A lithium-ion battery

Abstract

The application provides a lithium ion battery, comprising a battery cell and an electrolyte; the battery cell comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises a lithium nickel manganese oxide material; the lithium nickel manganese oxide material has a general formula: LiNi x Mn (2‑x) O4,0

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a lithium-ion battery. Background Technology

[0002] With the rapid development of markets such as electronic devices, electric vehicles, smart homes, power tools, and intelligent transportation, the demand for batteries is constantly increasing. Lithium-ion batteries, for example, are widely used in consumer electronics, energy storage and power batteries, and smart homes due to their advantages such as high specific energy, long cycle life, and low self-discharge. Typically, a battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte usually includes a solvent, a lithium salt electrolyte, and electrolyte additives. Adding electrolyte additives can effectively improve battery performance. However, current electrolyte additives still present problems in practical applications.

[0003] Existing electrolytes are not resistant to high voltage. Electrolyte additives such as FEMC (trifluoroethyl methyl carbonate) have good high-voltage performance and are suitable for use. However, FEMC has too much fluorine substitution, resulting in excessive fluorine content, which enhances molecular polarity, increases electrolyte viscosity, and reduces activity. This leads to excessively low electrolyte ionic conductivity, which in turn affects ion diffusion, increases polarization, reduces constant current capacity, and increases constant voltage capacity. In severe cases, the upper limit voltage is reached immediately after charging, affecting the material's capacity utilization, deteriorating cycle performance, and potentially causing problems such as lithium plating. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a lithium-ion battery having a low cycle resistance (DCR) growth rate and a superior cycle capacity retention rate.

[0005] This invention provides a lithium-ion battery, comprising a cell and an electrolyte;

[0006] The battery cell includes a positive electrode and a negative electrode;

[0007] The positive electrode sheet includes a positive electrode active material, which includes lithium nickel manganese oxide material; the lithium nickel manganese oxide material has the general formula: LiNi x Mn (2-x) O4, 0 <x<1;

[0008] The electrolyte comprises a fluorinated organic compound having the structure of Formula I:

[0009]

[0010] Only one of R1, R3, R4, and R5 can be a functional group, and the rest are all H; the functional group is selected from -CH3, -CH2CH3, or -N(CH3)2;

[0011] R2 is selected from -O-COO-, -COO-, -SO2-, -SO3- or

[0012] Any one of R6 and R7 is selected from -F;

[0013] The mass content of the fluorinated organic compound having the structure of Formula I in the electrolyte is a;

[0014] The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes graphite, and the degree of graphite ordering of the graphite is b;

[0015] a and b satisfy the relationship: 0.018 ≤ a × b ≤ 0.165.

[0016] The present invention provides a lithium ion battery, including a battery cell and an electrolyte; the battery cell includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium nickel manganese oxide material; the lithium nickel manganese oxide material has a general formula: LiNi x Mn (2-x) O4, 0 < x < 1; the electrolyte includes a fluorinated organic compound having the structure of Formula I; the mass content of the fluorinated organic compound having the structure of Formula I in the electrolyte is a; the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes graphite, and the degree of graphite ordering of the graphite is b; a and b satisfy the relationship: 0.018 ≤ a × b ≤ 0.165. The battery provided by the present invention has a lower DCR growth rate and excellent cycle capacity retention rate by adding a fluorinated organic compound having the structure of Formula I with a mass content of a in the electrolyte, under the condition that the degree of graphite ordering b of the negative electrode active material graphite in the negative electrode sheet satisfies the relationship: 0.018 ≤ a × b ≤ 0.165. Detailed Embodiments

[0017] To make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] In the present invention, for the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution including the listed features.

[0019] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0020] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0021] This invention provides a lithium-ion battery, comprising a cell and an electrolyte;

[0022] The battery cell includes a positive electrode and a negative electrode;

[0023] The positive electrode sheet includes a positive electrode active material, which includes lithium nickel manganese oxide material; the lithium nickel manganese oxide material has the general formula: LiNi x Mn (2-x) O4, 0 <x<1;

[0024] The electrolyte comprises a fluorinated organic compound having the structure of Formula I:

[0025]

[0026] Only one of R1, R3, R4, and R5 can be a functional group, and the rest are all H; the functional group is selected from -CH3, -CH2CH3, or -N(CH3)2;

[0027] The R2 is selected from -O-COO-, -COO-, -SO2-, -SO3- or

[0028] R6 or R7 is selected from -F;

[0029] The mass content of the fluorinated organic compound having the structure of Formula I in the electrolyte is a;

[0030] The negative electrode sheet includes a negative electrode active material, which includes graphite, wherein the degree of graphite ordering of the graphite is b.

