A negative electrode active material, a method for manufacturing the same, a negative electrode sheet, a battery, a battery pack, and an electric device

Abstract

The application provides a negative electrode active material and a preparation method thereof, a negative electrode sheet, a battery, a battery pack, and an electric device. The negative electrode active material comprises graphite, N-doped graphene, and an iodine-containing additive. At least part of the iodine-containing additive is adsorbed on at least part of the surface of the N-doped graphene. The N-doped graphene comprises a structure shown in formula 1. The negative electrode active material can be activated and oxidized to lithium ions which can be embedded and removed again after lithium ions embedded in the inside of the negative electrode material are precipitated as metal lithium, so that the effect of inhibiting lithium precipitation is achieved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode active material and its preparation method, a negative electrode sheet, a battery, a battery pack, and electrical equipment. Background Technology

[0002] In recent years, with the rapid expansion of the energy storage industry, the market has put forward higher requirements for energy storage lithium-ion batteries, which can be summarized as "long life, high safety, and low cost". Among them, "low cost" is related to "long cycle life", that is, extending the cycle life of the battery cell will effectively reduce the cost per kilowatt-hour of the battery cell.

[0003] There are many factors that affect the cycle life of a battery cell, including lithium plating, electrolyte consumption, and the stability of the SEI film. In particular, lithium plating is one of the main reasons for the accelerated degradation of battery cell life, and it will accelerate the consumption of electrolyte, thereby further affecting the degradation of battery cell capacity.

[0004] Lithium plating mainly refers to the process by which lithium ions gain electrons on the surface of the negative electrode and are reduced to lithium metal. Currently, porous electrode design is mainly used to slow down lithium plating, such as optimizing the pore distribution of the electrode by starting with particle size distribution. However, this method has high requirements for raw materials and presents certain difficulties in actual production. Summary of the Invention

[0005] This invention provides a negative electrode active material that oxidizes "dead lithium" and regenerates lithium ions, thereby suppressing lithium plating and reducing the self-discharge rate of the battery cell, thus improving the cycle life of the battery cell at low temperature or high rate.

[0006] This invention provides a method for preparing a negative electrode active material. The method is simple to operate and can successfully prepare the aforementioned negative electrode active material.

[0007] The present invention also provides a negative electrode sheet, which, since it includes the above-mentioned negative electrode active material, can effectively suppress lithium plating and improve the cycle stability of the battery cell.

[0008] The present invention also provides a battery comprising the above-mentioned negative electrode, which has better rate performance and longer cycle life.

[0009] The present invention also provides a battery pack including the above-mentioned battery, which has the advantages of good rate performance and long cycle life.

[0010] The present invention also provides an electrical device, which has a relatively long service life because it includes the aforementioned battery or battery pack.

[0011] In detail, in a first aspect, the present invention provides a negative electrode active material comprising graphite, N-doped graphene, and an iodine-containing additive, wherein at least a portion of the iodine-containing additive is adsorbed onto at least a portion of the surface of the N-doped graphene; wherein the N-doped graphene comprises the structure shown in Formula 1:

[0012]

[0013] R1, R2, R3, R4, R5, R6, R7, and R8 are each independently H, a C1-C10 alkyl group, an F-substituted C1-C10 alkyl group, or F.

[0014] Furthermore, the mass ratio of the N-doped graphene, graphite, and iodine-containing additive is 1-5:100:0.1-1.

[0015] Furthermore, the iodine-containing additive includes at least one of elemental iodine, alkali metal compounds of iodine, and alkaline earth metal compounds of iodine.

[0016] Furthermore, the specific surface area of ​​the graphite is 1.3 m². 2 / g-2m 2 / g.

[0017] And / or, the specific surface area of ​​the N-doped graphene is 2.5 m². 2 / g-3m 2 / g.

