A secondary battery and an electronic device

Abstract

A secondary battery and electronic device are disclosed. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode material layer, which includes a positive electrode active material containing cobalt and magnesium. Based on the mass of the positive electrode material layer, the mass percentage of magnesium is A%, with a content of 0.1 ≤ A ≤ 5%. The electrolyte includes a fluorinated solvent, which includes at least one of the compounds shown in formula (I), (II), (III), or (IV). Based on the mass of the electrolyte, the mass percentage of the fluorinated solvent is B%, with a content of 41.7 ≤ B ≤ 83.2% and a mass percentage of 0.1 ≤ 100A / B ≤ 6. The provided secondary battery exhibits good high-temperature storage performance and high-temperature cycling performance.

Description

Secondary battery and electronic device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the advantages of high specific energy, light weight, and long cycle life, and are widely used in consumer batteries.

[0003] As electronic products become thinner and more portable, the energy density can be greatly improved by increasing the charging cut-off voltage of lithium-ion batteries. However, the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries are facing higher challenges.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electronic device to improve the high-temperature storage performance and high-temperature cycle performance of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, the positive electrode active material includes cobalt and magnesium, and based on the mass of the positive electrode material layer, the mass percentage of the magnesium element is divided into A%, 0.1≤A≤5, preferably 0.5≤A≤3. For example, the value of A can be 0.1, 0.2, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any two values ​​therein. The electrolyte includes a fluorinated solvent, and the fluorinated solvent includes at least one of the compound represented by formula (I), the compound represented by formula (II), the compound represented by formula (III) or the compound represented by formula (IV):

[0007] wherein R1 to R2 are each independently selected from fluorine-substituted or unsubstituted C1 to C5 alkyl, fluorine-substituted or unsubstituted C2 to C5 alkenyl, fluorine-substituted or unsubstituted C2 to C5 alkynyl, sulfonic acid-substituted C2 to C5 alkyl, or cyano-substituted C2 to C5 alkyl; R3 to R8 are each independently selected from H, F, fluorine-substituted or unsubstituted C1 to C5 alkyl, fluorine-substituted or unsubstituted C2 to C5 alkenyl, fluorine-substituted or unsubstituted C2 to C5 alkynyl, sulfonic acid-substituted C2 to C5 alkyl, or cyano-substituted C2 to C5 alkyl; at least one of R1 to R2 contains at least one fluorine atom, at least one of R3 to R4 contains at least one fluorine atom, at least one of R5 to R6 contains at least one fluorine atom, and at least one of R7 to R8 contains at least one fluorine atom. Based on the mass of the electrolyte, the mass percentage of the fluorinated solvent is B%, 41.7≤B≤83.2, preferably 45.9≤B≤75; 0.1≤100A / B≤6, for example, the value of B can be 41.7, 43, 45, 45.9, 50, 55, 60, 65, 70, 75, 80, 83.2 or a range consisting of any two values ​​therein, and the value of 100A / B can be 0.1, 0.2, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or a range consisting of any two values ​​therein.

[0008] The secondary battery provided by the present application comprises a positive electrode active material including cobalt and magnesium elements, and the mass percentage of the magnesium element is regulated within the above-mentioned range, which can improve the stability of the positive electrode active material, thereby improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery. At the same time, the electrolyte comprises a fluorinated solvent and its mass percentage B% is regulated within the above-mentioned range. On the one hand, since a higher content of the fluorinated solvent can form a higher content of fluorine-containing interface protective film in situ on the surface of the positive electrode plate during the charge and discharge cycle, and this process continues during the charge and discharge cycle, it can continuously improve the dissolution problem of the transition metal in the positive electrode material layer, reduce the release of oxygen in the positive electrode active material, and improve the oxidative decomposition and gas production of the electrolyte at high temperature, thereby improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery. On the other hand, since a higher content of fluorinated solvent has the function of continuously repairing the interface, it can not only improve the interfacial stability between the positive electrode material layer and the electrolyte, but also reduce the content of interface repair additives (such as vinylene carbonate, 1,3-propane sultone or acrylonitrile) in the electrolyte, so that the initial impedance of the above interface is smaller, thereby further improving the high temperature cycle performance and high temperature cycle performance of the secondary battery. When the value of A is too small, for example, less than 0.1, it cannot play a role in improving the stability of the positive electrode active material, which is not conducive to improving the high temperature storage performance and high temperature cycle performance of the secondary battery; when the value of A is too large, for example, greater than 5, the impedance of the positive electrode sheet will be too large, reducing the gram capacity of the positive electrode active material, thereby reducing the energy density of the secondary battery, and is not conducive to improving its high temperature cycle performance. When the value of B is too small, for example, less than 41.7, the role of the fluorinated solvent cannot be brought into play, which is not conducive to improving the problem of transition metal dissolution in the positive electrode material layer, and is not conducive to improving the high temperature storage performance and high temperature cycle performance of the secondary battery; when the value of B is too large, for example, greater than 83.2, although the conductivity can be lowered, the above-mentioned in-situ formed interface protective film is too thick, which will hinder the transmission of ions (such as lithium ions), and thus is not conducive to improving the high temperature cycle performance of the secondary battery. When the value of 100A / B is too small, for example, less than 0.1, it is not conducive to the synergistic effect between the positive electrode sheet and the fluorinated solvent, and it is impossible to improve the stability of the positive electrode active material and the oxidative decomposition and gas production of the electrolyte at high temperature, thereby affecting the high temperature storage performance and high temperature cycle performance of the secondary battery. When the value of 100A / B is too large, for example greater than 6, the impedance of the positive electrode plate will be too large, hindering the transmission of ions. The synergistic effect between the positive electrode plate and the fluorinated solvent cannot be exerted, thereby failing to improve the high-temperature storage performance and high-temperature cycle performance of the secondary battery. Therefore, the positive electrode active material includes cobalt and magnesium elements, the electrolyte includes a fluorinated solvent, and the values ​​of A, B, and 100A / B are regulated within the above range. A synergistic effect is generated between the positive electrode plate and the electrolyte, which can make the secondary battery have high energy density while having good high-temperature storage performance and high-temperature cycle performance, thereby improving the comprehensive performance of the secondary battery.In this application, "high temperature" refers to a temperature greater than or equal to 35°C.

