An alkali metal fluoride / carbon composite material, its preparation and application

Abstract

The present invention belongs to the field of energy materials, and discloses an alkali metal fluoride / carbon composite material and its preparation and application. The composite material is formed by a redox reaction between a carbon fluoride-based raw material and an alkali metal source raw material. The reaction generates an alkali metal fluoride MF and a carbon material, and MF is distributed on the carbon material. Among them, M represents the alkali metal element contained in the alkali metal source raw material, which is lithium, sodium or potassium; the alkali metal fluoride MF is LiF, NaF or KF. Taking the alkali metal element as lithium as an example, by adjusting the composition and structure of the composite material, the corresponding lithium fluoride (LiF) / carbon (C) composite material obtained can be used as a lithium compensation additive for the positive electrode of a lithium-ion battery to compensate for the lithium loss occurring during the first charge and discharge process of the lithium-ion battery, thereby improving the energy density of the lithium-ion battery; moreover, the LiF / C composite material of the present invention has good stability, and the operation process of using it as a lithium compensation additive for a lithium-ion battery is simple, and it has good compatibility with the existing battery production process.

Description

Technical Field

[0001] The present invention belongs to the field of energy materials, and more specifically, relates to an alkali metal fluoride (MF) / carbon (C) composite material and its preparation and application, and can be used as a cathode lithium compensation additive material in lithium ion batteries. Background Art

[0002] Currently, due to the urgent needs of wireless communication, electrification of transportation, and increasingly developed mobile electronic products, electrochemical energy storage technology has become the focus of global attention. Taking lithium ion batteries as an example, lithium ion batteries are widely used in various fields due to their many advantages such as high energy density, high power density, and long cycle life.

[0003] During the initial charging process of lithium ion batteries, side reactions occur between the negative electrode and the electrolyte, inevitably causing the loss of active lithium, resulting in battery capacity loss and reduced energy density.

[0004] The cathode lithium compensation method refers to introducing a lithium-containing active material with a high lithium ion capacity into the cathode. During the first charging operation of the battery, this material can release a high lithium ion specific capacity to compensate for the irreversible active lithium loss of the negative electrode and improve the energy density of the lithium ion battery. Currently, the materials reported as cathode lithium compensation additives mainly include: lithium-rich compounds, nano-composite materials based on conversion reactions, and binary lithium compounds, etc. However, these cathode lithium compensation additive materials generally have disadvantages such as poor environmental stability in the electrolyte and incompatibility with existing battery processes, which are not conducive to large-scale commercial applications.

[0005] Similar to lithium ion batteries, sodium ion batteries and potassium ion batteries also have the same problem. Summary of the Invention

[0006] In view of the above deficiencies or improvement requirements of the prior art, the purpose of the present invention is to provide an alkali metal fluoride / carbon composite material and its preparation and application. The alkali metal element M is selected from Li, Na, and K. The composite material can be formed by an oxidation-reduction reaction of a carbon fluoride-based raw material in a reducing alkali metal ion-containing solution or by an electrochemical reduction reaction of a carbon fluoride-based raw material. The generated alkali metal fluoride MF is uniformly distributed on the carbon-based material substrate. Taking the alkali metal element M as lithium as an example, by adjusting the composition of the composite material, etc., the corresponding lithium fluoride (LiF) / carbon (C) composite material can be used as a novel lithium compensation additive for the lithium ion positive electrode, compensating for the lithium loss at the negative electrode of the lithium ion battery, thereby improving the energy density of the lithium ion battery. Moreover, the preparation of the LiF / C composite material of the present invention can be carried out by both chemical lithiation and electrochemical lithiation methods. Compared with the existing positive electrode lithium compensation additives, the LiF / C composite material prepared by the present invention solves the problems of complex process, poor stability, and poor battery compatibility of the lithium compensation additive, and is compatible with the actual lithium ion battery production process. Based on the same principle of the present invention, the sodium fluoride (NaF) / carbon (C) composite material, the potassium fluoride (KF) / carbon (C) composite material and their preparation and application also have similar characteristics.

[0007] To achieve the above object, according to one aspect of the present invention, an alkali metal fluoride / carbon composite material is provided, characterized in that the composite material is formed by an oxidation-reduction reaction of a carbon fluoride-based raw material and an alkali metal source raw material, and the reaction generates an alkali metal fluoride MF and a carbon material, and the alkali metal fluoride MF is distributed on the carbon material, and thus the composite is obtained; wherein, M represents the alkali metal element contained in the alkali metal source raw material, specifically lithium, sodium or potassium; correspondingly, the alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF or potassium fluoride KF.

