WO2019228496A1 - Anode material and preparation method therefor, and lithium ion battery - Google Patents

Abstract

The present application proposes an anode material, a preparation method for the anode material, and a lithium ion battery. The anode material comprises: a hollow shell, the hollow shell containing carbon; and a lithium metal located inside the hollow shell.

Description

Anode material, preparation method thereof, and lithium ion battery

Priority information

This application claims the priority and rights of the patent application filed with the State Intellectual Property Office of China on May 31, 2018, with a patent application number of 201810549211.9, and the entire contents of which are hereby incorporated by reference.

Technical field

The present application relates to the field of lithium ion batteries, and in particular, to a negative electrode material and a preparation method thereof, a lithium ion battery, and a vehicle.

Background technique

As the negative electrode material of lithium ion batteries, metallic lithium has the advantages of high specific capacity and low reduction potential, and its specific capacity can reach more than 10 times that of graphite anodes for industrial applications. However, the negative electrode material containing metallic lithium is prone to generate lithium dendrites during the battery cycling process, which results in low battery cycling performance. In addition, the growth of lithium dendrites can easily cause short circuits in the battery, which in turn makes it difficult to ensure the safety of the battery. At present, the above problems can be improved by using a solid electrolyte or reducing the activity of metallic lithium.

However, at present, the anode materials based on metallic lithium, as well as the preparation methods, need to be improved.

Application content

In one aspect of the present application, the present application proposes a negative electrode material. The negative electrode material includes a hollow case, and metallic lithium filled inside the hollow case. The negative electrode material can use a hollow shell as a deposition substrate for metallic lithium, and fill the lithium metal inside the hollow shell, which can effectively alleviate the growth of lithium dendrites. Moreover, the structure of the negative electrode material is simple, can be obtained without a complicated synthesis method, and has good stability.

In another aspect of the present application, the present application proposes a method for preparing a negative electrode material. The method includes forming a hollow case, and filling the inside of the hollow case with lithium metal by electrodeposition to obtain the negative electrode material. Thereby, a negative electrode material can be easily obtained, the negative electrode material can alleviate or even prevent the growth of lithium dendrites, and the obtained negative electrode material has a simple structure and good stability.

In yet another aspect of the present application, the present application proposes a negative electrode material. The negative electrode material is prepared by the method described above. Therefore, the negative electrode material has all the characteristics and advantages of the negative electrode material obtained by the method described above, and details are not described herein again.

In yet another aspect of the present application, the present application proposes a lithium-ion battery. The lithium-ion battery includes the anode material described above. Therefore, the lithium ion battery has a high specific capacity and a good cycle life.

In yet another aspect of the present application, the present application proposes a vehicle. The vehicle includes the aforementioned lithium-ion battery. Therefore, the vehicle has all the features and advantages of the lithium-ion battery described above, which will not be repeated here.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic flowchart of a preparation method according to an embodiment of the present application;

FIG. 2 is a schematic flowchart of a part of a preparation method according to an embodiment of the present application; FIG.

3 shows a scanning electron microscope photograph of a material prepared according to an embodiment of the present application;

FIG. 4 shows a photograph of an energy spectrum surface scanning area of a material prepared according to an embodiment of the present application;

FIG. 5 shows an energy spectrum surface scanning result of a material prepared according to an embodiment of the present application; FIG.

FIG. 6 shows an energy spectrum surface scanning result of a material prepared according to a comparative example of the present application; FIG.

FIG. 7 shows the results of a charge-discharge cycle test of a negative electrode material prepared according to an embodiment of the present application.

Detailed ways

Hereinafter, embodiments of the present application are described in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.

In one aspect of the present application, the present application proposes a negative electrode material. The negative electrode material includes a hollow case and metallic lithium inside the hollow case. The negative electrode material can use a hollow shell as a deposition substrate for metallic lithium, and fill the lithium metal inside the hollow shell, which can effectively alleviate the growth of lithium dendrites. Moreover, the structure of the negative electrode material is simple, can be obtained without a complicated synthesis method, and has good stability.

