An electrolyte solution, an electrochemical device comprising the electrolyte solution, and an electronic device

Abstract

The present application provides an electrolyte, an electrochemical device comprising the electrolyte, and an electronic device. The electrolyte includes a compound represented by formula (I), and the mass percentage content X of the compound represented by formula (I) is from 0.05% to 3%. This is beneficial to form a stable positive electrode electrolyte interface on the surface of the positive electrode and a stable solid electrolyte interface on the surface of the negative electrode. Thus, during the cycling process of the electrochemical device, it is beneficial to reduce the loss of solvents and additives in the electrolyte, reduce the heat generation of the positive electrode and the negative electrode; and reduce the influence on the crystal structure of the positive electrode active material, thereby reducing the fragmentation of the positive electrode active material particles, alleviating the dissolution phenomenon of transition metals, and improving the cycling performance and safety performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemistry technology, and particularly relates to an electrolyte, an electrochemical device including the electrolyte, and an electronic device. Background Art

[0002] Lithium-ion batteries have the advantages of large energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, good safety, etc., and are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptop computers, and smart watches.

[0003] With the continuous expansion of the application range of lithium-ion batteries, the market has put forward higher requirements for lithium-ion batteries, such as requiring lithium-ion batteries to have a longer life and higher safety performance. Therefore, in view of this, developing a suitable electrolyte has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte, an electrochemical device including the electrolyte, and an electronic device to improve the cycle performance and safety performance of the electrochemical device.

[0005] The first aspect of this application provides an electrolyte, which includes a compound shown in formula (I). Based on the mass of the electrolyte, the mass percentage content X of the compound shown in formula (I) is 0.05% to 3%:

[0006]

[0007] Wherein, R1 and R2 each independently selected from H, F, C1-C5 alkyl, C1-C5 alkoxy, or C2-C5 alkenyl, C2-C5 alkynyl; R is selected from O or -CH(R3)-, and R3 is selected from H, F, C1-C5 alkyl, or C1-C5 alkoxy; Rb is selected from H, F, C1-C5 alkyl, or C1-C5 alkoxy; A and B each independently selected from -CO- or -SO2-; W is selected from CH2 or O; M - is selected from one of the groups M1 to M3:

[0008]

[0009] The electrolyte includes the compound shown in formula (I), and the mass percentage content X of the compound shown in formula (I) is 0.05% to 3%, which is beneficial to form a stable cathode electrolyte interface (CEI) on the cathode surface and a stable solid electrolyte interface (SEI) on the anode surface, can reduce the side reactions between the electrolyte and the cathode active material or the anode active material, and improve the cycle performance and safety performance of the electrochemical device.

[0010] In some embodiments of the present application, the electrolyte includes at least one of the following compounds I-1 to I-13:

[0011]

[0012]

[0013] In some embodiments of the present application, the electrolyte further includes a cyclic sulfonate, and the cyclic sulfonate includes a cyclic monosulfonate and / or a cyclic disulfonate. Based on the mass of the electrolyte, the mass percentage content of the cyclic sulfonate is 0.01% to 10%; the cyclic monosulfonate includes at least one of 1,3-propane sultone, 1,2-propane sultone, 1,4-butane sultone, 1,2-butane sultone, 1,3-butane sultone, 2,4-butane sultone or 1,3-pentane sultone; the cyclic disulfonate includes methylene methanedisulfonate and / or ethylene methanedisulfonate. By selecting the above cyclic monosulfonate, it is beneficial to improve the cycling performance and safety performance of the electrochemical device. By selecting the above cyclic sulfonate and regulating the mass percentage content of the cyclic sulfonate within the above range, it is beneficial to improve the cycling performance and safety performance of the electrochemical device.

[0014] In some embodiments of the present application, the electrolyte includes a compound represented by formula (II):

[0015]

[0016] Wherein, D and E each independently selected from C1 to C8 alkylene or C1 to C8 fluoroalkylene, and L is selected from a single bond or -OSO2-.

[0017] In some embodiments of the present application, the electrolyte includes a compound represented by formula (II-1) and / or a compound represented by formula (II-2):

[0018]

[0019] Wherein, R6 and R7 each independently selected from H, F or C1 to C4 alkyl, and n3 is 1, 2, 3 or 4;

[0020]

[0021] Wherein, D and E each independently selected from C1 to C8 alkylene or C1 to C8 fluoroalkylene.

[0022] In some embodiments of the present application, the electrolyte further includes a compound represented by formula (III), and based on the mass of the electrolyte, the mass percentage content C of the compound represented by formula (III) is 0.5% to 16%, and 0.03 ≤ X / C ≤ 1:

[0023]

[0024] Among them, R 12 to R 15 are each independently selected from H, F, C1 to C 10 fluoroalkyl, C1 to C 10 fluoroalkoxy, or C1 to C 10 fluoroalkoxyalkyl, and R 12 to R 15 are not simultaneously H.

[0025] By controlling the mass percentage content C of the compound shown in formula (III) within the above range, it is beneficial to better improve the cycle performance of the electrochemical device and reduce the impedance of the electrochemical device; by controlling the value of X / C within the above range, it is beneficial to form a synergistic effect between the compound shown in formula (I) and the compound shown in formula (III) to improve the cycle performance and safety performance of the electrochemical device.

[0026] In some embodiments of the present application, the electrolyte includes at least one of the following compounds III-1 to III-6:

[0027]

[0028] In some embodiments of the present application, the electrolyte further includes a cyano-containing compound, and the cyano-containing compound includes at least one of the compounds shown in formula (IV) to formula (VII). Based on the mass of the electrolyte, the mass percentage content D of the cyano-containing compound is 0.2% to 10%.

