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 adiponitrile and succinonitrile. On the basis of the mass of the electrolyte, the mass percentage content of adiponitrile is B1, and the mass percentage content of succinonitrile is B2, wherein 0.01≤X×B1 / B2≤90. 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 increasingly applied in various fields of new energy, and thus the requirements for their performance in various aspects have been improved.

[0003] With the increasing diversification of use scenarios, it is an urgent problem to be solved to provide a secondary battery with more stable and efficient performance under high-low temperature conversion conditions. SUMMARY

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

[0005] 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 mole percentage content of nickel element in the lithium nickel cobalt manganese oxide compound being X based on the total mole amount of metal elements other than lithium, and X>80%; the electrolyte comprising adiponitrile and butanedinitrile, the mass percentage content of adiponitrile being B1 and the mass percentage content of butanedinitrile being B2 based on the mass of the electrolyte, and 0.01≤X×B1 / B2≤90.

[0006] In the present application, the composite current collector and the high-nickel ternary positive electrode material jointly act, and cooperate with adiponitrile and butanedinitrile present in the electrolyte at a specific ratio, so as to 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, 0.02≤X×B1 / B2≤40. Satisfying this condition can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test. Based on the first aspect, in some possible implementation manners, 0.01%≤B1≤3.5%. Satisfying this condition 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, 0.03%≤B2≤4%. Satisfying this condition 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 electrolyte further includes vinylene carbonate, and a mass percentage of the vinylene carbonate in the electrolyte is B3, 0.01%≤B3≤2%, based on a mass of the electrolyte. Satisfying the condition can further improve the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0010] In some possible implementation manners based on the first aspect, the electrolyte further includes 1,3-propanesultone, and a mass percentage of the 1,3-propanesultone in the electrolyte is B4, 0.01%≤B4≤4.5%, a sum of mass percentages of the adiponitrile, the succinonitrile, the vinylene carbonate and the 1,3-propanesultone is greater than or equal to 0.1% and less than or equal to 10%. Satisfying the condition can further improve the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0011] In some possible implementation manners based on the first aspect, the composite current collector includes a polymer support layer and a metal conductive layer arranged on at least one surface of the polymer support layer. Satisfying the condition can further improve the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0012] In some possible implementation manners based on the first aspect, the polymer support layer includes polyethylene terephthalate or / and polypropylene. Satisfying the condition can further improve the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0013] In some possible implementation manners based on the first aspect, the metal conductive layer contains aluminum elements, and a thickness of the metal conductive layer is greater than or equal to 0.8 μm and less than or equal to 3 μm. Satisfying the condition can further improve the capacity retention rate and the lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0014] In some possible implementation manners based on the first aspect, the negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes graphite and silicon material, and the graphite includes artificial graphite and / or natural graphite.

[0015] The second aspect of the present application provides an electronic device including the secondary battery. The secondary battery supplies power for the electronic device, and the secondary battery has good capacity retention rate and lithium ion acceptance after the high-low temperature impact test, which is beneficial to improve the universality of the electronic device in the conversion between high temperature and low temperature. DETAILED DESCRIPTION

[0016] 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.

[0017] 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.

[0018] 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 or the like.

[0019] The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, and the separator 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 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 and the negative electrode sheet after being stacked.

[0020] 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, 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, X>80%; and the electrolyte comprises adiponitrile (ADN) and succinonitrile (SN), the mass percentage content of adiponitrile is B1 and the mass percentage content of succinonitrile is B2 based on the mass of the electrolyte, 0.01≤X×B1 / B2≤90.

[0021] In the secondary battery provided by the present application, the composite current collector and the high-nickel ternary positive electrode material jointly act, and cooperate with adiponitrile and succinonitrile existing in the electrolyte in a specific ratio, so as to improve 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 the electrolyte system in the present application can improve the binding force between the composite current collector and the high-nickel ternary positive electrode material, and enhance the temperature difference resistance of adiponitrile and succinonitrile in the electrolyte of the present application to form a film on the high-nickel ternary positive electrode interface under the support of the composite current collector. The above-mentioned synergistic effect makes the secondary battery resistant to the impact of high-low temperature conversion.

