An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The positive electrode material layer comprises a positive electrode active material. The positive electrode active material comprises cobalt elements and nickel elements. The mass percentage of the nickel elements in the positive electrode active material is B%, and 0.05<=B<=20 based on the mass of the positive electrode active material. The electrolyte comprises lithium bisoxalate borate and 1,3,6-hexanetricarbonitrile. The mass percentage of the lithium bisoxalate borate in the electrolyte is C%, and the mass percentage of the 1,3,6-hexanetricarbonitrile in the electrolyte is D% based on the mass of the electrolyte. The electrochemical device satisfies 0.1<=(C+D) / B<=23. The electrochemical device provided by the application can balance the energy density and the high-temperature cycle performance.

Description

Technical Field

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

[0002] Lithium-ion batteries have advantages such as high energy density, light weight, and long cycle life, and are widely used in consumer batteries. As electronic products become increasingly thinner and more portable, higher demands are being placed on batteries in terms of energy density, high-temperature cycling performance, and charging speed.

[0003] To further improve the energy density of lithium-ion batteries, other elements can be doped into the positive and / or negative electrode active materials, such as nickel doping into the positive electrode active material LiCoO2. Ni doping can increase the specific capacity of the positive electrode active material, thereby improving the energy density of the lithium-ion battery; at the same time, nickel is inexpensive and environmentally friendly. However, the inherent lithium-nickel mixing after nickel doping can hinder the LiCoO2 process. + The migration of these molecules and the accelerated structural collapse of the positive electrode active material during cycling make it difficult to achieve both high energy density and high-temperature cycling performance in lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device that balance energy density and high-temperature cycling performance in the electrochemical device. The specific technical solution is as follows:

[0005] It should be noted that the invention description in this application uses lithium-ion batteries as an example of electrochemical devices to explain this application, but the electrochemical devices in this application are not limited to lithium-ion batteries.

[0006] A first aspect of this application provides an electrochemical device comprising a positive electrode and an electrolyte. The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material comprising cobalt and nickel. Based on the mass of the positive electrode active material, the mass percentage of nickel is B%, and 0.05 ≤ B ≤ 20. In some embodiments of this application, 0.1 ≤ B ≤ 10. For example, the mass percentage of nickel B% can be 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or a range consisting of any two values ​​therein. The electrolyte comprises lithium bis(oxalato)borate (LiBOB) and 1,3,6-hexanetrionitrile (HTCN), with the mass percentage of lithium bis(oxalato)borate being C% and the mass percentage of 1,3,6-hexanetrionitrile being D% based on the mass of the electrolyte; the electrochemical device satisfies 0.1 ≤ (C+D) / B ≤ 23. In some embodiments of this application, 0.1 ≤ (C+D) / B ≤ 4.6. For example, the value of (C+D) / B can be 0.1, 0.5, 1, 3, 4.6, 5, 8, 10, 13, 15, 18, 20, 23, or a range of any two values ​​therein.

[0007] The electrochemical device provided in this application can achieve a high energy density when the mass percentage of nickel is within the aforementioned range. By simultaneously introducing lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile into the electrolyte, on the one hand, lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile can simultaneously participate in the construction of the positive electrode electrolyte interface film (CEI film), inhibiting the dissolution of transition metals (such as nickel, cobalt, manganese, etc.) in the positive electrode active material; on the other hand, the boron in lithium bis(oxalato)borate can also combine with oxygen in the positive electrode active material, and the nitrogen atoms in 1,3,6-hexanetrionitrile can combine with high-valence nickel ions (such as Ni). 2+ Ni 3+ To reduce the presence of high-valence nickel ions in Li +The presence of nickel at specific sites improves the structural stability of the positive electrode active material. Furthermore, lithium bis(oxalate-borate) stabilizes lithium salts in the electrolyte, reduces the generation of substances like HF, suppresses side reactions at the interface between the positive and negative electrodes, and forms a solid electrolyte interphase (SEI) film on the surface of the negative electrode, mitigating the damage to the negative electrode active material caused by dissolved transition metals. This improves lithium-ion transport and structural instability issues caused by nickel doping in the positive electrode active material, thereby enhancing the high-temperature cycling performance of the electrochemical device. When the nickel content is too low, such as below 0.05%, the energy density of the electrochemical device cannot be increased; when the nickel content is too high, such as above 20%, the structural stability of the positive electrode active material decreases, and transition metals are easily dissolved, thus affecting the high-temperature cycling performance of the electrochemical device. When the (C+D) / B value is too small, for example, less than 0.1, the nickel content in the positive electrode active material is high, or the total content of lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile is low, affecting the high-temperature cycling performance of the electrochemical device. When the (C+D) / B value is too large, for example, greater than 23, the nickel content in the positive electrode active material is low, and the energy density of the electrochemical device is also low. Alternatively, the total content of lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile is high, which will generate more interfacial products at the interface between the positive electrode and the electrolyte, hindering the transport of Li+ at the interface and affecting the high-temperature cycling performance of the electrochemical device. By controlling the mass percentage of Ni within the above range, and simultaneously introducing lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile into the electrolyte, and controlling the (C+D) / B value within the above range, a synergistic effect is generated between the positive electrode and the electrolyte, enabling the electrochemical device provided in this application to balance energy density and high-temperature cycling performance, thereby improving the overall performance of the electrochemical device. In this application, "high temperature" means a temperature greater than or equal to 35°C.

