A lithium ion battery and electronic device

Abstract

The application discloses a lithium ion battery and an electronic device, the lithium ion battery comprising a positive electrode sheet, a diaphragm, a negative electrode sheet and an electrolyte, the diaphragm being arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material containing a cobalt element and a T element, the T element being selected from at least one element in the 4-6 period V B subgroup and the 6 B subgroup, the content A of the T element and the content B of the cobalt element in the positive electrode active material layer satisfying 0.002<=A / B<=0.01; the electrolyte containing a nitrile compound; the content of the nitrile compound in the electrolyte being C, the porosity of the positive electrode sheet being D, the resistance value at 50% SOC being R, and satisfying 15<=R*D / A<=110 and 30<=B*R / (A+C)<=100. The lithium ion battery can balance the high-temperature cycle capacity retention rate, the safety performance and the low-temperature discharge performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery and an electronic device. BACKGROUND

[0002] Lithium ion batteries are very promising energy storage devices in power tools, electric vehicles and energy storage systems due to their high energy and power density, long cycle life, low self-discharge rate and high safety.

[0003] With the increasingly wide application of lithium ion batteries, people have higher and higher requirements for lithium batteries, but the existing lithium ion battery technology often cannot well balance the low-temperature discharge performance while meeting the high-temperature cycle performance and safety performance, which to some extent limits the application space of lithium ion batteries. Therefore, it is very necessary to develop a lithium ion battery that simultaneously balances high-temperature cycle performance, safety performance and low-temperature discharge performance. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a lithium ion battery and an electronic device.

[0005] In a first aspect of the present application, a lithium ion battery is provided, comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte; the separator is arranged between the positive electrode sheet and the negative electrode sheet;

[0006] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material comprises a cobalt element and a T element, the T element is selected from at least one element in the V B and VI B subgroups of the 4-6 period of the periodic table of elements; the mass percentage content of the T element in the positive electrode active material is A, the mass percentage content of the cobalt element in the positive electrode active material is B, and A and B satisfy: 0.002≤A / B≤0.01;

[0007] The electrolyte contains a nitrile compound; the mass percentage content of the nitrile compound in the electrolyte is C, the porosity of the positive electrode sheet is D, and the resistance value of the positive electrode sheet at 50% SOC is R, A, B, C, D and R satisfy: 15≤R*D / A≤110, 30≤B*R / (A+C)≤100.

[0008] According to the lithium ion battery of the embodiment of the present application, at least the following beneficial effects are achieved: the lithium ion battery adopts a positive electrode active material containing cobalt elements and T elements (at least one element in the V B sub-group and the VI B sub-group of the 4th to 6th periods of the periodic table of elements) to construct a positive electrode sheet, and the content A and B of the T elements and the cobalt elements in the positive electrode active material satisfy the condition 0.002≤A / B≤0.01, the T elements can maximally improve the conductivity of the positive electrode material, and after the T elements are doped into the cobalt positions, the T elements can act as a supporting element to effectively reduce the migration resistance of lithium ions in the deintercalation process and improve the migration rate of the lithium ions; in addition, by controlling the proportional relationship of the content A of the T elements in the positive electrode active material, the porosity D of the positive electrode sheet, and the resistance R of the positive electrode sheet at 50% SOC to satisfy 15≤R*D / A≤110, the positive electrode sheet has excellent electronic transmission channels, and the electronic conductivity is improved due to the doping of the T elements; and the porosity control of the positive electrode sheet guarantees the transmission rate of the lithium ions in the electrolyte, optimizes the electronic conductivity and the ionic conductivity, and effectively improves the discharge performance of the lithium ion battery at low temperatures. Furthermore, a nitrile compound with a mass content of C in the electrolyte is added, and 30≤B*R / (A+C)≤100 is controlled, the T elements in the positive electrode material can have a synergistic effect with the nitrile compound in the electrolyte, which can effectively improve the electrode-electrolyte interface contact, thereby improving the low-temperature discharge performance, effectively improving the high-temperature cycle performance and safety performance of the lithium ion battery.

[0009] The resistance value of the positive electrode sheet at 50% SOC can be obtained by the following method: the lithium ion battery is charged at a rate of 0.5C to 50% SOC, and the cutoff current is 0.025C; then the positive electrode sheet in the lithium ion battery is disassembled, placed in an environment with a humidity of 5% to 15% for 30 minutes, and then the resistance value of the positive electrode sheet is tested, which is recorded as R. The positive electrode sheet can be sealed and transferred to the resistance test site for resistance testing, and a BER1200 type membrane resistance tester can be used for positive electrode sheet resistance testing. Further, the above resistance test can require that the adjacent test points are spaced 2mm to 3mm apart, at least 15 different points are tested, and the average resistance of all test points is recorded as the final resistance value.

