A surface-modified battery composite material and its preparation method and application

Abstract

The present invention discloses a surface-modified battery composite material, a preparation method thereof, and an application thereof. The preparation method comprises: uniformly coating a fluorinated carbon material on the surface of a battery active material to obtain an initial composite material; pretreating the initial composite material, and allowing the fluorinated carbon material on the surface of the battery active material to generate a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material; the surface film of the battery composite material comprises nano-LiF and inorganic carbon; the particle size of the nano-LiF is 3nm-8nm; the mass of the nano-LiF accounts for greater than 0 to less than or equal to 4.5wt% of the total mass of the battery composite material; and applying the battery composite material of the present invention to a secondary battery can enable the secondary battery to have a high discharge specific capacity, an initial coulombic efficiency, and excellent cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a surface-modified battery composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, currently the most advanced energy storage and conversion devices, are widely used in new energy vehicles, large-scale energy storage, 3C electronics, and other fields. Lithium-ion batteries primarily consist of three components: a positive electrode, a negative electrode, and an electrolyte. Currently, positive electrode materials are primarily transition metal oxides, oxides, and some lithium salts. A negative electrode is primarily composed of carbonaceous materials, metallic lithium, silicon, and its derivatives. The electrolyte is typically a combination of an organic solvent and a lithium salt.

[0003] In lithium-ion batteries, due to the low and narrow voltage window of organic solvents, complex interfacial side reactions will occur between the positive and negative electrodes at high voltages. Among them, the lithium deintercalation reaction of the positive electrode material at high voltage will cause a large volume change, resulting in the rupture of the surface film (CEI film) and the bulk structure of the positive electrode material. After the electrolyte enters through the rupture, it will undergo further side reactions with the positive electrode. This process will lead to the consumption of a large amount of electrolyte and active lithium, causing the battery performance to decay rapidly (reference Hyungyeon Cha, et al. Boosting Reaction Homogeneity in High-EnergyLithium-Ion Battery Cathode Materials. Advanced Materials, 2020, 32, 39).

[0004] Currently used high specific energy negative electrode materials such as silicon oxycarbon (SiO x / C), silicon oxide (SiO x ), silicon-carbon (Si / C), and even Si materials and metallic lithium, all experience huge volume changes during the charge and discharge process. The solid electrolyte film (SEI) on the negative electrode surface will continuously destroy and reorganize during the cycle, continuously consuming electrolyte and active lithium. In addition, an unstable SEI film will also cause uneven deposition of metallic lithium, making it more likely to form lithium dendrites. Therefore, how to form a stable CEI / SEI has become the key to improving battery performance.

[0005] Studies have shown that the CEI film rich in LiF and organic matter has a weak bond with the cathode material itself and can withstand large volume changes to ensure the cycle stability of the cathode material; while the negative electrode SEI rich in LiF will make Li +In addition, when LiF forms a nanoscale interface with lithium compounds (such as Li2O, Li2CO3, LiOH, etc.), it transforms from an insulator into a conductor with a certain ionic conductivity and surface energy, which provides a solution for constructing a stable CEI / SEI film.

[0006] The methods for constructing a LiF-rich interface disclosed in the prior art mainly include: ① using a liquid phase method or a solid phase method, such as the patent application CN201410342892.3 (published on October 22, 2014) discloses that a solvent containing LiF is prepared and coated on the surface of the active material particles; the patent application CN202210284986.4 (published on April 22, 2022) discloses that a LiF-coated positive electrode material is obtained by directly mixing LiF in the positive electrode material; ② generating LiF by converting fluorine-containing substances, such as the patent application CN20 1910842716.9 (publication date December 17, 2019), LiPF6 is used, and patent application CN201711180928.2 (publication date April 24, 2018), NH4F and other fluorine-containing substances are used to convert to generate LiF on the surface of the electrode material; ③ Fluorination treatment, such as patent application CN202111005565.5 (publication date December 10, 2021), directly fluoridating the target active material from the perspective of fluorination process; ④ Increasing the electrolyte concentration or using a locally high-concentration electrolyte. However, the above methods have certain limitations: First, since LiF itself is an insulator, directly introducing LiF into battery materials will increase the polarization of the battery and thus deteriorate the battery performance. LiF is also almost insoluble in conventional solvents, making it very difficult to distribute evenly, and therefore it is difficult to ensure that LiF can be evenly distributed on the surface of the active material. Second, the conversion of fluorine-containing substances to obtain LiF requires intermediate processing steps, which can affect the active material. At the same time, the byproducts generated can cause varying degrees of harm to materials, equipment and human body. Third, the fluorination process is expensive and the operation process is complex and dangerous. Fourth, the high cost of high-concentration electrolytes is not conducive to popularization and application, and it is difficult to control the LiF content.

[0007] In summary, the current methods of directly adding LiF or converting LiF through fluorine-containing substances simply introduce LiF into battery materials. However, the introduction of LiF does not bring about significant improvements in material performance. On the contrary, it leads to a deterioration in the conductivity of battery active materials. The fluorination process is too complicated and costly. The introduction of LiF into a high-concentration electrolyte has relatively better performance, but the generated LiF content still cannot be accurately controlled, and its economic applicability is low. Therefore, from the perspective of practical application, it is still difficult to effectively construct a useful LiF coating layer on the surface of battery active materials, and the preparation method is complicated and difficult to promote on a large scale. Summary of the Invention

[0008] The present invention provides a surface-modified battery composite material, a preparation method, and applications thereof. In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to overcome the difficulty in effectively constructing a coating layer on the surface of current high-capacity battery materials, which leads to defects such as poor battery material performance and easy rupture of the surface interface film (SEI or CEI) during cycling. To this end, the present invention provides a surface-modified battery composite material, a preparation method, and applications thereof. The LiF in the surface film layer of the battery composite material obtained by the preparation method of the present invention is nano-sized, has a controllable and uniform distribution of LiF, and has a stable surface interface layer. When used in a battery, it is not prone to rupture during normal charge and discharge cycles and has good electronic and ionic conductivity. It exhibits properties such as high discharge capacity, high initial coulombic efficiency, and excellent cycling performance.

[0009] To this end, in a first aspect, an embodiment of the present invention provides a method for preparing a surface-modified battery composite material, the method comprising:

[0010] Step S1, uniformly coating the surface of the battery active material with a carbon fluoride material to obtain an initial composite material;

[0011] Step S2, pre-treating the initial composite material, whereby the fluorinated carbon material on the surface of the battery active material generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material;

[0012] The fluorine-carbon ratio in the fluorinated carbon material is x, and 0.5≤x≤1.25; the fluorinated carbon material accounts for more than 0 and less than 15 wt% of the total mass of the initial composite material;

[0013] The surface film of the battery composite material includes nano-LiF and inorganic carbon; the particle size of the nano-LiF is 3nm-8nm; the mass of the nano-LiF accounts for greater than 0 to less than or equal to 4.5wt% of the total mass of the battery composite material.

[0014] Preferably, the battery active material is a positive electrode active material, and the pretreatment of the initial composite material in step S2 is a pre-discharge treatment, the specific process being: assembling the initial composite material and the lithium-containing negative electrode material into a lithium battery, and then discharging the lithium battery at a current density of 10 mA / g to 80 mA / g until the voltage is less than or equal to 2.0 V.

[0015] Preferably, the battery active material is a negative electrode active material, and the pretreatment of the initial composite material in step S2 is a pre-discharge treatment or battery formation;

[0016] The specific process of the pre-discharge treatment is as follows: assembling the initial composite material and the lithium-containing negative electrode material into a lithium battery, and then discharging the lithium battery at a current density of 10 mA / g to 80 mA / g to a voltage of ≤2.0 V, preferably, to a voltage of 0 V;

[0017] The specific process of battery formation is: assembling the initial composite material and the lithium-containing positive electrode material into a battery, and then performing battery formation. The battery formation condition is charging and discharging at a rate of less than or equal to 0.1C.

[0018] Preferably, in step S1, the percentage of the carbon fluoride material to the total mass of the initial composite material is 0.5wt%-5wt%;

[0019] The fluorinated carbon material includes one or more of fluorinated graphite, fluorinated graphite polymer, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fiber, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated coke, fluorinated soft carbon, and fluorinated graphene.

[0020] Preferably, in step S1, the fluorinated carbon material is coated on the surface of the battery active material by a solid phase method or a liquid phase method;

[0021] The solid phase method includes one or more of blender mixing, grinding mixing or ball mill mixing;

[0022] The liquid phase method includes dispersing the carbon fluoride material in an organic solvent, and then adding the electrode active material and stirring and mixing; the organic solvent includes one or more of ethyl acetate, ethanol, isopropanol, n-heptane, butanol, acetic acid, octane, N,N-dimethylformamide, cyclohexanone, cycloethanol, N,N-dimethylacetamide, 1,2-propylene glycol, ethylene glycol, N-methylpyrrolidone, acetamide, diethylene glycol, and glycerol, mixed in any volume ratio.

[0023] Preferably, the battery active material is a positive electrode active material, and the positive electrode active material includes: a material having the structural formula Li x M y O z Compounds and derivatives thereof, wherein 0≤x / z≤2, 1 / 2≤x / y≤6, x, y, z≥0, and M is one or more of the elements B, C, N, Na, Mg, Al, Si, P, Cl, K, Ca, Sc, Ti, V, Cr, Ni, Co, Mn, Cu, Fe, Ga, Ge, As, Se, Br, Mo, Zn, Y, Zr, Nb, Tc, Ru, Pb, Pd, Rh, Ag, Cd, Sb, Ba, La, Hf, Ta, W, Os, Pb, and I.

[0024] Preferably, the battery active material is a negative electrode active material, and the negative electrode active material includes: one or more of an embedded negative electrode material, an alloy negative electrode material, and a metal oxide negative electrode material;

[0025] The embedded negative electrode material includes one or more of carbon materials and lithium titanate materials;

[0026] The alloy-type negative electrode material includes silicon-based negative electrodes and their derivatives, including one or more of silicon materials, silicon-oxygen materials, and silicon-carbon materials;

[0027] The metal oxide negative electrode material includes one or more of SnO2, Co3O4, NiO, Fe3O4, and MnO2.

[0028] In a second aspect, an embodiment of the present invention provides a surface-modified battery composite material prepared by the preparation method described in the first aspect, wherein the battery composite material comprises a battery active material and a surface film coated on the outer surface of the battery active material;

[0029] The battery active material includes a positive electrode active material or a negative electrode active material;

[0030] The surface film comprises nano-LiF and inorganic carbon; the particle size of the nano-LiF is 3nm-8nm, and the mass percentage of the nano-LiF to the mass percentage of the battery composite material is greater than 0 and less than or equal to 4.5%.

