CN114551888A

CN114551888A - Method for inhibiting lithium precipitation of lithium ion battery negative electrode, slurry, negative electrode, battery and vehicle

Info

Publication number: CN114551888A
Application number: CN202210441287.6A
Authority: CN
Inventors: 不公告发明人
Original assignee: Beijing Sanchuan Eneng Technology Co ltd
Current assignee: Beijing Sanchuan Eneng Technology Co ltd
Priority date: 2022-04-26
Filing date: 2022-04-26
Publication date: 2022-05-27
Also published as: CN118748253A

Abstract

The invention discloses a method for inhibiting lithium separation of a lithium ion battery cathode, slurry, the cathode, a battery and a vehicle, wherein the method for inhibiting lithium separation of the lithium ion battery cathode comprises the following steps: MXene material is used as additive to be added into the negative electrode of the lithium ion battery. The invention provides a simple and effective technical scheme for inhibiting lithium separation of the negative electrode of the lithium ion battery, can effectively inhibit the dendritic crystal growth of the negative electrode lithium under a low-temperature environment or a high-rate charging and discharging condition, improves the lithium separation state, and further obtains obvious improvement on low-temperature performance or rate performance.

Description

Method for inhibiting lithium precipitation of lithium ion battery negative electrode, slurry, negative electrode, battery and vehicle

Technical Field

The invention belongs to the field of lithium batteries, and particularly relates to a method for inhibiting lithium precipitation of a negative electrode of a lithium ion battery, slurry, the negative electrode, the battery and a vehicle.

Background

The lithium ion battery is an environment-friendly energy storage device and has the advantages of high energy density, long service life, portability, easy carrying and the like. The temperature is an important external characteristic parameter when the lithium ion battery works, and generally, the working temperature of the lithium ion battery is-20 to 50 ℃. However, the further application of lithium ion batteries is hindered by the problem that lithium precipitation from graphite negative electrodes at high rates and low temperatures leads to low temperature failure of the batteries. The mechanism of low temperature failure is as follows: the performance of the lithium ion battery is greatly influenced by the dynamic characteristics, and Li⁺The need to first desolvate during intercalation into graphitic materials requires a certain energy consumption, which hinders Li⁺Diffusing into the graphite. And conversely Li⁺The solvation process occurs first upon release of the graphitic material into solution, and does not require energy consumption, Li⁺The graphite can be rapidly removed, so that the charge acceptance of the graphite material is obviously inferior to the discharge acceptance. At low temperature, the dynamic characteristics of the graphite negative electrode are improved and deteriorated, so that the electrochemical polarization of the negative electrode is obviously increased in the charging process, and metal lithium is easily precipitated on the surface of the negative electrode. The precipitated lithium metal further grows into lithium dendrites, thereby piercing the separator causing safety problems. With the fact that lithium ion batteries are widely used on new energy automobiles, the problem of low-temperature lithium separation of graphite cathodes is more and more emphasized, so that the research on the low-temperature lithium separation mechanism of the graphite cathodes and the inhibition of the low-temperature lithium separation of the graphite cathodes are extremely important, and the safety performance of the lithium ion batteries is improved.

At present, the low-temperature performance of the negative electrode of the lithium battery is mainly improved through the following two ways: the electrolyte composition is optimized, and a solvent or an additive with good low-temperature performance is added into the electrolyte, so that the conductivity of the electrolyte is improved, the SEI film impedance is reduced, and the ion transmission is accelerated; secondly, modifying the negative electrode, and improving the low-temperature performance of the lithium battery by adopting a negative electrode material with good low-temperature lithium storage performance, such as a two-dimensional material/soft and hard carbon coated or blended small-particle graphite, wherein the problem of lithium separation cannot be solved.

Disclosure of Invention

The invention aims to solve the technical problems that lithium is easy to separate out and lithium dendrites are generated to further influence the electrochemical performance and safety of a battery under a low-temperature environment or a high-rate charge and discharge condition of a lithium ion battery cathode, and a first aspect of the invention provides a method for inhibiting lithium separation of the lithium ion battery cathode, which comprises the following steps: MXene material is used as additive to be added into the negative electrode of the lithium ion battery.

