Lithium ion battery and application thereof

Abstract

The invention provides a lithium ion battery and application thereof, the lithium ion battery at least comprises: a positive pole piece, the positive pole piece comprises a positive active material, the positive active material comprises Lix [NiyCozMntM (1-y-z-t)] O2-delta, the element M is selected from one or more of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 lt; xlt; 1.1, 0.65 < = y < lt >; 1.0, 0 < = zlt; 0.5, 0 < = tlt; 0 < = delta < = 0.1; a negative pole piece; the diaphragm is arranged between the positive pole piece and the negative pole piece; the space among the positive pole piece, the negative pole piece and the diaphragm is filled with the electrolyte, the electrolyte comprises fluoro-carboxylic ester, the structural general formula of the fluoro-carboxylic ester is # imgabs0 #, R1 and R2 are fluorine atoms, alkyl or alkenyl with the carbon atom number of 0-5 or ester groups with the carbon atom number of 2-4 respectively, and R3 is phenyl or alkyl or alkenyl with the carbon atom number of 1-5. According to the lithium ion battery and the application thereof provided by the invention, the energy density of the lithium ion battery can be improved, and the fast charge and cycle performance of the lithium ion battery can be 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 applications thereof. Background Art

[0002] With cameras, laptops, and electric vehicles becoming increasingly common in our daily lives, the battery industry is increasingly demanding smaller and lighter batteries, higher energy density, and longer lifespans. To meet this growing demand, developing lithium-ion batteries with high energy density and fast charging capabilities has become a hot research topic.

[0003] At present, the demand for high energy density is met by selecting silicon-based composite materials with high gram capacity for the negative electrode. However, the conductivity of silicon-based composite materials themselves is average, and the cyclic charge and discharge process is accompanied by the continuous rupture and repair of the solid electrolyte interface (SEI), making it difficult to balance fast charging and energy density. By selecting a nickel-cobalt-manganese ternary system with high gram capacity and high energy density for the positive electrode, graphite is used for the negative electrode, and an electrolyte with high kinetic performance is selected to meet the fast charging performance, but the electrolyte needs to use a low-viscosity organic solvent to ensure its good kinetic performance. However, these organic solvents easily react with the active positive and negative electrode surfaces at high temperatures, causing battery swelling. Although adding additives to the electrolyte can solve the decomposition of the electrolyte, the products of the additive reaction will increase the internal resistance of the battery, which in turn affects the fast charging performance of the lithium-ion battery. Summary of the Invention

[0004] The present invention provides a lithium-ion battery and its application. The lithium-ion battery and its application provided by the present invention can increase the energy density of the lithium-ion battery, improve the dynamics and fast charging capability of the battery cell, and improve the cycle performance of the lithium-ion battery.

[0005] To solve the above technical problems, the present invention provides a lithium-ion battery comprising at least:

[0006] A positive electrode sheet, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein the element M is selected from one or more of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.65≤y<1.0,0≤z<0.5,0≤t<0.5,0≤δ≤0.1;

[0007] negative electrode;

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

[0009] An electrolyte is filled between the positive electrode sheet, the negative electrode sheet, and the separator, wherein the electrolyte includes a fluorocarboxylate, and the general structural formula of the fluorocarboxylate is:

[0010] Wherein, R1 and R2 are each a fluorine atom, an alkyl or alkenyl group having 0 to 5 carbon atoms, or an ester group having 2 to 4 carbon atoms, and R3 is a phenyl group or an alkyl or alkenyl group having 1 to 5 carbon atoms.

[0011] In one embodiment of the present invention, the fluorocarboxylate comprises One or a mixture of the two.

[0012] In one embodiment of the present invention, the mass content of the fluorocarboxylate in the electrolyte is 0.5%-8%.

[0013] In one embodiment of the present invention, the mass content of the fluorocarboxylate in the electrolyte is 1%-3%.

[0014] In one embodiment of the present invention, the electrolyte further includes a lithium salt, and the lithium salt is selected from any one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate), lithium difluorophosphate or lithium trifluoromethanesulfonate, or a combination of at least two thereof.

[0015] In one embodiment of the present invention, the mass content of the lithium salt in the electrolyte is 8%-18%.

[0016] In one embodiment of the present invention, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes any one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, or diethyl carbonate, or a combination of at least two thereof.

[0017] 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.

[0018] In one embodiment of the present invention, the mass content of the non-aqueous solvent in the electrolyte is 60%-85%.

