Electrolyte, secondary battery, and electric device

Abstract

The application discloses an electrolyte, a secondary battery and a power utilization device, and belongs to the technical field of secondary batteries. The non-aqueous solvent contained in the electrolyte can effectively separate lithium salt in the electrolyte under low-temperature conditions based on the diamide group contained in the special structure of the non-aqueous solvent, is beneficial to forming a solvation structure, promotes the transmission of lithium ions, and improves the ionic conductivity in the electrolyte; meanwhile, the non-aqueous solvent has a high reduction potential and is not decomposed in the charging and discharging process of the battery, so that the lithium salt can be stably dissolved, and the impedance of the battery in the charging and discharging process is reduced; the additive with a low reduction potential preferentially reacts with the non-aqueous solvent with a high reduction potential, a stable SEI layer is formed on the negative electrode surface, the decomposition of the non-aqueous solvent is reduced, in addition, a small amount of decomposed non-aqueous solvent and decomposed additive form a stable SEI film, a uniform and stable protective layer is formed, and the capacity retention rate of the battery in the cycle process is improved.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, aerospace, and outdoor equipment due to their high energy density and long cycle life. However, lithium batteries exhibit problems such as decreased charge / discharge capacity, increased internal resistance, and shortened battery life in low-temperature environments below -20°C, limiting their use in some aerospace, military, and polar exploration fields, as well as in high-altitude and high-latitude regions.

[0003] At low temperatures, the performance of lithium batteries deteriorates significantly, primarily in the following ways: First, the viscosity of the electrolyte increases as the temperature decreases, reducing ionic conductivity and slowing the diffusion rate of lithium ions. Second, the solid electrolyte interphase (SEI) film on the negative electrode surface cannot be effectively formed or stabilized at low temperatures, hindering the transport of lithium ions between the electrolyte and the negative electrode. Third, lithium deposition caused by excessive polarization may also pose safety hazards, such as the formation of lithium dendrites, increasing the risk of short circuits. Fourth, low temperatures also exacerbate the decomposition of lithium salts (such as LiPF6), leading to instability in the electrolyte composition.

[0004] Therefore, how to improve the performance of lithium batteries in low-temperature environments below -20°C has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide an electrolyte, a secondary battery and an electrical device. The electrolyte can effectively separate lithium salts in the electrolyte under low temperature conditions, which is conducive to the formation of a solvation structure, promotes the transport of lithium ions, improves the ionic conductivity in the electrolyte, and forms a stable SEI film, thereby improving the performance of the battery under low temperature conditions.

[0006] To achieve the above objectives, the technical solution adopted in this disclosure is as follows: In the first aspect of this application, an electrolyte is provided, comprising a non-aqueous solvent, a lithium salt, and an additive, wherein the non-aqueous solvent comprises at least one compound with the structure shown in Formula I:

[0007]

[0008] R1 and R2 are each independently selected from at least one of cyano, sulfonic acid, C1-C5 perfluoroalkyl, imidazole, alkynyl, alkenyl, ether, carboxyl, isocyanate, and ester.

[0009] As a preferred embodiment of this application, the non-aqueous solvent includes at least one of the compounds with the following structures:

[0010]

[0011] As a preferred embodiment of this application, the mass percentage of the compound with the structure shown in Formula I is 10-40% based on the total mass of the electrolyte.

[0012] As a preferred embodiment of this application, the mass ratio of the compound with the structure shown in Formula I to the additive is 3-14.

[0013] As a preferred embodiment of this application, the additive is at least one selected from fluoroethylene carbonate, ethylene glycol dimethyl ether, trifluorophosphate, vinylene carbonate, 1,3-propane sulpholol, and methyl methacrylate.

[0014] As a preferred embodiment of this application, the non-aqueous solvent further includes an ester solvent, and the mass ratio of the compound with the structure shown in Formula I to the ester solvent is 0.1-1.

[0015] As a preferred embodiment of this application, the ester solvent is a carbonate solvent, which includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, and methyl butyl carbonate.

[0016] In a preferred embodiment of this application, the mass ratio of the compound with the structure shown in Formula I to the lithium salt is 0.6-3.

[0017] In a second aspect, this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte.

[0018] In a third aspect, this application provides an electrical device including the aforementioned secondary battery.

