Secondary battery and electronic device

Abstract

This application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector. The positive electrode material layer includes a lithium nickel cobalt manganese oxide compound. Based on the total molar amount of metal elements other than lithium, the molar percentage of nickel in the lithium nickel cobalt manganese oxide compound is X, where X > 80%. The electrolyte includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is Y1, and the mass percentage of fluoroethylene carbonate is Y2, where 1 ≤ Y1 / Y2 ≤ 35. This application can improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests.

Description

[0001] This application is a divisional application of application number 202410876578.7, filed on July 2, 2024, entitled "Secondary Battery and Electronic Device". Technical Field

[0002] This application relates to the field of electrochemical energy storage, and in particular to a secondary battery and an electronic device using the secondary battery. Background Technology

[0003] Rechargeable batteries have seen rapid development in the fields of new energy vehicles and large-scale energy storage. With the diversification of application areas, usage regions, and application scenarios of end products, the market demands higher and higher performance from rechargeable batteries. How to provide a rechargeable battery with more stable and efficient performance under high and low temperature conversion conditions has become an urgent problem to be solved. Summary of the Invention

[0004] This application provides a secondary battery and an electronic device.

[0005] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector. The composite current collector includes a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer. The positive electrode material layer includes a lithium nickel cobalt manganese oxide compound, wherein the molar percentage of nickel in the lithium nickel cobalt manganese oxide compound is X, where X > 80%, based on the total molar amount of metal elements other than lithium. The electrolyte includes ethylene carbonate and fluoroethylene carbonate, wherein the mass percentage of ethylene carbonate is Y1, and the mass percentage of fluoroethylene carbonate is Y2, where 1 ≤ Y1 / Y2 ≤ 35, based on the mass of the electrolyte.

[0006] In this application, the composite current collector and the high-nickel ternary cathode material work together, and cooperate with ethylene carbonate and fluoroethylene carbonate present in the electrolyte in a specific ratio, which can improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests.

[0007] Based on the first aspect, in some possible implementations, 5% ≤ Y 1 ≤ 40% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0008] Based on the first aspect, in some possible implementations, 10% ≤ Y 1 ≤ 20% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0009] Based on the first aspect, in some possible implementations, 0.3% ≤ Y2 ≤ 7% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0010] Based on the first aspect, in some possible embodiments, the electrolyte further includes 1,3,6-hexanetrionitrile, wherein the mass percentage of 1,3,6-hexanetrionitrile is Y3, based on the mass of the electrolyte, 0.1% ≤ Y3 ≤ 4%, and 1 ≤ Y2 / Y3 ≤ 60. Meeting these conditions can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0011] Based on the first aspect, in some possible embodiments, the polymer support layer comprises polyethylene terephthalate and / or polypropylene. Meeting the above conditions can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0012] Based on the first aspect, in some possible implementations, the thickness of the polymer support layer is T, where 3 μm ≤ T ≤ 12 μm. Meeting these conditions can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0013] Based on the first aspect, in some possible implementations, the electrolyte also includes butene sulfite. Meeting the above conditions can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0014] Based on the first aspect, in some possible implementations, the electrolyte also includes lithium salicylate. Meeting the above conditions can further improve the capacity retention and lithium-ion acceptability of the secondary battery after high and low temperature shock tests.

[0015] Based on the first aspect, in some possible embodiments, the negative electrode sheet includes a negative electrode material layer, which comprises graphite and silicon materials, wherein the graphite includes artificial graphite and / or natural graphite. When this negative electrode is applied in the battery of this application, it can better synergize with the positive electrode and electrolyte to improve the performance of the secondary battery.

[0016] A second aspect of this application provides an electronic device including a secondary battery. Detailed Implementation

[0017] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0018] One embodiment of this application provides a secondary battery, which includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0019] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0020] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding layers of the positive electrode, separator, and negative electrode.

[0021] The positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector. The composite current collector includes a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer. The positive electrode material layer includes a lithium nickel cobalt manganese oxide compound. Based on the total molar amount of metal elements other than lithium, the molar percentage of nickel element in the lithium nickel cobalt manganese oxide compound is X, where X > 80%.

[0022] The electrolyte includes ethylene carbonate (EC) and fluoroethylene carbonate (FEC). Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is Y1, and the mass percentage of fluoroethylene carbonate is Y2, where 1≤Y1 / Y2≤35.

