Lithium ion battery and electronic equipment

Abstract

The invention discloses a lithium ion battery and electronic equipment, the lithium ion battery comprises a positive pole piece and an electrolyte, the positive pole piece comprises a positive active material, the positive active material comprises Lix [NiyCozMntM (1-y-z-t)] O2-delta, M is at least one selected from Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 lt; xlt; 1.1, 0.8 < = y < lt >; 1.0, 0 < = zlt; 0.1, 0 < = tlt; 0 < = delta < = 0.1; the electrolyte comprises an additive, the additive comprises an ionic liquid, the chemical formula of the ionic liquid is # imgabs0 #, R1 and R2 are alkyl with the carbon atom number of 1-6, and X is selected from any one of bis (fluorosulfonyl) imide, bis (trifluoromethyl) sulfonyl imide, tetrafluoroborate and acetate. The imidazolyl ionic liquid and the high-nickel positive electrode system are matched for use, so that the high-temperature cycle performance of the battery cell can be effectively improved.

Description

Technical Field

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

[0002] With the increasing exhaustion of fossil energy and the increasing pressure of environmental pollution, the automotive industry is in urgent need of a new type of energy to drive it. Lithium-ion batteries stand out due to their high energy density, no memory effect, and high operating voltage, making them the preferred power source for new energy vehicles. However, with the expansion of market demand for electronic products and the development of power and energy storage equipment, people's requirements for lithium-ion batteries are constantly increasing, and the development of lithium-ion batteries with high energy density has become a top priority.

[0003] Positive electrode materials and electrolytes are an indispensable part of lithium-ion batteries, and have a direct impact on improving battery energy density and safety, reducing usage costs, etc. 0.5 Co 0.2 Mn 0.3 ]O 2 (NCM523), Li[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 (NCM622), Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 High nickel cathode materials such as (NCM811) have attracted people's attention due to their high capacity, low cost, safety and environmental protection, and are considered to be the most promising cathode materials. However, research on electrolytes that match high nickel ternary materials has received little attention. At present, the electrolyte widely used in lithium-ion batteries is usually lithium hexafluorophosphate (LiPF 6 ) as the electrolyte salt, and a mixture of cyclic carbonate and chain carbonate as the organic solvent. However, there are many disadvantages in the use of the above electrolyte with high-nickel positive electrode materials. In particular, under high voltage, lithium-ion batteries face the problem of rapid capacity decay after long-term cycling. Therefore, it is of great significance to find an electrolyte suitable for use with high-nickel positive electrode materials and effectively improving the electrochemical performance of lithium-ion batteries for the development of lithium-ion batteries. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a lithium ion battery and an electronic device to improve the electrochemical performance of the battery cell, especially the high temperature cycle performance.

[0005] To achieve the above-mentioned and other related purposes, the present invention provides a lithium-ion battery in a first aspect, comprising at least:

[0006] A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein the element M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.8≤y<1.0,0≤z<0.1,0≤t<0.1,0≤δ≤0.1;

[0007] Negative electrode;

[0008] A separator, disposed between the positive electrode sheet and the negative electrode sheet; and

[0009] The electrolyte is filled between the positive electrode plate, the negative electrode plate and the separator, and the electrolyte includes an additive, and the additive includes an ionic liquid. The chemical structure of the ionic liquid is as follows:

[0010]

[0011] Among them, R 1 and R 2 Each is an alkyl group having 1 to 6 carbon atoms, and X is selected from any one of bis(trifluoromethyl)sulfonyl imide, bis(trifluoromethyl)sulfonyl imide, tetrafluoroborate and acetate.

[0012] In one embodiment of the present invention, the ionic liquid is selected from at least one of the following compounds I to V:

[0013]

[0014] In one embodiment of the present invention, the mass content of the ionic liquid in the electrolyte is 0.1% to 10%.

[0015] In one embodiment of the present invention, the mass content of the ionic liquid in the electrolyte is 0.5% to 5%.

[0016] In one embodiment of the present invention, the electrolyte further includes a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide salt, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate), lithium difluorophosphate and lithium trifluoromethanesulfonate.

[0017] In one embodiment of the present invention, the mass content of the lithium salt in the electrolyte is 8% to 18%.

[0018] In one embodiment of the present invention, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate and diethyl carbonate.