In some embodiments, the MXene material has the formula: m_n+1X_nT_xWherein M is one or more selected from transition metal elements; and/or X is selected from one or more of carbon, nitrogen or boron elements; and/or, T_xRepresentative functional groups include: -one or more of-O, -F, -Cl, -Br, -I, -S; and/or the presence of a gas in the gas, n between 1 and 4.

In some embodiments, M in the MXene material comprises one or more of Ti, V, Nb, Cr, Ta, Hf, Mo, W, Fe, Mn, Y, or Sc elements;

in some embodiments, the functional groups in the MXene material include: at least one of-O, -F or-Cl.

In some embodiments, the MXene material is present in less than 20wt.% of the dry material of the negative electrode;

in some embodiments, the MXene is mixed in a negative electrode material of a lithium ion battery;

in some embodiments, the MXene is sprayed on a surface of a film layer formed from a negative electrode material of a lithium ion battery;

in some embodiments, the anode material in the anode includes: one or more of graphite, silicon oxide, silica, hard carbon, soft carbon, or mesocarbon microbeads.

In a second aspect, the present invention provides a composite paste for a lithium ion battery, comprising: MXene material, conductive agent and solvent in the above method.

In some embodiments, the ratio of the MXene to the conductive agent is 1:1 to 1:100 by mass.

In some embodiments, the conductive agent is selected from: one or more of graphene, carbon nanotubes and carbon black.

In some embodiments, the solvent in the composite slurry is selected from: one or more of water, N-methylpyrrolidone, N-dimethylformamide, ethanol, isopropanol, acetone, toluene or N-hexane.

The lithium ion battery negative electrode comprises a current collector and a negative electrode material layer coated on the current collector layer, wherein the negative electrode material layer contains MXene materials, and the MXene materials account for less than 20 wt% of dry materials in the negative electrode material layer.

In some embodiments, the surface functional groups of the MXene material in the anode material layer include: one or more of-O, -F, -Cl, -Br, -I or-S.

In some embodiments, the MXene material in the anode material layer accounts for less than 5 wt% of the dry material in the anode material layer.

In some embodiments, the negative electrode material in the negative electrode of the lithium ion battery comprises: one or more of graphite, silicon oxide, silica, hard carbon, soft carbon, and mesocarbon microbeads.

The fourth aspect of the present invention provides a method for preparing the above lithium ion battery cathode, which comprises the steps of:

mixing the composite slurry and a negative electrode material to prepare slurry, coating the slurry on a current collector, and drying to obtain the composite material; or pressing and forming MXene material powder and the negative electrode material; or spraying the MXene material dispersion liquid on the surface of a film layer formed by the negative electrode material and drying to obtain the MXene material dispersion liquid.

The fifth aspect of the invention provides a battery, which comprises a negative plate obtained by adopting the method for inhibiting lithium evolution of the negative electrode of the lithium ion battery; or, the battery comprises the lithium ion battery negative electrode; or the battery comprises the lithium ion battery cathode obtained by the preparation method of the lithium ion battery cathode.

A sixth aspect of the invention provides a vehicle comprising the battery described above.

The invention has the beneficial technical effects that: the invention provides a simple and effective technical scheme for inhibiting lithium precipitation of the negative electrode of the lithium ion battery, namely MXene material is used as an additive in the negative electrode material, so that dendritic crystal growth of negative electrode lithium under a low-temperature environment or under a high-rate charge-discharge condition can be effectively inhibited, the lithium precipitation state is improved, and further obvious improvement on low-temperature performance or rate performance is obtained; particularly, for electric vehicles (such as electric automobiles and electric bicycles), the performance of the battery at low temperature in winter can be obviously improved, and the driving mileage and the safety can be improved.

