Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery comprises an electrolyte, which comprises a first organic compound and a second organic compound. The first organic compound comprises fluoroethylene carbonate, and the second organic compound comprises a compound of formula I. In the compound of formula I, R is selected from a C2 to C6 alkyl group which is substituted with fluorine or unsubstituted, and a C6 to C12 aryl group which is substituted with fluorine or unsubstituted. Based on the total mass of the electrolyte, the mass percentage of the first organic compound is A, and the mass percentage of the second organic compound is B, wherein 2%≤A≤30%, and 5%≤B≤85%. By adjusting and controlling the electrolyte to comprise the first organic compound and the second organic compound, as well as the types and mass percentages of the first and second organic compounds within the scope of the present application, the secondary battery can have both good cycling performance and low-temperature discharge performance.

Description

A secondary battery and electronic device Technical Field

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

[0002] Lithium-ion batteries have significant advantages such as high energy density, miniaturization, and lightweight design, and are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and energy storage systems. A typical lithium-ion battery consists of a positive electrode, a negative electrode, and an electrolyte. The electrolyte is responsible for maintaining ion transport between the positive and negative electrodes and for maintaining a stable interface, ensuring stable operation of the lithium-ion battery.

[0003] To form a stable interface in lithium-ion batteries, film-forming additives are usually added to the electrolyte. However, these additives often form a high-resistivity interfacial film on the surface of the positive or negative electrode. Although the resulting interfacial film is beneficial for the stable operation of lithium-ion batteries, it makes ion conduction more difficult, which limits the low-temperature discharge performance of lithium-ion batteries.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that enable the secondary battery to simultaneously possess good cycle performance and low-temperature discharge performance. The specific technical solution is as follows:

[0006] A first aspect of this application provides a secondary battery comprising an electrolyte, the electrolyte comprising a first organic compound and a second organic compound, the first organic compound comprising fluoroethylene carbonate (FEC), and the second organic compound comprising a compound of formula I:

[0007] Wherein, R is selected from fluorinated or unsubstituted C2 to C6 alkyl groups and fluorinated or unsubstituted C6 to C12 aryl groups. Based on the total mass of the electrolyte, the mass percentage of the first organic compound is A, and the mass percentage of the second organic compound is B, where 2% ≤ A ≤ 30% and 5% ≤ B ≤ 85%. By adjusting the electrolyte to include the first and second organic compounds, and the mass percentages of the first and second organic compounds within the scope of this application, the secondary battery can simultaneously possess good cycle performance and low-temperature discharge performance.

[0008] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0009] By selecting the above-mentioned Formula I compound, a positive electrode interface passivation layer and / or a negative electrode interface passivation layer of lithium-containing inorganic compound rich in S and F elements can be formed at the electrode interface, thereby further reducing the possibility of excessive polymerization of FEC. The two can work together to form a thinner solid electrolyte interphase (SEI) film and / or positive electrode electrolyte interphase (CEI) film. Therefore, while improving the cycle performance of the secondary battery, it can also further improve the low-temperature discharge performance of the secondary battery.

[0010] In one embodiment of this application, 0.66 ≤ B / A ≤ 28.33. By adjusting the value of B / A within the range of this application, the mass percentage content of the first organic compound and the mass percentage content of the second organic compound are matched. The first organic compound and the second organic compound further work synergistically to form a thinner polymer protective layer with high ionic conductivity, thereby further improving the cycle performance and low-temperature discharge performance of the secondary battery.

[0011] In one embodiment of this application, the secondary battery satisfies at least one of the following characteristics: (1) 3% ≤ A ≤ 15%; (2) 10% ≤ B ≤ 85%; (3) 1 ≤ B / A ≤ 12.

[0012] In one embodiment of this application, the secondary battery satisfies at least one of the following characteristics: (1) 5% ≤ A ≤ 10%; (2) 10% ≤ B ≤ 60%.

[0013] In one embodiment of this application, the electrolyte further includes a lithium salt, which comprises at least one of lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide; based on the total mass of the electrolyte, the mass percentage of the lithium salt is C, 7.5% ≤ C ≤ 35%. The lithium salt mainly functions as an ion conductor in the electrolyte. By controlling the type and mass percentage of the lithium salt within the scope of this application, the aforementioned lithium salt exhibits good solubility and dissociation ability in the combination of the first and second organic compounds, enabling the electrolyte to have high ion conductivity and further improving the cycle performance and low-temperature discharge performance of the secondary battery.

[0014] In one embodiment of this application, the electrolyte further includes a fluorinated linear ester, which includes at least one selected from methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, or hexafluoroisopropyl propionate. Based on the total mass of the electrolyte, the mass percentage of the fluorinated linear ester is D, where 10% ≤ D ≤ 30%. The electrolyte also includes fluorinated linear esters. The types and mass percentages of fluorinated linear esters are within the scope of this application. Adding fluorinated linear esters can further increase the F content in the electrolyte, further improve the overall antioxidant capacity of the solvent, and further increase the LiF content in the positive electrode passivation layer and / or negative electrode passivation layer, making the positive electrode passivation layer and / or negative electrode passivation layer more inert and resistant to high voltage, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0015] In one embodiment of this application, the electrolyte further includes a compound of formula II, which includes at least one of the following compounds:

[0016] The above-mentioned compound II is selected. Compound II is a nitrile compound. Nitrile compounds can work synergistically with compound I to form a positive electrode interface passivation layer rich in LiF and cyano groups, which can improve the stability of the positive electrode interface and further enhance the oxidation resistance of the electrolyte, thereby further improving the high-temperature storage performance of the secondary battery.