[0031] a and b satisfy the relationship: 0.018≤a×b≤0.165.

[0032] The lithium-ion battery provided by this invention achieves a low DCR growth rate and excellent cycle capacity retention by adding a fluorinated organic compound with a mass content of a to the electrolyte and the graphite ordering degree b of the graphite active material in the negative electrode sheet, which satisfies the relationship: 0.018≤a×b≤0.165.

[0033] The lithium-ion battery provided by this invention includes an electrolyte; the electrolyte includes a fluorinated organic compound having the structure of Formula I. The fluorinated organic compound having the structure of Formula I in this invention has a mass content of a in the electrolyte of 0.05 ≤ a ≤ 0.9. The specific values ​​of 'a' are 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, or 0.9.

[0034] In this invention, the preferred value of 'a' is 0.58 ≤ a ≤ 0.85; within this preferred range, the battery DCR growth rate is lower and the cycle life is better. Specifically, the value of 'a' is 0.741, 0.582, 0.849, 0.605, 0.751, 0.578, 0.852, 0.848, 0.581, 0.592, 0.701, 0.554, 0.501, 0.509, 0.859, 0.898, 0.722, 0.731, 0.591, 0.501, 0.834, 0.694, 0.749, 0.589, 0.582, 0.788, 0.692, 0.85, 0.581, or 0.742.

[0035] The fluorinated organic compound having the structure of Formula I described in this invention was purchased from Hebei Shengtai Materials Co., Ltd.

[0036] In a specific embodiment of the present invention, the fluorinated organic compound having the structure of Formula I is shown as Formula 101, Formula 102, or Formula 103:

[0037]

[0038] The electrolyte of this invention comprises, by mass percentage, 5-90% fluorinated organic compound having the structure of Formula I, 8-85% solvent, 2-15% lithium salt, and 0.5-2% additives; the additives are selected from one or more of vinyl sulfate (DTD), 1,3-propenesulfonyl lactone (PST), 1,3-propanesulfonyl lactone (PS), lithium difluorooxalate borate (LiODFB), lithium dioxalate borate (LiBOB), and lithium difluorophosphate (LiPO2F2).

[0039] The lithium-ion battery provided by this invention includes a battery cell, the battery cell including a negative electrode sheet, the negative electrode sheet including a negative electrode active material, the negative electrode active material including graphite, and in a specific embodiment, the graphite being artificial graphite; the degree of graphite ordering of the graphite is b; the degree of graphite ordering of the graphite in this invention is determined according to the following method:

[0040] In this invention, after disassembling the empty battery, the negative electrode sheet is removed, and 2 grams of negative electrode powder is scraped off. The negative electrode powder is soaked in DMC for 6 hours and then dried at 80°C for 240 minutes. The powder sample is then spread evenly on a glass slide, and the sample is gently pressed with the slide to flatten it. The slide is then placed on a three-dimensional platform, and the parameters are set under a microscope after focusing: laser wavelength of 514 nm and scanning range of 100-3100 cm⁻¹. -1 The powder was tested.

[0041] The peak intensity of the G peak (IG) at approximately 1580±5 wavenumbers and the peak intensity of the D peak (ID) at approximately 1360±5 wavenumbers are measured. IG represents lattice vibrations and the degree of order, while ID represents defects and disorder in the carbon material. Therefore, the ratio of the two peak intensities (ID / IG) can intuitively reflect the degree of ordering in the carbon material, denoted as b, where 0.02≤b≤0.40.

[0042] In this invention, if the graphite ordering degree (b) of the graphite is too high, the graphite activity will be higher, and it will be more prone to side reactions with fluorinated organic compounds having the structure of Formula I; if the b value is too low, the graphite activity will be lower, the lithium intercalation rate will be slower, and the battery performance will be affected. Therefore, the graphite ordering degree of the graphite needs to be controlled within a certain range: 0.02 ≤ b ≤ 0.40. The graphite described in this invention is a commercially available product, such as that purchased from BTR or Shanshan.

