Silicon negative electrode material, preparation method thereof and battery

Abstract

The invention provides a silicon negative electrode material, a preparation method thereof and a battery, and relates to the technical field of energy storage. The silicon negative electrode material comprises an inner core, a middle layer and an outer layer, the inner core comprises a silica material; the middle layer comprises SnF4, a Li-Sn-Si-O compound and a conductive metal nanowire; the outer layer comprises an MXene material, and the chemical formula of the MXene material is Ti < 3 > C < 2 > T < x >. The synergistic effect of the MXene on the outer layer and the fluorine-rich inorganic layer on the middle layer promotes ion / electron transmission at a particle interface, effectively buffers the volume expansion of the silicon-oxygen negative electrode, and improves the electrochemical performance of the battery.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a silicon negative electrode material and a preparation method thereof, and a battery. Background Art

[0002] With the rapid development of portable electronic devices and new energy vehicles, people have higher and higher requirements for battery energy density. On the one hand, the energy density of the battery can be improved by increasing the discharge voltage of the battery, and on the other hand, the specific capacity of the positive and negative electrode materials needs to be increased. However, the actual specific capacity of the current commercial graphite negative electrode is 360mAh / g~365mAh / g, which is very close to its theoretical specific capacity of 372mAh / g, and there is limited room for improving the battery energy density.

[0003] In comparison, the silicon-oxygen negative electrode has a higher theoretical specific capacity (about 2100mAh / g) and a suitable lithium insertion potential (about 0.4V). Compared with the pure silicon negative electrode, the volume expansion is smaller. In addition, silicon-based negative electrode materials have a wide source, abundant reserves, and are environmentally friendly. They are the most promising next-generation lithium-ion battery negative electrode materials.

[0004] However, the silicon-oxygen negative electrode still faces many difficulties during the lithium insertion process, especially the volume expansion caused by lithium insertion. The huge volume will cause the solid electrolyte interface layer (SEI) on the surface of the silicon-oxygen particles to continuously rupture, repeatedly exposing new particle surfaces and continuously reacting with the electrolyte to form SEI. The continuous rearrangement of the SEI layer will consume a large amount of active lithium from the counter electrode, resulting in a rapid decrease in battery capacity. Summary of the invention

[0005] Based on this, in order to solve the volume expansion of silicon-oxygen negative electrode materials and avoid excessive consumption of active lithium, the present application provides a silicon negative electrode material and a preparation method and a battery.

[0006] In a first aspect, the present application provides a silicon negative electrode material, the silicon negative electrode material comprising a core, an intermediate layer and an outer layer; the core comprises a silicon-oxygen material; the intermediate layer comprises SnF4, a Li-Sn-Si-O compound and a conductive metal nanowire; the outer layer comprises a MXene material, and the chemical formula of the MXene material is Ti3C2T x .

[0007] In some of the embodiments, the mass fraction of the conductive metal nanowires in the middle layer is 14% to 52%.

[0008] In some embodiments, the thickness of the intermediate layer is 30nm~70nm, and the thickness of the outer layer is 5nm~15nm.

[0009] In some of the embodiments, the MXene material is formed by etching with HF or a fluorine-containing salt.

[0010] In a second aspect, the present application also provides a method for preparing a silicon negative electrode material, comprising the following steps:

[0011] Forming conductive nanowires on the surface of the silicon-oxygen material to obtain a first intermediate;

[0012] Mixing the first intermediate and Li2SnF6 solution, and removing the solvent to obtain a second intermediate;

[0013] forming a cationic homopolymer on the surface of the second intermediate to obtain a third intermediate;

[0014] Mixing the MXene material with the third intermediate to obtain a fourth intermediate;

[0015] The fourth intermediate is calcined to obtain a silicon negative electrode material.

[0016] In some embodiments, preparing the first intermediate comprises the following steps:

[0017] Mixing the silicon-oxygen material, the alkaline solution, the metal salt solution, the first solvent and hydrazine hydrate to obtain a first intermediate solution, wherein the mass ratio of the metal salt to the silicon-oxygen material in the first intermediate solution is (6-15):100;

[0018] The first intermediate solution is stirred at 60° C. to 100° C., and the first intermediate is obtained by filtering and washing.

[0019] In some embodiments, the step of preparing the second intermediate comprises:

[0020] Adding the first intermediate to a second solvent containing Li2SnF6 to obtain a second intermediate solution; the mass ratio of Li2SnF6 to the first intermediate is (4-11):100;

[0021] The second intermediate solution is stirred at 60° C. to 100° C. until the second solvent evaporates to obtain the second intermediate.

[0022] In some embodiments, the step of preparing the third intermediate comprises:

[0023] Adding the second intermediate to the cationic homopolymer solution, stirring to obtain a third intermediate solution; wherein the mass fraction of the cationic homopolymer in the cationic homopolymer solution is 5% to 12%, and the mass volume ratio of the second intermediate to the cationic homopolymer solution is 25 g / L to 35 g / L;

[0024] The third intermediate solution is filtered, and the precipitate is retained to obtain the third intermediate.

[0025] In some embodiments, the steps of preparing the fourth intermediate include:

[0026] The third intermediate and the MXene material are mixed in a third solvent at a mass ratio of (2-6):1 to obtain a fourth intermediate solution;

[0027] The fourth intermediate solution is stirred, washed and dried to obtain the fourth intermediate.

[0028] In some embodiments, the calcination process satisfies at least one of the following (1) to (3):

[0029] (1) Calcination in an inert gas atmosphere; this step of calcination will transform Li2SnF6 into SnF4 and Li-Sn-Si-O (Li2SnSi3O 6y ).