[0022] In some embodiments, X can be 82%, 85%, 87%, 90%, 92%, 95%, or any value within a range defined by any two of the above values. The value of X x B1 / B2 can be 0.01, 1, 2, 5, 7, 9, 12, 15, 17, 19, 22, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or any value within a range defined by any two of the above values.

[0023] The lithium nickel cobalt manganese oxide compound includes lithium nickel cobalt manganese oxide and a lithium nickel cobalt manganese oxide derivative such as a coated material or a derivative 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.

[0024] Preferably, 0.02 ≤ X x B1 / B2 ≤ 40. Satisfying this condition, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved.

[0025] In some embodiments, 0.01% ≤ B1 ≤ 3.5%. Satisfying this condition, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved. In some alternative embodiments, B1 can be 0.01%, 0.02%, 0.05%, 0.07%, 0.1%, 0.15%, 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.4%, 2.5%, 3%, 3.2%, 3.5%, or any value within a range defined by any two of the above values.

[0026] In some embodiments, 0.03% ≤ B2 ≤ 4%. Satisfying this condition, the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test can be further improved. In some alternative embodiments, B2 can be 0.03%, 0.05%, 0.1%, 0.15%, 0.3%, 0.5%, 1%, 1.2%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.5%, 3.7%, 4%, or any value within a range defined by any two of the above values.

[0027] In some embodiments, the electrolyte further comprises vinylene carbonate (VC) in a mass percentage of B3, 0.01%≤B3≤2%, based on the mass of the electrolyte. Satisfying this condition can further strengthen the synergistic effect between the positive electrode comprising the composite current collector and the high-nickel ternary and the electrolyte comprising adiponitrile and succinonitrile, further improving the capacity retention rate and lithium ion acceptance of the secondary battery after high and low temperature impact test. In some alternative embodiments, B3 can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.5%, 1%, 1.5%, 1.7%, 2%, or any value within a range defined by any two of the above values.

[0028] In some embodiments, the electrolyte further comprises 1,3-propane sultone (PS) in a mass percentage of B4, 0.01%≤B4≤4.5%, 0.1%≤B1+B2+B3+B4≤10%, based on the mass of the electrolyte. Satisfying this condition can further strengthen the synergistic effect between the positive electrode comprising the composite current collector and the high-nickel ternary and the electrolyte comprising adiponitrile and succinonitrile, further improving the capacity retention rate and lithium ion acceptance of the secondary battery after high and low temperature impact test. In some alternative embodiments, B4 can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.5%, 1%, 1.5%, 1.7%, 2%, 2.5%, 2.8%, 3%, 3.7%, 4%, 4.5%, or any value within a range defined by any two of the above values. The sum of B1+B2+B3+B4 can be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 9.5%, 10%, or any value within a range defined by any two of the above values.

[0029] In some embodiments, the electrolyte further comprises lithium salicylate in a mass percentage of 0.4% to 0.6%, based on the mass of the electrolyte. Satisfying this condition can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high and low temperature impact test. The mass percentage of lithium salicylate can be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, or any value within a range defined by any two of the above values.

[0030] Electrolyte

[0031] According to some embodiments of the present application, the electrolyte comprises the above-described adiponitrile, succinonitrile, vinylene carbonate, 1,3-propane sultone, and lithium salt.

[0032] 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.

[0033] 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).

[0034] In some embodiments, the lithium salt 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 fluoroethylene carbonate and adiponitrile.

[0035] Positive electrode tab

[0036] In some embodiments, 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. This is conducive to further improving the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0037] The polymer support layer can be selected from polyethylene terephthalate or / and polypropylene. The above-mentioned polymer materials have good thermal stability and mechanical properties as the polymer support layer.

[0038] In some embodiments, the metal conductive layer contains aluminum elements, and the thickness T of the metal conductive layer is greater than or equal to 0.8 μm and less than or equal to 3 μm. Meeting the above conditions is conducive to further improving the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test. In some embodiments, T can be 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm or any value within the range of any two of the above values.

