A negative electrode material for sodium ion batteries and a preparation method and application thereof

Abstract

The application discloses a kind of negative electrode material for sodium ion battery and its preparation method and application.It relates to the technical field of sodium ion battery.The above-mentioned negative electrode material includes the following structure: a first carbon layer;Second carbon layer, the second carbon layer covers the first carbon layer;Third carbon layer, the third carbon layer covers the second carbon layer;The composition of the first carbon layer includes hard carbon material and sodium-containing polymer binder;The third carbon layer is a modified carbon layer, and the raw material for modification includes carbon material and carbon-hydrogen compound containing carbon-carbon double bond.The negative electrode material of the application is assembled on the sodium ion electrode, which can improve the cycle performance of the battery, specifically, the first coulomb efficiency of the battery can reach at least 97.6%, and the capacity retention rate of the battery after 50 cycles can reach at least 98.2.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a negative electrode material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their high capacity and lightweight characteristics, are widely used as power sources in new energy vehicles. However, limited lithium resources and continuously rising lithium raw material prices restrict the large-scale development of lithium-ion batteries. Sodium is extremely abundant (ranking fourth among metallic elements in the Earth's crust, accounting for 2.64% of total reserves) and inexpensive. It belongs to the same group as lithium, has similar chemical properties, and its electrode potentials are also quite close. Based on these factors, sodium-ion batteries have attracted considerable attention due to their use of abundant sodium resources.

[0003] Current sodium-ion batteries generally use hard carbon as the anode material. Hard carbon refers to carbon that is difficult to graphitize. Compared with traditional graphite, hard carbon is more suitable as an anode material for sodium-ion batteries due to its highly disordered structure, large interlayer spacing, and numerous defects. However, the low degree of graphitization of hard carbon materials results in poor rate performance. At the same time, in order to ensure a high reversible capacity, a portion of the capacity of hard carbon materials comes from a low voltage (around 0V). This voltage is close to the sodium deposition voltage, which may lead to serious safety hazards during fast charging.

[0004] Therefore, there is an urgent need for a new type of negative electrode material for sodium-ion batteries to solve the above problems. Summary of the Invention

[0005] The first technical problem to be solved by this invention is:

[0006] A negative electrode material is provided.

[0007] The second technical problem to be solved by this invention is:

[0008] A method for preparing the aforementioned negative electrode material is provided.

[0009] The third technical problem to be solved by this invention is:

[0010] The present invention also proposes a sodium-ion battery.

[0011] To solve the first technical problem, the technical solution adopted by the present invention is as follows:

[0012] A negative electrode material, comprising the following structure:

[0013] First carbon layer;

[0014] A second carbon layer, wherein the second carbon layer covers the first carbon layer;

[0015] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0016] The first carbon layer comprises hard carbon material and a sodium-containing polymer binder;

[0017] The third carbon layer is a modified carbon layer, and the raw materials for modification include carbon materials and hydrocarbons containing carbon-carbon double bonds.

[0018] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0019] 1. The negative electrode material of the present invention has a multi-layer coating structure, wherein the first carbon layer at the core comprises a sodium-containing polymer binder. This binder promotes the coating effect between the first and second carbon layers and makes the first carbon layer more compact. This results in the negative electrode material of the present invention exhibiting a structure that is tight inside and loose outside, facilitating sodium storage internally and sodium flow externally. Furthermore, the sodium in the sodium-containing polymer binder helps to compensate for the irreversible loss of sodium during sodium-ion battery cycling.

[0020] 2. The second carbon layer is a transition layer between the first carbon layer and the third carbon layer, used to improve the conductivity of the negative electrode material.

[0021] 3. The raw materials for the third carbon layer include carbon materials and hydrocarbons containing carbon-carbon double bonds. Due to the thermal instability of hydrocarbons containing carbon-carbon double bonds, they readily undergo addition reactions with carbon materials to construct a network-like cross-linked carbon layer on the outermost layer of the negative electrode material. This network-like cross-linked carbon layer serves as a protective layer for the negative electrode material, promoting compatibility between the negative electrode material and the electrolyte. Furthermore, if the network-like cross-linked carbon layer is damaged after long-term operation of the negative electrode containing the negative electrode material, simply reheating the negative electrode material will promote the addition reaction between the carbon materials in the third carbon layer and the hydrocarbons containing carbon-carbon double bonds, thus constructing a completely new network-like cross-linked carbon layer.