[0008] In some embodiments of this application, the mass percentage of cobalt is A%, 40 ≤ A ≤ 60%, based on the mass of the positive electrode active material. For example, the mass percentage of cobalt A% can be 40, 42, 45, 48, 50, 52, 55, 58, 60, or any two values ​​within this range. By controlling the mass percentage of cobalt within the above range, the obtained positive electrode active material has a higher specific capacity, which is beneficial to improving the energy density of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, enabling the electrochemical device provided by this application to achieve a balance between energy density and high-temperature cycling performance, thereby improving the overall performance of the electrochemical device.

[0009] In some embodiments of this application, the mass percentage of cobalt element is A%, and 0.1 ≤ A / 20B ≤ 30, based on the mass of the positive electrode active material. In some embodiments of this application, 0.1 ≤ A / 20B ≤ 3. For example, the value of A / 20B can be 0.1, 0.5, 1, 3, 5, 10, 15, 20, 25, 30, or a range of any two values ​​in between. By adjusting the value of A / 20B within the above range, the obtained positive electrode active material has a higher specific capacity, which is beneficial to improving the energy density of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, so that the energy density and high-temperature cycling performance of the electrochemical device provided by this application are both taken into account, that is, the overall performance of the electrochemical device is improved.

[0010] In some embodiments of this application, based on the mass of the positive electrode active material, the mass percentage of cobalt is A%, 40≤A≤60, and 0.1≤A / 20B≤30. By controlling the mass percentage of cobalt and the value of A / 20B within the above ranges, the obtained positive electrode active material has a high specific capacity, which is beneficial to improving the energy density of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, enabling the electrochemical device provided by this application to achieve a balance between energy density and high-temperature cycling performance, that is, to improve the overall performance of the electrochemical device.

[0011] In some embodiments of this application, 0.05 ≤ C ≤ 5. In some embodiments of this application, 0.3 ≤ C ≤ 3. For example, the mass percentage C% of lithium bis(oxalato)borate can be 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two values ​​within this range. By controlling the mass percentage of lithium bis(oxalato)borate within the above range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, thereby enhancing the high-temperature cycling performance of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, enabling the electrochemical device provided by this application to balance energy density and high-temperature cycling performance, thus improving the overall performance of the electrochemical device.

[0012] In some embodiments of this application, 0.1 ≤ D ≤ 8. In some embodiments of this application, 1 ≤ D ≤ 6. For example, the mass percentage C% of lithium bis(oxalato)borate can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any two values ​​in between. By controlling the mass percentage of 1,3,6-hexanetrionitrile within the above range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, thereby enhancing the high-temperature cycling performance of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, enabling the electrochemical device provided by this application to balance energy density and high-temperature cycling performance, thus improving the overall performance of the electrochemical device.

[0013] In some embodiments of this application, 0.05 ≤ C ≤ 5, 0.1 ≤ D ≤ 8. In some embodiments of this application, 0.3 ≤ C ≤ 3, 1 ≤ D ≤ 6. For example, the mass percentage C% of lithium bis(oxalato)borate can be 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two values ​​thereof, and the mass percentage C% of lithium bis(oxalato)borate can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any two values ​​thereof. By controlling the mass percentages of lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile within the above ranges, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, thereby enhancing the high-temperature cycling performance of the electrochemical device. Therefore, the electrochemical device provided by this application includes the above-mentioned positive electrode active material, which works synergistically with the electrolyte in the electrochemical device, so that the energy density and high-temperature cycling performance of the electrochemical device provided by this application can be taken into account, that is, the overall performance of the electrochemical device is improved.

[0014] In some embodiments of this application, the positive electrode active material includes Li α Co 1-x-y Ni x M y O β Wherein, 0.95≤α≤1.4, 0.0005<x≤0.4, 0≤y≤0.02, 1.90≤β≤2.10, and M includes at least one of Mg, Al, Ca, Ti, Zr, V, Cr, Fe, Mn, Cu, Zn, Rb, or Sn. For example, the positive electrode active material may include, but is not limited to, LiCo. 0.94 Ni 0.05 Mn 0.01 O2, LiCo 0.89 Ni 0.1Mn 0.01 O2, LiCo 0.84 Ni 0.15 Mn 0.01 O2, LiCo 0.79 Ni 0.2 Mn 0.01 O2, LiCo 0.85 Ni 0.15 O2, LiCo 0.83 Ni 0.15 Mn 0.02 O2, LiCo 0.83 Ni 0.15 Al 0.02 O2 or LiCo 0.83 Ni 0.15 Mg 0.02 At least one of O2. By selecting the above-mentioned positive electrode active material, the energy density and high-temperature cycling performance of the electrochemical device provided in this application are balanced, thereby improving the overall performance of the electrochemical device.

[0015] In some embodiments of this application, the electrolyte further includes the compound shown in formula (I):

[0016]

[0017] R1, R2, and R3 are each independently selected from substituted or unsubstituted C1 to C10 alkyl groups, substituted or unsubstituted C1 to C10 unsaturated alkyl groups, substituted or unsubstituted C1 to C10 alkoxy groups, substituted or unsubstituted C2 to C10 alkoxyalkyl groups, substituted or unsubstituted C2 to C10 heterocyclic alkyl groups, substituted or unsubstituted C1 to C10 carbonyl groups, and substituted or unsubstituted C2 to C10 ester groups. When substituted, the substituent is a fluorine atom or a cyano group. The heteroatom in the heteroalkyl group is selected from an oxygen atom. For example, the C1 to C10 alkyl groups are selected from methyl, ethyl, propyl, butyl, or pentyl, etc.; the C1 to C10 unsaturated alkyl groups are selected from vinyl, propenyl, butenyl, pentenyl, ethynyl, propynyl, butynyl, or pentynyl, etc.; the C1 to C10 alkoxy groups are selected from methoxy (CH3O-), ethoxy (C2H5O-), propoxy (C3H7O-), etc.; and the C2 to C10 alkoxyalkyl groups are selected from... etc., C2 to C10 cycloheteroalkyl groups are selected from The C1 to C10 carbonyl groups are selected from... The C2 to C10 ester groups are selected from... Etc. The asterisk (*) in the above groups indicates a linking site. In this application, the name "alkoxyalkyl" is used according to systematic nomenclature, specifically referring to a group obtained by substituting an alkoxy group for a hydrogen atom on an alkyl group.