[0008] According to another aspect of the present invention, a preparation method of the above alkali metal fluoride / carbon composite material is provided, characterized in that the preparation method is to carry out an oxidation-reduction reaction of a carbon fluoride-based raw material in a reducing alkali metal ion-containing solution to prepare an alkali metal fluoride / carbon composite material, specifically including the following steps:

[0009] (1) Under an inert atmosphere condition, dissolve a polycyclic aromatic hydrocarbon in a solvent, and then add an alkali metal single substance to react with the polycyclic aromatic hydrocarbon to obtain a reducing M-containing solution; wherein, the alkali metal single substance is lithium, sodium or potassium; the reducing M-containing solution is specifically a reducing lithium-containing solution, a reducing sodium-containing solution or a reducing potassium-containing solution;

[0010] (2) React the carbon fluoride-based material with the reducing M-containing solution obtained in the above step (1). An alkali metal fluoride MF and a carbon material are formed by the reaction, and the alkali metal fluoride MF is distributed on the carbon material. Then, the obtained product is separated, washed, and dried to obtain the alkali metal fluoride / carbon composite material. The alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF, or potassium fluoride KF.

[0011] As a further preference of the present invention, in the above step (1):

[0012] The solute of the reducing M-containing solution is one or more of lithium naphthalide, lithium biphenyl, lithium indene, lithium anthracene, lithium phenanthrene, lithium pyrene, 1-methyl lithium naphthalide, 2-methyl lithium naphthalide, lithium benzophenone, or one or more of sodium naphthalide, sodium biphenyl, sodium indene, sodium anthracene, sodium phenanthrene, sodium pyrene, 1-methyl sodium naphthalide, 2-methyl sodium naphthalide, sodium benzophenone, or one or more of potassium naphthalide, potassium biphenyl, potassium indene, potassium anthracene, potassium phenanthrene, potassium pyrene, 1-methyl potassium naphthalide, 2-methyl potassium naphthalide, potassium benzophenone;

[0013] The solvent is one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethyl ether, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, toluene;

[0014] The concentration of the reducing M-containing solution is 0.01 - 10 mol / L.

[0015] As a further preference of the present invention, in the above step (2):

[0016] The carbon fluoride-based material is at least one of fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fibers, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated soft carbon, fluorinated graphdiyne;

[0017] Before the reaction, the mass ratio of the carbon fluoride-based material to the M element contained in the reducing M-containing solution is 1:0.01 - 10;

[0018] The reaction time of the reaction is 1 min - 48 h, and the reaction temperature is 0 - 150 °C;

[0019] Preferably, the reagent used for washing is one or more of esters, alcohols, carboxylic acids, amides, sulfones, tetrahydrofuran, water.

[0020] According to another aspect of the present invention, the present invention provides a method for preparing the above alkali metal fluoride / carbon composite material, which is characterized in that the preparation method is to prepare the alkali metal fluoride / carbon composite material by electrochemically reducing a carbon fluoride-based raw material, and specifically includes the following steps:

[0021] (1) Prepare a carbon fluoride-based material into an electrode as the working electrode, and then use an alkali metal element M as the counter electrode to assemble a battery with the participation of an electrolyte; the alkali metal element M is lithium, sodium or potassium;

[0022] (2) Perform electrochemical discharge treatment on the battery obtained in the step (1) to reduce the working electrode in the battery, and react to generate an alkali metal fluoride MF and a carbon material, and the alkali metal fluoride MF is distributed on the carbon material, so that the carbon fluoride-based material in the working electrode is transformed into a composite of carbon and an alkali metal fluoride; the composite of carbon and an alkali metal fluoride is the alkali metal fluoride / carbon composite material, and the alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF or potassium fluoride KF;

[0023] (3) Separate and collect the active substances of the electrode electrochemically reduced in the step (2), and finally clean and dry to obtain the alkali metal fluoride / carbon composite material.