According to the embodiment of the present application, the main body of the above-mentioned hollow casing may be made of a carbon-based material. For example, the hollow casing may be a hollow carbon sphere. The lithium intercalation potential of carbon is about 0.2V, which is higher than the lithium intercalation potential of metal lithium (about 0V). Therefore, a hollow carbon sphere filled with metal lithium can be used as a negative electrode material of a lithium ion battery. Charges can be evenly distributed on the surface of the hollow shell. The inner space of the hollow shell is a static shielding field, which is beneficial to the uniform deposition of lithium ions inside the hollow shell. Therefore, when metal lithium is filled in a hollow shell (for example, metal lithium can be filled into the hollow shell by electrodeposition), the metal lithium is preferentially deposited inside the hollow shell, and is not preferentially deposited in the hollow shell On the outer surface of the body. The hollow carbon sphere has a quasi-spherical structure, and metallic lithium is filled inside the hollow shell, thereby reducing or even preventing the formation of lithium dendrites. In addition, there is a certain space inside the hollow carbon sphere, which can meet the volume change of lithium during the insertion and removal of lithium. The inventors have found that the carbon material has a better lithium deintercalation function, so the introduction of the carbon material will not have a great impact on the energy density of the battery using the anode material. On the other hand, carbon materials are currently more commonly used anode materials, so the anode materials used in combination with them have similar process requirements to the current process, which is conducive to the large-scale promotion and application of this anode material. In addition, carbon materials are cheaper than other materials and easy to industrialize.

The inventors have discovered that, in order to ease the growth of lithium dendrites, whether it is a solid electrolyte or a strategy of adding a solid electrolyte interface membrane (SEI membrane) to a liquid electrolyte, there are complex chemical components and various types of electrolyte membranes Interface issues, stability issues are difficult to guarantee. Taking the SEI film as an example, a new SEI film is generated during each battery cycle, which affects the stability of the battery. Therefore, the above-mentioned strategies to alleviate the growth of lithium dendrites are not suitable for large-scale promotion and application in a short period of time. Reducing the activity of metal lithium will inevitably introduce other impurities, which will have a new and unpredictable effect on the battery. In addition, as the cycle progresses, the inert metal lithium can still be activated again, so it is difficult to effectively alleviate lithium The growth of dendrites. If the anode material can be improved to provide a deposition substrate for lithium metal that can effectively alleviate the growth of lithium dendrites, and then metal lithium is formed on the deposition substrate, the lithium dendrites can be blocked by the deposition substrate. Grow, radically alleviate or solve the above problems.

The negative electrode material will be explained in detail according to the specific embodiments of the present application:

According to the embodiment of the present application, the above-mentioned hollow shell may have a porous structure, thereby facilitating lithium ions (which can be distributed in a solution) from the above-mentioned porous structure to enter the inside of the hollow shell to form metallic lithium. According to the embodiment of the present application, the specific morphology of the porous structure of the hollow shell is not particularly limited, as long as a solution containing lithium ions can be penetrated into the hollow shell through the pores. For example, according to a specific embodiment of the present application, the porosity of the hollow shell may be 30-80%. For example, the porosity of the hollow shell may be 45%, 50%, 55%, 70%, and so on. The specific surface area of the hollow shell can be 10-80m ² / g, such as 25m ² / g, 30m ² / g, 40m ² / g, 50m ² / g, 60m ² / g, 65m ² / g, 75m ² / g and so on. When the porosity or specific surface area of the hollow shell meets the above requirements, it can ensure that the surface of the hollow shell can have sufficient porosity, so that the solution can enter the interior of the hollow shell to form metallic lithium, and it will not be caused by excessive porosity. The mechanical properties and electrical conductivity of the hollow shell are significantly reduced. When the porosity or specific surface area of the hollow shell satisfies the above-mentioned range, it can also be ensured that the hollow shell can effectively prevent the growth of lithium dendrites. It should be particularly noted that the term "specific surface area" used in this application is based on data obtained from a BET specific surface area test, and the specific surface area reflected by the data includes both the outer surface of the hollow shell and the Contribution of the inner surface, as well as the porous structure on the shell, to the surface area.

According to the embodiment of the present application, the specific content of the hollow case and the metal lithium in the negative electrode material is not particularly limited, as long as the metal lithium is filled inside the hollow case. For example, according to the embodiment of the present application, based on the total mass of the negative electrode material, the content of metallic lithium may be 0.1 wt% to 80 wt%. According to other embodiments of the present application, based on the total mass of the negative electrode material, the content of the hollow case may be 20 wt% to 99.9 wt%. The mass ratio of the metallic lithium and the hollow shell can be (0.5 to 3): (12 to 18), for example, it can be 1:12, 1:15, 1:17, 2:14, 2:17. When the content of the hollow case or the content of metal lithium is in the above range, or the mass ratio of the metal lithium and the hollow case meets the above requirements, that is, the specific capacity of the anode material cannot be reflected because the content of the metal lithium is too low The advantage is that the internal space of the hollow case is completely filled due to the excessive filling of metal lithium, which makes the hollow case unable to reserve a margin for the volume change in the process of lithium insertion and removal of the battery, or the excessive filling of the lithium metal. Metal lithium is formed on the outside of the hollow case. Therefore, the negative electrode material can have better performance. According to the embodiment of the present application, after the hollow shell is filled with metallic lithium, the porosity may be 5-30%, and the specific surface area may be 2-10m ² / g. That is to say, the porosity of the negative electrode material can be 5-30%, and the specific surface area can be 2-10 m ² / g. The porosity test in this application can be performed using test instruments and methods commonly used in the art.