[0018] Secondly, the present invention provides a method for preparing a negative electrode active material, comprising the following steps:

[0019] The iodine-containing additive is dispersed in a solvent and stirred. The N-doped graphene is then added while the stirring process is maintained. Subsequently, the graphite is added to obtain the negative electrode active material.

[0020] Furthermore, the stirring process satisfies the following conditions:

[0021] The stirring temperature is 20-40℃, and the stirring speed is 1000-3000 rpm;

[0022] And / or, the stirring time before adding the N-doped graphene is 0.5-5 h, the stirring time after adding the N-doped graphene is 0.5-5 h, and the stirring time after adding the graphite is 0.5-5 h.

[0023] Thirdly, the present invention provides a negative electrode sheet, comprising a current collector and an active layer disposed on at least one functional surface of the current collector; the active layer comprises the negative electrode active material described in the first aspect.

[0024] Furthermore, the active layer also includes a conductive agent other than graphite, the conductive agent including heteroatom-doped carbon black.

[0025] Furthermore, the heteroatom includes at least one of N, F, S, and O;

[0026] And / or, the doping amount of the heteroatom is 2wt%-5wt%.

[0027] Fourthly, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0028] Fifthly, the present invention provides a battery pack comprising the battery described in the fourth aspect.

[0029] In a sixth aspect, the present invention provides an electrical device comprising the battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0030] The negative electrode active material provided by this invention, by introducing an iodine-containing additive and restricting at least a portion of the iodine-containing additive to adsorb on at least a portion of the surface of N-doped graphene, can effectively improve the cycle life of the battery at low temperatures or high rates. The main reasons include: firstly, the iodine additive can generate iodine-containing inorganic layers such as LiI during battery formation, reducing the impedance of the SEI film; moreover, the iodine-containing additive has strong oxidizing properties, which can oxidize "dead lithium" and regenerate lithium ions, thereby suppressing lithium plating and improving the low-temperature cycle life of the battery; however, iodine easily undergoes side reactions with the positive electrode material, increasing the self-discharge rate of the cell. Therefore, this invention... The invention defines the iodine additive as binding to at least a portion of the surface of the N-doped graphene through adsorption (including chemisorption and physisorption), which can stably anchor iodine ions and / or elemental iodine, restricting the shuttle of iodine between the positive and negative electrodes, reducing the self-discharge rate of the battery cell, thereby further improving the cycle life of the battery at low temperatures or high rates and reducing self-discharge; on the other hand, nitrogen-doped graphene has high electronegativity and conductivity, improving the conductivity of the negative electrode active material, reducing charge transport resistance, allowing lithium ions to be inserted and extracted more quickly, thereby improving the rate performance of the negative electrode and making it more stable during high-rate charge and discharge. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1This is a comparison diagram of the negative electrode interfaces of the negative electrode sheets of Embodiment 1 and Comparative Example 1 after cycling at 0°C.

[0033] Figure 2 This is a comparison chart of the cycle stability of the negative electrode sheets of Example 1 and Comparative Example 1 under 25℃ / 1C conditions. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Introducing iodine additives into electrolytes or negative electrode materials can generate iodine-containing inorganic layers such as LiI during battery formation, reducing the impedance of the SEI film. Furthermore, iodine-containing additives have strong oxidizing properties, which can oxidize "dead lithium" and regenerate lithium ions, thereby suppressing lithium plating and improving the battery's low-temperature cycle life. However, iodine readily undergoes side reactions with the positive electrode, increasing the cell's self-discharge rate. Therefore, this invention provides the following technical solution:

[0036] In a first aspect, the present invention provides a negative electrode active material comprising graphite, N-doped graphene, and an iodine-containing additive, wherein at least a portion of the iodine-containing additive is adsorbed onto at least a portion of the surface of the N-doped graphene; wherein the N-doped graphene comprises the structure shown in Formula 1:

[0037]

[0038] R1, R2, R3, R4, R5, R6, R7, and R8 are each independently H, a C1-C10 alkyl group, an F-substituted C1-C10 alkyl group, or F.

