A low-temperature charging lithium-ion battery and its preparation method

Abstract

The present invention provides a low-temperature chargeable lithium-ion battery and a preparation method thereof. Among them, the negative electrode material of the low-temperature chargeable lithium-ion battery includes modified graphene and carbon-coated lithium titanate. After being modified by the modified graphene, the carbon-coated lithium titanate can significantly reduce the defects on the surface of the negative electrode, reduce the risk of aggregation and uneven deposition of lithium ions on the surface of the negative electrode, eliminate the lithium dendrites generated during low-temperature charging, obtain a new negative electrode material with higher specific capacity, better cycle stability and lower lithium precipitation tendency, and significantly improve its low-temperature chargeability and the like. The low-temperature chargeable lithium-ion battery provided by this application can also be used normally in a low-temperature environment, greatly broadening the application range of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and particularly relates to a low-temperature charging lithium-ion battery and a preparation method thereof. Background Art

[0002] At low temperatures, the migration rate of lithium ions in the electrolyte and the diffusion rate in the negative electrode decrease, resulting in an exacerbation of polarization during charging, and the actual amount of electricity charged is much lower than the rated capacity of the battery. In addition, lithium ions that fail to be embedded in the graphite layer of the negative electrode in time will accumulate on the surface of the negative electrode and be reduced to metallic lithium, forming lithium dendrites. These lithium dendrites may pierce the battery separator, causing a short circuit and posing a safety hazard. Therefore, in a low-temperature environment, traditional power batteries for electric vehicles are difficult to meet the usage requirements and cannot ensure the safety performance of electric vehicles.

[0003] Currently, there are two commonly used solutions: one is to install a heating device in the battery module. However, this heating system needs to rapidly and uniformly increase the temperature of the module within a short time so that the battery cells can work normally at a suitable temperature. It not only consumes part of the energy of the battery system, but also the space occupied by the heating device will reduce the energy density of the system, thus having an adverse impact on the driving range of new energy vehicles; the other is to optimize the low-temperature performance of individual battery cells, and the main approach is to select a suitable negative electrode material. However, there are currently few low-temperature-resistant batteries available, and there is an urgent need in this field for a low-temperature-resistant battery that can be normally charged and discharged without an external heating device under low-temperature conditions of -40°C to 0°C. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a low-temperature charging lithium-ion battery and a preparation method thereof. The lithium-ion battery prepared by the low-temperature charging lithium-ion battery provided by the present invention can be normally used in a relatively wide temperature environment, broadening the application field of lithium-ion batteries.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] On the one hand, the present invention provides a low-temperature charging lithium-ion battery, which includes modified graphene and carbon-coated lithium titanate; wherein, the modified graphene is fluorine-doped carbon-coated graphene;

[0007] Furthermore, the negative electrode material of the lithium-ion battery further includes a binder;

[0008] Optionally, the binder includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, and polyimide;

[0009] Furthermore, the doping amount of fluorine is 5wt% - 15wt%;

[0010] Specifically, the fluorine doping amount can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%;

[0011] Furthermore, in the negative electrode material of the lithium ion battery, the mass ratio of the carbon-coated lithium titanate, the modified graphene and the binder is 8:1-3:0.5-1.5;

[0012] Preferably, the mass ratio of the carbon-coated lithium titanate, the modified graphene and the binder is 8:1-3:0.8-1.2;

[0013] More preferably, the mass ratio of the carbon-coated lithium titanate, the modified graphene and the binder is 8:2:1;

[0014] Furthermore, the lithium-ion battery also includes an electrolyte, a positive electrode and a separator;

[0015] Optionally, the electrolyte comprises one or more of dimethyl carbonate, diethyl carbonate and ethylene carbonate;

[0016] Optionally, the separator includes one or more of a PP / PE separator, a polyethylene terephthalate separator, a poly(p-phenylene benzobisoxazole) separator, a polyimide separator, a modified glass fiber membrane, a coated separator, and an electrospinning separator;

[0017] Optionally, the material of the positive electrode includes one or more of lithium sheet, lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium manganese oxide.

