Negative active material, negative pole piece, lithium ion battery and electric device

Abstract

The invention provides a negative active material, a negative pole piece, a lithium ion battery and an electric device, and belongs to the technical field of batteries. The negative electrode active material has the core-shell structure, the coating layer is arranged on the surface of the graphite core, and through the synergistic effect of molybdenum disulfide in the coating layer and a carbon material except graphite, lithium ions can be rapidly conducted into crystal lattices of graphite for embedding, so that the electron transmission efficiency and the ion diffusion rate of the negative electrode active material are improved, and the service life of the negative electrode active material is prolonged. Therefore, the rate capability and the cycle performance of the negative electrode active material are improved, and the lithium precipitation phenomenon is relieved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode active material, a negative electrode plate, a lithium-ion battery, and an electrical device. Background Art

[0002] Graphite, due to its abundant resources, low price, low charge / discharge voltage plateau, and excellent safety, has become the most widely used negative electrode active material in lithium-ion batteries. With the widespread adoption of lithium-ion batteries in consumer electronics and power batteries, performance and safety requirements for these batteries are increasing. In terms of performance, long battery life and fast charging are the two most important development directions for lithium-ion batteries.

[0003] Graphite has a high degree of crystallization, poor structural stability, and poor compatibility with the electrolyte. In addition, due to the low diffusion rate of lithium ions in its ordered layered structure, graphite produces lithium deposition during high current charging and discharging, resulting in a decrease in the rate performance of lithium-ion batteries and a significant reduction in cycle life. Summary of the Invention

[0004] The purpose of the present disclosure is to overcome the deficiencies of the prior art and to provide a negative electrode active material, a negative electrode plate, a lithium ion battery and an electrical device.

[0005] To achieve the above objectives, the present disclosure adopts the following technical solutions: In a first aspect, a negative electrode active material is provided, the negative electrode active material comprising a core and a coating layer located on at least a portion of the surface of the core, the core comprising graphite, and the coating layer comprising molybdenum disulfide and a carbon material other than graphite;

[0006] The negative electrode active material satisfies 0.2≤ωa / ωb*y≤4.2, wherein y is the OI value of graphite powder, ωa is the mass percentage of molybdenum disulfide in the negative electrode active material, and ωb is the mass percentage of carbon material other than graphite in the negative electrode active material.

[0007] In some embodiments, the ωa satisfies: 0.1%≤ωa≤0.6%.

[0008] In some embodiments, the ωb satisfies: 1%≤ωb≤4%.

[0009] In some embodiments, y satisfies: 4≤y≤7.

[0010] In some embodiments, the particle size of the negative electrode active material satisfies at least one of the following conditions: 4 μm ≤ D10 ≤ 6 μm, 8 μm ≤ D50 ≤ 12 μm, 18 μm ≤ D90 ≤ 30 μm, and 1.00 ≤ (D90-D10) / D50 ≤ 3.25.

[0011] In a second aspect, a method for preparing the negative electrode active material is provided, comprising the following steps:

[0012] S1, dispersing molybdenum disulfide in a liquid coating agent to obtain a molybdenum disulfide liquid coating agent;

[0013] S2, mixing the graphite with the molybdenum disulfide liquid coating agent obtained in step S1 to obtain a precursor;

[0014] S3. Placing the precursor obtained in step S2 in an inert atmosphere for carbonization treatment and cooling to obtain the negative electrode active material.

[0015] In some embodiments, the method for preparing the negative electrode active material satisfies at least one of the following conditions:

[0016] (a) In step S1, the liquid coating agent is a mixture of one or more heterocyclic aromatic hydrocarbons, ketones, hydrocarbons, resins, petroleum asphalt, and coal tar;

[0017] (b) In step S1, the residual carbon value of the liquid coating agent is 20-50%;

[0018] (c) In step S1, the particle size D50 of molybdenum disulfide satisfies: 1 nm <D50<100nm;

[0019] (d) In step S1, the dispersion method is ultrasonic dispersion, the ultrasonic frequency is 30-80 Hz, the power is 1000-3000 W, and the ultrasonic stirring time is 0.5-5 h;

[0020] (e) In step S3, the temperature of the carbonization treatment is 1100-1200° C., the heating time is 9-15 hours, the holding time is 5-8 hours, and the cooling time is 6-12 hours.

[0021] In a third aspect, a negative electrode plate is provided, which includes a negative electrode collector and a negative electrode active layer arranged on at least one side of the surface of the negative electrode collector, and the negative electrode active layer includes the negative electrode active material or the negative electrode active material prepared by the preparation method of the negative electrode active material.