[0019] The beneficial effects of this application are as follows: The non-aqueous solvent of Formula I contains a diamide group in its molecular structure. The diamide group has high polarity, which enables the non-aqueous solvent of Formula I to effectively separate lithium salts in the electrolyte under low temperature conditions. This is beneficial for forming a solvation structure, promoting lithium ion transport, and improving the ionic conductivity in the electrolyte. Secondly, the non-aqueous solvent of Formula I has a relatively high reduction potential, which ensures that it is not decomposed during the charging and discharging process of the battery, thereby stabilizing the dissolution of lithium salts and reducing the impedance of the battery during charging and discharging. Thirdly, the additive has a low reduction potential. During charging and discharging, it preferentially reduces the non-aqueous solvent of Formula I to form a stable SEI layer on the negative electrode surface, reducing the decomposition of the non-aqueous solvent of Formula I. At the same time, a small amount of decomposed non-aqueous solvent of Formula I forms a stable SEI film with the decomposed additive, forming a uniform and stable protective layer and improving the capacity retention rate of the battery during cycling. Attached Figure Description

[0020] Figure 1 The image shows the Raman spectrum of the compound with structural formula A1.

[0021] Figure 2 The image shows the Raman spectrum of the compound with structural formula A2.

[0022] Figure 3 The image shows the Raman spectrum of the compound with structural formula A3.

[0023] Figure 4 The image shows the Raman spectrum of the compound with structural formula A4.

[0024] Figure 5 The Raman spectrum of the compound with structural formula A5;

[0025] Figure 6 The image shows the Raman spectrum of the compound with structural formula A6.

[0026] Figure 7 The image shows the Raman spectrum of the compound with structural formula A7.

[0027] Figure 8 The image shows the Raman spectrum of the compound with structural formula A8.

[0028] Figure 9 The Raman spectrum of the compound with structural formula A9 is shown below.

[0029] Figure 10 This is the Raman spectrum of the compound with structural formula A10. Detailed Implementation

[0030] To facilitate understanding of this disclosure, a more complete description will be provided below. However, this disclosure may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0031] As used in this article:

[0032] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0033] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0034] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0035] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0036] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0037] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0038] To address the issue of significant performance degradation of lithium batteries in low-temperature environments below -20°C in existing technologies.

[0039] This application provides an electrolyte comprising a non-aqueous solvent, a lithium salt, and an additive, wherein the non-aqueous solvent comprises at least one compound with the structure shown in Formula I:

[0040]

[0041] R1 and R2 are each independently selected from at least one of cyano, sulfonic acid, C1-C5 perfluoroalkyl, imidazole, alkynyl, alkenyl, ether, carboxyl, isocyanate, and ester.

[0042] The non-aqueous solvent of Formula I in this application contains a diamide group in its molecular structure. The high polarity of the diamide group enables the non-aqueous solvent of Formula I to effectively separate lithium salts in the electrolyte under low-temperature conditions, which is conducive to the formation of a solvation structure, promotes lithium ion transport, and improves the ionic conductivity in the electrolyte. Secondly, the non-aqueous solvent of Formula I has a relatively high reduction potential, which ensures that it is not decomposed during the charging and discharging process of the battery, thereby stabilizing the dissolution of lithium salts and reducing the impedance of the battery during charging and discharging. Thirdly, the additive has a low reduction potential. During charging and discharging, it preferentially reduces the non-aqueous solvent of Formula I to form a stable SEI layer on the negative electrode surface, reducing the decomposition of the non-aqueous solvent of Formula I. At the same time, a small amount of decomposed non-aqueous solvent of Formula I forms a stable SEI film with the decomposed additive, forming a uniform and stable protective layer and improving the capacity retention rate of the battery during cycling.

[0043] An exemplary method for preparing a compound with the structure shown in Formula I includes the following steps:

[0044] In the presence of a first catalyst, oxalamide and a compound containing an R1 functional group are subjected to a first reaction to obtain a first compound substituted with an R1 functional group.

[0045] The first compound, which is substituted with the R1 functional group, is reacted with the compound containing the R2 functional group in a second reaction. After neutralization with a pH adjuster and filtration, the compound with the structure shown in Formula I is obtained.

[0046] For example, solvents include dichloromethane, dichloroethane, and THF, and there is no particular limitation on the amount of solvent added.

[0047] For example, the molar ratio of oxalamide to the compound containing the R1 functional group is 1:1-1.1.