[0017] In one embodiment of this application, based on the total mass of the electrolyte, the mass percentage of compound II is E, where 0.1% ≤ E ≤ 10% and 0.005 ≤ E / B ≤ 1. By adjusting the mass percentage of compound II and the ratio of the mass percentage of compound II to the mass percentage of compound I within the range of this application, compound II has a suitable mass percentage, and the mass percentage of compound II matches the mass percentage of compound I. Compound II and compound I work synergistically to form a positive electrode interface passivation layer rich in LiF and cyano groups, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0018] In one embodiment of this application, the secondary battery satisfies at least one of the following characteristics: (1) 0.5% ≤ E ≤ 5%; (2) 0.01 ≤ E / B ≤ 0.1.

[0019] In one embodiment of this application, the electrolyte further includes compound Z, which includes compounds represented by formula III and / or formula IV.

[0020] In this embodiment, R1, R2, R3, R4, and R5 are each independently selected from hydrogen atoms, fluorine atoms, vinyl groups, acetylene groups, or anhydride groups. Adjacent groups in R1, R2, R3, R4, and R5 can be covalently linked to form a ring. Based on the total mass of the electrolyte, the mass percentage content of compound Z is F, where 0.1% ≤ F ≤ 1%. By adjusting the electrolyte, compound Z is also included. Compound Z includes compounds represented by formula III and / or formula IV, and the mass percentage content of compound Z is within the scope of this application. The addition of compounds represented by formula III and / or formula IV can further improve the toughness of the polymer protective layer, while also giving the polymer protective layer higher ionic conductivity, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0021] In one embodiment of this application, the compound of formula III includes at least one of the following compounds:

[0022] By selecting the above-mentioned compound of formula III, the toughness of the polymer protective layer can be further improved, and the polymer protective layer can also have higher ion conductivity, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0023] In one embodiment of this application, the compound of formula IV includes at least one of the following compounds:

[0024] By selecting the above-mentioned Formula IV compound, the toughness of the polymer protective layer can be further improved, and the polymer protective layer can also have higher ion conductivity, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0025] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0026] The beneficial effects of this application are:

[0027] This application provides a secondary battery and an electronic device. The secondary battery includes an electrolyte comprising a first organic compound and a second organic compound. The first organic compound includes fluoroethylene carbonate, and the second organic compound includes a compound of formula I. In the compound of formula I, R is selected from fluorinated or unsubstituted C2-C6 alkyl groups or fluorinated or unsubstituted C6-C12 aryl groups. Based on the total mass of the electrolyte, the mass percentage of the first organic compound is A, and the mass percentage of the second organic compound is B, where 2% ≤ A ≤ 30% and 5% ≤ B ≤ 85%. By adjusting the composition of the first and second organic compounds in the electrolyte, and considering the types and mass percentages of the first and second organic compounds within the scope of this application, the secondary battery can simultaneously possess good cycle performance and low-temperature discharge performance. Attached Figure Description

[0028] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0029] Figure 1 is a schematic cross-sectional structure of the negative electrode sheet in one embodiment of this application;

[0030] Figure 2 is a schematic cross-sectional view of the negative electrode sheet in another embodiment of this application;

[0031] Figure 3 is a schematic cross-sectional view of the negative electrode sheet in another embodiment of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0033] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0034] This application provides a secondary battery comprising an electrolyte, the electrolyte comprising a first organic compound and a second organic compound, the first organic compound comprising fluoroethylene carbonate, and the second organic compound comprising a compound of formula I:

[0035] Wherein, R is selected from fluorinated or unsubstituted C2 to C6 alkyl groups and fluorinated or unsubstituted C6 to C12 aryl groups. Based on the total mass of the electrolyte, the mass percentage of the first organic compound is A, and the mass percentage of the second organic compound is B, where 2% ≤ A ≤ 30%, preferably 3% ≤ A ≤ 15%, more preferably 5% ≤ A ≤ 10%; exemplaryly, the value of A can be 2%, 3%, 5%, 7%, 9%, 10%, 13%, 15%, 17%, 19%, 20%, 23%, 25%, 27%, 29%, 30%, or a range consisting of any two of the above values. 5% ≤ B ≤ 85%, preferably 10% ≤ B ≤ 85%, more preferably 10% ≤ B ≤ 60%; for example, the value of B can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or a range of any two of the above values.

