Secondary battery and electronic device

Abstract

Provided in the present application are a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte solution. The positive electrode sheet comprises a composite current collector and a positive electrode material layer provided on at least one surface of the composite current collector. The positive electrode material layer comprises a lithium nickel cobalt manganese oxide compound. On the basis of the total molar amount of metal elements other than lithium, the molar percentage content of nickel in the lithium nickel cobalt manganese oxide compound is X, wherein X>80%. The electrolyte solution comprises ethylene carbonate and fluoroethylene carbonate. On the basis of the mass of the electrolyte solution, the mass percentage content of the ethylene carbonate is Y1, and the mass percentage content of the fluoroethylene carbonate is Y2, wherein 1≤Y1 / Y2≤35. The present application can improve the capacity retention ratio and lithium ion acceptance of a secondary battery after a high- or low-temperature impact test.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a secondary battery and an electronic device using the same. BACKGROUND

[0002] Secondary batteries have been rapidly developed in the field of new energy vehicles and large-scale energy storage. With the diversification of application fields, use regions and use scenarios of terminal products, the market has increasingly high performance requirements for secondary batteries. How to provide a secondary battery with more stable and efficient performance under high-low temperature conversion conditions has become an urgent problem to be solved. SUMMARY

[0003] The present application provides a secondary battery and an electronic device.

[0004] The first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a composite current collector and a positive electrode material layer arranged on at least one surface of the composite current collector, the positive electrode material layer comprising a lithium nickel cobalt manganese oxide compound, the molar percentage content of nickel element in the lithium nickel cobalt manganese oxide compound being X based on the total molar amount of metal elements other than lithium, X>80%; the electrolyte comprising ethylene carbonate and fluoroethylene carbonate, the mass percentage content of ethylene carbonate being Y1 and the mass percentage content of fluoroethylene carbonate being Y2 based on the mass of the electrolyte, 1≤Y1 / Y2≤35.

[0005] In the present application, the composite current collector and the high-nickel ternary positive electrode material act together and cooperate with ethylene carbonate and fluoroethylene carbonate present in the electrolyte at a specific ratio, which can improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0006] Based on the first aspect, in some possible implementation manners, 5%≤Y1≤40%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0007] Based on the first aspect, in some possible implementation manners, 10%≤Y1≤20%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0008] Based on the first aspect, in some possible implementation manners, 0.3%≤Y2≤7%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0009] In some possible implementation manners based on the first aspect, the composite current collector comprises a polymer support layer and a metal conductive layer arranged on at least one surface of the polymer support layer. With the above condition met, the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0010] In some possible implementation manners based on the first aspect, the polymer support layer comprises polyethylene terephthalate or / and polypropylene. With the above condition met, the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0011] In some possible implementation manners based on the first aspect, the thickness of the polymer support layer is T, and 3 μm≤T≤12 μm. With the above condition met, the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0012] In some possible implementation manners based on the first aspect, the electrolyte further comprises 1,3,6-hexanetricarbonitrile, and the mass percentage of the 1,3,6-hexanetricarbonitrile in the electrolyte is Y3, 0.1%≤Y3≤4%, and 1≤Y2 / Y3≤60. With the above condition met, the synergistic effect of the composite current collector, the high-nickel ternary positive electrode material, and the specific proportion of the vinyl carbonate and the fluoroethylene carbonate can be strengthened, and the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0013] In some possible implementation manners based on the first aspect, the electrolyte further comprises lithium salicylate. With the above condition met, the synergistic effect of the composite current collector, the high-nickel ternary positive electrode material, and the specific proportion of the vinyl carbonate and the fluoroethylene carbonate can be strengthened, and the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0014] In some possible implementation manners based on the first aspect, the electrolyte further comprises butylene sulfite. With the above condition met, the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0015] In some possible implementation manners based on the first aspect, the negative electrode sheet comprises a negative electrode material layer, and the negative electrode material layer comprises graphite and silicon material, and the graphite comprises artificial graphite and / or natural graphite. The negative electrode is applied to the battery of the application, and can better synergize with the positive electrode and the electrolyte to improve the performance of the secondary battery.