[0048] For example, the molar ratio of the first compound substituted with the R1 functional group to the compound containing the R2 functional group is 1:1.5-2.

[0049] For example, the first catalyst is tetrabutylammonium bromide (TBAB);

[0050] For example, the temperature of the first reaction is 20-30°C.

[0051] For example, the temperature of the second reaction is not specifically limited, but is selected according to the different compounds containing the R2 functional group. For example, when the R2 functional group is a carboxyl group, a sulfonic acid group, or an acyl group, the reaction temperature is 0-5℃, and when the R2 functional group is a cyano group, the reaction temperature is 20-30℃.

[0052] For example, the raw materials for the second reaction may also include an activator or a second catalyst. The type of activator or catalyst is not specifically limited and is selected according to the functional group of R2. For example, when the functional group of R2 is a carboxyl or sulfonic acid group, the activator is thionyl chloride; for example, when the functional group of R2 is an alkenyl or phenyl group, the second catalyst is a basic catalyst such as potassium carbonate.

[0053] For example, the reaction equation for the compound with the structure shown in Formula I is as follows:

[0054]

[0055] Wherein, X1 is a compound containing the R1 functional group, and X2 is a compound containing the R2 functional group.

[0056] In one embodiment, the compound containing the R1 functional group includes at least one of pentafluoroethyl iodine, pyrazole, acetic acid, hexafluoroethylene, ethylene oxide, bromobenzene, bromomethane, and bromoethane.

[0057] In one embodiment, the compound containing the R2 functional group includes at least one of chlorosulfonic acid, sodium cyanide, methanol, bromobenzene, oxaloyl chloride, formyl chloride, acetyl chloride, and vinyl bromide.

[0058] In one embodiment, the non-aqueous solvent comprises at least one of compounds with the following structures:

[0059]

[0060] When a compound with the above structure is selected as a non-aqueous solvent, the resulting electrolyte has better performance due to the further optimization of the functional groups contained in the structure, and the product can achieve higher low-temperature performance when applied to secondary batteries.

[0061] Specifically, the non-aqueous solvents A1, A4, A5, and A10 all possess relatively long chain structures. At low temperatures, these chain structures can alter the molecular structure and interatomic interactions, which helps improve the fluidity of the electrolyte at low temperatures, ensuring sufficient migration ability for lithium ions. The non-aqueous solvents A7 and A9 have shorter chains, and their effect on improving lithium-ion diffusion at low temperatures is slightly less than that of A1, A4, A5, and A10.

[0062] The fluorine-containing functional groups and sulfate ester functional groups in the compound with the structure shown in Formula I can reduce the freezing point and viscosity of the electrolyte, thereby maintaining the fluidity of the electrolyte under low temperature conditions and ensuring good migration of lithium ions at low temperatures.

[0063] The ether group in the compound with the structure shown in Formula I can reduce the viscosity of the electrolyte on the one hand, and on the other hand, its polarity increases the solubility of lithium salt in the electrolyte, which helps to improve the separation ability between lithium ions and anions and improve the ionic conductivity of lithium ions.

[0064] The unsaturated bonds in the compound with the structure shown in Formula I reduce the molecular rotational freedom to some extent, which will affect the viscosity of the electrolyte. However, it helps to cause cross-linking reactions, forming a denser SEI film on the negative electrode surface and improving the overall stability of the battery.

[0065] The non-aqueous solvents A2, A3, and A6 contain cyclic structures, which affect the viscosity of the electrolyte to some extent.

[0066] In one embodiment, the mass percentage of the compound with the structure shown in Formula I is 10-40% based on the total mass of the electrolyte, for example, but not limited to 10%, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%.

[0067] In one embodiment, based on the total mass of the electrolyte, the mass percentage of the compound with the structure shown in Formula I is 15-40%, for example, but not limited to 15%, 15.5%, 17%, 17.5%, 20%, 23%, 25%, 28%, 30%, 35.5%, and 40%. The compound with the structure shown in Formula I has high polarity, which enhances the solubility of the electrolyte at low temperatures, thereby promoting lithium-ion transport efficiency. If the content of the compound with the structure shown in Formula I is too high, it will lead to an excessively thick or uneven SEI film, which not only reduces the stability of the negative electrode but also increases the difficulty of lithium-ion passage, resulting in a decrease in the low-temperature performance of the secondary battery.