[0036] The inventors discovered that FEC is an excellent electrolyte additive for secondary batteries. During the formation of secondary batteries, FEC in the electrolyte can form a cross-linked, highly tough polymer protective layer at the electrode interface, which can effectively maintain the stability of the electrode materials and thus improve the cycle performance of the secondary battery. However, the polymer protective layer formed by FEC is relatively thick, which can hinder the conduction of lithium ions to some extent. At lower operating temperatures, such as below 0°C, this can lead to a decrease in the discharge capacity of the secondary battery. Adding compound I can form a positive electrode passivation layer and / or a negative electrode passivation layer of lithium-containing inorganic compounds rich in S and F elements at the electrode interface, thereby effectively reducing the possibility of excessive polymerization of FEC. The two work together to form a thinner solid electrolyte interphase (SEI) film and / or positive electrode electrolyte interphase (CEI) film. Therefore, while improving the cycle performance of the secondary battery, it also enables the secondary battery to have good low-temperature discharge performance. When the mass percentage of FEC is too low, for example, below 2%, the amount of FEC added is too small, and a complete polymer protective layer cannot be formed at the electrode interface during the formation process. The interface is unstable and cannot effectively maintain the working stability of the electrode material. There are many side reactions at the electrode interface, resulting in poor cycle performance of the secondary battery. When the mass percentage of FEC is too high, for example, above 30%, the polymer protective layer formed by FEC will be too thick, which will hinder the lithium ion transport at the interface and result in poor low-temperature discharge performance of the secondary battery. When the mass percentage of compound I is too low, for example, below 5%, the amount of compound I added is too small, making it impossible to form a positive electrode interface passivation layer and / or a negative electrode interface passivation layer rich in S and F elements at the electrode interface. This prevents the formation of a thinner SEI film and / or CEI film in conjunction with FEC, thus failing to improve the low-temperature discharge performance of the secondary battery. When the mass percentage of compound I is too high, for example, above 85%, it leads to excessive inorganic components in the positive electrode interface passivation layer and / or the negative electrode interface passivation layer. This makes the passivation layer prone to breakage, reduces interface stability, and affects the cycle performance of the secondary battery. By adjusting the electrolyte to include a first organic compound and a second organic compound, and the mass percentages of the first and second organic compounds within the scope of this application, the secondary battery can simultaneously possess good cycle performance and low-temperature discharge performance. In this application, "low temperature" refers to a temperature below 0°C.

[0037] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0038] By selecting the above-mentioned Formula I compound, a positive electrode interface passivation layer and / or a negative electrode interface passivation layer of lithium-containing inorganic compound rich in S and F elements can be formed at the electrode interface, thereby further reducing the possibility of excessive polymerization of FEC. The two can work together to form a thinner solid electrolyte interphase (SEI) film and / or positive electrode electrolyte interphase (CEI) film. Therefore, while improving the cycle performance of the secondary battery, it can also further improve the low-temperature discharge performance of the secondary battery.

[0039] In one embodiment of this application, 0.66 ≤ B / A ≤ 28.33, preferably 1 ≤ B / A ≤ 12. Exemplarily, the value of B / A can be 0.66, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 3, 5, 7, 9, 10, 12, 13, 15, 17, 19, 20, 23, 25, 27, 28.33, or a range consisting of any two of the above values. By adjusting the value of B / A within the range of this application, the mass percentage content of the first organic compound and the mass percentage content of the second organic compound are matched, and the first and second organic compounds further synergistically act to form a thinner polymer protective layer with higher ionic conductivity, further improving the cycle performance and low-temperature discharge performance of the secondary battery.

[0040] In one embodiment of this application, the electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate or lithium bisfluorosulfonylimide; the mass percentage of the lithium salt is C based on the total mass of the electrolyte, 7.5% ≤ C ≤ 35%. Exemplarily, the value of C can be 7.5%, 9%, 10%, 11%, 13%, 15%, 17%, 19%, 20%, 21%, 23%, 25%, 27%, 29%, 30%, 31%, 33%, 35%, or a range of any two of the above values. The lithium salt mainly plays a role in ion conduction in the electrolyte. By controlling the type and mass percentage of the lithium salt within the scope of this application, the lithium salt exhibits good solubility and dissociation ability in the combination of the first organic compound and the second organic compound, enabling the electrolyte to have high ion conduction capacity, further improving the cycle performance and low-temperature discharge performance of the secondary battery.

[0041] In one embodiment of this application, the electrolyte further includes fluorinated linear esters, which include at least one selected from methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, or hexafluoroisopropyl propionate. Based on the total mass of the electrolyte, the mass percentage of the fluorinated linear ester is D, where 10% ≤ D ≤ 30%. For example, the value of D can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range of any two of the above values. The electrolyte also includes fluorinated linear esters. The type and mass percentage of the fluorinated linear esters are within the scope of this application. Adding fluorinated linear esters can further increase the F element content in the electrolyte, further improve the overall antioxidant capacity of the solvent, and further increase the LiF content in the positive electrode passivation layer and / or the negative electrode passivation layer, making the positive electrode passivation layer and / or the negative electrode passivation layer more inert and resistant to high voltage, further improving the cycle performance and high-temperature storage performance of the secondary battery. In this application, "high temperature" refers to a temperature higher than 60°C.