[0030] (2) Calcination temperature is 200℃~400℃;

[0031] (3) Calcination time is 2h~4h.

[0032] In a third aspect, the present application further provides a battery, wherein the battery comprises a negative electrode plate, wherein the negative electrode plate comprises the silicon negative electrode material, or comprises the silicon negative electrode material prepared by the preparation method.

[0033] In the above silicon negative electrode material, the silicon oxide material is used as the core and an intermediate layer and an outer layer are formed on its surface. The high mechanical strength of the outer layer MXene is conducive to buffering the volume expansion of the silicon oxide negative electrode, and the high electronic conductivity of MXene can maintain high electrical connectivity between particles. At the same time, MXene is located in the outer layer, and the fluorine group at the outer end is conducive to the formation of an interface layer containing LiF, which is conducive to the homogenized transmission of lithium ions. The SnF4 in the intermediate layer can inhibit the corrosion of HF in the electrolyte, improve the mechanical strength of the intermediate layer, and the synergistic effect of SnF4 and LiF establishes a uniform lithium ion transmission channel, effectively improving the overall performance of the SEI layer. During the use of the battery, the Li-Sn-Si-O compound (Li2SnSi3O 6y) can be quickly converted into fast ion conductor Li2SnO3 and Li2SiO3 with buffering expansion effect, so as to limit the volume expansion of the core silicon oxygen material, provide good ionic conductivity, and will not consume the lithium source in the electrolyte. At the same time, the conductive metal nanowires can form a conductive network between the core and the outer layer, improving the electronic conductivity of the silicon negative electrode material. In summary, the outer layer MXene and the middle layer of conductive metal nanowires provide good electronic conductivity, the outer layer MXene and the middle layer Li-Sn-Si-O limit the volume expansion of the core silicon oxygen material, and the middle layer Li-Sn-Si-O and SnF4 provide good ionic conductivity, so that a good synergistic effect is formed between the core, the middle layer and the outer layer, which promotes the ion and electron transfer at the particle interface, effectively buffers the volume expansion of the silicon oxygen negative electrode, and improves the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a schematic diagram of the structure of a silicon negative electrode material according to one embodiment.

[0035] FIG. 2 is a schematic diagram of a method for preparing a silicon negative electrode material according to an embodiment. DETAILED DESCRIPTION

[0036] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0037] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0038] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0039] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0040] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0042] If there is no special explanation, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S12 and S14, which means that the method may include steps S12 and S14 performed sequentially, or may include steps S14 and S12 performed sequentially. For example, it is mentioned that the method may also include step S16, which means that step S16 may be added to the method in any order, for example, the method may include steps S12, S14 and S16, or may include steps S12, S16 and S14, or may include steps S16, S12 and S14, etc.

[0043] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0044] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] The silicon oxide negative electrode still faces many challenges during the lithium insertion process: (1) The huge volume will cause the solid electrolyte interface layer (SEI) on the surface of the silicon oxide material particles to continuously break, repeatedly exposing new particle surfaces, and continuously reacting with the electrolyte to form SEI. The continuous rearrangement of the SEI layer will consume a large amount of active lithium from the counter electrode, resulting in a rapid decrease in battery capacity. (2) Trace amounts of water in the electrolyte will cause LiPF6 to decompose, producing HF that destroys the passivation layer on the surface of the particles. HF can react with the silicon oxide material to produce water and gas, seriously affecting battery performance. (3) The SEI layer of traditional technology is mainly composed of organic matter, which is not strong and dense enough, and the interfacial ion transmission energy barrier is high. (4) The low electronic conductivity leads to a slow electrochemical reaction rate.

[0046] To address these issues, traditional technologies use some methods to stabilize the surface of silicon negative electrodes, such as coating with a carbon layer to reduce the reaction activity with the electrolyte while buffering the volume expansion, constructing a LiF-rich SEI on the surface of the silicon negative electrode to improve interface stability and ionic conductivity, and doping the surface with Al2O3 to consume the residual HF in the electrolyte in advance. However, the interface problem of silicon negative electrodes has not been well solved, especially the lack of solutions to solve the above four technical difficulties at the same time.

[0047] In one aspect of the present application, a silicon negative electrode material is provided. Referring to FIG. 1 , the silicon negative electrode material comprises a core, an intermediate layer and an outer layer; the core comprises a silicon-oxygen material; the intermediate layer comprises SnF4, a Li-Sn-Si-O compound and a conductive metal nanowire; the outer layer comprises a MXene material, and the chemical formula of the MXene material is Ti3C2T x .

[0048] Exemplarily, the chemical formula of the Li-Sn-Si-O compound is Li2SnSi3O 6y ; The value of y depends on the valence state of silicon in the silicon-oxygen material.

[0049] For example, the conductive metal nanowires may be copper nanowires, silver nanowires, aluminum nanowires, or the like.

[0050] The fluorine group of MXene materials is conducive to the formation of an interfacial layer containing LiF, and the reaction formula is:

[0051] -Ti-F+Li + + e - →-Ti + LiF

[0052] In this way, when a fluorine-based MXene material is used for the outer layer, it is more conducive to the formation of a LiF-containing interface layer in the middle layer, which is beneficial to the homogenized transmission of lithium ions, buffering the volume expansion of silicon oxide, and avoiding further decomposition of the electrolyte.