[0018] For example, the compound shown in formula (I) includes at least one of the following compounds:

[0019]

[0020] Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is E%, where 0.05 ≤ E ≤ 1. In some embodiments of this application, 0.1 ≤ E ≤ 0.5. For example, the mass percentage E% of the compound shown in formula (I) can be 0.05%, 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 values ​​in between. The compound shown in formula (I) can be oxidized on the surface of the positive electrode to form a phosphate-containing CEI film, which is beneficial for lithium-ion transport and reduces the interfacial impedance between the positive electrode and the electrolyte. Therefore, when the electrolyte is based on lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, and the compound shown in formula (I) is added and its mass percentage is controlled within the above range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, thereby improving the high-temperature cycle performance and kinetic performance of the electrochemical device. This allows the energy density, high-temperature cycle performance and kinetic performance of the electrochemical device provided in this application to be balanced, thus improving the overall performance of the electrochemical device.

[0021] In some embodiments of this application, the electrolyte further includes a dinitrile compound, which includes at least one selected from malononitrile, butadionitrile, glutaronitrile, adiponitrile, octanoic acid dinitrile, terephthalonitrile, tetradecanedionitrile, azomalononitrile, methyleneglutaronitrile, or pentenedionitrile; the mass percentage of the dinitrile compound is F%, based on the mass of the electrolyte, and 0.1 ≤ F ≤ 8. For example, the mass percentage F% of the dinitrile compound can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range consisting of any two values ​​therein. The aforementioned dinitrile compound can improve the interfacial stability of the CEI membrane and enhance the high-temperature cycling performance of the electrochemical device. Therefore, when the electrolyte is based on lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, the above-mentioned dinitrile compound is added and its mass percentage is controlled within the above range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, further improving the high-temperature cycle performance of the electrochemical device. This allows the energy density and high-temperature cycle performance of the electrochemical device provided in this application to be balanced, thus improving the overall performance of the electrochemical device.

[0022] In some embodiments of this application, the electrolyte further includes a polynitrile compound, which includes at least one of the following compounds:

[0023]

[0024]

[0025] Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is G%, 0.1 ≤ G ≤ 8. For example, the mass percentage G% of the polynitrile compound can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any two values ​​within this range. The aforementioned polynitrile compound can improve the interfacial stability of the CEI membrane and enhance the high-temperature cycling performance of the electrochemical device. Therefore, when the electrolyte, based on lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, is supplemented with the aforementioned polynitrile compound and its mass percentage is controlled within the above range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, further enhancing the high-temperature cycling performance of the electrochemical device. This allows the energy density and high-temperature cycling performance of the electrochemical device provided in this application to be balanced, improving the overall performance of the electrochemical device.

[0026] In some embodiments of this application, the electrolyte further includes the aforementioned dinitrile compound and polynitrile compound, which can improve the interfacial stability of the CEI membrane, resulting in better high-temperature cycling performance of the electrochemical device. Therefore, when the electrolyte is based on lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, the aforementioned dinitrile compound and polynitrile compound are added, and their mass percentages are controlled within the aforementioned range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, further enhancing the high-temperature cycling performance of the electrochemical device. This allows the electrochemical device provided by this application to balance energy density and high-temperature cycling performance, improving the overall performance of the electrochemical device.

[0027] In some embodiments of this application, the electrolyte further includes the aforementioned dinitrile compound and the aforementioned polynitrile compound, wherein the sum of the mass percentages of the dinitrile compound and the polynitrile compound satisfies: 0.1 ≤ F + G ≤ 8. For example, the value of F + G can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or any two values ​​in between. By controlling the value of F + G and the mass percentages of the aforementioned dinitrile compound and the aforementioned polynitrile compound within the aforementioned range, it is beneficial for the aforementioned dinitrile compound and the aforementioned polynitrile compound to synergistically improve the interfacial stability of the CEI membrane, resulting in better high-temperature cycling performance of the electrochemical device. Therefore, when the electrolyte is based on lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, the aforementioned dinitrile compound and the aforementioned polynitrile compound are added and their mass percentages are controlled within the aforementioned range, the lithium-ion transport problem caused by nickel doping in the positive electrode active material and the structural instability of the positive electrode active material can be improved, further enhancing the high-temperature cycling performance of the electrochemical device. This allows the energy density and high-temperature cycling performance of the electrochemical device provided in this application to be balanced, improving the overall performance of the electrochemical device.

