of the present application, the negative electrode sheet includes lithium metal or lithium alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

FIG1 is a voltage curve diagram of a button cell in Comparative Example 1 of the present application;

FIG2 is a voltage curve diagram of a button cell in Comparative Example 2 of the present application;

FIG3 is a voltage curve diagram of a button cell in Example 1 of the present application;

FIG4 is a voltage curve diagram of the fully-electric button-type batteries in Example 1, Comparative Example 1 and Comparative Example 2 of the present application.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and/or" used herein includes any and all combinations of one or more related listed items.

In this application, unless otherwise stated, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order.

In this application, "and/or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and/or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

In this application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

At present, electrochemical devices (e.g., lithium metal batteries) have been widely used in new energy electric vehicles, electronic products such as cameras, digital cameras, and 3C products due to their high energy density, high operating voltage, long life, and green environmental protection.

Lithium metal batteries generally include a positive electrode, a negative electrode, a separator and an electrolyte. In the related art, the electrolyte of lithium metal batteries has problems such as low conductivity, difficulty in ion movement, and high cost, which limits the further improvement of its performance and practical application. In addition, the electrolyte used for lithium metal batteries is generally a high-concentration or locally high-concentration electrolyte (for example, the concentration of lithium salt is above 1 mol/L), which has low conductivity and difficulty in ion movement, resulting in safety hazards such as overheating and even combustion inside the lithium metal battery with this electrolyte.

In view of this, the present application provides an electrolyte for a lithium metal battery. The concentration of lithium salt in the electrolyte of the present application is low, and the lithium metal battery having the electrolyte has high performance, high safety and long life. The electrolyte and lithium metal battery of the present application are further described in combination with the embodiments below.

The present application embodiment provides an electrolyte, the electrolyte comprising: a lithium salt, a solvent and an additive, wherein the additive comprises a compound shown in Formula 1;

Formula 1,

Wherein, R ₁ , R ₂ and R ₃ are each independently selected from substituted or unsubstituted C ₆ to C ₂₀ aryl, substituted or unsubstituted C ₁ to C ₁₀ alkyl, substituted or unsubstituted C ₁ to C ₁₀ alkoxy, substituted or unsubstituted C ₂ to C ₆ alkenyl, substituted or unsubstituted C ₃ to C ₂₀ heterocyclyl, and halogen.

It should be noted that _C6 to _C20 aryl refers to an aryl having 6 to 20 carbon atoms. Exemplarily, _C6 to _C20 aryl includes phenyl, tolyl, xylyl, etc. Similarly, C1 to _C10 alkyl refers to an alkyl having 1 to 10 carbon atoms. Exemplarily, _C1 to _C10 alkyl includes methyl, ethyl, propyl, isopropyl, butyl, etc. _C1 to _C10 alkoxy refers to an alkoxy having 1 to 10 carbon atoms. Exemplarily, _C1 to _C10 alkoxy includes methoxy, ethoxy, propoxy, butoxy, etc. _C2 to _C6 alkenyl refers to an alkenyl having 2 to 6 carbon atoms. Exemplarily, _C2 to _C6 alkenyl includes vinyl, propenyl, butenyl, etc. _C3 to _C20 heterocyclic refers to an oxirane, furanyl, thienyl, pyrrolyl, etc. having 3 to 20 _carbon atoms. Halogen includes fluorine (F), chlorine (Cl), bromine (Br) and the like.

Preferably, R1, R2 and R3 are each independently selected from substituted or unsubstituted C ₆ to C ₁₂ aryl, substituted or unsubstituted C ₁ to C ₆ alkyl, substituted or unsubstituted C ₁ to C ₆ alkoxy, halogen.

Preferably, at least one of R ₁ , R ₂ and R ₃ is a substituted or unsubstituted C ₆ to C ₁₂ aryl group.

Specifically, the additive is selected from at least one of triphenyl phosphine, tri-p-phenyl phosphine, diphenyl methoxy phosphine, tri(1-naphthyl) phosphine, tri-m-phenyl phosphine, dimethyl phenyl phosphine, diphenyl phosphine chloride and diethyl phenyl phosphine.

In the embodiment of the present application, the concentration of the lithium salt is 0.01 mol / L to 0.3 mol / L. Preferably, the concentration of the lithium salt is 0.2 mol / L to 0.3 mol / L.

Compared with the existing electrolyte for lithium metal batteries, the concentration of lithium salt in the electrolyte provided by the embodiment of the present application is 0.01 mol/L to 0.3 mol/L, and the lithium salt in the electrolyte has an ultra-low concentration, which is conducive to reducing the production cost of the electrolyte. At the same time, by adding an additive containing the compound shown in Formula 1 to the electrolyte, the synergistic combination of the additive with a special structure and the ultra-low concentration of lithium salt is conducive to promoting the movement of lithium ions and improving the conductivity of the electrolyte; when the electrolyte is used in a lithium metal battery, it is conducive to promoting the formation of a dense and uniform SEI film, promoting the uniform deposition of lithium ions, and improving the performance, safety and life of the lithium metal battery.