[0022] In a fourth aspect, a lithium-ion battery is provided, comprising a positive electrode plate, the negative electrode plate, an electrode liquid and a separator; the electrolyte comprises fluoroethylene carbonate;

[0023] The lithium-ion battery satisfies the following relationship: 10≤ωc / ωa≤100, wherein ωc is the mass percentage of fluoroethylene carbonate in the electrolyte.

[0024] In some embodiments, the ωc satisfies: 6%≤ωc≤10%.

[0025] In a fifth aspect, an electrical device is provided, comprising the lithium-ion battery.

[0026] Compared with the prior art, the beneficial effects of the present disclosure are as follows: In the present application, a coating layer is provided on the surface of the graphite core. Through the synergistic effect of molybdenum disulfide in the coating layer and the carbon material other than graphite, lithium ions are quickly conducted into the graphite lattice for embedding, thereby improving the electron transfer efficiency and ion diffusion rate of the negative electrode active material, thereby improving the rate performance and cycle performance of the negative electrode active material, and slowing down the lithium desorption phenomenon. Specifically, molybdenum disulfide has a two-dimensional layered structure with a large interlayer spacing (0.62nm), which can improve the ionic conductivity and cycle stability of the negative electrode active material. The carbon material other than graphite improves the dispersion uniformity of molybdenum disulfide on the graphite surface, effectively preventing the agglomeration of molybdenum disulfide, and further improving the rate performance and cycle performance of the negative electrode active material. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present disclosure, a more comprehensive description will be given below. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present disclosure.

[0028] As used herein:

[0029] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0030] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0031] When amount, concentration or other value or parameter are represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope " 1-5 ", described scope should be interpreted as including scope " 1-4 ", " 1-3 ", " 1-2 ", " 1-2 and 4-5 ", " 1-3 and 5 " etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0032] In these examples, parts and percentages are by mass unless otherwise indicated.

[0033] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0034] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0035] In a first aspect, a negative electrode active material is provided, comprising a core and a coating layer located on at least a portion of a surface of the core, wherein the core comprises graphite, and the coating layer comprises molybdenum disulfide and a carbon material other than graphite;

[0036] The negative electrode active material satisfies 0.2≤ωa / ωb*y≤4.2, wherein y is the OI value of graphite powder, ωa is the mass percentage of molybdenum disulfide in the negative electrode active material, and ωb is the mass percentage of carbon material other than graphite in the negative electrode active material.

[0037] In the present application, a coating layer is provided on the surface of the graphite core. Through the synergistic effect of molybdenum disulfide in the coating layer and carbon materials other than graphite, lithium ions are quickly conducted into the graphite lattice for embedding, thereby improving the electron transfer efficiency and ion diffusion rate of the negative electrode active material, thereby improving the rate performance and cycle performance of the negative electrode active material, and slowing down the lithium desorption phenomenon. Specifically, molybdenum disulfide has a two-dimensional layered structure with a large interlayer spacing (0.62nm), which can improve the ionic conductivity and cycle stability of the negative electrode active material. The carbon material other than graphite improves the dispersion uniformity of molybdenum disulfide on the graphite surface, effectively preventing the agglomeration of molybdenum disulfide, and further improving the rate performance and cycle performance of the negative electrode active material.

[0038] In some embodiments, the ωa satisfies: 0.1%≤ωa≤0.6%; specifically, the ωa can be a value in the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any two thereof.

[0039] In the present application, by ensuring that the mass percentage of molybdenum disulfide in the negative electrode active material is within the above-mentioned range, the ionic conductivity and mechanical strength of the coating layer are improved, as well as the uniformity of the dispersion of molybdenum disulfide on the graphite surface, thereby improving the rate performance and cycle performance of the negative electrode active material. If the mass percentage of molybdenum disulfide in the negative electrode active material is too low, the ionic conductivity of the coating layer will decrease, thereby reducing the rate performance of the negative electrode active material. If the mass percentage of molybdenum disulfide in the negative electrode active material is too high, the mechanical strength of the coating layer will be poor, and molybdenum disulfide will easily agglomerate on the graphite surface, thereby reducing the rate performance and cycle performance of the negative electrode active material.