[0039] In Formula 1, the negative electrode active material provided by this invention, by introducing iodine-containing additives and restricting at least a portion of the iodine-containing additives to adsorb on at least a portion of the surface of N-doped graphene, can effectively improve the cycle life of the battery at low temperatures or high rates. The main reasons include: firstly, iodine additives can generate iodine-containing inorganic layers such as LiI during battery formation, reducing the impedance of the SEI film; moreover, iodine-containing additives have strong oxidizing properties, which can oxidize "dead lithium" and regenerate lithium ions, thereby suppressing lithium plating and improving the low-temperature cycle life of the battery; however, iodine easily undergoes side reactions with the positive electrode, increasing the self-discharge rate of the cell. Therefore, this invention defines the iodine additive as binding to at least a portion of the surface of the N-doped graphene through adsorption (including chemical adsorption and / or physical adsorption), which can stably anchor iodine ions and / or elemental iodine, restrict the shuttle of iodine between the positive and negative electrodes, reduce the self-discharge rate of the cell, and thus further improve the cycle life of the battery at low temperature or high rate and reduce self-discharge. On the other hand, nitrogen-doped graphene has high electronegativity and conductivity, which improves the conductivity of the negative electrode active material, reduces charge transport resistance, and allows lithium ions to be inserted and extracted more quickly, thereby improving the rate performance of the negative electrode and making it more stable during high rate charge and discharge.

[0040] It should be noted that at least a portion of the surface of the N-doped graphene includes, but is not limited to, the interlayer surface and the inner and outer surfaces of the pores of the N-doped graphene. Furthermore, the source of the aforementioned N-doped graphene is not specifically limited in this invention; it can be prepared by those skilled in the art using conventional preparation methods. For example, it can be prepared according to the method disclosed in the literature Nanographene Metallaprisms: Structure, Stimulated Transformation, and Emission Enhancement, DOI:10.1002 / ange.202210268. Optionally, N-doped graphene with different substituents can be prepared by changing the peripheral substituents to R1, R2, R3, R4, R5, R6, R7, and R8.

[0041] This invention does not limit the adsorption principle of the adsorption, but since bonding occurs between the N and iodine ions in N-doped graphene, in some embodiments the adsorption includes chemisorption, and since N-doped graphene is rich in pores, in some embodiments the adsorption also includes physisorption.

[0042] To reduce costs, in some embodiments, at least one of R1, R2, R3, R4, R5, R6, R7, and R8 is H; to further improve the dispersibility of N-doped graphene and make it uniformly dispersed in the negative electrode slurry, in some embodiments, at least one of R1, R2, R3, R4, R5, R6, R7, and R8 is a C1-C10 alkyl group; to further form a structurally stable SEI film during battery formation, thereby improving battery cycle performance, in some embodiments, at least one of R1, R2, R3, R4, R5, R6, R7, and R8 is an F-substituted C1-C10 alkyl group or one of F.

[0043] In one specific embodiment, the mass ratio of the N-doped graphene, graphite, and iodine-containing additive is 1-5:100:0.1-1.

[0044] Among them, N-doped graphene, graphite, and iodine-containing additives within the above quality range can achieve a good balance between reducing lithium plating in the cell, cell rate, and cell self-discharge. Iodine-containing additives within the above range can reactivate most dead molecules into lithium ions and inhibit lithium plating in the cell. If the content of iodine-containing additives is too high or the content of N-doped graphene is too low, the N-doped graphene cannot fully anchor the iodine-containing additives, the cell self-discharge increases, the battery capacity gradually decreases, the energy storage efficiency of the battery is affected, and the battery aging is accelerated. Graphite is the main active component of the negative electrode material, responsible for the lithium insertion and extraction process. If the graphite content is too low, the capacity of the negative electrode will be significantly reduced, resulting in a decrease in the total capacity of the battery.