[0009] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the cobalt element is C%, 51.1≤C≤58.8. For example, the value of C can be 51.1, 52, 53, 54, 55, 56, 57, 58, 58.8 or a range consisting of any two values ​​therein. By regulating the value of C within the above range, the obtained positive electrode active material has a higher gram capacity, which is beneficial to improving the energy density of the secondary battery. In addition, it can also make the structure of the positive electrode active material more stable, reduce the release of oxygen in the positive electrode active material, improve the oxidative decomposition and gas production of the electrolyte at high temperature, and be more conducive to the synergistic effect between the positive electrode sheet and the electrolyte, thereby improving the high temperature storage performance and high temperature cycle performance of the secondary battery, so that the secondary battery has high energy density while having good high temperature storage performance and high temperature cycle performance, thereby improving the comprehensive performance of the secondary battery.

[0010] In one embodiment of the present application, the positive electrode active material includes Li α Co 1-x-y Mg x M y O β , wherein 0.95≤α≤1.4, 0.004≤x≤0.192, 0≤y≤0.34, 1.9≤β≤2.1, and M includes at least one of Mn, Al, Ni, Ca, Ti, Zr, V, Cr, Fe, Cu, Zn, Rb or Sn. For example, the value of α can be 0.95, 1, 1.1, 1.2, 1.3, 1.4, or a range consisting of any two of them, the value of x can be 0.004, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15, 0.17, 0.192, or a range consisting of any two of them, the value of y can be 0, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.34, or a range consisting of any two of them, and the value of β can be 1.9, 1.95, 1.98, 2, 2.02, 2.05, 2.1, or a range consisting of any two of them. The positive electrode active material can include but is not limited to LiCo 0.92 Mg 0.08 O2、LiCo 0.996 Mg 0.004 O2、LiCo 0.98 Mg 0.02 O2、LiCo 0.96 Mg 0.04 O2、LiCo 0.88 Mg 0.12 O2、LiCo0.81 Mg 0.19 O2、LiCo 0.87 Mg 0.08 Mn 0.05 O2、LiCo 0.87 Mg 0.08 Al 0.05 O2、LiCo 0.915 Mg 0.08 Al 0.005 O2 or LiCo 0.58 Mg 0.08 Al 0.34 By selecting the above-mentioned positive electrode active materials, the structure of the positive electrode material layer can be made more stable, the oxidative decomposition and gas production of the electrolyte at high temperatures can be reduced, and the synergistic effect between the positive electrode sheet and the electrolyte can be more effectively exerted, so that the secondary battery provided by the present application has good high-temperature storage performance and high-temperature cycle performance.

[0011] In one embodiment of the present application, the compound represented by formula (I) includes at least one of the following compounds:

[0012] The compound represented by formula (II) includes at least one of the following compounds:

[0013] The compound represented by formula (III) includes at least one of the following compounds:

[0014] The compound represented by formula (IV) includes at least one of the following compounds:

[0015] In one embodiment of the present application, the electrolyte includes a compound represented by formula (V):

[0016] Wherein, X is selected from Any of; Represents a binding site with an adjacent atom; Y and Z are each independently selected from any one of C and O; R9, R 10 and R 11 are each independently selected from H, substituted or unsubstituted C1 to C 10 Alkyl, substituted or unsubstituted C2 to C 10 Alkenyl, substituted or unsubstituted C2 to C 10 Alkynyl, substituted or unsubstituted C6 to C 10 Aryl, substituted or unsubstituted C1 to C 10 Alkoxy, substituted or unsubstituted C2 to C 10Cycloalkoxy, substituted or unsubstituted C2 to C 10 Alkenyloxy, substituted or unsubstituted C2 to C 10 Alkynyloxy, substituted or unsubstituted C6 to C 10 Aryloxy, substituted or unsubstituted C1 to C 10 Carboxyl, substituted or unsubstituted C1 to C 10 Carbonyl, substituted or unsubstituted C1 to C 10 cyano, substituted or unsubstituted C1 to C 10 amino, substituted or unsubstituted C2 to C 10 Carbonate group, substituted or unsubstituted C1 to C 10 Sulfate, substituted or unsubstituted C1 to C 10 Sulfite group, substituted or unsubstituted C1 to C 10 borate group, substituted or unsubstituted C1 to C 10 Silyl, substituted or unsubstituted C1 to C 10 Siloxane, substituted or unsubstituted C1 to C 10 a phosphate group; when substituted, the substituent of each group is independently selected from at least one of a halogen atom and a cyano group; the mass percentage of the compound represented by formula (V) is D% based on the mass of the electrolyte, and 0.05≤D≤5. For example, the value of D can be 0.05, 0.1, 0.5, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two of these values. The electrolyte includes a compound represented by formula (V) and regulates the value of D within the above range. The compound represented by formula (V) can preferentially undergo an oxidation reaction on the surface of the positive electrode to generate a more oxidation-resistant sulfur-containing compound, thereby improving the antioxidant capacity of the positive electrode solid electrolyte interface film (CEI film); at the same time, the above-mentioned fluorinated solvent is easy to undergo a reduction reaction on the negative electrode plate, and the stability of its reduction product needs to be further improved. The compound represented by formula (V) can also react on the negative electrode surface before the fluorinated solvent, reducing the possibility of the fluorinated solvent undergoing a reduction reaction on the surface of the negative electrode plate, further improving the interface stability between the negative electrode plate and the electrolyte, thereby further improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery.

[0017] In one embodiment of the present application, the compound represented by formula (V) includes at least one of the following compounds:

[0018] The compound represented by formula (V) includes the above-mentioned compound, which is more conducive to exerting the effect of the compound represented by formula (V), further improving the antioxidant ability of the CEI film and the interface stability between the negative electrode plate and the electrolyte, thereby making the secondary battery have good high-temperature storage performance while further improving its high-temperature cycle performance.

