A secondary battery and electrical device

Abstract

This invention provides a secondary battery and an electrical device. The secondary battery includes a negative electrode and an electrolyte. The negative electrode includes lithium metal, and the surface of the lithium metal has an interface film. The interface film contains fluoride and nitride, and the molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22). The interface film formed by the combination of nitride and fluoride in a molar ratio of 1:(1.63~2.22) facilitates fast ion conduction, induces uniform deposition of lithium ions, effectively reduces the growth of lithium dendrites, achieves high coulombic efficiency of the battery, and can also slow down interfacial side reactions and electrolyte consumption, thereby extending the cycle life of the lithium metal negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a secondary battery and electrical device. Background Technology

[0002] Lithium metal has an ultra-high theoretical specific capacity, low redox potential and density, making it an ideal anode material for lithium metal batteries.

[0003] However, lithium metal itself has high chemical and electrochemical activity, which leads to harmful side reactions between lithium metal and the electrolyte when lithium metal is used as the negative electrode. This will continuously consume lithium metal and electrolyte. At the same time, uneven lithium deposition leads to dendrite growth, which can easily puncture the separator and cause battery short circuits, posing a great safety hazard. In addition, dendrite growth exposes a larger specific surface area, accelerating interfacial side reactions between the lithium metal and the electrolyte. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a secondary battery and electrical device to solve the problem of unstable lithium metal anode / electrolyte interface in existing lithium metal batteries, which easily leads to lithium and electrolyte consumption and performance degradation.

[0005] To solve the above problems, the present invention is achieved through the following technical solution:

[0006] This invention proposes a secondary battery, comprising a negative electrode and an electrolyte; the negative electrode comprises lithium metal, the surface of which has an interface film, the interface film comprising fluoride and nitride, wherein the molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22).

[0007] Furthermore, in the secondary battery, the molar content of fluoride in the interface film is 8-10%, and the molar content of nitride in the interface film is 4-5%.

[0008] Furthermore, in the secondary battery, the fluoride includes lithium fluoride, and the nitride includes at least one of lithium nitride and lithium azide.

[0009] Furthermore, in the secondary battery, the electrolyte includes lithium salt, organic solvent, additives and ring-opening initiator, wherein the additives include at least one of lithium nitrate and azidotrimethylsilane.

[0010] Furthermore, in the secondary battery, the organic solvent includes dipropylene glycol dimethyl ether and a dioxapentane analog; the volume ratio of the dipropylene glycol dimethyl ether and the dioxapentane analog is 1:0.1 to 4; the dioxapentane analog includes at least one of 1,3-dioxapentane, 2-methyl-1,3-dioxapentane, and 4-methyl-1,3-dioxapentane.

[0011] Furthermore, in the secondary battery, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

[0012] Furthermore, in the electrolyte, the concentration of the additive is 0.1–0.5 mol / L.

[0013] Furthermore, in the electrolyte, the concentration of the lithium salt is 0.5–4 mol / L.

[0014] Furthermore, in the electrolyte, the ring-opening initiator includes at least one of N-fluorobisbenzenesulfonamide and its derivatives.

[0015] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0016] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0017] In this embodiment of the invention, the provided secondary battery includes a negative electrode and an electrolyte; the negative electrode includes lithium metal, and the surface of the lithium metal has an interface film containing fluoride and nitride. The molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22). When the molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22), it can improve fast ion conduction, induce uniform lithium deposition, achieve high coulombic efficiency dendrite-free cycling, and also slow down interfacial side reactions and electrolyte consumption, thereby extending the cycle life of the lithium metal negative electrode.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0019] Figure 1 This is a morphology diagram of the lithium metal anode deposition of the battery prepared in Example 1. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The applicant of this invention discovered that harmful side reactions exist between lithium metal and the electrolyte when lithium metal is used as the negative electrode, which continuously consumes lithium metal and electrolyte. At the same time, uneven deposition of lithium ions leads to dendrite growth, which can easily puncture the separator and cause battery short circuits, posing a great safety hazard. In addition, dendrite growth exposes a larger specific surface area, accelerating interfacial side reactions between the lithium metal and the electrolyte.

[0022] To address the aforementioned problems, this invention provides a secondary battery comprising a negative electrode and an electrolyte; the negative electrode comprises lithium metal, the surface of which has an interface film containing fluoride and nitride, wherein the molar ratio of nitride to fluoride in the interface film is 1:(1.63-2.25).