In some embodiments of the present application, the electrolyte includes: 1 wt % to 6 wt % of lithium salt; 93 wt % to 98 % of solvent; and 0.1 wt % to 3 wt % of additives.

In some embodiments of the present application, the lithium salt is selected from one or more of lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LIDFOP), lithium nitrate (LINO ₃ ), lithium dioxalatoborate (LiBOB), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiCLO ₄ ), lithium difluorophosphate (LiCLO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bistrifluoromethanesulfonyl imide (LiTFSI), and lithium bisfluorosulfonyl imide (LiFSI).

In some embodiments of the present application, the solvent is selected from cyclic ethers and/or esters. It is understood that the selection of cyclic ethers and/or esters as solvents is beneficial to increase the voltage window. Exemplarily, the voltage window of the electrolyte is greater than 4.2V.

Exemplarily, the cyclic ether is selected from at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 4-methyl-1,3-dioxolane (4-MeDOL), and dioxane.

Illustratively, the ester is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

The present application also provides a lithium metal secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte. Exemplarily, the negative electrode sheet is a lithium metal negative electrode.

The positive electrode includes a positive electrode active material. Exemplarily, the positive electrode active material is selected from at least one of iron phosphate, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, or nickel cobalt manganese oxide.

Example 1

(1) Preparation of electrolyte

0.0091g triphenylphosphine (TPP) was added to 1ml tetrahydropyran (THP), and stirred for 1H. After being fully dissolved, 0.0003mol lithium difluorooxalatoborate (LiDFOB, 0.051g) was added and stirred to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.28M.

(2) Preparation of positive electrode

The ternary positive electrode material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ), conductive agent Super P, and binder PVDF were mixed in a mass ratio of 8:1:1, dispersed in an organic solvent NMP (N-methylpyrrolidone), and stirred until stable and uniform to form a positive electrode slurry. The positive electrode slurry was scraped onto an aluminum foil with a thickness of 10 μm, dried at 80°C, and then heated to 120°C for further vacuum drying, and then rolled and sliced into positive electrode sheets.

(3) Battery preparation

Button cell: In the inert atmosphere of the glove box, the moisture and oxygen content is <0.1 PPM. Assemble the negative electrode shell丨spring sheet丨gasket丨lithium sheet丨electrolyte丨diaphragm丨lithium sheet丨positive electrode shell in order to assemble the button cell. The thickness of the lithium sheet is 20μm and the diameter is 14 mm. The thickness of the diaphragm is 9μm PE diaphragm and the diameter is 16 mm. The amount of electrolyte used for each button cell is 20μL, and 10μL is added to each side. Press at 800 kPa for 5s to complete the assembly and prepare the required secondary battery.

All-electric button cell: In the inert atmosphere of the glove box, with moisture and oxygen content <0.1 PPM, assemble the negative electrode shell丨spring sheet丨gasket丨lithium sheet丨electrolyte丨diaphragm丨positive electrode sheet丨positive electrode shell in order to assemble the all-electric button cell.

Example 2

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 2%, and the concentration of lithium salt in the electrolyte was 0.28M.

Example 3

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 3%, and the concentration of lithium salt in the electrolyte was 0.28M.

Example 4

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.1 M.

Example 5

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.4 M.

Example 6

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.8 M.

Example 7

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of diphenylphosphine chloride (CDPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of CDPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.28M.

Example 8

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of tri(1-naphthyl)phosphine (TNPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of CDPP in the electrolyte was 1%, and the concentration of lithium salt in the electrolyte was 0.28M.

Example 9

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of tri(1-naphthyl)phosphine (TPP) and diphenylphosphine chloride (CDPP) were added to 1 ml of tetrahydropyran (THP), stirred for 1 hour, and then lithium difluorooxalate borate (LiDFOB) was added after being fully dissolved, and stirred to obtain an electrolyte. The mass percentage of TPP in the electrolyte was 0.5%, the mass percentage of CDPP in the electrolyte was 0.5%, and the concentration of lithium salt in the electrolyte was 0.28M.

Example 10

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of triphenylphosphine (TPP) was added to 1 ml of tetrahydropyran (THP), and stirred for 1 hour. After being fully dissolved, lithium difluorooxalate borate (LiDFOB) was added thereto, and stirred thoroughly to obtain an electrolyte. The mass percentage of TNPP in the electrolyte was 0.1%, and the concentration of lithium salt in the electrolyte was 0.28M.

Comparative Example 1

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of lithium difluorooxalatoborate (LiDFOB) is added to 1 ml of tetrahydropyran (THP) and stirred thoroughly to obtain an electrolyte solution, wherein the concentration of lithium salt in the electrolyte solution is 1M.

