Secondary batteries and electrical equipment

Abstract

This application discloses a secondary battery and its electrical device. The secondary battery contains an electrolyte, which includes a first additive with a nitrogen-phosphorus structure and polymerizable acrylates linked to this structure. Under overheating conditions, the additive rapidly solidifies the liquid electrolyte through the action of a thermal initiator, forming a highly cross-linked solid polymer. If the solidification speed is insufficient and combustion occurs, the flame-retardant components, such as the nitrogen-phosphorus structure in the molecule, can further retard the flame. Therefore, the secondary battery and its electrical device of this application have good safety features.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] In recent years, spontaneous combustion accidents caused by secondary batteries have occurred frequently. Adding flame-retardant additives to the electrolyte is one effective method, but traditional flame-retardant additives not only have poor effects on improving the safety performance of secondary batteries, but also participate in film formation to a certain extent, usually forming a high-resistivity interfacial film, leading to the deterioration of the performance of secondary batteries.

[0003] Therefore, this application is submitted. Summary of the Invention

[0004] This application provides a secondary battery and electrical device that can effectively improve the flame retardant effect of existing secondary batteries and reduce the impedance of the interface film, thereby enhancing the safety performance of the secondary battery.

[0005] A first aspect of this application provides a secondary battery, including an electrolyte, the electrolyte comprising a first additive, the first additive comprising a compound having the structure shown in Formula I:

[0006]

[0007] R1, R2, R3, and R4 each independently contain at least one of C3-C10 unsaturated cycloalkanes, C1-C20 alkyl groups, C1-C20 alkenyl groups, or C1-C20 alkynyl groups; R1' and R2' each independently contain substituted or unsubstituted C1-C10 unsaturated hydrocarbon groups, wherein the substituted groups contain C1-C5 haloalkoxy groups.

[0008] Optionally, the halogen in the haloalkoxy group is F.

[0009] Optionally, the first additive comprises a compound with the following structure:

[0010]

[0011] Optionally, the first additive comprises at least one of the compounds having the following structure:

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] Optionally, the electrolyte further includes a second additive, which includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl peroxide, and methyl ethyl ketone peroxide.

[0019] Optionally, the mass ratio of the second additive to the first additive is 1:(50-500).

[0020] Optionally, the mass of the first additive is 0.5% to 5% of the total mass of the electrolyte.

[0021] Optionally, the electrolyte further includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxaloyl)borate (LiBOB), lithium difluorooxaloylborate (LiDFOB), lithium difluorodioxaloyl phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0022] Optionally, the electrolyte further includes an organic solvent, which includes chain esters and cyclic esters, wherein the mass ratio of the chain esters to the cyclic esters is (6-9):(3-6).

[0023] Optionally, the chain ester includes one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB); the cyclic ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), and γ-butyrolactone (γ-GBL).

[0024] A second aspect of this application provides an electrical device including a secondary battery as described above.

[0025] The superior effect of this application is that it provides a secondary battery and electrical equipment. The flame-retardant components such as the nitrogen-phosphorus structure in the first additive molecule have excellent flame-retardant effect, which further improves the safety performance of the secondary battery and creates sufficient escape time for passengers. In addition, the first additive can effectively reduce the impedance of the interface film, thereby reducing the impedance of the secondary battery and effectively improving the cycle life of the secondary battery. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a temperature-voltage relationship diagram between the secondary battery provided in the embodiments of this application and the secondary battery provided in the comparative example. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0029] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of".

[0030] In this specification, the range of values ​​indicated by “~” represents the range containing the minimum and maximum values ​​recorded before and after “~”, respectively.

[0031] This application provides a secondary battery, the secondary battery comprising an electrolyte, the electrolyte comprising a first additive, the first additive comprising a compound having the structure shown in Formula I:

[0032]

[0033] R1, R2, R3, and R4 each independently contain at least one of C3-C10 unsaturated cycloalkanes, C1-C20 alkyl groups, C1-C20 alkenyl groups, or C1-C20 alkynyl groups; R1' and R2' each independently contain substituted or unsubstituted C1-C10 unsaturated hydrocarbon groups, wherein the substituted groups contain C1-C5 haloalkoxy groups.

[0034] Preferably, the halogen in the haloalkoxy group is F.