[0053] In the above silicon negative electrode materials, an interface layer with expansion resistance, densification, high ion / electron transfer rate, and HF corrosion resistance is constructed on the surface of the silicon oxide material. The double-layer encapsulation of fluorine-rich inorganics and MXene effectively improves the electrochemical performance of the silicon oxide material negative electrode. In view of the shortcomings of traditional technologies, a double-layer encapsulation strategy based on fluorine-rich inorganics-MXene is proposed, with the silicon oxide material as the core and an intermediate layer and an outer layer formed on its surface. The high mechanical strength of the outer layer MXene is conducive to buffering the volume expansion of the silicon oxide negative electrode, and the high electronic conductivity of MXene can maintain high electrical connectivity between particles. At the same time, MXene is located in the outer layer, and the fluorine group is conducive to the formation of an interface layer containing LiF, which is conducive to the homogenized transmission of lithium ions. SnF4 in the middle layer can inhibit the corrosion of HF in the electrolyte, improve the mechanical strength of the middle layer, and the synergistic effect of SnF4 and LiF establishes a uniform lithium ion transmission channel, effectively improving the overall performance of the SEI layer. Li-Sn-Si-O compound (Li2SnSi3O 6y ) can be quickly converted into fast ion conductor Li2SnO3 and Li2SiO3 with buffer expansion effect during battery use without consuming lithium source in the electrolyte. At the same time, conductive metal nanowires can form a conductive network between the inner core and the outer layer, improving the electronic conductivity of the middle layer.

[0054] In summary, the MXene in the outer layer and the conductive metal nanowires in the middle layer provide good electronic conductivity. The MXene in the outer layer and the Li-Sn-Si-O compound in the middle layer limit the volume expansion of the silicon-oxygen material in the inner core. The Li-Sn-Si-O and SnF4 compounds in the middle layer provide good ionic conductivity, thus forming a good synergistic effect between the inner core, the middle layer and the outer layer, promoting the transport of ions and electrons at the particle interface, effectively buffering the volume expansion of the silicon-oxygen negative electrode, and improving the electrochemical performance of the battery.

[0055] In some embodiments, the mass fraction of the conductive metal nanowires in the middle layer is 14% to 52%. For example, the mass fraction of the conductive metal nanowires in the middle layer may be, but is not limited to, 14%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50% or 52%, etc. In this way, the conductive metal wires can improve the electronic conductivity of the silicon negative electrode material and avoid affecting the ionic conductivity, and the conductive metal nanowires can also support the core-shell structure to avoid structural collapse.

[0056] In some embodiments, the thickness of the intermediate layer is 30nm~70nm, and the thickness of the outer layer is 5nm~15nm. Exemplarily, the thickness of the intermediate layer can be but not limited to 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm or 70nm, etc. The thickness of the outer layer can be but not limited to 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm or 15nm, etc. Within the above range, the combination of the intermediate layer and the outer layer can limit the volume expansion of the core silicon oxide material, and ensure the electronic conductivity and ionic conductivity, so as to avoid affecting the transmission of lithium ions.

[0057] In some embodiments, the MXene material may be formed by HF etching or by fluorine-containing salt etching.

[0058] In a second aspect, referring to FIG. 2 , the present application further provides a method for preparing a silicon negative electrode material, comprising the following steps S21 to S25 .

[0059] S21, forming conductive nanowires on the surface of the silicon-oxygen material to obtain a first intermediate.

[0060] Exemplarily, the silicon-oxygen material may be in a granular form, and the conductive nanowires grow on the surface of the silicon-oxygen material. Exemplarily, the conductive nanowires are copper nanowires (CuNWs, Cu Nano Wires).

[0061] S22, mixing the first intermediate and Li2SnF6 solution, and removing the solvent to obtain a second intermediate.

[0062] S23, forming a cationic homopolymer on the surface of the second intermediate to obtain a third intermediate.

[0063] In some embodiments, the cationic homopolymer includes one or more of poly(3-acrylamidopropyl)trimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, trimethylallylammonium chloride, dimethyldiallylammonium chloride, and ethyleneimine.

[0064] S24, mixing the MXene material with the third intermediate to obtain a fourth intermediate.

[0065] S25, calcining the fourth intermediate to obtain a silicon negative electrode material.

[0066] In the preparation method of the above-mentioned silicon negative electrode material, a double-layer encapsulation strategy based on fluorine-rich inorganic material-MXene is proposed to construct an intermediate layer and an outer layer on the surface of the silicon-oxygen negative electrode that are resistant to expansion, densification, high ion / electron transfer rate, and HF corrosion resistance.

[0067] Specifically, the present application first forms a conductive metal nanowire on the surface of the silicon oxide material to obtain a first intermediate, and then mixes the first intermediate with a Li2SnF6 solution to obtain a second intermediate. In order to achieve uniform coating of the MXene material, a cationic homopolymer is first adsorbed on the surface of the second intermediate, and after mixing with the MXene material, the negatively charged MXene material is uniformly adsorbed to the particle surface through electrostatic adsorption, and then calcined to react the Li2SnF6 coated between the MXenes with the silicon oxide material to form SnF4 and a Li-Sn-Si-O compound eutectic layer. Furthermore, the constructed SnF4 can inhibit the corrosion of HF in the electrolyte, improve the mechanical strength of the intermediate layer, and the synergistic effect of SnF4 and LiF establishes a uniform lithium ion transmission channel, effectively improving the overall performance of the SEI layer; and in the subsequent use of the battery, the Li-Sn-Si-O compound can be quickly converted into a fast ion conductor Li2SnO3 and Li2SiO3 with a buffering expansion effect, and will not consume the lithium source in the electrolyte. At the same time, the conductive metal nanowires can form a conductive network between the inner core and the outer layer, improving the electronic conductivity of the middle layer. Overall, the synergistic effect of MXene and the fluorine-rich inorganic layer promotes ion / electron transport at the particle interface, effectively buffers the volume expansion of the silicon-oxygen negative electrode, and improves the electrochemical performance of the battery.