[0039] The metal conductive layer can include at least one of aluminum or aluminum alloy.

[0040] The metal conductive layer is obtained by a vapor deposition method or an electroplating method, and the thickness of the metal conductive layer can be adjusted by changing the deposition time or the electroplating time.

[0041] 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.

[0042] 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 fibers, or any combination thereof. In some embodiments, the metal-based materials can include, but are not limited to, metal powder or metal fibers, in some alternative embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0043] Negative electrode tab

[0044] In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode material layer includes graphite and a silicon material. The graphite includes artificial graphite and / or natural graphite.

[0045] 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.

[0046] 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.

[0047] In this application, the mass percentage of graphite in the negative electrode material layer is 35 wt.% to 95 wt.%. The mass percentage of 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Separator film

[0053] 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.

[0054] 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.

[0055] 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 comprises inorganic particles and a binder, 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 comprises a polymer, 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).

[0056] The secondary battery described above is applied to electronic devices to supply power to loads in the electronic devices. The electronic devices can include, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, lithium-ion capacitors and the like.

[0057] 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 merely examples, and any other suitable preparation method is within the scope of the present application.

[0058] Example 1

[0059] 1. Preparation of the positive electrode

[0060] LiNi 0.88 Co 0.1 Mn 0.02 O2, Super-P and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2, and 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 of the base material by an advanced vacuum plating process), dried, cold-pressed, and then cut into pieces and the tabs were welded to obtain a positive electrode.

[0061] 2. Preparation of negative electrode

[0062] Artificial graphite and SiO2(mass ratio 90:10), styrene butadiene rubber, sodium hydroxyethyl carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 96.5%:1.5%:2%, and a triazine compound was added, followed by stirring to obtain a slurry. The slurry was coated on a 9-μm copper foil. After drying, cold pressing, and cutting, a tab was welded to obtain a negative electrode.

[0063] 3. Preparation of electrolyte

[0064] Propylene carbonate (PC), diethyl carbonate (DMC), and ethyl propionate (EP) (weight ratio 2:2:3) were mixed in a dry argon environment, and LiPF6was added, with the concentration of LiPF6being 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.

[0065] 4. Preparation of separator

[0066] A 7-μm polyethylene porous polymer film was used as a separator.

[0067] 5. Preparation of secondary battery

[0068] The obtained positive electrode, separator, and negative electrode were wound in order and placed in an outer packaging foil, leaving a filling port. The electrolyte was filled from the filling port, and the secondary battery was obtained after encapsulation, formation, and capacity processes.

[0069] Examples 2 to 18

[0070] Examples 2 to 18 are different from Example 1 in that, in addition to adjusting the electrolyte or composite current collector-related parameters according to Table 1, the rest is the same as Example 1.

[0071] Examples 19 to 22

[0072] Examples 19 to 22 are different from Example 12 in that, in addition to adjusting the composite current collector-related parameters according to Table 1, the rest is the same as Example 12.

[0073] Comparative Examples 1 to 5

[0074] Comparative Example 1 is the same as Example 1 except that a conventional positive electrode current collector with a thickness of 10 μm is used. Comparative Examples 2 to 5 are the same as Example 1 except that the electrolyte-related preparation parameters are adjusted according to Table 1.

[0075] Test method

[0076] 1. Capacity retention rate after high-low temperature impact test

[0077] Three pieces of each group of the prepared secondary batteries were taken out, and the three lithium ion batteries were charged and discharged by the following steps, and the discharge capacity retention rate of the batteries was calculated.

[0078] First, in an environment of 25°C, the first charging and discharging was carried out, first using a current of 0.5C for constant current charging, charging to 4.3V for constant voltage charging, then discharging at a current of 1C for constant current discharging, discharging to 2.8V, and recording the discharge capacity of the first cycle; then the lithium ion battery was placed in an environment of -20°C for 100 cycles of charging and discharging. After the low-temperature cycle, the lithium ion battery was transferred to an environment of 45°C within one hour for 200 cycles of charging and discharging, and the discharge capacity of the 200th cycle under the condition of 45°C was recorded.