Drawings

FIG. 1 is a constant current discharge curve of graphite +0% MXene negative electrode deposition of 1 times capacity lithium (a) and 1.5 times capacity lithium (b) at-25 ℃ in inventive example 1;

FIG. 2 is a constant current discharge curve of graphite +3% MXene negative electrode deposition of 1X capacity lithium (a) and 1.5X capacity lithium (b) at-25 ℃ in inventive example 1;

FIG. 3 is a constant current discharge curve of graphite +5% MXene negative electrode deposited 1 times capacity lithium (a) and 1.5 times capacity lithium (b) at-25 ℃ in example 1 of the present invention;

FIG. 4 is a constant current discharge curve of graphite + sprayed MXene negative electrode deposited 1 times capacity lithium (a) and 1.5 times capacity lithium (b) at-25 ℃ in example 1 of the present invention;

FIG. 5 is an SEM photograph and corresponding optical photograph of the graphite +0% MXene negative electrode 1 times capacity lithium (a) and 1.5 times capacity lithium (b) after constant current discharge at-25 ℃ in example 1 of the present invention;

FIG. 6 is an SEM photograph and corresponding optical photograph of the graphite +3% MXene negative electrode 1 times capacity lithium (a) and 1.5 times capacity lithium (b) after constant current discharge at-25 ℃ in example 1 of the present invention;

FIG. 7 is an SEM photograph and corresponding optical photograph of a graphite +5% MXene negative electrode 1 times capacity lithium (a) and 1.5 times capacity lithium (b) after constant current discharge at-25 ℃ in example 1 of the present invention;

FIG. 8 is an SEM photograph and a corresponding optical photograph of a graphite + sprayed MXene negative electrode with 1 times capacity of lithium (a) and 1.5 times capacity of lithium (b) after constant current discharge at-25 ℃ in example 1 of the invention;

FIG. 9 shows SEM photographs (a) of a graphite +3% MXene negative electrode, element distribution mapping photographs (d), Ti (b), C (c), O (e) and F (f) element distribution photographs in example 1 of the present invention;

FIG. 10 is a charging curve at-25 ℃ of a full cell assembled from a different graphite negative electrode and lithium cobaltate in example 2 of the present invention;

FIG. 11 is SEM photographs of graphite +0% MXene negative electrode in a full cell at-25 ℃ in example 2 of the invention under different magnifications;

FIG. 12 is SEM pictures of graphite +3% MXene negative electrode in a full cell at-25 ℃ in example 2 of the invention under different magnifications;

FIG. 13 is SEM pictures of graphite +5% MXene negative electrode in a full cell at-25 ℃ in example 2 of the invention under different magnifications;

FIG. 14 is SEM photographs of graphite + sprayed MXene negative electrodes in a full cell at-25 ℃ in example 2 of the invention under different magnifications;

FIG. 15 shows overpotentials for deposition of lithium at-25 ℃ for MXene materials of different functional groups in example 3 of the present invention.

Detailed Description

The technical solution of the present invention will be described below by way of specific examples. It is to be understood that one or more of the steps referred to in the present application do not exclude the presence of other methods or steps before or after the combination of steps, or that other methods or steps may be intervening between those steps specifically referred to. It should also be understood that these examples are intended only to illustrate the invention and are not intended to limit the scope of the invention. Unless otherwise indicated, the numbering of the method steps is only for the purpose of identifying the steps, and is not intended to limit the scope of the invention, the relative relationship between the steps may be changed or adjusted without substantial technical change.

The raw materials and apparatuses used in the examples are not particularly limited in their sources, and may be purchased from the market or prepared according to a conventional method well known to those skilled in the art.

Example 1

This example uses MXene material Ti₃C₂T_xIllustrating the technical features of the present invention, wherein Ti₃C₂T_xEtching MAX phase material Ti by liquid phase method₃AlC₂To obtain, more specifically, Ti₃AlC₂Adding hydrofluoric acid solution (HF 40%) into the mixed solution, etching the mixed solution for 24 hours at normal temperature, centrifugally washing a reaction product, and drying the reaction product in vacuum at 60 ℃ to obtain MXene material Ti₃C₂T_xWherein the functional groups on MXene are mainly-F, -OH and-O.