[0016] The second aspect of the application provides an electronic device comprising the secondary battery. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0018] An embodiment of the present application provides a secondary battery, which comprises a shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are both located in the shell.

[0019] The shell can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), and the secondary battery can be a soft package battery. In other embodiments, the secondary battery can also be a steel shell battery, an aluminum shell battery, etc.

[0020] The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film, and the separator film is arranged between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a stacked structure formed by alternately stacking the positive electrode sheet, the separator film and the negative electrode sheet. In other embodiments, the electrode assembly can also be a winding structure formed by winding the positive electrode sheet, the separator film and the negative electrode sheet after being stacked.

[0021] The positive electrode sheet comprises a composite current collector and a positive electrode material layer arranged on at least one surface of the composite current collector, and the positive electrode material layer comprises a lithium nickel cobalt manganese oxide compound, the mole percentage content of nickel element in the lithium nickel cobalt manganese oxide compound is X based on the total mole amount of metal elements other than lithium, and X>80%;

[0022] The electrolyte comprises ethylene carbonate (EC), fluoroethylene carbonate (FEC), 1,3,6-hexanetricarbonitrile and lithium salicylate, the mass percentage content of ethylene carbonate is Y1 based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is Y2, 1≤Y1 / Y2≤35; the mass percentage content of 1,3,6-hexanetricarbonitrile is Y3 based on the mass of the electrolyte, 0.1%≤Y3≤4%, and 1≤Y2 / Y3≤60.

[0023] The positive electrode and electrolyte in the secondary battery provided by the application can synergize to improve the stability of the secondary battery, thereby improving the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test. It is speculated that the positive electrode system and electrolyte system in the application can improve the bonding force between the composite current collector and the high-nickel ternary positive electrode material, and under the support of the composite current collector, the temperature difference resistance of the ethylene carbonate and fluoroethylene carbonate in the electrolyte of the application to form a film on the high-nickel ternary positive electrode interface is enhanced. The above-mentioned synergistic effect makes the secondary battery resistant to the impact of high-low temperature conversion. The addition of 1,3,6-hexanetricarbonitrile and lithium salicylate can further strengthen the synergistic effect between the positive electrode including the composite current collector and the high-nickel ternary and the electrolyte including ethylene carbonate and fluoroethylene carbonate, and further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0024] The lithium nickel cobalt manganese oxide compound includes lithium nickel cobalt manganese oxide and lithium nickel cobalt manganese oxide derivatives, such as coated materials or derivatives doped with other metal elements. For example, the lithium nickel cobalt manganese oxide compound can be LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2. The lithium nickel cobalt manganese oxide derivative can be Li 0.8 Ni 0.8982 Co 0.0589 Mn 0.0409 Zr 0.002 O2.

[0025] In some optional embodiments, X can be 82%, 85%, 87%, 90%, 92%, 95%, or any value within the range composed 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 composed of any two of the above values.

[0026] In some embodiments, 5%≤Y1≤40%. The capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test can be further improved.

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

[0028] In some embodiments, 10%≤Y1≤20%, which is more conducive to improving the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0029] In some embodiments, 0.3%≤ Y2≤ 7%. The capacity retention and lithium ion acceptance of the secondary battery after high-low temperature impact test can be further improved.

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

[0031] In some alternative embodiments, 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 a range between any two of the above values. The ratio of Y2 / 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 a range between any two of the above values.

[0032] In some embodiments, the electrolyte further comprises butylenesulfite. The capacity retention and lithium ion acceptance of the secondary battery after high-low temperature impact test can be further improved. The mass percentage of butylenesulfite in the electrolyte is 0.1% to 0.5%, which is conducive to improving the capacity retention and lithium ion acceptance of the secondary battery after high-low temperature impact test. In some embodiments, the mass percentage of butylenesulfite can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value within a range between any two of the above values.