[0028] In some embodiments of this application, the electrolyte comprises lithium bis(oxalato)borate, 1,3,6-hexanetrionitrile, a lithium salt, and an organic solvent. The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, or lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of the lithium salt is H%, 8 ≤ H ≤ 20. For example, the mass percentage H% of the lithium salt can be 8%, 9%, 10%, 11%, 12%, 12.5%, 15%, 17%, 18%, 20%, or a range consisting of any two values ​​therein. The organic solvent includes carbonate compounds and carboxylic acid ester compounds. The carbonate compounds include at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate, or propyl carbonate. The carboxylic acid ester compounds include at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, or pentyl propionate. Based on the mass of the electrolyte, the organic solvent content is 67% to 90% by mass, the carbonate compound content is J% by mass, and the carboxylic acid ester compound content is K% by mass, with 14 ≤ J ≤ 90 and 0 ≤ K ≤ 60. For example, the mass percentage J% of the organic solvent can be 67%, 70%, 75%, 80%, 85%, 90%, or any combination of two values ​​within this range; the mass percentage J% of the carbonate compound can be 14%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, or any combination of two values ​​within this range; the mass percentage K% of the carboxylic acid ester compound can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, or any combination of two values ​​within this range. The mass percentages of lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile are within their respective ranges mentioned above. The electrolyte comprises lithium bis(oxalato)borate, 1,3,6-hexanetrionitrile, the aforementioned lithium salt, and the aforementioned organic solvent, with their respective mass percentages controlled within the aforementioned range. This is beneficial for improving the lithium-ion transport rate, reducing side reactions at the interface between the positive and negative electrodes, and improving the high-temperature cycling performance and kinetic performance of the electrochemical device. Therefore, the electrochemical device provided by this application, comprising the aforementioned electrolyte, works synergistically with the positive electrode active material in the electrochemical device, enabling a balance between energy density and high-temperature cycling performance, thus improving the overall performance of the electrochemical device.

[0029] In some embodiments of this application, the electrolyte comprises lithium bis(oxalato)borate, 1,3,6-hexanetrionitrile, the aforementioned lithium salt, and an organic solvent, as well as at least one of the compounds represented by formula (I), dinitrile compounds, or polynitrile compounds. The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, or lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of the lithium salt is H%, 8 ≤ H ≤ 20. For example, the mass percentage H% of the lithium salt can be 8%, 9%, 10%, 11%, 12%, 12.5%, 15%, 17%, 18%, 20%, or a range consisting of any two values ​​therein. The organic solvent includes carbonate compounds and carboxylic acid ester compounds. The carbonate compounds include at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate, or propyl carbonate. The carboxylic acid ester compounds include at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, or pentyl propionate. Based on the mass of the electrolyte, the organic solvent content is 67% to 90% by mass, the carbonate compound content is J% by mass, and the carboxylic acid ester compound content is K% by mass, with 14 ≤ J ≤ 90 and 0 ≤ K ≤ 60. For example, the mass percentage J% of the organic solvent can be 67%, 70%, 75%, 80%, 85%, 90%, or any two values ​​thereof; the mass percentage J% of the carbonate compound can be 14%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, or any two values ​​thereof; the mass percentage K% of the carboxylic acid ester compound can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, or any two values ​​thereof. The mass percentages of lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile are within the aforementioned ranges, and when the electrolyte includes at least one of the compounds shown in formula (I), dinitrile compounds, or polynitrile compounds, their respective mass percentages are within the aforementioned ranges. The electrolyte includes lithium bis(oxalato)borate, 1,3,6-hexanetrionitrile, the above-mentioned lithium salt and the above-mentioned organic solvent, as well as at least one of the compounds shown in formula (I), dinitrile compounds or polynitrile compounds. By controlling the mass percentage of each of them within the above-mentioned range, it is beneficial to further improve the lithium ion transport rate, reduce the side reactions at the interface between the positive and negative electrodes, and improve the high-temperature cycle performance and kinetic performance of the electrochemical device.Therefore, the electrochemical device provided by this application includes the above-mentioned electrolyte, which works synergistically with the positive electrode active material in the electrochemical device, so that the energy density and high-temperature cycle performance of the electrochemical device provided by this application can be taken into account, as well as the kinetic performance, that is, the overall performance of the electrochemical device is improved.

[0030] This application does not impose any particular limitation on the preparation method of the positive electrode active material, as long as it achieves the purpose of this application. For example, the preparation method of the positive electrode active material may include, but is not limited to, the following steps: mixing LiCoO2 (CAS No.: 12190-79-3) with a nickel-containing compound uniformly, and then heat-treating in an air atmosphere to obtain the positive electrode active material. The nickel-containing compound may include, but is not limited to, at least one of NiCO3, NiO, and Ni(OH)2. This application does not impose any particular limitation on the temperature, time, and heating rate of the above heat treatment, as long as it achieves the purpose of this application. For example, the heat treatment temperature may be 650°C to 850°C, the time may be 22h to 26h, and the heating rate may be 2°C / min to 8°C / min. This application does not impose any particular limitation on the mass ratio of LiCoO2 to the nickel-containing compound, as long as it achieves the purpose of this application.

[0031] Typically, the mass percentages of Co and Ni in the cathode active material can be controlled by altering the mass ratio of LiCoO2 to the nickel-containing compound. For example, increasing the mass ratio of LiCoO2 to the nickel-containing compound increases the mass percentage of Co and decreases the mass percentage of Ni; decreasing the mass ratio of LiCoO2 to the nickel-containing compound decreases the mass percentage of Co and increases the mass percentage of Ni.

[0032] When the positive electrode active material contains the aforementioned element M, a compound containing element M can be added simultaneously with a nickel-containing compound during the preparation of the positive electrode active material. For example, when element M is Mg, Al, Ca, Ti, Zr, V, Cr, Fe, Mn, Cu, Zn, Rb, or Sn, the corresponding added compound containing element M can be an oxide, hydroxide, or carbonate compound containing element M. This application does not limit the type of oxide, hydroxide, or carbonate compound containing element M, as long as it achieves the purpose of this application. The content of element M in the positive electrode active material can be controlled by adjusting the amount of compound containing element M added.