[0023] In the secondary battery provided by the present invention, the electrolyte forms an interface film on the surface of metallic lithium through reduction, and the molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22), which makes the interface film convenient for fast ion conduction, can induce uniform lithium deposition, suppress lithium dendrite formation, achieve high coulombic efficiency cycling, and also slow down interfacial side reactions and electrolyte consumption, thereby extending the cycle life of lithium metal anode.

[0024] Optionally, the molar ratio of nitride to fluoride in the interfacial film can be one of or any two of the following: 1:1.63, 1:75, 1:82, 1:1.95, 1:2.05, 1:2.22.

[0025] Optionally, in one embodiment, the molar content of fluoride in the interface film is 8-10%, and the molar content of nitride in the interface film is 4-5%. This ensures that the interface film has a sufficient amount of inorganic components while effectively forming a solid electrolyte interface film, thereby further accelerating ion conduction. Optionally, the molar content of fluoride in the interface film can be one or any two of 8%, 8.5%, 9%, 9.5%, and 10%, and the molar content of nitride in the interface film can be one or any two of 4%, 4.2%, 4.4%, 4.5%, 4.8%, and 5%.

[0026] Optionally, in one embodiment, the fluoride includes lithium fluoride, and the nitride includes at least one of lithium nitride and lithium azide. The lithium fluoride-containing interface film can effectively suppress side reactions between the electrode, reaction intermediate, and electrolyte. In addition, lithium nitride and other lithium-nitrogen compounds have high ionic conductivity and good chemical stability, which can provide a stable lithium-ion transport channel, enabling lithium ions to be deposited uniformly, which helps to improve the charge-discharge efficiency and cycle stability of the battery. The interface film formed in this way is more conducive to ion transport, has excellent corrosion resistance, makes lithium deposition more uniform, and improves cycle stability.

[0027] In the secondary battery provided in this embodiment of the invention, the electrolyte includes lithium salt, organic solvent, additives and ring-opening initiator, wherein the additives include at least one of lithium nitrate and trimethylsilane azido.

[0028] The additives described above can enter the solvent sheath and coordinate with lithium, thereby preferentially reducing lithium metal anodes to form a fast-conducting interface film rich in lithium-nitrogen compounds. This induces uniform lithium deposition, improves coulombic efficiency, enables in-situ polymerization in the electrolyte, and effectively extends the cycle life of lithium metal anodes.

[0029] Among them, the nitrate anion in lithium nitrate can interact with dioxapentane analog molecules, inhibiting the ring-opening of dioxapentane analogs. This allows control over the ring-opening polymerization time of dioxapentane analogs in the electrolyte. In other words, after the nitrate anion is consumed, dioxapentane analogs begin to undergo ring-opening polymerization, which is suitable for electrolyte preparation and large-scale production.

[0030] Optionally, in the electrolyte of the secondary battery provided in this embodiment of the invention, the concentration of the above-mentioned additive is 0.1 to 0.5 mol / L, for example, it can be one or any two of the following: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L. When the additive content is within the above range, it can effectively form a solid electrolyte interface rich in lithium-nitrogen compounds with fast ion conduction, thereby inducing uniform lithium deposition and extending the cycle life of the lithium metal anode.

[0031] Optionally, in one embodiment, the organic solvent includes dipropylene glycol dimethyl ether and dioxolane analogues; wherein, the dioxolane analogues can form polydioxolane (DOL) in situ during cycling, and polydioxolane has better elasticity, which can better adapt to the volume expansion of the lithium metal anode; while dipropylene glycol dimethyl ether (DPGDME), as a co-solvent for dioxolane analogues, can not only reasonably reduce the cost of electrolyte; at the same time, the low density of dipropylene glycol dimethyl ether and polydioxolane is beneficial to improving the energy density of the whole battery; in addition, the high boiling point property of dipropylene glycol dimethyl ether combined with polydioxolane can effectively improve the battery safety performance from the battery material level, and the moderate solvation capability of dipropylene glycol dimethyl ether can realize the entry of nitrate ions into the solvent sheath and lithium coordination at low lithium nitrate concentrations, thereby preferentially reducing the lithium metal anode and forming a solid electrolyte interface rich in lithium-nitrogen compounds with fast ion conduction.