[0040] In this application, the mass percentage of molybdenum disulfide in the negative electrode active material is tested using conventional methods in the art; as an example, the testing method can be: the lithium-ion battery is completely discharged, disassembled, the negative electrode plate is removed, and it is soaked in DMC (ethylene carbonate) for 30 minutes, then washed with DMC and acetone to remove the residual electrolyte and the SEI film on the negative electrode surface, placed in an 80°C oven for 12 hours, and the active material of the negative electrode plate is scraped off with a scraper. It is placed in an argon atmosphere tube furnace for 400°C for 4 hours to remove the binder on the surface of the negative electrode active material to obtain the negative electrode active material. The negative electrode active material is placed in a 1 mol / L nitric acid solution for 30 minutes to dissolve the molybdenum disulfide coated on the surface of the negative electrode active material. The metal element content in the solution is tested using an inductively coupled plasma spectrometer (ICP-OES (PE Avio 200)) to obtain the molybdenum disulfide content in the negative electrode active material.

[0041] In some embodiments, the ωb satisfies: 1%≤ωb≤4%; specifically, the ωb may be a value within a range of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any two thereof.

[0042] In the present application, by ensuring that the mass percentage of carbon materials other than graphite in the negative electrode active material is within the above-mentioned range, the uniformity of the dispersion of molybdenum disulfide on the graphite surface is improved, while the reaction between the negative electrode active material and the electrolyte is reduced, thereby improving the rate performance and cycle performance of the negative electrode active material. If the mass percentage of carbon materials other than graphite in the negative electrode active material is too low, molybdenum disulfide tends to agglomerate on the graphite surface, resulting in reduced rate performance and cycle performance of the negative electrode active material. If the mass percentage of carbon materials other than graphite in the negative electrode active material is too high, the reaction between the negative electrode active material and the electrolyte is intensified, resulting in reduced cycle performance of the negative electrode active material.

[0043] In this application, the mass percentage of carbon materials other than graphite in the negative electrode active material is measured using conventional methods in the art. As an example, the testing method can be: fully discharge the lithium-ion battery, disassemble it, remove the negative electrode plate, soak it in DMC (ethylene carbonate) for 30 minutes, then rinse it with DMC and acetone to remove the residual electrolyte and the SEI film on the negative electrode surface, place it in an 80°C oven to dry for 12 hours, scrape the active material from the negative electrode plate with a scraper, and heat treat it in an argon atmosphere tube furnace at 400°C for 4 hours to remove the binder on the surface of the negative electrode active material to obtain the negative electrode active material. The amorphous carbon content can be measured by thermogravimetric analysis (TGA) according to standard DB35 / T1558-2016.

[0044] In some embodiments, y satisfies: 4≤y≤7; specifically, it can be a range value between one of 4, 4.2, 4.5, 4.7, 5, 5.3, 5.5, 5.8, 6, 6.3, 6.5, 6.8, 7, or any two thereof.

[0045] In the present application, the graphite powder OI value is within the above range, which improves the structural stability of the graphite and shortens the diffusion path of lithium ions between graphite layers, thereby improving the rate performance and cycle performance of the negative electrode active material. If the graphite powder OI value is too low, the disorder of the graphite crystal arrangement increases, and during the charge and discharge process, the graphite is prone to structural changes and collapse, resulting in poor cycle stability of the negative electrode active material. If the graphite powder OI value is too high, the order of the graphite crystal arrangement increases, the diffusion path of lithium ions between graphite layers becomes longer, and the diffusion resistance increases, resulting in a decrease in the rate performance of the negative electrode active material.

[0046] In this application, the test method for the OI value of graphite powder is well known in the art. As an example, the test method can be: disassembling the lithium-ion battery, removing the negative electrode plate, cleaning and drying, scraping the negative electrode active material on the negative electrode active layer, and testing by X-ray diffraction (XRD). Since the morphology of graphite particles is different from the morphology of the additives (binders, conductive agents, etc.), the graphite powder OI value test can be performed based on the national standard GB / T 24533-2019 to obtain an X-ray diffraction spectrum; the graphite powder OI value is calculated according to the formula OI=C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction spectrum, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction spectrum.

[0047] In some embodiments, artificial graphite having an OI value and gram capacity within the above-mentioned ranges of this application can be selected from existing commercially available artificial graphites, or artificial graphite having the above-mentioned OI value and gram capacity can be artificially prepared. For example, artificial graphite having the above-mentioned OI value can be obtained by adjusting the raw materials of the artificial graphite (such as petroleum green coke, needle green coke, calcined petroleum coke, calcined needle coke, metallurgical coke, pitch coke, etc.) and the amount of binder added. For example, when needle green coke is used, the greater the amount of binder pitch added during granulation, the lower the OI value of the resulting graphite; when no binder pitch is added to the calcined petroleum coke or the amount of binder pitch added is low, the resulting graphite has a higher OI value.