[0033] In this application, the aforementioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive electrode current collector, or it can be a partial surface area of ​​the positive electrode current collector. 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 electrode current collector, as long as the purpose of this application is achieved. For example, it can include aluminum foil, aluminum alloy foil, or composite current collectors (e.g., aluminum-carbon composite current collectors).

[0034] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. 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 polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0035] This application does not impose any particular limitation on the thickness of the positive current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive current collector is 6 μm to 15 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. The application also does not impose any particular limitation on the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved; for example, the thickness of the positive electrode sheet is 50 μm to 250 μm.

[0036] In this application, the electrochemical device 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 phrase "the negative electrode material layer is 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 thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0037] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. 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 (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.). The negative electrode current collector can be a metal plate without through holes or a porous metal plate with through holes.

[0038] The negative electrode material layer 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, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0039] The negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not impose any particular limitation on the types of conductive agents, binders, and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders, and the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer. Those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0040] This application 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 negative electrode material layer can be 30 μm to 120 μm. 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 6 μm to 12 μm. This application does not impose any particular limitation on the thickness of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode sheet can be 50 μm to 250 μm.

[0041] In this application, the electrochemical device also includes a separator membrane for separating the positive and negative electrode plates, preventing internal short circuits, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane 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. Exemplarily, polyethylene includes at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0042] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer 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, at least one surface of the substrate layer is provided with a surface treatment layer, which 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. The inorganic particles are not particularly limited 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. The binder is not particularly limited and may be at least one of the binders described above. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0043] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any 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 the electrochemical device. Alternatively, 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 the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0044] A second aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0045] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, 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.

[0046] The beneficial effects of this application are:

[0047] This application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode and an electrolyte. The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, which includes cobalt and nickel. Based on the mass of the positive electrode active material, the mass percentage of nickel is B%, and 0.05 ≤ B ≤ 20. The electrolyte includes lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile. Based on the mass of the electrolyte, the mass percentage of lithium bis(oxalato)borate is C%, and the mass percentage of 1,3,6-hexanetrionitrile is D%. The electrochemical device satisfies 0.1 ≤ (C + D) / B ≤ 23. The electrochemical device provided in this application achieves a synergistic effect between the positive electrode and the electrolyte by adjusting the mass percentage of Ni within the above-mentioned range, simultaneously introducing lithium bis(oxalatoborate) and 1,3,6-hexanetrionitrile into the electrolyte, and adjusting the (C+D) / B value within the above-mentioned range. This allows the energy density and high-temperature cycling performance of the electrochemical device provided in this application to be balanced, thereby improving the overall performance of the electrochemical device.

[0048] Of course, implementing any product or method of this application does not necessarily require achieving all of the above advantages at the same time. Detailed Implementation

[0049] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0050] Test methods and apparatus:

[0051] Test of Co and Ni metal element content in positive electrode active materials:

[0052] The lithium-ion battery was discharged to 3V at 0.2C, and the positive electrode sheet was obtained by disassembly. The positive electrode material layer of the positive electrode sheet, after being cleaned with DMC (dimethyl carbonate), was scraped off with a scraper to obtain a powder of the positive electrode material layer. 0.4g of the positive electrode material powder was dissolved in 12mL of a mixed solvent, which was prepared by mixing aqua regia and HF in a volume ratio of 5:1. The solution was then diluted to 100mL, and the content of metal elements such as Co and Ni in the solution was tested using an inductively coupled plasma atomic emission spectrometer (ICP), expressed as a percentage. Aqua regia was prepared by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:1. The content of Co and Ni elements in the positive electrode active material was calculated based on the mass percentage of the positive electrode active material in the positive electrode material layer.

[0053] Lithium-ion battery discharge capacity test:

[0054] Preparation of lithium-ion button batteries: In a glove box, the negative electrode shell, gasket, lithium metal sheet, separator, positive electrode, spring contact, and positive electrode shell are assembled in sequence, and the battery is packaged on a packaging machine. Electrolyte is added dropwise after placing the gasket, lithium metal sheet, separator, and positive electrode to wet them. The positive electrode, separator, and electrolyte mentioned above are the same as those used in the various embodiments or comparative examples. The diameter of the positive electrode is 14 mm, the diameter of the lithium metal sheet is 16 mm, and the diameter of the separator is 16.5 mm.

[0055] The prepared lithium-ion coin cell was charged at 25°C at a rate of 0.2C until the voltage reached 4.5V. It was then further charged at a constant voltage of 4.5V until the current dropped below 0.05C, bringing it to a fully charged state at 4.5V. Subsequently, it was discharged at a constant current rate of 0.2C until the voltage reached 3.0V. The discharge capacity of the lithium-ion battery was then tested. The specific discharge capacity of the lithium-ion battery = discharge capacity / mass of the positive electrode active material. The mass of the positive electrode active material can be calculated based on the size of the positive electrode sheet and the formulation of the positive electrode sheet preparation in each embodiment or comparative example.