In this embodiment, the negative electrode material is graphite, and the preparation method of the negative electrode sheet is as follows:

(1) pulping: according to the proportion of graphite: conductive carbon black (super P): mixing a binder (polytetrafluoroethylene PVDF) =8:1:1, weighing 3 parts of 1.25g of solid powder, and grinding and uniformly mixing the solid powder by using a mortar; sequentially ultrasonically dispersing 0mg, 37mg and 64mg of MXene materials in an N-methylpyrrolidone (NMP) solvent, and stirring for 1h to form MXene slurry; meanwhile, 40mg of MXene is ultrasonically dispersed in 8mL of ethanol solvent to prepare 5mg/mL of MXene suspension. Slowly adding the 1.25g of graphite negative electrode material into MXene slurry, and stirring for 48 hours, wherein the MXene accounts for 0%, 3% and 5% respectively;

(2) coating: coating the uniformly mixed cathode slurry on a copper foil by using a scraper with the diameter of 100 mu m, and drying in a vacuum oven at the temperature of 60 ℃ for 12 hours; taking a piece of dried graphite and 0% MXene negative electrode (namely a graphite electrode without MXene), and spraying 5mg/mL of MXene suspension on the surface of the unmodified graphite negative electrode to obtain the graphite +0% MXene, graphite +3% MXene, graphite +5% MXene and graphite + MXene spraying negative electrode, wherein the surface loading amount of MXene in the graphite + MXene spraying composite negative electrode is about 0.7 mg/mL; and slitting and rolling the graphite and 0% MXene, the graphite and 3% MXene, the graphite and 5% MXene and the graphite and MXene spraying respectively to prepare the negative plates. And weighing the negative plate, and recording the mass of the graphite.

In order to test the electrochemical performance of the negative plate, the assembled Li/graphite half-cell was subjected to a-25 ℃ constant current discharge test. The assembling method of the half cell comprises the following steps: selecting stonesNegative plates with uniform ink electrode quality (specific quality is shown in table 1) are assembled into a CR2032 lithium battery from bottom to top according to the sequence of negative shell-lithium plate-electrolyte-diaphragm-composite graphite electrode plate-gasket-shrapnel-positive shell. The test method comprises the following steps: calculating the nominal capacity of the battery (see table 1) by taking 372mAh/g as the standard multiple capacity of the graphite cathode, and performing constant current discharge according to the capacities of 1 time and 1.5 times, wherein the current density of the constant current discharge is 0.25mAcm^-2The discharge curves of the cells are shown in figures 1 to 4, and the results show that the discharge potential of the cell can quickly drop below 0V under the low-temperature condition of-25 ℃, and the graphite cathode can rapidly separate lithium. And the graphite +0% MXene-1 (a battery with a number of phi) has a remarkable voltage rise after being discharged to 0.95mAh, which indicates that the battery has a lithium extraction short circuit.

The above (r) -viii cell was disassembled to obtain a (over) deposited graphite negative electrode, and the surface of the negative electrode was characterized by an optical camera and a Scanning Electron Microscope (SEM), and the results obtained are shown in fig. 5 to 8. In either case, the predominant color was black when 1 x capacity lithium was deposited, indicating that the graphite was not fully lithiated. Compared with other composite negative electrodes deposited with 1 time of capacity of lithium, partial lithiation of graphite and 3% MXene is changed into golden yellow, and Li is promoted⁺The rapid transmission of the graphite is reduced, and the lithium precipitation of the graphite is reduced. In contrast, a small amount of white matter on the surfaces of graphite +0% MXene, graphite +5% MXene and graphite + MXene sprayed indicated that metallic lithium was precipitated on the surfaces. When the composite negative electrode deposits 1.5 times of lithium, the surfaces of the graphite and MXene sprayed surfaces are yellow except for large-area black, which indicates that a large amount of metallic lithium may be generated on the graphite and MXene sprayed surfaces. Therefore, when MXene is used as an additive for inhibiting the precipitation of metal lithium of the negative electrode, compared with MXene on the surface of the negative electrode layer, MXene mixed in the negative electrode material has a better performance improvement effect.