[0048] In some embodiments, the particle size of the negative electrode active material satisfies at least one of the following conditions: 4 μm ≤ D10 ≤ 6 μm, 8 μm ≤ D50 ≤ 12 μm, 18 μm ≤ D90 ≤ 30 μm, 1.00 ≤ (D90-D10) / D50 ≤ 3.25; for example, the D10 can be 4 μm, 4.2 μm, 4.5 μm, 4.7 μm, 5 μm, 5.3 μm, 5.5 μm, 5.8 μm, 6μm or a range value between one or any two of them; for example, the D50 can be 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm or a range value between any two of them; for example, the D90 can be 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm or a range value between any two of them.

[0049] In the present application, when the particle size of the negative electrode active material meets the above conditions, the negative electrode active material has good structural stability, which is beneficial to improving the cycle stability of the lithium ion battery.

[0050] It should be noted that, in the present application, the D10, D50 and D90 are the particle sizes of the negative electrode active material measured by volume particle size distribution, wherein D10 is the particle size corresponding to when the volume cumulative percentage of the material reaches 10%, the D50 is the particle size corresponding to when the volume cumulative percentage of the material reaches 50%, and the D90 is the particle size corresponding to when the volume cumulative percentage of the material reaches 90%.

[0051] It should be noted that in this application, the test method for the particle size of the negative electrode active material is well known in the art. As an example, the test method can be: the lithium-ion battery is completely discharged, disassembled, the negative electrode plate is taken out, soaked in DMC (ethylene carbonate) for 30 minutes, and then washed with DMC and acetone to remove the residual electrolyte and the SEI film on the surface of the negative electrode, placed in an 80°C oven to dry for 12 hours, and the active material of the negative electrode plate is scraped off with a scraper, placed in an argon atmosphere tube furnace at 400°C for 4 hours to remove the binder on the surface of the negative electrode active material to obtain the negative electrode active material. The particle size determination method can refer to GB / T19077-2016 / ISO 13320:2009 and is measured using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer.

[0052] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, and microcrystalline graphite.

[0053] In some embodiments, the graphite includes at least one of primary particles and secondary particles.

[0054] In some embodiments, the carbon material other than graphite includes at least one of soft carbon and hard carbon.

[0055] In a second aspect, a method for preparing the negative electrode active material is provided, comprising the following steps:

[0056] S1, dispersing molybdenum disulfide in a liquid coating agent to obtain a molybdenum disulfide liquid coating agent;

[0057] S2, mixing the graphite with the molybdenum disulfide liquid coating agent obtained in step S1 to obtain a precursor;

[0058] S3. Placing the precursor obtained in step S2 in an inert atmosphere for carbonization treatment and cooling to obtain the negative electrode active material.

[0059] Specifically, the present application adjusts the addition amounts of molybdenum disulfide and the liquid coating agent to obtain negative electrode active materials with different ωa and ωb values.

[0060] In some embodiments, in step S1, the liquid coating agent is a mixture of one or more of ketones, hydrocarbons, liquid resins, petroleum asphalt, and coal asphalt.

[0061] Exemplarily, ketones refer to compounds in which a carbonyl group is connected to two hydrocarbon groups, including at least one of monoketone, diketone, and polyketone.

[0062] Exemplary monoketones include acetone, butanone, and acetophenone.

[0063] Exemplary diketones include butanedione, hexanedione, and pentanedione.

[0064] Illustratively, the polyketone includes compounds having 4 or more carbon atoms and 3 or more carbonyl groups.

[0065] Exemplarily, hydrocarbons refer to compounds composed of carbon atoms and hydrogen atoms, including at least one of alkanes, cycloalkanes, alkenes, alkynes, and aromatic hydrocarbons.

[0066] Exemplary alkanes include methane, ethane, propane, butane, pentane, and hexane.

[0067] Exemplary cycloalkanes include cyclopropane, cyclobutane, cyclopentane, and cyclohexane.

[0068] Exemplary olefins include ethylene, propylene, butene, and cycloolefins.

[0069] Illustratively, the alkynes include acetylene, propyne, butyne, and polyalkynes.

[0070] Exemplarily, the aromatic hydrocarbons include benzene, toluene, xylene, and polycyclic aromatic hydrocarbons.

[0071] Exemplarily, the liquid resin refers to a resin that is liquid at 25° C., including at least one of epoxy resin, polyurethane resin, acrylic resin, polyester resin, and phenolic resin.