[0033] In some embodiments, the addition of lithium salicylate in the electrolyte is conducive to further improving the capacity retention and lithium ion acceptance of the secondary battery after high-low temperature impact test. The mass percentage of lithium salicylate in the electrolyte is 0.2% to 0.5%, which is conducive to improving the capacity retention and lithium ion acceptance of the secondary battery after high-low temperature impact test. 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 a range between any two of the above values.

[0034] Electrolyte

[0035] According to some embodiments of the present application, the electrolyte comprises the above-described vinyl carbonate, fluoro-vinyl carbonate, 1,3,6-hexanetricarbonitrile, butylenesulfite, and lithium salicylate.

[0036] In some embodiments, the electrolyte further comprises 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.

[0037] In some embodiments, the organic solvent further comprises an ether solvent, which in some alternative embodiments includes at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME).

[0038] In some embodiments, the electrolyte can further comprise a lithium salt, which includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of adiponitrile.

[0039] Positive electrode tab

[0040] In some embodiments, the composite current collector comprises a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer. The use of the polymer support layer has good structural strength, which can improve the structural strength of the composite current collector, thereby further improving the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0041] In some embodiments, the polymer support layer comprises polyethylene terephthalate or / and polypropylene. The above-mentioned polymer materials have good thermal stability and mechanical properties as the polymer support layer.

[0042] The metal conductive layer can comprise at least one of aluminum or aluminum alloy.

[0043] In some embodiments, the thickness of the polymer support layer is T, 3 μm≤T≤12 μm. Within the above range, the polymer support layer has good structural strength, which supports the metal conductive layer, improves the structural stability of the composite current collector, and further improves the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test. In some alternative embodiments, T can be 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, or any value within the range between any two of the above values.

[0044] The positive electrode material layer also includes a binder to bind the positive electrode active material particles to facilitate formation of the film layer and to improve the adhesion between the positive electrode material layer and the positive electrode current collector. In some embodiments, the binder can include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0045] The positive electrode material layer can also 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, the carbon-based materials can include, but are not limited to, at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials can include, but are not limited to, metal powder or metal fiber, in some alternative embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0046] Negative electrode tab

[0047] In some embodiments, the negative electrode material layer includes graphite and a silicon material. The graphite includes artificial graphite and / or natural graphite.

[0048] The silicon material includes at least one of a silicon-based substance and a silicon oxide (SiOx, 0 < x < 2). The silicon-based substance can be silicon particles, silicon alloy particles, or the like.

[0049] Since the graphite has a certain flexibility, it cooperates with the silicon-carbon composite material to relieve the volume expansion of the negative electrode material layer as a whole. Meanwhile, the graphite and the silicon-carbon composite material as negative electrode active materials can fully utilize the advantages of both the silicon-carbon composite material and the graphite to achieve better electrochemical performance.

[0050] In this application, the mass percentage of the graphite in the negative electrode material layer is 35 wt.% to 95 wt.%, and the mass percentage of the graphite in the negative electrode material layer within the above range can further improve the cycle performance of the negative electrode material layer, thereby improving the cycle performance of the secondary battery.

[0051] The negative electrode current collector can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, and can also be any composite current collector disclosed in the prior art, in some alternative embodiments, but not limited to, the aforementioned conductive foils and polymer substrates combined to form a current collector.

[0052] The negative material layer can further include a binder to bind the negative active material particles to facilitate formation of the film layer and to improve the adhesion between the negative material layer and the negative current collector. In some embodiments, the binder can include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0053] The negative material layer can further include a conductive material, which can include, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials can include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials can include, but are not limited to, metal powder or metal fibers, such as copper, nickel, aluminum, or silver in some alternative embodiments. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0054] The negative material layer can further include a dispersant, which can include at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose, or hydroxyethyl carboxymethyl cellulose.

[0055] Separator film

[0056] The material and shape of the separator film used in the secondary battery of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer or inorganic material formed of a material stable to the electrolyte of the present application, etc.

[0057] In some alternative embodiments, the separator film can include a base layer and a surface treatment layer. The base layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, 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 can be used.