TABLE 1 graphite quality for graphite negative electrode sheet preparation and negative electrode capacity for-25 deg.C constant current discharge test

The results in fig. 5 show that at-25 ℃, lithium precipitation from the pure graphite negative electrode is unavoidable, which may be a significant cause of graphite negative electrode failure at low temperatures. In contrast, the results of fig. 6 to 8 show that MXene, when added to the negative electrode, does not grow lithium dendrites although it precipitates lithium on the surface, indicating that MXene may significantly improve the lithium precipitation state of the graphite negative electrode. However, when the mixing content or mixing manner of MXene is changed, the surface state thereof is different. The amount of metallic lithium on the surface of the graphite + sprayed MXene is obviously more than that of the composite electrode mixed with MXene in the graphite, which is basically consistent with the result of the optical photograph. Although the surface states of SEM images of graphite +3% MXene and graphite +5% MXene are not very different, the optical results show that the graphite +3% MXene negative electrode is better than the graphite +5% MXene negative electrode in promoting lithium storage in graphite. Meanwhile, by SEM photograph (a in FIG. 9) and element distribution mapping photograph (b-F in FIG. 9, original image is colored) of graphite +3% MXene negative electrode, it can be seen that Ti, C, O and F elements are uniformly distributed in the graphite electrode, and that Ti is shown₃C₂T_xAre uniformly distributed in the graphite cathode. Therefore, MXene (the mass content is less than 5 wt.%) is added into the negative electrode material in a small amount, so that the growth of lithium dendrites in a low-temperature environment can be effectively inhibited, the lithium precipitation state is improved, and the obvious improvement on low-temperature performance is further obtained; optionally, the addition amount of MXene in the negative electrode material is 0.01-5 wt.%; preferably 1wt.% to 4 wt.%; more preferably, 1wt.% to 3 wt.%. Of course, according to the disclosure of the present invention, a limited number of optimization experiments may be performed for different anode materials, and the addition amount of MXene may be in a range of 0.01wt.% to 20wt.% in some embodiments, which is adjusted to obtain a more optimized value of MXene content.

The invention is described by a low-temperature environment test in order to explain the effect of MXene in inhibiting the growth of lithium dendrites in a negative electrode of a lithium battery. In the actual charging and discharging process of the battery, the technical problem of lithium dendrite growth of the negative electrode can also be caused by charging and discharging (high multiplying power) under high current density, and the technical effect of inhibiting the lithium dendrite growth can be generated under the high current density by adding MXene component in the invention. That is, the low-temperature performance and rate performance of the battery can be improved by adding an MXene material to the negative electrode.

Example 2

To better illustrate that MXene of the present invention can produce the effect of inhibiting lithium deposition of the negative electrode of a lithium battery, the graphite negative electrode sheet prepared as described above and a positive electrode material lithium cobaltate (LiCoO) were used₂) The graphite anode is assembled into a CR2032 full cell to test the low-temperature (-25 ℃) performance of the full cell and characterize the appearance of the graphite anode. The preparation method of the positive plate comprises the following steps: subjecting LiCoO to condensation₂Conductive carbon black (super P): and (3) mixing the binder (polytetrafluoroethylene PVDF) =8:1:1, adding NMP, mixing into a slurry, coating on an aluminum foil, and drying to obtain the aluminum foil.

As shown in fig. 10, when the assembled full cell was charged to 4.2V at-25 ℃ and 1/30C, the charging capacities of the graphite +0% MXene, graphite +3% MXene, graphite +5% MXene, and graphite + MXene-sprayed negative electrodes were 151.8mAh/g, 251.9 mAh/g, 186.2mAh/g, and 96.6mAh/g, respectively. The lowest charge capacity of the graphite and MXene sprayed negative electrode is consistent with the test result of the Li/graphite half-cell, and a large amount of metallic lithium is precipitated in the graphite and MXene sprayed negative electrode. The results show that the mixed MXene material can promote the lithiation of graphite and improve the lithium storage capacity of the graphite negative electrode, and the MXene with the mass ratio of 3% is best, so that the MXene is doped in the negative electrode material and the addition amount is less than 3%.