[0042] In one embodiment of this application, the electrolyte further includes a compound of formula II, which includes at least one of the following compounds:

[0043] The above-mentioned compound II is selected. Compound II is a nitrile compound. Nitrile compounds can work synergistically with compound I to form a positive electrode interface passivation layer rich in LiF and cyano groups, which can improve the stability of the positive electrode interface and further enhance the oxidation resistance of the electrolyte, thereby further improving the high-temperature storage performance of the secondary battery.

[0044] In one embodiment of this application, the mass percentage of compound II is E based on the total mass of the electrolyte, where 0.1% ≤ E ≤ 10%, preferably 0.5% ≤ E ≤ 5%. Exemplarily, the value of E can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range consisting of any two of the above values. 0.005≤E / B≤1, preferably 0.01≤E / B≤0.1; for example, the value of E / B can be 0.005, 0.007, 0.009, 0.01, 0.02, 0.05, 0.07, 0.09, 0.1, 0.15, 0.17, 0.19, 0.2, 0.25, 0.27, 0.29, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range of any two of the above values. Within the scope of this application, by adjusting the mass percentage content of compound II and the ratio of the mass percentage content of compound II to that of compound I, compound II has a suitable mass percentage content, and the mass percentage content of compound II matches that of compound I. Compound II and compound I work synergistically to form a positive electrode interface passivation layer rich in LiF and cyano groups, further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0045] In one embodiment of this application, the electrolyte further includes compound Z, which includes compounds represented by formula III and / or formula IV.

[0046] In this embodiment, R1, R2, R3, R4, and R5 are each independently selected from hydrogen atoms, fluorine atoms, vinyl groups, acetylene groups, or anhydride groups. Adjacent groups among R1, R2, R3, R4, and R5 can be covalently linked to form a ring. Based on the total mass of the electrolyte, the mass percentage content of compound Z is F, where 0.1% ≤ F ≤ 1%. For example, the value of F can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of the above values. By adjusting the electrolyte, compound Z is also included. Compound Z includes compounds represented by Formula III and / or Formula IV, and the mass percentage content of compound Z is within the scope of this application. The addition of compounds represented by Formula III and / or Formula IV can further improve the toughness of the polymer protective layer, while also giving the polymer protective layer higher ionic conductivity, further improving the cycle performance and high-temperature storage performance of the secondary battery. In this application, compound Z includes compounds represented by Formula III and Formula IV. This application does not impose any particular limitation on the mass percentage of each compound, as long as the sum of the mass percentages of the compounds represented by Formula III and Formula IV meets the scope of this application. In this application, the aforementioned "covalent bond" can be a single bond.

[0047] In one embodiment of this application, the compound of formula III includes at least one of the following compounds:

[0048] By selecting the above-mentioned compound of formula III, the toughness of the polymer protective layer can be further improved, and the polymer protective layer can also have higher ion conductivity, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0049] In one embodiment of this application, the compound of formula IV includes at least one of the following compounds:

[0050] By selecting the above-mentioned Formula IV compound, the toughness of the polymer protective layer can be further improved, and the polymer protective layer can also have higher ion conductivity, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0051] In this application, the characteristics of the different components contained in the electrolyte can be combined, and the implementation methods covered by the above combinations are all within the protection scope of this application.

[0052] In this application, the electrolyte also includes a non-aqueous organic solvent. This application does not impose any particular limitation on the non-aqueous organic solvent, as long as it achieves the purpose of this application. For example, the non-aqueous organic solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds and cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters. This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage G of the non-aqueous organic solvent is 10% to 70%.