[0023] The positive electrode and electrolyte in the secondary battery provided in this application can work synergistically to improve the stability of the secondary battery, thereby improving the capacity retention and lithium-ion acceptance after high and low temperature shock tests. It is speculated that the positive electrode system and electrolyte system in this application can improve the bonding force between the composite current collector and the high-nickel ternary positive electrode material, and, supported by the composite current collector, enhance the temperature difference resistance of the ethylene carbonate and fluoroethylene carbonate films formed at the high-nickel ternary positive electrode interface in the electrolyte of this application. This synergistic effect enables the secondary battery to withstand the shock of high and low temperature switching.

[0024] Lithium nickel cobalt manganese oxide compounds include lithium nickel cobalt manganese oxide and its derivatives, such as coating materials or derivatives doped with other metal elements. For example, lithium nickel cobalt manganese oxide compounds can be LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2. Lithium nickel cobalt manganese oxide derivatives can be Li 0.8 Ni 0.8982 Co 0.0589 Mn 0.0409 Zr 0.002 O2.

[0025] In some alternative implementations, X can be 82%, 85%, 87%, 90%, 92%, 95%, or any value within the range of any two of the above values. The value of Y1 / Y2 can be 1, 2, 5, 7, 9, 12, 15, 17, 19, 22, 25, 30, 35, or any value within the range of any two of the above values.

[0026] In some embodiments, 5% ≤ Y 1 ≤ 40%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0027] In some alternative implementations, Y1 can be 5%, 7%, 10%, 15%, 20%, 22%, 25%, 30%, 32%, 35%, 37%, 40%, or any value within the range of any two of the above values.

[0028] In some embodiments, 10% ≤ Y 1 ≤ 20% is more conducive to improving the capacity retention and lithium-ion acceptance of secondary batteries after high and low temperature shock tests.

[0029] In some embodiments, 0.3% ≤ Y2 ≤ 7%. This can further improve the capacity retention and lithium-ion acceptance of secondary batteries after high and low temperature shock tests.

[0030] In some alternative implementations, Y2 can be 0.3%, 0.5%, 1%, 3%, 4%, 5%, 7%, or any value within the range of any two of the above values.

[0031] In some embodiments, the electrolyte further includes 1,3,6-hexanetrionitrile, wherein the mass percentage of 1,3,6-hexanetrionitrile is Y3, based on the mass of the electrolyte, 0.1% ≤ Y3 ≤ 4%, and 1 ≤ Y2 / Y3 ≤ 60. This can further enhance the synergistic effect between the positive electrode, which includes a composite current collector and a high-nickel ternary cathode, and the electrolyte, which includes ethylene carbonate and fluoroethylene carbonate, further improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0032] In some optional implementations, Y3 can be 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.2%, 3.5%, 4%, or any value within the range of any two of the above values. The ratio of Y2 to Y3 can be 1, 1.5, 1.7, 2, 2.5, 3, 4, 5, 5.5, 6, 10, 20, 30, 40, 50, 60, or any value within the range of any two of the above values.

[0033] In some embodiments, the electrolyte further includes butene sulfite. This is beneficial for further improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. Based on the mass of the electrolyte, the mass percentage of butene sulfite is 0.1% to 0.5%, which is beneficial for improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some embodiments, the mass percentage of butene sulfite can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value within the range of any two of the above values.

[0034] In some embodiments, the electrolyte further includes lithium salicylate. This is beneficial for further improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. Based on the mass of the electrolyte, the mass percentage of lithium salicylate is 0.2% to 0.5%, which is beneficial for improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some embodiments, the mass percentage of lithium salicylate can be 0.2%, 0.25%, 0.3%, 0.4%, 0.45%, 0.5%, or any value within the range of any two of the above values.

[0035] electrolyte

[0036] According to some embodiments of this application, the electrolyte includes the ethylene carbonate, fluoroethylene carbonate, 1,3,6-hexanetrionitrile, butene sulfite, and lithium salicylate described above.

[0037] In some embodiments, the electrolyte further includes an organic solvent, which includes, but is not limited to: propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0038] In some embodiments, the organic solvent further includes ether solvents, including at least one of 1,3-dioxapentane (DOL) and ethylene glycol dimethyl ether (DME) in some optional embodiments.

[0039] In some embodiments, the electrolyte may further comprise a lithium salt, which includes at least one of organic or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2)(LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of adiponitrile.

[0040] Positive electrode sheet

[0041] The polymer support layer in this application has good structural strength, which can improve the structural strength of the composite current collector, thereby helping to improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests.

[0042] In some embodiments, the polymer support layer comprises polyethylene terephthalate and / or polypropylene. The above-mentioned polymer materials, as polymer support layers, exhibit good thermal stability and mechanical properties.