[0043] In this invention, the degree of graphite ordering is preferably 0.03 ≤ b ≤ 0.275; when the degree of graphite ordering is within the preferred range, the graphite exhibits excellent lithium-ion extraction and insertion capabilities. In specific embodiments of this invention, the value of b is 0.095, 0.275, 0.031, 0.145, 0.273, 0.083, 0.029, 0.276, 0.274, 0.031, 0.313, 0.385, 0.324, 0.025, 0.021, 0.125, 0.032, 0.271, 0.389, 0.022, 0.145, 0.04, 0.255, 0.266, 0.031, 0.123, 0.032, 0.274, or 0.033.

[0044] In this invention, a and b satisfy the following relationship: 0.018≤a×b≤0.165. If the relationship exceeds the lower limit, the electrolyte has poor high voltage resistance and is prone to significant side reactions with the negative electrode, resulting in severe battery cycle drops. If the relationship exceeds the upper limit, the electrolyte has poor coordination ability with lithium ions, the DCR value of the battery system increases, and the battery performance is affected.

[0045] Preferably, in this invention, 0.023 ≤ a × b ≤ 0.160; within the preferred range, the overall impedance of the battery is low, and the electrolyte is less likely to undergo side reactions with the negative electrode, while the negative electrode has excellent lithium-ion extraction and insertion rates; in specific embodiments of this invention, the value of a × b is 0.070, 0.160, 0.026, 0.088, 0.023, 0.158, 0.071, 0.025, 0.160, 0.162, 0.022, 0.173, 0.194, 0.165, 0.021, 0.019, 0.090, 0.195, 0.018, 0.101, 0.030, 0.150, 0.155, 0.024, 0.085, 0.027, 0.159, or 0.024.

[0046] The greater the total number of carbon atoms in the fluorinated organic compound with Formula I in this invention, the greater its impact on the viscosity of the electrolyte system. Therefore, the total number of carbon atoms in the fluorinated organic compound with Formula I in this application is preferably no more than 4.

[0047] In this invention, R6 and R7 are positioned at positions α and β, respectively, and R6 or R7 is selected from -F; if one is selected as F, the other is selected as H. In a certain embodiment of this invention, when R7 is -F and R6 is -H, 0.03 ≤ a × b ≤ 0.150.

[0048] The electrolyte of the present invention further includes a solvent. Based on the total mass of the electrolyte, the mass content of the solvent is 8-85%; specifically, the mass content is 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. The solvent in the present invention includes carbonate solvents; the carbonate solvents are selected from cyclic carbonates and / or chain carbonates; the cyclic carbonates are selected from one or more of fluoroethylene carbonate, ethylene carbonate and propylene carbonate; the chain carbonates are selected from one or more of ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and dibutyl carbonate.

[0049] The electrolyte of the present invention further includes a lithium salt, and the lithium salt is preferably selected from lithium hexafluorophosphate (LiPF6) and / or lithium bis(fluorosulfonyl)imide (LiFSi). Based on the total mass of the electrolyte, the mass content of the lithium salt in the electrolyte is 2-15%.

[0050] The battery cell in the present invention further includes a positive electrode sheet; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium nickel manganate material; the lithium nickel manganate material has a general formula: LiNi x Mn (2-x) O4, 0 < x < 1; in specific embodiments, the lithium nickel manganate material is LiNi 0.5 Mn 1.5 O4 or LiNi 0.8 Mn 1.2 O4.

[0051] The positive electrode sheet preferably further includes a binder and a conductive agent; the binder is selected from polytetrafluoroethylene or PVDF; the conductive agent is selected from one or more of conductive carbon black, acetylene black and carbon nanotubes. The binder is PVDF, and the conductive agent is SP; the mass ratio of the lithium nickel manganate material, the binder and the conductive agent is (92-98):(1-3):(0.5-2.5).

[0052] The preparation method of lithium nickel manganese oxide (LNMO) in this invention is as follows: A nickel manganese hydroxide compound and a lithium source are uniformly mixed at a ratio of Li / (Ni+Mn) = (0.45-0.55) / 1, where (Ni+Mn) is the total molar amount of nickel and manganese metals. The mixture is then sintered. The sintering procedure is as follows: the temperature is increased to 490-520℃ at a heating rate of 1.5-2.5℃ / min, held at 490-520℃ for 6 hours, then increased to 930-950℃ at a heating rate of 1.5-2.5℃ / min, held at 930-950℃ for 14-16 hours, and then cooled to room temperature. The resulting material is crushed and sieved to obtain LNMO. The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium sulfate.