[0068] In one embodiment, the mass percentage of the compound with the structure shown in Formula I is 15-30% based on the total mass of the electrolyte, for example, but not limited to 15%, 15.5%, 17%, 17.5%, 20%, 23%, 25%, 28%, and 30%.

[0069] In one embodiment, the mass ratio of the compound with the structure shown in Formula I to the additive is 3-14, for example, but not limited to 3, 3.33, 4, 5, 5.5, 6, 6.67, 8, 10, 12, 13.33, 14.

[0070] In one embodiment, the additive is at least one selected from fluoroethylene carbonate (FEC), dimethyl glycol ether (DME), trifluorophosphate (TFP), vinylene carbonate (VC), 1,3-propane sulpholol (PS), and methyl methacrylate (MMA).

[0071] Preferably, the additive is fluoroethylene carbonate.

[0072] Under low-temperature conditions, fluoroethylene carbonate facilitates the formation of a stable SEI film on the negative electrode, while the compound with the structure shown in Formula I improves the fluidity of the electrolyte at low temperatures, ensuring lithium-ion transport efficiency. The two complement each other, increasing battery capacity retention while reducing battery impedance. However, if the ratio between the two is excessive, it will lead to uneven SEI film formation on the negative electrode surface, thereby reducing the capacity retention of the secondary battery.

[0073] For example, in this application, the additive accounts for 0.1-6% of the total mass of the electrolyte, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0074] Under low-temperature conditions, fluoroethylene carbonate effectively helps the electrolyte form a stable SEI film on the negative electrode surface and prevents the decomposition of EC. However, if the mass percentage of fluoroethylene carbonate is too high, it will first lead to an excessively thick SEI, thus increasing the difficulty for lithium ions to enter the negative electrode. In addition, excessive fluoroethylene carbonate will also lead to the generation of more HF in the electrolyte, thereby corroding the positive electrode.

[0075] In one embodiment, the non-aqueous solvent further includes an ester solvent, wherein the mass ratio of the compound with the structure shown in Formula I to the ester solvent is 0.1-1, for example, but not limited to 0.1, 0.14, 0.22, 0.32, 0.34, 0.37, 0.4, 0.57, 0.94, or 1.

[0076] Taking a mixture of ethylene carbonate, propylene carbonate and diethyl carbonate as an example, the polarity of the diamide group and the high dielectric constant of EC in the compound with the structure shown in Formula I can effectively dissolve lithium salt and separate lithium ions and anions, effectively improving the solubility of lithium salt in the electrolyte; the mixing of PC and DEC helps lithium ions diffuse and form an SEI film under low temperature conditions, thereby reducing battery impedance and improving battery capacity retention.

[0077] In one embodiment, the non-aqueous solvent further includes an ester solvent, wherein the mass ratio of the compound with the structure shown in Formula I to the ester solvent is 0.15-0.6, for example, but not limited to 0.15, 0.22, 0.32, 0.34, 0.37, 0.4, 0.57, or 0.6.

[0078] In one embodiment, the ester solvent is a carbonate solvent, which includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), methyl propyl carbonate (MPC), methyl ethyl carbonate (MEC), and methyl butyl carbonate (MBIC).

[0079] Preferably, the carbonate solvent is a mixture of ethylene carbonate, propylene carbonate and diethyl carbonate, wherein the mass ratio of ethylene carbonate, propylene carbonate and diethyl carbonate is 1:1:1 to 1:1:3.

[0080] Diethyl carbonate has a low viscosity, which is beneficial for improving the transport capacity of lithium ions in the electrolyte. However, due to its low dielectric constant, further increasing the diethyl carbonate content will reduce the electrolyte's solubility, making it difficult to effectively separate lithium ions and anions in the lithium salt, thus reducing the lithium ion transport capacity. Furthermore, excessive ethylene carbonate leads to an excessively low electrolyte viscosity, making it difficult for the SEI film to form, affecting the stability of the battery's negative electrode, and thus reducing capacity retention.

[0081] In one embodiment, the ester solvent content is greater than 30% based on the total mass of the electrolyte.

[0082] In one embodiment, the content of the fluoroethylene carbonate and the compound of formula I is greater than 12% based on the total mass of the electrolyte.

[0083] In one embodiment, the content of the fluoroethylene carbonate and the compound of formula I is less than 40% based on the total mass of the electrolyte.

[0084] In one embodiment, the content of the fluoroethylene carbonate and the compound A1 of formula I is greater than 10% based on the total mass of the electrolyte.