[0058] A surface treatment layer is provided on at least one surface of the substrate layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing polymer and inorganic material. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, 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 vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0059] The secondary battery described above is applied to an electronic device to supply power to a load in the electronic device. The electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flash, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0060] The present application is described below by way of specific examples and comparative examples. Those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0061] Example 1

[0062] 1. Preparation of positive electrode sheet

[0063] LiNi 0.88 Co 0.1 Mn 0.02O2, Super-P and polyvinylidene fluoride were mixed with N-methyl pyrrolidone (NMP) in a mass ratio of 96:2:2, stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated on a 12 μm composite aluminum foil (commercially available, a composite current collector made of polyethylene terephthalate (PET) as a base material, and a metal aluminum layer deposited on both sides thereof by an advanced vacuum plating process), dried, cold-pressed, and then subjected to a piece cutting and tab welding process to obtain a positive electrode tab.

[0064] 2. Preparation of a negative electrode tab

[0065] Artificial graphite and SiO2 (mass ratio 90:10), butadiene-styrene rubber, and sodium hydroxyethyl carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96.5%:1.5%:2%, and a triazine compound was added thereto, and the mixture was stirred uniformly to obtain a slurry. The slurry was coated on a 9 μm copper foil, dried, cold-pressed, and then subjected to a piece cutting and tab welding process to obtain a negative electrode tab.

[0066] 3. Preparation of an electrolyte

[0067] Propylene carbonate (PC), diethyl carbonate (DMC) and ethyl propionate (EP) (weight ratio 2:2:3) were mixed in a dry argon environment, and LiPF6 was added thereto, wherein the concentration of LiPF6 was 12.5%, to obtain a base electrolyte. Ethylene carbonate (EC) and fluoroethylene carbonate (FEC) and optional other substances were added to the base electrolyte in the amounts shown in Table 1 to obtain electrolytes for different examples and comparative examples.

[0068] 4. Preparation of a separator

[0069] A 7 μm polyethylene porous polymer film was used as a separator.

[0070] 5. Preparation of a secondary battery

[0071] The obtained positive electrode, separator and negative electrode were sequentially wound, placed in an outer packaging foil, and a liquid injection port was left. An electrolyte was injected from the liquid injection port, and the secondary battery was packaged and then subjected to a formation, capacity and other processes.

[0072] Examples 2 to 21

[0073] Examples 2 to 21 are different from Example 1 in that, in addition to adjusting the electrolyte-related parameters according to Table 1, the rest is the same as Example 1.

[0074] Examples 22 to 27

[0075] Examples 22 to 27 are different from Example 15 in that, in addition to adjusting the composite current collector-related parameters according to Table 1, the rest is the same as Example 1.

[0076] Comparative Example 1 to Comparative Example 5

[0077] Comparative Example 1 is identical to Example 1 except that a conventional cathode current collector having a thickness of 10 μm is used. Comparative Examples 2 to 5 are identical to Example 1 except that the electrolyte-related preparation parameters are adjusted as shown in Table 1.

[0078] Test Method

[0079] 1. Capacity retention rate after high-low temperature impact test

[0080] Three pieces of each of the prepared secondary batteries were taken, and the three lithium ion batteries were charged and discharged by the following procedures, and the discharge capacity retention rate of the secondary batteries was calculated.

[0081] First, at 25°C, the first charge and discharge were performed, and first, constant current charging was performed using a current of 0.5 C, and after charging to 4.3 V, constant voltage charging was performed, and then constant current discharging was performed at a current of 1 C, and discharging to 2.8 V was performed, and the discharge capacity of the first cycle was recorded. Then, the lithium ion battery was placed in an environment of -20°C and subjected to 100 cycles of charge and discharge. After the low-temperature cycle, the lithium ion battery was transferred to an environment of 45°C within one hour and subjected to 200 cycles of charge and discharge, and the discharge capacity of the 200th cycle at 45°C was recorded.

[0082] Capacity retention rate = (discharge capacity of the 200th cycle / discharge capacity of the first cycle) x 100%.