[0019] In one embodiment of the present application, the electrolyte includes a nitrile compound, and the content of the nitrile compound is E%, based on the mass of the electrolyte, 0.1≤E≤8; for example, the value of E can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or a range consisting of any two values ​​thereof. The nitrile compound includes malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, terephthalonitrile, tetradecane dicarbonitrile, azomalononitrile, methylene glutaronitrile, glutarenedinitrile, 1,3,5-benzenetrinitrile, 2,4,6-trifluorobenzene-1,3,5-trinitrile, 2-bromobenzene-1,3,5-trinitrile, 1,3,6-hexanetrinitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,6-hexanetricarbonitrile, or at least one of the compounds represented by the following formula (VI):

[0020] The electrolyte includes nitrile compounds and the value of E is regulated within the above range. The fluorinated solvent and the nitrile compound synergistically participate in the construction of the CEI membrane, so that the composition of the CEI membrane includes both fluorinated compounds and cyanide-containing compounds, thereby improving the antioxidant ability of the CEI membrane while stabilizing the transition metal in the positive electrode active material, reducing side reactions in the electrolyte, and improving the oxidative decomposition and gas production of the electrolyte at high temperature. At the same time, because the nitrile compound has a strong complexing effect on the transition metal, the high-temperature storage performance and high-temperature cycle performance of the secondary battery can be further improved.

[0021] In one embodiment of the present application, the electrolyte includes a carbonate compound and a carboxylate compound, and the mass percentage of the carbonate compound is F%, the mass percentage of the carboxylate compound is G%, based on the mass of the electrolyte, 8.2≤F≤24.9, 8.2≤F+G≤41.5; for example, the value of F can be 8.2, 9, 10, 12, 14, 15, 16, 18, 20, 22, 24.9 or a range consisting of any two values ​​therein, and the value of F+G can be 8.2, 10, 15, 20, 23, 25, 28, 30, 33, 35, 38, 40, 41.5 or a range consisting of any two values ​​therein. The carbonate compounds include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate, methylpropyl carbonate (MPC), ethylpropyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate or propyl carbonate; the carboxylate compounds include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), ethyl propionate (EP), propyl propionate (PP), butyl propionate or pentyl propionate. The electrolyte includes carbonate compounds and carboxylate compounds, and the values ​​of F and F+G are regulated within the above ranges, which is beneficial to the dissociation of lithium salts and the appropriate viscosity of the electrolyte, is beneficial to the interface repair effect of the fluorinated solvent, is beneficial to the transmission of lithium ions, and can also reduce side reactions in the electrolyte, improve the oxidative decomposition and gas production of the electrolyte at high temperatures, thereby improving the high-temperature storage performance, high-temperature cycle performance and rate performance of the secondary battery.

[0022] In one embodiment of the present application, 0≤G≤33.3. For example, the value of G can be 0, 3, 5, 8, 9, 10, 12, 14, 15, 16, 18, 20, 23, 25, 28, 30, 32, 33.3, or a range consisting of any two of these values. By regulating the value of G within the above range, the electrolyte can have a suitable viscosity, accelerate the transmission of lithium ions, and at the same time reduce side reactions in the electrolyte, improve the oxidative decomposition and gas production of the electrolyte at high temperatures, thereby improving the high-temperature storage performance, high-temperature cycle performance, and rate performance of the secondary battery.

[0023] In one embodiment of the present application, the electrolyte includes a lithium salt, and the mass percentage of the lithium salt is H%, based on the mass of the electrolyte, and 8≤H≤20; for example, the value of H can be 8, 9, 10, 12, 13, 15, 16, 18, 20, or a range consisting of any two values ​​therein. The lithium salt includes at least one of lithium hexafluorophosphate (LiPF4), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate, or lithium difluorophosphate. The electrolyte includes a lithium salt and regulates the value of H within the above range, which is beneficial to improving the ion conductivity of the electrolyte, shortening the charging time of the secondary battery, and reducing the oxidation reaction in the electrolyte, thereby improving the high-temperature cycle performance of the secondary battery.

[0024] In some embodiments of the present application, the electrolyte comprises a lithium salt, a fluorinated solvent and a carbonate compound, and optionally the electrolyte comprises at least one of a compound represented by formula (V) or a nitrile compound, the mass percentages of the lithium salt, the fluorinated solvent, the compound represented by formula (V), and the nitrile compound are as described above, and the mass percentage content F% of the carbonate compound is 8.2% to 38.3%, for example, the value of F can be 8.2, 10, 12, 14, 15, 16, 18, 20, 24.9, 25.3, 28, 30, 30.3, 33.3, 35, 38.3 or a range consisting of any two values ​​thereof. In some embodiments, the electrolyte comprises a lithium salt, a fluorinated solvent and a carbonate compound, the mass percentages of the lithium salt and the fluorinated solvent are as described above, and the mass percentage content F% of the carbonate compound is 8.2% to 38.3%. In some embodiments, the electrolyte comprises a lithium salt, a fluorinated solvent, a compound represented by Formula (V), and a carbonate compound; the weight percentages of the lithium salt, the fluorinated solvent, and the compound represented by Formula (V) are as described above, and the weight percentage of the carbonate compound (F%) is 8.2% to 33.3%. In some embodiments, the electrolyte comprises a lithium salt, a fluorinated solvent, a nitrile compound, and a carbonate compound; the weight percentages of the lithium salt, the fluorinated solvent, and the nitrile compound are as described above, and the weight percentage of the carbonate compound (F%) is 8.2% to 30.3%. In some embodiments, the electrolyte comprises a lithium salt, a fluorinated solvent, a compound represented by Formula (V), a nitrile compound, and a carbonate compound; the weight percentages of the lithium salt, the fluorinated solvent, the compound represented by Formula (V), and the nitrile compound are as described above, and the weight percentage of the carbonate compound (F%) is 8.2% to 25.3%. Application of the above electrolyte in secondary batteries can improve the high-temperature storage performance, high-temperature cycle performance, and rate performance of the secondary batteries.

[0025] In other embodiments of the present application, the electrolyte includes a lithium salt, a fluorinated solvent, a carbonate compound and a carboxylate compound. Optionally, the electrolyte also includes at least one of a compound represented by formula (V) or a nitrile compound, and the mass percentages of the lithium salt, the fluorinated solvent, the compound represented by formula (V), the nitrile compound, the carbonate compound and the carboxylate compound are as described above. Applying the above electrolyte to a secondary battery can improve the high-temperature storage performance, high-temperature cycle performance and rate performance of the secondary battery.

