Lithium ion battery and electronic device

Abstract

The invention discloses a lithium ion battery and an electronic device, the lithium ion battery comprises a positive plate, a diaphragm, a negative plate and an electrolyte, and the diaphragm is arranged between the positive plate and the negative plate; the positive plate comprises a positive current collector and a positive material layer arranged on the surface of at least one side of the positive current collector, the positive material layer comprises a positive active material containing a cobalt element and a T element, the T element is selected from at least one element of a VB subgroup and a VIB subgroup in periods 4-6, and the content A of the T element and the content B of the cobalt element in the positive active material layer meet the condition that A / B is larger than or equal to 0.002 and smaller than or equal to 0.01; the electrolyte contains nitrile compounds; the content of nitrile compounds in the electrolyte is C, the porosity of the positive plate is D, the resistance value under 50% SOC is R, and R * D / A is larger than or equal to 15 and smaller than or equal to 110, and B * R / (A + C) is larger than or equal to 30 and smaller than or equal to 100. The lithium ion battery can give consideration to high-temperature cycle capacity retention rate, safety performance and low-temperature discharge performance.

Description

Technical Field

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

[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] As the application of lithium-ion batteries becomes more and more extensive, people's requirements for lithium batteries are also getting higher and higher. However, the existing lithium-ion battery technology often cannot well take into account the low-temperature discharge performance while meeting the high-temperature cycle performance and safety performance, which limits the application space of lithium-ion batteries to a certain extent. Therefore, it is very necessary to develop a lithium-ion battery that takes into account the high-temperature cycle performance, safety performance and low-temperature discharge performance at the same time. Summary of the invention

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

[0005] In a first aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte; the separator is sandwiched 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 disposed 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 of a VB subgroup and a VIB subgroup of periods 4 to 6 of the periodic table; 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 nitrile compounds; the mass percentage of the nitrile compounds in the electrolyte is C, the porosity of the positive electrode sheet is D, the resistance value of the positive electrode sheet at 50% SOC is R, and 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 invention, there are at least the following beneficial effects: the lithium ion battery uses a positive electrode active material containing cobalt and T element (i.e., at least one element in the VB subgroup and VIB subgroup of the 4th to 6th period of the periodic table) to construct a positive electrode sheet, and the contents A and B of the T element and the cobalt element in the positive electrode active material satisfy the condition of 0.002≤A / B≤0.01, and the T element can maximize the conductivity of the positive electrode material. At the same time, after the T element is doped into the cobalt position, it can serve as a supporting element to effectively reduce the lithium ion in the desorption process. The migration resistance during the insertion process is improved, and the migration rate of lithium ions is increased; in addition, by controlling the ratio of the T element content A 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 meet 15≤R*D / A≤110, the positive electrode sheet has an excellent electron transmission channel, and thanks to the T element doping, the electronic conductivity is improved; and the porosity control of the positive electrode sheet ensures the transmission rate of lithium ions in the electrolyte, while optimizing the electronic conductivity and ionic conductivity, effectively improving the discharge performance of the lithium-ion battery at low temperatures. Furthermore, by adding a nitrile compound with a mass content of C in the electrolyte and controlling 30≤B*R / (A+C)≤100, the T element 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 while effectively improving the high-temperature cycle performance and safety performance of the lithium-ion battery.

[0009] Among them, the resistance value of the positive electrode sheet at 50% SOC can be tested by the following method: charge the lithium-ion battery at a constant current of 0.5C to 50% SOC, and the cut-off current is 0.025C; then disassemble the positive electrode sheet in the lithium-ion battery, place it in an environment with a humidity of 5% to 15% for 30 minutes, and then test the resistance value of the positive electrode sheet, which is recorded as R. Among them, the positive electrode sheet can be sealed and transferred to the resistance test site to test the resistance value of the positive electrode sheet. Specifically, the BER1200 film resistance tester can be used to test the resistance of the positive electrode sheet. Furthermore, the above resistance test can require that the adjacent test points be spaced 2mm to 3mm apart, and 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 invention, 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 invention, 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 invention, the chemical formula of the positive electrode active material is 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 of the VB subgroup and the VIB subgroup of the 4th to 6th periods of the periodic table, specifically at least one of vanadium, chromium, niobium, molybdenum, tantalum, and tungsten; and 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 invention, the nitrile compound is selected from one or more of a dinitrile compound, a trinitrile compound, and a tetranitrile compound.