[0032] Optionally, in one specific embodiment, the volume ratio of dipropylene glycol dimethyl ether to dioxapentane analogue is 1:0.1 to 4. Within this range, the stability of the lithium metal anode / electrolyte interface, reduction of battery polarization, electrolyte cost, battery energy density, and battery safety performance can be effectively balanced. Optionally, the volume ratio of dipropylene glycol dimethyl ether to dioxapentane analogue can be one or any two of the following: 1:0.1, 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4.

[0033] Optionally, in one specific embodiment, the above-mentioned dioxapentane analogue includes at least one of 1,3-dioxapentane, 2-methyl-1,3-dioxapentane, and 4-methyl-1,3-dioxapentane.

[0034] Optionally, in the electrolyte of the secondary battery provided in the embodiments of the present invention, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate, which can be adapted with the above-mentioned additives to form an interface film rich in lithium-nitrogen compounds that facilitates fast ion conduction.

[0035] Optionally, in the electrolyte of the secondary battery provided in this embodiment of the invention, the concentration of the lithium salt is 0.5–4 mol / L, for example, it can be one or any two of the following: 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L. A lithium salt concentration within the above range not only effectively constructs a fast-conducting solid electrolyte interface dominated by inorganic components, but also avoids the problem of decreased ionic conductivity due to increased electrolyte viscosity.

[0036] Optionally, in the electrolyte of the secondary battery provided in the embodiments of the present invention, the ring-opening initiator includes at least one of N-fluorobis(benzenesulfonimide) (NFSI) and its derivatives.

[0037] In this embodiment of the invention, the molecular formula of N-fluorobisbenzenesulfonamide and its derivatives is NF(SO2R1)(SO2R2), wherein R1 and R2 are aromatic groups. Optionally, R1 and R2 are each independently selected from phenyl, benzyl, and xylyl groups.

[0038] N-Fluorobis(benzenesulfonyl)imide and its derivatives are nonionic DOL ring-opening initiators. They can generate NSI radicals and F radicals through FN bond cleavage. NSI radicals can initiate DOL ring opening, so the DOL polymerization rate can be slowed down and controlled by adjusting the concentration of NFSI initiator. F radicals can react in situ with lithium metal anodes to construct a LiF-rich interfacial protective layer, which can induce uniform lithium deposition, optimize SEI, reduce interfacial side reactions and electrolyte consumption, thereby extending the cycle life of lithium metal anodes.

[0039] In this embodiment of the invention, lithium nitrate is added to the electrolyte. In the early stages of cycling, lithium nitrate is preferentially reduced at the lithium metal anode interface to construct an SEI rich in lithium-nitrogen compounds, achieving high coulombic efficiency and dendrite-free cycling. As cycling progresses, the limited lithium nitrate is gradually consumed and loses its interaction with polydioxanone. Subsequently, NSI radicals generated from N-fluorobenzenesulfonimide (NFSI) and its derivatives initiate the ring-opening polymerization of polydioxanone, constructing a lithium metal / polyDOL-based electrolyte solid-solid interface. At the same time, the generated F radicals form lithium fluoride in situ.

[0040] Optionally, the initial concentration of the ring-opening initiator is 0.005–0.2 mol / L. Within this range, the gelation effect and the interfacial protection of the SEI can be effectively balanced. In practical applications, within the above concentration range, the polymerization rate of DOL can be effectively controlled while ensuring a degree of polymerization greater than 90%.

[0041] Optionally, in one embodiment, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, which includes a lithium-ion transition metal oxide. The lithium-ion transition metal oxide includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0042] Optionally, in one embodiment, the positive electrode further includes a conductive agent, which may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0043] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material including the above-mentioned positive electrode material, binder and conductive agent, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector such as aluminum foil; after drying, rolling, die cutting and other processes, the positive electrode sheet can be obtained.

[0044] In practical applications, the negative electrode sheet, positive electrode sheet, and separator are wound together to obtain a core, the core is packaged to obtain a dry cell, and the dry cell is baked and then injected with electrolyte, formed, resealed, and sorted to obtain the above-mentioned secondary battery.

[0045] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0046] The above-described electrical equipment embodiment includes the aforementioned secondary battery and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the secondary battery embodiment.

[0047] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0048] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] The present invention will be described in detail below through embodiments.