[0022] 4. Assembling the negative electrode material of the present invention onto a sodium-ion electrode can improve the cycle performance of the battery. Specifically, it can enable the battery to achieve an initial coulombic efficiency of at least 97.6% and a capacity retention rate of at least 98.2% after 50 cycles.

[0023] According to one embodiment of the present invention, the thickness ratio of the first carbon layer, the second carbon layer and the third carbon layer is 1:0.1-0.6:0.05-0.08.

[0024] According to one embodiment of the present invention, the particle size of the hard carbon material is 5-10 μm.

[0025] According to one embodiment of the present invention, the sodium-containing polymer binder includes at least one of sodium polyacrylate, sodium carboxymethyl cellulose, and sodium alginate.

[0026] According to one embodiment of the present invention, the molar ratio of the hard carbon material to the sodium-containing polymer binder is 10-30:1-5.

[0027] According to one embodiment of the present invention, the components of the second carbon layer include at least one of graphene, carbon nanotubes, hard carbon, and acetylene black.

[0028] According to one embodiment of the present invention, the components of the second carbon layer further include an adhesive.

[0029] According to one embodiment of the present invention, the hydrocarbon containing a carbon-carbon double bond includes at least one of thiophene, dimethylthiophene, and N-methylmaleimide.

[0030] According to one embodiment of the present invention, the molar ratio of carbon material to hydrocarbon containing carbon-carbon double bonds in the third carbon layer is 80-150:5-10.

[0031] To solve the second technical problem, the technical solution adopted by the present invention is as follows:

[0032] A method for preparing the negative electrode material includes the following steps:

[0033] S1 is mixed with hard carbon material and sodium-containing polymer binder to obtain the first carbon layer;

[0034] S2 covers the surface of the first carbon layer with the material of the second carbon layer to obtain the second carbon layer;

[0035] S3 mixed carbon material and hydrocarbons containing carbon-carbon double bonds are reacted in a solvent and heated. After the reaction, the reaction products are coated on the surface of the second carbon layer to obtain the negative electrode material.

[0036] According to one embodiment of the present invention, before mixing the hard carbon material with the sodium-containing polymer binder, a pretreatment step of the hard carbon material is included. Specifically, the hard carbon material is heat-treated in a protective atmosphere. Pretreatment of the hard carbon material improves its sodium storage stability, allowing the sodium deposited on its surface to form an SEI film without consuming sodium ions extracted from the positive electrode. After pretreatment, a carbon coating layer is formed on the surface, reducing the specific surface area and ensuring better stability so that the insertion and extraction of sodium ions do not cause other effects on the material structure. This further improves the initial coulombic efficiency, extends the battery cycle life, and facilitates ion insertion and extraction, thus increasing the charge and discharge rates.

[0037] According to one embodiment of the present invention, the heat treatment temperature is 100-500°C and the time is 1-3 hours.

[0038] In another aspect, the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises a negative electrode material as described in any one of claims 1 to 8. The negative electrode comprises the negative electrode material described in the first aspect embodiment above. Since this application employs all the technical solutions of the aforementioned negative electrode material, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below. Throughout the embodiments, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0041] In the description of this invention, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.

[0042] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the embodiments, and are only for the purpose of facilitating the description of this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0043] In the description of this invention, it should be noted that, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0045] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0046] Example 1

[0047] A negative electrode material, comprising the following structure:

[0048] First carbon layer;

[0049] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0050] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0051] The components of the first carbon layer mentioned above include hard carbon material and sodium alginate;

[0052] The aforementioned third carbon layer is a modified carbon layer, and the modifying raw materials include graphene and N-methylmaleimide.

[0053] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0054] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0055] S1 involves heat-treating hard carbon material in nitrogen at a temperature of 50°C for 16 hours, and then mixing hard carbon material with sodium alginate at a molar ratio of 10:1 to obtain the first carbon layer.

[0056] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0057] Graphene and N-methylmaleimide in a molar ratio of 80:5 were mixed in dimethyl carbonate and heated at 60°C for 72 hours. After the reaction, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solvent was removed by washing, and the mixture was then dried to obtain the product. The product was then coated onto the surface of the second carbon layer to obtain the negative electrode material.

[0058] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0059] Example 2

[0060] A negative electrode material, comprising the following structure:

[0061] First carbon layer;

[0062] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0063] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0064] The components of the first carbon layer mentioned above include hard carbon material and sodium alginate;

[0065] The aforementioned third carbon layer is a modified carbon layer, and the modifying raw materials include graphene and N-methylmaleimide.