[0068] In some embodiments, the preparation of the first intermediate in step S21 includes the following steps: mixing a silicon-oxygen material, an alkaline solution, a metal salt solution, a first solvent, and hydrazine hydrate to obtain a first intermediate solution; wherein, in the first intermediate solution, the mass ratio of the metal salt to the silicon-oxygen material is (6-15):100; stirring the first intermediate solution at 60°C-100°C, filtering, and washing to obtain the first intermediate.

[0069] For example, the mass ratio of the metal salt to the silicon-oxygen material may be, but is not limited to, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100 or 15:100, etc.

[0070] Illustratively, the alkaline solution may be a sodium hydroxide solution, a potassium hydroxide solution or aqueous ammonia.

[0071] Exemplarily, the metal salt solution is a salt solution of conductive metal nanowires, such as when the conductive metal is copper, the metal salt is a copper salt, such as copper nitrate. The mass ratio of the metal salt to the silicon oxide material refers to the mass ratio of copper nitrate to the silicon oxide material.

[0072] Illustratively, the first solvent may be ethylenediamine.

[0073] In some embodiments, in step S22, the step of preparing the second intermediate includes: adding the first intermediate to a second solvent containing Li2SnF6 to obtain a second intermediate solution; the mass ratio of Li2SnF6 to the first intermediate is (4~11):100; stirring the second intermediate solution at 60℃~100℃ until the second solvent evaporates to obtain a second intermediate.

[0074] Exemplarily, the mass ratio of Li2SnF6 to the first intermediate may be, but is not limited to, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, etc. In this way, the thickness ratio of the formed core and the intermediate layer can be controlled by the mass ratio of Li2SnF6 to the first intermediate. If the intermediate layer is too thick, the transmission channel of lithium ions close to the silicon oxide material will be extended, thereby reducing the electrochemical performance of the negative electrode. If the intermediate layer is too thin, the content of SnF4 and the Li-Sn-Si-O compound eutectic layer will be small, thereby reducing the optimization effect on the electrolyte.

[0075] Illustratively, the second solvent may be deionized water.

[0076] In some embodiments, in step S23, the step of preparing the third intermediate includes: adding the second intermediate to a cationic homopolymer solution, stirring to obtain a third intermediate solution; wherein the mass fraction of the cationic homopolymer in the cationic homopolymer solution is 5% to 12%, and the mass volume ratio of the second intermediate to the cationic homopolymer solution is 25 g / L to 35 g / L; filtering the third intermediate solution, retaining the precipitate to obtain the third intermediate.

[0077] For example, the cationic homopolymer solution may be an aqueous solution of a cationic homopolymer. The stirring treatment may be magnetic stirring.

[0078] Exemplarily, the mass fraction of the cationic homopolymer in the cationic homopolymer solution may be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%. Exemplarily, the mass volume ratio of the first intermediate and the cationic homopolymer solution may be, but is not limited to, 25g / L, 26g / L, 27g / L, 28g / L, 29g / L, 30g / L, 31g / L, 32g / L, 33g / L, 34g / L or 35g / L. In this way, the positively charged cationic homopolymer is adsorbed onto the surface of the second intermediate. At the same time, within the above range, the surface of the second intermediate can adsorb an appropriate amount of cationic homopolymer, further making the amount of subsequent adsorption of MXene material a suitable value. Avoid MXene material being adsorbed too much to reduce the ability of lithium ions to pass, or being adsorbed too little to reduce conductivity.

[0079] In some embodiments, in step S24, the step of preparing the fourth intermediate includes: mixing the third intermediate and the MXene material in a third solvent at a mass ratio of (2-6):1 to obtain a fourth intermediate solution; stirring the fourth intermediate solution, washing and drying to obtain the fourth intermediate.

[0080] Exemplarily, the third solvent is deionized water.

[0081] Exemplarily, MXene is prepared by a fluorine-containing salt etching method. The preparation method includes: first dissolving 4g LiF in 50ml of 9M hydrochloric acid and stirring for 30min, then adding 2g Ti3AlC2, heating and stirring at 35°C for 24h, adding the resulting suspension into a centrifuge tube and centrifuging for 10min, adding distilled water, repeating the centrifugation several times until the pH>5, and freeze-drying the resulting material to obtain MXene powder. During the etching process, -OH and -F groups are introduced at the same time, so that the MXene material has fluorine atoms.

[0082] For example, MXene can also be prepared by HF etching. The preparation method includes: taking 10 ml of 40% HF solution and slowly adding it to 50 ml of deionized water, taking 2 g of Ti3AlC2 powder and slowly adding it to the prepared HF solution, stirring continuously at room temperature for 24 hours, adding the resulting suspension to a centrifuge tube and centrifuging for 10 minutes, adding distilled water, repeating the centrifugation several times until the pH is greater than 5, and then further washing with ethanol, and finally freeze-drying the resulting material to obtain MXene.

[0083] For example, the mass ratio of the third intermediate to MXene may be, but is not limited to, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, etc. In this way, MXene can be uniformly coated on the surface of the particles.