[0072] In some embodiments, in step S1, the residual carbon value of the liquid coating agent is 20-50%; for example, it can be 20%, 22%, 25%, 27%, 30%, 35%, 40%, 43%, 45%, 48%, 50% or any range value between two of them.

[0073] Specifically, in step S1, the mass of the liquid-phase coating agent = the mass percentage of the carbon material excluding graphite in the negative electrode active material / the residual carbon value of the liquid-phase coating agent.

[0074] In some embodiments, in step S1, the particle size D50 of molybdenum disulfide satisfies: 1 nm < D50 < 100 nm. For example, it can be 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 95 nm, or a range value between any two of them.

[0075] In some embodiments, in step S1, the dispersion method is ultrasonic dispersion. The ultrasonic frequency is 30 - 80 Hz. For example, it can be 30 Hz, 40 Hz, 50 Hz, 60 Hz, 70 Hz, 80 Hz, or a range value between any two of them; the power is 1000 - 3000 W. For example, it can be 1000 W, 1200 W, 1500 W, 1700 W, 2000 W, 2300 W, 2500 W, 2800 W, 3000 W, or a range value between any two of them; the ultrasonic dispersion time is 0.5 - 5 h. For example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, or a range value between any two of them.

[0076] Ultrasonic dispersion can improve the dispersion of molybdenum disulfide in the liquid-phase coating agent. During the mixing process with graphite, molybdenum disulfide is evenly dispersed on the surface of graphite along with the liquid-phase coating agent, improving the rate performance and cycle stability of the anode active material. <000,0174>

[0077] In some embodiments, in step S2, the mixing method of graphite and the molybdenum disulfide liquid-phase coating agent is a conventional mixing method in the art. As an example, the mixing method is mixing with a fusion machine.

[0078] In some embodiments, in step S3, the temperature of the carbonization treatment is 1100 - 1200 °C. For example, it can be 1100 °C, 1120 °C, 1140 °C, 1160 °C, 1180 °C, 1200 °C, or a range value between any two of them; the heating-up time is 9 - 15 h. For example, it can be 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, or a range value between any two of them; the heat preservation time is 5 - 8 h. For example, it can be 5 h, 6 h, 7 h, 8 h, or a range value between any two of them; the cooling time is 6 - 12 h. For example, it can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or a range value between any two of them.

[0079] In this application, when the parameters of the carbonization treatment are within the above ranges, the liquid-phase coating agent can be carbonized to form a carbon layer structure, and at the same time, molybdenum disulfide is evenly distributed in the carbon layer.

[0080] In some embodiments, the inert atmosphere is at least one of nitrogen and argon.

[0081] In a third aspect, a negative electrode plate is provided, which includes a negative electrode collector and a negative electrode active layer arranged on at least one side of the surface of the negative electrode collector, and the negative electrode active layer includes the negative electrode active material or the negative electrode active material prepared by the preparation method of the negative electrode active material.

[0082] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0083] In some embodiments, the negative electrode active layer may further include other negative electrode active materials for lithium ion batteries that are well known in the art. As an example, other negative electrode active materials may include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for lithium ion batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0084] In some embodiments, the negative electrode active layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0085] In some embodiments, the negative electrode active layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the negative electrode active layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0087] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0088] In a fourth aspect, a lithium-ion battery is provided, comprising a positive electrode sheet, the negative electrode sheet, an electrolyte and a separator; the electrolyte comprises fluoroethylene carbonate;

[0089] The lithium-ion battery satisfies: 10≤ωc / ωa≤100, wherein ωc is the mass percentage of fluoroethylene carbonate in the electrolyte; ωc / ωa can be, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or a range value between any two thereof.

[0090] In the present application, the electrolyte includes fluoroethylene carbonate, which can form a stable lithium fluoride-rich SEI film on the surface of molybdenum disulfide, effectively reducing further decomposition of the electrolyte and side reactions of the negative electrode active material, and further improving the electrochemical performance of the lithium-ion battery.

[0091] In some embodiments, ωc satisfies the following: 6% ≤ ωc ≤ 10%, and may be, for example, but not limited to, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. A mass percentage of fluoroethylene carbonate in the electrolyte within the above range is beneficial for improving the cycling performance of the lithium-ion battery.

[0092] In this application, the mass percentage of fluoroethylene carbonate in the electrolyte is measured using conventional methods in the art. As an example, the testing method is: the composition of the electrolyte can be measured using equipment and methods known in the art, such as liquid chromatography, gas chromatography, ion chromatography, liquid-phase nuclear magnetic resonance, etc. For example, the qualitative and quantitative analysis of organic components in the electrolyte can be performed using gas chromatography with reference to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents."