[0085] In one embodiment, the content of the fluoroethylene carbonate and the compound A1 of formula I is less than 45% based on the total mass of the electrolyte.

[0086] In one embodiment, the mass ratio of the compound with the structure shown in Formula I to the lithium salt is 0.6-3, for example, but not limited to 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, or 3.

[0087] Because the diamide group in the compound shown in Formula I has high polarity, it can effectively separate lithium ions and anions in the electrolyte, thus effectively improving the transport capacity of lithium ions in the electrolyte. However, excessive lithium salt can lead to the formation of a large number of ion pairs or ion clusters, which in turn hinders the transport of lithium ions.

[0088] In one embodiment, the lithium salt includes at least one of MClO4, MBF4, MPF6, MAsF6, MBOB, MFSI, MTFSI, MPF2O2, MCF3SO3, MCF3SO3, and MPF2(C2O4), wherein M is Li, Na, or K.

[0089] In one embodiment, the lithium salt includes at least one of LiPF6, LiPF2(C2O4), and LiFSI.

[0090] For example, in this application, the lithium salt accounts for 5-20% of the total mass of the electrolyte, such as 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0091] Too low a percentage of lithium salt by mass will reduce the number of lithium ions available for conduction in the electrolyte, resulting in very low conductivity. Conversely, too high a percentage of lithium salt by mass will increase the viscosity of the electrolyte and lead to the formation of excessive ion pairs or clusters, both of which reduce the transport capacity of lithium ions in the electrolyte. Only an appropriate amount of lithium salt is sufficient to ensure that the electrolyte can effectively function as a link in the battery charging and discharging process.

[0092] It should be noted that this application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing organic solvents, lithium salts, and additives evenly.

[0093] In one embodiment of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0094] For example, the positive electrode includes a positive electrode active material capable of extracting and inserting lithium ions, and the negative electrode includes a negative electrode active material capable of inserting and extracting lithium ions.

[0095] Specifically, the positive electrode active material is a lithium-containing composite oxide. Examples of lithium-containing composite oxides include LiMnO2, LiFeO2, LiMn2O4, Li2FeSiO4, LiNi5CO2Mn3O2, and Li... z Ni (1-x-y) Co x M y O2 (x, y, and z are values ​​satisfying 0.01≤x≤0.20, 0≤y≤0.20, and 0.97≤z≤1.20, and M represents at least one element selected from Mn, V, Mg, B, and Al), LiFePO4, and Li z CO (1-x) M x O2 (where x and z are values ​​satisfying 0 ≤ x ≤ 0.1 and 0.97 ≤ z ≤ 1.20, and M represents at least one element selected from the group consisting of Mn, V, Mg, B, and Al) is used. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0096] Specifically, the negative electrode active material can be selected from graphite-based materials, silicon-based materials, metal oxides, metal sulfides, and metallic materials. The graphite-based materials can be selected from at least one of artificial graphite, natural graphite, soft carbon, and hard carbon. The silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The metal oxides can be selected from at least one of tin oxide, zinc oxide, and vanadium dioxide. The metal sulfides can be selected from at least one of tin sulfide, molybdenum sulfide, and zinc sulfide. The alloy materials can be selected from at least one of tin, aluminum, gallium, germanium, lithium, and lithium-silicon alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0097] In the secondary battery mentioned in this application, the specific type of separator is not limited. It can be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and their multilayer composite films, but is not limited to these.

[0098] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0099] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0100] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0101] For example, in the secondary battery of this application, the charging cutoff voltage of the battery may be no less than 4.2V, that is, the battery can be used in a high voltage state of no less than 4.2V. Preferably, the battery can operate in the range of 4.2V-4.9V, and more preferably, the battery can operate in the range of 4.3V-4.8V.

[0102] According to one embodiment of this application, an electrical device is provided, including the aforementioned secondary battery.

[0103] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0104] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A1 is as follows:

[0105] S1: At room temperature, tetrabutylammonium bromide (TBAB) (1.0 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and pentafluoroethyl iodine (0.1 mol), and the mixture was stirred for 6 h to obtain a solution of the first compound.

[0106] S2: The solution of the first compound obtained in step S1 was cooled to 3°C, and chlorosulfonic acid (0.1 mol) and thionyl chloride (20 mL) were added. After stirring for 6 h, a solution of the second compound was obtained. Saturated sodium bicarbonate was added until the pH of the solution of the second compound was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A1. The Raman spectrum of the compound with structural formula A1 is as follows: Figure 1 As shown.