[0029]

[0030]

[0031]

[0032]

[0033] Among them, R 16 is selected from unsubstituted or Ra-substituted C1 to C 12 alkylene, unsubstituted or Ra-substituted C1 to C 12 alkoxy; R 17 and R 18 are each independently selected from a single bond, unsubstituted or Ra-substituted C1 to C 12 alkylene, unsubstituted or Ra-substituted C1 to C 12 alkoxy; R 19 to R 21Each independently selected from a single bond, an unsubstituted or Ra-substituted C1-C 12 alkylene group, an unsubstituted or Ra-substituted C1-C 12 alkoxy group, an unsubstituted or Ra-substituted C1-C 12 alkoxyalkyl group; R 22 and R 23 Each independently selected from an unsubstituted or Ra-substituted C1-C 12 alkylene group, an unsubstituted or Ra-substituted C2-C 12 alkenylene group, an unsubstituted or Ra-substituted C6-C 26 arylene group, an unsubstituted or Ra-substituted C2-C 12 heteroarylene group; R 24 to R 27 Each independently selected from an unsubstituted or Ra-substituted C1-C 12 alkoxyalkyl group; The substituent Ra of each group is independently selected from halogen.

[0034] By controlling the mass percentage content D of the cyanide compound within the above range, it is beneficial to better improve the cycle performance and high-temperature performance of the electrochemical device.

[0035] In some embodiments of the present application, 0.05 ≤ X / D ≤ 1. By controlling the value of X / D within the above range, it is beneficial to form a synergistic effect between the compound shown in formula (I) and the cyanide compound to improve the cycle performance and safety performance of the electrochemical device.

[0036] In some embodiments of the present application, the electrolyte includes at least one of the following compounds IV-1 to IV-4, V-1 to V-3, VI-1 to VI-4, VII-1 or VIII-1:

[0037]

[0038]

[0039] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions: (i) the electrolyte includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium difluoro(oxalato)borate. Based on the mass of the electrolyte, the mass percentage content Y of the first lithium salt is 5% to 13%; (ii) the electrolyte includes a second lithium salt, and the second lithium salt includes lithium difluorophosphate and / or lithium bis(oxalato)borate. Based on the mass of the electrolyte, the mass percentage content Y1 of the second lithium salt is 0.05% to 1%. By selecting the above first lithium salt and / or second lithium salt and regulating the mass percentage content of the first lithium salt and / or second lithium salt within the above range, it is beneficial to form a synergistic effect between the first lithium salt and / or second lithium salt and the electrolyte, thereby improving the cycling performance and safety performance of the electrochemical device.

[0040] The second aspect of the present application provides an electrochemical device, including a positive electrode and the electrolyte in any of the foregoing embodiments. After the electrochemical device undergoes at least 400 cycles, in the Raman spectrum of the positive electrode obtained by disassembling, 2 ≤ R2 / R1 ≤ 4 is satisfied, where R1 is the maximum peak intensity value between 620 cm -1 and 700 cm -1 , and R2 is the maximum peak intensity value between 500 cm -1 and 600 cm -1 .

[0041] In some embodiments of the present application, the electrochemical device further includes a negative electrode, and the negative electrode includes a negative electrode material layer. After the electrochemical device undergoes at least 400 cycles, based on the mass of the negative electrode material layer, the mass percentage content of Co on the surface of the disassembled negative electrode is less than or equal to 0.12%.

[0042] In some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions: (iii) in a differential scanning calorimetry (DSC) with a heating rate of 10 °C / min, at least one endothermic peak appears in the range of 140 °C to 163 °C; (iv) the electrochemical device further includes a separator, and the thermal shrinkage rate of the separator at 135 °C is 2% to 5%, where the thermal shrinkage rate includes the thermal shrinkage rate in the width direction (TD direction) and the thermal shrinkage rate in the length direction (MD direction).

[0043] The third aspect of the present application provides an electronic device, including the electrochemical device in any of the foregoing embodiments of the present application.

[0044] The present application provides an electrolyte, an electrochemical device and an electronic device comprising the electrolyte. The electrolyte comprises a compound represented by formula (I), and the mass percentage content X of the compound represented by formula (I) is 0.05% to 3%, which is beneficial to form a stable CEI on the surface of the positive electrode and a stable SEI on the surface of the negative electrode. In this way, during the cycling of the electrochemical device, it is beneficial to reduce the loss of solvents and additives in the electrolyte, reduce the heat generation of the positive electrode and the negative electrode; and reduce the influence on the crystal structure of the positive electrode active material, thereby reducing the fragmentation of the positive electrode active material particles and alleviating the dissolution phenomenon of transition metals, thus improving the cycling performance and safety performance of the electrochemical device. Description of the Drawings

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the drawings required for use in the embodiments and the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application.

[0046] Figure 1 It is the Raman spectrum of the positive electrode disassembled in Examples 1-4 and Comparative Examples 1-1 of the present application. Detailed Embodiments

[0047] To make the objectives, technical solutions and advantages of the present application more clearly understood, the present application will be further described in detail below with reference to the drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other technical solutions obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0048] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is taken as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries.

[0049] The first aspect of the present application provides an electrolyte, which comprises a compound represented by formula (I). Based on the mass of the electrolyte, the mass percentage content X of the compound represented by formula (I) is 0.05% to 3%:

[0050]

[0051] Wherein, R1 and R2 are each independently selected from H, F, C1-C5 alkyl, C1-C5 alkoxy, or C2-C5 alkenyl, C2-C5 alkynyl; R is selected from O or -CH(R3)-, and R3 is selected from H, F, C1-C5 alkyl, or C1-C5 alkoxy; Rb is selected from H, F, C1-C5 alkyl, or C1-C5 alkoxy; A and B are each independently selected from -CO- or -SO2-; W is selected from CH2 or O; M -One selected from groups M1 to M3:

[0052]

[0053] For example, the mass percentage content X of the compound represented by formula (I) can be 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the electrolyte includes the compound represented by formula (I) and the mass percentage content X of the compound represented by formula (I) is 0.05% to 3%, it is beneficial to form a stable CEI on the positive electrode surface and a stable SEI on the negative electrode surface, and can reduce the side reactions between the electrolyte and the positive electrode active material or the negative electrode active material. Thus, during the cycling of the electrochemical device, it is beneficial to reduce the loss of solvents and additives in the electrolyte, reduce the heat generation of the positive electrode and the negative electrode; and reduce the influence on the crystal structure of the positive electrode active material, thereby reducing the fragmentation of the positive electrode active material particles and alleviating the dissolution phenomenon of transition metals, so as to improve the cycling performance and safety performance of the electrochemical device.