[0019] In some embodiments of the present invention, the structural formula of the dinitrile compound is NC-R 21 -CN;

[0020] The structural formula of the trinitrile compound is:

[0021] The structural formula of the four nitrile compounds is:

[0022] Among them, R 21 , R 22 and R 23 Each is 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 invention, the dinitrile compound is selected from one or more of succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, 3,3'-[1,2-ethanediylbis(oxy)]bispropionitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, butylene dinitrile, ethylene glycol bis(propionitrile) ether and 1,4,5,6-tetrahydro-5,6-dioxy-2,3-pyrazine dicarbonitrile; and / or,

[0024] The trinitrile compound is selected from one or more of 1,3,6-hexane trinitrile, 1,3,5-cyclohexane trinitrile, 1,3,5-benzene trinitrile, 1,2,3-propane tricarbonitrile and glycerol trinitrile; and / or,

[0025] The tetranitrile 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-tetracyanoquinodimethane.

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

[0027] In some embodiments of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium difluorophosphate (LiPO2F2), 2-trifluoromethyl-4,5-dicyanoimidazole lithium (C6F3LiN4), lithium difluorooxalatoborate (LiODFB), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalate)borate (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiN(SO2CF3)2), and lithium bis(fluorosulfonyl imide) (LiN(SO2F)2).

[0028] In some embodiments of the present invention, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, ethyl methyl 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, and ethylene glycol dimethyl ether.

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

[0030] In some embodiments of the present invention, the conductive agent is selected from one or more of natural graphite, artificial graphite, conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, carbon fibers, conductive polymers, and metal powders.

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

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

[0033] In some embodiments of the present invention, 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 invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material, a conductive agent and a binder.

[0035] In some embodiments of the present invention, the lithium-ion battery further comprises a packaging shell, wherein 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 invention, the positive electrode sheet, the separator and the negative electrode sheet are wound to form a bare battery cell, and the bare battery 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] A positive electrode slurry is prepared by using a raw material including the positive electrode active material, and then coated on at least one side of the 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 battery cell, and then the bare battery cell is placed in a packaging shell and injected with the electrolyte to obtain a lithium ion battery.

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

[0041] During the preparation of the positive electrode active material, the calcination temperature can be controlled at 650°C to 850°C; the calcination time can be controlled at 22h to 26h; and the heating rate can be controlled at 2°C / min to 8°C / min.

[0042] In the process of preparing the positive electrode sheet, after the positive electrode slurry is coated on the surface of the positive electrode current collector, it is further dried and rolled to obtain the positive electrode sheet. The drying temperature can be controlled at 100°C to 150°C, for example, it can be any value of 100°C, 110°C, 120°C, 125°C, 130°C, 140°C, 150°C or any range of two values; the drying time can be 6h to 10h, for example, it can be any value of 6h, 7h, 8h, 8.5h, 9h, 10h or any range of two values. And the structural parameters of the positive electrode sheet can be controlled by controlling the rolling thickness of the positive electrode sheet during the rolling process. Furthermore, the rolling process can be further cut.

[0043] In addition, during the battery assembly process, after the electrolyte is injected, it further goes through vacuum packaging, standing, forming, and shaping steps to obtain a lithium-ion battery.

[0044] According to a second aspect of the present invention, an electronic device is provided. The electronic device comprises any one of the aforementioned lithium-ion batteries. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0046] Example 1

[0047] This embodiment proposes a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the separator is sandwiched between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on two opposite surfaces of the positive electrode current collector; the positive electrode material layer includes a positive electrode active material, a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5; the positive electrode active material includes cobalt and T elements, wherein the T element is specifically tantalum, and in the positive electrode active material, the mass percentage A of the tantalum element and the mass percentage B of the cobalt element are 0.37% and 59.94% respectively, and furthermore, 0.002<A / B=0.006<0.01; and the porosity D of the positive electrode sheet is 15%, and the thickness is 80μm.