[0019] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0020] In summary, the present invention proposes a lithium-ion battery and its application, which can reduce the viscosity of the electrolyte, improve the transmission capacity of lithium ions, accelerate the wetting ability of high-voltage positive electrode active materials, and improve the dynamics and fast charging capacity of the battery cell. It can improve the wetting ability of the electrolyte on the diaphragm and the electrode, and the electron-rich nature of the sulfur-oxygen double bond can coordinate with the transition metal ions dissolved from the positive electrode, thereby improving the stability of the CEI film on the positive electrode surface. At the same time, the fluorocarboxylic acid ester also forms an inorganic salt with a good coating effect on the negative electrode side, thereby improving the stability of the SEI film and ensuring the long-term performance of the battery cell. It can increase the energy density of the lithium-ion battery and improve the cycle performance of the lithium-ion battery. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0023] The technical solutions of the present invention are further described in detail below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] The present invention provides 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, a soft-pack secondary battery is used as an example for explanation.

[0025] In an embodiment of the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode active layer coated at least on one surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, a binder, a conductive agent, etc. Among them, the positive electrode current collector can be, for example, a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. In addition to the foil, the positive electrode current collector can also be used in any one or a combination of multiple forms such as film, mesh, porous, foam, or non-woven fabric. Among them, the thickness of the positive electrode current collector is, for example, 8 μm - 15 μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil.

[0026] In an 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 , where the element M is selected from one or more of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, and Zn, 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1. The binder is selected, for example, from any one or more of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, or polymerized styrene butadiene rubber (SBR). The conductive agent is selected, for example, from any one or more of conductive carbon black (Super P, SP), acetylene black, carbon nanotubes, and graphene. By selecting a nickel-cobalt-manganese ternary system with high specific capacity and high energy density as the positive electrode active material, the energy density of the lithium-ion battery is improved.

[0027] In an embodiment of the present invention, the positive electrode active material is, for example, LiNi 0.9 Co 0.05 Mn 0.05O2, the binder is selected from, for example, polyvinylidene fluoride, and the conductive agent is selected from, for example, conductive carbon black. After mixing the cathode active material, conductive carbon black, and polyvinylidene fluoride, for example, in a mass ratio of 95:3:2, an organic solvent is added and stirred until the system becomes homogeneous to obtain a cathode slurry. Among them, the organic solvent is selected from, for example, N-methylpyrrolidone (NMP). After uniformly coating the cathode slurry on an aluminum foil, it is air-dried and then vacuum-dried, and then the dried aluminum foil is subjected to processes such as cold pressing to obtain a cathode electrode sheet.

[0028] In an embodiment of the present invention, the anode electrode sheet includes, for example, an anode current collector and at least an anode active layer coated on one side of the anode current collector. The anode active layer includes an anode active material, a binder, a conductive agent, a thickening agent, etc. Among them, the anode current collector is selected from, for example, 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, etc. The thickness of the anode current collector is, for example, 8 μm - 15 μm.

[0029] In an embodiment of the present invention, the anode active material includes a silicon-based composite material, and for example, includes at least one of silicon oxides (SiO n , 0 < n < 2) or carbon-silicon composite materials, etc. The anode active material includes at least one of metal elements such as Ti, Fe, Cu, Ni, Co, Mn, Ag, Au, or Sn, etc. The content of the metal element in the anode active material is, for example, 10 ppm - 500 ppm, and for example, exists in the anode 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, other silicon-based composite materials can be selected as the anode active material. The adhesive is selected from, for example, any one or more of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, or styrene-butadiene rubber, etc. The conductive agent is selected from, for example, any one or more of conductive carbon black, acetylene black, carbon nanotubes, and graphene, etc. The thickening agent is selected from, for example, sodium carboxymethyl cellulose, etc.

[0030] In an embodiment of the present invention, the anode current collector is selected from, for example, copper foil, the anode active material is selected from, for example, silicon oxide, the conductive agent is selected from, for example, conductive carbon black, the adhesive is selected from, for example, styrene-butadiene rubber, and the thickening agent is selected from, for example, sodium carboxymethyl cellulose. In an embodiment of the present invention, 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 stirred充分 to obtain an anode slurry. The anode slurry is uniformly coated on the copper foil, and then transferred to an oven for drying after air-drying at room temperature, and an anode electrode sheet is obtained through processes such as drying and cold pressing.