[0019] In one embodiment of the present invention, the non-aqueous solvent includes the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate, and the mass ratio of the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate is 3:5:2.

[0020] In one embodiment of the present invention, the mass content of the non-aqueous solvent in the electrolyte is 60% to 90%.

[0021] A second aspect of the present invention provides an electronic device, comprising the lithium-ion battery as described in the first aspect.

[0022] As described above, the lithium ion battery and electronic device of the present invention have the following beneficial effects:

[0023] In the lithium ion battery provided by the present invention, an imidazolyl ionic liquid is added to the electrolyte as an additive. In a system where the Ni content is higher than 65% and the voltage is higher than 4.25V, the π electrons of the sulfur-oxygen double bond of the ionic liquid can coordinate with transition metal ions such as Ni and Mn dissolved from the positive electrode, so that the anion loses a single electron at the positive electrode and participates in the oxidation reaction, thereby obtaining a Li+ with a good coating effect. 3 N and Li 2 S and other substances; on the other hand, its cations can obtain electrons at the negative electrode and obtain coated organic components through reduction polymerization. The combined effect of these two aspects greatly improves the overall high-temperature cycle performance of the battery cell. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0026] The technical scheme of the present invention is further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The present invention proposes a lithium-ion battery, comprising at least a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator. The present invention does not limit the type and shape of the lithium-ion battery. In one embodiment of the present invention, the lithium-ion battery is a primary battery or a secondary battery, and the secondary battery is, for example, a soft-pack battery, a square-shell battery or a cylindrical battery. In this embodiment, for example, a soft-pack secondary battery is used as an example for explanation.

[0028] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one side of the positive current collector, and the positive active layer includes a positive active material, a binder, and a conductive agent. Among them, the positive current collector can be, for example, a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel or carbon. In addition to the foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam and non-woven fabric. Among them, the thickness of the positive current collector is, for example, 8μm to 15μm. In this embodiment, the positive current collector is, for example, aluminum foil.

[0029] In one embodiment of the present invention, the positive electrode active material includes, for example, Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ, wherein the element M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, and Zn, 0.9 < x < 1.1, 0.8 ≤ y < 1.0, 0 ≤ z < 0.1, 0 ≤ t < 0.1, and 0 ≤ δ ≤ 0.1. The binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, and polymerized styrene butadiene rubber (SBR). The conductive agent is, for example, selected from at least one of super P (SP), acetylene black, carbon nanotubes, and graphene.

[0030] In one embodiment of the present invention, the positive electrode active material is, for example, Li[Ni 0.8 Co 0.1 Mn 0.1 O 2 , the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from super P. After mixing the positive electrode active material, super P, and polyvinylidene fluoride in a mass ratio of, for example, 95:3:2, an organic solvent is added and stirred until the system becomes homogeneous to obtain a positive electrode slurry. Among them, the organic solvent is, for example, selected from N-methylpyrrolidone (NMP). After uniformly coating the positive electrode slurry on the aluminum foil, it is air-dried and then vacuum-dried, and then the dried aluminum foil is cold-pressed and other processes are carried out to obtain a positive electrode plate.

[0031] In one embodiment of the present invention, the negative electrode plate includes a negative electrode current collector and at least a negative electrode active layer coated on one side of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a binder, a conductive agent, a thickening agent, and the like. Among them, the negative electrode current collector is, for example, selected from one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector, and the thickness of the negative electrode current collector is, for example, 8 μm to 15 μm.

[0032] In one embodiment of the present invention, the negative electrode active material includes a silicon-based composite material, and for another example, it includes silicon oxide (SiO n, at least one of silicon-carbon composite materials, etc., where 0 < n < 2), the negative electrode active material further includes at least one of metal elements such as Ti, Fe, Cu, Ni, Co, Mn, Ag, Au, and Sn. The content of the metal element in the negative electrode active material is, for example, 10 ppm to 500 ppm, and for another example, it exists in the negative electrode active material by means of doping or coating, etc., to meet the requirements of high energy density and improve the cycling performance of the lithium-ion battery. In other embodiments, the negative electrode active material can select other silicon-based composite materials. The binder is, for example, selected from at least one of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, and styrene-butadiene rubber, etc. The conductive agent is, for example, selected from at least one of conductive carbon black, acetylene black, carbon nanotubes, and graphene, etc., and the thickener is, for example, selected from sodium carboxymethyl cellulose, etc.