[0045] For example, the mass ratio of the N-doped graphene, graphite and iodine-containing additive is any ratio within the range of 0.5-4.5:100:0.2-0.5, 0.2-0.4:100:0.3-0.7, 0.35-0.5:100:0.3-0.5, 0.4-0.5:100:0.6-0.8, 0.45-0.5:100:0.7-0.9.

[0046] In one specific embodiment, the iodine-containing additive includes at least one of elemental iodine, alkali metal compounds of iodine, and alkaline earth metal compounds of iodine.

[0047] In this context, graphite with a suitable specific surface area contributes to the uniform distribution of iodine-containing additives while avoiding an increase in side reactions, thus further ensuring the battery's cycle life. Therefore, to balance the suppression of lithium plating, the reduction of battery internal resistance, and the minimization of side reactions, in one specific embodiment, the specific surface area of ​​the graphite is 0.5 m². 2 / g-2m 2 / g.

[0048] Among them, N-doped graphene with a suitable specific surface area has more edge active sites, which helps to improve the electrochemical activity and capacity of the negative electrode material, and provides more adsorption sites for iodine-containing additives, reducing the self-discharge of the cell. However, excessively high specific surface area may lead to an increase in side reactions. Therefore, in order to balance the electrochemical activity and stability of the battery, in one specific embodiment, the specific surface area of ​​the N-doped graphene is 2.5 m². 2 / g-3m 2 / g.

[0049] The present invention does not specifically limit the preparation method of the above-mentioned negative electrode active material. In some embodiments, the above-mentioned negative electrode active material is prepared by a method including the following process:

[0050] The iodine-containing additive is dispersed in a solvent and stirred. The N-doped graphene is then added while the stirring process is maintained. Subsequently, the graphite is added to obtain the negative electrode active material.

[0051] The temperature, rotation speed, and time of the above stirring treatment are not specifically limited in this invention. Those skilled in the art can adjust them according to the surface area of ​​the iodine-containing additive adsorbed on the N-doped graphene. For example, the temperature of the above stirring treatment is 20-40℃, the rotation speed is 1000-3000 rpm, the stirring time is 0.5-5h before adding the N-doped graphene, the stirring time is 0.5-5h after adding the N-doped graphene, and the stirring can continue for 0.5-5h after adding the graphite.

[0052] Thirdly, the present invention provides a negative electrode sheet, comprising a current collector and an active layer disposed on at least one functional surface of the current collector; the active layer comprises the negative electrode active material described in the first aspect.

[0053] In one specific embodiment, the active layer further includes a conductive agent other than graphite, the conductive agent including heteroatom-doped carbon black.

[0054] In one specific embodiment, the heteroatom includes at least one of N, F, S, and O;

[0055] As described above, heteroatom-doped carbon black has better conductivity and can be bound to at least a portion of the surface of the N-doped graphene through adsorption (including chemisorption and physisorption). This can stably anchor iodine ions and / or elemental iodine, further restricting the shuttle of iodine between the positive and negative electrodes, reducing the self-discharge rate of the cell, thereby further improving the cycle life of the battery at low temperatures or high rates and reducing self-discharge.

[0056] The present invention does not particularly limit the amount of heteroatom doping. In some embodiments, the amount of heteroatom doping is 2wt%-5wt%, and more specifically, any value or a range consisting of 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0057] In one specific embodiment, the heteroatom-doped carbon black has a specific surface area of ​​300 m². 2 / g-500m 2 / g.

[0058] For example, the specific surface area of ​​heteroatom-doped carbon black is 300 m². 2 / g, 350m 2 / g、400m 2 / g、450m 2 / g、500m 2 A range consisting of any value in / g, or any combination of both.

[0059] The material of the current collector is not specifically limited in this invention. For example, it can be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals.

[0060] To improve the energy density of the battery, preferably, the active layer is sequentially disposed on the two functional surfaces of the current collector.

[0061] It is understood that the amount of negative electrode active material used will directly affect the energy density of the battery. In order to ensure the energy density of the battery, in one specific embodiment, the mass ratio of negative electrode active material in the active layer is 90-96%.