[0053] The lithium-ion battery provided by the present invention also includes a separator; the separator is PE or PP.

[0054] The present invention stacks the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator sheet between the positive electrode sheet and the negative electrode sheet, and then winds them to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum sealing, standing, formation, shaping and other processes, a lithium-ion battery is obtained.

[0055] To further illustrate the present invention, the following detailed description of a lithium-ion battery provided by the present invention is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0056] In the following examples and comparative examples, the fluorinated organic compounds used were commercially available products. Graphite used was a commercially available product.

[0057] The method for preparing the positive electrode sheet described in this invention:

[0058] Lithium nickel manganese oxide, binder, and conductive agent are dispersed in N-methylpyrrolidone (NMP) at a mass ratio of (92–98.5):(1–3):(0.5–2.5). This positive electrode slurry is coated on aluminum foil to obtain aluminum foil with the positive electrode slurry coated on its surface. The wet film thickness of the positive electrode slurry coating on one side of the aluminum foil is controlled to be 50–250 μm. Then, it is rolled and cut to obtain the positive electrode sheet.

[0059] Lithium nickel manganese oxide has the general formula LiNi x Mn (2-x) O4, 0 <x<1

[0060] The adhesive is selected from polytetrafluoroethylene or PVDF.

[0061] The conductive agent is selected from one or more of conductive carbon black, acetylene black, and carbon nanotubes.

[0062] The method for preparing the negative electrode sheet described in this invention:

[0063] The negative electrode material, binder, and conductive agent are dispersed in deionized water at a mass ratio of (94-98):(2.5-4.5):(0.5-1.5). This negative electrode slurry is coated onto a copper foil to obtain a copper foil with the negative electrode slurry coated on its surface. The wet film thickness of the negative electrode slurry coating on one side of the copper foil is controlled to be 60-300 μm. Then, the foil is rolled and cut to obtain a negative electrode sheet.

[0064] The negative electrode material is selected from one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0065] The adhesive is selected from one or more of polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC);

[0066] The conductive agent is selected from conductive carbon black and / or carbon nanotubes.

[0067] The method for preparing the electrolyte described in this invention:

[0068] The solvent, fluorinated organic compound, lithium salt and additives are mixed in a mass ratio of (8-85):(5-90):(2-15):(0.5-2) to obtain the electrolyte.

[0069] Examples and Comparative Examples

[0070] The present invention prepares the negative electrode and electrolyte according to the values ​​of a and b shown in Table 1.

[0071] 1) Preparation of positive electrode sheet

[0072] Preparation method of lithium nickel manganese oxide (LNMO) as the main cathode material: Nickel manganese hydroxide and lithium source (lithium sulfate) are uniformly mixed at a molar ratio of Li / (Ni+Mn) = 0.5 / 1, where (Ni+Mn) is the total molar number of nickel and manganese metals. Then, sintering is carried out. The sintering procedure is as follows: the temperature is increased to 500℃ at a heating rate of 2℃ / min, held at 500℃ for 6 hours, and then increased to 950℃ at a heating rate of 2℃ / min. After holding at this temperature for 15 hours, the temperature is reduced to room temperature. The obtained material is crushed and sieved to obtain LNMO.

[0073] The positive electrode material, binder PVDF and conductive agent SP are dispersed in NMP at a mass ratio of 90:2.5:2.5 to obtain a positive electrode slurry; the positive electrode slurry is coated on aluminum foil, and the wet film thickness of the positive electrode slurry coating on one side of the aluminum foil is controlled to be 170 μm. Then it is rolled and cut to obtain a positive electrode sheet.

[0074] 2) Preparation of negative electrode sheet

[0075] Artificial graphite, carboxymethyl cellulose, and acetylene black are dispersed in deionized water at a mass ratio of 96:3.4:0.6. After homogenization, a negative electrode slurry is obtained. The negative electrode slurry is coated onto a copper foil, and the wet film thickness of the negative electrode slurry coating on one side of the copper foil is controlled to be 140 μm. Then, it is rolled and cut to obtain a negative electrode sheet.