[0033] In an embodiment of the present invention, the negative electrode current collector is, for example, selected from copper foil, the negative electrode active material is, for example, selected from silicon oxides, the conductive agent is, for example, selected from conductive carbon black, the binder is, for example, selected from styrene-butadiene rubber, and the thickener is, for example, selected from sodium carboxymethyl cellulose. In an embodiment of the present invention, the silicon oxide, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed, for example, in a mass ratio of 96:2:1:1, deionized water is added, and the mixture is fully stirred to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated on the copper foil, then dried at room temperature and transferred to an oven for drying, and the negative electrode plate is obtained through processes such as drying and cold pressing.

[0034] In an embodiment of the present invention, the separator is, for example, a polyethylene membrane (Polyethylene, PE), a polypropylene membrane (Polypropylene, PP), a glass fiber membrane, a polyethylene membrane, or a composite membrane, etc. And the thickness of the separator is, for example, 9 μm to 15 μm. In an embodiment of the present invention, a polyethylene with a thickness of 8 μm to 10 μm is, for example, selected as the base film of the separator, and a nano-aluminum oxide coating with a thickness of 2 μm to 4 μm is coated on the base film to obtain the separator. In an embodiment of the present invention, the separator is, for example, a 12-μm polypropylene membrane, etc.

[0035] In an embodiment of the present invention, the electrolyte at least includes a non-aqueous solvent, a lithium salt, and additives, etc. Among them, the additive, for example, includes an ionic liquid, and the chemical structural formula of the ionic liquid is:

[0036] Among them, R 1 and R 2Each is an alkyl group with 1 to 6 carbon atoms, and X is selected from any one of bis(trifluoromethyl)sulfonyl imide, bis(trifluoromethyl)sulfonyl imide, tetrafluoroborate and acetate. The ionic liquid is an imidazole-based ionic liquid. In a system where the Ni content is higher than 65% and the voltage is higher than 4.25V, the π electrons of the sulfur-oxygen double bond can coordinate with transition metal ions such as Ni and Mn dissolved from the positive electrode, so that the anion loses a single electron at the positive electrode and participates in the oxidation reaction, thereby obtaining Li with good coating effect. 3 N and Li 2 S and other substances; on the other hand, its cations can obtain electrons at the negative electrode and obtain coated organic components through reduction polymerization. The combined effect of these two aspects greatly improves the overall high-temperature cycle performance of the battery cell.

[0037] In one embodiment of the present invention, the ionic liquid includes, for example, compound I: Compound II: Compound III: Compound IV:

[0038] And compound V: At least one of the above.

[0039] In one embodiment of the present invention, the mass content of the ionic liquid in the electrolyte is 0.1% to 10%, and for example 0.5% to 5%. Among them, when the mass content of the imidazole-based ionic liquid is too low, the fast charging performance and cycle performance of the lithium-ion battery are not significantly improved. When the mass content of the ionic liquid is too high, the high-temperature cycle performance will be deteriorated. This may be due to excessive addition of the imidazole-based ionic liquid, and there are many unreacted components remaining in the electrolyte. If the unreacted part appears partially exposed at the interface between the positive and negative electrodes, it will react immediately, deteriorating the battery performance.

[0040] In one embodiment of the present invention, the lithium salt includes, for example, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorobis(oxalatophosphate) (LiDODFP), lithium difluorophosphate (LiDFP), and lithium trifluoromethanesulfonate (CF 3 SO 3 In this embodiment, the mass content of lithium salt in the electrolyte is 8% to 18%.

[0041] In one embodiment of the present invention, the non-aqueous solvent includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) and diethyl carbonate (DEC). In one embodiment of the present invention, the mass percentage of the non-aqueous solvent in the electrolyte is, for example, 60% to 90%. In this embodiment, the non-aqueous solvent includes, for example, battery-grade ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 3:5:2. By controlling the content of the non-aqueous solvent, while exerting the performance of the electrolyte, it is prevented that the non-aqueous solvent content is too high, resulting in excessive viscosity of the electrolyte, thereby causing problems such as reduced ionic conductivity and wettability of the electrolyte.