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

[0049] The electrolyte includes lithium salt LiPF6, an organic solvent and a nitrile compound; the mass percentage of LiPF6 in the electrolyte is 15%, and the nitrile compound uses adiponitrile, and its mass percentage C in the electrolyte satisfies 0.1%<C=0.5%<1%; and thus 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 positive electrode active material: lithium cobalt oxide and tantalum carbonate, a tantalum-containing compound, were mixed evenly at a molar ratio of 1:0.007, and then heated to 750° C. at a rate of 5° C. / min in an air atmosphere and calcined for 24 hours to obtain a positive electrode active material;

[0052] Preparation of positive electrode sheet: positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a uniform and fluid positive electrode slurry; the positive electrode slurry is evenly coated on the two opposite surfaces of the positive electrode current collector aluminum foil; the coated aluminum foil is placed in an oven and baked at 100°C, 110°C, 120°C, 110°C, 100°C for 1 minute, and then dried in an oven at 120°C for 8 hours, and then rolled and cut to obtain a positive electrode sheet. The core element T in the positive electrode active material is tantalum. Based on the mass of the positive electrode active material, the tantalum content in the positive electrode sheet is 0.37%, the thickness of the positive electrode sheet after rolling is 80μm, and the porosity of the positive electrode sheet is 15%.

[0053] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5, and then coated on the two opposite surfaces of the negative electrode current collector Cu foil, and then dried, cold pressed, and slit to obtain the negative electrode sheet.

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

[0055] Assembly and preparation of lithium-ion batteries: Use polyethylene (PE) porous polymer film as the separator, stack the positive electrode sheet, isolation membrane, and negative electrode sheet in order, so that the isolation membrane is between the positive and negative electrode sheets to play an isolating role, and then wind them to obtain a bare battery cell, place the bare battery cell in an outer packaging foil, inject the above-prepared electrolyte into the dried battery, and after vacuum packaging, standing, formation, shaping and other processes, a lithium-ion battery is obtained.

[0056] Example 2 Group

[0057] This embodiment group includes embodiments 2a to 2b, and embodiments 2a to 2b respectively provide a lithium-ion battery, which differs from embodiment 1 in that the tantalum element content A in the positive electrode active material of the positive electrode material layer on the positive electrode sheet is different from that in embodiment 1, and thus the resistance value of the positive electrode sheet is different from that of the positive electrode sheet in embodiment 1, and the rest is basically the same as the lithium-ion battery in embodiment 1.

[0058] The preparation of the lithium-ion batteries of Examples 2a-2b was carried out with reference to Example 1, except that in the preparation process of the positive electrode active material in Examples 2a-2b, the molar ratio of lithium cobalt oxide and tantalum carbonate was adjusted from 1:0.007 in Example 1 to 1:0.0036 and 1:0.01, respectively, to adjust the tantalum element content A in the positive electrode active material, see Table 1 for details.

[0059] Example 3 Group

[0060] This embodiment group includes embodiments 3a to 3c. Embodiments 3a to 3c respectively provide a lithium ion battery, which differs from embodiment 1 in that the content C of adiponitrile in the electrolyte is different from that in embodiment 1, and the rest is basically the same as the lithium ion battery in embodiment 1.

[0061] The preparation of the lithium ion battery of this embodiment group is carried out with reference to the embodiment 1, except that the content C of adiponitrile in the electrolyte is adjusted, as shown in Table 1 for details.

[0062] Example 4 Group

[0063] This embodiment group includes embodiments 4a to 4c. Embodiments 4a to 4c respectively provide a lithium-ion battery, which differs from embodiment 1 in that the porosity and thickness of the positive electrode sheet are different from those of embodiment 1, and the rest are basically the same as the lithium-ion battery of embodiment 1.

[0064] The preparation of the lithium-ion battery of this embodiment group is carried out with reference to the embodiment 1, except that the porosity of the positive electrode sheet is adjusted, which is specifically achieved by adjusting the thickness of the positive electrode sheet after rolling. The thickness of the positive electrode sheet is adjusted in the range of 70 μm to 90 μm, see Table 1 for details.