[0093] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one side of a surface of the positive electrode current collector.

[0094] As an example, the positive electrode current collector may be a metal foil, a conductive polymer material, a carbon material or a composite current collector. For example, as the metal foil, a pure metal, an alloy, a surface-treated metal may be used, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0095] In some embodiments, the positive electrode active layer includes a positive electrode active material, a binder, and a conductive agent.

[0096] In some embodiments, the positive electrode active material may be a positive electrode active material for lithium ion batteries that is well known in the art. The positive electrode active material may include at least one of the following materials: lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for lithium ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium-containing phosphates may include but are not limited to at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Examples of lithium transition metal oxides may include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, also known as NCM333, LiNi 0.5 Co 0.2 Mn 0.3 O2, also known as NCM523, LiNi 0.5 Co 0.25 Mn 0.25 O2, also referred to as NCM211, LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM622, LiNi 0.8 Co 0.1 Mn 0.1 O2, also referred to as NCM811), lithium nickel cobalt aluminum oxide (LiNi 0.85 Co0.05 Al 0.05 O2) and at least one of its modified compounds. The modified compound refers to a substance obtained by modifying the above substances by means of doping or coating.

[0097] As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0098] The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the mass ratio of the positive electrode active material, the binder and the conductive agent is (95 to 98): (1 to 3): (1 to 3), wherein the content of the positive electrode active material (95 to 98) can be, for example, 95, 95.5, 96, 96.5, 97 or 98 or a range value between any two of them, the content of the binder (1 to 3) can be, for example, 1, 1.5, 2, 2.5 or 3, etc., and the content of the conductive agent (1 to 3) can be, for example, 1, 1.5, 2, 2.5 or 3 or a range value between any two of them.

[0100] The present application does not limit the preparation method of the positive electrode sheet. For example, the positive electrode active material, the conductive agent and the binder are added to the solvent in a certain ratio and stirred, and the fluidity of the slurry is adjusted to obtain the positive electrode slurry. The prepared positive electrode slurry is then coated on the positive electrode collector, dried and rolled to obtain the positive electrode sheet.

[0101] In some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent.

[0102] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0103] In some embodiments, the non-aqueous solvent includes any one of a carbonate compound, a carboxylate compound, and an ether compound, or a combination of at least two of them, for example, a combination of a carbonate compound and a carboxylate compound, a combination of a carboxylate compound and an ether compound, or a combination of a carbonate compound, a carboxylate compound, and an ether compound, etc.

[0104] In some embodiments, the carbonate compound includes any one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC) or ethylene carbonate (EC), or a combination of at least two thereof, for example, a combination of diethyl carbonate and dimethyl carbonate, a combination of dimethyl carbonate and dipropyl carbonate, a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, or a combination of diethyl carbonate, dimethyl carbonate, dipropyl carbonate and ethylene carbonate, etc.

[0105] In some embodiments, the carboxylate compound includes any one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate or methyl formate, or a combination of at least two thereof, such as a combination of methyl acetate and ethyl acetate, a combination of ethyl acetate and methyl propionate, a combination of ethyl propionate and methyl formate, and the like.

[0106] In some embodiments, the ether compound includes any one of dibutyl ether, tetraglyme, ethoxymethoxyethane or tetrahydrofuran, or a combination of at least two thereof, for example, a combination of dibutyl ether and tetraglyme, a combination of tetraglyme and ethoxymethoxyethane, or a combination of tetraglyme, ethoxymethoxyethane and tetrahydrofuran, etc.

[0107] In some embodiments, the diaphragm includes any one of polyethylene, polypropylene, polyvinylidene fluoride or polyimide, or a combination of at least two thereof, for example, it can be a diaphragm of polyethylene and polypropylene, a diaphragm of polypropylene and polyvinylidene fluoride, or a diaphragm of polyethylene, polypropylene, polyvinylidene fluoride and polyimide, etc.

[0108] In this application, the method of assembling a lithium-ion battery using the negative electrode sheet is prior art, and those skilled in the art can refer to the methods disclosed in the prior art for assembly. For example, the positive electrode sheet, separator, and negative electrode sheet are sequentially wound or stacked to form a battery cell, which is then placed in a battery case, and an electrolyte is injected, followed by formation and packaging to obtain a lithium-ion battery.

[0109] In a fifth aspect of the present application, an electrical device is provided, comprising the lithium-ion battery.