[0066] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0067] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0068] S1 involves heat-treating hard carbon material in nitrogen at a temperature of 50°C for 16 hours, and then mixing hard carbon material with sodium alginate at a molar ratio of 10:1 to obtain the first carbon layer.

[0069] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0070] Graphene and N-methylmaleimide in a 150:10 molar ratio were mixed in dimethyl carbonate and heated at 60°C for 72 hours. After the reaction, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solvent was removed by washing, and the mixture was then dried to obtain the product. The product was then coated onto the surface of the second carbon layer to obtain the negative electrode material.

[0071] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0072] Example 3

[0073] A negative electrode material, comprising the following structure:

[0074] First carbon layer;

[0075] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0076] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0077] The components of the first carbon layer mentioned above include hard carbon material and sodium alginate;

[0078] The aforementioned third carbon layer is a modified carbon layer, and the modifying raw materials include graphene and N-methylmaleimide.

[0079] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0080] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0081] S1 involves heat-treating hard carbon material in nitrogen at a temperature of 50°C for 16 hours, and then mixing hard carbon material with sodium alginate at a molar ratio of 10:1 to obtain the first carbon layer.

[0082] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0083] Graphene and N-methylmaleimide in a molar ratio of 80:10 were mixed in dimethyl carbonate and heated at 60°C for 72 hours. After the reaction, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solvent was removed by washing, and the mixture was then dried to obtain the product. The product was then coated onto the surface of the second carbon layer to obtain the negative electrode material.

[0084] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0085] Example 4

[0086] The difference between Example 4 and Example 1 is that the material used for the first carbon layer in Example 1 is not pretreated.

[0087] A negative electrode material, comprising the following structure:

[0088] First carbon layer;

[0089] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0090] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0091] The components of the first carbon layer mentioned above include hard carbon material and sodium alginate;

[0092] The aforementioned third carbon layer is a modified carbon layer, and the modifying raw materials include graphene and N-methylmaleimide.

[0093] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0094] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0095] S1 mixes hard carbon material with sodium alginate in a molar ratio of 10:1 to obtain the first carbon layer;

[0096] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0097] Graphene and N-methylmaleimide in a molar ratio of 80:5 were mixed in dimethyl carbonate and heated at 60°C for 72 hours. After the reaction, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solvent was removed by washing, and the mixture was then dried to obtain the product. The product was then coated onto the surface of the second carbon layer to obtain the negative electrode material.

[0098] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0099] Comparative Example 1

[0100] The difference between Comparative Example 1 and Example 1 is that the first carbon layer of Comparative Example 1 consists only of hard carbon material.

[0101] A negative electrode material, comprising the following structure:

[0102] First carbon layer;

[0103] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0104] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0105] The components of the first carbon layer mentioned above include hard carbon materials;

[0106] The aforementioned third carbon layer is a modified carbon layer, and the modifying raw materials include graphene and N-methylmaleimide.

[0107] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0108] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0109] S1 involves heat-treating the hard carbon material in nitrogen at a temperature of 50°C for 16 hours to obtain the first carbon layer.

[0110] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0111] Graphene and N-methylmaleimide in a molar ratio of 80:5 were mixed in dimethyl carbonate and heated at 60°C for 72 hours. After the reaction, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solvent was removed by washing, and the mixture was then dried to obtain the product. The product was then coated onto the surface of the second carbon layer to obtain the negative electrode material.

[0112] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0113] Comparative Example 2

[0114] The difference between Comparative Example 2 and Example 1 is that the third carbon layer in Comparative Example 2 is a graphene layer.

[0115] A negative electrode material, comprising the following structure:

[0116] First carbon layer;

[0117] The second carbon layer covers the first carbon layer, and the second carbon layer is a graphene layer.

[0118] A third carbon layer, wherein the third carbon layer covers the second carbon layer;

[0119] The components of the first carbon layer mentioned above include hard carbon material and sodium alginate;

[0120] The third carbon layer mentioned above is a graphene layer.

[0121] The thickness ratios of the first carbon layer, the second carbon layer, and the third carbon layer are 1:0.1:0.05, respectively.

[0122] The method for preparing the above-mentioned negative electrode material includes the following steps:

[0123] S1 involves heat-treating hard carbon material in nitrogen at a temperature of 50°C for 16 hours, and then mixing hard carbon material with sodium alginate at a molar ratio of 10:1 to obtain the first carbon layer.

[0124] S2 sprays the material of the second carbon layer onto the surface of the first carbon layer to obtain the second carbon layer;

[0125] S3 coats graphene onto the surface of the second carbon layer to obtain the negative electrode material.