As can be seen from fig. 10, the voltage curve characteristics of the graphite electrode are not changed by the graphite electrode added with MXene, but the voltage plateau values of the graphite electrode are slightly higher than those of a pure graphite electrode, which can be interpreted that the MXene material itself has excellent conductivity, and the conductivity of the negative electrode can be improved after the MXene material is added into the graphite negative electrode, so that a relatively slightly higher voltage plateau is shown. That is, MXene as an additive does not change the voltage characteristic curve of the battery and does not affect the applicability of the battery.

The graphite negative electrodes of the above-described full cells were characterized, and as a result, as shown in fig. 11 to 14, similar to the test results of the Li/graphite half cells, lithium was precipitated on the surface of the pure graphite negative electrode in a large amount, and lithium dendrites were generated (fig. 11). The graphite + sprayed MXene surface produced a lot of lithium metal (FIG. 14), but did not produce dendrites. The graphite +3% MXene and graphite +5% MXene surfaces did not produce lithium dendrites and the amount of precipitated lithium was small (FIGS. 12 and 13). Through the test of the low-temperature electrochemical performance of the full battery, MXene is further proved to be used as an additive, the growth of lithium dendrite is effectively inhibited, the effect of a negative electrode lithium precipitation state is improved, the lithium storage capacity of the battery under a low-temperature condition and a high multiplying power is further improved, and the safety performance and the cycle performance of the battery can be improved.

Example 3

The effect generated by MXene can be explained as related to the lithium affinity of MXene materials, the lithium affinity of MXene materials is mainly caused by the effects of abundant functional groups (such as-O, -F, -Cl and the like) on the surfaces of the MXene materials and metallic lithium, and the MXene materials dispersed in the negative electrode materials under the low-temperature environment can still play the role of nucleating agents and reduce the nucleation potential of the metallic lithium. FIG. 15 shows a comparative test plot of overpotential for lithium deposition at low temperature (-25 deg.C) for various MXene materials, where Ti₃C₂F₂MXene, TiNbCF containing-F functional group obtained by liquid phase etching with hydrofluoric acid in example 1₂MXene obtained by etching TiNbAlC by the same method; ti₃C₂Cl₂MXene and Ti containing-Cl functional groups are obtained by adopting a gas phase method and taking chlorine-containing gas as an etchant₃C₂O₂To add the above Ti₃C₂Cl₂By comparison, the nucleation overpotential of the MXene materials for metallic lithium is obviously lower than that of the Cu matrix, which shows that the MXene materials containing-O obtained after further oxidation (the specific implementation method is described in patent application 202011466046.4), and the MXene materials can generate the effect of reducing the nucleation potential of the metallic lithium. It can also be seen by comparison that MXene containing halogen functional groups (-F and-Cl) had a lower low temperature nucleation overpotential than MXene containing-O functional groups; MXene containing-F functional group has lower low-temperature nucleation overpotential than MXene containing-Cl; accordingly, MXene for use as an additive according to the present invention preferably contains chalcogen (-O, -S) and halogen (-F, -Cl, -Br, -I)MXene of a functional group; more preferably MXene of a functional group of the halogen element (-F, -Cl, -Br, -I); MXene having a-F functional group is preferable among the halogen elements; MXene containing an-O functional group is preferred among chalcogenides.

Since MXene materials are a class of materials, they are represented by the formula: m is a group of_n+1X_nT_xWherein M is selected from one or more of transition metals; x is selected from one, two or three of carbon, nitrogen or boron elements; t is_xRepresentative functional groups include: at least one of elements of the fifth main group, the sixth main group or the seventh main group;nbetween 1 and 4; wherein, MXene with M selected from one, two, three, four or five of Ti, V, Nb, Cr, Ta, Hf, Mo, W, Fe, Mn, Y or Sc is common; t is_xThe functional groups are associated with the etchant used to etch the MAX phase and typically include: -O, -OH, -F, -Cl, -Br, -I, -S or-NH₄. Through the teaching of the present invention, one skilled in the art can select MXene material with different elemental compositions and use it as an additive for improving the low temperature performance of lithium batteries.