[0018] On the other hand, the present invention also provides a method for preparing a low-temperature rechargeable lithium-ion battery, which comprises the following steps:

[0019] (1) Preparation of modified graphene and carbon-coated lithium titanate;

[0020] (2) Preparing a negative electrode slurry: taking the modified graphene, then adding the carbon-coated lithium titanate, mixing evenly, adding a binder, mixing evenly again, adding deionized water, and stirring thoroughly to obtain a uniform negative electrode slurry; wherein the mass ratio of the carbon-coated lithium titanate, the modified graphene, the binder, and the deionized water is 8:1-3:0.5-1.5:85-95;

[0021] (3) Preparing a lithium-ion battery: uniformly coating the negative electrode slurry on a current collector, drying the negative electrode slurry, and obtaining a pole piece, and then using the pole piece as a negative electrode to prepare the lithium-ion battery.

[0022] Preferably, the mass ratio of the carbon-coated lithium titanate, the modified graphene, the binder, and deionized water is 8:1-3:0.8-1.2:86-92;

[0023] More preferably, the mass ratio of the carbon-coated lithium titanate, the modified graphene, the binder, and deionized water is 8:2:1:88-90;

[0024] Further, the mass ratio of the carbon-coated lithium titanate, the modified graphene, the binder, and deionized water can also be 8:2:1:89;

[0025] Further, the specific steps for preparing the modified graphene in step (1) are as follows: Take expanded graphite and disperse it in an ethanol solution, then add carbon source 1. After dispersing evenly, freeze-dry to obtain precursor 1. Then, in an inert atmosphere, heat precursor 1 to 650-800 °C at a heating rate of 4-6 °C / min and hold for 5-7 h to obtain carbon-coated graphene. Then, perform fluorine doping treatment on the carbon-coated graphene to obtain modified graphene;

[0026] Further, the dispersion method in the step of taking expanded graphite and dispersing it in an ethanol solution is ultrasonic dispersion, and the ultrasonic time is 2-4 h. The purpose of ultrasonic dispersion is to convert expanded graphite into graphene;

[0027] Further, the mass ratio of the expanded graphite to the carbon source 1 is 1-3:1;

[0028] Specifically, the mass ratio of the expanded graphite to the carbon source 1 can be 1:1, 2:1, 3:1;

[0029] Further, the carbon source 1 includes one or more of ascorbic acid, citric acid, glucose, and ethylene glycol citrate;

[0030] Further, the specific steps for performing fluorine doping treatment on the carbon-coated graphene include: The specific steps for performing fluorine doping treatment on the carbon-coated graphene include: Put the carbon-coated graphene into a tube furnace. After replacing the reaction furnace with N2, introduce a mixed gas of N2 and F2 with a molar ratio of 4-6:1, and react at a temperature of 180-220 °C for 6-8 h of fluorine-nitrogen mixed gas. Control the system pressure at 0.08-0.12 Mpa, and control the gas flow rate at 0.08-0.12 L / min. After fluorination for 1-3 h, stop introducing the fluorine-nitrogen mixed gas, and change to introduce nitrogen and keep warm for 1 h to complete the preliminary fluorination reaction to obtain modified graphene. Preferably, the fluorine content in the modified graphene is 5 wt%-15 wt%;

[0031] More preferably, the fluorine content in the modified graphene is 8 wt%-12 wt%;

[0032] Further, the specific steps for preparing carbon-coated lithium titanate in step (1) are as follows: Take Li2CO3 and TiO2, mix and blend them evenly. After thorough drying, place them in a muffle furnace and pre-calcine at a temperature of 600 - 700 °C for 10 - 14 h. Subsequently, add them to anhydrous ethanol, mix evenly, filter, and dry. Place the dried sample in a high-temperature furnace at 750 - 850 °C and calcine for 8 - 12 h to obtain lithium titanate. Then, ultrasonically disperse the lithium titanate in deionized water, add carbon source 2, mix evenly, and freeze-dry to obtain precursor 2. Then, in an inert atmosphere, heat precursor 2 at a heating rate of 4 - 6 °C / min to 650 - 800 °C and hold for 5 - 7 h to obtain carbon-coated lithium titanate;

[0033] Further, the molar ratio of Li2CO3 to TiO2 is 0.4 - 0.45:1;

[0034] Specifically, the molar ratio of Li2CO3 to TiO2 can be 0.4:1, 0.41:1, 0.42:1, 0.425:1, 0.43:1, 0.44:1, 0.45:1;

[0035] Further, the mass ratio of lithium titanate to carbon source 2 is 5:2 - 4;