[0035] In some embodiments of this application, R1, R2, R3, and R4 each independently contain at least one of the following groups:

[0036]

[0037]

[0038] In some embodiments of this application, R1' and R2' each independently comprise at least one of the following groups:

[0039]

[0040] In some embodiments of this application, the first additive is selected from compounds with the following structures:

[0041]

[0042] In some embodiments of this application, the first additive comprises at least one of compounds having the following structure:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] The flame-retardant components in the first additive, such as the nitrogen-phosphorus (NP) structure, produce nitrogen-containing, flame-retardant gases (such as nitrogen N2) and a heat-resistant glassy carbon layer during combustion, further enhancing the flame retardancy and improving the safety performance of the secondary battery.

[0050] Furthermore, the first additive contains some CF bonds in its molecular structure, which facilitates the formation of an SEI film rich in LiF and Li2O on the negative electrode surface, and provides ion channels to enhance Li...+ The transmission capacity is improved, the SEI film impedance is reduced, thus forming a more stable SEI film, which inhibits further consumption of flame retardants, while reducing the secondary battery impedance and improving the cycle life of the secondary battery.

[0051] In some embodiments of this application, the electrolyte further includes a second additive, which includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl peroxide, and methyl ethyl ketone peroxide. Specifically, the second additive is a thermal initiator. Since the first additive is formed by attaching polymerizable acrylates to a nitrogen-phosphorus (NP) structure, it can be thermally initiated by the second additive under overheating conditions (approximately 100°C). That is, the second additive can rapidly decompose to generate free radicals under overheating conditions (approximately 100°C) of the secondary battery, thereby initiating the polymerization of the first additive. This causes the liquid electrolyte in the secondary battery to solidify, protectively shutting down the secondary battery, preventing internal short circuits and thermal runaway, and ensuring the safety of the secondary battery under overheating conditions.

[0052] The solidification of the liquid electrolyte is achieved by the rapid polymerization of the first additive under the catalysis of the second additive. The reaction formula of the first additive initiated by the second additive under superheated conditions is as follows:

[0053]

[0054] As can be seen from the above reaction formula, under overheating conditions, the second additive causes the acrylate grafted onto the nitrogen-phosphorus structure in the first additive to polymerize into a highly cross-linked solid polymer, thereby solidifying the liquid electrolyte.

[0055] The secondary battery provided by this invention, if the solidification rate of the liquid electrolyte is insufficient and combustion occurs, can be further enhanced by the flame-retardant properties of the nitrogen and phosphorus components in the first additive, thus improving its safety performance. By formulating the second additive catalyst and the multifunctional first additive into the electrolyte, when the secondary battery is in normal operating condition at a normal temperature (e.g., <60°C), the polymerization of the first additive will not be triggered because the second additive has not decomposed. However, when the secondary battery overheats (to approximately 100°C) due to unforeseen reasons (e.g., battery collision, overheating of the operating environment), the second additive decomposes under heat, and the first additive polymerizes and cross-links, causing the liquid electrolyte to solidify and the secondary battery to automatically shut down.

[0056] Compared with existing thermal shutdown methods for secondary batteries (such as membrane pore closure or PTC), the present invention directly solidifies the liquid electrolyte, which greatly restricts its fluidity and fundamentally reduces the continuation of side reactions in the secondary battery.

[0057] In some embodiments of this application, the mass ratio of the second additive to the first additive is 1:(50-500). The mass ratio of the second additive to the first additive needs to be controlled within the range specified in this application. The second additive acts as a catalyst for the first additive in the electrolyte. If the content of the second additive is too high, it will result in a waste of resources; if the content is too low, it will not be able to effectively catalyze the first additive. Therefore, it is necessary to control the mass ratio of the second additive to the first additive within a reasonable range.

[0058] In some embodiments of this application, the mass of the first additive is 0.5% to 5% of the total mass of the electrolyte, preferably 1% to 3%. Specifically, the mass of the first additive can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the total mass of the electrolyte, or any two of these values. Too little first additive may slow down the polymerization reaction, while too much may increase the viscosity of the system. Moreover, excessive first additive does not significantly improve the actual flame retardant performance but instead increases the cell impedance, affecting the performance of the secondary battery. When the mass content of the first additive in the electrolyte is within the above-mentioned range, the polymerization reaction rate can be guaranteed, the flame retardant effect can be ensured, and the viscosity of the electrolyte will not be increased.

[0059] In some embodiments of this application, the electrolyte is at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxaloyl)borate (LiBOB), lithium difluorooxaloylborate (LiDFOB), lithium difluorodioxaloyl phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0060] In some embodiments of this application, the mass of the lithium salt is 12% to 15% of the total mass of the electrolyte, preferably 12% to 13%. Specifically, the mass of the lithium salt can be 8%, 9%, 10%, 11%, 12%, 13% of the total mass of the electrolyte, or any two of these values.