[0084] In some embodiments, in step S25, the calcination treatment satisfies at least one of the following (1) to (3): (1) calcination treatment is carried out under an inert gas atmosphere; (2) the calcination temperature is 200° C. to 400° C.; (3) the calcination time is 2 h to 4 h.

[0085] For example, the inert gas may be argon, helium or nitrogen, etc. For example, the calcination temperature may be, but not limited to, 200° C., 250° C., 300° C., 350° C. or 400° C., etc. For example, the calcination time may be, but not limited to, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc.

[0086] In this way, the introduction of impurities can be avoided, and the calcination process facilitates the reaction between the silicon oxide material and Li2SnF6 to form a stable interface layer.

[0087] In a third aspect, the present application also provides a battery, the battery comprising a negative electrode plate, the negative electrode plate comprising a silicon negative electrode material, or comprising a silicon negative electrode material prepared by a preparation method.

[0088] The following are specific embodiments.

[0089] Example 1

[0090] Anode material preparation

[0091] (1) Preparation of the first intermediate. 320 ml of 15 M sodium hydroxide aqueous solution, 8 ml of 0.2 M copper nitrate solution, 2.4 ml of ethylenediamine, and 0.4 ml of 35% hydrazine hydrate were mixed, and 3 g of silicon oxide material (Hunan Jinsi Technology Co., Ltd., silicon oxide precursor product (silicon oxide material without carbon layer)) was added, that is, the mass ratio of metal salt to silicon oxide material was about 10:100. After stirring and mixing, the mixture was stirred at 80 ° C and 200 rpm for 100 min to grow copper nanowires (CuNWs) on the surface of the silicon oxide material. Finally, the suspension was filtered and washed with water and ethanol three times respectively to generate copper nanowires on the surface of the silicon oxide material to obtain the first intermediate SiO@CuNWs.

[0092] (2) The second intermediate was prepared by solution evaporation method. 0.24 g Li2SnF6 was dissolved in 100 mL deionized water at 80 °C, 3 g of the first intermediate SiO@CuNWs was added (i.e., the mass ratio of Li2SnF6 to the first intermediate was 8:100), and the mixture was stirred at 1800 rpm and kept at 80 °C until the solvent was completely evaporated to obtain the second intermediate SiO@CuNWs@LSF.

[0093] (3) Preparation of the third intermediate. Take 3 g of the second intermediate and add it to 100 ml of an aqueous solution of poly(3-acrylamidepropyl)trimethylammonium chloride (mass fraction 10%), stir it magnetically for 12 h, and then filter the suspension. This process allows the positively charged poly(3-acrylamidepropyl)trimethylammonium chloride to adsorb onto the surface of the second intermediate SiO@CuNWs@LSF to obtain the third intermediate.

[0094] (4) MXene was prepared by fluorine-containing salt etching. First, 4 g of LiF was dissolved in 50 ml of 9 M hydrochloric acid and stirred for 30 min. Then, Ti3AlC2 (2 g) was added and heated at 35 °C and stirred for 24 h. The resulting suspension was added to a centrifuge tube and centrifuged for 10 min. Distilled water was added and centrifuged repeatedly until the pH was > 5. The resulting material was freeze-dried to obtain MXene powder.

[0095] (5) Take 3 g of the third intermediate and MXene powder in a mass ratio of 4:1 and mix them in 100 ml of deionized water. Ultrasonic dispersion is performed for 1 h, and then magnetic stirring is performed for 12 h to allow MXene to be evenly coated on the surface of the third intermediate particles. The mixture is washed with water and ethanol several times and dried to obtain the fourth intermediate.

[0096] (6) The fourth intermediate obtained above is placed in a tubular furnace for calcination, and an inert gas Ar2 is introduced at a gas flow rate of 0.05 L / min. The calcination temperature is 300°C and the calcination time is 3 h, thereby achieving an interfacial reaction between the silicon oxide material and Li2SnF6 to form SnF4 and Li-Sn-Si-O compounds.

[0097] Among them, the mass fraction of the conductive metal nanowires in the middle layer is 27%; the thickness of the middle layer is 50nm, and the thickness of the outer layer is 10nm.

[0098] Half-cell assembly

[0099] The obtained negative electrode material was mixed with PAA (Acrylic acid Polymers), SuperP (ultrafine carbon powder), and CNT (carbon nanotube) in a mass ratio of 8:1:0.5:0.5, and deionized water was added to prepare a slurry, which was then evenly coated on a copper foil, and the mass loading was controlled to be 1 mg / cm 2 The negative electrode sheet was then placed in a vacuum dryer at 120°C for 12 hours. Celgard 2500 was used as the separator, the electrolyte was 1 mol / l LiPF6 dispersed in ethylene carbonate, diethyl carbonate, and dimethyl carbonate (mass ratio of 1:1:1) solvent, and contained 5wt% FEC (FluorocarbonElectrolyte Complex, fluoroethylene carbonate) additives. Lithium metal was used as the counter electrode and assembled into a CR2023 half-cell in a glove box.

[0100] Full battery assembly

[0101] 4g of NCM523, 0.5g of SuperP, and 0.5g of PVDF (Polyvinylidene fluoride) were mixed in a NMP (N-Methyl-2-pyrrolidone) solvent at a mass ratio of 8:1:1 to obtain a slurry, which was cast on aluminum foil and then dried in a vacuum oven to obtain an NCM positive electrode sheet. After that, the above negative electrode sheet was first assembled into a half-cell and electrochemically pre-lithiated at 0.1C for 3 cycles, and then the above negative electrode sheet was taken out and assembled into a full cell with the NCM positive electrode sheet, and the NP ratio was controlled at 1.1.