According to the embodiment of the present application, the specific chemical composition of the hollow shell is not particularly limited as long as it includes a carbon element. For example, according to other embodiments of the present application, the hollow housing may further include at least one of silicon, titanium, and aluminum. For example, at least one of Si, Al ₂ O ₃ , SiO _x (0.1 ≦ _x ≦ 1.99), and TiO ₂ may be included, such as one or two or three of the above compounds. The introduction of the above materials in the hollow case will not cause a significant negative impact on the performance of the negative electrode material, and it can also improve the strength of the hollow case.

According to the embodiment of the present application, the size and shape of the above-mentioned hollow casing are not particularly limited, as long as the interior thereof has a space where metal lithium can be deposited. For example, according to a specific embodiment of the present application, the above-mentioned hollow casing may be similar to a spherical shape. The average diameter of the hollow shell can be 3-50 microns, such as 5-20 microns. The thickness of the hollow shell can be 1-10 microns. The thickness of the hollow shell can be obtained through a cross-section test. The cross-section test is a test method commonly used in the art. Conventionally, the thickness of the hollow shell is measured by EDS / SEM. The average diameter of the anode material may be 3-50 microns.

In summary, the negative electrode material according to the embodiment of the present application has the advantages of effectively alleviating the growth of lithium dendrites, simple structure, which can be obtained without complicated synthesis methods, good stability, and high specific capacity.

In another aspect of the present application, the present application proposes a method for preparing a negative electrode material. According to the embodiment of the present application, the negative electrode material may be the negative electrode material described above. Referring to FIG. 1, the method may include:

S100: forming a hollow shell

According to an embodiment of the present application, in this step, a hollow casing is formed. The specific manner of forming the hollow casing is not particularly limited, and those skilled in the art can choose according to the actual situation, as long as the formed hollow casing has a hollow internal structure, it can satisfy the following steps to allow lithium ions to fill the interior of the casing to form metal. Lithium is sufficient. According to an embodiment of the present application, the above-mentioned hollow shell may be mainly formed of a carbon-carbon-based material, and the above-mentioned hollow shell may be formed by first forming carbon particles such as a spherical shape, and then forming an inner hollow shell by annealing. Therefore, a shell with a hollow structure can be easily obtained, which is convenient for filling lithium metal in subsequent steps.

Referring to FIG. 2, the above-mentioned hollow shell may be obtained by using the following steps:

S110: forming a hollow shell precursor

According to the embodiment of the present application, in this step, a hollow shell precursor without a hollow structure may be formed first. The hollow shell precursor may be formed by a solvothermal method or a template method. As mentioned before, the finally formed hollow shell may be mainly composed of a carbon-based material. Therefore, the hollow shell precursor formed in this step may also be mainly composed of a carbon-based material. In this step, the solution containing the carbon source may be placed in a closed space for heat treatment, so as to obtain a hollow shell precursor by a solvothermal method.

In addition, most of the currently used template particles are formed by particles containing the above elements, such as nano-silicon, carbon dioxide pellets or silicon monoxide pellets of various particle sizes. Therefore, the introduction of the above elements in the hollow shell is also beneficial to the use of the above-mentioned nanoparticles, or template particles, as a template for forming the hollow shell, and thus the hollow shell can be easily formed without the need to form the hollow shell. Introduced a complicated process to remove the template.

Specifically, according to the embodiment of the present application, the solution containing the carbon source may be placed in a closed reaction container, such as a hydrothermal reaction kettle, and reacted at 150-280 degrees Celsius for 1-20 hours. As a result, a hollow-shell precursor can be easily obtained. In this step, the carbon source removed from the solution in the hydrothermal reaction kettle may also contain other components, such as other metal salts. Thereby, other metal elements can be easily doped into the hollow shell precursor. The specific type of the carbon source is not particularly limited as long as it has good solubility in a solvent. For example, the carbon source may be an organic carbon source, such as glucose or other organic polymers with good solubility, or an inorganic carbon-containing substance such as carbon powder. According to the embodiment of the present application, the solvent used to configure the solution in this step is not particularly limited, such as water (deionized water or secondary water, etc.), or a mixed solvent of an inorganic solvent and an organic solvent. For example, it can be an aqueous solution mixed with organic substances including, but not limited to, ethanol and methanol.