[0010] In some embodiments of the present application, A, B, C, D, and R satisfy: 15≤R*D / A≤70, and 30≤B*R / (A+C)≤90.

[0011] In some embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions:

[0012] 1) A satisfies: 0.5%≤A≤0.55%;

[0013] 2) B satisfies: 55%≤B≤65%;

[0014] 3) C satisfies: 0.1%≤C≤1%;

[0015] 4) D satisfies: 10%≤D≤20%;

[0016] 5) R satisfies: 0.5Ω≤R≤1Ω.

[0017] In some embodiments of the present application, the positive electrode active material has a chemical formula of Li a Co 1-x-y T x N y O b , wherein 0.90≤a≤1.10, 0.001≤x≤0.05, 0≤y≤0.02, 1.90≤b≤2.10; T is at least one element in the V B and VI B subgroups of the 4th to 6th periods of the periodic table of elements, and can specifically be at least one of vanadium, chromium, niobium, molybdenum, tantalum and tungsten; N is at least one of aluminum, magnesium, titanium, zirconium, yttrium and lanthanum.

[0018] The nitrile compound is specifically a compound containing a cyano group (-CN). In some embodiments of the present application, the nitrile compound is selected from one or more of a di-nitrile compound, a tri-nitrile compound and a tetra-nitrile compound.

[0019] In some embodiments of the present application, the di-nitrile compound has a structural formula of NC-R 21 -CN;

[0020] The tri-nitrile compound has a structural formula of:

[0021] The tetra-nitrile compound has a structural formula of:

[0022] wherein R 21 , R 22 and R 23 are each independently selected from halogen-substituted or unsubstituted C1-C10 alkyl, halogen-substituted or unsubstituted C1-C10 alkenyl, halogen-substituted or unsubstituted C1-C10 alkynyl, halogen-substituted or unsubstituted C5-C10 heteroaryl and halogen-substituted or unsubstituted C6-C10 aryl.

[0023] In some embodiments of the present application, the dinitrile compound is selected from one or more of succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, nonanedinitrile, dicyanobenzene, terephthalonitrile, pyridine-3,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, 3,3'-[l,2-ethanediylbis(oxy)]dipropanenitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyran methylenemalononitrile, maleonitrile, ethylene glycol bis(propionitrile) ether, and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile; and / or,

[0024] The trinitrile compound is selected from one or more of 1,3,6 hexanetristrinitrile, 1,3,5-cyclohexanetristrinitrile, 1,3,5-benzene tristrinitrile, 1,2,3-propanetrinitrile, and glycerol trinitrile; and / or,

[0025] The tetranitrile compound is selected from one or more of 1,1,3,3-propanetetranitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-l,l,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoparabenzoquinone dimethane.

[0026] In some embodiments of the present application, the electrolyte further comprises a lithium salt and an organic solvent.

[0027] In some embodiments of the present application, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium triflate (LiCF3SO3), lithium difluorophosphate (LiPO2F2), lithium 2-trifluoromethyl-4,5-dicyanimidazole (C6F3LiN4), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2).

[0028] In some embodiments of the present application, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, γ-butyrolactone, 1,3-propane sultone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, 1,3-dioxolane, ethylene glycol dimethyl ether.

[0029] In some embodiments of the present application, the positive electrode material layer further comprises a conductive agent and a binder.

[0030] In some embodiments of the present application, the conductive agent is selected from one or more of natural graphite, artificial graphite, conductive carbon black, acetylene black, ketjen black, graphene, carbon nanotube, carbon fiber, conductive polymer, and metal powder.

[0031] In some embodiments of the present application, the binder is selected from one or more of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, butadiene-styrene rubber-based material, and polyacrylate-based material.

[0032] In some embodiments of the present application, the positive electrode material layer comprises 93wt% to 99wt% of the positive electrode active material, 0.5wt% to 5wt% of the conductive agent, and 0.5wt% to 2wt% of the binder. That is, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is 93 to 99:0.5 to 5:0.5 to 2.

[0033] In some embodiments of the present application, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 97:1.5:1.5.

[0034] In some embodiments of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, a conductive agent, and a binder.