[0102] Example 2

[0103] The preparation method of Example 2 is substantially the same as that of Example 1, except that:

[0104] Anode material preparation

[0105] (1) Preparation of the first intermediate. Mix 320 ml of 15 M sodium hydroxide aqueous solution, 8 ml of 0.2 M copper nitrate solution, 2.4 ml of ethylenediamine, and 0.4 ml of 35% hydrazine hydrate, and add 5 g of silicon oxide material (Hunan Jinsi Technology Co., Ltd., silicon oxide precursor product (silicon oxide material without carbon layer)), that is, the mass ratio of metal salt to silicon oxide material is 6:100. After stirring and mixing, stir at 60 ° C and 200 rpm for 100 min to grow copper nanowires (CuNWs) on the surface of the silicon oxide material. Finally, filter the suspension and wash it with water and ethanol three times respectively to generate copper nanowires on the surface of the silicon oxide material to obtain the first intermediate SiO@CuNWs.

[0106] (2) The second intermediate was prepared by solution evaporation method. 0.33 g of Li2SnF6 was dissolved in 100 mL of deionized water at 80 °C, 3 g of the first intermediate SiO@CuNWs was added (i.e., the mass ratio of Li2SnF6 to the first intermediate was 11:100), and the mixture was stirred at 1800 rpm and kept at 60 °C until the solvent was completely evaporated to obtain the second intermediate SiO@CuNWs@LSF.

[0107] (3) Preparation of the third intermediate. Take 3 g of the second intermediate and add it to 100 ml of an aqueous solution of methacryloyloxyethyl trimethyl ammonium chloride (mass fraction 5%), stir it magnetically for 12 h, and then filter the suspension. This process allows the positively charged poly (3-acrylamide propyl) trimethyl ammonium chloride to adsorb onto the surface of the second intermediate SiO@CuNWs@LSF to obtain the third intermediate.

[0108] (4) MXene was prepared by fluorine-containing salt etching. First, 4 g of LiF was dissolved in 50 ml of 9 M hydrochloric acid and stirred for 30 min. Then, Ti3AlC2 (2 g) was added and heated at 35 °C and stirred for 24 h. The resulting suspension was added to a centrifuge tube and centrifuged for 10 min. Distilled water was added and centrifuged repeatedly until the pH was > 5. The resulting material was freeze-dried to obtain MXene powder.

[0109] (5) Take 3 g of the third intermediate and MXene powder in a mass ratio of 2:1 and mix them in 100 ml of deionized water. Ultrasonic dispersion is performed for 1 h, and then magnetic stirring is performed for 12 h to allow MXene to be evenly coated on the surface of the third intermediate particles. The mixture is washed with water and ethanol several times and dried to obtain the fourth intermediate.

[0110] (6) The fourth intermediate obtained above is placed in a tubular furnace for calcination, and an inert gas Ar2 is introduced at a gas flow rate of 0.05 L / min. The calcination temperature is 200°C and the calcination time is 4 h, thereby achieving an interfacial reaction between the silicon oxide material and Li2SnF6 to form SnF4 and Li-Sn-Si-O compounds.

[0111] Among them, the mass fraction of the conductive metal nanowires in the middle layer is 14%; the thickness of the middle layer is 37nm, and the thickness of the outer layer is 14nm.

[0112] Example 3

[0113] The preparation method of Example 3 is substantially the same as that of Example 1, except that:

[0114] Anode material preparation

[0115] (1) Preparation of the first intermediate. Mix 320 ml of 15 M sodium hydroxide aqueous solution, 8 ml of 0.2 M copper nitrate solution (trihydrate), 2.4 ml of ethylenediamine, and 0.4 ml of 35% hydrazine hydrate, and add 2 g of silicon oxide material (Hunan Jinsi Technology Co., Ltd., silicon oxide precursor product (silicon oxide material without carbon layer)), that is, the mass ratio of metal salt to silicon oxide material is 15:100. After stirring and mixing, stir at 100 ° C and 200 rpm for 100 min to grow copper nanowires (CuNWs) on the surface of the silicon oxide material. Finally, filter the suspension and wash it with water and ethanol three times respectively to generate copper nanowires on the surface of the silicon oxide material to obtain the first intermediate SiO@CuNWs.

[0116] (2) The second intermediate was prepared by solution evaporation method. 0.12 g Li2SnF6 was dissolved in 100 mL deionized water at 80 °C, 3 g of the first intermediate SiO@CuNWs was added (i.e., the mass ratio of Li2SnF6 to the first intermediate was 4:100), and the mixture was stirred at 1800 rpm and kept at 100 °C until the solvent was completely evaporated to obtain the second intermediate SiO@CuNWs@LSF.

[0117] (3) Preparation of the third intermediate. Take 3 g of the second intermediate and add it to 100 ml of an aqueous solution of dimethyldiallylammonium chloride (mass fraction 12%). Stir it magnetically for 12 h, and then filter the suspension. This process allows the positively charged poly (3-acrylamidepropyl) trimethylammonium chloride to adsorb onto the surface of the second intermediate SiO@CuNWs@LSF to obtain the third intermediate.

[0118] (4) MXene was prepared by HF etching method. 10 ml of 40% HF solution was slowly added to 50 ml of deionized water. 2 g of Ti3AlC2 powder was slowly added to the prepared HF solution. Stirring was continued at room temperature for 24 h. The resulting suspension was added to a centrifuge tube and centrifuged for 10 min. Distilled water was added and the centrifugation was repeated several times until the pH value was greater than 5. The material was then further washed with ethanol and freeze-dried to obtain MXene.