[0107] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A2 is as follows:

[0108] S1: At room temperature, tetrabutylammonium bromide (0.3 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and pyrazole (0.1 mol), and the mixture was stirred for 6 h to obtain a solution of the first compound.

[0109] S2: Add sodium cyanide (0.15 mol) to the first compound solution obtained in step S1, stir for 6 hours to obtain the second compound solution, add acetic acid until the pH of the second compound solution is 7, and then successively extract, wash, and recrystallize to obtain the compound with structural formula A2; the Raman spectrum of the compound with structural formula A2 is as follows. Figure 2 As shown.

[0110] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A4 is as follows:

[0111] S1: At room temperature, 20 mL of thionyl chloride was added to a mixed solution of 50 mL of dichloromethane containing 0.1 mol of oxalamide and 0.1 mol of acetic acid. After stirring for 12 h, a solution of the first compound was obtained.

[0112] S2: To the first compound solution obtained in step S1, methanol (0.1 mol), methyl chloride (0.1 mol), and hydrogen chloride were added. After stirring under reflux for 6 hours, a second compound solution was obtained. Saturated sodium bicarbonate was added until the pH of the second compound solution was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A4. The Raman spectrum of the compound with structural formula A4 is as follows: Figure 4 As shown.

[0113] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A5 is as follows:

[0114] S1: At room temperature, tetrabutylammonium bromide (TBAB) (1g) was added to a mixed solution of dichloromethane (50mL) containing oxalamide (0.1mol) and hexafluoroethylene (0.1mol), and the mixture was stirred for 6h to obtain a solution of the first compound.

[0115] S2: Add sodium cyanide (0.15 mol) to the first compound solution obtained in step S1, stir for 6 hours to obtain the second compound solution, add acetic acid until the pH of the second compound solution is 7, and then successively extract, wash, and recrystallize to obtain the compound with structural formula A5; the Raman spectrum of the compound with structural formula A5 is as follows. Figure 2 As shown.

[0116] In a specific embodiment of the present invention, the method for preparing the compound with structural formula A6 is as follows:

[0117] S1: At room temperature, tetrabutylammonium bromide (TBAB) (0.2 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and pyrazole (0.1 mol), and the mixture was stirred for 6 h to obtain a solution of the first compound.

[0118] S2: Bromobenzene (0.1 mol) and potassium carbonate (4.2 g) were added to the first compound solution obtained in step S1. After stirring and reacting under reflux for 8 hours, a second compound solution was obtained. Acetic acid was added until the pH of the second compound solution was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A6. The Raman spectrum of the compound with structural formula A6 is as follows: Figure 6 As shown.

[0119] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A7 is as follows:

[0120] S1: At room temperature, tetrabutylammonium bromide (TBAB) (0.3 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and ethylene oxide (0.1 mol), and the mixture was stirred for 12 h to obtain a solution of the first compound.

[0121] S2: The solution of the first compound obtained in step S1 was cooled to 3°C, and 0.1 mol of oxaloyl chloride was added. After stirring for 6 hours, a solution of the second compound was obtained. Acetic acid was added until the pH of the solution of the second compound was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A7. The Raman spectrum of the compound with structural formula A7 is as follows: Figure 7 As shown.

[0122] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A8 is as follows:

[0123] S1: At room temperature, tetrabutylammonium bromide (TBAB) (0.5 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and bromobenzene (0.1 mol), and the mixture was stirred for 12 h to obtain a solution of the first compound.

[0124] S2: The solution of the first compound obtained in step S1 was cooled to 3°C, and formyl chloride (0.1 mol) was added. After stirring for 6 hours, a solution of the second compound was obtained. Acetic acid was added until the pH of the solution of the second compound was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A8. The Raman spectrum of the compound with structural formula A8 is as follows: Figure 8 As shown.

[0125] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A9 is as follows:

[0126] S1: At room temperature, tetrabutylammonium bromide (TBAB) (1g) was added to a mixed solution of dichloromethane (50mL) containing oxalamide (0.1mol) and bromomethane (0.1mol), and the mixture was stirred for 12h to obtain a solution of the first compound.