[0126] A nano-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the aforementioned negative electrode material. The separator is made of glass fiber. The nano-ion battery also includes an electrolyte, which is 1 mol / L NaPF6, and the electrolyte solvent is diethyl carbonate and dimethyl carbonate, wherein the volume ratio of diethyl carbonate to dimethyl carbonate is 1:1.

[0127] Performance testing:

[0128] The batteries of Examples 1-4 and Comparative Examples 1-2 were subjected to the following tests, and the test results are shown in Table 1.

[0129] The first coulombic efficiency test was conducted at 23±2℃ and atmospheric pressure (0.1MPa). The sodium-ion batteries prepared in the examples and comparative examples were charged at a constant current rate of 0.1C to the upper limit of the charge / discharge cutoff voltage. The charging capacity at this time was recorded as the first charging capacity of the sodium-ion battery. After resting for 5 minutes, the batteries were discharged at a constant current rate of 0.1C to the lower limit of the charge / discharge cutoff voltage. After resting for 5 minutes, the discharge capacity at this time was recorded as the first discharge capacity of the sodium-ion battery.

[0130] The capacity retention test for 50 cycles was conducted as follows: First, the coin cell was placed in an environment of 25±2℃ and left to stand for 8 hours. Then, it was discharged at a constant current of 0.2C to 0.005V. Next, it was left to stand for 5 minutes and then charged at a constant current of 0.2C to 3.0V. This process was repeated 50 times. Finally, the operation was stopped, and the capacity of the first and 50th discharge cycles was recorded. The capacity retention rate was the capacity of the 50th discharge cycle divided by the capacity of the first discharge cycle.

[0131] Table 1

[0132] First Coulomb Efficiency Test / % Capacity retention rate after 50 cycles Example 1 97.6 97.5 Example 2 98.2 98.2 Example 3 95.1 95.0 Example 4 94.6 93.5 Comparative Example 1 82.5 80.3 Comparative Example 2 76.3 70.1

[0133] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A negative electrode material for a sodium-ion battery, characterized by: The negative electrode material comprises the following structures: a first carbon layer; a second carbon layer, the second carbon layer covering the first carbon layer; a third carbon layer, the third carbon layer covering the second carbon layer; a component of the first carbon layer comprises a hard carbon material and a sodium-containing polymer binder; a raw material of the third carbon layer comprises a carbon material and a carbon-hydrogen compound containing a carbon-carbon double bond, the carbon material and the carbon-hydrogen compound containing a carbon-carbon double bond undergo an addition reaction to form a reticular cross-linked carbon layer on the outermost layer of the negative electrode material; the carbon-hydrogen compound containing a carbon-carbon double bond comprises at least one of thiophene, dimethyl thiophene and N-methyl maleimide.

2. The anode material for sodium-ion batteries according to claim 1, characterized in that: a thickness ratio of the first carbon layer, the second carbon layer and the third carbon layer is 1:0.1-0.6:0.05-0.08 in sequence.

3. The anode material for sodium-ion batteries according to claim 1, characterized in that: a particle size of the hard carbon material is 5-10 μm.

4. The anode material for sodium-ion batteries according to claim 1, characterized in that: the sodium-containing polymer binder comprises at least one of sodium polyacrylate, sodium carboxymethyl cellulose and sodium alginate.

5. The anode material for sodium-ion batteries according to claim 4, characterized in that: a molar ratio of the hard carbon material to the sodium-containing polymer binder is 10-30:1-5.

6. The anode material for sodium-ion batteries according to claim 1, characterized in that: a component of the second carbon layer comprises at least one of graphene, carbon nanotube, hard carbon and acetylene black.

7. The anode material for sodium-ion batteries according to claim 1, characterized in that: the component of the second carbon layer further comprises an adhesive.

8. A method of preparing a negative electrode material for a sodium-ion battery according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: S1 mixing a hard carbon material and a sodium-containing polymer binder to obtain a first carbon layer; S2 covering a material of a second carbon layer on a surface of the first carbon layer to obtain the second carbon layer; S3 mixing a carbon material and a carbon-hydrogen compound containing a carbon-carbon double bond in a solvent, heating, covering a reaction product on a surface of the second carbon layer after the reaction to obtain a negative electrode material.

9. A sodium-ion battery, characterized in that: The sodium ion battery comprises a positive electrode, a negative electrode and a separator, wherein the negative electrode comprises the negative electrode material according to any one of items 1 to 7.