[0076] 3) Preparation of electrolyte

[0077] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a solvent. After the solvent and fluorinated organic compound are mixed evenly, fully dried lithium salt LiPF6 and additive ethylene sulfate (DTD) are added to obtain the electrolyte.

[0078] 4) Preparation of the separating membrane

[0079] PP was chosen as the separator.

[0080] 5) Assembly and formation

[0081] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0082] The types of raw materials and the values ​​of various parameters used in the embodiments and comparative examples of this invention are shown in Table 1:

[0083] Table 1

[0084]

[0085]

[0086]

[0087] The battery performance of the present invention was tested at 45°C for capacity retention and DCR growth rate in the examples and comparative examples. The results are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] The method for testing the battery's capacity retention rate at 45°C using this invention is as follows:

[0092] Charge the battery at a constant current and constant voltage rate of 0.33C to 4.75V, with a cutoff current of 0.05C. Let it rest for 10 minutes, then discharge it at a constant current rate of 0.33C to 3.5V. Repeat this cycle twice, taking the actual discharge capacity of the second cycle as the initial capacity, denoted as A1. Next, let the battery rest for 10 minutes, then charge it at a constant current and constant voltage rate of 1C to 4.75V, with a cutoff current of 0.05C. Let it rest for 10 minutes, then discharge it at a constant current rate of 1C to 3.5V. Repeat this test procedure for 300 cycles, recording the discharge capacity of the 300th cycle as A2. The capacity retention rate is calculated as (A2 / A1) × 100%.

[0093] The method for testing the DCR growth rate of a battery provided by this invention is as follows:

[0094] Charge the battery at a constant current and constant voltage of 0.33C to 4.75V with a cutoff current of 0.05C; let it rest for 10 minutes, then discharge it at a constant current of 0.33C to 3.5V. Repeat this cycle twice. Let it rest for 10 minutes, then charge it at a constant current and constant voltage of 0.33C to 4.75V. Discharge it to 50% of the SOC of the second cycle, then let it rest for 2 hours (the discharge capacity of the second cycle). Discharge at 1C for 18 seconds, RDCR1 discharge (I1, 18S) = |V1-V2| / I1. Record the voltage at the start of discharge as V1, the voltage at the end of the 18-second discharge as V2, and I1 as the 18-second discharge capacity. Charge the battery at a constant current and constant voltage of 0.33C to 4.75V at a temperature of 45℃ with a cutoff current of 0.05C; let it rest for 10 minutes, then discharge it at a constant current of 0.33C. Charge the battery to 3.5V, let it rest for 10 minutes, and repeat this cycle 200 times. Then charge the battery at a constant current and constant voltage of 0.33C to 4.75V, with a cutoff current of 0.05C. Let it rest for 10 minutes, then discharge it at a constant current of 0.33C to 3.5V. Repeat this cycle 2 times, let it rest for 10 minutes, then charge it at a constant current and constant voltage of 0.33C to 4.75V. Discharge the battery to 50% of the discharge capacity of the second cycle, and then let it rest for 2 hours. (Discharge capacity of the second cycle) Discharge at 1C for 18 seconds, RDCR2 discharge (I2, 18s) = |V3-V4| / I2. Record the voltage value at the start of discharge as V3, the voltage value at the end of 18 seconds as V4, and I2 as the discharge capacity of 18 seconds. Calculate the DCR growth rate using the formula DCR growth rate = (RDCR2-RDCR1) / RDCR1.

[0095] The method for testing the content of fluorinated organic compounds having the structure of Formula I described in this invention:

[0096] In a glove box (H2O≤1ppm, O2≤10ppm), disassemble the battery to collect electrolyte samples. There are three methods for collecting electrolyte samples: After removing the battery cover, ① if there is free electrolyte, collect the sample into a 10mL sample tube using a pipette and seal it with sealant to prevent leakage. ② if there is no free electrolyte, use a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) to continuously pressurize until free electrolyte appears, collect the sample into a sample tube, and seal it. ③ Add an appropriate amount of a mixture of dichloromethane and cyclohexylbenzene to the battery as an extractant. The mass ratio of dichloromethane to cyclohexylbenzene is 1:9, and the amount of extractant added is 5g / Ah. After adding the extractant, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and let it stand for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the extractant, thus obtaining an electrolyte sample. Then, use a pipette to draw the electrolyte sample into a 5mL sample tube and seal the sample tube with sealing glue.