[0053] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, and a lithium salt. The mass percentages of the first organic compound and the lithium salt are as described above, and the mass percentage of the second organic compound B is 35% to 85%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0054] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, and one of a fluorinated linear ester and a non-aqueous organic solvent. The mass percentage of the first organic compound, the lithium salt, and one of the fluorinated linear ester and the non-aqueous organic solvent is as described above, and the mass percentage B of the second organic compound is 5% to 80%. The secondary battery including the above electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0055] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, and a compound of formula II. The mass percentages of the first organic compound, the lithium salt, and the compound of formula II are as described above, and the mass percentage B of the second organic compound is 25% to 85%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0056] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, and compound Z. The mass percentages of the first organic compound, lithium salt, and compound Z are as described above, and the mass percentage of the second organic compound B is 34% to 85%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0057] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a fluorinated linear ester, and one of either compound II or compound Z. The mass percentages of the first organic compound, lithium salt, fluorinated linear ester, and one of either compound II or compound Z are as described above, and the mass percentage B of the second organic compound is 5% to 80%. The secondary battery including the above electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0058] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a compound of formula II, and compound Z. The mass percentages of the first organic compound, lithium salt, compound II, and compound Z are as described above, and the mass percentage of the second organic compound B is 24% to 85%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0059] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a compound of formula II, a compound Z, and one of a fluorinated linear ester and a non-aqueous organic solvent. The mass percentage of the first organic compound, the lithium salt, the compound of formula II, the compound Z, and one of the fluorinated linear ester and the non-aqueous organic solvent is as described above, and the mass percentage B of the second organic compound is 5% to 80%. The secondary battery including the above electrolyte simultaneously exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0060] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a fluorinated linear ester, and a non-aqueous organic solvent. The mass percentages of the first organic compound, lithium salt, fluorinated linear ester, and non-aqueous organic solvent are as described above, and the mass percentage B of the second organic compound is 5% to 70%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0061] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a non-aqueous organic solvent, and one of either compound II or compound Z. The mass percentages of the first organic compound, lithium salt, non-aqueous organic solvent, and one of either compound II or compound Z are as described above, and the mass percentage B of the second organic compound is 5% to 80%. The secondary battery including the above-described electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0062] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a fluorinated linear ester, a non-aqueous organic solvent, and one of either compound II or compound Z. The mass percentages of the first organic compound, lithium salt, fluorinated linear ester, non-aqueous organic solvent, and one of either compound II or compound Z are as described above, and the mass percentage B of the second organic compound is 5% to 70%. The secondary battery including the above electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0063] In one embodiment of this application, the electrolyte may include a first organic compound, a second organic compound, a lithium salt, a fluorinated linear ester, a compound of formula II, compound Z, and a non-aqueous organic solvent. The mass percentages of the first organic compound, lithium salt, fluorinated linear ester, compound II, compound Z, and non-aqueous organic solvent are as described above, and the mass percentage B of the second organic compound is 5% to 70%. The secondary battery including the above electrolyte exhibits good low-temperature discharge performance, cycle performance, and high-temperature storage performance.

[0064] In this application, the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0065] The cathode material layer of this application includes a cathode active material, which comprises a substance capable of reversibly inserting and de-intercalating active ions such as lithium ions. The cathode material layer can be one or more layers, and each layer in a multilayer cathode material layer can contain the same or different cathode active materials. This application does not impose any particular limitation on the cathode active material, as long as it can achieve the purpose of this application. For example, the cathode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The cathode material layer of this application also includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the cathode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder may include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose (CMC-Na), potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0066] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer is 30 μm to 120 μm.

[0067] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and it can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0068] In this application, the secondary battery further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved, for example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors, etc.

[0069] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 The negative electrode material layer of this application includes at least one of the following: Li-Al alloy or metallic lithium. The negative electrode material layer of this application also includes a binder. This application does not impose any particular limitation on the binder in the negative electrode material layer, as long as it achieves the purpose of this application. For example, the binder can be at least one of the aforementioned binders. The negative electrode material layer of this application also includes a conductive agent. This application does not impose any particular limitation on the conductive agent in the negative electrode material layer, as long as it achieves the purpose of this application. For example, the conductive agent can be at least one of the aforementioned conductive agents. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, binder, and conductive agent in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved.

[0070] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 5 μm to 16 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer can be from 30 μm to 120 μm.

[0071] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, which can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the thickness of the conductive layer, as long as the purpose of this application can be achieved; for example, the thickness of the conductive layer is 1 μm to 10 μm. Exemplarily, FIG1 shows a schematic cross-sectional structure of a negative electrode sheet according to one embodiment of this application. The negative electrode sheet 10 includes a negative electrode current collector 11, a conductive layer 12, and a negative electrode material layer 13. The conductive layer 12 is disposed between the negative electrode current collector 11 and the negative electrode material layer 13, and the conductive layer 12 and the negative electrode material layer 13 are sequentially disposed on the A surface of the negative electrode current collector 11. In one embodiment, as shown in FIG2, the conductive layer 12 and the negative electrode material layer 13 are sequentially disposed on the B surface of the negative electrode current collector 11. In another embodiment, as shown in FIG3, the conductive layer 12 and the negative electrode material layer 13 are disposed on the A surface and the B surface of the negative electrode current collector 11, respectively.

[0072] In this application, the secondary battery also includes a separator, which separates the positive electrode and the negative electrode to prevent internal short circuits, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitations on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0073] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0074] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0075] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0076] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0077] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0078] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0079] Example

[0080] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0081] Test methods and equipment:

[0082] Cyclic performance test:

[0083] The lithium-ion battery was placed in a constant temperature environment of 25°C and left to stand for 30 minutes to allow it to reach the constant temperature state of 25°C. It was then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V. The initial discharge capacity was recorded as C0. This charge-discharge cycle was repeated 500 times, and the discharge capacity after 500 cycles was recorded as C1.

[0084] Cyclic capacity retention rate = C1 / C0 × 100%.