[0050] Example 1

[0051] Preparation of a lithium metal battery:

[0052] (1) Preparation of electrolyte:

[0053] At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), 0.05 mol of N-fluorobis(benzenesulfonyl)imide (NFSI) was added to 1 L of dioxapentane analog (1,3-dioxapentane) and stirred until completely dissolved to obtain a solution with a concentration of 0.05 mol / L NFSI. DPGDME solvent was added to the above solution, wherein the volume ratio of DPGDME solvent to dioxapentane analog was 3:1. After stirring evenly, lithium nitrate (LiNO3) and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved sequentially and stirred for 4 h to obtain an electrolyte (MPE). The concentration of lithium nitrate in the electrolyte was 0.4 M, and the concentration of lithium bis(fluorosulfonyl)imide was 1 M.

[0054] (2) Preparation of lithium metal batteries

[0055] LiNi, the positive electrode active material 0.92 Co 0.07 Mn 0.01O2, conductive agent acetylene black (Super P) and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of Na3V2(PO4)3:Super P:PVDF = 90:6:4, and then evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0056] The prepared positive electrode sheet, separator (PP separator), and lithium metal negative electrode sheet are stacked in sequence so that each positive electrode film layer and negative electrode film layer are covered with a separator. Then they are stacked into a cell, hot-pressed, and the tabs are welded and put into an outer packaging shell. After baking and drying, the electrolyte is injected. Then, after standing, formation, aging and capacity testing, a lithium metal battery is made.

[0057] Examples 2-4

[0058] The only difference from Example 1 is that the amount of NFSI added is adjusted during the preparation of the electrolyte.

[0059] Example 5

[0060] The difference between Example 5 and Example 1 is that, in the preparation of the electrolyte, NFSI is adjusted to N-fluorobis(p-toluenesulfonyl)amine.

[0061] Examples 6-9

[0062] The only difference from Example 1 is that the concentration of LiFSI is adjusted during the preparation of the electrolyte.

[0063] Example 10

[0064] The difference between Example 10 and Example 1 is that, in the preparation of the electrolyte, lithium bis(fluorosulfonyl)imide is changed to lithium tetrafluoroborate (LiBF4).

[0065] Examples 11-14

[0066] The difference from Example 1 is that the concentration of lithium nitrate is adjusted during the preparation of the electrolyte.

[0067] Example 15

[0068] The difference between Example 15 and Example 1 is that, in the preparation of the electrolyte, lithium nitrate is replaced with azide-trimethylsilane.

[0069] Examples 16-20

[0070] The difference from Example 1 is that the amount of DPGDME solvent added is adjusted during the preparation of the electrolyte to adjust the volume ratio of DPGDME solvent and dioxane analog in the electrolyte.

[0071] Example 21

[0072] The difference between Example 21 and Example 1 is that, in the preparation of the electrolyte, 1,3-dioxopentane is adjusted to 2-methyl-1,3-dioxopentane.

[0073] Example 22

[0074] The difference between Example 22 and Example 1 is that, in the preparation of the electrolyte, 1,3-dioxapentane is adjusted to 4-methyl-1,3-dioxapentane.

[0075] Comparative Examples 1-2

[0076] The difference between Comparative Example 1 and Example 1 is that, in the preparation of the electrolyte, the lithium nitrate and lithium bis(fluorosulfonyl)imide were adjusted, and the content of nitrides and fluorides in the interface film was adjusted.

[0077] Test example:

[0078] 1) The electrolytes prepared in the above embodiments and comparative examples were assembled with lithium and copper sheets to form lithium-copper button batteries, and their coulombic efficiency was tested. The test method was as follows: at 25°C, the lithium-copper button battery was subjected to a coulombic efficiency test at 0.2 mA cm⁻¹. -2 At the current density, a 2.64 mAh cm⁻¹ deposit was first deposited. -2 Lithium-to-copper current collector, charge stripping 0.66mAh cm⁻¹ -2 Lithium was subsequently deposited at a rate of 0.66 mAh cm⁻¹. -2 Lithium was cycled 10 times, and finally charged to 1.0V to completely strip the lithium from the copper current collector. The average coulombic efficiency CE was calculated as (x + 0.66 * 10) / (2.64 + 0.66 * 10), where x is the capacity of the stripped lithium in mAh cm⁻¹. -2 The results are shown in Table 2. The preparation steps for the lithium-copper button cell are as follows:

[0079] A punching machine was used to cut lithium sheets with a diameter of 15 mm and a thickness of 200 μm, copper sheets with a diameter of 18 mm and a thickness of 12 μm, and polyethylene diaphragms with a diameter of 19 mm and a thickness of 20 μm.