[0035] In some embodiments of the present application, the lithium ion battery further comprises a packaging shell, and the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte are contained in the packaging shell.

[0036] In some embodiments of the present application, the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a bare cell, and the bare cell and the electrolyte are contained in the packaging shell.

[0037] The above lithium ion battery can be prepared by a preparation method comprising the following steps:

[0038] An electrode slurry comprising the positive electrode active material is prepared, and then coated on at least one side surface of a positive electrode current collector to obtain a positive electrode sheet;

[0039] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to form a bare cell, and then the bare cell is placed in a packaging shell, and the electrolyte is injected to obtain a lithium ion battery.

[0040] The positive electrode active material can be prepared by a method comprising the following steps: mixing lithium cobaltate and a compound containing the T element uniformly, and calcining under an air atmosphere to obtain a positive electrode active material. The compound containing the T element can be selected from one or more of a T element-containing carbonate, a T element-containing oxide, and a T element-containing hydroxide.

[0041] In the preparation process of the positive electrode active material, the calcination temperature can be controlled at 650℃-850℃; the calcination time can be controlled at 22h-26h; and the temperature rising speed can be controlled at 2℃ / min-8℃ / min.

[0042] In the preparation process of the positive electrode sheet, after the positive electrode paste is coated on the surface of the positive electrode current collector, the positive electrode sheet is obtained by further drying and roller pressing. The drying temperature can be controlled at 100℃-150℃, for example, can be any one of 100℃, 110℃, 120℃, 125℃, 130℃, 140℃, 150℃ or a range value of any two thereof; and the drying time can be 6h-10h, for example, can be any one of 6h, 7h, 8h, 8.5h, 9h, 10h or a range value of any two thereof. Further, the structure parameters of the positive electrode sheet can be controlled by controlling the roller pressing thickness of the positive electrode sheet in the roller pressing process. Further, after the roller pressing process, further slitting can be performed.

[0043] In addition, in the process of assembling the battery, after the electrolyte is injected, the lithium ion battery is obtained by further vacuum packaging, standing, formation and shaping processes.

[0044] In a second aspect of the present application, an electronic device is provided, which comprises any one of the lithium ion batteries described above. DETAILED DESCRIPTION

[0045] The concept and technical effects of the present application will be described below in conjunction with the embodiments to make the purpose, features and effects of the present application clear. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0046] Embodiment 1

[0047] The present embodiment provides a lithium ion battery, which comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, and the separator is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on the two opposite surfaces of the positive electrode current collector; the positive electrode material layer comprises positive electrode active material, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) with a mass ratio of 97:1.5:1.5; the positive electrode active material contains cobalt element and T element, wherein the T element is specifically tantalum element, and the mass percentage content A of the tantalum element and the mass percentage content B of the cobalt element in the positive electrode active material are 0.37% and 59.94% respectively, and further 0.002

[0048] In addition, the resistance value R of the positive plate of the lithium ion battery at 50% SOC is 0.76 Ω, and the resistance value is specifically tested by the following method: the lithium ion battery is charged at a rate of 0.5C to 50% SOC, and the cutoff current is 0.025C; then the positive plate in the lithium ion battery is disassembled, placed in an environment with a humidity of 10% for 30 min, sealed and transferred to the resistance test site, and the resistance value of the positive plate is tested using a BER1200 type diaphragm resistance tester, and during the test, the adjacent test points are spaced 2-3 mm apart, 15 different points are tested, and the average resistance of all test points is calculated to obtain the final resistance value R.

[0049] The electrolyte includes lithium salt LiPF6, organic solvent and nitrile compound; the mass percentage content of LiPF6 in the electrolyte is 15%, and the nitrile compound is adiponitrile, and the mass percentage content C of adiponitrile in the electrolyte satisfies 0.1% < C = 0.5% < 1%; and further, the lithium ion battery satisfies: 15 < R*D / A = 30.8 < 110, 30 < B*R / (A+C) = 52.4 < 100.

[0050] The lithium ion battery is prepared by a preparation method comprising the following steps:

[0051] Preparation of the positive active material: lithium cobaltate and tantalum-containing compound tantalum carbonate are uniformly mixed according to a molar ratio of 1:0.007, calcined at 750°C under an air atmosphere at a rate of 5°C / min for 24h to obtain the positive active material;

[0052] Preparation of the positive plate: the positive active material, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 97:1.5:1.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive slurry with uniform fluidity; the positive slurry is uniformly coated on the two sides of the positive current collector aluminum foil; the coated aluminum foil is placed in an oven and baked at 5 different temperature gradients of 100°C, 110°C, 120°C, 110°C and 100°C for 1 min respectively, and then dried at 120°C for 8h, and then rolled and cut to obtain the positive plate. The core element T in the positive active material is tantalum element, the content of tantalum element in the positive plate is 0.37% based on the mass of the positive active material, the thickness of the positive plate after rolling is 80μm, and the porosity of the positive plate is 15%.