[0026] This application does not specifically limit the preparation method of the positive electrode active material, as long as the objectives of this application can be achieved. For example, the preparation method of the positive electrode active material may include, but is not limited to, the following steps: LiCoO2 (CAS No.: 12190-79-3) is uniformly mixed with a magnesium-containing compound, and then heat-treated in an air atmosphere to obtain the positive electrode active material. The magnesium-containing compound may include, but is not limited to, at least one of MgCO3, MgO, or Mg(OH)2. This application does not specifically limit the temperature, time, and heating rate of the above-mentioned heat treatment, as long as the objectives of this application can be achieved. For example, the heat treatment temperature is 650°C to 850°C, the time is 22 hours to 26 hours, and the heating rate is 2°C / min to 8°C / min. This application does not specifically limit the mass ratio of LiCoO2 to the magnesium-containing compound, as long as the objectives of this application can be achieved. Generally, the mass percentages of Co and Mg in the positive electrode active material can be controlled by varying the mass ratio of LiCoO2 to the magnesium-containing compound. For example, increasing the mass ratio of LiCoO2 to the magnesium-containing compound increases the mass percentage of Co and decreases the mass percentage of Mg; decreasing the mass ratio of LiCoO2 to the magnesium-containing compound decreases the mass percentage of Co and increases the mass percentage of Mg.

[0027] When the positive electrode active material contains the above-mentioned M element, a compound containing the M element can be added while mixing LiCoO2 with the magnesium-containing compound when preparing the positive electrode active material. For example, when the M element is Al, Ca, Ti, Zr, V, Cr, Fe, Mn, Cu, Zn, Rb, Sn, or Ni, the corresponding compound containing the M element added can be an oxide containing the M element, a hydroxide containing the M element, and a carbonate compound containing the M element. This application does not limit the oxide containing the M element, the hydroxide containing the M element, and the carbonate compound containing the M element, as long as the purpose of this application can be achieved. The content of the M element in the positive electrode active material can be regulated by regulating the amount of the compound containing the M element added.

[0028] In the present application, the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or it can be provided 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 area of ​​the positive electrode current collector surface, or it can be a partial area of ​​the positive electrode current collector surface. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0029] The positive electrode material layer may also include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent 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-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder 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-mentioned conductive polymer may include but is 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. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer. Those skilled in the art can select it according to actual needs as long as the purpose of the present application can be achieved.

[0030] This application does not impose any particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 15 μm, and the thickness of the positive electrode material layer is 30 μm to 125 μm. This application does not impose any particular restrictions on the thickness of the positive electrode sheet, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode sheet is 50 μm to 260 μm.

[0031] In the present application, the negative electrode sheet includes 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 both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in the present application, as long as the purpose of this application can be achieved.

[0032] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). The negative electrode current collector can be a metal plate without through holes, or a porous metal plate with through holes.

[0033] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, 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 a Li-Al alloy. The negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of the conductive agent, binder, and thickener, as long as the purpose of this application can be achieved. For example, the conductive agent and binder may be at least one of the above-mentioned 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 particularly limit 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 may select according to actual needs, as long as the purpose of this application can be achieved.

[0034] This application does not impose any particular restrictions on the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 180 μm. This application does not impose any particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 12 μm. This application does not impose any particular restrictions on the thickness of the negative electrode pole piece, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode pole piece is 50 μm to 370 μm.

[0035] In the present application, the secondary battery also includes a diaphragm, which is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, 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 diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5μm to 500μm.

[0036] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, they may include at least one of aluminum oxide, 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, for example, it may be at least one of the above-mentioned binders. The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0037] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheets, diaphragms and negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, diaphragms and negative electrode sheets in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent the pressure inside the secondary battery from rising and overcharging and discharging. The packaging bag is a packaging bag known in the art, and is not limited in the present application.

[0038] The second aspect of the present application provides an electronic device, which includes the secondary battery provided by the first aspect of the present application. The secondary battery provided by the first aspect of the present application has good high temperature storage performance and high temperature cycle performance, so that the electronic device provided by the second aspect of the present application has a long service life. The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, 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 head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, 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.

[0039] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, the positive electrode active material includes cobalt and magnesium, and the weight percentage of the magnesium element is A% based on the weight of the positive electrode material layer, and 0.1≤A≤5; the electrolyte includes a fluorinated solvent, and the fluorinated solvent includes at least one of the compound represented by formula (I), the compound represented by formula (II), the compound represented by formula (III), or the compound represented by formula (IV). The weight percentage of the fluorinated solvent is B% based on the weight of the electrolyte, 41.7≤B≤83.2, and 0.1≤100A / B≤6. The positive electrode active material includes cobalt and magnesium elements, the electrolyte includes a fluorinated solvent, and the values ​​of A, B and 100A / B are regulated within the above ranges. A synergistic effect is generated between the positive electrode plate and the electrolyte, which is beneficial to improving the stability of the positive electrode active material and improving the oxidative decomposition and gas production of the electrolyte at high temperature, thereby improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions, and advantages of this application more clearly understood, the following examples are given to further describe this application in detail. Obviously, the described examples are only some examples of this application, rather than all examples. All other examples obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0041] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0042] Example

[0043] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0044] Test methods and equipment:

[0045] Test of mass percentage of magnesium and cobalt:

[0046] The lithium-ion battery was discharged to 3V at 0.2C and disassembled to obtain the positive electrode sheet. The positive electrode material layer of the positive electrode sheet after washing with DMC (dimethyl carbonate) was scraped off with a scraper to obtain the positive electrode material layer powder. 0.4g of the above powder was dissolved in 12mL of a mixed solvent, which was prepared by mixing aqua regia and hydrofluoric acid (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 Mg in the solution was tested using an inductively coupled plasma spectrometer (ICP). The mass percentage of magnesium element A% and the mass percentage of cobalt element C% based on the mass of the positive electrode material layer were calculated. Among them, aqua regia was prepared by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:1.