[0031] In a third aspect, an embodiment of the present invention provides an initial composite material, which is used to prepare the surface-modified battery composite material described in the second aspect, and the initial composite material includes a fluorinated carbon material and a battery active material; the fluorinated carbon material is uniformly coated on the surface of the battery active material; the fluorinated carbon ratio in the fluorinated carbon material is x, and 0.5≤x≤1.25; the fluorinated carbon material accounts for greater than 0 to less than 15wt% of the total mass of the initial composite material, preferably 0.5wt%-5wt%; preferably, the battery active material includes a positive electrode active material or a negative electrode active material.

[0032] In a fourth aspect, an embodiment of the present invention provides a secondary battery, comprising a surface-modified battery composite material prepared by the preparation method described in the first aspect, or the surface-modified battery composite material described in the second aspect, or a surface-modified battery composite material prepared from the initial composite material described in the third aspect; the secondary battery is a lithium-ion battery or a lithium metal battery.

[0033] The present invention provides a battery composite material, a preparation method thereof, and an application thereof, which have the following technical effects:

[0034] First, the preparation method of the present invention can effectively construct the required coating layer on the surface of the battery active material. It utilizes the mechanism of in-situ generation of LiF and inorganic carbon during the electrochemical reaction of carbon fluoride. After the surface of the battery active material is coated with the carbon fluoride material, it is pretreated so that a LiF-rich interface layer is pre-constructed in situ on the surface of the battery active material. LiF with nanometer size, controllable content and uniform distribution on the surface of the battery active material can be obtained. At the same time, the generated inorganic carbon can improve the conductivity of the battery active material.

[0035] The present invention utilizes the electrochemical reaction mechanism of carbon fluoride to pre-deposit nano-sized LiF on the surface of the battery active material in situ. Therefore, when the surface-modified battery composite material of the present invention is applied to the battery, during normal charge and discharge, the nano-LiF layer further synergizes with substances such as Li2CO3 and Li2O generated during the charge and discharge process, transforming it from an insulator into a conductor with certain ionic and electronic conductivity. Therefore, from the perspective of structure-activity relationship (i.e., the positive effect generated during implementation), the inventors construct a nano-scale interface through the electrochemical reaction mechanism, thereby overcoming the problem of battery material polarization caused by the insulating properties of LiF itself and effectively improving battery performance. The preparation method of the present invention obtains a LiF layer through the electrochemical reaction of carbon fluoride, which can be evenly coated on the surface of the battery active material. By controlling the conditions of the electrochemical reaction, the coating amount of LiF can also be effectively controlled, thereby effectively solving the problem of too low a proportion of active material due to the introduction of modifying substances.

[0036] In particular, the present invention converts the fluorinated carbon material into LiF before the normal charge and discharge cycle of the battery, thereby participating in the film formation on the electrode surface, and the resulting surface-modified battery composite material is used for the battery electrode. This is significantly different from the battery active material surface-coated with the fluorinated carbon material for use in the battery electrode. Since the fluorinated carbon material has the characteristics of insulation, hydrophobicity and oleophobicity, when the battery active material with the fluorinated carbon material on the surface is used for the battery electrode, it will consume the lithium ions in the electrode material, thereby causing the battery capacity to decrease, that is, due to the reaction of the fluorinated carbon, the battery has some irreversible capacity loss. In addition, it will also lead to problems such as increased battery polarization, battery voltage hysteresis, uneven electrolyte infiltration, and poor SEI / CEI film formation quality. However, after the surface of the battery active material of the present invention is coated with the fluorinated carbon material, it is first pretreated to obtain a surface-modified battery composite material, and then applied to the battery electrode. This will not cause the above problems, and can effectively overcome the disadvantages of directly applying the battery active material coated with the fluorinated carbon material to the battery electrode.

[0037] Secondly, after the LiF-rich CEI / SEI film is constructed on the surface of the battery active material, the positive and negative electrode materials can withstand greater volume changes during the charge and discharge cycle, thereby maintaining the structural stability of the material, and the film layer can isolate the positive and negative electrode materials from direct contact with the electrolyte and inhibit the occurrence of side reactions. In addition, the LiF-rich CEI / SEI film can also effectively regulate the Li + The transport of lithium metal can be promoted, which in turn promotes the deposition of lithium metal and comprehensively improves the electrochemical performance of the battery active materials. In addition, the inorganic carbon obtained during the electrochemical reaction of carbon fluoride will also be evenly coated on the surface of the active material, thereby helping to improve the conductivity of the battery material.

[0038] Furthermore, the pretreatment process can be a pre-discharge treatment method. For example, the initial composite material and the lithium-containing negative electrode are assembled into a battery and then pre-discharged. If the active material in the initial composite material is the negative electrode material, the carbon fluoride can be converted into LiF in advance through the formation process. Due to the presence of additional LiF, it can also bring capacity compensation effect to the negative electrode material itself.

[0039] The preparation method of the present invention is simple, convenient, has high material utilization rate, and can be promoted on a large scale; the surface-modified battery composite material obtained by the present invention has a stable surface interface layer. When the surface-modified battery composite material is applied to a battery, it is not easy to break during normal charge and discharge cycles, and has good electronic and ionic conductivity. The battery composite material has high discharge specific capacity, high first coulombic efficiency, and excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The technical solutions of the embodiments of the present invention are further described in detail below through the accompanying drawings and examples.

[0041] Figure 1 A flow chart of a method for preparing a battery composite material provided by an embodiment of the present invention;

[0042] Figure 2 The scanning electron microscope (SEM) morphology images of the lithium-rich positive electrode material, the fluorinated graphite, and the lithium-rich + 2 wt% carbon fluoride material in Example 1 of the present invention, and the transmission electron microscope (TEM) image of the fluorinated graphite after discharge;

[0043] Figure 3 The pre-discharge and formation charge-discharge curves of the lithium button cell of Example 1 and Comparative Example 1 of the present invention are shown;

[0044] Figure 4 Schematic diagram of the cycling performance of lithium button batteries according to Example 1 of the present invention and Comparative Example 1;

[0045] Figure 5 Schematic diagram showing the comparison of the cycling performance of lithium-rich positive electrodes with different carbon fluoride coating amounts on lithium button cells in Example 2 of the present invention;

[0046] Figure 6 The pre-discharge and formation charge-discharge curves of the lithium button cell of Example 3 and Comparative Example 3 of the present invention are shown;

[0047] Figure 7 Schematic diagram of the cycling performance of lithium button batteries according to Example 3 of the present invention and Comparative Example 3;

[0048] Figure 8 The pre-discharge and formation charge-discharge curves of the lithium button cell of Example 4 and Comparative Example 4 of the present invention are shown;

[0049] Figure 9 Schematic diagram of the cycling performance of lithium button batteries according to Example 4 of the present invention and Comparative Example 4;

[0050] Figure 10 (a) is the pre-discharge and formation charge-discharge curves of the lithium button cells of Example 5 of the present invention and Comparative Example 5; (b) is a schematic diagram of the cycle performance of the lithium button cells of Example 5 of the present invention and Comparative Example 5;

[0051] Figure 11 (a) is the pre-discharge and formation charge-discharge curves of the lithium button cells of Example 6 of the present invention and Comparative Example 6; (b) is a schematic diagram of the cycle performance of the lithium button cells of Example 6 of the present invention and Comparative Example 6;

[0052] Figure 12 Schematic diagram of the cycling performance of lithium button batteries according to Example 7 of the present invention and Comparative Example 7;

[0053] Figure 13 Schematic diagram of the cycle performance of lithium button batteries of Example 8 of the present invention and Comparative Example 8. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below through the accompanying drawings and specific embodiments, but it should be understood that these embodiments are for a better understanding of the present invention, are not limited to the described best mode of implementation, and do not limit the content and scope of protection of the present invention. Any product that is identical or similar to the present invention and is obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0055] The term "in situ" in this invention refers to the spontaneous generation of the corresponding functional layer during the charge and discharge process, such as the automatic formation of the SEI / CEI film from the electrolyte during the charge and discharge process. It should be noted that in the context of this invention, lithium batteries are secondary batteries, including lithium metal batteries and lithium-ion batteries.

[0056] The present invention provides a method for preparing a surface-modified battery composite material. Figure 1 As shown, the specific steps include:

[0057] Step S1, uniformly coating the surface of the battery active material with a carbon fluoride material to obtain an initial composite material;

[0058] Step S2, pre-treating the initial composite material, the fluorinated carbon material on the surface of the battery active material generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, and obtains a surface-modified battery composite material.

[0059] The surface film of the prepared battery composite material includes nano-LiF and inorganic carbon, wherein the particle size of the nano-LiF is 3nm-8nm; the mass of the nano-LiF accounts for greater than 0 to less than or equal to 4.5wt% of the total mass of the battery composite material.

[0060] The materials, preparation process conditions and specific processes used in the above-mentioned preparation steps S1 and S2 are described in detail below.

[0061] In step S1, the fluorinated carbon material used in the present invention includes one or more of fluorinated graphite, fluorinated graphite polymer, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fiber, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated coke, fluorinated soft carbon, and fluorinated graphene.

[0062] The fluorinated carbon (CF x ) The fluorine-carbon ratio x of the material is between 0.5 and 1.25, and can be any value within the above range, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.25, but is not limited to the above values; when it is within the above fluorine-carbon ratio range, carbon fluoride can form sufficient LiF with lithium during the electrochemical reaction. When the fluorine-carbon ratio is too low, the generated LiF is insufficient to play a role in film formation. In this case, if the modification effect is to be guaranteed, it is necessary to increase CF x When the fluorine-carbon ratio x is too high, too many small LiF particles will agglomerate to form large-sized insulators, which will prevent LiF from participating in film formation and increase battery polarization.

[0063] In the initially coated composite material, the content of carbon fluoride is between greater than 0 wt% and less than 15 wt%. Within the above content range, LiF having a desired content can be obtained, and can be any value within the above range, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 14.5 wt%, but is not limited to the above values; preferably, the content of carbon fluoride is 0.5 wt%-5 wt%. When the content is within the preferred range, the carbon fluoride material can be electrochemically reacted to obtain an optimal content of nano-scale LiF on the surface of the battery active material, and the LiF content is controlled within a suitable range, and it is ensured that the nano-sized LiF does not agglomerate to form larger particles of insulators; at the same time, under the synergistic effect with Li2O, Li2CO3, LiOH, etc., this part of LiF has a certain ionic conductivity and surface energy, further improving the conductivity of the material. Too much or too little LiF content will not produce the optimal effect and may even deteriorate battery performance.