[0110] For example, the electronic device described in the present application may be a mobile computer, a portable phone, a memory card, an LCD TV, a car, a motorcycle, a motor, a clock, a camera, etc.

[0111] Example 1

[0112] (1) Preparation of negative electrode active materials

[0113] S1, molybdenum disulfide with a particle size D50 of 30 nm and a liquid phenolic resin with a residual carbon rate of 20% were added to an ultrasonic reactor in a mass ratio of 0.2:10, and ultrasonic stirring was performed for 2 h under the conditions of an ultrasonic frequency of 50 Hz and a power of 1500 W to obtain a molybdenum disulfide liquid phase coating agent;

[0114] S2. The molybdenum disulfide liquid coating agent obtained in step S1 and the artificial graphite with an OI value of 4.29 were added to a fusion machine in a mass ratio of 10.2:97.8, and mixed at a temperature of 25° C. and a rotation speed of 300 r / min for 60 min to obtain a precursor;

[0115] S3. Place the precursor obtained in step S2 in a carbonization furnace, perform carbonization treatment in a nitrogen atmosphere, cool, and sieve to obtain a negative electrode active material, wherein the carbonization treatment temperature is 1100°C, the heating time is 10 hours, the holding time is 2 hours, and the cooling time is 8 hours; the particle size of the negative electrode active material satisfies: D10 = 5.1 μm, D50 = 9.5 μm, D90 = 22.4 μm, (D90-D10) / D50 = 1.82.

[0116] (2) Preparation of negative electrode sheet

[0117] The negative electrode active material, SuperP, sodium carboxymethyl cellulose, and styrene-butadiene rubber latex were mixed in a mass ratio of 97:0.5:0.7:0.8 to prepare a negative electrode slurry, which was coated on a copper current collector and then cold-pressed and slit to obtain a negative electrode sheet.

[0118] (3) Preparation of positive electrode sheet

[0119] Lithium cobalt oxide positive electrode material, acetylene black, carbon nanotubes, and polyvinylidene fluoride are mixed in an N-methylpyrrolidone solvent system in a weight ratio of 97.8:0.6:0.4:1.2 to prepare a positive electrode slurry, which is coated on an aluminum current collector and then cold-pressed and slit to obtain positive electrode sheets.

[0120] (4) Preparation of electrolyte

[0121] At room temperature, in an argon-filled glove box (H2O<1ppm, O2<1ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a volume ratio of 1:1:4:4 and heated to 400 ℃. Molecular sieves are used to remove water to obtain a mixed solvent;

[0122] Adding lithium salt LiPF6 to the mixed solvent and mixing evenly, then adding fluoroethylene carbonate (FEC) and mixing evenly to obtain an electrolyte;

[0123] The electrolyte includes the following components in percentage by mass: 8% fluoroethylene carbonate, 15% LiPF6 and 77% mixed solvent.

[0124] (5) Preparation of lithium-ion batteries

[0125] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets. The bare battery cell is obtained by winding, hot pressing and shaping, and the tabs are welded. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The prepared electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of the lithium-ion soft-pack battery; wherein the separator is a polyethylene (PE) porous polymer film.

[0126] The remaining examples and comparative examples refer to Example 1, with the differences shown in Table 1.

[0127] Table 1

[0128]

[0129]

[0130] Test Case

[0131] (1) XRD: X-ray diffraction (XRD) was performed on the negative electrode sheets obtained in the examples and comparative examples at 25±2°C. The test conditions were: Cu Kα radiation, an operating current of 250 mA, continuous scanning, an operating voltage of 40 kV, a scanning range of 15-70° (2θ), a step size of 0.02, and a scanning speed of 10°·min-1.

[0132] (2) Gram capacity: At 25±2°C, five lithium-ion batteries each obtained from the example and comparative example were charged at a constant current rate of 0.1C until the voltage reached 4.3V. They were further charged at a constant voltage of 4.3V until the current was less than 0.05C, bringing them to a fully charged state of 4.3V. They were then discharged at a constant current rate of 0.1C until the voltage reached 3.0V. The average value was taken and the recorded data is shown in Table 2.

[0133] (3) Rate performance: The lithium-ion batteries obtained in the examples and comparative examples were placed at 25°C for 2 hours and then charged and discharged, wherein the charging rate was 2.0-4.0C, and the test was performed at intervals of 0.5C, i.e., charging was performed at 2.0C, 2.5C, 3.0C, and 4.0C, and discharging was performed at 1C. After 50 weeks of testing, each group of batteries was fully charged and disassembled to observe the severity of lithium deposition on the negative electrode surface. The ratio α of the lithium deposition area of ​​the negative electrode sheet to the area of ​​the negative electrode active layer was measured. α>20% was defined as severe lithium deposition (D grade), 10%<α≤20% was defined as moderate lithium deposition (C grade), 5%<α≤10% was defined as slight lithium deposition (B grade), and α≤5% was defined as no lithium deposition (A grade).