[0031] In one embodiment of the present invention, the separator is, for example, a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, a polyethylene film, or a composite film. The separator has a thickness of, for example, 9 μm to 15 μm. In one embodiment of the present invention, the separator is, for example, a polyethylene base film of 8 μm to 10 μm thick, and a nano-aluminum oxide coating having a thickness of 2 μm to 4 μm is applied to the base film to obtain the separator. In one embodiment of the present invention, the separator is, for example, a 12 μm polypropylene film.

[0032] In one embodiment of the present invention, the electrolyte includes at least a non-aqueous solvent, a lithium salt, and an additive, wherein the additive includes, for example, a fluorocarboxylate, and the fluorocarboxylate has the general structural formula:

[0033] Wherein, R1 and R2 are each a fluorine atom, an alkyl or alkenyl group having 0-5 carbon atoms, or an ester group having 2-4 carbon atoms, and R3 is a phenyl group or an alkyl or alkenyl group having 1-5 carbon atoms. Among them, the viscosity of the carboxylic acid ester is low, which can improve the transmission capacity of lithium ions, accelerate the wetting ability of high-voltage positive electrode active materials, and improve the dynamics and fast charging capacity of the battery cell. At the same time, the fluorocarboxylic acid ester contains a fluorosulfonyl functional group. On the one hand, the affinity of the fluorine atom is strong, which improves the wetting ability of the electrolyte to the diaphragm and the electrode. On the other hand, the electron-richness of the sulfur-oxygen double bond can coordinate with the Co and Mn transition metal ions dissolved from the positive electrode, so that under high voltage, the CF bond on the positive electrode side is broken to generate inorganic salts such as LiF and Li2S. The coating effect of the inorganic salt is good, which improves the stability of the positive electrode-electrolyte interface (Catheode Electrolyte Interphase, CEI) on the positive electrode surface, and can ensure the long-term performance of the battery cell. At the same time, fluorocarboxylates also form inorganic salts with good coating effects such as LiF and Li2S on the negative electrode side, which improves the stability of the SEI film and can ensure the long-term performance of the battery cell.

[0034] In one embodiment of the present invention, the fluorocarboxylic acid ester includes, for example, compound I Compound II or compound III In one embodiment of the present invention, the mass content of the fluorocarboxylate in the electrolyte is, for example, 0.5%-8%, and for example, 1%-3%. When the mass content of the fluorocarboxylate is too low, the fast charging performance and cycle performance of the lithium battery are not significantly improved. When the mass content of the fluorocarboxylate is too high, a thick coating layer will be formed at the negative electrode interface, blocking the effective transmission of lithium ions, thereby causing the cycle performance of the lithium battery to decline.

[0035] In one embodiment of the present invention, the lithium salt includes, for example, any one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorobis(oxalatophosphate) (LiDODFP), lithium difluorophosphate (LiDFP), or lithium trifluoromethanesulfonate (CF3SO3Li), or a combination of at least two thereof. In this embodiment, the mass content of the lithium salt in the electrolyte is 8 wt% to 18 wt%.

[0036] In one embodiment of the present invention, the non-aqueous solvent includes any one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) or diethyl carbonate (DEC), or a combination of at least two thereof. In one embodiment of the present invention, the mass percentage of the non-aqueous solvent in the electrolyte is, for example, 60%-85%. 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.

[0037] In one embodiment of the present invention, when preparing the electrolyte, the content of a 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 0.1 ppm, and the moisture content is less than or equal to 0.1 ppm. After uniformly mixing the non-aqueous solvent according to the mass ratio, a fully dried lithium salt is added to the non-aqueous solvent, and additives are added to prepare a non-aqueous electrolyte for a lithium-ion battery. The contents of each component other than the non-aqueous solvent are expressed as mass percentages calculated based on the total mass of the electrolyte.

[0038] In one embodiment of the present invention, the aforementioned positive electrode sheet, separator, and negative electrode sheet are sequentially placed, with the separator positioned between the positive and negative electrode sheets to provide isolation. The sheets are then wound or laminated to produce a bare cell. The bare cell is then enclosed in aluminum-plastic film, dried in a vacuum oven, injected with the aforementioned electrolyte, and sealed. The cell undergoes a series of steps, including standing, hot and cold pressing, formation, clamping, and capacity sizing, to produce a soft-pack lithium-ion secondary battery.

[0039] 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.

[0040] Example 1

[0041] Preparation of the electrolyte: In an argon-filled glove box, with a nitrogen content of 99.999%, an actual oxygen content of less than 0.1 ppm, and a moisture content of less than 0.1 ppm, battery-grade ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a mass ratio of 3:5:2. Based on the total mass of the electrolyte as 100%, the lithium salt in the electrolyte was LiPF6, with a mass content of 13%. The fluorocarboxylate was selected as Compound I, with a mass content of 0.5%.