[0062] In one specific embodiment, the conductive agent in the active layer accounts for 1-1.5% of the total mass. Within this range, the conductive agent can give the negative electrode higher ionic and electronic conductivity; when applied to a lithium-ion battery system, it can effectively reduce the battery's internal resistance.

[0063] Regarding the thickness, areal density, compaction, and thickness of the negative electrode active material layer, this invention does not specifically limit these parameters. However, to balance battery capacity, cycle life, and energy density, in one specific embodiment, the thickness of the negative electrode is 40-120 μm, specifically including but not limited to: 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, or any combination thereof; the areal density of the negative electrode is 3-10 mg / cm³. 2 Specifically, including but not limited to: 3.5 mg / cm³ 2 4mg / cm 2 4.5 mg / cm 2 5mg / cm2 5.5 mg / cm 2 6mg / cm 2 6.5 mg / cm 2 7mg / cm 2 7.5 mg / cm 2 8mg / cm 2 8.5 mg / cm 2 9mg / cm 2 9.5 mg / cm 2 or a range consisting of any two of them; the compaction density of the negative electrode sheet is 1 g / cm³. 3 1.2g / cm 3 1.5g / cm 3 2g / cm 3 2.2g / cm 3 2.5g / cm 3 The thickness of the negative electrode active material layer is 20-60 μm, specifically including but not limited to: 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, or any two of these ranges.

[0064] The present invention does not specifically limit the preparation method of the above-mentioned negative electrode sheet. In some embodiments, the preparation method of the above-mentioned negative electrode sheet includes the following steps:

[0065] Step 1): The negative electrode active material, binder, dispersant, solvent and conductive agent are mixed to form an electrode slurry;

[0066] Step 2): Coat at least one functional surface of the current collector with the electrode paste described above, dry and roll to obtain the negative electrode sheet.

[0067] Step 1) above specifically includes the following processes:

[0068] In a solution containing iodine additives, N-doped graphene is mechanically stirred to adsorb at least a portion of the iodine additives onto at least a portion of the surface of the N-doped graphene. Graphite is then added and mechanical stirring continues. Subsequently, a binder, dispersant, solvent, and conductive agent are directly added to the system to form an electrode slurry.

[0069] Fourthly, the present invention provides a battery comprising the negative electrode sheet of the third aspect.

[0070] Furthermore, it is understood that the battery of the present invention includes the negative electrode, the positive electrode, the separator, and the electrolyte.

[0071] The specific capacity of the positive electrode active material directly affects the energy density of the battery. This invention does not impose any particular limitation on the positive electrode active material. Exemplarily, the positive electrode active material can be one or more commonly used in the art, such as lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, and lithium iron phosphate; lithium manganese oxide can be LiMnO2 or LiMn2O4; and lithium nickel cobalt manganese oxide can be LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2.

[0072] The battery of the present invention can be manufactured according to conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence and assembled into a cell by winding or stacking process. After packaging and baking, electrolyte is injected and then the battery is manufactured by hot pressing and other processes.

[0073] This invention does not impose any particular limitation on the aforementioned diaphragm; any known porous diaphragm with electrochemical and chemical stability can be selected, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The diaphragm can be single-layered or multi-layered.

[0074] This invention does not impose any particular limitation on the electrolyte mentioned above. For example, an electrolyte comprising an organic solvent and an electrolyte salt may be selected. The organic solvent, as the medium for transporting ions in the electrochemical reaction, may be one or more organic solvents known in the art for use in battery electrolytes, such as fluorocarbonates, fluorocarboxylic acid esters, non-fluorocarbonates, fluorocarbonates, non-fluorocarboxylic acid esters, fluorocarboxylic acid esters, fluoroethers, non-fluoroethers, and tetrahydrofuran. The electrolyte salt, as the ion source, may be one or more electrolyte salts known in the art for use in battery electrolytes, such as lithium hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0075] Fifthly, the present invention provides a battery pack comprising the battery described in the fourth aspect.