[0042] In one embodiment of the present invention, when preparing the electrolyte, the content of stable gas such as nitrogen or argon in the glove box is 99.999%, the actual oxygen content in the glove box is less than or equal to 0.1ppm, and the water content is less than or equal to 0.1ppm. After the non-aqueous solvent is mixed uniformly according to the mass ratio, the fully dried lithium salt is added to the non-aqueous solvent, and additives are added to prepare a non-aqueous electrolyte for lithium ion batteries. Among them, the content of each component other than the non-aqueous solvent is the mass percentage calculated based on the total mass of the electrolyte.

[0043] In one embodiment of the present invention, the positive electrode sheet, the separator, and the negative electrode sheet are placed in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and a bare cell is obtained by winding or laminating. The bare cell is placed in an aluminum-plastic film, dried in a vacuum oven, and sealed after injecting the above-prepared electrolyte. After standing, hot and cold pressing, formation, clamping, and capacity division, a soft-pack lithium-ion secondary battery is obtained.

[0044] Another embodiment of the present invention further provides an electronic device, comprising at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. Among them, the electronic device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. Spacecraft include airplanes, rockets, space shuttles and spacecrafts, etc., and electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers, etc. The electronic device includes the above-mentioned lithium-ion battery, and therefore includes the advantages of the above-mentioned lithium-ion battery, which will not be elaborated here.

[0045] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0046] Example 1

[0047] Preparation of electrolyte: In a glove box filled with argon, when the nitrogen content in the glove box is 99.999%, the actual oxygen content in the glove box is less than 0.1ppm, and the moisture content is less than 0.1ppm, battery-grade ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 3:5:2. Taking the total mass of the electrolyte as 100%, the lithium salt in the electrolyte is LiPF 6 , and LiPF 6 The mass content of the ionic liquid is 12.5%. The mass content of the ionic liquid is compound I, and the mass content of the compound I is 0.1%.

[0048] Preparation of positive electrode sheet: The positive electrode active material Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 After mixing the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride, in a mass ratio of 95:3:2, NMP is added and stirred until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on an aluminum foil, and then transferred to an oven for vacuum drying after drying at room temperature, and then the dried aluminum foil is subjected to a cold pressing process to obtain a positive electrode sheet.

[0049] Preparation of negative electrode sheet: negative electrode active material SiO, conductive agent conductive carbon black, binder styrene butadiene rubber and thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:1:1, deionized water is added, and the mixture is stirred thoroughly to obtain negative electrode slurry. The negative electrode slurry is evenly coated on copper foil, and then dried at room temperature and transferred to an oven for drying, and the negative electrode sheet is obtained through drying and cold pressing processes.

[0050] Selection of diaphragm: Select 10μm polypropylene film as the diaphragm.

[0051] Preparation of battery: stack the positive electrode sheet, separator and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to isolate them, and stack them to obtain a bare battery cell. Then wrap it with aluminum plastic film, dry it in a vacuum oven, inject the above-prepared electrolyte, seal it, and perform electrolyte formation to obtain a soft-pack lithium-ion secondary battery.

[0052] Example 2

[0053] The ionic liquid is compound I, and the mass content of compound I is 1%. Other operations are the same as those in Example 1.

[0054] Example 3

[0055] The ionic liquid is compound I, and the mass content of compound I is 5%. Other operations are the same as those in Example 1.

[0056] Example 4

[0057] The ionic liquid is compound I, and the mass content of compound I is 10%. Other operations are the same as in Example 1.

[0058] Example 5

[0059] The ionic liquid is compound I, and the mass content of compound I is 1%, and the positive electrode active material is LiNi 0.5 Mn 0.5 O 2 , other operations are the same as those in Example 1.

[0060] Comparative Example 1

[0061] No ionic liquid is added to the electrolyte, and the positive electrode active material is Li[Ni 0.65 Co 0.15 Mn 0.2 ]O 2 , other operations are the same as those in Example 1.

[0062] Comparative Example 2

[0063] The ionic liquid is compound I, and the mass content of compound I is 15%, and the positive electrode active material is Li[Ni 0.65Co 0.15 Mn 0.2 ]O 2 , other operations are the same as those in Example 1.

[0064] Comparative Example 3

[0065] The ionic liquid is compound I, and the mass content of compound I is 1%, and the positive electrode active material is LiFePO 4 , other operations are the same as those in Example 1.

[0066] Comparative Example 4

[0067] The ionic liquid is compound I, and the mass content of compound I is 1%. The negative electrode active material is graphite. Other operations are the same as those in Example 1.