[0061] In some embodiments of this application, the organic solvent includes linear esters and cyclic esters, with a mass ratio of linear esters to cyclic esters of (6-9):(3-6), preferably (6-7):(3-4). When selecting an organic solvent, it is necessary to consider whether the selected organic solvent meets requirements such as high dielectric constant, low viscosity, low melting point, high boiling point, and low cost. Linear esters have low viscosity and good electrochemical stability, which can improve the low-temperature performance of the electrolyte. Although linear esters have the above advantages as electrolytes, the performance of a single organic solvent is no longer sufficient to meet market demands, therefore, it is necessary to use them in combination with other organic solvents. Cyclic esters have high dielectric constant and high ionic conductivity, enabling the formation of a stable SEI film on the negative electrode surface, but their viscosity is relatively high. Therefore, using a mixture of linear and cyclic esters as organic solvents for lithium-ion battery electrolytes allows the linear and cyclic esters to fully exert their synergistic effect, jointly improving the performance of the electrolyte.

[0062] In some embodiments of this application, the chain esters include one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB); the cyclic esters include at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), and γ-butyrolactone (γ-GBL).

[0063] In some embodiments of this application, the secondary battery further includes a positive electrode active material, wherein the positive electrode active material is selected from Li a Ni x Co y Mn 1-x-y One of O2, LiCoO2, and LiFePO4, where 0.9 ≤ a ≤ 1.1, 0 <x<1,0<y<1,x+y<1。

[0064] In some embodiments of this application, the positive electrode active material contains doping elements and / or coating elements. There are no special requirements for the doping elements and / or coating elements, as long as they can make the positive electrode active material more stable.

[0065] In addition, positive electrode active materials also include positive electrode conductive agents and positive electrode binders.

[0066] The preparation method of the secondary battery provided in this application is described below with reference to specific embodiments:

[0067] The preparation method of B1 is as follows:

[0068] 4.46 g of 4-methoxyphenyl phosphate dichloro, 2.76 g of catalyst K2CO3 and 100 ml of DMF (dimethylformamide) were placed in a 250 ml three-necked flask. 0.86 g of piperazine was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was reacted at room temperature for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=1) to obtain intermediate product A2.

[0069] In a 250 ml round-bottom flask, the aforementioned intermediate A2, 100 ml of DMF, and 2.76 g of K2CO3 were added sequentially. 2.1 g of diethanolamine was then slowly injected using a syringe. After the addition was complete, the reaction was allowed to proceed at room temperature, with TLC monitoring until the reaction was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.5) to obtain intermediate A3.

[0070] In a 250 ml round-bottom flask, the above intermediate product A3, 100 ml dichloromethane, and 5.52 g K2CO3 were added sequentially. The system was placed in an ice bath, and 3.6 g acetyl chloride was slowly injected dropwise using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until it was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain intermediate product A4.

[0071] Under an argon atmosphere, the aforementioned intermediate A4, 5.15 g AgOTf, 5.3 g Selectfluor reagent, 1.75 g KF, 1.94 g 2-fluoropyridine, 2.85 g TMSCF3, and 50 mL ethyl acetate were added sequentially to a 250 mL round-bottom flask. The mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 6) to give 1.75 g of the final product B1 (yield 19%).

[0072] The synthetic route of B1 is shown in the figure below:

[0073]

[0074] The preparation method of B2 is as follows:

[0075] 4.46 g of 4-methoxyphenyl phosphate dichloro, 2.76 g of catalyst K2CO3 and 100 ml of DMF (dimethylformamide) were placed in a 250 ml three-necked flask. 0.86 g of piperazine was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was reacted at room temperature for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=1) to obtain intermediate product A2.

[0076] In a 250 ml round-bottom flask, the above intermediate product A2, 100 ml of DMF, and 2.76 g of K2CO3 were added sequentially. 4.2 g of 4,4-iminodiphenol was slowly injected using a syringe. After the addition was complete, the reaction was allowed to proceed at room temperature, with TLC monitoring until the reaction was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.3) to obtain intermediate product A5.

[0077] In a 250 ml round-bottom flask, the above intermediate product A5, 100 ml of dichloromethane, and 5.52 g of K2CO3 were added sequentially. The system was placed in an ice bath, and 3.6 g of acetyl chloride was slowly injected dropwise using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until the reaction was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain intermediate product A6.