[0036] Specifically, the mass ratio of lithium titanate to carbon source 2 can be 5:2, 5:3, 5:4;

[0037] Further, carbon source 2 includes one or more of ascorbic acid, citric acid, glucose, and ethylene glycol citrate;

[0038] Further, the specific steps for preparing the lithium-ion battery in step (3) are as follows: Uniformly coat the negative electrode slurry on a Cu current collector with a coater, and vacuum dry to obtain the negative electrode. Use a Li sheet as the positive electrode, select LiPF6 as the solute, and an organic solution prepared with a solvent of dimethyl carbonate, diethyl carbonate, and ethylene carbonate with a volume ratio of 1:1:1 as the electrolyte, and a commercial PP / PE separator to prepare the lithium-ion battery.

[0039] On the other hand, the present invention also provides a low-temperature charging lithium-ion battery prepared by the above preparation method.

[0040] Advantages of the present invention:

[0041] The present invention provides a low-temperature charging lithium-ion battery and a preparation method thereof. Among them, the negative electrode material of the low-temperature charging lithium-ion battery includes modified graphene and carbon-coated lithium titanate. After being modified by the modified graphene, the carbon-coated lithium titanate can reduce the defects on the surface of the negative electrode, reduce the risk of aggregation and uneven deposition of lithium ions on the surface of the negative electrode, eliminate the lithium dendrites generated during low-temperature charging, obtain a new negative electrode material with a higher specific capacity, better cycle stability and a lower tendency of lithium precipitation, and significantly improve its low-temperature charging performance, etc. The low-temperature charging lithium-ion battery provided by this application can also be used normally in a low-temperature environment, greatly broadening the application range of lithium-ion batteries. Detailed Embodiments

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a 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 those of ordinary skill in the art without creative work belong to the protection scope of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In the description of this application, it should be understood that "and / or" describes the association relationship of associated objects and means that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one item (piece) below" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one item (piece) among a, b, or c", or, "at least one item (piece) among a, b, and c" can all mean: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively.

[0044] Example 1

[0045] This example provides a low-temperature charging lithium-ion battery and a preparation method thereof. The specific steps are as follows:

[0046] (1) Preparation of modified graphene: Take 10 g of expanded graphite and disperse it in an ethanol solution, then ultrasonicate for 3 h. Next, add 5 g of glucose and continue ultrasonication and stirring for 0.5 h. After freeze-drying, precursor 1 is obtained. Then, under a nitrogen atmosphere, heat precursor 1 to 700 °C at a heating rate of 5 °C / min and hold for 6 h to obtain carbon-coated graphene. Then, place the carbon-coated graphene in a tubular reaction furnace. After replacing the reaction furnace with nitrogen, introduce a mixed gas of nitrogen and fluorine with a molar ratio of 5:1, and react at 200 °C for 7 h. Control the system pressure at 0.1 Mpa and the gas flow rate at 0.1 L / min. After fluorination for 2 h, stop introducing the nitrogen-fluorine mixed gas and change to nitrogen, and keep warm for 1 h to complete the preliminary fluorination reaction to obtain modified graphene, where the fluorine content in the modified graphene is 10 wt%.

[0047] (2) Preparation of carbon-coated lithium titanate: Weigh a total of 10 g of Li2CO3 and TiO2 powders according to the stoichiometric ratio of n(Li / Ti) = 0.85, mix and blend them evenly. After thorough drying, place them in a muffle furnace and pre-burn at 650 °C for 12 h. Subsequently, add them to 5 mL of absolute ethanol and ball-mill for 5 h. Then, filter and dry. Place the dried sample in a high-temperature furnace at 800 °C and calcine for 10 h to obtain the product lithium titanate. Then, ultrasonically disperse 5 g of lithium titanate in deionized water, add 3 g of glucose, continue ultrasonication and stirring for 0.5 h, and obtain precursor 2 after freeze-drying. Then, under a nitrogen atmosphere, heat precursor 2 to 700 °C at a heating rate of 5 °C / min and hold for 6 h to obtain carbon-coated lithium titanate.

[0048] (3) Preparation of the negative electrode material: Take the above-mentioned modified graphene, add carbon-coated lithium titanate, and ball-mill for 4 h. Then, add PAA (polyacrylic acid) and continue ball-milling for 1 h. Then, add a small amount of deionized water as a solvent and stir well for 1 h to obtain a uniform negative electrode slurry; where the mass ratio of carbon-coated lithium titanate, modified graphene, PAA, and deionized water is 8:2:1:89.