[0047] Test of component content in electrolyte:

[0048] The lithium-ion battery was discharged to 3V at 0.2C and disassembled. The electrolyte was collected and the removed positive electrode, negative electrode, and separator were centrifuged. The liquid obtained after centrifugation was mixed with the electrolyte to obtain a liquid sample. The liquid sample was subjected to ion chromatography (IC) testing to measure the lithium salt content in the electrolyte. The liquid sample was tested using gas chromatography-mass spectrometry (GC-MS) to measure the mass ratio of each component in the electrolyte. The mass percentage of each component in the electrolyte was calculated based on the measured lithium salt content.

[0049] High temperature storage performance test:

[0050] The high-temperature storage performance of lithium-ion batteries is evaluated by the thickness expansion rate after storage at 85°C. The lower the thickness expansion rate, the better the high-temperature storage performance, and the higher the thickness expansion rate, the worse the high-temperature storage performance. At 25°C, the lithium-ion battery is allowed to stand for 5 minutes, charged at a constant current of 0.7C to 3.85V to reach a half-charged state, and the thickness of the lithium-ion battery is measured and recorded as H1. The lithium-ion battery is then charged at a constant current of 0.7C to 4.5V, and then charged at a constant voltage to a current of 0.05C, and allowed to stand for 10 minutes to reach a fully charged state. The fully charged lithium-ion battery is allowed to stand in an 85°C constant temperature box for 8 hours. After the lithium-ion battery is taken out, the thickness after storage is measured at 25°C and recorded as H2. The thickness expansion rate of the lithium-ion battery after high-temperature storage is calculated by the following formula: Thickness expansion rate = (H2 / H1-1) × 100%.

[0051] High temperature cycle performance test:

[0052] The high temperature cycle performance of lithium-ion batteries is evaluated by the capacity retention rate at 45°C. The higher the capacity retention rate, the better the high temperature cycle performance, and the lower the capacity retention rate, the worse the high temperature cycle performance. Under 45°C conditions, the lithium-ion battery is charged to 4.52V at a constant current of 0.7C, then charged to a current of 0.05C at a constant voltage of 4.5V, and then discharged to 3.0V at a constant current of 1C. This is a charge and discharge cycle, which is the first cycle. The discharge capacity of the first cycle of the lithium-ion battery is recorded as C1. The lithium-ion battery is charged and discharged 500 times according to the above method, and the discharge capacity of the 500th cycle is recorded as C1. 500 45℃ capacity retention rate = C 500 / C1×100%.

[0053] Example 1-1

[0054] <Preparation of positive electrode active material>

[0055] Magnesium carbonate (MgCO3) and LiCoO2 were mixed in a mass ratio of 6.7:90.1, mixed in a high-speed mixer at 300 r / min for 20 min to obtain a mixture, and the above mixture was placed in an air kiln, heated to 820°C at 5°C / min, maintained for 24 h, taken out after natural cooling, and passed through a 300-mesh sieve to obtain the positive electrode active material.

[0056] <Preparation of positive electrode sheet>

[0057] The prepared positive electrode active material, conductive carbon nanotubes (CNTs), and binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.7:1.4. N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on one surface of a 12 μm thick positive electrode current collector aluminum foil, dried at 85°C, and cold pressed to obtain a positive electrode sheet with a positive electrode material layer thickness of 100 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. The positive electrode sheet was cut into a size of 74 mm × 862 mm and the tabs were welded before use.

[0058] <Preparation of negative electrode sheet>

[0059] The negative electrode active materials, artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC), are mixed in a mass ratio of 95:2:3. Deionized water is then added as a solvent to form a slurry with a solid content of 70 wt%, which is then stirred thoroughly. The slurry is evenly coated on one surface of an 8 μm thick copper foil, dried at 110°C, and cold-pressed to produce a single-sided negative electrode sheet with a 150 μm thick negative electrode material layer. The above steps are repeated on the other surface of the copper foil to produce a double-sided negative electrode sheet. The negative electrode sheet is cut into 75 mm x 867 mm dimensions and the tabs are welded to it before use.

[0060] <Preparation of Electrolyte>

[0061] In an argon atmosphere glove box with a water content of less than 10 ppm, a fluorinated solvent (Formula (II-7)) and a carbonate compound (diethyl carbonate (DEC)) were mixed, and lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed thoroughly to obtain an electrolyte. The mass percentage H% of the lithium salt, based on the mass of the electrolyte, was 12.5%, and the mass percentages B% of the fluorinated solvent and F% of the carbonate compound were as shown in Table 1.

[0062] <Diaphragm>

[0063] A polyethylene porous film with a thickness of 15 μm (manufacturer: Celgard Membrane Co., Ltd., USA) was used as a separator.

[0064] <Preparation of lithium-ion batteries>

[0065] The prepared diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet are stacked in order so that the diaphragm is located between the positive electrode sheet and the negative electrode sheet to serve as an isolation. The electrode assembly is then wound into an electrode assembly, which is placed in an aluminum-plastic film packaging bag and placed in an 85°C vacuum oven to dry for 12 hours to remove moisture. The prepared electrolyte is then injected, and a lithium-ion battery is obtained after vacuum packaging, standing, formation (charging at a constant current of 0.05C to 4.3V, and then discharging at a constant current of 0.2C to 2.8V), shaping, capacity testing, and secondary packaging.

[0066] Example 1-2 to Example 1-8

[0067] The preparation parameters were adjusted according to Table 1, and the rest were the same as Example 1-1. When the mass percentage of the fluorinated solvent changed, the mass percentage of the carbonate compound also changed, while the mass percentage of the lithium salt remained unchanged.

[0068] Example 1-9 to Example 1-18

[0069] Except for further introducing the carboxylate compound ethyl propionate (EP) in <Preparation of Electrolyte> and adjusting the mass percentage of the fluorinated solvent B%, the mass percentage of the carbonate compound F%, the mass percentage of the carboxylate compound G%, and the mass percentage of the lithium salt according to Table 1, the rest is the same as Example 1-1.