[0078] Under an argon atmosphere, the aforementioned intermediate A6, 5.15 g of AgOTf, 5.3 g of Selectfluor reagent, 1.75 g of KF, 1.94 g of 2-fluoropyridine, 2.85 g of TMSCF3, and 50 mL of ethyl acetate were added sequentially to a 250 mL round-bottom flask. The mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 6) to give 1.56 g of the final product B2 (yield 14%).

[0079] The synthetic route for B2 is shown in the figure below:

[0080]

[0081] (1) Preparation of electrolyte

[0082] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), organic solvents are mixed evenly in proportion to obtain a mixed solvent. Then, lithium salt and additives are added and stirred evenly to obtain an electrolyte.

[0083] (2) Preparation of positive electrode sheet

[0084] The positive electrode active material Li(Ni) 0.8 Mn 0.1 Co 0.1 O2 (NMC811), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NMC811:Super P:PVDF = 94:3:3, 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.

[0085] (3) Preparation of negative electrode sheet

[0086] The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:SuperP:SBR = 94:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0087] (4) Making a secondary battery

[0088] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to complete the preparation of the secondary battery.

[0089] The examples and comparative examples respectively provide an electrolyte and a lithium-ion battery containing the electrolyte. The composition of the electrolyte is shown in Table 1.

[0090] Self-extinguishing time test:

[0091] Take out the electrolyte from the glove box, immerse a glass cotton ball weighing 0.01g and 3mm in diameter in the flame-retardant electrolyte, take it out and roll it on filter paper to remove the electrolyte on the surface, control the weight of the cotton ball to 0.1g, ignite it with an open flame, and test the extinguishing time of the glass cotton ball. Refer to Table 2 for the burning condition of the glass cotton ball.

[0092] Loop testing:

[0093] 25℃ Cyclic Test: At 25℃, the battery was left to stand for 30 minutes, then discharged at a constant current of 1C to the lower voltage limit, and left to stand for 10 minutes; it was then charged at a constant current and constant voltage of 1C to the fully charged state and the charging capacity was recorded, and left to stand for 10 minutes; then it was discharged at a constant current of 1C to the lower voltage limit and the discharge capacity C0 was recorded; then the lithium-ion battery was repeatedly charged and discharged at a current of 1C, and the discharge capacity of the Nth cycle was recorded as CN;

[0094] The capacity retention rate in the Nth cycle = CN / C0 × 100%.

[0095] DCR test:

[0096] 25℃ DC discharge resistance test: At 25℃, the battery was left to stand for 30 minutes, then charged to full capacity with a constant current and constant voltage of 1C, and left to stand for 5 minutes. Then, it was discharged with a constant current of 1C to 2.8V, and the actual discharge capacity C0 was recorded. Then, the battery was charged with a 1C current for 30 minutes to adjust the battery's state of charge to 50% SOC. The lithium-ion battery with the adjusted state of charge was transferred to a constant temperature environment of 25℃ and left to stand for more than 2 hours to make the internal and external temperatures of the battery uniform. Finally, the battery was discharged with a constant current of 0.3C for 10 seconds, and the voltage difference before and after discharge was recorded. The DC discharge resistance (DCR) of the battery at room temperature was calculated.

[0097] The performance of the secondary batteries in the examples and comparative examples is shown in Table 2.

[0098] Table 1. List of components of the electrolytes in the examples and comparative examples.

[0099]

[0100]

[0101] Note: The ratios of organic solvents in the table represent mass ratios, and the amount of each substance refers to its content in the total mass of the electrolyte.

[0102] Table 2 is a list of performance tests for the example and comparative batteries.

[0103]

[0104]

[0105] Analysis of experimental results:

[0106] Figure 1 It is the secondary battery prepared in Example 4 (i.e. Figure 1 A comparative experiment was conducted between the safety battery shown in Example 2 and the conventional battery used in Comparative Example 2. Figure 1 The display shows a comparison of the open-circuit voltage (OCV) of a conventional battery and a safety battery at high temperatures. This demonstrates that because the second additive can solidify the liquid electrolyte under overheating conditions, generating a highly cross-linked thermosetting material (with no melting point and maintaining dimensional stability at high temperatures), the safety battery maintains a stable open-circuit voltage even at high temperatures, without experiencing internal short circuits between the positive and negative electrodes. In contrast, the PE separator of the conventional battery provided in Comparative Example 2 melts at around 160°C, rapidly shrinks in size, and loses its barrier effect on the positive and negative electrodes, causing a short circuit between them.