[0043] The conductive metal layer may include at least one of aluminum or an aluminum alloy.

[0044] In some embodiments, the thickness of the polymer support layer is T, where 3 μm ≤ T ≤ 12 μm. Within this range, the polymer support layer exhibits good structural strength, supports the metal conductive layer, improves the structural stability of the composite current collector, and further enhances the capacity retention and lithium-ion acceptability of the secondary battery after high and low temperature impact tests. In some optional embodiments, T can be 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, or any value within the range of any two of the above values.

[0045] The positive electrode material layer further includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer and at the same time improve the bonding force between the positive electrode material layer and the positive electrode current collector. In some embodiments, the adhesive may include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0046] The positive electrode material layer may further include a conductive material, and the conductive material includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials may include but are not limited to metal powder or metal fiber, and in some optional embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0047] Negative electrode tab

[0048] In some embodiments, the negative electrode material layer includes graphite and a silicon material. The graphite includes artificial graphite and / or natural graphite.

[0049] The silicon material includes at least one of (a composite of silicon-based substances and carbon-based substances) or silicon oxide (SiOx, 0 < x ≤ 2). The silicon-based substances may be silicon particles, silicon alloy particles, etc.

[0050] Since graphite has a certain flexibility, its combination with the silicon-carbon composite material can relieve the overall volume expansion of the negative electrode material layer. At the same time, graphite and the silicon-carbon composite material as the negative electrode active material can also make full use of the advantages of both the silicon-carbon composite material and graphite to achieve better electrochemical performance.

[0051] In this application, the mass ratio of graphite in the negative electrode material layer is 35 wt.% to 95 wt.%. When the mass ratio of graphite in the negative electrode material layer is within the above range, the cycle performance of the negative electrode material layer can be further improved, thereby improving the cycle performance of the secondary battery.

[0052] The negative electrode current collector can use at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, etc., and can also be a composite current collector disclosed in any prior art, and in some optional embodiments, but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0053] The negative electrode material layer also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the negative electrode material layer and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0054] The negative electrode material layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powder or metal fibers, and in some optional embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0055] The negative electrode material layer may also include a dispersant, which may include at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose, or hydroxyethyl carboxymethyl cellulose.

[0056] Separating membrane

[0057] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0058] In some optional embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, 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 selected.

[0059] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0060] The aforementioned secondary batteries are used in electronic devices to power loads within those devices. These electronic devices may include, but are not limited to, laptops, pen-based 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.

[0061] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0062] Example 1

[0063] 1. Preparation of positive electrode sheet

[0064] LiNi 0.88 Co 0.1 Mn 0.02O2, Super-P, and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2 and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was coated onto a 12μm composite aluminum foil (commercially available, a composite current collector made by depositing aluminum layers on both sides of polyethylene terephthalate (PET) using an advanced vacuum deposition process), dried, cold-pressed, and then cut and welded to obtain the positive electrode sheet.

[0065] 2. Preparation of negative electrode sheet

[0066] Artificial graphite and SiO2 (mass ratio 90:10), styrene-butadiene rubber, and sodium hydroxyethyl carboxymethyl cellulose were mixed with deionized water at a mass ratio of 96.5%:1.5%:2%. A triazine compound was then added, and the mixture was stirred until homogeneous to obtain a slurry. The slurry was coated onto a 9μm copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode sheet.

[0067] 3. Preparation of electrolyte

[0068] Under a dry argon atmosphere, propylene carbonate (PC), diethyl carbonate (DMC), and ethyl propionate (EP) (weight ratio 2:2:3) were mixed, and LiPF6 with a mass concentration of 12.5% ​​was added to obtain a basic electrolyte. Ethylene carbonate (EC) and fluoroethylene carbonate (FEC), along with other optional substances, were added to the basic electrolyte in the amounts shown in Table 1 to obtain electrolytes for different examples and comparative examples.

[0069] 4. Preparation of the separating membrane

[0070] A 7-micron porous polyethylene polymer film was used as the separator.

[0071] 5. Preparation of secondary batteries

[0072] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving the electrolyte injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a secondary battery.

[0073] Examples 2 to 21

[0074] The difference between Examples 2 to 21 and Example 1 is that, except for adjusting the electrolyte parameters according to Table 1, they are the same as in Example 1.

[0075] Examples 22 to 27

[0076] The difference between Examples 22 to 27 and Example 15 is that, except for adjusting the relevant parameters of the composite current collector according to Table 1, they are the same as in Example 1.