[0064] In step S1, the battery active material is a positive electrode active material or a negative electrode active material; wherein the positive electrode active material includes: a material having a structural formula Li x M y O z Compounds and derivatives thereof, wherein 0≤x / z≤2, and can be any value within the above range, for example, 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 1 / 2≤x / y≤6, and can be any value within the above range, for example, 0.5, 0.6, 0.8, 1.0, 2, 3, 4, 5, 6, x, y, z≥0, and M is one or more of the elements B, C, N, Na, Mg, Al, Si, P, Cl, K, Ca, Sc, Ti, V, Cr, Ni, Co, Mn, Cu, Fe, Ga, Ge, As, Se, Br, Mo, Zn, Y, Zr, Nb, Tc, Ru, Pb, Pd, Rh, Ag, Cd, Sb, Ba, La, Hf, Ta, W, Os, Pb, and I. The negative electrode active materials include: one or more of embedded negative electrode materials, alloy negative electrode materials, and metal oxide negative electrode materials; embedded negative electrode materials include one or more of carbon materials and lithium titanate materials; alloy negative electrode materials include silicon-based negative electrodes and their derivatives, specifically including: one or more of silicon materials, silicon oxide materials, and silicon carbon materials; metal oxide negative electrodes include one or more of SnO2, Co3O4, NiO, Fe3O4, and MnO2.

[0065] In step S1 , the battery active material may be coated with carbon fluoride by a solid phase method or a liquid phase method.

[0066] Among them, the solid-phase method includes a combination of one or more methods such as mixer mixing, grinding mixing or ball mill mixing; specifically, the mixer mixing is to add the battery active material and carbon fluoride into the mixer in proportion, set the stirring speed to 200r / min-600r / min, and the stirring time is 0.5 hour-20 hours; grinding is to weigh an appropriate amount of carbon fluoride and battery active material, add them to a mortar, and grind for 0.5 hour-5 hours; ball milling is to weigh carbon fluoride and battery active material in an appropriate mass ratio, add them to a ball mill jar, set the ball-to-material ratio to 2 / 1~25 / 1, the ball milling speed is 100r / min-500r / min, and the ball milling time is 0.5 hour-12 hours.

[0067] The liquid phase method is to disperse carbon fluoride in a suitable organic solvent, then add the electrode active material and stir to uniformly coat the carbon fluoride on the surface of the electrode active material, and further post-process to obtain the carbon fluoride-coated electrode active material; the organic solvent used includes one or more of ethyl acetate, ethanol, isopropanol, n-heptane, butanol, acetic acid, octane, N,N-dimethylformamide, cyclohexanone, cycloethanol, N,N-dimethylacetamide, 1,2-propylene glycol, ethylene glycol, N-methylpyrrolidone, acetamide, diethylene glycol, and glycerol, mixed in any volume ratio; the post-processing method includes stirring and hot evaporation, filtration and then transferring to a blast drying oven or a vacuum oven for drying, or preparing the electrode and then drying it in a vacuum oven or a blast drying oven, or drying it by spray drying; in particular, the post-processing method needs to consider the physical and chemical properties of the selected organic solvent to ensure the best effect.

[0068] In step S2, when the battery active material is a positive electrode active material, the initial composite material is pretreated as a pre-discharge treatment. The specific process is: the initial composite material and the lithium-containing negative electrode material are assembled into a lithium battery, and then the lithium battery is discharged at a current density of 10mA / g to 80mA / g to a voltage less than or equal to 2.0V. The current density can be any value within the above range, for example, it can be 10mA / g, 20mA / g, 30mA / g, 40mA / g, 50mA / g, 60mA / g, 70mA / g and 80mA / g, etc. The discharge voltage can be any value within the above range, for example, it can be 2.0V, 1.9V, 1.8V, 1.6V, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; for the positive electrode active material, it is further formed after discharge.

[0069] In step S2, when the battery active material is a negative electrode active material, the initial composite material is pre-treated to undergo a pre-discharge treatment or a battery formation treatment. Among them, the specific process of the pre-discharge treatment is: assembling the initial composite material and the lithium-containing negative electrode material into a battery, and then discharging the lithium battery at a current density of 10mA / g to 80mA / g to a voltage ≤2.0V, the current density can be any value within the above range, for example, it can be 10mA / g, 20mA / g, 30mA / g, 40mA / g, 50mA / g, 60mA / g, 70mA / g and 80mA / g, etc., the discharge voltage can be any value within the above range, for example, it can be 2.0V, 1.9V, 1.8V, 1.6V, 1.5V, 1.3V, 1.2V, 1.0V, 0.8V, 0.6V, 0.4V, 0.2V, 0V, etc., preferably it can be a lower voltage, such as 0V. Due to the characteristics of the negative electrode material, it can be discharged to a lower voltage to facilitate the conversion of carbon fluoride. The specific process of battery formation is: the initial composite material and the lithium-containing positive electrode material are assembled into a battery and then the battery is formed. During the battery formation, part of the lithium can react with the carbon fluoride on the surface of the negative electrode material to obtain lithium fluoride. The battery formation condition is to charge and discharge at a rate of less than or equal to 0.1C.

[0070] In step S2, after the initial composite material pretreatment is complete, the carbon fluoride is in situ generated through an electrochemical reaction and evenly coated on the surface of the battery active material. During the subsequent normal formation and / or related electrochemical cycling of the battery, the LiF continuously participates in the formation of a more stable CEI / SEI film, thereby improving the electrochemical performance of the material.

[0071] The present invention provides a method for pre-in-situ construction of a nano-scale LiF-rich surface film on the surface of a battery active material. The method first coats the surface of the battery active material with carbon fluoride, and then utilizes the electrochemical reaction of the carbon fluoride to convert it into LiF. The LiF obtained by the above preparation method is nano-sized, and the LiF content is controllable and evenly distributed on the surface of the battery active material.

[0072] The inventors have found that the use of stable fluorinated compounds, such as carbon fluoride (CF x), after appropriate intermediate processing steps, such as high-temperature calcination after coating or the extraction of F and conversion to LiF, or the conversion of carbon fluoride during the battery's cyclic discharge process, LiF will be generated. The inventors further considered the practical application needs of lithium-ion batteries and came up with the idea of ​​using the electrochemical reaction mechanism of carbon fluoride to improve the current method of constructing LiF on the surface of battery active materials. That is, through pretreatment including pre-discharge or battery formation, a surface-modified battery composite material is first obtained, thereby overcoming the various problems currently caused by constructing a LiF coating layer on the surface of battery active materials, such as battery polarization, performance deterioration, and poor cycle performance. Therefore, a feasible method for in-situ construction of a LiF-rich surface film on the surface of battery active materials is proposed.

[0073] It should be noted that although the surface of the battery active material is coated with carbon fluoride material, if it is directly used as the positive or negative electrode of the battery, lithium fluoride will be generated during the normal use of the battery, that is, the charging and discharging process. However, the inventors found that, similar to the method of converting LiF by high temperature after coating with carbon fluoride, the following problems are unavoidable when the battery is converted into LiF during the charge and discharge cycle: 1) Carbon fluoride is an insulating material with poor conductivity. The carbon fluoride introduced on the surface of the battery active material will cause large battery polarization before it is converted into LiF, which will lead to problems such as voltage hysteresis; 2) Carbon fluoride is a super hydrophobic and oleophobic material with low surface energy. After the surface of the battery active material is coated with carbon fluoride, it is difficult for the electrolyte to infiltrate the battery active material. Poor infiltration will also increase the battery polarization, which will also lead to very uneven lithium extraction and insertion of the active material; 3) Although LiF is an important component of CEI and SEI, if the introduced carbon fluoride does not form LiF before the film formation reaction and LiF participates in the film formation, but is continuously converted into LiF during the reciprocating charge and discharge cycle, then the effect of improving the battery performance is limited. In this process, since lithium ions in the battery are continuously consumed, part of the battery capacity is irreversible, resulting in poor electrochemical performance of the battery. Therefore, the method of generating LiF by electrochemical conversion of carbon fluoride has no significant effect on improving battery performance if LiF is not obtained or formed before film formation, that is, if the pretreatment process of the present invention is not performed.

[0074] Therefore, the inventors found that CF xThe conversion and utilization of carbon fluoride not only needs to consider its characteristics of containing F elements, but also needs to be considered from the perspective of electrochemical conversion, based on the insulation, hydrophobicity and oleophobicity of carbon fluoride itself and the hysteresis of conversion, so as to overcome the disadvantages of the defects of the carbon fluoride material itself in its application in lithium battery active materials. Then, through the reasonable improvement of the surface modification method, that is, the pretreatment process includes pre-discharge or formation of the battery active material, so that it is pre-in-situ converted into lithium fluoride, and then used as an electrode material in lithium batteries, which effectively overcomes the problems caused by the defects of the carbon fluoride material itself.

[0075] Nano-scale LiF is generated in situ by carbon fluoride during discharge and is evenly coated on the surface of the positive and negative electrode materials, participating in the formation of the surface film; at the same time, the carbon produced by the discharge of carbon fluoride is also evenly coated on the surface of the electrode material, thereby improving the conductivity of the material. In particular, according to the reaction mechanism of carbon fluoride materials, carbon fluoride generates LiF and inorganic carbon during discharge, wherein LiF is deposited on the surface of the electrode active material in molecular form, and is closely bound to the active material, and the final product is nano-scale; from the perspective of structure-activity relationship, nano-scale LiF further synergizes with Li2CO3 and Li2O generated during the charge and discharge process, transforming from an insulator at a large size to a conductor with a certain conductivity; the generated carbon material will also further improve the conductivity of the material. In addition, the method of obtaining LiF through the electrochemical reaction of carbon fluoride can also effectively control its proportion in the battery composite material, so that the coating amount of LiF can be controlled, thereby ensuring the proportion of active material in the electrode material, and then ensuring the capacity of the battery, and obtaining a high-capacity battery with practical value.