[0054] Preferably, the compound represented by formula (I) is one of the following compounds I-1 to I-13. In some embodiments of the present application, the electrolyte includes at least one of the following compounds I-1 to I-13:

[0055]

[0056]

[0057] In some embodiments of the present application, the electrolyte further includes a cyclic sulfonate, which includes a cyclic monosulfonate and / or a cyclic disulfonate. Based on the mass of the electrolyte, the mass percentage content of the cyclic sulfonate is 0.01% to 10%, preferably 0.1% to 5%; the cyclic monosulfonate includes at least one of 1,3-propane sultone, 1,2-propane sultone, 1,4-butane sultone, 1,2-butane sultone, 1,3-butane sultone, 2,4-butane sultone or 1,3-pentane sultone; the cyclic disulfonate includes methylene methanedisulfonate and / or ethylene methanedisulfonate. For example, the mass percentage content of the cyclic sulfonate can be 0.01%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the mass percentage content of the cyclic sulfonate is too low (e.g., less than 0.01%), a stable SEI and CEI cannot be formed, thereby reducing the side reactions between the electrolyte and the positive electrode active material and the negative electrode active material, and thus the cycle performance and safety performance of the electrochemical device cannot be improved. When the mass percentage content of the cyclic sulfonate is too high (e.g., higher than 10%), the SEI and CEI will be too thick or too dense, affecting the transport of lithium ions, and thus affecting the kinetic performance of the electrochemical device, such as impedance and cycle performance. By selecting the above cyclic sulfonate and controlling the mass percentage content of the cyclic sulfonate within the above range, it is beneficial to improve the cycle performance and safety performance of the electrochemical device and reduce the impedance.

[0058] In some embodiments of the present application, the electrolyte includes a compound represented by formula (II):

[0059]

[0060] Wherein, D and E each independently selected from C1 to C8 alkylene or C1 to C8 fluoroalkylene, and L is selected from a single bond or -OSO2-.

[0061] In some embodiments of the present application, the electrolyte includes a compound represented by formula (II-1):

[0062]

[0063] Wherein, R6 and R7 each independently selected from H, F or C1 to C4 alkyl, and n3 is 1, 2, 3 or 4. The compound represented by formula (II-1) is a cyclic monosulfonate. By selecting the cyclic monosulfonate represented by formula (II-1), it is beneficial to improve the cycle performance and safety performance of the electrochemical device.

[0064] In some embodiments of the present application, the electrolyte includes a compound represented by formula (II-2):

[0065]

[0066] Among them, D and E are each independently selected from C1-C8 alkylene or C1-C8 fluoroalkylene. The compound represented by formula (II-2) is a cyclic disulfonate. By selecting the cyclic disulfonate represented by formula (II-2), it is beneficial to improve the cycle performance and safety performance of the electrochemical device.

[0067] In some embodiments of the present application, the electrolyte includes the compound represented by formula (II-1) and the compound represented by formula (II-2), that is, the electrolyte includes a cyclic monosulfonate and a cyclic disulfonate. When the electrolyte includes both a cyclic monosulfonate and a cyclic disulfonate, the ratio of the cyclic monosulfonate to the cyclic disulfonate is not particularly limited as long as the object of the present application can be achieved. For example, the mass ratio of the cyclic monosulfonate to the cyclic disulfonate is 1:1.

[0068] In some embodiments of the present application, the electrolyte further includes the compound represented by formula (III). Based on the mass of the electrolyte, the mass percentage content C of the compound represented by formula (III) is 0.5% to 16%, and 0.03 ≤ X / C ≤ 1, preferably 0.03 ≤ X / C ≤ 0.2:

[0069]

[0070] Among them, R 12 to R 15 are each independently selected from H, F, C1-C 10 fluoroalkyl, C1-C 10 fluoroalkoxy or C1-C 10 fluoroalkoxyalkyl, and R 12 to R 15 are not simultaneously H.

[0071] Preferably, the compound represented by formula (III) is one of the following compounds III-1 to III-6. In some embodiments of the present application, the electrolyte includes at least one of the following compounds III-1 to III-6:

[0072]

[0073] For example, the mass percentage content C of the compound represented by formula (III) can be 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 16%, or any range therebetween, and the value of X / C can be 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8, 1, or any range therebetween. Without being limited to any theory, the inventors of the present application have found that including the compound represented by formula (III) in the electrolyte is beneficial to improving the stability of the SEI, reducing the side reactions between the electrolyte and the negative electrode active material, and improving the cycling performance of the electrochemical device; and, improving the accumulation of by-products generated by side reactions during the cycling of the electrochemical device and reducing the impedance of the electrochemical device. However, when the mass percentage content C of the compound represented by formula (III) is too high (for example, higher than 16%), the SEI is too thick or too dense, affecting the transport of lithium ions and thus affecting the kinetic performance of the electrochemical device, such as impedance and cycling performance. By controlling the mass percentage content C of the compound represented by formula (III) within the above range, it is beneficial to better improve the cycling performance of the electrochemical device and reduce the impedance of the electrochemical device; by controlling the value of X / C within the above range, it is beneficial to form a synergistic effect between the compound represented by formula (I) and the compound represented by formula (III) to improve the cycling performance and safety performance of the electrochemical device.

[0074] In some embodiments of the present application, the electrolyte further includes a cyano-containing compound, and the cyano-containing compound includes at least one of the compounds represented by formula (IV) to formula (VII). Based on the mass of the electrolyte, the mass percentage content D of the cyano-containing compound is 0.2% to 10%:

[0075]

[0076]

[0077]

[0078]

[0079] Wherein, R 16 is selected from unsubstituted or Ra-substituted C1 to C 12 alkylene, unsubstituted or Ra-substituted C1 to C 12 alkoxy; R 17 and R 18 each independently is selected from a single bond, unsubstituted or Ra-substituted C1 to C 12 alkylene, unsubstituted or Ra-substituted C1 to C 12 alkoxy; R 19 to R 21 each independently is selected from a single bond, unsubstituted or Ra-substituted C1 to C 12an alkylene group, C1 to C which is unsubstituted or substituted by Ra 12 an alkoxy group, C1 to C which is unsubstituted or substituted by Ra 12 an alkoxyalkyl group; R 22 and R 23 each independently selected from an alkylene group, C1 to C which is unsubstituted or substituted by Ra 12 an alkenylene group, C2 to C which is unsubstituted or substituted by Ra 12 an arylene group, C6 to C which is unsubstituted or substituted by Ra 26 a heterocycloalkylene group, C2 to C which is unsubstituted or substituted by Ra 12 ; R 24 to R 27 each independently selected from an alkoxyalkyl group, C1 to C which is unsubstituted or substituted by Ra 12 The substituent Ra of each group is independently selected from halogen.