[0077] Comparative Examples 1 to 5

[0078] Comparative Example 1 was identical to Example 1 except that it used a conventional positive electrode current collector with a thickness of 10 μm. Comparative Examples 2 to 5 were identical to Example 1 except that the electrolyte preparation parameters were adjusted according to Table 1.

[0079] Test methods

[0080] 1. Capacity retention rate after high and low temperature shock tests

[0081] Take three batteries from each group of the prepared secondary batteries, and charge and discharge the three lithium-ion batteries respectively through the following steps, and calculate the discharge capacity retention rate of the secondary batteries.

[0082] First, the initial charge and discharge cycles were performed at 25°C. The battery was initially charged at a constant current of 0.5C until it reached 4.3V, then charged at a constant voltage. Finally, it was discharged at a constant current of 1C until it reached 2.8V. The discharge capacity of the first cycle was recorded. Next, the lithium-ion battery was placed at -20°C for 100 charge and discharge cycles. After the low-temperature cycle, the battery was transferred to a 45°C environment within one hour for 200 charge and discharge cycles. The discharge capacity of the 200th cycle at 45°C was recorded.

[0083] Capacity retention rate = (Discharge capacity of the 200th cycle / Discharge capacity of the first cycle) × 100%.

[0084] The following benchmarks are used for evaluation. A higher capacity retention rate indicates better performance of the secondary battery after high and low temperature shock tests.

[0085] A: Capacity retention rate is greater than 85%;

[0086] B: Capacity retention rate is greater than or equal to 80% and less than 85%;

[0087] C: Capacity retention rate is greater than or equal to 75% and less than 80%;

[0088] D: Capacity retention rate is less than 75%.

[0089] 2. Lithium-ion acceptability after high and low temperature impact testing

[0090] After the secondary battery was left to stand at 35°C for 24 hours, it was charged at a constant current of 1.0C for 1 hour at 35°C, and the high-temperature charging capacity (C0) was measured. Then, at 35°C, it was discharged at a constant current of 0.1C until it reached 3V, at which point the discharge was stopped. Next, at -15°C, it was charged at a constant current of 1.0C for 1 hour, and the low-temperature charging capacity (C1) was measured. The ratio of C1 to C0 (C1 / C0) was then calculated and evaluated using the following criteria. A higher C1 / C0 value indicates better lithium-ion acceptance of the secondary battery at low temperatures.

[0091] A: C1 / C0 is greater than 0.65;

[0092] B: C1 / C0 is greater than 0.55 and less than 0.65;

[0093] C: C1 / C0 is greater than 0.5 and less than 0.55;

[0094] D: C1 / C0 is less than 0.5.

[0095] Table 1

[0096]

[0097]

[0098] In the table above, " / " indicates that there are no relevant parameters.

[0099] Compared to the comparative example, in the embodiments, when the composite current collector and the high-nickel ternary cathode material work together, and interact with ethylene carbonate and fluoroethylene carbonate present in a specific ratio in the electrolyte, the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests can be improved.

[0100] In particular, the presence of a certain amount of 1,3,6-hexanetrionitrile in the electrolyte can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0101] In particular, the presence of butene sulfite and / or lithium salicylate in the electrolyte can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0102] In particular, when the polymer support layer of the composite current collector meets the scope defined in this application, it can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0103] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the principles and scope of the present application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector; The composite current collector includes a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer, wherein the polymer support layer includes polyethylene terephthalate and / or polypropylene. The positive electrode material layer includes a lithium nickel cobalt manganese oxide compound. Based on the total molar amount of metal elements other than lithium, the molar percentage of nickel in the lithium nickel cobalt manganese oxide compound is X, where X > 80%. The electrolyte comprises ethylene carbonate, fluoroethylene carbonate, and 1,3,6-hexanetrionitrile. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is Y1, the mass percentage of fluoroethylene carbonate is Y2, and the mass percentage of 1,3,6-hexanetrionitrile is Y3, where 1≤Y1 / Y2≤35, 5%≤Y1≤40%, 0.3%≤Y2≤7%, 0.1%≤Y3≤4%, and 1≤Y2 / Y3≤60.

2. The secondary battery as described in claim 1, characterized in that, The thickness of the polymer support layer is T, where 3μm≤T≤12μm.

3. The secondary battery as claimed in claim 1, characterized in that, The electrolyte also includes butene sulfite.

4. The secondary battery as described in claim 3, characterized in that, The electrolyte also includes lithium salicylate.

5. The secondary battery as described in claim 1, characterized in that, The negative electrode sheet includes a negative electrode material layer, which includes graphite and silicon materials, and the graphite includes artificial graphite and / or natural graphite.

6. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 5.

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