[0049] (4) Preparation of the lithium-ion battery: Uniformly coat the negative electrode slurry on a Cu current collector with a coater, and then place it in a vacuum drying oven at 100 °C and dry for 12 h to obtain the negative electrode. Use a Li sheet as the positive electrode, select LiPF6 as the solute, and an organic solution prepared with a volume ratio of 1:1:1 of dimethyl carbonate, diethyl carbonate, and ethylene carbonate as the electrolyte, and a commercial PP / PE separator to prepare the lithium-ion battery.

[0050] Example 2

[0051] This example provides a low-temperature charging lithium-ion battery and its preparation method, and the specific steps are as follows:

[0052] (1) Preparation of modified graphene: 10 g of expanded graphite was dispersed in an ethanol solution and sonicated for 3 h, then 5 g of glucose was added, and then sonication and stirring were continued for 0.5 h. The resulting mixture was freeze-dried to obtain precursor 1. Then, precursor 1 was heated to 700 °C at a heating rate of 5 °C / min in an N2 atmosphere and held for 6 h to obtain carbon-coated graphene. Then, the carbon-coated graphene was placed in a tubular reaction furnace. After replacing the reaction furnace with N2, a mixed gas of N2 and F2 with a molar ratio of 5:1 was introduced, and the reaction was carried out at 200 °C for 7 h with a fluorine-nitrogen mixed gas. The system pressure was controlled at 0.1 Mpa, and the gas flow rate was controlled at 0.1 L / min. After 2 h of fluorination, the introduction of the fluorine-nitrogen mixed gas was stopped, and nitrogen was introduced instead, and the temperature was kept for 1 h to complete the preliminary fluorination reaction to obtain modified graphene, where the fluorine content in the modified graphene was 10 wt%.

[0053] (2) Preparation of carbon-coated lithium titanate: Li2CO3 and TiO2 powders with a total mass of 10 g were weighed according to a stoichiometric ratio of n(Li / Ti) = 0.85, mixed and homogenized, and after being fully dried, they were placed in a muffle furnace and pre-calcined at 650 °C for 12 h. Subsequently, they were added to 5 mL of absolute ethanol and ball-milled for 5 h, then filtered and dried. The dried sample was calcined at 800 °C for 10 h to obtain the product lithium titanate. Then, 5 g of lithium titanate was ultrasonically dispersed in deionized water, then 3 g of glucose was added, and ultrasonic stirring was continued for 0.5 h. The resulting mixture was freeze-dried to obtain precursor 2. Then, precursor 2 was heated to 700 °C at a heating rate of 5 °C / min in an N2 atmosphere and held for 6 h to obtain carbon-coated lithium titanate.

[0054] (3) Preparation of the negative electrode material: The above-mentioned modified graphene was taken, then carbon-coated lithium titanate was added, and ball-milling was carried out for 4 h. Subsequently, PAA was added, and ball-milling was continued for 1 h. Then, a small amount of deionized water was added as a solvent, and after thorough stirring for 1 h, a uniform negative electrode slurry was obtained; where the mass ratio of carbon-coated lithium titanate, modified graphene, PAA, and deionized water was 8:1:1:89.

[0055] (4) Preparation of a lithium-ion battery: The negative electrode slurry was uniformly coated on a Cu current collector using a coater, and then placed in a vacuum drying oven at 100 °C for 12 h to obtain the negative electrode; a Li sheet was used as the positive electrode, LiPF6 was selected as the solute, and an organic solution prepared from dimethyl carbonate, diethyl carbonate, and ethylene carbonate with a volume ratio of 1:1:1 was used as the electrolyte, and a commercial PP / PE separator was used to prepare a lithium-ion battery.