[0065] Example 5 Group

[0066] This embodiment group includes embodiments 5a to 5c. Embodiments 5a to 5c respectively provide a lithium-ion battery, which is different from embodiment 1 in that the nitrile compound in the electrolyte is different from that in embodiment 1, and the rest is basically the same as the lithium-ion battery in embodiment 1.

[0067] The preparation of the lithium-ion battery of this embodiment group is carried out with reference to the embodiment 1, except that the selection of the nitrile compound in the electrolyte is adjusted, as shown in Table 1 for details.

[0068] Example 6 Group

[0069] This embodiment group includes embodiments 6a to 6e. Embodiments 6a to 6e respectively provide a lithium-ion battery, which differs from embodiment 1 in that the type of T element in the positive electrode active material on the positive electrode sheet is different from that in embodiment 1, and the rest is basically the same as the lithium-ion battery of embodiment 1.

[0070] The preparation of the lithium-ion battery of this embodiment group is carried out with reference to Example 1, except that: in the preparation of the positive electrode active material in Examples 6a to 6e, the compounds containing the T element are vanadium carbonate, chromium carbonate, niobium carbonate, tungsten carbonate, and molybdenum carbonate, respectively, and the molar ratio of lithium cobaltate to vanadium carbonate in Example 6a is 1:0.007, the molar ratio of lithium cobaltate to chromium carbonate in Example 6b is 1:0.0035, the molar ratio of lithium cobaltate to niobium carbonate in Example 6c is 1:0.007, the molar ratio of lithium cobaltate to tungsten carbonate in Example 6d is 1:0.007, and the molar ratio of lithium cobaltate to molybdenum carbonate in Example 6e is 1:0.007, thereby adjusting the type of T element in the positive electrode active material on the positive electrode sheet, see Table 1 for details.

[0071] Comparative Example 1

[0072] This comparative example provides a lithium ion battery, which is different from Example 1 in that the positive electrode active material on the positive electrode sheet does not contain the T element, and the electrolyte does not contain nitrile compounds, and the internal proportions of other substances remain unchanged, see Table 1 for details.

[0073] Comparative Example 2

[0074] The second comparative example group includes comparative examples 2a and 2b, and comparative examples 2a and 2b respectively provide a lithium-ion battery, which differs from Example 1 in that: the positive electrode active material on the positive electrode sheet does not contain the T element, 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

[0076] The present comparative example 3 group includes comparative examples 3a to 3f, and comparative examples 3a to 3f respectively provide a lithium ion battery, which differs from Example 1 in that: the positive electrode active material on the positive electrode sheet contains T element (specifically cobalt element), and the electrolyte contains nitrile compounds, but the proportional relationship among the T element content A, the cobalt element content B, the positive electrode sheet resistance R, the positive electrode sheet porosity D and the nitrile compound content C in the electrolyte cannot simultaneously satisfy the following conditions: 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 and 3d, the molar ratio of lithium cobalt oxide and tantalum carbonate is adjusted from 1:0.007 in Example 1 to 1:0.0016, 1:0.013, and 1:0.0036, respectively, thereby adjusting the tantalum element content A in the positive electrode active material.

[0077] Table 1

[0078]

[0079]

[0080] Performance Testing

[0081] (1) Cycle life test

[0082] The lithium-ion battery was placed in a constant temperature environment of 45°C and charged and discharged at a rate of 1.0C / 1.0C, with a charge cut-off voltage of 4.5V and a discharge cut-off voltage of 3.0V. The charge and discharge cycles were repeated 500 times, and the cycle discharge capacity was recorded and divided by the discharge capacity of the first cycle to obtain the cycle capacity retention rate.

[0083] (2) Low temperature discharge test

[0084] The lithium-ion battery was placed at room temperature and charged and discharged for 5 times at a rate of 1C, then charged to 4.5V at a rate of 1C, and the 1C charge capacity Q1 was recorded. The fully charged battery was placed at -20°C for 4 hours, and then discharged to 3.0V at a rate of 0.2C, and the discharge capacity Q2 was recorded. The low-temperature discharge capacity retention rate can be obtained by calculating Q2 / Q1.