[0070] Example 2-1 to Example 2-7

[0071] The preparation parameters were adjusted according to Table 2, and the remainder was the same as in Examples 1-15. When the mass percentage F% of the carbonate compound and / or the mass percentage G% of the carboxylate compound were changed, the mass percentage of the fluorinated solvent was changed accordingly, while the mass percentage of the lithium salt remained unchanged.

[0072] Examples 2-8

[0073] Except for using the electrolyte prepared in the following <Preparation of Electrolyte>, the rest is the same as Example 1-15.

[0074] <Preparation of Electrolyte>

[0075] In an argon atmosphere glove box with a water content of less than 10 ppm, a fluorinated solvent of formula (II-8), a carbonate compound diethyl carbonate (DEC), and a carboxylate compound ethyl propionate (EP) were mixed, and lithium hexafluorophosphate (LiPF6) was added to dissolve and mix thoroughly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage B% of the fluorinated solvent was 58.5%, the mass percentage F% of the carbonate compound was 29%, the mass percentage of EC was 10%, the mass percentage of DEC was 19%, and the mass percentage H% of the lithium salt was 12.5%.

[0076] Examples 2-9

[0077] The same procedures as in Example 2-8 were followed except that the type and mass percentage of the carbonate compound were adjusted according to Table 2. When the mass percentage of the carbonate compound was changed, the mass percentage of the fluorinated solvent was changed accordingly, while the mass percentage of the lithium salt remained unchanged.

[0078] Example 3-1

[0079] The preparation method was the same as that of Example 1-15 except that in the step of <Preparation of Positive Electrode Active Material>, manganese carbonate MnCO3, a compound containing manganese element, was added to the mixture to prepare a positive electrode active material having a composition shown in Table 3.

[0080] Example 3-2

[0081] Except that in <Preparation of Positive Electrode Active Material>, aluminum carbonate Al2(CO3)3, a compound containing aluminum element, is added to the mixture to prepare a positive electrode active material with a composition as shown in Table 3, the rest is the same as Example 1-15.

[0082] Example 3-3 to Example 3-4

[0083] Except for adjusting the amount of the aluminum-containing compound Al2(CO3)3 added so that the composition of the positive electrode active material is as shown in Table 3, the rest is the same as that of Example 1-15.

[0084] Example 4-1 to Example 4-10

[0085] The preparation process was the same as in Examples 1-15, except that the compound represented by formula (V) was further introduced in the preparation of the electrolyte solution, and the type and weight percentage of the compound represented by formula (V) were adjusted according to Table 4. When the weight percentage of the compound represented by formula (V) was changed, the sum of the weight percentages of the fluorinated solvent, the carbonate compound, and the carboxylate compound changed accordingly, while the weight ratio of the three compounds and the weight percentage of the lithium salt remained unchanged.

[0086] Example 5-1 to Example 5-16

[0087] The process was the same as in Examples 1-15, except that a nitrile compound was further introduced in the preparation of the electrolyte solution and the type and weight percentage of the nitrile compound were adjusted according to Table 5. When the weight percentage of the nitrile compound was changed, the sum of the weight percentages of the fluorinated solvent, carbonate compound, and carboxylate compound changed accordingly, while the weight ratio of the three compounds and the weight percentage of the lithium salt remained unchanged.

[0088] Example 6-1 to Example 6-3

[0089] The same procedures as in Examples 1-15 were used except that the type and weight percentage of the lithium salt were adjusted according to Table 6. When the weight percentage of the lithium salt was changed, the sum of the weight percentages of the fluorinated solvent, carbonate compound, and carboxylate compound changed accordingly, while the weight ratio of the three remained unchanged.

[0090] Example 7-1

[0091] In addition to further adding the compound (V-1) represented by formula (V) and the nitrile compound succinonitrile in the preparation of the electrolyte as shown in Table 7, the sum of the mass percentages of the fluorinated solvent, the carbonate compound, and the carboxylate compound changes accordingly, and the mass ratio of the three and the mass percentage of the lithium salt remain unchanged, the rest is the same as Examples 1-15.

[0092] Comparative Example 1

[0093] The process was the same as Example 1-1 except that LiCoO2 was used as the positive electrode active material after being sieved through a 300-mesh sieve, no fluorinated solvent was added to the electrolyte, the mass percentage of the carbonate compound was changed accordingly, and the mass percentage of the lithium salt remained unchanged.

[0094] Comparative Examples 2 to 6

[0095] The preparation parameters were adjusted according to Table 1, and the rest were the same as Example 1-1. When the mass percentage of the fluorinated solvent changed, the mass percentage of the carbonate compound also changed, while the mass percentage of the lithium salt remained unchanged.

[0096] The relevant parameters and performance tests of each embodiment and each comparative example are shown in Tables 1 to 7.

[0097] Table 1

[0098] Note: “ / ” in Table 1 indicates that there is no corresponding substance or parameter.

[0099] As can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 6, the positive electrode active material includes cobalt and magnesium, the electrolyte includes a fluorinated solvent, and the values ​​of A, B, and 100A / B are adjusted within the scope of this application. The results show a lower 85°C thickness expansion rate and a higher 45°C capacity retention rate, indicating that the lithium-ion battery has better high-temperature storage performance and high-temperature cycling performance. The positive electrode active material of Comparative Example 1 does not include magnesium, the electrolyte does not include a fluorinated solvent, and in Comparative Examples 2 to 6, at least one of A, B, or 100A / B is outside the scope of this application. The lithium-ion batteries in these examples have a higher 85°C thickness expansion rate and a lower 45°C capacity retention rate, indicating that the lithium-ion batteries have poor high-temperature storage performance and high-temperature cycling performance.

[0100] The value of A usually affects the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-6 and Comparative Examples 2 to 3 that when A is too small, such as Comparative Example 2, the 85°C thickness expansion rate of the lithium-ion battery is high and the 45°C capacity retention rate is low; when A is too large, such as Comparative Example 3, the 85°C thickness expansion rate of the lithium-ion battery is high and the 45°C capacity retention rate is low. This indicates that the value of A is not within the scope of this application and cannot improve the high-temperature storage performance and high-temperature cycle performance of the lithium-ion battery. Therefore, by regulating the value of A within the scope of this application, the lithium-ion battery has a lower 85°C thickness expansion rate and a higher 45°C capacity retention rate, indicating that the lithium-ion battery has good high-temperature storage performance and high-temperature cycle performance.