[0076] The present invention also provides an initial composite material for a battery, which includes a carbon fluoride material and a battery active material. The carbon fluoride material is uniformly coated on the surface of the battery active material. The fluoride-carbon ratio x in the carbon fluoride material is 0.5≤x≤1.25, and its percentage of the total mass of the initial composite material is greater than 0% to less than 15%. The fluorinated carbon ratio x can be any value within the above range, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.25, but is not limited to the above values; the content of fluorinated carbon is between greater than 0wt% and less than 15wt%, and can be any value within the above range, such as 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 14.5wt%, but is not limited to the above values; preferably, the content of fluorinated carbon is 0.5wt%-5wt%. For the initial composite material of the battery, its purpose is to construct a fluorinated carbon coating layer on the surface of the battery active material, and convert the fluorinated carbon material into a component mainly composed of lithium fluoride in advance through subsequent electrochemical reactions. The LiF generated thereby further participates in the construction of the SEI / CEI film on the electrode surface, generating a surface film with a more stable structure that can promote ion transport. For the construction of the coating layer, when it is within the above-mentioned fluorinated carbon ratio range, it is beneficial for the fluorinated carbon to form sufficient LiF with lithium during the electrochemical reaction. When the fluorinated carbon ratio is too low, the generated LiF is insufficient to play a role in participating in the film formation. If the modification effect is to be guaranteed, it is necessary to increase the CF x If the coating amount is too high, the resistance and cost of the active material will be greatly increased. When the fluorine-carbon ratio is too high, the excessive small LiF particles will agglomerate to form large insulators, which cannot participate in film formation and increase battery polarization. When the content is within the preferred range, it can ensure that the carbon fluoride produces a sufficient amount of nano-level LiF on the surface of the battery active material through electrochemical reaction, and the nano-sized LiF will not agglomerate to form larger insulator particles. At the same time, under the synergistic effect of Li2O, Li2CO3, LiOH, etc., this part of LiF has a certain ionic conductivity and surface energy, further improving the conductivity of the material. Too much or too little will not achieve the optimal effect and may even deteriorate battery performance.

[0077] The present invention also protects a surface-modified battery composite material prepared by the above-mentioned preparation method. The surface film of the battery composite material is rich in nano-LiF and inorganic carbon. The LiF particle size is 3nm-8nm, and the LiF content in the battery composite material is greater than 0 and less than or equal to 4.5wt%. The LiF particle size can be any value within the above-mentioned range, such as, but not limited to, 3nm, 4nm, 5nm, 6nm, 7nm, and 8nm. The LiF content can be any value within the above-mentioned range, such as, but not limited to, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, and 4.5wt%.

[0078] In the battery composite material of the present invention, CF is electrochemically x In the pretreatment process, including the pre-discharge and formation steps, LiF is pre-generated in situ and coated on the surface of the active material and participates in the subsequent SEI / CEI film formation. The LiF obtained in this process is deposited and aggregated at the molecular level, and the final LiF particle size is less than 10nm, which has a sufficiently small particle size and thus has a nano effect. In addition, the nano-sized LiF further synergizes with components such as Li2O and Li2CO3 generated on the surface of the active material during the battery preparation and discharge processes, which will improve the electronic and ionic insulation properties of LiF, reduce the polarization resistance of LiF when it is used as a surface modification component of the electrode material, and thus improve the battery performance.

[0079] The performance characteristics of the battery composite material obtained by in-situ construction of nano-LiF-rich material on the surface of the above-mentioned battery active material are described in detail below.

[0080] First, the present invention generates nano-scale LiF through in-situ reaction. Nano-sized LiF has nano-effect and can solve the insulation problem of LiF itself by synergistically acting with other substances. x Evenly coated on the surface of the electrode material, after the battery is prepared, the CF is directly converted into x LiF is generated in situ and evenly coated on the surface of the active material. x The discharge reaction mechanism will produce the following reactions:

[0081] CF x +Li→C+LiF

[0082] The LiF generated by the above electrochemical reaction is deposited and aggregated at the molecular level, and the LiF particle size is below 10nm, which allows the nano-level LiF to be evenly coated on the surface of the battery active material. In addition, components such as Li2O and Li2CO3 generated on the surface of the active material during the battery preparation and discharge processes can synergize with LiF, effectively improving the defects of LiF in electronic and ionic insulation, reducing the polarization resistance of LiF when used as a surface modification component of the electrode material, thereby effectively improving the conductivity of the battery material.

[0083] Second, the present invention makes full use of CF x The inherent reaction characteristics of the battery are used to solve the problems of reduced active material proportion and coating layer impedance caused by the introduction of modifying materials including carbon fluoride alone. In the prior art, when introducing surface coatings on the surface of battery active materials, the mass proportion of the coating material in the active material is often ignored. When the content of the coating material increases, the proportion of the battery active material will be relatively reduced, and thus the battery capacity will be correspondingly reduced, which is not conducive to the preparation of high-capacity batteries. In addition, an increase in the coating amount will also lead to an increase in battery impedance.

[0084] Third, the present invention overcomes the defects of carbon fluoride coated battery active materials. x , converted into LiF through high temperature or cycle process, there is also CF x Problems such as battery polarization and voltage hysteresis caused by poor conductivity; CF x The super-hydrophobic and oleophobic properties and low surface energy lead to poor electrolyte wetting and increased battery polarization, CF x The LiF obtained during the cycle cannot participate in film formation and thus has limited effect on improving battery performance.

[0085] In the present invention, according to different battery and battery material characteristics, first the battery is formed or before the formation of the CF x The electrochemical reaction generates LiF in situ, which then participates in the formation of a more stable and excellent surface SEI / CEI film, thus improving the electrochemical performance of the battery. x During the pre-discharge or battery formation process, the insulator is converted into the functional layer LiF and conductive inorganic carbon. The inorganic carbon will continue to coat the surface of the active material as a conductive agent to improve the conductivity of the material, eliminating the problems of voltage hysteresis, increased polarization and reduced capacity caused by the introduction of CFx. x During pre-discharge or formation, all of them are converted into parts useful for improving battery performance, and this process does not affect the subsequent normal performance of the battery; in addition, CF x The conversion of hydrophobic and oleophobic carbon materials into carbon materials with excellent moisture retention will solve the problem of CF xThe problem of poor wettability of composite electrode sheets caused by hydrophobicity and oleophobicity. For the positive electrode material, after the coated positive electrode material is assembled into a battery, the CF x Converted into LiF, and then charge and discharge cycle, this process does not affect the subsequent battery capacity; for the negative electrode material, CF is converted into LiF during the battery formation process. x Converted to LiF, CF x The capacity of the negative electrode material itself will have an appropriate capacity compensation, and will not affect the battery capacity. The coating layer introduced in the present invention will not have a negative impact on the battery capacity and conductivity.

[0086] Third, the preparation process of the present invention can obtain LiF with a controllable content in a uniform and controllable state.

[0087] The existing methods for constructing LiF-rich surface SEI / CEI films on the surface of battery active materials have difficulty in simultaneously balancing the content and quality of the coating. In other words, in order to ensure the precise content of LiF in the coating, it is inevitable to face the problems of LiF's own ionic insulation and large particle size, which will reduce the coating quality.

[0088] In the prior art, the reduction of LiF on the surface of battery materials from the perspective of electrolyte will face the problems of inability to accurately control the amount of LiF and high cost. This is because in addition to the product, it also contains a lot of impurities such as organic matter, and is greatly affected by external factors such as temperature and voltage range, which will lead to uncontrollable LiF content. In the present invention, LiF is made of CF x In situ electrochemical reaction generated due to CF x The products are LiF and C, and the amount of LiF produced can be converted into CF x The amount of LiF added can be precisely controlled; at the same time, the deposition and aggregation at the molecular level can make the LiF distribution more uniform and the coating quality higher, which can better play the nano-size effect. x LiF is generated by electrochemical in-situ reaction. It is only necessary to discharge the battery to less than or equal to 2.0V before formation (positive electrode material), or discharge the negative electrode material to less than or equal to 2.0V or formation to control CF x Discharge generates LiF. Therefore, the present invention can control CF x The coating amount is used to control the content of LiF, and the reaction at this voltage is a spontaneous redox reaction and is less affected by external factors. In addition, the electric field lines in the battery will make the first discharge process Li + The deposition is relatively uniform, that is, the generated LiF is evenly distributed on the surface of the active material.

[0089] Fourth, the present invention utilizes inorganic carbon generated by carbon fluorination reaction to further enhance the conductivity of the material, effectively solving the problem of reduced conductivity of battery materials.

[0090] The functional surface coating of battery materials usually leads to a decrease in the conductivity of the battery active material, and how to effectively maintain the conductivity of the material becomes a problem, especially when the coating material is a non-conductive material such as LiF. The reduction in the conductivity of the battery material will increase the polarization of the battery on the one hand, and inhibit the capacity of the electrode material on the other hand. x When LiF is generated in situ electrochemically on the surface of the active material, inorganic carbon is also produced. These generated carbon materials and LiF can also be evenly coated on the surface of the active material, which will help improve the conductivity of the material and be more conducive to Li + At the same time, it can also physically isolate the direct contact between the electrode material and the electrolyte, and to a certain extent inhibit the occurrence of side reactions.

[0091] Fifth, the preparation method of the present invention is more economical and affordable, is conducive to large-scale promotion, and the process is simple, efficient, low-carbon and environmentally friendly.

[0092] The method of in-situ electrochemical generation of LiF on the surface of electrode materials of the present invention only requires the addition of CF x Uniformly coated on the surface of the electrode material, using CF x The uniqueness of the material product allows the generation of a nanoscale LiF functional layer on the surface of the material without the need for a complex conversion process or expensive or special processing equipment. It is simple to prepare, produces a single product, has significant effects, is economical and applicable, and is suitable for large-scale promotion in the industry.

[0093] In general, the present invention provides a method for generating LiF by in-situ electrochemical reaction on the surface of an electrode active material, wherein CF x Uniformly coated on the surface of the electrode material, using CF x The unique properties of the material can generate a nanoscale LiF functional layer on the surface of the material without going through a complex conversion process or requiring expensive or special processing equipment. It is simple to prepare, has a single product, has significant effects, is economical and applicable, and is suitable for large-scale promotion in the industry.

[0094] Regarding the application of the battery composite material prepared by the above-mentioned preparation method of the present invention, the battery composite material of the present invention can be used in secondary batteries, which can enable the secondary batteries to have electrochemical properties such as higher specific capacity, better cycle performance and first coulombic efficiency, wherein secondary batteries include but are not limited to lithium-ion batteries and lithium metal batteries; the above-mentioned battery composite material of the present invention can also be used in lithium battery modules, and when used in terminal products, it also has high energy and excellent cycle characteristics.