[0042] Preparation of positive electrode sheet: LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:3:2, and NMP was added and stirred until the mixture became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for vacuum drying. The dried aluminum foil was then cold-pressed to obtain a positive electrode sheet.

[0043] Preparation of the negative electrode sheet: Mix the negative electrode active material SiO, the conductive agent conductive carbon black, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose in a mass ratio of, for example, 96:2:1:1. Add deionized water and stir thoroughly to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on copper foil, air-dried at room temperature, and then transferred to an oven for drying. After drying and cold pressing, the negative electrode sheet is obtained.

[0044] Selection of diaphragm: 10 μm polypropylene film was selected as the diaphragm.

[0045] Battery Preparation: The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The sheets are then laminated to form a bare cell. The cell is then wrapped with aluminum-plastic film and dried in a vacuum oven. The electrolyte prepared above is then injected and sealed, followed by electrolyte formation to produce a soft-pack lithium-ion secondary battery.

[0046] Example 2

[0047] The fluorocarboxylate was selected from Compound I, and the mass content of Compound I was 1.75%. Other operations were the same as in Example 1.

[0048] Example 3

[0049] The fluorocarboxylate is selected from Compound I, and the mass content of Compound I is 5%. Other operations are the same as in Example 1.

[0050] Example 4

[0051] The fluorocarboxylate was selected from Compound I, and the mass content of Compound I was 8%. Other operations were the same as in Example 1.

[0052] Comparative Example 1

[0053] No fluorocarboxylate was added to the electrolyte, and other operations were the same as in Example 1.

[0054] Comparative Example 2

[0055] The fluorocarboxylate was selected from Compound I, and the mass content of Compound I was 15%. Other operations were the same as in Example 1.

[0056] Comparative Example 3

[0057] The fluorocarboxylate is selected as compound I, and the mass content of compound I is 1%. The negative electrode active material is graphite. Other operations are the same as in Example 1.

[0058] Comparative Example 4

[0059] The fluorocarboxylate is selected as compound I, and the mass content of compound I is 1%. The positive electrode active material is lithium iron phosphate (LiFePO4). Other operations are the same as those in Example 1.

[0060] In the present invention, different electrolyte ratios and positive and negative electrode active materials were used to prepare lithium ion batteries in Examples 1-4 and Comparative Examples 1-4, and the performance of the lithium ion batteries was tested. The test results are shown in Table 1.

[0061] In one embodiment of the present invention, the initial direct current resistance (DCR) test is performed at 25°C, with a constant current of 0.33C charging to 4.35V, a constant voltage of 4.35V to 0.05C, and after standing for 30 minutes, a constant current of 0.33C discharging to 2.5V. After confirming the cell capacity C0, the cell is charged again to 4.35V at a constant current of 0.33C, and then a constant voltage of 4.35V to 0.05C, and after standing for 30 minutes, a constant current of 0.33C discharging to 50% C0 is performed. After standing for 30 minutes, the terminal voltage V1 is recorded, and the cell is discharged at a constant current of 4C0 for 30 seconds, and the terminal voltage V2 and current I are recorded. At this time, DCR = (V1-V2) / I.

[0062] In one embodiment of the present invention, the test of the capacity retention rate of the normal temperature cycle is to charge the lithium ion battery to 4.35V at a constant current of 0.5C at 25°C, then charge it at a constant voltage of 4.35V to a current less than 0.05C, and after standing for 30 minutes, discharge it to 2.8V at a constant current of 1C. The discharge capacity of the lithium ion battery at this time is tested, 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:

[0063] Capacity retention (%) = (discharge capacity corresponding to 500 cycles / discharge capacity of the first cycle) × 100%.

[0064] Table 1. Performance test results of lithium-ion batteries in Examples 1-4 and Comparative Examples 1-4

[0065]

[0066] As shown in Table 1, it can be seen from the comparison of Examples 1-4 that the initial DCR first decreases and then increases, and the capacity retention after 500 cycles at 25°C first increases and then decreases, indicating that the optimal dosage of Compound I in the fluorocarboxylate is around 1.75%. It also shows that in a positive electrode material system with a Ni content greater than 65%, the electron-rich sulfur-oxygen double bond of Compound I in the fluorocarboxylate can coordinate with the Co and Mn transition metal ions dissolved from the positive electrode, thereby forming a uniform and dense CEI film at the positive electrode interface, and Compound I in the fluorocarboxylate can well infiltrate the negative electrode active material and form a uniform and dense SEI film at the negative electrode interface, thereby ensuring stable high-temperature electrical performance.