[0101] The value of B usually affects the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-7 to Example 1-13, Comparative Example 4 to Comparative Example 5 that when B is too small, such as Comparative Example 4, the 85°C thickness expansion rate of the lithium-ion battery is high and the 45°C capacity retention rate is low; when B is too large, such as Comparative Example 5, the 85°C thickness expansion rate of the lithium-ion battery is high and the 45°C capacity retention rate is low. This indicates that the value of B is not within the scope of this application and cannot improve the high-temperature storage performance and high-temperature cycle performance of the lithium-ion battery. Therefore, by regulating the value of B within the scope of this application, the lithium-ion battery has a lower 85°C thickness expansion rate and a higher 45°C capacity retention rate, indicating that the lithium-ion battery has good high-temperature storage performance and high-temperature cycle performance.

[0102] The value of 100A / B generally affects the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-13 and Comparative Example 6, adjusting the value of 100A / B within the range of this application results in a lower 85°C thickness expansion rate and a higher 45°C capacity retention rate for lithium-ion batteries, indicating that the lithium-ion batteries have better high-temperature storage and cycling performance.

[0103] The value of C typically affects the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-6, by adjusting the value of C within the range of this application, the lithium-ion battery has a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, indicating that the lithium-ion battery has good high-temperature storage and cycling performance.

[0104] The type of fluorinated solvent typically affects the high-temperature storage and cycling performance of lithium-ion batteries. Examples 1-1, 1-14, and 1-18 show that using fluorinated solvents within the scope of this application results in lithium-ion batteries with a lower thickness expansion rate at 85°C and a higher capacity retention rate at 45°C, demonstrating excellent high-temperature storage and cycling performance.

[0105] Table 2

[0106] Note: “ / ” in Table 2 indicates that there is no corresponding substance or parameter.

[0107] The types of carbonate and carboxylate compounds generally affect the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1, and 2-4, using carbonate and carboxylate compounds within the scope of this application results in lithium-ion batteries with a lower thickness expansion rate at 85°C and a higher capacity retention rate at 45°C, demonstrating excellent high-temperature storage and cycling performance.

[0108] The mass percentage F% of the carbonate compound, the mass percentage G% of the carboxylate compound, and the value of F+G generally affect the high-temperature storage performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-15, 2-1, 2-5, and 2-9, by adjusting the values ​​of F, G, and F+G within the ranges of this application, the lithium-ion battery has a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, indicating that the lithium-ion battery has good high-temperature storage performance and high-temperature cycling performance.

[0109] Table 3

[0110] Note: “ / ” in Table 3 indicates that there is no corresponding substance or parameter.

[0111] The types of positive electrode active materials and M elements generally affect the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-15 and Examples 3-1 and 3-2, when the positive electrode active materials include M elements within the scope of this application, the lithium-ion batteries have a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, indicating that the lithium-ion batteries have good high-temperature storage and cycling performance.

[0112] The value of y typically affects the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-15, 3-1, 3-3, and 3-4, by adjusting the value of y within the range of this application, the lithium-ion battery exhibits a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, demonstrating good high-temperature storage and cycling performance.

[0113] Table 4

[0114] Note: “ / ” in Table 4 indicates that there is no corresponding substance or parameter.

[0115] The mass percentage D% of the compound represented by formula (V) generally affects the high-temperature storage performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 1-15 and Examples 4-1 to 4-5, when the value of D is adjusted within the range of this application, the lithium-ion battery has a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, indicating that the lithium-ion battery has good high-temperature storage performance and high-temperature cycling performance.

[0116] The type of compound represented by formula (V) generally affects the high-temperature storage performance and high-temperature cycling performance of lithium-ion batteries. As can be seen from Examples 4-6 to 4-10, using compounds represented by formula (V) within the scope of this application, lithium-ion batteries have a lower thickness expansion rate at 85°C and a higher capacity retention rate at 45°C, indicating that the lithium-ion batteries have good high-temperature storage performance and high-temperature cycling performance.

[0117] Table 5

[0118] Note: " / " in Table 5 indicates that the corresponding substance does not exist. In Examples 5-4 to 5-9, the mass ratio of succinonitrile to 1,3,6-hexanetrinitrile is 1:1.

[0119] The mass percentage E% of nitrile compounds typically affects the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-15 and 5-1 to 5-9, by adjusting the value of E within the range of this application, the lithium-ion batteries exhibit a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, demonstrating excellent high-temperature storage and cycling performance.

[0120] The type of nitrile compound generally affects the high-temperature storage and cycling performance of lithium-ion batteries. Examples 5-1, 5-10, and 5-16 show that using nitrile compounds within the scope of this application results in lithium-ion batteries with a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, demonstrating excellent high-temperature storage and cycling performance.

[0121] Table 6

[0122] Note: “0.5+12” in Table 6 indicates that the mass percentage of LiBOB is 0.5% and the mass percentage of LiTFSI is 12%.

[0123] The mass percentage H% of the lithium salt generally affects the high-temperature storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-15 and 6-1 to 6-2, by adjusting the H% value within the range of this application, the lithium-ion battery has a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, indicating that the lithium-ion battery has good high-temperature storage and cycling performance.

[0124] The type of lithium salt generally affects the high-temperature storage and cycling performance of lithium-ion batteries. As shown in Examples 6-1 and 6-3, using lithium salts within the scope of this application results in a low thickness expansion rate at 85°C and a high capacity retention rate at 45°C, demonstrating excellent high-temperature storage and cycling performance.

[0125] Table 7

[0126] Note: “ / ” in Table 7 indicates that the corresponding substance is not added.

[0127] It can be seen from Examples 1-15, 4-4, 5-1, and 7-1 that the electrolyte simultaneously includes a fluorinated solvent, a carbonate compound, a carboxylate compound, a compound represented by formula (V), and a nitrile compound, and by regulating the values ​​of B, D, E, F, G, and F+G within the scope of this application, the lithium-ion battery can have a lower thickness expansion rate at 85°C and a higher capacity retention rate at 45°C, indicating that the lithium-ion battery has better high-temperature storage performance and high-temperature cycle performance.