[0079] Capacity retention rate = (discharge capacity of the 200th cycle / discharge capacity of the first cycle) x 100%.

[0080] The following criteria were used for evaluation. The higher the capacity retention rate, the more excellent the performance of the secondary battery after high-low temperature impact test.

[0081] A: the capacity retention rate is greater than 85%;

[0082] B: the capacity retention rate is greater than or equal to 80% and less than 85%;

[0083] C: the capacity retention rate is greater than or equal to 75% and less than 80%;

[0084] D: the capacity retention rate is less than 75%.

[0085] 2. Lithium ion acceptance after high-low temperature impact test

[0086] After the prepared secondary battery was allowed to stand for 24 hours in an environment of 35°C, a charging operation was carried out at a constant current of 1.0C for 1 hour in an environment of 35°C, and the high-temperature charging capacity (C0) was measured. Then, in an environment of 35°C, discharging was stopped at the time when discharging was carried out at a constant current of 0.1C to 3V. Next, in an environment of -15°C, a charging operation was carried out at a constant current of 1.0C for 1 hour, and the low-temperature charging capacity (C1) was measured. Then, the ratio of C1 to C0 (C1 / C0) was calculated, and the following criteria were used for evaluation. The larger the value of C1 / C0, the more excellent the lithium ion acceptance of the secondary battery at low temperature.

[0087] A: C1 / C0 is 0.65 or more;

[0088] B: C1 / C0 is 0.55 or more and less than 0.65;

[0089] C: C1 / C0 is 0.5 or more and less than 0.55;

[0090] D: C1 / C0 is less than 0.5.

[0091] Table 1

[0092] As can be seen from Table 1 above, compared with the comparative examples, the positive electrode tab of the secondary battery in the examples includes a composite current collector and a high-nickel lithium nickel manganese oxide compound, cooperates with adiponitrile and butanedinitrile and meets the appropriate content relationship range in the present application, thereby improving the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0093] In Examples 11 to 12, the secondary battery is added with vinylene carbonate in the electrolyte, which further improves the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0094] In Examples 10 and 14 to 15, the secondary battery is added with 1,3-propanesulfonic acid lactone in the electrolyte, which further improves the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0095] In Examples 16 to 18, the secondary battery is added with lithium salicylate in the electrolyte, which improves the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0096] In Examples 19 to 22, the thickness T of the metal conductive layer is changed, which improves the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0097] 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 provided 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 hexanedinitrile and butanedinitrile, a mass percentage content of the hexanedinitrile is B1 based on a mass of the electrolyte, a mass percentage content of the butanedinitrile is B2 based on the mass of the electrolyte, and 0.01≤X×B1 / B2≤90.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following conditions: (1)0.01％≤B1≤3.5％； (2)0.03％≤B2≤4％； (3) 0.02≤X×B1 / B2≤40.

3. The secondary battery according to claim 1 or 2, wherein The electrolyte further includes vinylene carbonate, a mass percentage content of the vinylene carbonate is B3 based on a mass of the electrolyte, and 0.01%≤B3≤2%.

4. The secondary battery according to claim 3, wherein The electrolyte further includes 1,3-propanesultone, a mass percentage content of the 1,3-propanesultone is B4 based on a mass of the electrolyte, 0.01%≤B4≤4.5%, and a sum of mass percentage contents of the hexanedinitrile, the butanedinitrile, the vinylene carbonate, and the 1,3-propanesultone is greater than or equal to 0.1% and less than or equal to 10%.

5. The secondary battery according to any one of claims 1 to 4, wherein The composite current collector includes a polymer support layer and a metal conductive layer provided on at least one surface of the polymer support layer.

6. The secondary battery according to claim 5, wherein The metal conductive layer contains an aluminum element, and a thickness T of the metal conductive layer is greater than or equal to 0.8 μm and less than or equal to 3 μm.

7. The secondary battery according to claim 5, wherein the negative electrode is a lithium metal electrode. The polymer support layer includes polyethylene terephthalate or / and polypropylene.

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.

Images