[0119] (5) Take 3 g of the third intermediate and MXene powder in a mass ratio of 6:1 and mix them in 100 ml of deionized water. Ultrasonic dispersion is performed for 1 h, and then magnetic stirring is performed for 12 h to allow MXene to be evenly coated on the surface of the third intermediate particles. The mixture is washed with water and ethanol several times and dried to obtain the fourth intermediate.

[0120] (6) The fourth intermediate obtained above is placed in a tubular furnace for calcination, and an inert gas Ar2 is introduced at a gas flow rate of 0.05 L / min. The calcination temperature is 400°C and the calcination time is 2 h, thereby achieving an interfacial reaction between the silicon oxide material and Li2SnF6 to form SnF4 and Li-Sn-Si-O compounds.

[0121] Among them, the mass fraction of the conductive metal nanowires in the middle layer is 52%; the thickness of the middle layer is 64nm, and the thickness of the outer layer is 5nm.

[0122] Example 4

[0123] The preparation method of Example 4 is substantially the same as that of Example 1, except that the mass fraction of the conductive metal nanowires in the middle layer is 10%.

[0124] Specifically, 0.78 g of Li2SnF6 was added in step 2, and the remaining steps were consistent with Example 1.

[0125] Example 5

[0126] The preparation method of Example 5 is substantially the same as that of Example 1, except that the mass fraction of the conductive metal nanowires in the middle layer is 57%.

[0127] Specifically, 0.0677 g of Li2SnF6 was added in step 2, and the remaining steps were consistent with Example 1.

[0128] Example 6

[0129] The preparation method of Example 6 is substantially the same as that of Example 1, except that the thickness of the intermediate layer is 24 nm.

[0130] Specifically, 320 ml of 15 M sodium hydroxide aqueous solution, 6 mL of 0.2 M copper nitrate solution, 1.95 ml of ethylenediamine, and 0.33 mL of 35% by mass hydrazine hydrate were mixed, and 5 g of silicon oxide material (Hunan Jinsi Technology Co., Ltd., silicon oxide precursor product (silicon oxide material not coated with a carbon layer)) was added; in step (2), 0.12 g of Li2SnF6 was dissolved in 100 mL of deionized water at 80°C, and the rest was consistent with Example 1.

[0131] Example 7

[0132] The preparation method of Example 7 is substantially the same as that of Example 1, except that the thickness of the intermediate layer is 75 nm.

[0133] Specifically, 320 ml of 15 M sodium hydroxide aqueous solution, 13.2 ml of 0.2 M copper nitrate solution, 3.96 ml of ethylenediamine, and 0.66 ml of 35% by mass hydrazine hydrate were mixed, and 3 g of silicon oxide material (Hunan Jinsi Technology Co., Ltd., silicon oxide precursor product (silicon oxide material not coated with a carbon layer)) was added; in step (2), 0.33 g of Li2SnF6 was dissolved in 100 ml of deionized water at 80°C, and the rest was consistent with Example 1.

[0134] Example 8

[0135] The preparation method of Example 8 is basically the same as the preparation method of Example 1, except that the thickness of the outer layer is 3 nm.

[0136] Specifically, 3 g of the third intermediate and MXene powder were mixed in 100 ml of deionized water at a mass ratio of 7:1, and the remaining steps were consistent with Example 1.

[0137] Example 9

[0138] The preparation method of Example 9 is substantially the same as that of Example 1, except that the thickness of the outer layer is 20 nm.

[0139] Specifically, 3 g of the third intermediate and MXene powder were mixed in 100 ml of deionized water at a mass ratio of 1:2, and the remaining steps were consistent with Example 1.

[0140] Comparative Example 1

[0141] The preparation method of Comparative Example 1 is substantially the same as that of Example 1, except that the negative electrode material is a commercial silicon-oxygen material.

[0142] Comparative Example 2

[0143] The preparation method of Comparative Example 2 is substantially the same as that of Example 1, except that the negative electrode material is not subjected to the treatment of step (4) and step (5).

[0144] Comparative Example 3

[0145] The preparation method of Comparative Example 3 is substantially the same as that of Example 1, except that:

[0146] (1) MXene was prepared by fluoride salt etching. First, 4 g LiF was dissolved in 50 ml 9 M hydrochloric acid and stirred for 30 min. Then Ti3AlC2 (2 g) was added and heated at 35 °C and stirred for 24 h. The resulting suspension was added to a centrifuge tube and centrifuged for 10 min. Distilled water was added and centrifuged repeatedly until pH>5. The resulting material was freeze-dried to obtain MXene powder.

[0147] (2) Take 3 g of the silicon oxide material and add it to 100 ml of an aqueous solution of poly(3-acrylamidepropyl)trimethylammonium chloride (mass fraction 10%), stir it magnetically for 12 h, and then filter the suspension. This process allows the positively charged poly(3-acrylamidepropyl)trimethylammonium chloride to adsorb onto the surface of the silicon oxide material to obtain an intermediate.

[0148] (3) The above-mentioned 3 g of intermediate and MXene powder were mixed in 100 ml of deionized water at a mass ratio of 4:1 and stirred for 6 h to allow the MXene to be evenly coated on the surface of the intermediate particles. The mixture was washed with water and ethanol several times and dried to obtain the negative electrode material.

[0149] Comparative Example 4

[0150] The preparation method of Comparative Example 4 is substantially the same as that of Example 1, except that the treatment in step (6) of Example 1 is not performed.