[0128] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, the positive electrode active material contains cobalt element and magnesium element, and based on the mass of the positive electrode material layer, the mass percentage content of the magnesium element is A%, 0.1 ≤ A ≤ 5; The electrolyte includes a fluorinated solvent, and the fluorinated solvent includes at least one of the compounds represented by formula (I), the compounds represented by formula (II), the compounds represented by formula (III), or the compounds represented by formula (IV): Wherein, R 1 to R 2 each independently selected from fluorine-substituted or unsubstituted C 1 to C 5 alkyl, fluorine-substituted or unsubstituted C 2 to C 5 alkenyl, fluorine-substituted or unsubstituted C 2 to C 5 alkynyl, sulfonic acid group-substituted C 2 to C 5 alkyl or cyano group-substituted C 2 to C 5 alkyl; R 3 to R 8 each independently selected from H, F, fluorine-substituted or unsubstituted C 1 to C 5 alkyl, fluorine-substituted or unsubstituted C 2 to C 5 alkenyl, fluorine-substituted or unsubstituted C 2 to C 5 alkynyl, sulfonic acid group-substituted C 2 to C 5 alkyl or cyano group-substituted C 2 to C 5 alkyl; R 1 to R 2 at least one of which contains at least one fluorine atom, R 3 to R 4 at least one of which contains at least one fluorine atom, R 5 to R 6 at least one of which contains at least one fluorine atom, R 7 to R 8 at least one of which contains at least one fluorine atom; Based on the mass of the electrolyte, the mass percentage content of the fluorinated solvent is B%, 41.7 ≤ B ≤ 83.2, 0.1 ≤ 100A / B ≤ 6.

2. The secondary battery according to claim 1, Wherein, 0.5 ≤ A ≤ 3, 45.9 ≤ B ≤ 75.

3. The secondary battery according to claim 1, Wherein, Based on the mass of the positive electrode material layer, the mass percentage content of the cobalt element is C%, 51.1 ≤ C ≤ 58.

8.

4. The secondary battery according to claim 1, Wherein, The positive electrode active material includes Li α Co 1-x-y Mg x M y O β , where 0.95 ≤ α ≤ 1.4, 0.004 ≤ x ≤ 0.192, 0 ≤ y ≤ 0.34, 1.9 ≤ β ≤ 2.1, and M includes at least one of Mn, Al, Ni, Ca, Ti, Zr, V, Cr, Fe, Cu, Zn, Rb, or Sn.

5. The secondary battery according to claim 1, Wherein, The compound represented by the formula (I) includes at least one of the following compounds: The compound represented by the formula (II) includes at least one of the following compounds: The compound represented by the formula (III) includes at least one of the following compounds: The compound represented by the formula (IV) includes at least one of the following compounds:

6. The secondary battery according to claim 1, Wherein, The electrolyte solution includes a compound represented by formula (V): wherein, X is selected from any one of; represents the binding site with an adjacent atom; Y and Z are each independently selected from any one of C and O; R 9 , R 10 and R 11 are each independently selected from H, substituted or unsubstituted C 1 To C 10 Alkyl, substituted or unsubstituted C 2 To C 10 Alkenyl, substituted or unsubstituted C 2 To C 10 Alkynyl, substituted or unsubstituted C 6 To C 10 Aryl, substituted or unsubstituted C 1 To C 10 Alkoxy, substituted or unsubstituted C 2 To C 10 Cycloalkoxy, substituted or unsubstituted C 2 To C 10 Alkenyloxy, substituted or unsubstituted C 2 To C 10 Alkynyloxy, substituted or unsubstituted C 6 To C 10 Aryloxy, substituted or unsubstituted C 1 To C 10 Carboxyl, substituted or unsubstituted C 1 To C 10 Carbonyl, substituted or unsubstituted C 1 To C 10 Cyano, substituted or unsubstituted C 1 To C 10 Amino, substituted or unsubstituted C 2 To C 10 Carbonate group, substituted or unsubstituted C 1 To C 10 Sulfate, substituted or unsubstituted C 1 To C 10 Sulfite, substituted or unsubstituted C 1 To C 10 Boric acid ester group, substituted or unsubstituted Generation C 1 to C 10 silyl group, substituted or unsubstituted C 1 to C 10 siloxanyl group, substituted or unsubstituted C 1 to C 10 phosphate group; when substituted, the substituents of each group are each independently selected from at least one of a halogen atom or a cyano group; Based on the mass of the electrolyte, the mass percentage content of the compound represented by formula (V) is D%, 0.05 ≤ D ≤ 5.

7. The secondary battery according to claim 6, Wherein, The compound represented by the formula (V) includes at least one of the following compounds:

8. The secondary battery according to claim 1, Wherein, The electrolyte includes a nitrile compound, and based on the mass of the electrolyte, the content of the nitrile compound is E%, 0.1 ≤ E ≤ 8; The nitrile compounds include at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, terephthalonitrile, tetradecanedinitrile, azobisisobutyronitrile, methylglutaronitrile, pentenedinitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 2-bromobenzene-1,3,5-tricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-propane tricarbonitrile, 1,3,5-pentane tricarbonitrile, 1,2,6-hexane tricarbonitrile, or a compound represented by the following formula (VI):

9. The secondary battery according to claim 1, Wherein, The electrolyte includes a carbonate compound and a carboxylate compound. Based on the mass of the electrolyte, the mass percentage content of the carbonate compound is F%, and the mass percentage content of the carboxylate compound is G%, 8.2 ≤ F ≤ 24.9, 8.2 ≤ F + G ≤ 41.5; The carbonate compound includes 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, dibutyl carbonate, diisopropyl carbonate or propyl carbonate; The carboxylate compound includes at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate or pentyl propionate.

10. The secondary battery according to claim 9, Wherein, 0≤G≤33.3。 11. The secondary battery according to claim 1, Wherein, The electrolyte includes a lithium salt, and based on the mass of the electrolyte, the mass percentage content of the lithium salt is H%, 8 ≤ H ≤ 20; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate or lithium difluorophosphate.

12. An electronic device, which comprises the secondary battery according to any one of claims 1 to 11.