[0127] S2: The solution of the first compound obtained in step S1 was cooled to 3°C, acetyl chloride (0.1 mol) was added, and the mixture was stirred for 6 hours to obtain a solution of the second compound. Acetic acid was added until the pH of the second compound solution was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A9. The Raman spectrum of the compound with structural formula A9 is as follows: Figure 9 As shown.

[0128] In a specific embodiment of the present invention, the preparation method of the compound with structural formula A10 is as follows:

[0129] S1: At room temperature, tetrabutylammonium bromide (TBAB) (0.3 g) was added to a mixed solution of dichloromethane (50 mL) containing oxalamide (0.1 mol) and bromoethane (0.1 mol), and the mixture was stirred for 12 h to obtain a solution of the first compound.

[0130] S2: The solution of the first compound obtained in step S1 was cooled to 3°C, and 0.1 mol of ethylene bromide was added. After stirring for 10 h, the solution of the second compound was obtained. Acetic acid was added until the pH of the solution of the second compound was 7. Then, the solution was subjected to extraction, washing, and recrystallization to obtain the compound with structural formula A10. The Raman spectrum of the compound with structural formula A10 is as follows: Figure 10 As shown.

[0131] It should also be noted that the preparation methods of the compounds described in structural formulas A1-A10 of this invention are not limited to these methods. Those skilled in the art should know that the same products prepared by other synthetic methods are also applicable to the present invention.

[0132] The present invention is further illustrated below with specific embodiments:

[0133] Example 1

[0134] The method for preparing the electrolyte includes the following steps:

[0135] At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), EC (ethylene carbonate), PC (propylene carbonate), and DEC (diethyl carbonate) were mixed thoroughly in a mass ratio of 1:1:1 to obtain the first solvent. Then, the compound with structural formula A1 was added and mixed thoroughly. Molecular sieves are used to remove water, yielding a second solvent;

[0136] Fluoroethylene carbonate (FEC) and lithium difluorodioxarate phosphate (LiPF2(C2O4)) were added to a second solvent and mixed thoroughly to obtain a mixed solution. Then, lithium hexafluorophosphate (LiPF6) was added to the mixed solution and stirred thoroughly to obtain an electrolyte.

[0137] The electrolyte comprises the following components by mass percentage: 3% FEC, 5% compound of structural formula A1, 13% LiPF6, 1.5% LiPF2 (C2O4), and 77.5% primary solvent (ester solvent).

[0138] Preparation of secondary batteries:

[0139] (1) The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent acetylene black (Super P) and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NCM811:Super P:PVDF = 8:1:1, and then evenly dispersed in N-methylpyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0140] (2) The negative electrode active material silicon dioxide-carbon material, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:Super P:SBR=9:0.5:0.5 and evenly dispersed in deionized water to make 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.

[0141] (3) Stack the positive electrode, separator, and negative electrode in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a 2Ah bare cell is obtained. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24h. 10g of the electrolyte obtained in each example is injected into the dried battery. The battery is left to stand at 45℃ for 24h, formed, and tested for capacity to complete the preparation of the lithium-ion secondary soft pack battery.

[0142] Examples 2-19, Comparative Examples 1-3

[0143] The differences between Examples 2-19, Comparative Examples 1-3 and Example 1 are shown in Table 1, while the rest are the same as Example 1.

[0144] Example 20

[0145] The difference between Example 20 and Example 1 is that the content of lithium hexafluorophosphate is adjusted to 15%.

[0146] Test case

[0147] Battery performance test

[0148] (1) Low-temperature impedance test:

[0149] The soft-pack batteries obtained in the examples and comparative examples were left to stand for 1 hour at temperatures of 0°C, -20°C, and -40°C respectively to ensure uniform temperature distribution and stability. Then, the impedance of the batteries at temperatures of 0°C, -20°C, and -40°C was tested under AC signal with a frequency range from 100kHz to 0.01Hz and an applied voltage perturbation amplitude of 5-10mV.

[0150] (2) Low-temperature storage performance test: At -40℃, the manufactured battery was charged to 4.5V at a constant current of 0.5C, and then charged at a constant voltage of 4.5V (cutoff current of 0.01C); then discharged to 3.0V at a constant current of 0.5C, and the discharge capacity was recorded as the initial discharge capacity. The battery was then charged to 4.5V at a constant current of 0.5C, and then charged at a constant voltage of 4.5V (cutoff current of 0.01C), and stored in a -40℃ constant temperature chamber for 10 days. Then, it was discharged to 3.0V at a constant current of 0.5C at -40℃, and the discharge capacity was recorded as the retention capacity. Finally, at -40℃, it was cycled once at the same 0.5C, and the discharge capacity was recorded as the recovery capacity. The high-temperature storage performance of the battery was calculated as follows: Battery capacity retention rate = Retention capacity / Initial capacity × 100%; Battery capacity recovery rate = Recovery capacity / Initial capacity × 100%.