[0067] As shown in Table 1, a comparison of Examples 1-4 with Comparative Example 1 shows that the addition of a fluorocarboxylate improves both the initial DCR and capacity retention of the lithium-ion battery. This suggests that the addition of a fluorocarboxylate can form a coordination effect at the positive electrode interface, forming a CEI film under electrocatalysis, and simultaneously forming an SEI film at the negative electrode interface, thereby improving the performance of the lithium-ion battery. A comparison of Example 2 with Comparative Example 2 shows that increasing the fluorocarboxylate content deteriorates the cycling performance of the lithium-ion battery. This is likely due to an excess of fluorocarboxylate, with unreacted components remaining in the electrolyte. These excess components may undergo a reduction reaction at the negative electrode, resulting in excessive SEI film thickness and deteriorating battery performance.

[0068] As shown in Table 1, a comparison of Example 2 and Comparative Example 3 shows that when graphite is selected as the negative electrode active material, the initial DCR and capacity retention of the lithium-ion battery are poor. This is because the graphite negative electrode catalyzes the decomposition products of Compound I in the fluorocarboxylate, forming a thick SEI film, which deteriorates the cycling performance. This indicates that the fluorocarboxylate needs to be used in conjunction with a silicon-based composite negative electrode material system to effectively improve the performance of the lithium-ion battery. Compared with Example 2 and Comparative Example 4, when LiFePO4 is selected as the positive electrode active material, the initial DCR and capacity retention of the lithium-ion battery are poor. This is because the LiFePO4 positive electrode active material is relatively inert and does not catalyze the decomposition of the fluorocarboxylate. In addition, the undissolved metal in the LiFePO4 positive electrode active material can coordinate with Compound I in the fluorocarboxylate, thus deteriorating the cycling performance. This indicates that the fluorocarboxylate needs to be used in conjunction with a system with high catalytic activity and high cell voltage to effectively improve the performance of the lithium-ion battery.

[0069] The present invention also provides an electronic device, which includes at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. The electronic device may 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, which may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. The spacecraft includes airplanes, rockets, space shuttles, and spacecraft, etc. The electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. The 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 on here.

[0070] In summary, the present invention proposes a lithium-ion battery and its application. By adding a fluorocarboxylate as an additive to the electrolyte, the viscosity of the electrolyte can be reduced, the transmission capacity of lithium ions can be improved, the wetting ability of the high-voltage positive electrode active material can be accelerated, and the dynamics and fast charging capacity of the battery cell can be improved. Fluorocarboxylate contains a fluorosulfonyl functional group with strong affinity, which can improve the wetting ability of the electrolyte to the diaphragm and the electrode. The electron-rich nature of the sulfur-oxygen double bond can coordinate with the transition metal ions dissolved from the positive electrode, thereby improving the stability of the CEI film on the positive electrode surface. At the same time, the fluorocarboxylate also forms an inorganic salt with a good coating effect on the negative electrode side, thereby improving the stability of the SEI film and ensuring the long-term performance of the battery cell. It can increase the energy density of lithium-ion batteries and improve the cycle performance of lithium-ion batteries.

[0071] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0072] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A lithium ion battery, 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 one or more of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.65≤y<1.0,0≤z<0.5,0≤t<0.5,0≤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 a fluorocarboxylate, and the general structural formula of the fluorocarboxylate is: Wherein, R1 and R2 are each a fluorine atom, an alkyl or alkenyl group having 0 to 5 carbon atoms, or an ester group having 2 to 4 carbon atoms, and R3 is a phenyl group or an alkyl or alkenyl group having 1 to 5 carbon atoms.

2. The lithium-ion battery according to claim 1, characterized in that The fluorocarboxylic acid esters include One or a mixture of the two.

3. The lithium-ion battery according to claim 1, characterized in that The mass content of the fluorocarboxylic acid ester in the electrolyte is 0.5%-8%.

4. The lithium-ion battery according to claim 3, characterized in that: The mass content of the fluorocarboxylic acid ester in the electrolyte is 1%-3%.

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

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

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

8. The lithium-ion battery according to claim 7, 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, characterized in that: The mass content of the non-aqueous solvent in the electrolyte is 60%-85%.

10. An electronic device, characterized in that: Comprising a lithium ion battery as claimed in any one of claims 1 to 9.

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