[0056] High-temperature cycle performance test of lithium-ion batteries:

[0057] At 45℃, the lithium-ion battery was charged at a constant current of 0.7C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C, and finally discharged at a constant current of 1C to 3.0V. This constitutes one charge-discharge cycle, which is the first cycle. The discharge capacity of the lithium-ion battery in the first cycle was recorded. The lithium-ion battery was charged and discharged for 500 cycles using the above method, and the discharge capacity in the 500th cycle was recorded. The discharge capacity retention rate = discharge capacity in the 500th cycle / discharge capacity in the first cycle × 100%. The high-temperature cycle performance of the lithium-ion battery was evaluated by the discharge capacity retention rate. The higher the discharge capacity retention rate, the better the high-temperature cycle performance; the lower the discharge capacity retention rate, the worse the high-temperature cycle performance.

[0058] Lithium-ion battery impedance performance test:

[0059] The lithium-ion battery was charged to 4.5V at a constant current of 0.7C, and then charged to 0.05C at a constant voltage. After resting for 10 minutes, it was discharged at a constant current of 0.1C for 8 hours, and the voltage V1 was recorded. After resting for 15 minutes, the voltage was measured again and recorded as V2. The impedance Rss = (V2-V1) / 0.1C is used as an indicator to evaluate the kinetic performance of the lithium-ion battery. The higher the impedance, the worse the kinetic performance; the lower the impedance, the better the kinetic performance.

[0060] Example 1-1

[0061] <Preparation of Positive Electrode Active Materials>

[0062] LiCoO2 and nickel carbonate (NiCO3) were mixed at a mass ratio of X = 0.2 and mixed in a high-speed mixer at 300 r / min for 20 min. The mixture was then placed in an air furnace and heated to 820℃ at 5℃ / min and held for 24 h. After natural cooling, the mixture was removed and passed through a 300-mesh sieve to obtain the positive electrode active material.

[0063] <Preparation of the positive electrode>

[0064] The positive electrode active material, conductive carbon nanotubes (CNTs), and binder polyvinylidene fluoride prepared above were mixed at a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was formed. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil for the positive electrode current collector. After drying at 85°C and cold pressing, a positive electrode sheet with a positive electrode material layer thickness of 100 μm was obtained. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a positive electrode material layer coated on both sides. The positive electrode sheet was cut into 74 mm × 867 mm dimensions and tabs were welded on for later use.

[0065] <Preparation of Negative Electrode Sheets>

[0066] Artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 95:2:3. Deionized water was then added as a solvent to prepare a slurry with a solid content of 70 wt%, which was stirred evenly. The slurry was uniformly coated onto one surface of an 8 μm thick copper foil, dried at 110°C, and cold-pressed to obtain a single-sided coated negative electrode sheet with a negative electrode material layer thickness of 150 μm. The above steps were repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. The negative electrode sheet was cut into 75 mm × 867 mm dimensions and tabs were welded on for later use.

[0067] <Preparation of Electrolyte>

[0068] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a weight ratio of 20:20:60. Lithium bis(oxalato)borate, 1,3,6-hexanetrionitrile, and lithium salt LiPF6 were then added and stirred until homogeneous to obtain the electrolyte. The electrolyte contained the following mass percentages: lithium bis(oxalato)borate (C%) was 0.3%, 1,3,6-hexanetrionitrile (D%) was 2%, lithium salt (H%) was 12.5%, and carbonate compounds (J%) was 85.2%.

[0069] <Isolation membrane>

[0070] A 15μm thick porous polyethylene polymer film (manufacturer: Celgard Diaphragm Company, USA) was used as the separator.

[0071] <Preparation of Lithium-ion Batteries>

[0072] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form the electrode assembly. This assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, and shaping processes to obtain the lithium-ion battery. The upper limit of the formation voltage is 4.15V, the formation temperature is 70°C, and the settling time is 2 hours.

[0073] Examples 1-2 to Examples 1-17

[0074] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the mass percentage of lithium bis(oxalato)borate and / or 1,3,6-hexanetrionitrile changes, the mass percentage of the organic solvent changes accordingly, while the mass percentage of the lithium salt remains unchanged.

[0075] Examples 2-1 to 2-7

[0076] Except for the addition of compound (I) as shown in Table 2 and the adjustment of its mass percentage according to Table 2 in the <Preparation of Electrolyte>, the mass percentage of organic solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-15.

[0077] Examples 3-1 to 3-14

[0078] Except for the addition of dinitrile compounds and / or polynitrile compounds as shown in Table 3 in the <Preparation of Electrolyte> and the adjustment of their mass percentages according to Table 3, the mass percentages of organic solvents are changed accordingly, and the mass percentages of lithium salts remain unchanged, the rest is the same as in Examples 1-3.

[0079] Example 4-1

[0080] Except for the preparation of the positive electrode active material according to the following steps, the rest is the same as in Examples 1-5.

[0081] <Preparation of Positive Electrode Active Materials>

[0082] LiCoO2, nickel carbonate (NiCO3), and MnCO3 were mixed in a molar ratio of 0.83:0.15:0.02 and mixed in a high-speed mixer at 300 r / min for 20 min. The mixture was then placed in an air furnace and heated to 820℃ at 5℃ / min and held for 24 h. After natural cooling, the mixture was removed and passed through a 300-mesh sieve to obtain the positive electrode active material.

[0083] Example 4-2

[0084] Except for the preparation of the positive electrode active material according to the following steps, the rest is the same as in Examples 1-5.

[0085] <Preparation of Positive Electrode Active Materials>

[0086] LiCoO2, nickel carbonate (NiCO3), and Al2(CO3)3 were mixed in a molar ratio of 0.83:0.15:0.02 in a high-speed mixer at 300 r / min for 20 min. The mixture was then placed in an air furnace and heated to 820℃ at 5℃ / min, held for 24 h, and allowed to cool naturally before being removed and passed through a 300-mesh sieve to obtain the positive electrode active material.