[0095] To better understand the technical solution provided by the present invention, the preparation method, specific applications and characteristics of the battery composite material of the present invention are further described in detail below with reference to a number of specific embodiments and accompanying drawings.

[0096] The carbon fluoride raw materials used in the following examples and comparative examples were purchased from Shandong Chongguang Optoelectronic Materials Co., Ltd.; the negative electrode materials were purchased from Shanghai Shanshan Technology Co., Ltd. and Liyang Tianmu Xiandao Battery Materials Technology Co., Ltd.; the positive electrode materials were purchased from Xiatung New Energy Materials Co., Ltd. and Haian Zhichuan Battery Materials Technology Co., Ltd.; and the electrolyte and electrolyte additives were obtained from Suzhou Duoduo Chemical Technology Co., Ltd. For experimental procedures or conditions not specified in the examples, the procedures or conditions were based on conventional experimental procedures described in literature in the field. All reagents or instruments used without manufacturer identification were commercially available.

[0097] Example 1

[0098] This embodiment provides a surface-modified battery composite material. The initial battery composite material is a lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The surface of O2 is coated with 2 wt% of fluorinated graphite (fluorine-carbon ratio x is 0.65), specifically comprising the following steps:

[0099] (1) Synthesis of lithium-rich cathode materials: The purchased precursor Ni 0.16 Co 0.16 Mn 0.68 CO3 and lithium salt Li2CO3 are mixed in proportion, fired at 500℃ for 5 hours in an inert gas environment, then heated to 800℃ for 8 hours, and then cooled to 500℃ for 1 hour to obtain the lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0100] (2) Uniformly coating graphite fluoride on the lithium-rich cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The surface of O2 is prepared by weighing 0.02g of graphite fluoride and 0.98g of lithium-rich positive electrode material in a ball mill, adding polyurethane balls with a ball-to-material ratio of 10:1, and ball milling at a speed of 500r / min for 2 hours to obtain the initial composite material (abbreviated as: lithium-rich + 2wt% carbon fluoride).

[0101] The initial composite material prepared in this example was characterized by the following structure:

[0102] like Figure 2 As shown, Figure 2 (a) is the SEM morphology of the original lithium-rich cathode material, which has a spherical structure with a diameter between 2μm and 10μm. Figure 2 (b) is the SEM morphology of fluorinated graphite, which shows that it has an irregular block structure with obvious layered structural characteristics. Figure 2 (c) is the SEM morphology of the initial composite material of this embodiment. It can be seen that after ball milling, a composite material of fluorinated graphite and lithium-rich positive electrode material is obtained, in which the lithium-rich positive electrode material still maintains a complete spherical structure, and the fluorinated graphite is uniformly coated on the surface of the spherical particles of the lithium-rich positive electrode material.

[0103] (3) Assembling a battery with the above-mentioned initial composite material and pre-discharging the battery to make the lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The fluorinated carbon material on the surface of O2 generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material, specifically:

[0104] Preparation of electrode: Take 100 mg of polyvinylidene fluoride (PVDF), dissolve it in 3 ml of N-methylpyrrolidone (NMP), stir to form a uniform solution, then add 800 mg of lithium-rich positive electrode composite material and 100 mg of superconducting carbon black (Super P), and stir for 8 hours to obtain active material slurry, which is evenly coated on aluminum foil with a coating thickness of 150 μm, and the electrode is dried in a forced air drying oven at 80°C.

[0105] Button Cell Assembly: The resulting electrode sheets were punched into 12mm Φ circular pieces and dried in a vacuum oven at 120°C for 12 hours. Subsequently, in a vacuum glove box, CR2032 button cells were assembled using a lithium metal sheet as the negative electrode and the aforementioned electrode sheet as the positive electrode. A conventional commercial electrolyte was used as the electrolyte.

[0106] Pre-discharge: The assembled battery was discharged to 2.0V at a current of 30mA / g on a blue power test system.

[0107] LiF detection: Set up parallel test samples, disassemble the battery with the same status as above to obtain the pole piece, wash and dry it with DMC solution, scrape off the active material and test TEM, select CF x Material observation, the results are as follows Figure 2(d) As shown. The semi-transparent layer is the carbon layer, and the black dot-like particles distributed in it are LiF. Therefore, it can be seen that the LiF generated during the discharge process is partially distributed on the surface and between the carbon layers. Further combined with Fourier transform and image recognition processing, it can be obtained that the generated LiF particle size is less than 10nm, and the vast majority of the particle size is between 3-8nm. At the same time, according to the above-mentioned electrode preparation and battery assembly test process, the CF x To prepare a button cell using the active material, the battery was discharged to 2.0V, the electrode was disassembled, washed with DMC, and dried. The active material was scraped and ground into a fine powder, then washed, filtered, and dried with hydrochloric acid. The resulting material was then titrated with a standard concentration of sulfuric acid. The measured LiF content was 30.03 wt%, indicating a LiF yield of 30.03 wt% under these conditions. In this example, the corresponding LiF content was 0.6 wt%.

[0108] (4) The battery containing the battery composite material of this embodiment assembled in step (3) was formed and subjected to electrochemical testing. Specifically, the battery was charged to 4.8 V at a current of 30 mA / g, then discharged to 2 V, and then charged and discharged in this voltage range at a current of 500 mA / g.

[0109] Pre-discharge and formation charge-discharge curves are as follows Figure 3 As shown in the figure, the cycle performance comparison curve is as follows Figure 4 The electrochemical performance data are shown in Table 1. The 100-cycle capacity retention rate is calculated based on the second discharge capacity as the basic value.

[0110] A lithium-rich positive electrode material not coated with graphite fluoride was used as comparative example 1 (abbreviated as original lithium-rich positive electrode), and the battery assembly and testing processes were the same as those in example 1.

[0111] Table 1 Summary of button cell test data prepared in Example 1 and Comparative Example 1:

[0112]

[0113] Table 1

[0114] In Example 1, the surface of the lithium-rich positive electrode material is coated with 2wt% of fluorinated graphite material, and Comparative Example 1 is an uncoated lithium-rich positive electrode material. The test results show that in the pre-discharge stage of button battery formation, the discharge capacity of the composite positive electrode material is increased from the original 23.3mAh / g to 32mAh / g due to the introduction of fluorinated graphite. In the subsequent normal formation and electrochemical performance test stage, the first discharge capacity of the composite positive electrode material was 315.3mAh / g, and the first coulombic efficiency was 92.01%; after increasing the current, the second discharge capacity was 249.5mAh / g. After 100 charge and discharge cycles, its discharge capacity was 232.6mAh / g, and the capacity retention rate was 93.23%. In Comparative Example 1, the lithium-rich positive electrode material without graphite fluoride coating has a first discharge specific capacity of 291.07 mAh / g and a first coulombic efficiency of 84.04%. After increasing the current, the second discharge specific capacity is 240.2 mAh / g. After 100 charge and discharge cycles, the discharge specific capacity is 208.8 mAh / g, and the capacity retention rate is 86.93%.

[0115] It can be seen from Example 1 and Comparative Example 1 that after the surface of the lithium-rich positive electrode material is coated with graphite fluoride, in the pre-discharge stage, the graphite fluoride reacts and converts into LiF and carbon during the discharge process, thereby evenly adhering to the surface of the positive electrode material. The in-situ generated LiF can participate in the formation of the positive electrode CEI film in the subsequent formation stage; at the same time, because the product contains carbon, the positive electrode material forms a carbon coating, which also improves the conductivity of the material. The stable CEI film and carbon coating isolate the direct contact between the electrolyte and the positive electrode material, inhibit the occurrence of side reactions, and simultaneously improve the structural stability of the material. The first discharge specific capacity of the button battery after coating increased by 24.23mAh / g, an increase of 8.3%, and the first coulombic efficiency increased by 7.97%; after 100 charge and discharge cycles, its residual discharge specific capacity increased by 23.8mAh / g, an increase of 11.4%. It can be seen that after the lithium-rich positive electrode material is coated on the surface of carbon fluoride, the first discharge capacity, the first coulombic efficiency and the discharge capacity after 100 cycles are significantly improved, and the battery performance is significantly improved.

[0116] Example 2

[0117] This example provides a preparation process and performance test of a battery composite material with different coating amounts of fluorinated graphite material, as follows:

[0118] The synthesis of lithium-rich materials, the preparation process of battery composite materials, the pre-discharge step, normal formation, electrochemical testing, and LiF detection were the same as in Example 1, with the only difference being the coating amount of graphite fluoride, which was 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt%, and 15wt%, respectively. The results showed that the LiF particle size was ≤10nm, with the majority of the particle size values ​​concentrated between 3-8nm. x The LiF contents corresponding to the coating amounts are 0.15wt%, 0.3wt%, 0.6wt%, 1.5wt%, 3wt% and 4.5wt%, respectively.

[0119] In addition, the lithium-rich cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 was used as comparative example 1.

[0120] The preparation of the electrode, assembly of button cells, and electrochemical performance test methods are all consistent with those in Example 1; the effects of different coating amounts of battery composite materials on the cycle performance of lithium button cells are as follows: Figure 5 As shown in the figure, the materials with different fluorinated graphite material coating amounts of 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt% and 15wt% are referred to as Example 2-1, Example 2-2, Example 2-3, Example 2-4, Example 2-5 and Comparative Example 2, respectively; the electrochemical performance comparison is shown in Table 2.

[0121] Table 2 Statistics of the cycling performance of lithium button batteries with different graphite fluoride coating content battery composite materials:

[0122]

[0123] Table 2

[0124] The test results show that for lithium button cells, when the carbon fluoride coating amount is 0wt%, 0.5wt%, 1wt%, 2wt%, 5wt%, 10wt% and 15wt%, respectively, the corresponding button cells have a second discharge specific capacity of 240.2mAh / g, 241.7mAh / g, 244.9mAh / g, 249.5mAh / g, 253.5mAh / g, 251.1mAh / g and 230.9mAh / g, respectively. It can be seen that the battery has a higher discharge specific capacity when the carbon fluoride coating amount is 2wt%, 5wt% and 10wt%.