[0097] Structural testing: 1 mL of fluorinated organic compound was placed in a sample tube, and 0.5 mL of CDCl3 (deuterated chloroform) was injected into the sample tube using a syringe. The fluorinated organic compound was allowed to dissolve completely for 30 min. The dissolved fluorinated organic compound was then placed in a magnetic resonance spectrometer (Bruker 400MHz NMR spectrometer) to test its NMR spectrum and obtain a standard curve. 1 mL of the collected electrolyte sample was placed in a sample tube, and 0.5 mL of CDCl3 (deuterated chloroform) was injected into the sample tube using a syringe. The electrolyte sample was allowed to dissolve completely for 30 min. The electrolyte sample was then placed in a magnetic resonance spectrometer (Bruker 400MHz NMR spectrometer) to test its NMR spectrum and compared with the standard curve of the fluorinated organic compound to confirm the presence of fluorinated organic compound in the sample.

[0098] Content testing: 2 mL of fluorinated organic compounds were injected into an Agilent Intuvo 9000 gas chromatograph and ion chromatograph using a microsyringe to test the chromatogram of fluorinated organic compounds. The chromatographic column was KB-200. A standard database of fluorinated organic compounds was obtained. 2 mL of the collected electrolyte sample was injected into the Agilent Intuvo 9000 gas chromatograph and ion chromatograph using a microsyringe to test the electrolyte components. The chromatographic column was KB-200. A data chromatogram of the electrolyte sample was obtained. The data chromatogram of the electrolyte sample was compared with the standard database of fluorinated organic compounds to confirm the content of fluorinated organic compounds in the electrolyte. The confirmation method was to compare the peak areas at the same elution position in the data chromatogram of the electrolyte sample with those in the standard database of fluorinated organic compounds. The peak area of ​​the data chromatogram of the electrolyte sample was recorded as S1, and the peak area in the standard database of fluorinated organic compounds was recorded as S2. The content of fluorinated organic compounds in the electrolyte sample = S1 / S2 × 100%.

[0099] As can be seen from the above embodiments, the present invention provides a lithium-ion battery, comprising a battery cell and an electrolyte; the battery cell includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium nickel manganate material; the lithium nickel manganate material has a general formula: LiNi x Mn (2-x) O4, 0 < x < 1; the electrolyte includes a fluorinated organic compound having a structure of Formula I; the mass content of the fluorinated ester having a structure of Formula I in the electrolyte is a; the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes graphite, and the degree of graphite ordering of the graphite is b; a and b satisfy the relationship: 0.018 ≤ a × b ≤ 0.165. The battery provided by the present invention has a lower DCR growth rate and excellent cycle capacity retention rate under the condition that the mass content a of the fluorinated organic compound having a structure of Formula I is added to the electrolyte and the degree of graphite ordering b of the negative electrode active material graphite in the negative electrode sheet satisfy the relationship: 0.018 ≤ a × b ≤ 0.165.

[0100] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A lithium-ion battery, comprising a cell and an electrolyte; The battery cell includes a positive electrode and a negative electrode; The positive electrode sheet includes a positive electrode active material, which includes lithium nickel manganese oxide material. The electrolyte includes fluorinated organic compounds; the fluorinated organic compounds are selected from... Formula 103; Or the fluorinated organic compounds are selected from Formula 101; The mass content of the fluorinated organic compound in the electrolyte is a; The negative electrode sheet includes a negative electrode active material, which includes graphite, wherein the degree of graphite ordering of the graphite is b; 0.58≤a≤0.85, 0.03≤b≤0.275; a and b satisfy the relationship: 0.023≤a×b≤0.

160.

2. The lithium-ion battery according to claim 1, characterized in that, The electrolyte contains solvent, and the solvent content is 8-85% based on the total mass of the electrolyte.

3. The lithium-ion battery according to claim 2, characterized in that, The solvent includes carbonate solvents; The carbonate solvent is selected from cyclic carbonates and / or chain carbonates.

4. The lithium-ion battery according to claim 3, characterized in that, The cyclic carbonate is selected from one or more of fluoroethylene carbonate, ethylene carbonate and propylene carbonate; The chain carbonate is selected from one or more of methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate.

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