[0087] Example 4-3

[0088] Except for the preparation of the positive electrode active material according to the following steps, the rest is the same as in Examples 1-5.

[0089] <Preparation of Positive Electrode Active Materials>

[0090] LiCoO2, nickel carbonate (NiCO3), and MgCO3 were mixed in a molar ratio of 0.83:0.15:0.02 in a high-speed mixer at 300 r / min for 20 min. The mixture was then placed in an air furnace and heated to 820℃ at 5℃ / min, held for 24 h, and allowed to cool naturally before being removed and passed through a 300-mesh sieve to obtain the positive electrode active material.

[0091] Comparative Examples 1 to 5

[0092] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the mass percentage of lithium bis(oxalato)borate and / or 1,3,6-hexanetrionitrile changes, the mass percentage of the organic solvent changes accordingly, while the mass percentage of the lithium salt remains unchanged.

[0093] The preparation parameters and performance tests of each embodiment and comparative example are shown in Tables 1 to 4.

[0094] Table 1

[0095]

[0096] Note: " / " in Table 1 indicates that there is no corresponding parameter. The mass ratio X in Table 1 refers to the mass ratio of LiCoO2 and NiCO3.

[0097] As can be seen from Examples 1-1 to 1-17 and Comparative Examples 1 to 5, the lithium-ion batteries of each embodiment of this application contain Ni in the positive electrode active material, and the mass percentage of Ni B% is within the scope of this application. The electrolyte contains lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile. Moreover, the relationship (C+D) / B between the mass percentages of lithium bis(oxalato)borate C%, 1,3,6-hexanetrionitrile D%, and Ni B% is within the scope of this application. However, the lithium-ion batteries in the comparative examples do not simultaneously meet the above characteristics. The lithium-ion batteries obtained in the embodiments have higher discharge specific capacity and higher discharge capacity retention rate, indicating that the energy density and high-temperature cycle performance of the lithium-ion batteries are improved, that is, the overall performance of the lithium-ion batteries is improved.

[0098] The mass percentage of Co, A%, and the value of A / 20B typically affect the overall performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-7, when the mass percentage of Co, A%, and the value of A / 20B are within the range of this application, the resulting lithium-ion batteries have higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion batteries have higher energy density and better high-temperature cycling performance, that is, the lithium-ion batteries have good overall performance.

[0099] The mass percentage C% of lithium bis(oxalato)borate typically affects the overall performance of lithium-ion batteries. As can be seen from Examples 1-5, 1-8 to 1-12, when the mass percentage C% of lithium bis(oxalato)borate is within the range of this application, the resulting lithium-ion batteries have higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion batteries have higher energy density and better high-temperature cycling performance, that is, the lithium-ion batteries have good overall performance.

[0100] The mass percentage D% of 1,3,6-hexanetrionitrile typically affects the overall performance of lithium-ion batteries. As can be seen from Examples 1-5, 1-13 to 1-17, when the mass percentage D% of 1,3,6-hexanetrionitrile is within the range of this application, the resulting lithium-ion batteries have higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion batteries have higher energy density and better high-temperature cycling performance, that is, the lithium-ion batteries have good overall performance.

[0101] Table 2

[0102]

[0103] Note: " / " in Table 2 indicates that the corresponding parameter does not exist.

[0104] As can be seen from Examples 1-15 and Examples 2-1 to 2-7, based on the electrolyte containing lithium dioxaborate and 1,3,6-hexanetrionitrile, the further introduction of compound (I) can further improve the discharge capacity retention rate of lithium-ion batteries, reduce Rss, and the discharge specific capacity remains basically unchanged. This indicates that the high-temperature cycle performance and kinetic performance of lithium-ion batteries are further improved. At the same time, lithium-ion batteries have high energy density, that is, the overall performance of lithium-ion batteries is further improved.

[0105] The mass percentage E% of the compound of formula (I) usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 2-1 to 2-5, when the mass percentage E% of the compound of formula (I) is within the range of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, and a lower Rss, indicating that the lithium-ion battery has a higher energy density and good high-temperature cycling performance and kinetic performance, that is, the lithium-ion battery has good overall performance.

[0106] The type of compound in formula (I) usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 2-3, 2-6 and 2-7, when the type of compound in formula (I) is within the scope of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, and a lower Rss, indicating that the lithium-ion battery has a higher energy density and good high-temperature cycling performance and kinetic performance, that is, the lithium-ion battery has good overall performance.

[0107] Table 3

[0108]

[0109] Note: " / " in Table 3 indicates that the corresponding parameter does not exist.

[0110] As can be seen from Examples 1-3 and Examples 3-1 to 3-5, based on the electrolyte containing lithium dioxaborate and 1,3,6-hexanetrionitrile, the further introduction of dinitrile compounds can further improve the discharge capacity retention rate of lithium-ion batteries. The discharge specific capacity remains basically unchanged, indicating that the high-temperature cycle performance of lithium-ion batteries is further improved. At the same time, lithium-ion batteries have high energy density, that is, the overall performance of lithium-ion batteries is further improved.

[0111] The mass percentage F% of the dinitrile compound usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 3-1 to 3-3, when the mass percentage F% of the dinitrile compound is within the range of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion battery has a higher energy density and better high-temperature cycling performance, that is, the lithium-ion battery has good overall performance.

[0112] The type of dinitrile compound usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 3-2, 3-4 and 3-5, when the type of dinitrile compound is within the scope of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion battery has a higher energy density and better high-temperature cycling performance, that is, the lithium-ion battery has good overall performance.