[0024] According to another aspect of the present invention, the present invention provides a method for preparing the above-mentioned alkali metal fluoride / carbon composite material, characterized in that the preparation method is to prepare an alkali metal fluoride / carbon composite material by electrochemically reducing a carbon fluoride-based raw material, specifically including the following steps:

[0025] (1) Prepare a carbon fluoride-based material into an electrode as the working electrode;

[0026] (2) Use the alkali metal element M as the negative electrode, and the alkali metal element M is lithium, sodium or potassium; wet the working electrode obtained in the step (1) with an electrolyte, and then short-circuit the wetted working electrode with the negative electrode to reduce the working electrode, and react to generate an alkali metal fluoride MF and a carbon material, and the alkali metal fluoride MF is distributed on the carbon material, so that the carbon fluoride-based material in the working electrode is transformed into a composite of carbon and an alkali metal fluoride; the composite of carbon and an alkali metal fluoride is the alkali metal fluoride / carbon composite material, and the alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF or potassium fluoride KF;

[0027] (3) Collect the alkali metal fluoride / carbon composite material obtained in the step (2), and finally clean and dry it.

[0028] As a further preference of the present invention, in the step (1):

[0029] The carbon fluoride-based material is at least one of fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fibers, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated soft carbon, fluorinated graphdiyne;

[0030] In the working electrode, in addition to containing a carbon fluoride-based material, it also contains a conductive agent and a binder; preferably, the sum of the masses of the conductive agent and the binder accounts for 0.5% to 95% of the total mass of the working electrode, and the mass percentage of the carbon fluoride-based material is 5% to 99.5%.

[0031] As a further preference of the present invention, in the step (2), the discharge cut-off voltage range of the discharge treatment is 0.01 - 1.5 V (vs. M + / M).

[0032] According to the last aspect of the present invention, the present invention provides the application of the above alkali metal fluoride / carbon composite material as a positive electrode alkali metal element compensation additive; preferably, the application is specifically to compensate for the corresponding alkali metal element in the positive electrode material of the alkali metal ion battery.

[0033] As a further preference of the present invention, the initial charge specific capacity of the positive electrode alkali metal element compensation additive is 250 mAh / g - 1200 mAh / g.

[0034] Through the above technical solution conceived by the present invention, compared with the prior art, taking the alkali metal element M as lithium as an example, the present invention can construct a LiF / C composite material, which can be used as a novel lithium compensation additive for the positive electrode of a lithium ion battery and can be used to donate and compensate lithium ions. This composite material can be prepared by both chemical lithiation and electrochemical lithiation methods. Existing lithium compensation additives often have disadvantages such as poor environmental stability and poor compatibility with existing battery processes. However, the lithium compensation additive of the present invention is composed of a LiF / C composite material. LiF and C have good chemical stability and environmental stability and do not react with moisture in the air. Therefore, this additive has the advantage of good stability, and the remaining material after de-lithiation will not damage the electrode and has no negative impact. The positive electrode lithium compensation additive in the present invention has characteristics such as high capacity (high lithium ion capacity), high air stability, good environmental stability, and good matching and compatibility with existing battery processes.

[0035] Taking the chemical preparation of LiF / C composite materials as an example, based on the principle of chemical reactions, in the present invention, the carbon fluoride material is chemically lithiated by a reducing lithium-containing solution, and a new LiF component is in-situ generated and loaded on the C substrate during lithiation, thereby obtaining a composite material of LiF component and C (for example, the generated LiF component can be uniformly distributed on the carbon material substrate in the form of LiF nanoparticles to obtain a LiF / C composite structure; this LiF / C composite material, that is, LiF / C nanocomposite material); the LiF nanoparticles tightly combined with the carbon matrix can realize the extraction of high-capacity active lithium ions within the voltage range matching the positive electrode charging process, and this LiF / C composite material has the characteristics of good chemical stability and environmental stability. Moreover, the preparation method of the LiF / C composite material provided by the present invention is realized by a one-step chemical reaction method. Compared with the method of first preparing LiF and then compounding with carbon materials, LiF and C are uniformly compounded, and a high specific capacity of extractable active lithium ions can be achieved. It has the advantages of simple process, low production cost, easy industrialization, and good lithium compensation effect, and can be applied to various carbon fluoride-based materials (such as various fluorine-containing carbon materials). The reaction product prepared by the preparation method of the present invention is easy to separate from the solution, and the separated solvent can be recycled, which has the advantage of being green and environmentally friendly. In addition, this chemical preparation method can be completed within a wide temperature range (the reaction temperature can be selected in the range of 0 - 150 °C), the preparation process is simple and controllable, and the production cost is low; and by preferably adjusting parameters such as the type, concentration, dosage of the reducing lithium-containing solution used and its reaction time with the carbon fluoride material, different LiF / C composite materials with different degrees of lithiation can be obtained by using different carbon fluoride materials.