[0085] Low-temperature discharge performance test:

[0086] The lithium-ion battery was placed in a constant temperature environment of 25℃ and left to stand for 30 minutes to reach the constant temperature state of 25℃. It was then charged at a constant current of 0.5C to 4.5V, charged at a constant voltage of 4.5V to a current of 0.025C, and discharged at a constant current of 0.2C to 3.0V. The discharge capacity at 25℃ was recorded as C2. The battery was then charged again at a constant current of 0.5C to 4.5V, charged at a constant voltage of 4.5V to a current of 0.025C, and transferred to a constant temperature test chamber of -10℃. It was left to stand for 60 minutes to reach the constant temperature state of -10℃, and then discharged at a constant current of 0.2C to 3.0V. The discharge capacity at -10℃ was recorded as C3.

[0087] -10℃ low-temperature discharge capacity retention rate = C3 / C2 × 100%.

[0088] High-temperature storage performance test:

[0089] The lithium-ion battery was placed in a constant temperature environment of 25℃ and left to stand for 30 minutes to reach the constant temperature state. It was then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. The thickness of the lithium-ion battery at this point was recorded as the initial thickness H0. The lithium-ion battery was then transferred to a constant temperature chamber at 60℃ and stored for 30 days. During this period, the thickness of the lithium-ion battery was measured and recorded every 6 days. The measured thickness recorded after 30 days was recorded as the storage thickness H1.

[0090] High-temperature storage thickness expansion rate = (H1-H0) / H0×100%.

[0091] Example 1-1

[0092] <Preparation of Negative Electrode Sheets>

[0093] The negative electrode active materials, artificial graphite, SBR, and CMC-Na, were mixed in a mass ratio of 98.5:1:0.5, and then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 54 wt%. The slurry was then stirred evenly in a vacuum mixer. The conductive agent Super P and the binder SBR were mixed in a mass ratio of 9:1, and then deionized water was added as a solvent to prepare a conductive layer slurry with a solid content of 10 wt%. The conductive layer slurry was uniformly coated onto one surface of an 8 μm thick copper foil used as a negative electrode current collector and dried at 85°C, forming a 2 μm thick conductive layer on one surface of the copper foil. Then, the negative electrode slurry was coated onto the surface of the conductive layer away from the copper foil and dried at 85°C, forming a 100 μm thick negative electrode material layer on the same surface. This yielded a negative electrode sheet with a single-sided conductive layer and a negative electrode material layer. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided conductive layer and a negative electrode material layer. After coating, the negative electrode sheet is cold-pressed and cut into 76mm × 851mm dimensions for later use. The compaction density of the negative electrode material layer after cold pressing is 1.70 g / cm³. 3 .

[0094] <Preparation of the positive electrode>

[0095] Lithium cobalt oxide (LiCoO2), a positive electrode active material, Super P, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred evenly in a vacuum mixer to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector and dried at 85°C to obtain a single-sided coated positive electrode sheet with a coating thickness of 110 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After coating, the positive electrode sheet was cold-pressed and cut into 74 mm × 867 mm dimensions for later use. The compaction density of the positive electrode layer after cold pressing was 4.15 g / cm³. 3 .

[0096] <Preparation of Electrolyte>

[0097] In an argon-atmospheric glove box with a water content of less than 10 ppm, FEC and compound I-1 of formula I were mixed, and then lithium hexafluorophosphate (LiPF6) was added and stirred until homogeneous to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage C of the lithium salt was 12.5%, the mass percentage A of the FEC was 3%, and the mass percentage B of compound I-1 was 84.5%.

[0098] <Septum>

[0099] A 5μm thick polyethylene (PE) porous membrane (supplied by Celgard) was used.

[0100] <Preparation of Lithium-ion Batteries>

[0101] The prepared positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), shaping, and capacity testing.

[0102] Examples 1-2 to Examples 1-7

[0103] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the content of at least one of FEC and Formula I compounds changes, the mass percentage content of the lithium salt remains unchanged.

[0104] Examples 1-8

[0105] Except for the preparation of the electrolyte as described below, the rest is the same as in Examples 1-1.

[0106] <Preparation of Electrolyte>

[0107] In an argon-atmospheric glove box with a water content of less than 10 ppm, FEC and compound I-1 of formula I were mixed, then lithium hexafluorophosphate (LiPF6) was added, followed by diethyl carbonate (DEC), and the mixture was stirred until homogeneous to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentages of the lithium salt (C) were 12.5%, FEC (A) were 5%, compound I (B) were 72.5%, and diethyl carbonate (G) were 10%.

[0108] Examples 1-9 to Examples 1-35

[0109] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-8. Specifically, when the content of at least one of FEC, Formula I compound, and diethyl carbonate changes, the mass percentage of lithium salt remains unchanged.

[0110] Examples 1-36 to Examples 1-44

[0111] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-5.

[0112] Examples 2-1 to 2-3

[0113] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-18. Among them, when the mass percentage of lithium salt changes, the mass percentage of compound I changes accordingly, while the mass percentages of FEC and diethyl carbonate remain unchanged.

[0114] Examples 3-1 to 3-15

[0115] Except for the addition of a fluorinated linear ester and adjustment of the relevant preparation parameters according to Table 3 in the <Preparation of Electrolyte> section, the rest is the same as in Examples 1-18. Specifically, when the mass percentage of the fluorinated linear ester changes, the mass percentage of diethyl carbonate changes accordingly, while the mass percentages of FEC, Formula I compound, and lithium salt remain unchanged.