[0080] The obtained lithium sheet, separator, and copper sheet are stacked in sequence, with the separator positioned between the lithium sheet and the copper sheet. The stack is placed in a 2032 battery case, and 30 μL of the electrolyte prepared in the above example is added dropwise using a pipette. The battery is then sealed under pressure using a button cell sealing machine at a pressure of 30 kPa to complete the preparation of the lithium-copper button cell.

[0081] 2) The lithium metal batteries prepared in each embodiment and comparative example were subjected to deposition morphology and battery cycle stability tests. The test data are shown in Table 2. The test methods are as follows:

[0082] 2.1 Deposition morphology test: After cycling the lithium metal battery 100 times at 1C rate, the battery was disassembled at 100% SOC and the deposition morphology and lithium deposition thickness on the surface of the negative electrode were observed by scanning tunneling microscope.

[0083] 2.2 Battery Cycle Stability Test: The lithium metal battery was subjected to deposition / stripping cycles at 25℃, and the battery voltage was recorded until the overpotential reached 60mV. The cycle time T of the lithium metal negative electrode at this point was recorded; this cycle time T is the cycle stability duration of the negative electrode. Cycling tests were continued until the cycle time reached the overpotential V. The smaller the overpotential V, the smaller the surface electrode polarization and the better the ion conduction at the negative electrode interface. The current density during the deposition / stripping cycle was 1mA cm⁻¹. -2 Surface capacity is 2mAh cm -2 .

[0084] The lithium deposition morphology of the battery prepared in Example 1 is as follows: Figure 1 As shown by Figure 1 As can be seen, the electrolyte provided in this embodiment of the invention can achieve dense bulk lithium deposition with a deposition thickness of 25 μm, and the surface is dense and free of dendrite lithium deposition.

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089]

[0090] The experimental results from Examples 1-22 and Comparative Examples 1-2 show that controlling the content of each component in the electrolyte has a significant impact on the negative electrode interface film. When the molar ratio of nitride to fluoride in the interface film on the surface of the negative electrode is in the range of 1:(1.63-2.22), it can induce uniform lithium deposition, achieve high coulombic efficiency dendrite-free cycling, and also slow down interfacial side reactions and electrolyte consumption, thereby extending the cycle life of the lithium metal negative electrode.

[0091] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0092] The present invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes lithium metal, the surface of the lithium metal has an interface film, the interface film contains fluoride and nitride, and the molar ratio of nitride to fluoride in the interface film is 1:(1.63~2.22). The electrolyte includes a ring-opening initiator, which includes at least one of N-fluorobisbenzenesulfonamide and its derivatives.

2. The secondary battery according to claim 1, characterized in that, The molar content of fluoride in the interface film is 8-10%, and the molar content of nitride in the interface film is 4-5%.

3. The secondary battery according to claim 1, characterized in that, The fluoride includes lithium fluoride, and the nitride includes at least one of lithium nitride and lithium azide.

4. The secondary battery according to claim 1, characterized in that, The electrolyte also includes lithium salt, organic solvent and additives, wherein the additives include at least one of lithium nitrate and azidotrimethylsilane.

5. The secondary battery according to claim 4, characterized in that, The organic solvent includes dipropylene glycol dimethyl ether and dioxapentane analogs; the volume ratio of dipropylene glycol dimethyl ether to dioxapentane analogs is 1:0.1 to 4; the dioxapentane analogs include at least one of 1,3-dioxapentane, 2-methyl-1,3-dioxapentane, and 4-methyl-1,3-dioxapentane.

6. The secondary battery according to claim 4, characterized in that, The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

7. The secondary battery according to claim 4, characterized in that, In the electrolyte, the concentration of the additive is 0.1 to 0.5 mol / L.

8. The secondary battery according to claim 4, characterized in that, In the electrolyte, the concentration of the lithium salt is 0.5–4 mol / L.

9. An electrical appliance, characterized in that, The device includes a secondary battery as described in any one of claims 1 to 8, wherein the secondary battery serves as the power supply for the electrical equipment.

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