[0080] Preferably, the compound represented by formula (IV) is one of the following compounds IV-1 to IV-4, the compound represented by formula (V) is one of the following compounds V-1 to V-3, the compound represented by formula (VI) is one of the following compounds VI-1 to VI-4, the compound represented by formula (VII) is VII-1, and the compound represented by formula (VIII) is VIII-1.

[0081] In some embodiments of the present application, the electrolyte includes at least one of the following compounds IV-1 to IV-4, V-1 to V-3, VI-1 to VI-4, VII-1 or VIII-1:

[0082]

[0083]

[0084] For example, the mass percentage content D of the cyano group-containing compound is 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween. Without being limited to any theory, the inventors of the present application have found that the energy level of the lone pair electrons in the cyano group of the cyano group-containing compound is close to the energy level of the vacant orbitals in the outermost layer of the transition metal atoms in the positive electrode active material. Thus, the cyano group-containing compound can form a complex structure with the positive electrode active material on the surface of the positive electrode, which can reduce the side reactions between the electrolyte and the positive electrode active material and is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device. However, when the mass percentage content D of the cyano group-containing compound is too high (for example, higher than 10%), too many complex structures are formed between the cyano group-containing compound and the positive electrode active material, which affects the transport of lithium ions and thus affects the kinetic performance of the electrochemical device, such as impedance and cycle performance. By adjusting the mass percentage content D of the cyano group-containing compound within the above range, it is beneficial to better improve the cycle performance and high-temperature performance of the electrochemical device.

[0085] In some embodiments of the present application, 0.05 ≤ X / D ≤ 1. For example, the value of X / D can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range therebetween. By adjusting the value of X / D within the above range, it is beneficial to form a synergistic effect between the compound represented by formula (I) and the cyano group-containing compound to improve the cycle performance and safety performance of the electrochemical device.

[0086] In some embodiments of the present application, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of fluorine element, boron element or phosphorus element. Without being limited to any theory, the inventors of the present application have found that the inclusion of the above elements in the lithium salt is beneficial to forming a synergistic effect between the lithium salt and the electrolyte, thereby improving the cycle performance and safety performance of the electrochemical device.

[0087] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions: (i) the electrolyte includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide or lithium difluorooxalate borate, and based on the mass of the electrolyte, the mass percentage content Y of the lithium salt is 5% to 13%; (ii) the electrolyte includes a second lithium salt, and the second lithium salt includes lithium difluorophosphate and / or lithium bis(oxalate) borate, and based on the mass of the electrolyte, the mass percentage content Y1 of lithium difluorophosphate and / or lithium bis(oxalate) borate is 0.05% to 1%.

[0088] For example, the mass percentage content Y of the first lithium salt can be 5%, 8%, 10%, 13% or any range therebetween. By selecting the above first lithium salt, it is beneficial to form a synergistic effect between the first lithium salt and the electrolyte, thereby improving the cycle performance and safety performance of the electrochemical device.

[0089] For example, the mass percentage Y1 of the second lithium salt can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range therebetween. By selecting the above-mentioned second lithium salt, it is more conducive to the formation of a synergistic effect between the second lithium salt and the electrolyte, thereby improving the cycle performance and safety performance of the electrochemical device.

[0090] The second aspect of the present application provides an electrochemical device, including a positive electrode and an electrolyte in any of the foregoing embodiments. After the electrochemical device undergoes at least 400 cycles, in the Raman spectrogram of the positive electrode obtained by disassembly, 2 ≤ R2 / R1 ≤ 4 is satisfied, where R1 is the maximum peak intensity value between 620 cm -1 to 700 cm -1 and R2 is the maximum peak intensity value between 500 cm -1 to 600 cm -1 For example, the value of R2 / R1 can be 2, 2.2, 2.5, 2.8, 3, 3.3, 3.5, 3.7, 4 or any range therebetween. When the value of R2 / R1 is within the above range, the positive electrode can maintain a stable crystal structure in the electrolyte provided in the present application, further improving the cycle performance of the electrochemical device.

[0091] In some embodiments of the present application, the electrochemical device further includes a negative electrode, and the negative electrode includes a negative electrode material layer. After the electrochemical device undergoes at least 400 cycles, based on the mass of the negative electrode material layer, the mass percentage of Co on the surface of the disassembled negative electrode is less than or equal to 0.12%, indicating that the electrolyte provided in the present application effectively inhibits the dissolution of cobalt elements in the positive electrode material and can effectively improve the cycle performance of the electrochemical device.

[0092] In some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions: (iii) in the differential scanning calorimetry (DSC) with a heating rate of 10 °C / min, at least one endothermic peak appears in the range of 140 °C to 163 °C; (iv) the electrochemical device further includes a separator, and the thermal shrinkage rate of the separator at 135 °C is 2% to 5%.

[0093] For example, in the DSC curve of the positive electrode, the temperature corresponding to the endothermic peak can be 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 163 °C or any range therebetween. It shows that the positive electrode has good thermal stability.

[0094] For example, the thermal shrinkage rate of the separator film at 135 °C can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range therebetween. This indicates that the separator film has good thermal stability, which is conducive to improving the safety performance of the electrochemical device.

[0095] The positive electrode generally includes a positive electrode current collector and a positive electrode material layer. In this application, there is no particular limitation on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collector, etc. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness is 8 μm to 12 μm. In this application, the positive electrode material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector. There is no particular limitation in this application, as long as the purpose of this application can be achieved.