[0116] Examples 4-1 to 4-16

[0117] Except for the addition of compound II in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-18. Specifically, when the mass percentage of compound II changes, the mass percentage of compound I changes accordingly, while the mass percentages of FEC, diethyl carbonate, and lithium salt remain unchanged.

[0118] Examples 5-1 to 5-13

[0119] Except for the addition of compound Z in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 5, the rest is the same as in Examples 1-18. Specifically, when the mass percentage of compound Z changes, the mass percentage of compound I changes accordingly, while the mass percentages of FEC, diethyl carbonate, and lithium salt remain unchanged.

[0120] Examples 6-1 to 6-4

[0121] Except for adjusting the relevant preparation parameters according to Table 6, the rest is the same as in Examples 1-18. Among them, when the mass percentage of at least one of the fluorinated linear ester, compound II, or compound Z changes, the mass percentage of compound I changes accordingly, while the mass percentages of FEC, diethyl carbonate, and lithium salt remain unchanged.

[0122] Comparative Examples 1 to 2

[0123] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-8. Specifically, when the content of at least one of FEC, Formula I compound, and diethyl carbonate changes, the mass percentage of lithium salt remains unchanged.

[0124] Comparative Examples 3 to 4

[0125] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the content of at least one of FEC and Formula I compounds changes, the mass percentage content of the lithium salt remains unchanged.

[0126] Comparative Example 5

[0127] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-8. Specifically, based on the mass of the electrolyte, the mass percentage of lithium salt C is 12.5%, the mass percentage of FEC A is 5%, the mass percentage of compound I B is 2.5%, and the mass percentage of diethyl carbonate G is 80%.

[0128] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 6.

[0129] Table 1

[0130] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0131] Referring to Table 1, and as shown in Examples 1-1 to 1-44 and Comparative Examples 1 to 5, by adjusting the electrolyte to include a first organic compound and a second organic compound, and ensuring that the mass percentages of the first and second organic compounds are within the scope of this application, the lithium-ion battery exhibits high cycle capacity retention and high -10°C low-temperature discharge capacity retention, indicating that the lithium-ion battery simultaneously possesses good cycle performance and low-temperature discharge performance. In contrast, in Comparative Examples 1 to 5, the lithium-ion battery exhibits low cycle capacity retention and low -10°C low-temperature discharge capacity retention, indicating poor cycle performance and low-temperature discharge performance.

[0132] As can be seen from Examples 1-1 to 1-7, FEC mainly affects the cycle performance of lithium-ion batteries. As the mass percentage of FEC increases, the cycle capacity of lithium-ion batteries increases first and then decreases. When the mass percentage of FEC is 10%, the cycle performance of lithium-ion batteries is optimal. As the mass percentage of FEC continues to increase, the polymer protective layer on the electrode surface becomes thicker, which will affect the cycle performance of lithium-ion batteries.

[0133] The type of compound of Formula I typically affects the cycle performance and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-5, 1-36 to 1-44, when the above-mentioned Formula I compound is selected, the lithium-ion battery exhibits higher cycle capacity retention and higher low-temperature discharge capacity retention at -10℃, indicating that the lithium-ion battery has both good cycle performance and low-temperature discharge performance.

[0134] The B / A ratio typically affects the cycle performance and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-35, when the B / A ratio is within the range specified in this application, the lithium-ion battery exhibits high cycle capacity retention and high low-temperature discharge capacity retention at -10°C, indicating that the lithium-ion battery simultaneously possesses good cycle performance and low-temperature discharge performance, and also exhibits good high-temperature storage performance.

[0135] Table 2

[0136] The type and mass percentage of lithium salts typically affect the cycle performance and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-18 and Examples 2-1 to 2-3, when the type and mass percentage of lithium salts are within the range of this application, the lithium-ion batteries exhibit high cycle capacity retention and high low-temperature discharge capacity retention at -10℃, indicating that the lithium-ion batteries possess both good cycle performance and low-temperature discharge performance.

[0137] Table 3

[0138] Note: In Table 3, " / " indicates that there are no relevant preparation parameters.

[0139] The electrolyte also includes fluorinated linear esters. The type and mass percentage of fluorinated linear esters typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-18 and Examples 3-1 to 3-15, when the electrolyte also includes fluorinated linear esters, and the type and mass percentage of fluorinated linear esters are within the scope of this application, the lithium-ion battery exhibits higher cycle capacity retention and lower high-temperature storage thickness expansion rate, indicating that the lithium-ion battery simultaneously possesses good cycle performance and high-temperature storage performance.

[0140] Table 4

[0141] Note: In Table 4, " / " indicates that there are no relevant preparation parameters.

[0142] The electrolyte also includes compounds of formula II, the types of which typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-18 and Examples 4-1 to 4-10, when the electrolyte also includes compounds of formula II, and the types of these compounds are within the scope of this application, the lithium-ion battery exhibits higher cycle capacity retention and lower high-temperature storage thickness expansion rate, indicating that the lithium-ion battery simultaneously possesses good cycle performance and high-temperature storage performance.