[0076] In a sixth aspect, the present invention provides an electrical device comprising the battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0077] It should be noted that the above-mentioned electrical equipment can be any equipment that conventionally requires electricity, such as, but not limited to, computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0078] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. All parts, percentages and ratios recorded in the following embodiments are based on weight. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0079] Example 1

[0080] This example provides a negative electrode active material, comprising: graphite, N-doped graphene, and elemental iodine, wherein at least a portion of the elemental iodine is adsorbed on at least a portion of the surface of the N-doped graphene; wherein the N-doped graphene has the structure shown in Formula 1, wherein R1, R2, R3, R4, R5, R6, R7, and R8 are H; the mass ratio of N-doped graphene, graphite, and elemental iodine is 3:100:0.5; and the specific surface area of ​​graphite is 1.5 m². 2 / g; the specific surface area of ​​N-doped graphene is 2.5m². 2 / g.

[0081] This example also provides a negative electrode sheet, including a current collector and an active layer disposed on two functional surfaces of the copper foil of the current collector. By mass, the active layer comprises 100 parts of the aforementioned negative electrode active material, 3 parts of styrene-butadiene rubber (SBR) as a binder, 1.5 parts of carboxymethyl cellulose (CMC) as a dispersant, and 1.5 parts of carbon black as a conductive agent. The specific surface area of ​​the conductive agent is 350 m². 2 / g.

[0082] The above-mentioned method for preparing the negative electrode includes the following steps:

[0083] 1. At room temperature, elemental iodine and deionized water were stirred evenly at 2000 rpm. N-doped graphene was added and stirring was continued for 1 hour. Graphite was added and stirring was continued for 2 hours to obtain a mixture containing the negative electrode active material.

[0084] 2. Add binder, conductive agent, and dispersant, and stir until homogeneous to obtain the final product;

[0085] 3. The above electrode paste is coated on the two functional surfaces of the current collector, and after drying and rolling, a surface density of 2 g / cm³ is obtained. 2 The compaction density is 1.32 g / cm³. 3 The negative electrode.

[0086] Example 2

[0087] It is basically the same as Example 1, except that the mass ratio of N-doped graphene, graphite and iodine is 1:100:0.5.

[0088] Example 3

[0089] It is basically the same as Example 1, except that the mass ratio of N-doped graphene, graphite and iodine is 3:100:1.

[0090] Example 4

[0091] It is basically the same as Example 1, except that the mass ratio of N-doped graphene, graphite and iodine is 6:100:0.5.

[0092] Example 5

[0093] It is basically the same as Example 1, except that the mass ratio of N-doped graphene, graphite and iodine is 3:100:2.

[0094] Example 6

[0095] It is basically the same as Example 1, except that the conductive agent is N-doped carbon black with an N doping amount of 3wt%.

[0096] Example 7

[0097] This is essentially the same as Example 1, except that the specific surface area of ​​the N-doped graphene is 3 m². 2 / g.

[0098] Example 8

[0099] This is basically the same as Example 1, except that the specific surface area of ​​graphite is 2m². 2 / g.

[0100] Example 9

[0101] It is basically the same as Example 1, except that iodine is replaced with MgI2.

[0102] Example 10

[0103] It is basically the same as Example 1, except that: N-doped graphene includes the structure shown in Formula 1, wherein R1, R2, R3, R4, R5, R6, R7 and R8 are all methyl groups.

[0104] Example 11

[0105] It is basically the same as Example 1, except that: N-doped graphene includes the structure shown in Formula 1, wherein R1, R2, R3, R4, R5, R6, R7 and R8 are all trifluoromethyl groups.

[0106] Comparative Example 1

[0107] It is basically the same as Example 1, except that no elemental iodine is added.