[0053] Preparation of the negative electrode sheet: the negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) were mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5, and then coated on the two sides of the negative electrode current collector Cu foil, followed by drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0054] Preparation of the electrolyte: in an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and dimethyl carbonate (DMC) were mixed at a mass ratio of 20:10:10:10:50 to obtain a non-aqueous solvent, and then 15 wt.% of LiPF6 based on the total mass of the electrolyte was slowly added to the non-aqueous solvent, followed by stirring until the LiPF6 was completely dissolved, and then 0.5 wt.% of adiponitrile based on the total mass of the electrolyte was added to obtain the electrolyte.

[0055] Preparation of the lithium ion battery: the positive electrode sheet, the separator, and the negative electrode sheet were stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then the bare battery was obtained by winding, and the bare battery was placed in an outer packaging foil, and the electrolyte prepared above was injected into the dried battery, and then the lithium ion battery was obtained by vacuum packaging, standing, formation, shaping, and other processes.

[0056] Example 2 group

[0057] This example group includes examples 2a-2b, and examples 2a-2b respectively provide a lithium ion battery, which is different from example 1 in that the content A of tantalum element in the positive electrode active material of the positive electrode material layer on the positive electrode sheet is different from that in example 1, and then the resistance value of the positive electrode sheet is different from that in example 1, and the other aspects are basically the same as those of the lithium ion battery in example 1.

[0058] The preparation of the lithium ion battery in examples 2a-2b was performed according to example 1, except that the molar ratio of lithium cobaltate to tantalum carbonate was adjusted from 1:0.007 in example 1 to 1:0.0036 and 1:0.01 respectively, so as to adjust the content A of tantalum element in the positive electrode active material, and the specific adjustment is shown in Table 1.

[0059] Example 3 group

[0060] This example group includes examples 3a-3c, and examples 3a-3c respectively provide a lithium ion battery, which is different from example 1 in that the content C of adiponitrile in the electrolyte is different from that in example 1, and the other aspects are basically the same as those of the lithium ion battery in example 1.

[0061] The preparation of the lithium ion batteries in this embodiment group was performed according to the preparation of the lithium ion batteries in Example 1, except that the content C of adiponitrile in the electrolyte was adjusted. See Table 1 for details.

[0062] Example 4 group

[0063] This embodiment group includes Examples 4a-4c, each of which provides a lithium ion battery, which is different from the lithium ion battery in Example 1 in that the porosity and thickness of the positive electrode sheet are different from those in Example 1, and is basically the same as the lithium ion battery in Example 1 in other aspects.

[0064] The preparation of the lithium ion batteries in this embodiment group was performed according to the preparation of the lithium ion batteries in Example 1, except that the porosity of the positive electrode sheet was adjusted, which was achieved by adjusting the thickness of the positive electrode sheet after rolling. The thickness of the positive electrode sheet was adjusted to be in the range of 70 μm-90 μm. See Table 1 for details.

[0065] Example 5 group

[0066] This embodiment group includes Examples 5a-5c, each of which provides a lithium ion battery, which is different from the lithium ion battery in Example 1 in that the nitrile compound in the electrolyte is different from that in Example 1, and is basically the same as the lithium ion battery in Example 1 in other aspects.

[0067] The preparation of the lithium ion batteries in this embodiment group was performed according to the preparation of the lithium ion batteries in Example 1, except that the nitrile compound in the electrolyte was adjusted. See Table 1 for details.

[0068] Example 6 group

[0069] This embodiment group includes Examples 6a-6e, each of which provides a lithium ion battery, which is different from the lithium ion battery in Example 1 in that the type of T element in the positive electrode active material on the positive electrode sheet is different from that in Example 1, and is basically the same as the lithium ion battery in Example 1 in other aspects.