[0083] Evaluation was performed by the following criteria. The higher the capacity retention rate, the more excellent the performance of the secondary battery after the high-low temperature impact test.

[0084] A: capacity retention rate is greater than 85%;

[0085] B: capacity retention rate is greater than or equal to 80% and less than 85%;

[0086] C: capacity retention rate is greater than or equal to 75% and less than 80%;

[0087] D: capacity retention rate is less than 75%.

[0088] 2. Lithium ion acceptance after high-low temperature impact test

[0089] After the prepared secondary battery was left to stand for 24 hours in an environment of 35°C, high-temperature charge capacity (C0) was measured by performing a charge operation for 1 hour at a constant current of 1.0C in an environment of 35°C. Then, at the time when discharge was stopped at 3V by performing discharge at a constant current of 0.1C in an environment of 35°C. Next, low-temperature charge capacity (C1) was measured by performing a charge for 1 hour at a constant current of 1.0C in an environment of -15°C. Then, the ratio of C1 to C0 (C1 / C0) was calculated, and evaluated by the following criteria. The larger the value of C1 / C0, the more excellent the lithium ion acceptance of the secondary battery at low temperature.

[0090] A: C1 / C0 is 0.65 or more;

[0091] B: C1 / C0 is 0.55 or more and less than 0.65;

[0092] C: C1 / C0 is 0.5 or more and less than 0.55;

[0093] D: C1 / C0 is less than 0.5.

[0094] Table 1

[0095] In the above table, " / " indicates no relevant parameter.

[0096] Compared with the comparative examples, in the examples, when the composite current collector and the high-nickel ternary positive electrode material jointly act, and interact with the ethylene carbonate and fluoroethylene carbonate present in the electrolyte in a specific ratio, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be improved.

[0097] In particular, when a certain content of 1,3,6-hexanetricarbonitrile exists in the electrolyte, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0098] In particular, when butylene sulfite and / or lithium salicylate exist in the electrolyte, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0099] In particular, when the polymer support layer of the composite current collector meets the range defined in the present application, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0100] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be interpreted as a limitation of the present application, and 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 by comprising: The secondary battery includes a positive electrode tab, a negative electrode tab, and an electrolyte, the positive electrode tab 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, a molar percentage content of a nickel element in the lithium nickel cobalt manganese oxide compound is X based on a total molar amount of metal elements other than lithium, and X > 80%; The electrolyte includes ethylene carbonate and fluoroethylene carbonate, a mass percentage content of the ethylene carbonate is Y1 and a mass percentage content of the fluoroethylene carbonate is Y2 based on a mass of the electrolyte, and 1 ≤ Y1 / Y2 ≤ 35.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following conditions: (1)5％≤Y1≤40％； (2)0.3％≤Y2≤7％。 3. The secondary battery according to claim 1 or 2, wherein 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.

4. The secondary battery according to claim 3, wherein The polymer support layer includes polyethylene terephthalate or / and polypropylene.

5. The secondary battery according to claim 3 or 4, wherein A thickness of the polymer support layer is T, and 3 μm ≤ T ≤ 12 μm.

6. The secondary battery according to any one of claims 1 to 5, wherein The electrolyte further includes butylene sulfite.

7. The secondary battery according to any one of claims 1 to 6, wherein The electrolyte further includes 1,3,6-hexanetricarbonitrile, a mass percentage content of the 1,3,6-hexanetricarbonitrile is Y3 based on a mass of the electrolyte, and 0.1% ≤ Y3 ≤ 4%, 1 ≤ Y2 / Y3 ≤ 60.

8. The secondary battery according to any one of claims 1 to 7, wherein The electrolyte further includes lithium salicylate.

9. The secondary battery according to any one of claims 1 to 8, wherein The negative electrode tab includes a negative electrode material layer, the negative electrode material layer includes graphite and a silicon material, and the graphite includes artificial graphite and / or natural graphite.

10. An electronic device, comprising: The secondary battery includes the secondary battery according to any one of claims 1 to 9.

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