[0108] Comparative Example 2

[0109] It is basically the same as Example 1, except that N-doped graphene is not added.

[0110] Comparative Example 3

[0111] It is basically the same as Example 1, except that N-doped graphene is replaced with graphene.

[0112] Experimental Example 1

[0113] Assemble the above-mentioned negative electrode sheet into a soft-pack battery cell, including the following steps:

[0114] Preparation of the positive electrode sheet: LiFePO4 positive electrode material, conductive agent SuperP (conductive carbon black), conductive agent CNT (carbon nanotubes), and binder PVDF (polyvinylidene fluoride) were mixed evenly in a mass ratio of 96.3:2:0.5:1.2 and vacuum stirred until the fluidity was uniform. Then, the slurry was evenly coated on both sides of aluminum foil (coating thickness of 50μm). After drying at 85℃, cold pressing, edge trimming, cutting, slitting, and vacuum drying at 85℃ for 12 hours, the electrode tabs were welded to obtain a surface density of 33mg / cm³. 2 The positive electrode has an N / P ratio of 1.1.

[0115] Electrolyte: ethylene carbonate 30 wt%; dimethyl carbonate 22 wt%; diethyl carbonate 14 wt%; methyl ethyl carbonate 30 wt%; vinylene carbonate 2.6 wt%; fluoroethylene carbonate 1.4 wt%; LiPF6 1 mol / L.

[0116] Assembly: Using a 14μmpp separator, it is assembled into a soft-pack cell with 7 positive electrodes, 8 negative electrodes, and an aluminum-plastic film as the outer shell.

[0117] Test case

[0118] Test Example 1:

[0119] Low-temperature cycle disassembly interface verification

[0120] The aforementioned pouch cells will be used for low-temperature cycling tests to verify their lithium plating performance.

[0121] Experimental steps:

[0122] 1) Capacity calibration:

[0123] ① Charging: At room temperature (25±3℃), charge at a constant current and constant voltage of 0.25C to 3.8V, cut off at 0.02C, and let stand for 30 minutes;

[0124] ② Discharge: At room temperature (25±3℃), discharge at a constant current of 0.25C to 2.0V, and let stand for 30 minutes.

[0125] A total of 3 discharges were performed. The discharge capacity of the 3rd discharge was recorded as the battery's nominal discharge capacity C0.

[0126] 2) After resting for 10 hours, ensure the battery temperature is 0℃;

[0127] 3) Charge to 3.8V using a 0.5C0 constant current and constant voltage method;

[0128] 3) Let it sit for 30 minutes;

[0129] 4) Discharge to 2.0V using a constant current of 0.5C0;

[0130] 5) Let it sit for 30 minutes;

[0131] 6) Repeat steps 2)-5) 10 times.

[0132] Test Example 2:

[0133] High-rate cycling test at room temperature

[0134] The soft-pack battery cells prepared using the above invention were subjected to high-rate cycling tests at room temperature to verify their lithium plating performance.

[0135] Experimental steps:

[0136] 1) Capacity calibration:

[0137] ① Charging: At room temperature (25±3℃), charge at a constant current and constant voltage of 0.25C to 3.8V, cut off at 0.02C, and let stand for 30 minutes;

[0138] ② Discharge: At room temperature (25±3℃), discharge at a constant current of 0.25C to 2.0V, and let stand for 30 minutes;

[0139] A total of 3 discharges were performed. The discharge capacity of the 3rd discharge was recorded as the battery's nominal discharge capacity C0.

[0140] 2) After resting for 10 hours, ensure the battery temperature is 25℃;

[0141] 3) Charge to 3.8V using a 1.5C0 constant current and constant voltage method;

[0142] 3) Let it sit for 30 minutes;

[0143] 4) Discharge to 2.0V at a constant current of 1.5C0;

[0144] 5) Let it sit for 30 minutes;

[0145] 6) Cyclic steps 2)-5) 500 revolutions.