[0096] In this application, the positive electrode material layer includes a positive electrode active material. There is no particular limitation on the positive electrode active material in this application, as long as the purpose of this application can be achieved. For example, it can include at least one of composite oxides of lithium or transition metal elements. There is no particular limitation on the above-mentioned transition metal elements in this application, as long as the purpose of this application can be achieved. For example, it can include at least one of nickel, manganese, cobalt, or iron. Specifically, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0097] The positive electrode material layer may further include a binder. There is no particular limitation on the binder in this application, as long as the purpose of this application can be achieved. For example, it can include at least one of, but is not limited to, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0098] In the present application, the positive electrode material layer may further include a conductive agent. There is no particular limitation on the conductive agent in the present application, as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials, or conductive polymers. The above carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal 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 above conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0099] Optionally, the positive electrode may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. There is no particular limitation on the composition of the conductive layer in the present application, and it may be a commonly used conductive layer in the art. For example, it may include but is not limited to the above conductive agent and the above binder.

[0100] The negative electrode generally includes a negative electrode current collector. There is no particular limitation on the negative electrode current collector in the present application, as long as the object of the present application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors, etc. In the present application, there is no particular limitation on the thickness of the current collector of the negative electrode, as long as the object of the present application can be achieved. For example, the thickness is 4 μm to 12 μm. In the present application, the negative electrode material layer may be disposed on one surface in the thickness direction of the negative electrode current collector or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here may be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no particular limitation in the present application, as long as the object of the present application can be achieved.

[0101] In the present application, the negative electrode material layer includes a negative electrode active material. Among them, there is no particular limitation on the negative electrode active material, as long as the object of the present application can be achieved. For example, it may include but is not limited to natural graphite, artificial graphite, mesophase microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloy.

[0102] In the present application, the negative electrode material layer may further include a conductive agent. There is no particular limitation on the conductive agent in the present application, as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of the above conductive agents.

[0103] In the present application, the negative electrode material layer may further include a binder. There is no particular limitation on the binder in the present application, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned binders.

[0104] Optionally, the negative electrode may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. There is no particular limitation on the composition of the conductive layer in the present application. It may be a commonly used conductive layer in the art. The conductive layer may include, but is not limited to, the above-mentioned conductive agent and the above-mentioned binder.

[0105] There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) membranes mainly composed of polytetrafluoroethylene, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, rolled membranes or spun membranes, with PE being preferred. The separator of the present application may have a porous structure, and there is no particular limitation on the size of the pore diameter, as long as the object of the present application can be achieved. For example, the size of the pore diameter may be from 0.01 μm to 1 μm. In the present application, there is no particular limitation on the thickness of the separator, as long as the object of the present application can be achieved. For example, the thickness may be from 5 μm to 500 μm.

[0106] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a membrane or a composite membrane having a porous structure. The material of the substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven 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 layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0107] The inorganic layer may include, but is not limited to, inorganic particles and an inorganic layer binder. There is no particular limitation on the inorganic particles in this application. For example, it may include at least one of alumina, silica, magnesia, 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. There is no particular limitation on the inorganic layer binder in this application. For example, it may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride - hexafluoropropylene).

[0108] In the present application, the electrolyte may further include a non-aqueous solvent. There is no particular limitation on the non-aqueous solvent in the present application, as long as the object of the present application can be achieved. For example, it may include at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above-mentioned carbonate compounds may include at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include 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 (MEC). The above-mentioned cyclic carbonates may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compounds may include at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, or caprolactone. The above-mentioned ether compounds may include 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 above-mentioned other organic solvents may include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.

[0109] There is no particular limitation on the electrochemical device of the present application, and it may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device 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, etc.

[0110] The preparation process of the electrochemical device is well-known to those skilled in the art, and there is no special limitation in this application. 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 structure electrode assembly. Then, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly. Placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging / discharging.

[0111] The third aspect of this application provides an electronic device including the electrochemical device in any of the foregoing embodiments of this application. The electrochemical device provided by this application has good cycle performance and safety performance, so that the electronic device provided by this application has a long service life and good safety performance.

[0112] The electronic device of this application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0113] Examples

[0114] Hereinafter, examples and comparative examples are given to illustrate the embodiments of this application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0115] Testing method and device:

[0116] 80°C storage thickness expansion rate test:

[0117] Discharge the lithium-ion battery at 0.5C constant current to 3.0V at 25°C, then charge it at 0.5C constant current to 4.5V, and charge it at constant voltage of 4.5V to 0.05C. Use a micrometer to measure and record the thickness of the lithium-ion battery as H 11Place it in an oven at 80°C and apply a constant voltage of 4.5V for 7 hours. After 7 hours, measure and record the thickness of the battery using a micrometer, denoted as H 12 。

[0118] Swelling rate of storage thickness at 80°C = (H 12 - H 11 ) / H 11 × 100%.

[0119] High-temperature cycling test at 45°C:

[0120] Place the lithium-ion battery in an incubator at 45°C and let it stand for 30 minutes to reach a constant temperature. Charge the lithium-ion battery at a constant current of 0.2C to 4.5V at 45°C, then charge it at a constant voltage of 4.5V until the current reaches 0.05C. Let it stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V and let it stand for 5 minutes to test the initial capacity; then charge it at a constant current of 1.3C to 4.15V and charge it at a constant voltage of 4.15V until the current is 1C; then charge it at a constant current of 1C to 4.25V, and then charge it at a constant voltage of 4.25V until the current is 0.8C; then charge it at a constant current of 0.8C to 4.5V, and then charge it at a constant voltage of 4.5V until the current is 0.05C; place it for 5 minutes; then discharge it at a constant current of 1C until the voltage is 3.0V and let it stand for 5 minutes; this is one charge-discharge cycle. Charge / discharge in this way and calculate the capacity retention rate and thickness swelling rate of the lithium-ion battery after 400 cycles.

[0121] Capacity retention rate after 400 cycles at 45°C = Discharge capacity of the 400th cycle / Discharge capacity of the 1st cycle × 100%.

[0122] Thickness swelling rate after 400 cycles at 45°C = (Thickness of the lithium-ion battery after cycling - Thickness of the lithium-ion battery before cycling) / Thickness of the lithium-ion battery before cycling × 100%.

[0123] Hot-box test:

[0124] At 25°C, charge the lithium-ion battery at a constant current of 0.7C to 4.5V and then charge it at a constant voltage of 4.5V until the current is 0.05C. Place the lithium-ion battery in a high-temperature chamber and heat it to 135°C at a temperature rise rate of 5 ± 2°C / minute for the 135°C Hot-box test (heat it to 137°C at a temperature rise rate of 5 ± 2°C / minute for the 137°C Hot-box test), then hold for 1 hour and record the changes in the voltage, temperature of the lithium-ion battery, and the temperature of the hot-box. The lithium-ion battery passes the test if it does not catch fire, explode, or emit smoke. Test 10 lithium-ion batteries for each example or comparative example and record the number of lithium-ion batteries that pass the test.