[0125] When the carbon fluoride coating amount is 0wt%, that is, no carbon fluoride coating, the battery's second discharge specific capacity is 240.2mAh / g. After 100 charge and discharge cycles, its discharge specific capacity is 208.8mAh / g, and the capacity retention rate is 86.93%. When the coating amount is 0.5wt% and 1wt%, its second discharge specific capacity is 241.7mAh / g and 244.9mAh / g, respectively, which is not much different from the uncoated material; after 100 charge and discharge cycles, the remaining discharge specific capacity is 215mAh / g and 218.7mAh / g, respectively, with corresponding capacity retention rates of 88.95% and 89.30%. Compared with the uncoated material, the discharge capacity and cycle performance have been improved to a certain extent. When the coating amount is increased to 2wt%, 5wt%, and 10wt%, the second discharge capacity is 249.5mAh / g, 253.5mAh / g, and 251.1mAh / g, respectively. The 100th discharge capacity is 232.6mAh / g, 237.2mAh / g, and 227.2mAh / g, respectively, with capacity retention rates of 93.23%, 93.57%, and 90.48%, respectively. Compared with the positive electrode without carbon fluoride coating, the 100th discharge capacity increases by 23.8mAh / g, 28.4mAh / g, and 18.4mAh / g, respectively, and the capacity retention rate increases by 6.3%, 6.64%, and 3.55%, respectively. When the coating amount is further increased to 15wt%, the second discharge specific capacity is 239.6mAh / g, the 100th discharge specific capacity is 203.7mAh / g, and the capacity retention rate is 85.02%. At this time, the performance of the coated composite material is already lower than that of the original material.

[0126] It can be seen that when the coating amount is not higher than 5wt%, as the coating amount of carbon fluoride increases, the discharge capacity and cycle performance of the composite positive electrode material are significantly improved. When the coating amount is increased to 10wt%, the battery discharge capacity and cycle performance still have obvious advantages compared with the original material, but the performance at this time is lower than when the coating amount is 5wt%. When the coating amount is increased by 15wt%, the discharge capacity and cycle performance of the composite material are lower than those of the original material. At this time, too much LiF is generated, which will increase the battery polarization and reduce the capacity. This shows that when the coating amount is lower than 5wt%, as the coating amount increases, the amount of LiF converted from carbon fluoride in situ is just suitable for participating in the formation of a more stable CEI, but as the carbon fluoride further increases, the LiF content on the surface of the positive electrode material is too high, the nano effect of LiF cannot be exerted, and the insulating LiF will affect the conductivity of the material, increase the battery polarization, and thus affect the cycle performance and discharge capacity of the material. For lithium-rich positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54O2, 5wt% of carbon fluoride coating is the most cost-effective from the perspective of economy and electrochemistry.

[0127] Example 3

[0128] This embodiment describes the preparation process and performance testing of a surface-modified battery composite material.

[0129] The battery composite material is a lithium cobalt oxide positive electrode material LiCoO2 coated with 3wt% carbon fluoride material. The lithium cobalt oxide positive electrode material preparation and modification process specifically includes the following steps:

[0130] (1) Synthesis of lithium cobalt oxide positive electrode material: Cobalt sulfate and sodium sulfate were weighed in a stoichiometric ratio of 1:1, and CoCO3 was synthesized by coprecipitation. The mixture was then transferred to a muffle furnace and calcined at 600°C for 7 hours to obtain Co3O4. Co3O4 and Li2CO3 were weighed in a mass ratio of 1:1.05 and ground evenly. The mixture was then calcined in a high-temperature muffle furnace at 1000°C for 10 hours to obtain lithium cobalt oxide positive electrode material.

[0131] (2) The fluorinated graphite is uniformly coated on the surface of the lithium cobalt oxide positive electrode material. Specifically, a 100 mL beaker is taken, 50 mL of anhydrous ethanol is added, 0.06 g of fluorinated graphite and 1.94 g of commercial lithium cobalt oxide positive electrode material are weighed and added thereto, and stirred on a magnetic stirrer for 5 hours. Then, the mixture is filtered and transferred to a vacuum oven, and the temperature is set to 120 ° C and baked for 10 hours to obtain a composite positive electrode material.

[0132] (3) Assembling a battery using the above-mentioned initial composite material and pre-discharging, so that the carbon fluoride material on the surface of the lithium cobalt oxide positive electrode material generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material, specifically:

[0133] The battery assembly process is the same as in Example 1;

[0134] Pre-discharge: The assembled battery was discharged to 2V at a current of 20mA / g on a blue power test system.

[0135] The LiF detection method was the same as that in Example 1. The results showed that the LiF particle size was ≤10 nm, and the majority of the particle size values ​​were concentrated between 3 nm and 8 nm. The LiF content was determined to be 32 wt % by titration using the same method as in Example 1. The corresponding LiF content in this example was 0.96 wt %.

[0136] (4) The battery containing the battery composite material of this embodiment assembled in step (3) was formed and subjected to electrochemical testing. Specifically, the battery was charged to 4.5 V at a current of 20 mA / g, then discharged to 3 V, and then charged and discharged in this voltage range at a current of 150 mA / g.

[0137] Pre-discharge and formation charge-discharge curves are as follows Figure 6 As shown, the cycle performance and Coulomb efficiency comparison curves are as follows Figure 7 The electrochemical performance data are shown in Table 3. The 100-cycle capacity retention rate is calculated based on the second discharge capacity as the basic value.

[0138] In addition, a lithium cobalt oxide positive electrode material not coated with graphite fluoride was used as comparative example 3.

[0139] Table 3 is a summary table of the cycle performance test data of button-type batteries of Example 3 and Comparative Example 3:

[0140]

[0141] Table 3

[0142] The electrochemical performance test results show that before and after the lithium cobalt oxide surface is coated with 3wt% graphite fluoride, its discharge capacity in the pre-discharge stage increases from the original 0.3mAh / g to 13.9mAh / g. This shows that lithium cobalt oxide itself does not have capacity under low voltage conditions, but the coated graphite fluoride contributes part of the capacity through electrochemical reactions, generating LiF and carbon on the positive electrode surface and participating in the formation of the CEI film. In the subsequent normal formation and electrochemical performance test phase, the composite positive electrode material had an initial discharge capacity of 189.4mAh / g and an initial coulombic efficiency of 96.02%. After increasing the current, the second discharge capacity was 183.4mAh / g. After 100 charge and discharge cycles, its discharge capacity was 181.6mAh / g, and the capacity retention rate was 99.02%. In Comparative Example 3, the lithium cobalt oxide not coated with graphite fluoride has an initial discharge capacity of 184.8 mAh / g and an initial coulombic efficiency of 95.06%. After increasing the current, the second discharge capacity is 176.1 mAh / g. After 100 charge and discharge cycles, the discharge capacity is 154.7 mAh / g, and the capacity retention rate is 87.88%.

[0143] The test results show that after lithium cobalt oxide is coated with carbon fluoride to generate a LiF-rich surface layer in situ, the battery's first discharge specific capacity and first coulombic efficiency are not significantly improved. This is because the voltage range of lithium cobalt oxide itself is relatively high. Except for the first pre-discharge step, the voltage range during subsequent charge and discharge does not match. The carbon fluoride that did not fully react in the first step cannot continue to participate in the reaction. However, the LiF generated during the first discharge participates in the formation of a more stable CEI film, which greatly improves the cycle stability of lithium cobalt oxide. The capacity retention rate after 100 cycles increased by 11.14%, which will greatly promote the practical application of high-voltage lithium cobalt oxide.

[0144] Example 4

[0145] This embodiment is a preparation process and performance test of a surface-modified battery composite material. The battery composite material is a nickel-cobalt-manganese ternary positive electrode material LiNi 0.6 Co 0.2 Mn 0.2 The surface of O2 (NCM622) is coated with 3wt% of carbon fluoride material, specifically comprising the following steps:

[0146] (1) Graphite fluoride was uniformly coated on the surface of the nickel-cobalt-manganese ternary positive electrode material NCM622. Specifically, 0.03 g of graphite fluoride and 0.97 g of commercial nickel-cobalt-manganese ternary positive electrode material were weighed and added into an agate mortar, and then uniformly ground for 2 hours to obtain a composite positive electrode material.

[0147] (2) Assembling a battery using the above-mentioned initial composite material and pre-discharging the battery so that the fluorinated carbon material on the surface of the nickel-cobalt-manganese ternary positive electrode material NCM622 generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material, specifically:

[0148] The battery assembly process is the same as in Example 1;

[0149] Pre-discharge: The assembled battery was discharged to 2.0V at a current of 18mA / g on a blue power test system.

[0150] The LiF detection method was the same as that in Example 1. The results showed that the LiF particle size was ≤10 nm, and most of the particle size values ​​were concentrated between 3 nm and 8 nm. The LiF content was determined to be 32.5 wt % by titration. The corresponding LiF content in this example was 0.98 wt %.

[0151] (3) The battery containing the battery composite material of this embodiment assembled in step (2) was formed and subjected to electrochemical testing. Specifically, the battery was charged to 4.3 V at a current of 18 mA / g, then discharged to 3 V, and then charged and discharged in this voltage range at a current of 120 mA / g.

[0152] Pre-discharge and formation charge-discharge curves are as follows Figure 8 As shown, the cycle performance and Coulomb efficiency comparison curves are as follows Figure 9 The electrochemical performance data are shown in Table 4. The 100-cycle capacity retention rate is calculated based on the maximum discharge capacity as the basic value.

[0153] In addition, a nickel-cobalt-manganese ternary positive electrode not coated with graphite fluoride was used as comparative example 4.

[0154] Table 4 is a summary table of the cycle performance test data of the button-type batteries of Example 4 and Comparative Example 4:

[0155]

[0156] Table 4

[0157] Electrochemical performance test results show that the discharge capacity of the nickel-cobalt-manganese ternary cathode material NCM622 increased from the original 0.8 mAh / g to 12.3 mAh / g before and after coating the surface with 3 wt% graphite fluoride, confirming that the coated carbon fluoride undergoes an electrochemical reaction and produces the target LiF. In the subsequent formation and long-cycle testing phases, the battery composite material achieved an initial discharge capacity of 171.4 mAh / g and an initial coulombic efficiency of 86.13%. After increasing the current, the second discharge capacity reached 153.8 mAh / g. After 100 charge and discharge cycles, the discharge capacity remained at 151.4 mAh / g, with a capacity retention rate of 98.44%. The nickel-cobalt-manganese ternary material without carbon fluoride coating has a first discharge specific capacity of 167.2 mAh / g and a first coulombic efficiency of 85.79%. After increasing the current, the second discharge specific capacity is 145.3 mAh / g. After 100 charge and discharge cycles, its discharge specific capacity is 142.3 mAh / g, and the capacity retention rate is 92.70%.