[0134] (4) Cycling Performance: Five lithium-ion batteries each obtained in the Examples and Comparative Examples were subjected to charge-discharge cycling tests at a charge-discharge rate of 1C / 1C within the range of 3-4.3V at 25±2°C. The first-cycle discharge capacity and the discharge capacity after 600 cycles were recorded. The capacity retention rate after 600 cycles was calculated as follows: discharge capacity after 600 cycles / discharge capacity after the first cycle * 600%. The average value was taken. The recorded data are shown in Table 2.

[0135] The test results are shown in Table 2.

[0136] Table 2

[0137]

[0138]

[0139] It can be seen from the experimental data in Table 1 that in the present application, a coating layer is provided on the surface of the graphite core. Through the synergistic effect of molybdenum disulfide in the coating layer and carbon materials other than graphite, lithium ions are quickly conducted into the graphite lattice for embedding, thereby improving the electron transfer efficiency and ion diffusion rate of the negative electrode active material, thereby improving the rate performance and cycle performance of the negative electrode active material, and slowing down the lithium desorption phenomenon.

[0140] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A negative electrode active material, characterized in that The negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes molybdenum disulfide and a carbon material other than graphite; The negative electrode active material satisfies 0.2≤ωa / ωb*y≤4.2, wherein y is the OI value of graphite powder, ωa is the mass percentage of molybdenum disulfide in the negative electrode active material, and ωb is the mass percentage of carbon material other than graphite in the negative electrode active material.

2. The negative electrode active material according to claim 1, wherein The ωa satisfies: 0.1%≤ωa≤0.6%.

3. The negative electrode active material according to claim 1, wherein The ωb satisfies: 1%≤ωb≤4%.

4. The negative electrode active material according to claim 1, wherein The y satisfies: 4≤y≤7.

5. The negative electrode active material according to claim 1, wherein The particle size of the negative electrode active material satisfies at least one of the following conditions: 4 μm≤D10≤6 μm, 8 μm≤D50≤12 μm, 18 μm≤D90≤30 μm, and 1.00≤(D90-D10) / D50≤3.

25.

6. A method for preparing a negative electrode active material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, dispersing molybdenum disulfide in a liquid coating agent to obtain a molybdenum disulfide liquid coating agent; S2, mixing the graphite with the molybdenum disulfide liquid coating agent obtained in step S1 to obtain a precursor; S3. Placing the precursor obtained in step S2 in an inert atmosphere for carbonization treatment and cooling to obtain the negative electrode active material.

7. The method for preparing the negative electrode active material according to claim 6, wherein: At least one of the following conditions is met: (a) In step S1, the liquid coating agent is a mixture of one or more heterocyclic aromatic hydrocarbons, ketones, hydrocarbons, resins, petroleum asphalt, and coal tar; (b) In step S1, the residual carbon value of the liquid coating agent is 20-50%; (c) In step S1, the particle size D50 of molybdenum disulfide satisfies: 1 nm <D50<100nm; (d) In step S1, the dispersion method is ultrasonic dispersion, the ultrasonic frequency is 30-80 Hz, the power is 1000-3000 W, and the ultrasonic stirring time is 0.5-5 h; (e) In step S3, the temperature of the carbonization treatment is 1100-1200° C., the heating time is 9-15 hours, the holding time is 5-8 hours, and the cooling time is 6-12 hours.

8. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode active layer arranged on at least one side of the surface of the negative electrode current collector, and the negative electrode active layer includes the negative electrode active material according to any one of claims 1 to 5 or the negative electrode active material prepared by the preparation method of the negative electrode active material according to any one of claims 6 to 7.

9. A lithium-ion battery, characterized in that: The electrolyte comprises a positive electrode sheet, a negative electrode sheet as claimed in claim 8, an electrode liquid and a separator; the electrolyte comprises fluoroethylene carbonate; The lithium-ion battery satisfies the following relationship: 10≤ωc / ωa≤100, wherein ωc is the mass percentage of fluoroethylene carbonate in the electrolyte.

10. The lithium-ion battery according to claim 9, wherein The ωc satisfies: 6%≤ωc≤10%.

11. An electrical device, characterized in that: Comprising the lithium ion battery according to claim 9 or 10.

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