[0125] Test of DC resistance (DCR) at 25°C:

[0126] The lithium-ion battery was left standing in an incubator at 25°C for 1 hour to reach a constant temperature; it was charged at a constant current of 0.5C to 4.2V, then charged at a constant current of 0.3C to 4.5V, charged at a constant voltage of 4.5V until the current reached 0.02C, and left standing for 30 minutes; then it was discharged at a constant current of 0.1C to 3.4V and left standing for 30 minutes, and the capacity of this step was used as the benchmark. At 25°C, it was charged at a constant current of 0.5C to 4.2V, then charged at a constant current of 0.3C to 4.5V, charged at a constant voltage of 4.5V until the current reached 0.02C, and left standing for 30 minutes; it was discharged at a constant current of 0.1C for 60 minutes (the capacity was calculated based on the theoretical capacity of the lithium-ion battery), and the voltage at this time was recorded as V1; then it was discharged at a constant current of 1C for 1s (the capacity was calculated based on the theoretical capacity of the lithium-ion battery), and the voltage at this time was recorded as V2, and the DC impedance corresponding to the 20% state of charge (SOC) of the battery cell was calculated. 20% SOC DCR = (V1 - V2) / 1C.

[0127] Thermal shrinkage rate test:

[0128] The separator of the lithium-ion battery was disassembled, and the separator was laminated along the length direction to obtain three layers of separators with the upper edges aligned in the length direction. A knife die with a size of 72.5mm × 54.2mm was used. Among them, the edge with a length of 72.5mm of the knife die was placed parallel to the length direction of the separator, and three samples of the separator were obtained by punching with a stamping machine. The size X1 in the width direction (TD direction) and the size Z1 in the length direction (MD direction) of the separator samples were measured. The separator samples were laminated in the way that one white paper was placed between each two sheets (the size of the white paper was A6, 105mm × 148mm). The laminated separator samples were placed in a steel plate, the oven temperature was set to 135°C, and after the oven reached the set temperature, the separator was put into the oven together with the steel plate and baked for 1h. After baking, the samples were taken out and left standing at room temperature for 10min. The dimensions in the length direction and width direction of the separators with the same number were measured respectively. The average size of each sample in the width direction was recorded as X2, and the average size of each sample in the length direction was recorded as Z2. If the shrinkage of the sample edge was uneven, the position with the maximum shrinkage was taken as the standard.

[0129] Thermal shrinkage calculation: Shrinkage rate = (Size before baking - Size after baking) / Size before baking × 100%

[0130] That is: TD thermal shrinkage rate = (X1 - X2) / X1 × 100%,

[0131] MD thermal shrinkage rate = (Z1 - Z2) / Z1 × 100%.

[0132] Raman spectroscopy test:

[0133] After subjecting the lithium-ion battery to 400 charge-discharge cycles and fully discharging it, the positive electrode was disassembled and taken out in a glove box (argon atmosphere). The positive electrode was cut into electrode sheets with a size of 3 cm × 3 cm. The cut electrode sheets were rinsed several times with DMC and then dried for later use. The dried electrode sheets were cut and adhered to a flat glass plate, and tested with a Raman spectrometer (model: HR Evolution), and relevant data were collected.

[0134] As Figure 1 shown, for the lithium-ion batteries in Examples 1-4 and Comparative Examples 1-1 after 400 charge-discharge cycles (cls), the Raman spectra of the disassembled positive electrodes are shown. In Example 1-4, the maximum peak intensity value R1 between 620 cm -1 and 700 cm -1 is 59.29, and the maximum peak intensity value R2 between 500 cm -1 and 600 cm -1 is 194.11, and R2 / R1 = 3.27; in Comparative Example 1-1, the maximum peak intensity value R1 between 620 cm -1 and 700 cm -1 is 59.30, and the maximum peak intensity value R2 between 500 cm -1 and 600 cm -1 is 96.92, and R2 / R1 = 1.63. It can be seen that the value of R2 / R1 in Examples 1-4 is within the scope of this application, while the value of R2 / R1 in Comparative Example 1-1 is not within the scope of this application.

[0135] Example 1-1

[0136] <Preparation of Positive Electrode>

[0137] The positive electrode active material lithium cobaltate, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed according to a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) was added. The mixture was stirred in a vacuum blender until the system became homogeneous and transparent to obtain a positive electrode slurry, where the solid content of the positive electrode slurry was 70%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and the aluminum foil was dried at 120°C for 1 h to obtain a positive electrode with a positive electrode material layer coated on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode with positive electrode material layers coated on both sides. Then, after cold pressing, slicing, and slitting, it was dried under vacuum conditions at 120°C for 1 h to obtain a positive electrode with a specification of 74 mm × 867 mm.

[0138] <Preparation of Negative Electrode>

[0139] The artificial graphite as the negative electrode active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethyl cellulose (CMC) as the thickener are mixed at a mass ratio of 95:2:2:1, and deionized water is added. Under the action of a vacuum mixer, a negative electrode slurry is obtained, and the solid content of the negative electrode slurry is 75%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, and the copper foil is dried at 120 °C to obtain a negative electrode with a negative electrode material layer coated on one side and a coating thickness of 130 μm. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode with a negative electrode material layer coated on both sides. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 1 h to obtain a negative electrode with a specification of 74 mm × 867 mm.

[0140] <Preparation of electrolyte>

[0141] In an argon atmosphere glove box with a water content < 10 ppm, ethylene carbonate, diethyl carbonate, and propyl propionate are formulated into a basic solvent at a mass ratio of 3:4:3. Then, lithium salt lithium hexafluorophosphate (LiPF6) and compound I-1 shown in formula (I) are added to the basic solvent to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage content of LiPF6 is 12%, and the mass percentage content of the compound shown in formula (I) is 0.01%, and the balance is the basic solvent.

[0142] <Preparation of separator>

[0143] A porous PE film with a thickness of 7 μm (provided by Celgard) is used.