[0056] Example 3

[0057] This example provides a low-temperature charging lithium-ion battery and its preparation method, and the specific steps are as follows:

[0058] (1) Preparation of modified graphene: 10 g of expanded graphite was dispersed in an ethanol solution and ultrasonicated for 3 h, and then 5 g of glucose was added, and then ultrasonic stirring was continued for 0.5 h, and freeze-dried to obtain a precursor 1, and then the precursor 1 was heated to 700 ° C at a heating rate of 5 ° C / min in a N2 atmosphere and maintained for 6 h to obtain carbon-coated graphene, and then the carbon-coated graphene was placed in a tubular reactor, and after the reactor was replaced with N2, a mixed gas of N2 and F2 in a molar ratio of 5:1 was introduced, and a fluorine-nitrogen mixed gas was reacted at a temperature of 200 ° C for 7 h, and the system pressure was controlled at 0.1 MPa and the gas flow rate was controlled at 0.1 L / min. After fluorination for 2 h, the fluorine-nitrogen mixed gas was stopped and replaced with nitrogen, and kept warm for 1 h to complete the preliminary fluorination reaction to obtain modified graphene, wherein the fluorine content in the modified graphene was 10 wt%;

[0059] (2) Preparation of carbon-coated lithium titanate: 10 g of Li2CO3 and TiO2 powders were weighed in a stoichiometric ratio of n(Li / Ti)=0.85, mixed and thoroughly dried, and placed in a muffle furnace for pre-calcination at 650°C for 12 h. The mixture was then added to 5 mL of anhydrous ethanol and ball-milled for 5 h. The mixture was then filtered and dried. The dried sample was calcined at 800°C for 10 h to obtain the product lithium titanate. 5 g of lithium titanate was then ultrasonically dispersed in deionized water. 3 g of glucose was then added and ultrasonic stirring was continued for 0.5 h. The precursor 2 was freeze-dried to obtain the precursor 2. The precursor 2 was then heated to 700°C at a heating rate of 5°C / min in a N2 atmosphere and maintained for 6 h to obtain carbon-coated lithium titanate.

[0060] (3) Preparation of negative electrode material: Take the modified graphene mentioned above, then add carbon-coated lithium titanate, ball mill for 4 hours, then add PAA, continue ball milling for 1 hour, then add a small amount of deionized water as a solvent, stir thoroughly for 1 hour to obtain a uniform negative electrode slurry; wherein, the mass ratio of carbon-coated lithium titanate, modified graphene, PAA and deionized water is 8:3:1:89;

[0061] (4) Preparation of lithium-ion batteries: The negative electrode slurry was evenly coated on the Cu current collector using a coating machine, and then placed in a vacuum drying oven at 100°C for 12 hours to obtain the negative electrode; Li sheet was used as the positive electrode, LiPF6 was selected as the solute, the solvent was an organic solution prepared from dimethyl carbonate, diethyl carbonate and ethylene carbonate in a volume ratio of 1:1:1 as the electrolyte, and the diaphragm was a commercial PP / PE diaphragm to prepare a lithium-ion battery.

[0062] Comparative Example 1

[0063] Compared with Example 1, the negative electrode slurry consists only of modified graphene, PAA and deionized water, and the composition ratio is 2:1:89, that is, the negative electrode material only includes modified graphene and PAA.

[0064] Comparative Example 2

[0065] Compared with Example 1, the negative electrode slurry is only composed of carbon-coated lithium titanate, PAA and deionized water, and the composition ratio is 8:1:89, that is, the negative electrode material only includes carbon-coated lithium titanate and PAA.

[0066] Test and analysis

[0067] The lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-2 were tested for temperature resistance performance, and the electrical performance test method is as follows:

[0068] Charge efficiency: For each example and comparative example, 10 batteries were taken respectively. Using a Neware capacity cabinet, first, the obtained batteries were calibrated for 1C capacity at 25 °C, and the discharge capacity C0 was recorded. Then, they were left standing at -20 °C and -40 °C for 24 h respectively, and charged at a constant current and constant voltage of 1C. The charge capacities C1 of the batteries at -20 °C and -40 °C were recorded respectively. The charge efficiency = C1 / C0 × 100%, and the calculation results were averaged. The results are shown in Table 1.

[0069] Discharge efficiency: For each example and comparative example, 10 batteries were taken respectively. Using a Neware capacity cabinet, first, the obtained batteries were calibrated for 1C capacity at 25 °C, and the charge capacity C2 was recorded. Then, they were left standing at -20 °C and -40 °C for 24 h respectively, and discharged at a constant current and constant voltage of 1C. The discharge capacity C3 was recorded. The 1C discharge efficiency = C3 / C2 × 100%, and the calculation results were averaged. The results are shown in Table 1.