[0151] The test results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Table 2 Performance test data of the examples and comparative examples

[0156]

[0157] As shown in Examples 1-20, the electrolyte of this application yields batteries with a capacity retention rate greater than 31%, reaching a maximum of 44.13%; and a capacity recovery rate greater than 61%, reaching a maximum of 73.21%. This indicates that the compound with the structure shown in Formula I of this application can effectively separate lithium salts in the electrolyte under low-temperature conditions, which is beneficial for forming a solvated structure, promoting lithium ion transport, improving the ionic conductivity in the electrolyte, and simultaneously stabilizing the dissolution of lithium salts to form a stable SEI film, thereby improving the battery's capacity retention rate and capacity recovery rate.

[0158] Comparative examples 1-7 show that when the amount of compound with the structure shown in Formula I is 10-40% and the mass ratio of compound with the structure shown in Formula I to additive is 3-14, the resulting battery, after being stored in a -40℃ constant temperature chamber for 10 days, has a capacity retention rate of 38.29-44.13% and a capacity recovery rate of 68.51-73.21%. This indicates that when the amount of compound with the structure shown in Formula I is 10-40% and the mass ratio of compound with the structure shown in Formula I to additive is 3-14, the combined use of compound with the structure shown in Formula I and additive can further improve the capacity retention rate and capacity recovery rate of the battery under low temperature conditions.

[0159] Comparing Examples 4 and 11-13, it can be seen that when the additive is FEC, the battery has better capacity retention and capacity recovery rate after being stored in a -40°C constant temperature chamber for 10 days. This indicates that when the additive FEC is used in combination with the compound with the structure shown in Formula I, the battery has better performance at low temperatures.

[0160] Comparing Examples 4 and 14-19, it can be seen that when the compounds with the structure shown in Formula I are A1, A4, A5, and A10, the resulting batteries, after being stored in a -40°C constant temperature chamber for 10 days, have a capacity retention rate of 40.29-44.13% and a capacity recovery rate of 70.13-73.21%. This indicates that when the compounds with the structure shown in Formula I are A1, A4, A5, and A10, the batteries exhibit better capacity retention and capacity recovery rates under low-temperature conditions.

[0161] Comparing Example 4 with Comparative Examples 1-3, it can be seen that the compound and additive with the structure shown in Formula I of this application have a synergistic effect. Under low temperature conditions, the two work together to form a stable SEI film, which effectively improves the capacity retention rate and capacity recovery rate of the battery under low temperature conditions.

[0162] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this disclosure and not to limit the scope of protection of this disclosure. Although this disclosure has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this disclosure without departing from the substance and scope of the technical solutions of this disclosure.

Claims

1. An electrolyte, characterized in that, It includes a non-aqueous solvent, a lithium salt, and an additive, wherein the non-aqueous solvent comprises at least one of the compounds with the following structures: Based on the total mass of the electrolyte, the mass percentage of the compound with the structure shown is 10-40%.

2. The electrolyte as described in claim 1, characterized in that, The mass ratio of the compound with the structure shown to the additive is 3-14.

3. The electrolyte as described in claim 1, characterized in that, The additive is at least one selected from fluoroethylene carbonate, ethylene glycol dimethyl ether, trifluorophosphate, vinylene carbonate, 1,3-propane sulphol, and methyl methacrylate.

4. The electrolyte as described in claim 1, characterized in that, The non-aqueous solvent also includes ester solvents, and the mass ratio of the compound with the shown structure to the ester solvent is 0.1-1.

5. The electrolyte as described in claim 4, characterized in that, The ester solvent is a carbonate solvent, which includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, and methyl butyl carbonate.

6. The electrolyte as described in claim 1, characterized in that, The mass ratio of the compound with the structure shown to the lithium salt is 0.6-3.

7. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the electrolyte as described in any one of claims 1-6.

8. An electrical device, characterized in that, Includes the secondary battery as described in claim 7.

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