[0113] As can be seen from Examples 1-3, 3-6 to 3-8, based on the electrolyte containing lithium dioxaborate and 1,3,6-hexanetrionitrile, the further introduction of polynitrile compounds can further improve the discharge capacity retention rate of lithium-ion batteries. The discharge specific capacity remains basically unchanged, indicating that the high-temperature cycle performance of lithium-ion batteries is further improved. At the same time, lithium-ion batteries have high energy density, that is, the overall performance of lithium-ion batteries is further improved.

[0114] The mass percentage (G%) and type of polynitrile compounds typically affect the overall performance of lithium-ion batteries. As can be seen from Examples 3-6 to 3-8, when the mass percentage (G%) and type of polynitrile compounds are within the range of this application, the resulting lithium-ion batteries have higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion batteries have higher energy density and better high-temperature cycling performance, that is, the lithium-ion batteries have good overall performance.

[0115] The value of F+G usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 3-9 to 3-14, when the value of F+G is within the range of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion battery has a higher energy density and better high-temperature cycling performance, that is, the lithium-ion battery has good overall performance.

[0116] Table 4

[0117]

[0118] The type of positive electrode active material usually affects the overall performance of lithium-ion batteries. As can be seen from Examples 1-5 and Examples 4-1 to 4-3, when the type of positive electrode active material is within the scope of this application, the resulting lithium-ion battery has a higher discharge specific capacity and discharge capacity retention rate, indicating that the lithium-ion battery has a higher energy density and better high-temperature cycling performance, that is, the lithium-ion battery has good overall performance.

[0119] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0120] 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.

[0121] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. An electrochemical device comprising a positive electrode and an electrolyte, wherein, The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, which contains cobalt and nickel. Based on the mass of the positive electrode active material, the mass percentage of nickel is B%, and 0.05 ≤ B ≤ 20. The electrolyte comprises lithium bis(oxalato)borate and 1,3,6-hexanetrionitrile, and based on the mass of the electrolyte, the mass percentage of lithium bis(oxalato)borate is C%, and the mass percentage of 1,3,6-hexanetrionitrile is D%. The electrochemical device satisfies 0.1≤(C+D) / B≤23.

2. The electrochemical device according to claim 1, wherein, 0.1≤B≤10, and / or 0.1≤(C+D) / B≤4.

6.

3. The electrochemical device according to claim 1, wherein, Based on the mass of the positive electrode active material, the mass percentage of cobalt is A%, and 40≤A≤60, and / or 0.1≤A / 20B≤30.

4. The electrochemical device according to claim 3, wherein, 0.1≤A / 20B≤3.

5. The electrochemical device according to claim 1, wherein, 0.05≤C≤5, and / or 0.1≤D≤8.

6. The electrochemical device according to claim 1, wherein, The positive electrode active material includes Li α Co 1-x-y Ni x M y O β Wherein, 0.95≤α≤1.4, 0.0005<x≤0.4, 0≤y≤0.02, 1.90≤β≤2.10, and M includes at least one of Mg, Al, Ca, Ti, Zr, V, Cr, Fe, Mn, Cu, Zn, Rb or Sn.

7. The electrochemical device according to claim 1, wherein, The electrolyte also includes the compound shown in formula (I): R1, R2, and R3 are each independently selected from substituted or unsubstituted C1 to C10 alkyl groups, substituted or unsubstituted C1 to C10 unsaturated alkyl groups, substituted or unsubstituted C1 to C10 alkoxy groups, substituted or unsubstituted C2 to C10 alkoxyalkyl groups, substituted or unsubstituted C2 to C10 heterocyclic alkyl groups, substituted or unsubstituted C1 to C10 carbonyl groups, and substituted or unsubstituted C2 to C10 ester groups. When substituted, the substituent is a fluorine atom or a cyano group. The heteroatom in the heterocyclic alkyl group is selected from an oxygen atom. Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is E%, 0.05≤E≤1.

8. The electrochemical device according to claim 7, wherein, The compound represented by formula (I) includes at least one of the following compounds:

9. The electrochemical device according to claim 1, wherein it satisfies at least one of the following characteristics: (1) The electrolyte further includes a dinitrile compound, which includes at least one of malononitrile, butadionitrile, glutaronitrile, adiponitrile, octanoic acid dinitrile, terephthalonitrile, tetradecanedionitrile, azomalononitrile, methyleneglutaronitrile, or pentenedionitrile; based on the mass of the electrolyte, the mass percentage of the dinitrile compound is F%, 0.1≤F≤8; (2) The electrolyte further includes a polynitrile compound, which includes at least one of the following compounds: Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is G%, 0.1≤G≤8.

10. The electrochemical device according to claim 9, wherein, 0.1≤F+G≤8.

11. The electrochemical device according to any one of claims 1 to 10, wherein, The electrolyte comprises lithium salt and organic solvent; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalateborate), lithium difluorooxalateborate, or lithium difluorophosphate; based on the mass of the electrolyte, the mass percentage of the lithium salt is H%, 8≤H≤20. The organic solvent comprises carbonate compounds and carboxylic acid ester compounds. The carbonate compounds include at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate, or propyl carbonate. The carboxylic acid ester compounds include at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, or pentyl propionate. Based on the mass of the electrolyte, the organic solvent has a mass percentage of 67% to 90%, the carbonate compounds have a mass percentage of J%, and the carboxylic acid ester compounds have a mass percentage of K%, 14≤J≤90, 0≤K≤60.

12. An electronic device comprising the electrochemical device according to any one of claims 1 to 11.

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