[0036] Taking the electrochemical preparation of LiF / C composite materials as another example, based on the principle of electrochemical reactions, using carbon fluoride-based materials, lithiation is achieved through discharging to obtain a lithium compensation additive material. Compared with the prior art, it can effectively solve problems such as complex preparation process, poor safety, and harsh preparation environmental conditions of lithium compensation additives. Moreover, the prepared LiF / C composite material is similar to the material prepared by the above chemical method, and has the advantages of strong process controllability and high specific capacity of the material.

[0037] Specifically, taking the preparation by chemical lithiation as an example, especially the LiF / C composite material can be prepared by a one-step chemical reaction method, and the following beneficial effects can be obtained:

[0038] (1) The present invention adopts a reducing lithium-containing solution and a carbon fluoride material to be mixed and stirred, which is a one-step chemical reaction method with the advantages of simple process, low production cost, and easy industrialization.

[0039] (2) The degree of preparation of the LiF / C composite material by chemical reaction is controllable and the reaction is uniform.

[0040] (3) In the LiF / C nanocomposite prepared in situ through a chemical reaction, lithium fluoride is in the form of ultrafine nanoparticles and is tightly combined with the carbon matrix, enabling lithium fluoride to decompose at a lower decomposition potential (e.g., <4.5 V), which is lower than the decomposition potential of conventional lithium fluoride (~6.0 V). The prepared LiF / C nanocomposite can undergo an electrochemical delithiation reaction within the working voltage range of the positive electrode during the charging process, providing a relatively high lithium ion specific capacity and can be used as a high-capacity and high-stability positive electrode lithium compensation additive material.

[0041] It can be seen that the present invention uses a simple chemical reaction method to chemically lithiate a carbon fluoride material to obtain a LiF / C composite material. The material preparation process is simple, and it has good chemical and environmental stability, making it suitable for large-scale industrial production.

[0042] For the preparation of the LiF / C composite material by an electrochemical method, the following beneficial effects can be achieved:

[0043] (1) The preparation method of the present invention utilizes the electrochemical reaction process, which is controllable. The degree of lithiation of the prepared material is highly controllable, and the preparation method has an advantage in terms of safety; during the electrochemical lithiation process of the present invention, in particular, by controlling the discharge cut-off voltage of the carbon fluoride, the discharge cut-off voltage is preferably controlled within the range of  0.01 - 1.5 V (vs. Li + / Li), which can effectively ensure the smooth progress of the electrochemical lithiation and obtain the target LiF / C composite product;

[0044] (2) The active substance and output can be regulated by adjusting the scale of the electrode / battery, enabling controllable batch production of the material;

[0045] (3) The usage method of this lithium compensation additive is compatible with the existing electrode and battery preparation processes, and it can be produced under the existing process conditions, enabling large-scale application.

[0046] The above characteristics also apply to the sodium fluoride (NaF) / carbon (C) composite material and potassium fluoride (KF) / carbon (C) composite material obtained by the basic invention.

[0047] The pure MF has a high voltage (for example, lithium fluoride is ~6.0 V), and it cannot be decomposed under the positive electrode charging cut-off voltage of a conventional secondary alkali metal battery (generally less than 5 V). Therefore, it is not suitable as a lithium / sodium / potassium compensation material for the positive electrode. The MF / C composite material prepared in the present invention reduces the decomposition potential of MF and can release active alkali metal ions within the positive electrode cut-off charging voltage, realizing the compensation of active ions for the battery system. The lithiation (including sodiation / potassiation) reaction in the present invention can be achieved not only through chemical preparation methods but also through electrochemical preparation methods. By optimizing and controlling the parameters of the preparation methods, large-scale, uniform, and controllable lithiation (of course, also including sodiation / potassiation) can be achieved.

[0048] In summary, the present invention realizes the lithiation of carbon fluoride-based materials through simple chemical preparation methods or electrochemical preparation methods. The prepared LiF / C composite material can undergo an electrochemical delithiation reaction within the working voltage range matching the positive electrode during charging, providing a high lithium ion specific capacity. It can be used as a lithium compensation additive material for lithium ion batteries to compensate for the lithium loss occurring at the negative electrode of lithium ion batteries, thereby improving the energy density of lithium ion batteries. The LiF / C composite material prepared by the method of the present invention exhibits the advantages of high capacity, high chemical stability, and outstanding high environmental stability compared with common lithium compensation additive materials, and can match conventional electrode preparation and battery assembly processes and environments. And by preparing the LiF / C composite material through an electrochemical method, similar technical effects can also be achieved.