[0151] Comparative Example 5

[0152] The preparation method of Comparative Example 5 is substantially the same as that of Example 1, except that Li2SnF6 in step (2) is replaced by Li3AlF6.

[0153] The silicon negative electrode materials prepared in the above embodiments and comparative examples or the half-cell or full-cell products further prepared were subjected to performance tests, and the test results are shown in Table 1 below.

[0154] Among them, the test conditions or test standards for each performance test item are:

[0155] Battery test: The assembled half-battery is charged and discharged at 0.05C, the gram capacity is the first charge specific capacity, the first efficiency is the first charge specific capacity / first discharge specific capacity, and the test voltage window is 0.005-2V; the assembled half-battery is cycled for 10 times and then subjected to EIS test, with a test frequency of 100KHz~10mHz, to obtain the charge transfer impedance Rct; the assembled full battery is subjected to cycle test, first charged and discharged at 0.05C for 3 times at 25℃, then charged and discharged at 1C for cycling, and the test voltage window is 2.8~4.2V;

[0156] Table 1

[0157]

[0158] The commercial silicon-oxygen material in Comparative Example 1 has poor performance. In Comparative Example 2, the outer layer is not coated with MXene, resulting in large volume expansion and poor cycle performance. In Comparative Example 3, there is no intermediate layer, which makes it difficult to improve ion transmission and the interface strength is low. In Comparative Example 4, under continuous burning, LiSnF6 cannot react with the silicon-oxygen interface, the battery first efficiency is low, and the ion transmission effect at the interface is still not improved. In Comparative Example 5, LiSnF6 has better lithium affinity than Li3AlF6, which can promote the uniform transmission of lithium ions at the interface and is conducive to reducing interface polarization. Therefore, the interface impedance of Li3AlF6 is relatively high, which affects the performance of the battery.

[0159] As can be seen from Table 1 above, Examples 1 to 9 have at least partial performance improvements relative to Comparative Examples 1 to 5, indicating that the synergistic effect of MXene and the fluorine-rich inorganic layer promotes ion / electron transport at the particle interface, effectively buffers the volume expansion of the silicon-oxygen negative electrode, and improves the electrochemical performance of the battery.

[0160] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0161] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A silicon negative electrode material, characterized in that: The silicon negative electrode material includes a core, an intermediate layer and an outer layer; the core includes a silicon-oxygen material; the intermediate layer includes SnF4, a Li-Sn-Si-O compound and a conductive metal nanowire; the outer layer includes a MXene material, and the chemical formula of the MXene material is Ti3C2T x .

2. The silicon negative electrode material according to claim 1, characterized in that: The mass fraction of the conductive metal nanowires in the middle layer is 14% to 52%.

3. The silicon negative electrode material according to claim 1, characterized in that: The thickness of the middle layer is 30nm-70nm, and the thickness of the outer layer is 5nm-15nm.

4. The silicon negative electrode material according to claim 1, characterized in that: The MXene material is formed by etching with HF or a fluorine-containing salt.

5. A method for preparing the silicon negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Forming conductive nanowires on the surface of the silicon-oxygen material to obtain a first intermediate; Mixing the first intermediate and Li2SnF6 solution, and removing the solvent to obtain a second intermediate; forming a cationic homopolymer on the surface of the second intermediate to obtain a third intermediate; Mixing the MXene material with the third intermediate to obtain a fourth intermediate; The fourth intermediate is calcined to obtain a silicon negative electrode material.

6. The preparation method according to claim 5, characterized in that: The preparation of the first intermediate comprises the following steps: Mixing the silicon-oxygen material, the alkaline solution, the metal salt solution, the first solvent and hydrazine hydrate to obtain a first intermediate solution; wherein the mass ratio of the metal salt to the silicon-oxygen material in the first intermediate solution is (6-15):100; The first intermediate solution is stirred at 60° C. to 100° C., and the first intermediate is obtained by filtering and washing.

7. The preparation method according to claim 5, characterized in that: The steps of preparing the second intermediate include: Adding the first intermediate to a second solvent containing Li2SnF6 to obtain a second intermediate solution; the mass ratio of Li2SnF6 to the first intermediate is (4-11):100; The second intermediate solution is stirred at 60° C. to 100° C. until the second solvent evaporates to obtain the second intermediate.

8. The preparation method according to claim 5, characterized in that: The steps of preparing the third intermediate include: The second intermediate is added to the cationic homopolymer solution, and stirred to obtain a third intermediate solution; wherein the mass fraction of the cationic homopolymer in the cationic homopolymer solution is 5% to 12%; The third intermediate solution is filtered, and the precipitate is retained to obtain the third intermediate.

9. The preparation method according to claim 5, characterized in that: The steps of preparing the fourth intermediate include: The third intermediate and the MXene material are mixed in a third solvent at a mass ratio of (2-6):1 to obtain a fourth intermediate solution; The fourth intermediate solution is stirred, washed and dried to obtain the fourth intermediate.

10. The preparation method according to claim 5, characterized in that: The calcination treatment satisfies at least one of the following (1) to (3): (1) Calcination treatment under an inert gas atmosphere; (2) Calcination temperature is 200℃~400℃; (3) Calcination time is 2h~4h.

11. A battery, characterized in that: The battery comprises a negative electrode plate, and the negative electrode plate comprises the silicon negative electrode material according to any one of claims 1 to 4, or comprises the silicon negative electrode material prepared by the preparation method according to any one of claims 5 to 10.

Images