[0068] The performance of the lithium ion batteries in Examples 1 to 5 and Comparative Examples 1 to 4 was tested using the following method. The test results are shown in Table 1.

[0069] The test method is as follows:

[0070] 1. Capacity retention rate of high temperature cycle at 45°C:

[0071] Adjust the temperature of the environmental box to 45℃, let it stand for 1 hour, charge the lithium-ion battery to 4.4V at a constant current of 0.5C, then charge it at a constant voltage of 4.4V until the current is less than 0.05C, let it stand for 10 minutes, discharge it to 2.8V at a constant current of 1.0C, let it stand for 10 minutes, and record the discharge capacity of the lithium-ion battery at this time, which is the discharge capacity of the first cycle; the battery is cycled multiple times under the above conditions, and the capacity retention rate of the battery after 500 cycles is calculated. The capacity retention rate relative to the cycle is calculated according to the following formula:

[0072] Capacity retention rate (%) = (discharge capacity corresponding to 500 cycles / discharge capacity of the first cycle) × 100%.

[0073] 2. DCR growth after high temperature cycling at 45°C:

[0074] Adjust the temperature of the environmental box to 25℃, let it stand for 1h, charge it at 0.33C constant current to 4.4V, then charge it at 4.4V constant voltage to 0.05C current cutoff, let it stand for 30min, then discharge it at 0.33C constant current to 2.8V, cycle it twice, and take the last discharge capacity C 0 As the nominal capacity; 0.33C 0 Charge at constant current to 4.4V, then charge at constant voltage at 4.4V until the current is cut off at 0.05C, let stand for 30 minutes, then charge at 0.33C 0 Discharge to 50% SOC, let stand for 1h, and record the terminal voltage V 1 ,1C0 Discharge for 30 seconds and record the discharge end voltage V 2 and current I 1 , DCR1=(V 1 -V 2 ) / I 1 .

[0075] Adjust the temperature of the environmental chamber to 45°C, cycle 500 times, restore the temperature of the environmental chamber to 25°C, repeat the above operation, and record the terminal voltage V after 50% SOC is left for 1 hour. 3 、Terminal voltage V after 1C discharge for 30s 4 and current I 2 , DCR 2 =(V 3 -V 4 ) / I 2 The DCR growth rate is calculated using the following formula:

[0076] DCR growth rate (%) = (DCR 2 / DCR 1 -1)×100%.

[0077] Table 1. Performance test results of lithium ion batteries in Examples 1 to 5 and Comparative Examples 1 to 4

[0078]

[0079]

[0080] Please refer to Table 1. By comparing Examples 1 to 5, it can be seen that the capacity retention of the lithium ion batteries of Examples 1 to 4 increases first and then decreases after 500 cycles at 45°C, and the DCR growth rate decreases first and then increases. The capacity retention rate of the lithium ion battery of Example 5 is slightly lower than that of Examples 1 to 4 after 500 cycles at 45°C, and the DCR growth rate is slightly higher than that of Example 2, and slightly lower than that of Examples 1 and 3 to 4. On the one hand, this shows that the optimal dosage of the imidazolyl ionic liquid is around 1%. On the other hand, it shows that in the positive electrode material system with a Ni content of more than 65%, the π electrons of the sulfur-oxygen double bond in the imidazolyl ionic liquid compound I can coordinate with transition metal ions such as Ni and Mn dissolved from the positive electrode, so that the anion loses a single electron at the positive electrode and an oxidation reaction occurs, so that the Li-containing 3 N and Li 2At the same time, its cations can obtain electrons at the negative electrode, and through reduction polymerization, form a dense and uniform "solid electrolyte interface membrane" (solid electrolyte interface membrane, SEI membrane) composed of organic oligomers on the negative electrode, thereby ensuring stable high-temperature electrical properties.

[0081] As shown in Table 1, by comparing Example 2 with Comparative Example 1, it can be seen that it is very necessary to add Compound I to the electrolyte to form a CEI film at the positive electrode interface.

[0082] Please refer to Table 1. By comparing Example 2 and Comparative Example 2, it can be seen that excessive addition of imidazolyl ionic liquid compound I will deteriorate the high-temperature cycle performance. This may be due to excessive addition of imidazolyl ionic liquid, and many unreacted components remain in the electrolyte. If the unreacted part is partially exposed at the positive and negative electrode interfaces, it will react immediately and deteriorate the battery performance.