[0146] Test Example 3:

[0147] Self-discharge test

[0148] Experimental steps:

[0149] ① Charging: At room temperature (25±3℃), charge at a constant current and constant voltage of 0.25C to 3.8V, cut off at 0.02C, and let stand for 12 hours;

[0150] Record the voltage V0 of the 12 battery cells after charging and then leaving them idle;

[0151] ② After storing the battery cell at 25℃ for 30 days, test the voltage V1 of the battery cell;

[0152] ③ Calculate the self-discharge K = V0 - V1;

[0153] The test results are summarized in Table 1. The cell test results for Example 1 and the comparative example can be found in [reference needed]. Figure 1 and Figure 2 .

[0154] Table 1:

[0155]

[0156] As shown in Table 1, compared to the comparative example, the embodiments can suppress lithium plating while reducing cell self-discharge, thereby further improving the cycle life of the battery at low temperature or high rate. Specifically, the low temperature cycle test shows that the experimental example has a significantly higher capacity retention rate and a significantly slower degradation than comparative example 1. The disassembled interface shows that the lithium plating in the experimental example is significantly better than that in comparative example 1. The high rate cycle test at room temperature shows that compared to comparative example 1, the experimental group degrades more slowly. After 1000cls of cycling, no lithium plating occurred in the experimental example, while the cells in the comparative example showed obvious lithium plating. The self-discharge test shows that compared to comparative examples 2-3, the cell self-discharge in the experimental group is better suppressed.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 invention.

Claims

1. A negative electrode active material, characterized by, The material comprises graphite, N-doped graphene, and an iodine-containing additive, wherein at least a portion of the iodine-containing additive is adsorbed onto at least a portion of the surface of the N-doped graphene; wherein the N-doped graphene comprises the structure shown in Formula 1: R1, R2, R3, R4, R5, R6, R7, and R8 are each independently H, a C1-C10 alkyl group, an F-substituted C1-C10 alkyl group, or F.

2. The negative electrode active material according to claim 1, characterized by The mass ratio of the N-doped graphene, graphite, and iodine-containing additive is 1-5:100:0.1-1.

3. The negative electrode active material according to claim 1 or 2, characterized in that, The iodine-containing additive includes at least one of elemental iodine, alkali metal compounds of iodine, and alkaline earth metal compounds of iodine.

4. The negative active material according to any one of claims 1 to 3, characterized in that, The specific surface area of the graphite is 1.3 m 2 / g-2m 2 / g; and / or the N-doped graphene has a specific surface area of 2.5 m 2 / g-3m 2 / g.

5. A method for preparing a negative electrode active material as described in any one of claims 1-4, characterized in that, Includes the following steps: The iodine-containing additive is dispersed in a solvent and stirred. The N-doped graphene is then added while the stirring process is maintained. Subsequently, the graphite is added to obtain the negative electrode active material.

6. The production method according to claim 5, wherein The stirring process satisfies the following conditions: The stirring temperature is 20-40℃, and the stirring speed is 1000-3000 rpm; And / or, the stirring time before adding the N-doped graphene is 0.5-5 h, the stirring time after adding the N-doped graphene is 0.5-5 h, and the stirring time after adding the graphite is 0.5-5 h.

7. A negative electrode sheet characterized by comprising: It includes a current collector and an active layer disposed on at least one functional surface of the current collector; the active layer includes the negative electrode active material according to any one of claims 1-4.

8. The negative electrode sheet according to claim 7, characterized by The active layer also includes a conductive agent other than graphite, which includes heteroatom-doped carbon black.

9. The negative electrode sheet according to claim 8, characterized by The heteroatom includes at least one of N, F, S, and O; And / or, the doping amount of the heteroatom is 2wt%-5wt%.

10. A battery, characterized by It includes the negative electrode sheet according to any one of claims 7-9.

11. A battery pack, characterized by It includes the battery as described in claim 10.

12. An electrical device, characterized by Includes the battery of claim 10 or the battery pack of claim 11.

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