[0107] Meanwhile, we also tested the flame-retardant properties of the nitrogen-phosphorus structure in the additive. In the examples, combustion experiments were conducted again after the electrolyte was thermally cured. Comparison of Examples 1-7 and Comparative Example 2 shows that adding B1 and perazobisisobutyronitrile (PABN) after curing effectively improves the flame-retardant properties. With increasing B1 content, the extinguishing time is significantly shortened; when the content exceeds 3%, it is essentially non-ignitable. This indicates that the nitrogen-phosphorus structure is effective in flame retardancy. During combustion, the nitrogen-phosphorus structure produces nitrogen-containing flammable gas (N2) and a heat-resistant glassy char layer, effectively isolating oxygen and increasing the combustion temperature, thus enhancing its flame-retardant properties. Although adding excessive B1 can effectively improve its flame-retardant properties, excessive additives can significantly increase the viscosity of the electrolyte, affecting battery performance. Therefore, multiple experiments have shown that the content of the first additive needs to be controlled within a suitable range.

[0108] As can be seen from the comparison between Example 4 and Example 12, the curing rate slows down and the final curing is incomplete when the content of the second additive is reduced, resulting in a poorer flame retardant effect. Therefore, the mass ratio of the second additive to the first additive needs to be controlled at 1:(50-500) in this application.

[0109] A comparison of Example 4 and Comparative Example 1 shows that the cured nitrogen-phosphorus structure has a better flame retardant effect than the commercial flame retardant additive ethoxy(pentafluoro)cyclotriphosphazene, indicating that the cured nitrogen-phosphorus structure can effectively improve its heat resistance temperature and shorten the extinguishing time.

[0110] Examples 1-6 and Comparative Example 2 show that without the first additive, the initial DCR at room temperature and the DCR growth after 200 cycles at 60°C are both significant. After adding the first additive, the initial DCR and DCR growth are significantly improved, and the capacity retention rate at room temperature increases. However, as the concentration of the first additive increases to above 3%, the DCR growth begins to deteriorate, and the capacity retention rate decreases. This indicates that a small amount of the first additive can improve the film-forming performance of the battery, resulting in good film stability, thus reducing the DCR and DCR growth rate. However, excessive additives lead to an overly thick film, ultimately causing a decrease in DCR growth and cycle performance.

[0111] In summary, the electrolyte of this application can improve the safety performance of lithium-ion batteries, and the specific usage can be adjusted according to the application scenario.

[0112] The above provides a detailed description of a secondary battery and electrical device provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A secondary battery comprising an electrolyte, the electrolyte comprising a first additive, the first additive comprising a compound having a structure of Formula I: wherein: R 1, R 2, R 3, R 4 each independently comprises at least one of C 3-C 10 unsaturated cycloalkane, C 1-C 20 alkyl, C 1-C 20 alkenyl, or C 1-C 20 alkynyl; R 1' and R 2' each independently comprises a substituted or unsubstituted C 1-C 10 unsaturated alkyl, the substituted group comprising C 1-C 5 haloalkoxy. Formula I; wherein The first additive comprises a compound having a structure of:

2. The secondary battery according to claim 1, characterized by 3.The secondary battery of claim 2, the first additive comprising at least one of a compound having a structure of: Formula II. The electrolyte further comprises a second additive, the second additive comprising one or more of azobisdimethylisobutyronitrile, azobisdimethylisohexylnitrile, benzoyl peroxide, t-butyl peroxybenzoate, and methyl ethyl ketone peroxide. （B1）； （B2）； （B3）； （B4）； （B5）； （B6）。 4. The secondary battery according to claim 1, wherein A mass ratio of the second additive to the first additive is 1:(50-500).

5. The secondary battery according to claim 4, characterized by A mass of the first additive is 0.5%-5% of a total mass of the electrolyte.

6. The secondary battery according to claim 1, wherein The electrolyte further comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorodioxalate phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

7. The secondary battery according to claim 1, wherein The electrolyte further comprises an organic solvent, the organic solvent comprising a chain ester and a cyclic ester, a mass ratio of the chain ester to the cyclic ester being (6-9):(3-6).

8. The secondary battery according to claim 1, wherein The chain ester comprises one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate; the cyclic ester comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone.

9. The secondary battery according to claim 8, wherein A secondary battery as claimed in any one of claims 1-9.

10. An electric device, characterized by ​

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