[0083] Please refer to Table 1. By comparing Example 2 and Comparative Example 3, it can be seen that when the positive electrode active material is LiFePO 4 When the capacity retention rate of the lithium-ion battery is greatly reduced after 500 cycles at 45°C, the DCR growth rate is greatly increased. Compared with the lithium-ion battery of Example 2, the high temperature cycle performance is poor. This is because the LiFePO 4 The positive electrode active material is relatively inert and will not catalyze the decomposition of the imidazolyl ionic liquid, and LiFePO 4 The transition metal ions that are not dissolved in the positive electrode active material can coordinate with the π electrons of the sulfur-oxygen double bond in the imidazolyl ionic liquid, thereby deteriorating the high-temperature cycle performance. This shows that the imidazolyl ionic liquid needs to be used in combination with a system with high catalytic activity and high cell voltage to effectively improve the performance of lithium-ion batteries.

[0084] Please refer to Table 1. By comparing Example 2 and Comparative Example 4, it can be seen that when graphite is selected as the negative electrode active material, the capacity retention rate of the lithium ion battery is greatly reduced after 500 cycles at 45°C, while the DCR growth rate is greatly increased. Compared with Example 2, the high temperature cycle performance of the lithium ion battery is poor. This is because the negative electrode graphite has poor compatibility with the decomposition products of the imidazolyl ionic liquid, so the high temperature cycle performance is deteriorated, indicating that the imidazolyl ionic liquid needs to be used in combination with the silicon-based composite material negative electrode system to effectively improve the performance of the lithium ion battery.

[0085] In summary, the present invention adds imidazolyl ionic liquid as an additive to the electrolyte and uses it in combination with a positive electrode material system with a Ni content of more than 65% and a silicon-based composite material negative electrode system. On the one hand, the π electrons of the sulfur-oxygen double bond in the imidazolyl ionic liquid can coordinate with transition metal ions such as Ni and Mn dissolved from the positive electrode, so that the positive electrode is oxidized to form a Li-containing 3 N and Li 2 On the other hand, the cations of the imidazolyl ionic liquid can obtain electrons at the negative electrode, and form a dense and uniform SEI film composed of organic oligomers on the negative electrode through reduction polymerization, thereby greatly improving the high-temperature cycle performance of the battery cell.

[0086] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A lithium-ion battery, It is characterized in that At least: A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein the element M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.8≤y<1.0,0≤z<0.1,0≤t<0.1,0≤δ≤0.1; Negative electrode; A separator, disposed between the positive electrode sheet and the negative electrode sheet; and The electrolyte is filled between the positive electrode plate, the negative electrode plate and the separator, and the electrolyte includes an additive, and the additive includes an ionic liquid. The chemical structure of the ionic liquid is as follows: Among them, R 1 and R 2 Each is an alkyl group having 1 to 6 carbon atoms, and X is selected from any one of bis(trifluoromethyl)sulfonyl imide, bis(trifluoromethyl)sulfonyl imide, tetrafluoroborate and acetate.

2. The lithium ion battery according to claim 1, Features: The ionic liquid is selected from at least one of the following compounds I to V: Ⅰ： Ⅱ： Ⅲ： Ⅳ： Ⅴ： 3. The lithium ion battery according to claim 1, Features: The mass content of the ionic liquid in the electrolyte is 0.1% to 10%.

4. The lithium ion battery according to claim 3, Features: The mass content of the ionic liquid in the electrolyte is 0.5% to 5%.

5. The lithium ion battery according to claim 1, It is characterized in that The electrolyte also includes a lithium salt, which is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate), lithium difluorophosphate and lithium trifluoromethanesulfonate.

6. The lithium ion battery according to claim 5, It is characterized in that The mass content of the lithium salt in the electrolyte is 8% to 18%.

7. The lithium ion battery according to claim 1, It is characterized in that The electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, and diethyl carbonate.

8. The lithium ion battery according to claim 7, It is characterized in that The non-aqueous solvent includes the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate, and the mass ratio of the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate is 3:5:

2.

9. The lithium ion battery according to claim 7, It is characterized in that The mass content of the non-aqueous solvent in the electrolyte is 60% to 90%.

10. An electronic device, Features: It comprises a lithium ion battery as claimed in any one of claims 1 to 9.

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