[0144] <Preparation of lithium-ion battery>

[0145] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator placed in the middle of the positive electrode and the negative electrode to play an isolation role, and a wound electrode assembly is obtained. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried and then injected with electrolyte, and a lithium-ion battery is obtained through processes such as vacuum packaging, standing, formation, degassing, and edge trimming. The upper limit voltage of formation is 4.15 V, the formation temperature is 70 °C, and the formation standing time is 2 h.

[0146] In Examples 1-2 to 1-13, except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1.

[0147] In Examples 2-1 to 2-7, except that in the <Preparation of electrolyte>, a cyclic sulfonic acid ester is also added and the relevant preparation parameters are adjusted according to Table 2, the rest are the same as Example 1-4.

[0148] In Examples 3-1 to 3-12, except that in <Preparation of Electrolyte>, a compound represented by formula (III) was further added and the relevant preparation parameters were adjusted according to Table 3, the rest was the same as in Examples 1-4.

[0149] In Examples 4-1 to 4-11, except that in <Preparation of Electrolyte>, a cyanide compound was further added and the relevant preparation parameters were adjusted according to Table 4, the rest was the same as in Examples 1-4.

[0150] In Examples 5-1 to 5-4, except that in <Preparation of Electrolyte>, cyclic sulfonate, the compound represented by formula (III), and the cyanide compound were optionally added according to Table 5, the rest was the same as in Examples 1-4.

[0151] In Examples 6-1 to 6-7, except that the relevant preparation parameters were adjusted according to Table 6, the rest was the same as in Examples 1-4.

[0152] In Comparative Examples 1-1 to 1-3, except that the relevant preparation parameters were adjusted according to Table 1, the rest was the same as in Example 1-1.

[0153] The relevant preparation parameters and performance tests of Examples 1-1 to 1-13 and Comparative Examples 1-1 to 1-3 are shown in Table 1; the relevant preparation parameters and performance tests of Examples 2-1 to 2-7 are shown in Table 2; the relevant preparation parameters and performance tests of Examples 3-1 to 3-12 are shown in Table 3; the relevant preparation parameters and performance tests of Examples 4-1 to 4-11 are shown in Table 4; the relevant preparation parameters and performance tests of Examples 5-1 to 5-4 are shown in Table 5; the relevant preparation parameters and performance tests of Examples 6-1 to 6-7 are shown in Table 6.

[0154] Table 1

[0155]

[0156]

[0157] Note: " / " in Table 1 indicates the absence of corresponding preparation parameters or substances.

[0158] It can be seen from Examples 1-1 to 1-13 and Comparative Example 1-1 that when the electrolyte includes the compound shown in formula (I), the cycle and safety performance of the lithium-ion battery can be improved. It can be seen from Examples 1-1 to 1-13, Comparative Example 1-2 and Comparative Example 1-3 that when the mass percentage content of the compound shown in formula (I) is within the scope of the present application, the obtained lithium-ion battery has better cycle performance and safety performance at the same time. It can be seen from Examples 1-1 to 1-13 that by selecting the compound shown in formula (I) within the scope of the present application, the obtained lithium-ion battery has good cycle performance and safety performance at the same time.

[0159] Table 2

[0160]

[0161] Note: " / " in Table 2 indicates the absence of corresponding preparation parameters or substances.

[0162] It can be seen from Examples 1-4, 2-1 to 2-8 that when the electrolyte includes the cyclic sulfonate in addition to the compound shown in formula (I), the cycle performance and storage performance of the lithium-ion battery can be further improved, and the impedance of the lithium-ion battery can be reduced. It can be seen from Examples 2-1 to 2-7 that when the cyclic sulfonate within the scope of the present application is selected and the mass percentage content of the cyclic sulfonate is regulated within the scope of the present application, the obtained lithium-ion battery has good cycle performance and storage performance and a lower impedance at the same time.

[0163] Table 3

[0164]

[0165] Note: In the examples in Table 3, X = 0.5%, and " / " in Table 3 indicates the absence of corresponding preparation parameters or substances.

[0166] It can be seen from Examples 1-4, 3-1 to 3-12 that when the electrolyte includes the compound shown in formula (III) in addition to the compound shown in formula (I), the cycle performance and safety performance of the lithium-ion battery can be further improved. It can be seen from Examples 3-1 to 3-12 that when the compound shown in formula (III) within the scope of the present application is selected, the mass percentage content of the compound shown in formula (III) is regulated, and the value of X / C is regulated within the scope of the present application, the obtained lithium-ion battery has good cycle performance and safety performance at the same time.

[0167] Table 4

[0168]

[0169]

[0170] Note: In the examples in Table 4, X = 0.5%, and " / " in Table 4 indicates the absence of corresponding preparation parameters or substances.

[0171] It can be seen from Examples 1-4, Examples 4-1 to Examples 4-11 that when the electrolyte further includes a cyano-containing compound on the basis of the compound shown in formula (I), the cycle performance and storage performance of the lithium-ion battery can be further improved. It can be seen from Examples 4-1 to Examples 4-11 that when a cyano-containing compound within the scope of the present application is selected, the mass percentage content of the cyano-containing compound is regulated, and the value of X / D is regulated within the scope of the present application, the obtained lithium-ion battery has good cycle performance and storage performance at the same time.

[0172] Table 5

[0173]

[0174] Note: " / " in Table 5 indicates the absence of corresponding preparation parameters or substances.

[0175] It can be seen from Examples 1-4, Examples 5-1 to Examples 5-4 that when the electrolyte further includes at least two of a cyclic sulfonate, a compound shown in formula (III), or a cyano-containing compound on the basis of the compound shown in formula (I), the cycle performance of the lithium-ion battery can be further improved and the impedance can be reduced. It can be seen from Examples 5-1 to Examples 5-4 that the compound shown in formula (I) has good compatibility with the cyclic sulfonate, the compound shown in formula (III), and the cyano-containing compound, and the obtained lithium-ion batteries all have good cycle performance and safety performance, as well as a lower impedance.

[0176] Table 6

[0177]

[0178] Note: In the examples in Table 6, X = 0.5%, and " / " in Table 6 indicates the absence of corresponding preparation parameters or substances.