[0070] The preparation of the lithium ion batteries in this embodiment group was performed according to the preparation of the lithium ion batteries in Example 1, except that in the preparation of the positive electrode active material in Examples 6a-6e, the compound containing T element was vanadate, chromate, niobate, tungstate, or molybdate, respectively. In addition, the molar ratio of lithium cobaltate to vanadate in Example 6a was 1:0.007, the molar ratio of lithium cobaltate to chromate in Example 6b was 1:0.0035, the molar ratio of lithium cobaltate to niobate in Example 6c was 1:0.007, the molar ratio of lithium cobaltate to tungstate in Example 6d was 1:0.007, and the molar ratio of lithium cobaltate to molybdate in Example 6e was 1:0.007. Thus, the type of T element in the positive electrode active material on the positive electrode sheet was adjusted. See Table 1 for details.

[0071] Comparative Example 1

[0072] The comparative example 2 group includes comparative examples 2a-2b, and the comparative examples 2a-2b each provide a lithium ion battery, which is different from the example 1 in that the positive electrode active material on the positive electrode sheet does not contain the element T, or the electrolyte does not contain the nitrile compound, and the internal proportions of other substances remain unchanged, see Table 1 for details.

[0073] Comparative example 2 group

[0074] The comparative example 2 group includes comparative examples 2a-2b, and the comparative examples 2a-2b each provide a lithium ion battery, which is different from the example 1 in that the positive electrode active material on the positive electrode sheet does not contain the element T, or the electrolyte does not contain the nitrile compound, and the internal proportions of other substances remain unchanged, see Table 1 for details.

[0075] Comparative example 3 group

[0076] The comparative example 3 group includes comparative examples 3a-3f, and the comparative examples 3a-3f each provide a lithium ion battery, which is different from the example 1 in that the positive electrode active material on the positive electrode sheet contains the element T (specifically, the element cobalt), and the electrolyte contains the nitrile compound, but the proportional relationship of the content A of the element T, the content B of the element cobalt, the resistance R of the positive electrode sheet, the porosity D of the positive electrode sheet, and the content C of the nitrile compound in the electrolyte cannot simultaneously satisfy: 0.002≤A / B≤0.01, 0.1%≤C≤1%, 15≤R*D / A≤110, 30≤B*R / (A+C)≤100, see Table 1 for details. Among them, the preparation of the lithium ion batteries of comparative examples 3a-3b refers to example 1, except that: in the preparation process of the positive electrode active material in comparative examples 3a-3b, 3d, the molar ratio of lithium cobaltate to tantalum carbonate is adjusted from 1:0.007 in example 1 to 1:0.0016, 1:0.013, 1:0.0036, respectively, so as to adjust the content A of the tantalum element in the positive electrode active material.

[0077] Table 1

[0078]

[0079]

[0080] Performance test

[0081] (1) Cycle life test

[0082] The lithium ion battery is placed in a constant temperature environment of 45°C, and the charge and discharge test is carried out at a rate of 1.0C / 1.0C, wherein the charge cut-off voltage is 4.5V, the discharge cut-off voltage is 3.0V, the charge and discharge cycle is 500 times, the cycle discharge capacity is recorded and divided by the discharge capacity of the first cycle, and the cycle capacity retention rate is obtained.

[0083] (2) Low temperature discharge test

[0084] The lithium ion battery was placed at room temperature to perform 5 times of charge-discharge cycles at 1C rate, then charged to 4.5V at 1C rate, and the 1C charge capacity Q1 was recorded. The battery in full charge state was placed at -20℃ for 4h, then discharged to 3.0V at 0.2C rate, and the discharge capacity Q2 was recorded, and the low-temperature discharge capacity retention rate was calculated by Q2 / Q1.

[0085] (3)134℃ hot box test

[0086] The lithium ion battery was charged at 25℃ environment at 0.5C rate to 4.5V, and charged at constant voltage to the cut-off current of 0.025C, and rested for 2h. The battery in full charge was placed in a hot box to rise from room temperature to 134℃ at a heating rate of 5℃ / min, and kept for 60min. If the battery did not explode and did not catch fire, it was determined as PASS, otherwise as FAIL.

[0087] The performance of the lithium ion batteries of each example and comparative example was tested according to the above method, and the results are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] From the above Table 2, compared with each comparative example, the safety performance of the lithium ion battery of each example was obviously improved, the high-temperature cycle capacity retention rate was obviously improved, and the low-temperature discharge capacity retention rate was obviously improved, indicating that the T element and the cobalt element in the positive active material in the positive electrode sheet of each example lithium ion battery cooperated with the nitrile compound in the electrolyte, which could effectively limit the side reaction of the two-phase interface of the positive active material and the electrolyte, thereby improving the safety performance and high-temperature cycle stability of the battery. At the same time, thanks to the electronic conductivity improvement brought by the addition of the nitrile compound in the electrolyte (especially the low content design of the nitrile compound) and the T element doping, and the limited relationship between the positive electrode sheet resistance and the porosity, the low-temperature discharge performance of the battery was obviously improved.