[0049] Finally, as a supplement: when the alkali metal element is sodium or potassium, based on similar chemical preparation methods or electrochemical preparation methods, sodium fluoride / carbon composite materials and potassium fluoride / carbon composite materials can also be correspondingly obtained. The binding energies of sodium fluoride and potassium fluoride are lower than that of lithium fluoride. Therefore, after sodium fluoride and potassium fluoride are compounded with carbon materials through in-situ reactions, they can also decompose at appropriate potentials to provide sodium ions or potassium ions, and can be respectively applied to sodium ion batteries and potassium ion batteries, and can achieve technical effects similar to those of the above LiF / C composite material. Brief Description of the Drawings

[0050] Figure 1 It is a scanning electron microscope (SEM) image of the LiF / C composite material.

[0051] Figure 2 It is an X-ray diffraction (XRD) pattern of the LiF / C composite material in the initial state and after being placed in air for 10 days.

[0052] Figure 3 It is the first charge-discharge curve of the chemically lithiated LiF / C composite material.

[0053] Figure 4Charge curve of chemically lithiated LiF / C composite after being placed in air for 10 days.

[0054] Figure 5 Half-cell first-cycle charge-discharge curves of lithium cobalt oxide (LiCoO2) positive electrode sheets with and without LiF / C composite.

[0055] Figure 6 Half-cell cycle capacity curve of lithium cobalt oxide (LiCoO2) positive electrode sheet with LiF / C composite.

[0056] Figure 7 Half-cell first-cycle charge-discharge curves of lithium iron phosphate (LiFePO4) positive electrode sheets with and without LiF / C composite.

[0057] Figure 8 Half-cell first-cycle charge-discharge curves of lithium nickel 0.6 Co 0.2 Mn 0.2 O2) positive electrode sheets with and without LiF / C composite.

[0058] Figure 9 First charge-discharge curve of electrochemically lithiated LiF / C composite.

[0059] Figure 10 First charge-discharge curve of chemically lithiated sodium fluoride / carbon composite. Detailed implementation mode

[0060] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0061] Embodiment 1

[0062] Under normal temperature and pressure, dissolve naphthalene in tetrahydrofuran (THF), add metallic lithium with an equimolar ratio to naphthalene, stir to dissolve, and prepare a 1 mol / L naphthalene lithium solution. Subsequently, immerse graphite fluoride in the naphthalene lithium solution for 1 h. After the reaction is complete, centrifuge and separate the powder, wash it with tetrahydrofuran, and dry it to obtain the LiF / C composite, which can be used as a lithium compensation additive for the positive electrode of a lithium-ion battery.

[0063] Take 0.7 g of LiF / C composite material, 0.2 g of conductive agent (acetylene black), and 0.1 g of polyvinylidene fluoride (PVDF). Here, the mass fraction of PVDF in N-methylpyrrolidone (NMP) solvent is 5%. Mix the weighed materials evenly, homogenize, coat, bake at 80 °C under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic lithium into a half-cell, and conduct electrochemical performance tests on the LiF / C composite material.

[0064] In addition, after the prepared LiF / C composite material is placed in air containing water and oxygen for 10 days, take 0.7 g of LiF / C composite material, 0.2 g of conductive agent (acetylene black), and 0.1 g of polyvinylidene fluoride (PVDF). Here, the mass fraction of PVDF in N-methylpyrrolidone (NMP) solvent is 5%. Mix the weighed materials evenly, homogenize, coat, bake at 80 °C under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic lithium into a half-cell, and conduct electrochemical performance tests on the LiF / C composite material.

[0065] Take 0.8 g of lithium cobaltate, 0.1 g of conductive agent (acetylene black), and 0.1 g of PVDF (5 wt% PVDF / NMP solution), mix them, add 6 wt% (based on the total mass of lithium cobaltate active material, conductive agent, and binder) of LiF / C composite material, homogenize, coat, bake at 80 °C under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic lithium into a half-cell, and conduct electrochemical performance tests on the lithium cobaltate positive pole piece containing LiF / C additive material.

[0066] Figure 1 It is the scanning electron microscope image of the LiF / C composite material prepared in the first preferred embodiment constructed according to the present invention. It can be seen from the figure that most of the lithium fluoride particles are evenly distributed in a circular shape, and their particle size is ~20 nm. It can be seen that in the prepared LiF / C composite material, lithium fluoride nanoparticles are evenly distributed on the carbon-based material substrate.