[0179] The mass percentage content of the lithium salt, the type of the lithium salt, and the thermal shrinkage rate of the separator in the electrolyte usually affect the performance of the lithium-ion battery, such as cycle performance and safety performance. It can be seen from Examples 1-4, Examples 6-1 to Examples 6-7 that when the mass percentage content of the first lithium salt and the second lithium salt, the types of the first lithium salt and the second lithium salt, and the thermal shrinkage rate of the separator are within the scope of the present application, the obtained lithium-ion battery has good cycle performance and safety performance.

[0180] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrolyte, which comprises a compound represented by formula (I), and based on the mass of the electrolyte, the mass percentage content X of the compound represented by formula (I) is 0.05% to 3%: Wherein, R1 and R2 are each independently selected from H, F, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms; R is selected from O or -CH(R3)-, and R3 is selected from H, F, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms; Rb is selected from H, F, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms; A and B are each independently selected from -CO- or -SO2-; W is selected from CH2 or O; M - selected from one of the groups M1 to M3:

2. The electrolyte according to claim 1, which comprises at least one of the following compounds I-1 to I-13:

3. The electrolyte according to claim 1, which further comprises a cyclic sulfonate, and the cyclic sulfonate comprises a cyclic monosulfonate and / or a cyclic disulfonate. Based on the mass of the electrolyte, the mass percentage content of the cyclic sulfonate is 0.01% to 10%; The cyclic monosulfonate comprises at least one of 1,3-propane sultone, 1,2-propane sultone, 1,4-butane sultone, 1,2-butane sultone, 1,3-butane sultone, 2,4-butane sultone, or 1,3-pentane sultone; The cyclic disulfonate comprises methylene methanedisulfonate and / or ethylene methanedisulfonate.

4. The electrolyte according to claim 1, which further comprises a compound represented by formula (II): Among them, D and E are each independently selected from an alkylene group having 1 to 8 carbon atoms or a fluoroalkylene group having 1 to 8 carbon atoms, and L is selected from a single bond or -OSO2-.

5. The electrolyte according to claim 1, which comprises a compound represented by formula (II-1) and / or a compound represented by formula (II-2): Among them, R6 and R7 are each independently selected from H, F, or an alkyl group having 1 to 4 carbon atoms, and n3 is 1, 2, 3, or 4; Wherein, D and E are each independently selected from an alkylene group having 1 to 8 carbon atoms or a fluoroalkylene group having 1 to 8 carbon atoms.

6. The electrolyte according to claim 1, which further comprises a compound represented by formula (III). Based on the mass of the electrolyte, the mass percentage content C of the compound represented by formula (III) is 0.5% to 16%, and 0.03 ≤ X / C ≤ 1: Among them, R 12 to R 15 are each independently selected from H, F, C1 to C 10 fluoroalkyl, C1 to C 10 fluoroalkoxy or C1 to C 10 fluoroalkoxyalkyl, and R 12 to R 15 are not simultaneously H.

7. The electrolyte according to claim 1, which comprises at least one of the following compounds III-1 to III-6:

8. The electrolyte according to claim 1, which further comprises a cyano-containing compound, and the cyano-containing compound comprises at least one of the compounds represented by formula (IV) to formula (VII). Based on the mass of the electrolyte, the mass percentage content D of the cyano-containing compound is 0.2% to 10%: Among them, R 16 selected from C1-C 12 alkylene which is unsubstituted or substituted by Ra, C1-C 12 alkoxy; R 17 and R 18 each independently selected from a single bond, C1-C 12 alkylene which is unsubstituted or substituted by Ra, C1-C 12 alkoxy; R 19 to R 21 each independently selected from a single bond, C1-C 12 alkylene which is unsubstituted or substituted by Ra, C1-C 12 alkoxy, C1-C 12 alkoxyalkyl which is unsubstituted or substituted by Ra; R 22 and R 23 each independently selected from C1-C 12 alkylene which is unsubstituted or substituted by Ra, C2-C 12 alkenyl which is unsubstituted or substituted by Ra, C6-C 26 arylene which is unsubstituted or substituted by Ra, C2-C 12 heteroarylene which is unsubstituted or substituted by Ra; R 24 to R 27 each independently selected from C1-C 12 alkoxyalkyl which is unsubstituted or substituted by Ra; the substituents Ra of each group are each independently selected from halogen.

9. The electrolyte according to claim 8, which satisfies 0.05 ≤ X / D ≤ 1.

10. The electrolyte according to claim 1, which comprises at least one of the following compounds IV-1 to IV-4, V-1 to V-3, VI-1 to VI-4, VII-1 to VIII-1:

11. The electrolyte according to claim 1 satisfies at least one of the following conditions: (i) The electrolyte includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium difluoro(oxalato)borate. Based on the mass of the electrolyte, the mass percentage Y of the first lithium salt is 5% to 13%. (ii) The electrolyte includes a second lithium salt, and the second lithium salt includes lithium difluorophosphate and / or lithium bis(oxalato)borate. Based on the mass of the electrolyte, the mass percentage Y1 of the second lithium salt is 0.05% to 1%.

12. An electrochemical device, comprising a positive electrode and the electrolytic solution according to any one of claims 1 to 11, after the electrochemical device has undergone at least 400 cycles, in the Raman spectrogram of the positive electrode obtained by disassembling, 2 ≤ R2 / R1 ≤ 4 is satisfied, where R1 is the maximum peak intensity value between 620 cm -1 and 700 cm -1 ; R2 is the maximum peak intensity value between 500 cm -1 and 600 cm -1 .

13. The electrochemical device according to claim 12 further includes a negative electrode, and the negative electrode includes a negative electrode material layer. After at least 400 cycles of the electrochemical device, based on the mass of the negative electrode material layer, the mass percentage of Co on the surface of the disassembled negative electrode is less than or equal to 0.12%.

14. The electrochemical device according to claim 12 satisfies at least one of the following conditions: (iii) In the differential scanning calorimetry of the positive electrode with a heating rate of 10 °C / min, at least one endothermic peak appears in the range of 140 °C to 163 °C. (iv) The electrochemical device further includes a separator, and the thermal shrinkage rate of the separator at 135 °C is 2% to 5%.

15. An electronic device includes the electrochemical device according to any one of claims 12 to 14.

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