[0143] The mass percentage of compound II and the ratio of the mass percentage of compound II to the mass percentage of compound I typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 4-11 to 4-16, when the mass percentage of compound II and the ratio of the mass percentage of compound II to the mass percentage of compound I are within the range of this application, the lithium-ion battery exhibits a high cycle capacity retention rate and a low high-temperature storage thickness expansion rate, indicating that the lithium-ion battery simultaneously possesses good cycle performance and high-temperature storage performance. In Examples 4-16, the relatively high mass percentage of compound II leads to a decrease in cycle capacity retention rate and -10°C low-temperature discharge capacity retention rate, which affects the cycle performance and low-temperature discharge performance of the lithium-ion battery.

[0144] Table 5

[0145] Note: In Table 5, " / " indicates that there are no relevant preparation parameters.

[0146] The electrolyte also includes compound Z. The type and mass percentage of compound Z typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-18 and Examples 5-1 to 5-13, when the electrolyte also includes compound Z, and the type and mass percentage of compound Z are within the scope of this application, the lithium-ion battery exhibits higher cycle capacity retention and lower high-temperature storage thickness expansion rate, indicating that the lithium-ion battery simultaneously possesses good cycle performance and high-temperature storage performance. In Examples 5-13, the relatively high mass percentage of compound Z leads to a lower low-temperature discharge capacity retention rate at -10°C, which affects the low-temperature discharge performance of the lithium-ion battery.

[0147] Table 6

[0148] Note: In Table 6, " / " indicates that there are no relevant preparation parameters.

[0149] As can be seen from Examples 1-18 and Examples 6-1 to 6-4, when the electrolyte also includes at least two of the following: fluorinated linear ester, compound of formula II, and compound Z, the lithium-ion battery has a high cycle capacity retention rate and a low high-temperature storage thickness expansion rate, indicating that the lithium-ion battery has both good cycle performance and high-temperature storage performance.

[0150] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0151] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0152] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrolyte, the electrolyte comprising a first organic compound and a second organic compound, the first organic compound comprising fluoroethylene carbonate, and the second organic compound comprising a compound of formula I: in, R is selected from alkyl groups of C2 to C6 that are fluorinated or unsubstituted, and aryl groups of C6 to C12 that are fluorinated or unsubstituted. Based on the total mass of the electrolyte, the mass percentage of the first organic compound is A, the mass percentage of the second organic compound is B, 2% ≤ A ≤ 30%, and 5% ≤ B ≤ 85%.

2. The secondary battery according to claim 1, wherein, The compound of formula I includes at least one of the following compounds:

3. The secondary battery according to claim 1, wherein, 0.66≤B / A≤28.

33.

4. The secondary battery according to claim 1, wherein, The secondary battery satisfies at least one of the following characteristics: (1)3％≤A≤15％； (2)10％≤B≤85％； (3) 1≤B / A≤12.

5. The secondary battery according to claim 1, wherein, The secondary battery satisfies at least one of the following characteristics: (1)5％≤A≤10％； (2)10％≤B≤60％。 6. The secondary battery according to claim 1, wherein, The electrolyte also includes a lithium salt, which includes at least one of lithium hexafluorophosphate or lithium bisfluorosulfonylimide; the mass percentage of the lithium salt is C based on the total mass of the electrolyte, 7.5% ≤ C ≤ 35%.

7. The secondary battery according to claim 1, wherein, The electrolyte further includes fluorinated linear esters, which include at least one of methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, or hexafluoroisopropyl propionate. Based on the total mass of the electrolyte, the mass percentage of the fluorinated linear ester is D, where 10% ≤ D ≤ 30%.

8. The secondary battery according to claim 1, wherein, The electrolyte further includes a compound of formula II, which includes at least one of the following compounds:

9. The secondary battery according to claim 8, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound of formula II is E, where 0.1% ≤ E ≤ 10% and 0.005 ≤ E / B ≤ 1.

10. The secondary battery according to claim 9, wherein, The secondary battery satisfies at least one of the following characteristics: (1)0.5％≤E≤5％； (2) 0.01≤E / B≤0.

1.

11. The secondary battery according to claim 1, wherein, The electrolyte also includes compound Z, which includes compounds represented by formula III and / or formula IV. Among them, R1, R2, R3, R4, and R5 are each independently selected from hydrogen atoms, fluorine atoms, vinyl groups, ethynyl groups, or acid anhydride groups, and adjacent groups in R1, R2, R3, R4, and R5 can be connected to form a ring through covalent bonds; Based on the total mass of the electrolyte, the mass percentage of compound Z is F, where 0.1% ≤ F ≤ 1%.

12. The secondary battery according to claim 11, wherein, The compound of formula III includes at least one of the following compounds:

13. The secondary battery according to claim 11, wherein, The compound of formula IV includes at least one of the following compounds:

14. An electronic device comprising a secondary battery as described in any one of claims 1 to 13.

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