[0067] Figure 2 It is the X-ray diffraction pattern of the LiF / C composite material in the first preferred embodiment constructed according to the present invention, which has characteristic peaks of lithium fluoride and carbon, proving the successful synthesis of the LiF / C composite material. It can be seen by comparison that even after being placed in air for 10 days, the diffraction peaks of XRD have not changed, indicating that the LiF / C composite material has good air stability.

[0068] Figure 3 It is the charge-discharge capacity diagram of the LiF / C composite material prepared in the first preferred embodiment constructed according to the present invention. The charging cut-off voltage is 4.5 V (vs. Li + / (Li), the charging capacity can reach 600 mAh / g at a current of 50 mA / g.

[0069] Figure 4 It is the charging capacity diagram of the LiF / C composite material prepared in the first preferred embodiment constructed according to the present invention after being placed in air for 10 days. The charging cut-off voltage is 4.5 V (vs. Li + / (Li), the charging capacity can reach 300 mAh / g at a current of 50 mA / g, and the capacity retention rate is 50%. It can be seen that the LiF / C composite material has good air stability.

[0070] Figure 5 It is the first-cycle charge-discharge capacity comparison diagram of the lithium cobalt oxide cathode containing the LiF / C composite material prepared in the first preferred embodiment constructed according to the present invention. It can be seen from the figure that when the charging cut-off voltage is 4.5 V (vs. Li + / (Li), the lithium cobalt oxide cathode material is charged at a rate current of 0.1 C (1 C = 140 mAh / g). When 6 wt% LiF / C composite material is added, the first charging capacity of the lithium cobalt oxide cathode increases by 50 mAh / g, indicating that the LiF / C composite material helps to improve the first charging lithium ion capacity of the lithium cobalt oxide battery, can compensate for the lithium ion consumption on the negative electrode surface during the first charge-discharge process of the lithium ion battery, and thus improve the energy density of the lithium ion battery.

[0071] Figure 6 It is the cycle performance diagram of the LiF / C composite material prepared in the first preferred embodiment constructed according to the present invention added to the lithium cobalt oxide cathode material. It can be seen from the figure that when 6 wt% LiF / C composite material is added, the first three activation charging currents are 0.1 C, and the charging current size during the cycle process is 1 C. After 60 cycles of the lithium cobalt oxide cathode material, the charge-discharge performance basically does not decay, indicating that the addition of the lithium compensator will not have a negative impact on the cycle stability of the cathode material.

[0072] Example 2

[0073] At 0 °C and normal pressure, anthracene and lithium are mixed in an equimolar ratio of 1:1 and dissolved in ethylene glycol dimethyl ether (DME) to prepare a 10 mol / L anthracene-lithium solution. Subsequently, graphene fluoride is immersed in the anthracene-lithium solution for 1 min. After the reaction is complete, the powder is centrifuged, washed with ethanol, and dried to obtain a lithium fluoride / graphene composite material, which can be used as a lithium compensation additive for the positive electrode of a lithium ion battery.

[0074] Mix 0.9 g of lithium iron phosphate, 0.05 g of conductive agent (carbon black), and 0.05 g of binder PVDF (2 wt% PVDF / NMP solution), add 2 wt% (based on the total mass of lithium iron phosphate active material, conductive agent, and binder) of lithium fluoride / graphene composite material, homogenize, coat, bake at 80 °C and under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic lithium into a half-cell, and conduct electrochemical performance tests on the lithium iron phosphate positive pole piece containing the lithium fluoride / graphene additive material.

[0075] Figure 7 It is the first-cycle charge-discharge capacity comparison chart of the lithium iron phosphate positive electrode containing the lithium fluoride / graphene composite material prepared in the second preferred embodiment constructed according to the present invention. It can be seen from the figure that when the charging cut-off voltage is 4.5 V (vs. Li + / Li), the lithium iron phosphate positive electrode material is charged at a rate current of 0.1 C (1 C = 150 mAh / g). After adding 2 wt% of the lithium fluoride / graphene composite material, the first charging capacity of the lithium iron phosphate positive electrode increases by 20 mAh / g, indicating that the lithium fluoride / graphene composite material helps to improve the first charging active lithium capacity of the lithium iron phosphate positive electrode, can make up for the lithium ion consumption brought about during the first charge-discharge process of the lithium ion battery, and thus improve the energy density of the lithium ion battery.

[0076] Example 3

[0077] At 150 °C and normal pressure, dissolve biphenyl in ethylene glycol dimethyl ether (DME), add metallic lithium with an equimolar ratio to biphenyl, stir to dissolve, and prepare a 0.1 mol / L solution of lithium biphenyl. Subsequently, soak carbon fluoride nanotubes in the lithium biphenyl solution for 48 h. After the reaction is complete, centrifuge and separate the powder, wash it with tetrahydrofuran, and obtain the LiF / C (carbon nanotube) composite material after drying, which can be used as a lithium compensation additive for the positive electrode of a lithium ion battery.