[0085] (3) 134℃ hot box test

[0086] The lithium-ion battery is charged at a constant current of 0.5C to 4.5V at 25℃, and charged at a constant voltage to a cut-off current of 0.025C. It is left to stand for 2h. The fully charged battery is placed in a hot box and heated from room temperature to 134℃ at a heating rate of 5℃ / min. It is kept for 60min. If the battery does not explode or catch fire, it can be judged as PASS, otherwise it is FAIL.

[0087] The performance of the lithium-ion batteries of the embodiments and comparative examples were tested according to the above method, and the results are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] As shown in Table 2 above, compared with each comparative example, the safety performance of the lithium ion battery of each embodiment is significantly improved, the high temperature cycle capacity retention rate is significantly improved, and the low temperature discharge capacity retention rate is significantly improved, indicating that the T element and the cobalt element in the positive electrode active material in the positive electrode sheet of the lithium ion battery of each embodiment, synergistically with the nitrile compound in the electrolyte, can effectively limit the side reaction of the positive electrode active material and the electrolyte two-phase interface, thereby improving the safety performance and high temperature cycle stability of the battery. At the same time, thanks to the addition of nitrile compounds in the electrolyte (especially the low content design of nitrile compounds) and the electronic conductivity improvement brought about by T element doping, as well as the limiting relationship between the resistance and porosity of the positive electrode sheet, the low temperature discharge performance of the battery has been significantly improved.

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

[0093] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: It includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte; the separator is sandwiched 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 disposed 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 of a VB subgroup and a VIB subgroup of periods 4 to 6 of the periodic table; 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; The electrolyte contains nitrile compounds; the mass percentage of the nitrile compounds 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.

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

3. The lithium-ion battery according to claim 1, characterized in that The lithium-ion battery satisfies at least one of the following conditions: 1) A satisfies: 0.5% ≤ A ≤ 0.55%; 2) B satisfies: 55% ≤ B ≤ 65%; 3) C satisfies: 0.1% ≤ C ≤ 1%; 4) D satisfies: 10% ≤ D ≤ 20%; 5) R satisfies: 0.5Ω≤R≤1Ω.

4. The lithium-ion battery according to claim 1, characterized in that: The chemical formula of the positive electrode active material is 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 of the VB subgroup and the VIB subgroup of the 4th to 6th periods of the periodic table, and N is at least one of aluminum, magnesium, titanium, zirconium, yttrium and lanthanum.

5. The lithium-ion battery according to claim 1, characterized in that: The nitrile compound is selected from one or more of dinitrile compounds, trinitrile compounds and tetranitrile compounds.

6. The lithium-ion battery according to claim 5, characterized in that: The structural formula of the dinitrile compound is NC-R 21 -CN; The structural formula of the trinitrile compound is: The structural formula of the four nitrile compounds is: Among them, R 21 , R 22 and R 23 Each is 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.

7. The lithium-ion battery according to claim 5, characterized in that The dinitrile compound is selected from one or more of succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, 3,3'-[1,2-ethanediylbis(oxy)]bispropionitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, fumaronitrile, ethylene glycol bis(propionitrile) ether and 1,4,5,6-tetrahydro-5,6-dioxy-2,3-pyrazine dicarbonitrile; and / or, The trinitrile compound is selected from one or more of 1,3,6-hexane trinitrile, 1,3,5-cyclohexane trinitrile, 1,3,5-benzene trinitrile, 1,2,3-propane tricarbonitrile and glycerol trinitrile; and / or, The tetranitrile 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-tetracyanoquinodimethane.

8. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The electrolyte also includes a lithium salt and an organic solvent.

9. The lithium-ion battery according to claim 8, characterized in that: The positive electrode material layer further includes a conductive agent and a binder.

10. An electronic device, characterized in that: A lithium ion battery comprising the lithium ion battery according to any one of claims 1 to 9.

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