[0158] Similar to lithium cobalt oxide, due to the mismatch between the voltage range of carbon fluoride and nickel-cobalt-manganese ternary materials, starting from normal formation and cycling, the effect of carbon fluoride coating on the discharge specific capacity and first coulomb efficiency of nickel-cobalt-manganese ternary materials is not obvious. However, after coating with carbon fluoride, the carbon material generated in the pre-discharge link improves the conductivity of the material, overcoming the phenomenon that the original material has a low capacity in the initial cycle stage, and the capacity first recovers and then decreases in the later stage. The LiF generated at the same time participates in the surface film formation, which also greatly improves the cycle performance of the material. The residual capacity retention rate of 100 high-current cycles is increased by nearly 7%. Therefore, the cycle performance of the nickel-cobalt-manganese ternary material is effectively improved after carbon fluoride coating.

[0159] Example 5

[0160] This embodiment provides a preparation process and performance test of a surface-modified battery composite material. The battery composite material is a silicon-carbon negative electrode material coated with a 5 wt% carbon fluoride material. The process specifically includes the following steps:

[0161] (1) Graphite fluoride is uniformly coated on the surface of the silicon-carbon negative electrode material to prepare a negative electrode plate, specifically: 200 mg of styrene-butadiene rubber (SBR) is weighed and dissolved in 5 mL of deionized water, stirred to form a uniform solution, and then 35 mg of graphite fluoride is added, and stirred at a speed of 1200 r / min for 0.5 hours to form a uniform composite solution, and then 665 mg of silicon-carbon negative electrode and 100 mg of superconducting carbon black conductive agent (Super P) are weighed and added to the obtained composite solution, and stirred at 1500 r / min for 0.5 hours to obtain an active material slurry, which is evenly coated on a copper foil with a coating thickness of 200 μm, and the plate is dried in a blast drying oven at 60°C to obtain a silicon-carbon negative electrode plate with a surface coated with graphite fluoride.

[0162] (2) Assembling a battery using the negative electrode sheet prepared above and pre-discharging the battery so that the fluorinated carbon material on the surface of the silicon-carbon negative electrode material generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material, specifically:

[0163] The button cell assembly is the same as in Example 1;

[0164] Pre-discharge: The assembled battery was discharged to 1.5V at a current of 65mA / g on a blue power test system.

[0165] The LiF detection method was the same as that in Example 1. The results showed that the LiF particle size was ≤10 nm, and most of the particle size values ​​were concentrated between 3 nm and 8 nm. The LiF content was determined to be 33.5 wt % by titration. The corresponding LiF content in this example was 1.68 wt %.

[0166] (3) The battery containing the battery composite material of this embodiment assembled in step (2) was formed and electrochemically tested. Specifically, the battery was discharged to 0 V at a current of 65 mA / g and then charged to 2.0 V. Subsequently, the battery was charged and discharged in this voltage range at a current of 330 mA / g.

[0167] Pre-discharge and formation charge curves are as follows Figure 10 As shown in (a), the cycle performance and Coulomb efficiency comparison curves are as follows Figure 10 (b) and the electrochemical performance data are shown in Table 5.

[0168] In addition, a silicon-carbon negative electrode material not coated with graphite fluoride was used as comparative example 5.

[0169] Table 5 is a summary of the button cell test data prepared in Example 5 and Comparative Example 5:

[0170]

[0171] Table 5

[0172] From the results of the electrochemical performance test, it can be seen that after the surface of the silicon-carbon negative electrode material is coated with 5wt% of graphite fluoride, the discharge specific capacity and the first coulombic efficiency do not change much, and are slightly improved compared to the unmodified material. This is because the silicon-carbon material itself has a high capacity, and the addition of a trace amount of graphite fluoride is not enough to significantly improve the battery capacity. However, it can be seen from the battery discharge curve that at a position close to 2.3V, the silicon-carbon negative electrode coated with graphite fluoride has a small discharge platform, which is a sign that the graphite fluoride undergoes an electrochemical reaction to generate LiF, indicating that the method provided by the present invention can indeed generate a LiF-rich SEI film in situ on the surface of the silicon-carbon negative electrode material. In further high current cycling tests, when the current density rose to 330mA / g, the discharge specific capacity of the silicon-carbon material coated with graphite fluoride was 643.61mAh / g, and the discharge specific capacity of the original silicon-carbon material was 640.41mAh / g. After 50 charge and discharge cycles, the capacity retention rates of the silicon-carbon materials coated with and without carbon fluoride were 96.83% and 95.84%, respectively. The cycle performance was improved after coating, and the discharge capacity curve trend showed that the silicon-carbon coated with carbon fluoride decayed more slowly in the later period, indicating that a stronger SEI film was formed on the surface of the silicon-carbon after coating with carbon fluoride. On the other hand, the coulombic efficiency of the silicon-carbon material coated with carbon fluoride has remained at a relatively stable level. Figure 10 (b) Clearly, the Coulombic efficiency of the uncoated carbon fluoride-coated silicon-carbon material is unstable and exhibits significant fluctuations, with the coulombic efficiency continuously changing during cycling. This indicates that under high current conditions, lithium precipitation has occurred at the negative electrode, forming lithium dendrites, which deteriorates battery performance and poses a short-circuit risk. This further demonstrates that the LiF-rich SEI film on the surface promotes the dissolution and deposition of lithium ions, resulting in superior overall electrochemical performance.

[0173] Example 6

[0174] This embodiment describes the preparation process and performance testing of a surface-modified battery composite material. The battery composite material is a graphite negative electrode material coated with a 5 wt% carbon fluoride material. The process specifically includes the following steps:

[0175] The preparation and testing process of the carbon fluoride-coated graphite negative electrode material is the same as that of Example 5, except that:

[0176] Pre-discharge in step (2): The assembled battery was discharged to 1.0 V at a current of 36 mA / g on a blue light test system.

[0177] The LiF detection method was the same as that in Example 1. The results showed that the LiF particle size was ≤10 nm, with most particle sizes concentrated between 3 nm and 8 nm. The LiF content was measured to be 34.6 wt %. The corresponding LiF content in this example was 1.73 wt %.

[0178] (3) The battery containing the battery composite material of this embodiment assembled in step (2) was formed and subjected to electrochemical testing, specifically: the battery was discharged to 0 V at a current of 36 mA / g, then charged to 3 V, and then charge and discharge cycled in this voltage range at a current of 200 mA / g.

[0179] Pre-discharge and formation charge-discharge curves are as follows Figure 11 As shown in (a), the cycle performance and Coulomb efficiency comparison curves are as follows Figure 11 (b) and the electrochemical performance data are shown in Table 6. The 100-cycle capacity retention rate is calculated based on the second discharge capacity. A graphite negative electrode without fluorinated graphite was used as Comparative Example 6.

[0180] Table 6 summarizes the test data of button batteries prepared in Example 6 and Comparative Example 6:

[0181]

[0182] Table 6

[0183] The electrochemical performance test results show that before and after the graphite negative electrode surface is coated with 5wt% carbon fluoride, the first discharge capacity is increased from the original 507.2mAh / g to 530.8mAh / g, and the first coulomb efficiency is increased from 73.28% to 74.36%. The discharge platform where the electrochemical reaction of carbon fluoride occurs can be clearly seen from the position of the discharge curve at around 2.3V. Further large current long cycle testing was carried out, and the second discharge capacity was increased from 320mAh / g to 344.2mAh / g, and the discharge capacity was increased by 24.2mAh / g, an increase of more than 7.6%. After 100 charge and discharge cycles, the remaining discharge capacity increased from 303.7mAh / g to 341.6mAh / g, and the corresponding capacity retention rate increased from 94.90% to 99.24%. It can be seen that the graphite coated with carbon fluoride has almost no capacity decay. This shows that LiF generated by carbon fluoride during the first discharge process participates in the formation of SEI film on the graphite surface, promoting the deposition of metallic lithium. The dense SEI film ensures the structural stability of the material during large current cycling, achieving a significant improvement in the performance of the graphite negative electrode.

[0184] Example 7

[0185] This embodiment describes the preparation process and performance testing of a surface-modified battery composite material. The battery composite material is a graphite negative electrode material coated with 5 wt% carbon fluoride material. The composite material preparation and electrode preparation process are the same as those in Example 6. The battery positive electrode adopts the lithium-rich positive electrode material synthesized in step (1) of Example 1. The synthesis of the lithium-rich positive electrode material and the electrode preparation method are as shown in Example 1.

[0186] The negative electrode of the button-type full cell assembled in this example was designed to have an areal capacity 1.1 times that of the positive electrode (i.e., an N / P ratio of 1.1). The electrolyte and separator were both conventional commercial electrolytes and separators. Because the negative electrode did not contain metallic lithium, a conventional formation method was used for the first cycle. The assembled battery was charged to 4.7V at a 0.1C rate on a BlueDyne test system and then discharged to 2.1V. Charge and discharge cycles were then repeated within this voltage range at a current of 100mA / g.

[0187] Comparison curve of button-type full battery cycle performance and coulombic efficiency Figure 12 The electrochemical performance data are shown in Table 7. The 50-cycle capacity retention rate is calculated based on the 3rd discharge capacity as the basic value. A button-type full battery was assembled using a graphite negative electrode without fluorinated graphite to prepare a negative electrode sheet as Comparative Example 7. The assembly method of the button-type full battery was the same as that of Example 7. The positive electrode still used the lithium-rich positive electrode material synthesized in step (1) of Example 1, and all battery parameters remained consistent.

[0188] Table 7 is a summary of the button cell test data prepared in Example 7 and Comparative Example 7:

[0189]

[0190] Table 7

[0191] The electrochemical performance test results show that a button-type full battery assembled with a graphite negative electrode coated with 5wt% carbon fluoride on the surface and a lithium-rich positive electrode synthesized in Example 1 was subjected to charge and discharge cycles in the voltage range of 2.1V-4.7V. Compared with a button-type full battery with a graphite negative electrode not coated with carbon fluoride, the first discharge specific capacity increased from the original 168.66mAh / g to 210.44mAh / g, and the first coulombic efficiency increased from 66.96% to 69.58%. In the full battery, since the initial formation process requires the formation of an SEI film on the negative electrode surface, a large amount of active lithium is consumed and side reactions occur, further reducing the discharge capacity. After the negative electrode graphite is coated with carbon fluoride, the LiF converted from carbon fluoride during the formation process will participate in the formation of the SEI film, reducing the occurrence of side reactions and improving the lithium ion transmission efficiency, thereby significantly improving the battery capacity.