[0070] Table 1

[0071] Charging efficiency (-20°C) Discharging efficiency (-20°C) Charging efficiency (-40°C) Discharging efficiency (-40°C) 1C discharge specific capacity / m·Ah / g 1C charging specific capacity / m·Ah / g Example 1 91.16% 96.28% 81.48% 87.74% 184.6 188.5 Example 2 90.03% 93.45% 80.90% 87.38% 182.2 185.7 Example 3 83.14% 88.69% 76.09% 81.62% 172.4 174.8 Comparative example 1 48.56% 51.76% 30.65% 33.26% 145.6 148.4 Comparative example 2 56.12% 63.83% 34.23% 42.48% 158.5 160.2

[0072] The lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-2 were charged at 1C in environments of -40 °C, -20 °C, and 0 °C respectively, and then the batteries were disassembled respectively. The disassembled batteries were in a fully charged state. After disassembly, it can be observed that the negative electrode sheets of the lithium-ion batteries prepared in Examples 1-3 were in normal state at -20 °C and 0 °C, without lithium deposition phenomenon, but there was a slight lithium deposition phenomenon at -40 °C. For the lithium-ion batteries prepared in Comparative Examples 1-2, although there was no obvious lithium deposition phenomenon during charging at 0 °C, there was a relatively obvious lithium deposition phenomenon at -20 °C. Especially at -40 °C, there was a very obvious lithium deposition phenomenon for both of them.

[0073] As can be seen from the above, the batteries prepared in Examples 1-3 of the present application have a charging efficiency higher than 83.14% and a discharging efficiency higher than 88.69% at -20°C, and a charging efficiency higher than 76.09% and a discharging efficiency higher than 81.62% at -40°C, which are all much higher than those of Comparative Examples 1-2. It can be seen that the lithium-ion batteries prepared by the technical solutions described in the present application all have excellent electrochemical performance, especially low-temperature charging performance.

[0074] The above has introduced in detail a low-temperature charging lithium-ion battery and its preparation method provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the technical solution and its core idea of the present application; those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A low-temperature charging lithium-ion battery, characterized in that, The negative electrode material of the lithium-ion battery is composed of modified graphene, carbon-coated lithium titanate and a binder in a mass ratio of 8:1-3:0.5-1.5; The specific preparation steps of the modified graphene are as follows: taking expanded graphite and dispersing it in an ethanol solution, then adding glucose, and after uniform dispersion, freeze-drying to obtain a precursor 1, and then heating the precursor 1 to 650-800 ° C at a heating rate of 4-6 ° C / min in an inert atmosphere and maintaining it for 5-7 hours to obtain carbon-coated graphene, placing the carbon-coated graphene in a tubular reactor, replacing the reactor with N2, and then introducing a mixed gas of N2 and F2 in a molar ratio of 4-6:1, and reacting the fluorine-nitrogen mixed gas at a temperature of 180-220 ° C for 6-8 hours, controlling the system pressure at 0.08-0.12 MPa, and the gas flow rate at 0.08-0.12 L / min, after fluorination for 1-3 hours, stop introducing the fluorine-nitrogen mixed gas, introduce nitrogen instead, and keep warm for 1 hour to complete the preliminary fluorination reaction to obtain modified graphene, wherein the fluorine content in the modified graphene is 5wt%-15wt%, wherein the mass ratio of the expanded graphite to glucose is 1-3:1; The specific preparation steps of the carbon-coated lithium titanate are: take Li2CO3 and TiO2, mix them evenly, and after sufficient drying, place them in a muffle furnace and pre-calcine them at a temperature of 600-700°C for 10-14 hours, then add them to anhydrous ethanol, mix them evenly, filter and dry them, and place the dried sample at a high temperature of 750-850°C and calcine them for 8-12 hours to obtain lithium titanate, then ultrasonically disperse the lithium titanate in deionized water, and then add glucose, mix them evenly and freeze-dry to obtain precursor 2, and then heat the precursor 2 to 650-800°C at a heating rate of 4-6°C / min in an inert atmosphere and maintain it for 5-7 hours to obtain carbon-coated lithium titanate, wherein the mass ratio of lithium titanate to glucose is 5:2-4.

2. The low-temperature charging lithium-ion battery according to claim 1, wherein The mass ratio of the carbon-coated lithium titanate, the modified graphene and the binder is 8:1-3:0.8-1.

2.

3. The low-temperature charging lithium-ion battery according to claim 1, wherein, The mass ratio of the carbon-coated lithium titanate, the modified graphene and the binder is 8:2:

1.