Comparative Example 2

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of lithium difluorooxalatoborate (LiDFOB) is added to 1 ml of tetrahydropyran (THP) and stirred thoroughly to obtain an electrolyte solution, wherein the concentration of lithium salt in the electrolyte solution is 0.6 M.

Comparative Example 3

The difference between it and Example 1 is that:

(1) Preparation of electrolyte

A certain amount of lithium difluorooxalatoborate (LiDFOB) was added to 1 ml of tetrahydropyran (THP) and stirred thoroughly to obtain an electrolyte solution, wherein the concentration of lithium salt in the electrolyte solution was 0.28 M.

The compositions of the electrolytes in Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1.

Table 1

Note: “/” means not added.

Conductivity test: The electrolytes prepared in Examples 1 to 10 and Comparative Examples 1 to 3 were tested using a conductivity meter at room temperature and pressure. The test results are shown in Table 2.

Battery life test: The batteries prepared in the examples and comparative examples were subjected to symmetrical battery tests at 25°C with a current density of ¹ mA/cm2 and a load of 1 mAh/ ^cm2 . The time when the battery experienced a hard short circuit or a polarization potential of >0.3 V was the battery life.

Cycle performance test: The batteries prepared in the examples and comparative examples were charged to 4.2 V at 0.2 C constant current and constant voltage at 25° C., and then discharged to 3.0 V at 0.5 C constant current. This was considered one cycle.

The test results of the battery performance are shown in Figures 1 to 4 and Table 2. Figure 1 is a voltage curve of the symmetrical battery prepared in Comparative Example 1, Figure 2 is a voltage curve of the symmetrical battery prepared in Comparative Example 2, Figure 3 is a voltage curve of the symmetrical battery prepared in Example 1, and Figure 4 is a cycle performance curve of the fully electric button-type batteries prepared in Example 1 (ie, Example 1), Comparative Example 1, and Comparative Example 2.

Table 2

As shown in Figures 1 to 4 and Table 2, compared with Comparative Examples 1 to 3, the life of the symmetrical batteries in Examples 1 to 10 is improved, indicating that adding the additive shown in Formula 1 to the electrolyte is beneficial to improving the life of the battery. As shown in the comparison of Examples 1 to 3, when the mass ratio of the additive in the electrolyte exceeds 3%, increasing the mass ratio of the additive in the electrolyte decreases the effect of improving the battery life and cycle performance.

As can be seen from Table 2, the capacity retention rate of the full battery prepared in Examples 1 to 4 is above 90% after 80 cycles, the capacity retention rate of the full battery prepared in Examples 1 and 4 is as high as 94% after 80 cycles, and the number of cycles of Examples 5 and 6 at 80% capacity retention rate is less than 40. By comparing Examples 1 and 4 to 6, it can be seen that the effect of the additives in the present application on improving the battery life and cycle performance is greatly affected by the concentration of lithium salt. In the electrolyte system with a lithium salt concentration of less than 0.3M, the additives have a significant effect on improving the battery life and cycle performance. Both additives and low-concentration lithium salts are beneficial to improving the battery life and cycle performance. When the concentration of lithium salt in the electrolyte is about 0.1M and the mass ratio of the additive in the electrolyte is about 1%, the battery life and cycle performance are better.

The technical solutions provided by the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technicians in this field, according to the idea of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims (8)

1. An electrolyte for a secondary battery, characterized in that the electrolyte comprises an additive accounting for 0.1 wt to 3wt% of the electrolyte

The electrolyte also comprises lithium salt and a solvent, wherein the concentration of the lithium salt in the electrolyte is 0.1mo1/L to 0.3 mo1/L, and the additive is at least one of tri-p-phenylphosphine, diphenyl methoxy phosphorus, tri (1-naphthyl) phosphorus, tri-m-phenylphosphine, dimethylphenylphosphine, diphenyl phosphorus chloride and diethylphenylphosphine.

2. The electrolyte of claim 1 wherein the additive is selected from at least one of tris (1-naphthyl) phosphorus and diphenyl phosphorus chloride.

3. The electrolyte of claim 1 wherein the additive comprises from 0.5 wt% to 2% by weight of the electrolyte.

4. The electrolyte of claim 1, wherein the electrolyte comprises, in mass percent: 93% to 98% of solvent.

5. The electrolyte of claim 4 wherein the lithium salt is selected from one or more of lithium difluorooxalato borate, lithium difluorophosphate, lithium nitrate, lithium dioxaoxalato borate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bistrifluoro-methylsulfonimide, lithium bistrifluorosulfonylimide.

6. The electrolyte of claim 1 wherein the solvent is selected from the group consisting of cyclic ethers and/or esters; or alternatively

The solvent is at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1, 3-dioxolane, dioxane, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate.

7. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as set forth in any one of claims 1 to 6.

8. The secondary battery of claim 7, wherein the negative electrode sheet comprises lithium metal or a lithium alloy.