[0192] Further high-current long-cycle testing showed that the third discharge specific capacity of the full battery before and after the graphite negative electrode was coated was 176.18mAh / g and 198.65mAh / g, respectively. The discharge specific capacity of the full battery after the graphite negative electrode was coated was increased by 22.47mAh / g, an increase of more than 12.76%. After 50 charge and discharge cycles, the residual discharge capacity of the graphite negative electrode before and after coating was 135.93mAh / g and 161.50mAh / g, respectively. The discharge specific capacity after coating was greatly improved, and the corresponding capacity retention rate was increased from 77.15% to 81.30%. It can be seen that the graphite negative electrode material coated with carbon fluoride, after being converted into lithium fluoride through the formation stage, still showed significantly improved electrochemical performance in the full battery.

[0193] Example 8

[0194] This example demonstrates the preparation and performance testing of a surface-modified battery composite material. The composite material consists of NCM622 coated with a 3wt% carbon fluoride material. The assembled battery undergoes a pre-discharge process followed by formation. All materials, battery preparation, and testing procedures used in this example are consistent with those in Example 4.

[0195] Another group of batteries assembled in this embodiment were taken as Comparative Example 8, which was formed and cycled directly at a conventional voltage (3.0-4.3 V) without the pre-discharge step.

[0196] Except for the pre-discharge, the other conditions of the two battery groups remain the same.

[0197] The comparison curves of the cycle performance and coulombic efficiency of the two groups of batteries are as follows: Figure 13 The electrochemical performance data are shown in Table 8. The 100-cycle capacity retention rate is calculated based on the maximum discharge capacity.

[0198] Table 8 is a summary table of the cycle performance test data of the button-type batteries of Example 8 and Comparative Example 8:

[0199]

[0200] Table 8

[0201] The electrochemical performance test results show that the NCM622 surface is coated with 3wt% of graphite fluoride in the pre-discharge stage, releasing a capacity of 12.3mAh / g. During this stage, the carbon fluoride undergoes an electrochemical reaction to produce LiF. Batteries directly formed in the conventional voltage range do not have this stage capacity. In the subsequent formation stage, the composite positive electrode coated with carbon fluoride in Example 8 has a discharge capacity of 171.4mAh / g and an initial coulombic efficiency of 86.13%. After increasing the current, the second discharge capacity is 153.8mAh / g. After 100 charge and discharge cycles, the remaining discharge capacity is 151.4mAh / g, and the capacity retention rate is 98.44%. The battery of Comparative Example 8, which was directly conventionally formed without pre-formation, had a first discharge specific capacity of 165.1 mAh / g and a first coulombic efficiency of 85.92%. After increasing the current, the second discharge specific capacity was 144.6 mAh / g. After 100 charge and discharge cycles, the remaining discharge specific capacity was 142 mAh / g, and the capacity retention rate was 94.04%.

[0202] As can be seen from the above results, the surface of Comparative Example 8 is coated with carbon fluoride, but it is not converted into LiF by pre-discharge treatment first, but is formed in a conventional manner. Since its discharge cut-off voltage is higher than the reaction potential of carbon fluoride, carbon fluoride cannot react to participate in the formation of CEI film, and the insulation of carbon fluoride itself will increase the battery polarization, so that the first discharge specific capacity and the second discharge specific capacity are both lower than the uncoated material (Comparative Example 4). However, the coating of carbon fluoride can reduce side reactions to a certain extent, and the cycle performance is improved relative to the original NCM622, mainly manifested in that the capacity retention rate after 100 cycles is higher than that of Comparative Example 4. However, whether it is capacity play or cycle retention rate, Comparative Example 8 is lower than the composite material of Example 8 that has been pre-discharged. This fully illustrates the necessity of the pre-discharge link for the modified material and the promotion of the electrochemical properties of the material. Even if the surface of the positive electrode material is coated with the same proportion of carbon fluoride material, whether it is pre-treated, that is, the pre-discharge treatment step, its performance including capacity and cycle performance has obvious gaps. Because the pretreatment of carbon fluoride forms LiF prior to the film-forming reaction, and the LiF participates in the film formation, the present invention exhibits superior electrochemical performance. In summary, the present invention provides a method for preparing a composite material for lithium-ion or lithium metal batteries. Due to the unique structure and chemical composition, the composite material exhibits excellent discharge capacity and cycle performance. Furthermore, the present invention can significantly reduce the environmental burden posed by waste carbon fluoride electrodes in lithium / carbon fluoride batteries.

[0203] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

[0204] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a surface-modified battery composite material, characterized in that: The preparation method comprises: Step S1, uniformly coating the surface of the battery active material with a carbon fluoride material to obtain an initial composite material; Step S2, pre-treating the initial composite material, whereby the fluorinated carbon material on the surface of the battery active material generates a surface film rich in nano-LiF and inorganic carbon through an in-situ reaction, thereby obtaining a surface-modified battery composite material; The fluorine-carbon ratio in the fluorinated carbon material is x, and 0.5≤x≤1.25; the proportion of the fluorinated carbon material in the total mass of the initial composite material is greater than 0 and less than 15wt%; The surface film of the battery composite material includes nano-LiF and inorganic carbon; the particle size of the nano-LiF is 3nm-8nm; the mass of the nano-LiF accounts for greater than 0 to less than or equal to 4.5wt% of the total mass of the battery composite material.

2. The preparation method according to claim 1, characterized in that The battery active material is a positive electrode active material, and the pretreatment of the initial composite material in step S2 is a pre-discharge treatment. The specific process is: assembling the initial composite material and the lithium-containing negative electrode material into a lithium battery, and then discharging the lithium battery at a current density of 10mA / g to 80mA / g until the voltage is less than or equal to 2.0V.

3. The preparation method according to claim 1, characterized in that The battery active material is a negative electrode active material, and the pretreatment of the initial composite material in step S2 is a pre-discharge treatment or battery formation; The specific process of the pre-discharge treatment is as follows: assembling the initial composite material and the lithium-containing negative electrode material into a lithium battery, and then discharging the lithium battery at a current density of 10 mA / g to 80 mA / g to a voltage of ≤2.0 V; The specific process of battery formation is: assembling the initial composite material and the lithium-containing positive electrode material into a battery, and then performing battery formation. The battery formation condition is charging and discharging at a rate of less than or equal to 0.1C.

4. The preparation method according to claim 3, characterized in that The specific process of the pre-discharge treatment is: assembling the initial composite material and the lithium-containing negative electrode material into a lithium battery, and then discharging the lithium battery at a current density of 10mA / g to 80mA / g to a voltage of 0V.

5. The preparation method according to any one of claims 1 to 4, characterized in that In step S1, the percentage of the fluorinated carbon material to the total mass of the initial composite material is 0.5wt%-5wt%; The fluorinated carbon material includes one or more of fluorinated graphite, fluorinated graphite polymer, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fiber, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated coke, fluorinated soft carbon, and fluorinated graphene.

6. The preparation method according to claim 5, characterized in that In the step S1, a fluorinated carbon material is coated on the surface of the battery active material by a solid phase method or a liquid phase method; The solid phase method includes one or more of blender mixing, grinding mixing or ball mill mixing; The liquid phase method includes dispersing the carbon fluoride material in an organic solvent, and then adding the battery active material and stirring and mixing; the organic solvent includes one or more of ethyl acetate, ethanol, isopropanol, n-heptane, butanol, acetic acid, octane, N,N-dimethylformamide, cyclohexanone, cycloethanol, N,N-dimethylacetamide, 1,2-propylene glycol, ethylene glycol, N-methylpyrrolidone, acetamide, diethylene glycol, and glycerol, mixed in any volume ratio.

7. The preparation method according to claim 1 or 2, characterized in that The battery active material is a positive electrode active material, and the positive electrode active material includes: a material having a structural formula Li x M y O z Compounds and derivatives thereof, wherein 0≤x / z≤2, 1 / 2≤x / y≤6, x, y, z≥0, and M is one or more of the elements B, C, N, Na, Mg, Al, Si, P, Cl, K, Ca, Sc, Ti, V, Cr, Ni, Co, Mn, Cu, Fe, Ga, Ge, As, Se, Br, Mo, Zn, Y, Zr, Nb, Tc, Ru, Pb, Pd, Rh, Ag, Cd, Sb, Ba, La, Hf, Ta, W, Os, Pb, and I.

8. The preparation method according to claim 1 or 3, characterized in that The battery active material is a negative electrode active material, and the negative electrode active material includes: one or more of an embedded negative electrode material, an alloy negative electrode material, and a metal oxide negative electrode material; The embedded negative electrode material includes one or more of carbon materials and lithium titanate materials; The alloy-type negative electrode material includes silicon-based negative electrodes and their derivatives, including one or more of silicon materials, silicon-oxygen materials, and silicon-carbon materials; The metal oxide negative electrode material includes one or more of SnO2, Co3O4, NiO, Fe3O4, and MnO2.

9. A surface-modified battery composite material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The battery composite material includes a battery active material and a surface film coated on the outer surface of the battery active material; The battery active material includes a positive electrode active material or a negative electrode active material; The surface film includes nano-LiF and inorganic carbon; the particle size of the nano-LiF is 3nm-8nm, and the mass percentage of the nano-LiF to the mass percentage of the battery composite material is greater than 0 and less than or equal to 4.5%.

10. An initial composite material, characterized in that The initial composite material is used to prepare the surface-modified battery composite material according to claim 9, wherein the initial composite material includes a fluorinated carbon material and a battery active material; the fluorinated carbon material is uniformly coated on the surface of the battery active material; the fluorinated carbon ratio in the fluorinated carbon material is x, and 0.5≤x≤1.25; the fluorinated carbon material accounts for greater than 0 to less than 15wt% of the total mass of the initial composite material.

11. The initial composite material according to claim 10, characterized in that The carbon fluoride material accounts for 0.5wt% to 5wt% of the total mass of the initial composite material; The battery active material includes a positive electrode active material or a negative electrode active material.

12. A secondary battery, characterized in that: The secondary battery comprises a surface-modified battery composite material prepared by the preparation method according to any one of claims 1 to 8, or a surface-modified battery composite material according to claim 9, or a surface-modified battery composite material prepared from the initial composite material according to claim 10; the secondary battery is a lithium ion battery or a lithium metal battery.

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