The MXene material is used as a functional additive in the lithium battery cathode material to improve the low-temperature performance of the battery, is simple and effective, and is easy to introduce into the existing production for popularization and use. Particularly, for electric vehicles (such as electric automobiles and electric bicycles), the performance of the battery at low temperature in winter can be obviously improved, and the driving mileage and the safety can be improved.

Example 4

The embodiments can show that a better low-temperature performance improvement effect can be obtained when the MXene material is dispersed in the negative electrode material, and in order to improve the dispersibility of the MXene material in the negative electrode slurry and improve the electrode production efficiency, in the actual production, the MXene adding mode of the invention preferably firstly disperses the MXene material and the conductive agent in the solvent to form the slurry (primary dispersion), then mixes the slurry and the negative electrode material to form the negative electrode slurry (secondary dispersion), and then coats the negative electrode slurry on the current collector, so as to solve the problem that the MXene material and the conductive agent are difficult to disperse uniformly in the negative electrode material. Therefore, the invention also provides composite slurry, which comprises an MXene material, a conductive agent and a solvent, wherein the mass ratio of the MXene material to the conductive agent is 1:1 to 1: 100; optionally, the conductive agent is selected from: one or more of graphene, carbon nanotubes and carbon black; the solvent is selected from: one or more of water, N-methylpyrrolidone, N-dimethylformamide, ethanol, isopropanol, acetone, toluene or N-hexane.

In this embodiment, taking the preparation of graphite +5% MXene in example 1 as an example, the preparation of the composite slurry includes: first, 64mg of MXene and 125mg of conductive carbon black were mixed and added to 20ml of NMP, and the mixture was stirred and ultrasonically dispersed uniformly to prepare a slurry.

When the negative plate is prepared, the prepared slurry is added into graphite powder according to the calculated proportion, and NMP is added to adjust the viscosity, so that the negative slurry can be obtained. The process method can improve the dispersibility of MXene and the conductive agent in the negative electrode material, reduce the stirring and dispersing time of the negative electrode slurry and improve the production efficiency of the negative electrode plate.

In some embodiments, the conductive agent may also be replaced with one or more of graphene, carbon nanotubes, carbon black. In the formulation of the negative electrode sheet in example 1, the mass ratio of MXene to the conductive agent in the prepared composite slurry is preferably 1:3.4, but those skilled in the art can further optimize the mass ratio of MXene to the conductive agent in the composite slurry according to the kind of the negative electrode material, for example, the ratio of MXene to the conductive agent is between 1:1 and 1: 100.

Because MXene material also has good conductivity, the MXene material can also play a role of a conductive agent when added into a negative electrode material, but because the MXene material is difficult to industrially synthesize in batches and is high in price (about 200 yuan/g), the MXene material is used as the conductive agent and is inevitably high in cost when applied to actual production, so that a small amount of MXene material is matched with the common conductive agent for use, the composite slurry is used for solving the problems of battery failure and potential safety hazard caused by easy generation of lithium dendrites on a negative electrode of a lithium battery when charging and discharging at low temperature or high rate, the MXene material is mainly used for inhibiting the growth of the lithium dendrites and improving the state of lithium precipitation, the MXene material can also improve the lithium storage capacity at low temperature and obviously improve the low-temperature performance of the battery when added into the negative electrode, and the method provided by the invention is easy to be introduced into the existing battery production process and has cost advantages, has industrial applicability.