[0092] The above lithium ion battery can be applied to electronic devices, and thus the present application further proposes an electronic device, which includes but is not limited to notebook computers, e-book players, portable phones, portable printers, watches, game consoles, toys, lighting devices, calculators, video recorders, radios, portable power supplies, automobiles, motorcycles, household large storage batteries, etc.

[0093] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte solution; the separator is clamped between the positive electrode sheet and the negative electrode sheet; The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode active material, the positive electrode active material contains a cobalt element and a T element, the T element is selected from at least one element in the V B subgroup and the VI B subgroup of the 4-6 period of the periodic table of elements; the mass percentage content of the T element in the positive electrode active material is A, the mass percentage content of the cobalt element in the positive electrode active material is B, and A and B satisfy: 55%≤B≤65%, 0.002≤A / B≤0.01; The electrolyte solution contains a nitrile compound; the mass percentage content of the nitrile compound in the electrolyte solution is C, the porosity of the positive electrode sheet is D, and the resistance value of the positive electrode sheet at 50% SOC is R; A, B, C, D and R satisfy: 0.1%≤C≤1%, 10%≤D≤20%, 0.5Ω≤R≤1Ω, 15≤R*D / A≤110, and 30≤B*R / (A+C) ≤100.

2. The lithium-ion battery of claim 1, wherein, A, B, C, D and R satisfy: 15≤R*D / A≤70, and 30≤B*R / (A+C) ≤90.

3. The lithium-ion battery of claim 1, wherein, A satisfies: 0.5%≤A≤0.55%.

4. The lithium-ion battery of claim 1, wherein, The positive active material has a chemical formula of Li a Co 1-x-y T x N y O b wherein 0.90≤a≤1.10, 0.001≤x≤0.05, 0≤y≤0.02, 1.90≤b≤2.10, T is at least one element in the V B subgroup and the VI B subgroup of the 4th to 6th period of the periodic table of elements, and N is at least one of aluminum, magnesium, titanium, zirconium, yttrium, and lanthanum.

5. The lithium-ion battery of claim 1, wherein, The nitrile compound is selected from one or more of a di-nitrile compound, a tri-nitrile compound and a tetra-nitrile compound.

6. The lithium-ion battery of claim 5, wherein, The structural formula of the dinitrile compound is NC-R 21 -CN; The structure of the tri-nitrile compound is: The structure of the tetra-nitrile compound is: wherein R 21 , R 22 , and R 23 are each independently selected from halogen-substituted or unsubstituted C1-C10alkyl, halogen-substituted or unsubstituted C1-C10alkenyl, halogen-substituted or unsubstituted C1-C10alkynyl, halogen-substituted or unsubstituted C5-C10heteroaryl, halogen-substituted or unsubstituted C6-C10aryl.

7. The lithium-ion battery of claim 5, wherein, The di-nitrile compound is selected from one or more of butanedinitrile, pentanedinitrile, hexanedinitrile, decanedinitrile, nonanedinitrile, dicyanobenzene, terephthalonitrile, pyridine-3,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorobutanedinitrile, 3,3'-[1,2-ethanediylbis(oxy)]dipropanenitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranemethylenepropanedinitrile, maleonitrile, ethyleneglycolbis(propanenitrile)ether and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile; and / or, The tri-nitrile compound is selected from one or more of 1,3,6-hexanetristitnitrile, 1,3,5-cyclohexanetristitnitrile, 1,3,5-benzenetricarbonitrile, 1,2,3-propanetricarbonitrile and glyceroltrinitrile; and / or, The tetra-nitrile compound is selected from one or more of 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile and 7,7,8,8-tetracyanoparacyclophanedimethane.

8. The lithium-ion battery of any one of claims 1 to 7, wherein, The electrolyte solution further comprises a lithium salt and an organic solvent.

9. The lithium-ion battery of claim 8, wherein, The positive electrode material layer further comprises a conductive agent and a binder.

10. An electronic device, comprising: The lithium ion battery comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte solution; the separator is clamped between the positive electrode sheet and the negative electrode sheet;

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