[0078] Mix 0.9 g of lithium nickel cobalt manganese oxide, 0.05 g of conductive agent (Ketjen black), and 0.05 g of PVDF (1 wt% PVDF / NMP solution), add 1 wt% (based on the total mass of lithium nickel cobalt manganese oxide active material, conductive agent, and binder) of the LiF / C composite material, homogenize, coat, bake at 80 °C and under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic lithium into a half-cell, and conduct electrochemical performance tests on the lithium nickel cobalt manganese oxide positive pole piece containing the LiF / C additive material.

[0079] Figure 8 It is the first-cycle charge-discharge capacity comparison chart of the LiF / C composite material added to the lithium nickel cobalt manganese oxide positive electrode prepared in the third preferred embodiment constructed according to the present invention. It can be seen from the figure that when the charging cut-off voltage is 4.5 V (vs. Li+ / Li), the nickel cobalt manganese oxide positive electrode material was charged at a rate current of 0.1C (1C = 180mAh / g). When 1wt% of the LiF / C composite material was added, the first charge capacity of the nickel cobalt manganese oxide positive electrode increased by 10mAh / g, indicating that the LiF / C composite material helps to increase the first charge active lithium capacity of the nickel cobalt manganese oxide positive electrode, which can make up for the lithium ion consumption caused by the first charge and discharge process of the lithium ion battery, thereby improving the energy density of the lithium ion battery.

[0080] Example 4

[0081] The carbon fluoride material is rolled onto carbon-coated aluminum foil to form an electrode serving as a working electrode. Metallic lithium is used as a counter electrode, and an electrolyte is added to assemble a battery. The resulting battery is then discharged to 0.5V to lithiate the working electrode, thereby converting the carbon fluoride material in the working electrode into a composite of elemental carbon and lithium fluoride. The discharged battery is then disassembled, and the LiF / C composite material is separated and collected. The LiF / C composite material is then cleaned and dried to obtain the positive electrode lithium compensation additive material.

[0082] Take 0.7g of LiF / C composite material, 0.2g of conductive agent (acetylene black) and 0.1g of polyvinylidene fluoride (PVDF), where the mass fraction of PVDF in N-methylpyrrolidone (NMP) solvent is 5%. The weighed materials are mixed evenly, slurried, coated, and baked at 80°C under vacuum conditions for 12h. The electrodes are punched into 10mm diameter pieces and assembled into half-cells with metallic lithium. The electrochemical properties of the LiF / C composite material are tested.

[0083] Figure 9 This is a charge and discharge capacity diagram of the LiF / C composite material prepared in the preferred embodiment 4 constructed according to the present invention, with a charge cut-off voltage of 4.8V (vs. Li + / Li), the charging capacity can reach 900mAh / g at a current of 50mA / g.

[0084] Example 5

[0085] At room temperature and pressure, naphthalene is dissolved in tetrahydrofuran (THF), and metallic sodium is added in an equal molar ratio to naphthalene, stirred and dissolved to prepare a 0.5 mol / L sodium naphthalene solution. Graphite fluoride is then immersed in the sodium naphthalene solution for 12 hours. After the reaction is complete, the powder is centrifuged, washed with tetrahydrofuran, and dried to obtain a sodium fluoride / carbon composite material, which can be used as a sodium compensation additive for the positive electrode of sodium ion batteries.

[0086] Take 0.7 g of sodium fluoride / carbon composite material, 0.2 g of conductive agent (acetylene black), and 0.1 g of polyvinylidene fluoride (PVDF). The mass fraction of PVDF in N-methylpyrrolidone (NMP) solvent is 5%. Mix the weighed materials evenly, homogenize, coat, bake at 80 °C under vacuum conditions for 12 h, punch into a pole piece with a diameter of 10 mm, assemble it with metallic sodium into a half-cell, and conduct electrochemical performance tests on the sodium fluoride / carbon composite material.

[0087] Figure 10 It is the charge-discharge capacity diagram of the sodium fluoride NaF / carbon C composite material prepared in the preferred sodium example 5 constructed according to the present invention. The charging cut-off voltage is 4.5 V (vs. Na + / Na). The charging capacity can reach 485 mAh / g at a current of 50 mA / g.