Example 5

This embodiment also provides another dry-process electrode preparation method, which includes the following steps: mixing MXene powder, a negative electrode material and a binder, and then pressing and molding to obtain the electrode. Taking the electrochemical material as silicon powder as an example, in a specific embodiment, the electrochemical material comprises: the more specific implementation steps are as follows: mixing silicon powder, MXene material, conductive carbon black and PVDF according to the mass ratio of 7:0.4:1.1: 1.5; and then the mixed powder is filled into a powder feeder, and the powder is sprayed on the copper foil by using a dry spraying machine. And (3) after the dry spraying is finished, carrying out hot pressing at a constant temperature of 175 ℃ (because the melting point of PVDF is 155-160 ℃) to obtain the negative plate with the active substance layer being silicon and MXene materials.

In other embodiments of the present invention, the negative electrode material may also be selected from one or more of graphite, silicon oxide, silica, hard carbon, soft carbon, and mesocarbon microbeads.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.

Claims

1. A method for inhibiting lithium evolution from a negative electrode of a lithium ion battery, comprising: MXene material is used as additive to be added into the negative electrode of the lithium ion battery.

2. The method of claim 1, wherein the method further comprises the step of comparing the measured signal with a reference signalThe chemical formula of MXene material is shown as: m_n+1X_nT_xWherein M is one or more selected from transition metal elements;

and/or X is selected from one or more of carbon, nitrogen or boron elements;

and/or, T_xRepresentative functional groups include: -one or more of-O, -F, -Cl, -Br, -I or-S;

and/or the presence of a gas in the gas,nbetween 1 and 4.

3. The method of claim 2, wherein M comprises one or more of Ti, V, Nb, Cr, Ta, Hf, Mo, W, Fe, Mn, Y, or Sc elements;

and/or, the functional groups include: at least one of-O, -F or-Cl.

4. The method according to any one of claims 1 to 3, wherein the MXene material is present in an amount of less than 20wt.% of the dry mass of the negative electrode;

and/or the MXene is mixed in a negative electrode material of the lithium ion battery;

and/or the MXene is sprayed on the surface of a film layer formed by a negative electrode material of the lithium ion battery;

and/or the anode material in the anode comprises: one or more of graphite, silicon oxide, silica, hard carbon, soft carbon or mesocarbon microbeads.

5. A composite paste for a lithium ion battery, comprising: the MXene material, conductive agent and solvent in the method of any one of claims 1 to 4; wherein the mass ratio of the MXene to the conductive agent is 1:1 to 1: 100.

6. The composite paste according to claim 5, wherein the conductive agent is selected from the group consisting of: one or more of graphene, carbon nanotubes and carbon black;

and/or, the solvent is selected from: one or more of water, N-methylpyrrolidone, N-dimethylformamide, ethanol, isopropanol, acetone, toluene or N-hexane.

7. The lithium ion battery negative electrode is characterized by comprising a current collector and a negative electrode material layer coated on the current collector layer, wherein the negative electrode material layer contains MXene materials, and the MXene materials account for less than 20 wt% of dry materials in the negative electrode material layer.

8. The lithium ion battery negative electrode of claim 7, wherein the negative electrode material in the lithium ion battery negative electrode comprises: one or more of graphite, silicon oxide, silicon monoxide, hard carbon, soft carbon and mesocarbon microbeads;

and/or the epi-functional groups of the MXene material include: -one or more of-O, -F, -Cl, -Br, -I or-S;

and/or the MXene material accounts for less than 5 wt% of the dry material in the negative electrode material layer.

9. A method for preparing the negative electrode of the lithium ion battery according to claim 7 or 8, comprising the steps of:

mixing the composite slurry as claimed in claim 5 or 6 with a negative electrode material to prepare a slurry, coating the slurry on a current collector, and drying to obtain the composite slurry;

or pressing and forming MXene material powder and the negative electrode material;

or spraying the MXene material dispersion liquid on the surface of a film layer formed by the negative electrode material and drying to obtain the MXene material dispersion liquid.

10. A battery comprising a negative electrode sheet obtained by the method according to any one of claims 1 to 4;

or, the battery comprises the lithium ion battery negative electrode of claim 7 or 8;

or, the battery comprises the lithium ion battery cathode obtained by the preparation method of claim 9.

11. A vehicle comprising the battery of claim 10.