4. The low-temperature charging lithium-ion battery according to claim 1, wherein The binder includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene and polyimide.

5. The low-temperature charging lithium-ion battery according to claim 1, wherein, The lithium-ion battery also includes an electrolyte, a positive electrode and a separator; the electrolyte includes one or more of dimethyl carbonate, diethyl carbonate and ethylene carbonate; the separator includes one or more of PP / PE separator, polyethylene terephthalate separator, poly(p-phenylene benzobisazole) separator, polyimide separator, modified glass fiber membrane, coated separator and electrospinning separator; the material of the positive electrode includes one or more of lithium sheet, lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide and lithium manganese oxide.

6. A preparation method of a low-temperature charging lithium-ion battery, characterized in that, The following steps are involved: (1) Preparation of modified graphene and carbon-coated lithium titanate; The specific steps of preparing the modified graphene are as follows: taking expanded graphite and dispersing it in an ethanol solution, then adding glucose, and after uniform dispersion, freeze-drying to obtain a precursor 1, and then heating the precursor 1 to 650-800°C at a heating rate of 4-6°C / min under an inert atmosphere and maintaining it for 5-7h to obtain carbon-coated graphene, placing the carbon-coated graphene in a tubular reactor, replacing the reactor with N2, and then introducing a mixed gas of N2 and F2 in a molar ratio of 4-6:1, and reacting the fluorine-nitrogen mixed gas at a temperature of 180-220°C for 6-8h, controlling the system pressure at 0.08-0.12Mpa, and the gas flow rate at 0.08-0.12 L / min, after fluorination for 1-3 hours, stop introducing the fluorine-nitrogen mixed gas, introduce nitrogen instead, and keep warm for 1 hour to complete the preliminary fluorination reaction to obtain modified graphene, wherein the fluorine content in the modified graphene is 5wt%-15wt%, wherein the mass ratio of the expanded graphite to glucose is 1-3:1; The specific steps of preparing carbon-coated lithium titanate are: taking Li2CO3 and TiO2, mixing and mixing, and after fully drying, placing them in a muffle furnace and pre-calcining them at a temperature of 600-700°C for 10-14 hours, then adding them to anhydrous ethanol, mixing them evenly, filtering and drying them, and calcining the dried sample at a high temperature of 750-850°C for 8-12 hours to obtain lithium titanate, and then ultrasonically dispersing the lithium titanate in deionized water, and then adding glucose, mixing them evenly, and freeze-drying to obtain a precursor 2, and then heating the precursor 2 to 650-800°C at a heating rate of 4-6°C / min under an inert atmosphere and maintaining it for 5-7 hours to obtain carbon-coated lithium titanate, wherein the mass ratio of the lithium titanate to the glucose is 5:2-4; (2) Preparing a negative electrode slurry: taking the modified graphene, then adding the carbon-coated lithium titanate, mixing evenly, adding a binder, mixing evenly again, adding deionized water, and stirring thoroughly to obtain a uniform negative electrode slurry; wherein the mass ratio of the carbon-coated lithium titanate, the modified graphene, the binder, and the deionized water is 8:1-3:0.5-1.5:85-95; (3) Preparing a lithium-ion battery: uniformly coating the negative electrode slurry on a current collector, drying the negative electrode slurry, and obtaining a pole piece, and then using the pole piece as a negative electrode to prepare the lithium-ion battery.

7. The preparation method of the low-temperature chargeable lithium-ion battery according to claim 6, wherein, The dispersing method in the step of dispersing the expanded graphite in the ethanol solution is ultrasonic dispersion, and the ultrasonic time is 2-4 hours.

8. The preparation method of the low-temperature charge lithium-ion battery according to claim 6, wherein, The molar ratio of the Li2CO3 to the TiO2 is 0.4-0.45:

1.

9. The preparation method of the low-temperature chargeable lithium-ion battery according to claim 6, wherein The specific steps of preparing the lithium-ion battery in step (3) are: uniformly coating the negative electrode slurry on a Cu current collector with a coating machine, vacuum drying, and obtaining a negative electrode; using a Li sheet as a positive electrode, selecting LiPF6 as a solute, an organic solution prepared by dimethyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:1:1 as a solvent, and a commercial PP / PE separator to prepare the lithium-ion battery.