[0088] Example 6

[0089] In addition, for the preparation of LiF / C composite material by an electrochemical method, when separating and collecting the target product: (1) If the electrode is prepared by compounding with a conductive agent and a binder during preparation, the discharged battery can be disassembled, the electrolyte on the surface of the working electrode can be removed, the working electrode and the current collector can be mechanically separated, and the separated working electrode can be mechanically crushed into powder materials to obtain a crude product containing the substance obtained after the transformation of the active material. Then, the crude product can be separated to separate the conductive agent and the binder to obtain a refined product containing the substance obtained after the transformation of the active material. (2) If the carbon fluoride-based material is directly roll-pressed on the current collector during preparation, the active material can be directly separated after lithiation, and the target composite material can be obtained. In addition, for an electrode with a low content of conductive agent and binder, substance separation may not be necessary.

[0090] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an alkali metal fluoride / carbon composite material, characterized in that, The preparation method is to carry out an oxidation-reduction reaction of a carbon fluoride-based raw material in a reducing alkali metal ion-containing solution to prepare an alkali metal fluoride / carbon composite material, which specifically includes the following steps: (1) Under an inert atmosphere condition, dissolve a polycyclic aromatic hydrocarbon in a solvent, and then add an alkali metal element to react with the polycyclic aromatic hydrocarbon to obtain a reducing M-containing solution; wherein, the alkali metal element is lithium, sodium or potassium; the reducing M-containing solution is specifically a reducing lithium-containing solution, a reducing sodium-containing solution or a reducing potassium-containing solution; (2) React the carbon fluoride-based material with the reducing M-containing solution obtained in step (1). The reaction generates an alkali metal fluoride MF and a carbon material, and the alkali metal fluoride MF is distributed on the carbon material; then separate and wash the obtained product, and after drying, an alkali metal fluoride / carbon composite material can be obtained; the alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF or potassium fluoride KF.

2. The preparation method according to claim 1, characterized in that, In step (1): The solute of the reducing M-containing solution is one or more of lithium naphthalide, lithium biphenyl, lithium indene, lithium anthracene, lithium phenanthrene, lithium pyrene, lithium 1-methylnaphthalene, lithium 2-methylnaphthalene, lithium benzophenone, or one or more of sodium naphthalide, sodium biphenyl, sodium indene, sodium anthracene, sodium phenanthrene, sodium pyrene, sodium 1-methylnaphthalene, sodium 2-methylnaphthalene, sodium benzophenone, or one or more of potassium naphthalide, potassium biphenyl, potassium indene, potassium anthracene, potassium phenanthrene, potassium pyrene, potassium 1-methylnaphthalene, potassium 2-methylnaphthalene, potassium benzophenone; The solvent is one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethyl ether, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, toluene; The concentration of the reducing M-containing solution is 0.01 - 10 mol / L.

3. The preparation method according to claim 1, characterized in that, In step (2): The carbon fluoride-based material is at least one of fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, fluorinated carbon black, fluorinated carbon fiber, fluorinated activated carbon, fluorinated porous carbon, fluorinated hard carbon, fluorinated soft carbon, fluorinated graphdiyne; Before the reaction, the mass ratio of the carbon fluoride-based material to the M element contained in the reducing M-containing solution is 1:0.01 - 10; The reaction time of the reaction is 1 min - 48 h, and the reaction temperature is 0 - 150 °C.

4. The preparation method according to claim 3, characterized in that, The reagent used for washing is one or more of esters, alcohols, carboxylic acids, amides, sulfones, tetrahydrofuran, water.

5. Application of an alkali metal fluoride / carbon composite material as a compensating additive for alkali metal elements in a positive electrode, characterized in that, The alkali metal fluoride / carbon composite material is formed by an oxidation-reduction reaction of a carbon fluoride-based raw material and an alkali metal source raw material. The reaction generates an alkali metal fluoride MF and a carbon material, and the alkali metal fluoride MF is distributed on the carbon material, and thus is obtained by compounding; wherein, M represents the alkali metal element contained in the alkali metal source raw material, specifically lithium, sodium or potassium; correspondingly, the alkali metal fluoride MF is lithium fluoride LiF, sodium fluoride NaF or potassium fluoride KF.

6. The application according to claim 5, characterized in that, The application is specifically to compensate for the corresponding alkali metal element in the cathode material of an alkali metal ion battery.

7. The application according to claim 5, wherein The initial charge specific capacity of the cathode alkali metal element compensation additive is 250 mAh / g - 1200 mAh / g.

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