According to other embodiments of the present application, the hollow shell precursor may also be prepared by a template method. For example, according to some embodiments of the present application, the carbon source and the template particles can be uniformly mixed to configure a precursor solution, and then the precursor solution is spray-dried to form a hollow shell precursor. According to a specific embodiment of the present application, a carbon source such as glucose can be configured into a solution with a certain concentration, and then mixed with particles including, but not limited to, nano-silicon, titanium dioxide pellets, alumina pellets, etc., which can be used as a template. In order to increase the uniformity of the mixing, the mixed solution may be sonicated, or a solvent such as ethanol may be added to the solution during the sonication. Subsequently, the mixed mixture is dried by a spray drying method, and a hollow shell precursor can be easily obtained. The above-mentioned spray drying method can be achieved by supplying a mixed solution to a spray drying apparatus.

S120: Annealed

According to an embodiment of the present application, in this step, the hollow shell precursor is annealed to form a hollow shell. Specifically, in order to prevent the hollow shell precursor from being oxidized during the annealing process, the annealing process may be performed under an inert atmosphere. The temperature of the annealing treatment is not particularly limited, and those skilled in the art can adjust the temperature according to the specific chemical composition of the hollow shell precursor. According to some specific embodiments of the present application, the hollow shell precursor may contain more carbon elements, the annealing temperature may be 300-1200 degrees Celsius, and the processing time may be 1-30 hours. Therefore, most of the carbon elements in the center region of the hollow shell precursor can be easily removed, thereby forming a hollow structure. The inventors found that performing the annealing treatment within the above-mentioned processing temperature and processing time range can effectively form a hollow structure, and the hollow space inside the formed hollow shell is moderate in size, suitable for filling lithium metal, and will not be caused by the harsh annealing conditions. As a result, the shell forms an opening or the shell structure collapses, and the hollow structure cannot be formed due to insufficient annealing.

S200: Filled with lithium metal

According to an embodiment of the present application, in this step, a metallic case is filled with metallic lithium in order to obtain a negative electrode material. Specifically, the filling of metallic lithium may be performed by electrodeposition under an inert atmosphere. Those skilled in the art can understand that, due to the active nature of metallic lithium, the electrodeposition process needs to be performed under the protection of an inert atmosphere.

According to the embodiment of the present application, the specific conditions of electrodeposition are not particularly limited, as long as lithium ion can be controlled to be deposited inside the hollow shell. For example, according to a specific embodiment of the present application, the above process may be performed under constant current conditions. For example, according to particular embodiments of the present disclosure, may be used as the positive electrode of said hollow housing, at a current density of 0.1mA / cm ² -1mA / cm ^2, the use of constant current discharge, the lithium ions are deposited in the interior of the hollow body Metal lithium is formed. The specific deposition time of the electrodeposition is also not particularly limited, and may be, for example, 1 to 30 hours. As mentioned earlier, since the charge is basically uniformly distributed on the surface of the hollow shell, and its internal space is an electrostatic shielding field, it is conducive to the uniform deposition of lithium ions. Therefore, metal lithium will not be preferentially deposited on the hollow during electrodeposition. The outer surface of the shell will instead preferentially deposit inside the hollow shell. The electrolyte solution in the above-mentioned electrodeposition process is also not particularly limited, as long as it does not react with the electrode, lithium ions can be freely moved to the electrode having a hollow case therein, and deposition can occur. This can prevent the metal lithium from generating lithium dendrites during battery cycling.

According to a specific embodiment of the present application, the above-mentioned hollow case can be used as a positive electrode, and metallic lithium can be used as a negative electrode to form a lithium ion battery, and then subjected to a constant current discharge treatment under a constant current. Therefore, metal lithium can be formed inside the hollow case of the positive electrode sheet by using the process of lithium insertion. Because the interior of the lithium-ion battery is a sealed environment, it can easily provide an inert atmosphere for the electrodeposition process.

In yet another aspect of the present application, the present application proposes a negative electrode material. According to the embodiment of the present application, the negative electrode material is prepared by the method described above. Therefore, the negative electrode material has all the characteristics and advantages of the negative electrode material obtained by the method described above, and details are not described herein again.

In yet another aspect of the present application, the present application proposes a lithium-ion battery. The lithium-ion battery includes the anode material described above. Therefore, the lithium-ion battery has all the features and advantages of the foregoing negative electrode material, which will not be repeated here. In general, the lithium ion battery has the advantages of a negative electrode material that can prevent the growth of lithium dendrites, better battery stability, and higher specific capacity.

In yet another aspect of the present application, the present application proposes a vehicle. According to an embodiment of the present application, the vehicle includes the aforementioned lithium-ion battery. For example, a plurality of battery packs composed of the aforementioned lithium-ion batteries may be included. Therefore, the vehicle has all the features and advantages of the lithium-ion battery described above, which will not be repeated here.

The following describes the application through specific examples. It should be noted that the following specific examples are for illustration purposes only, and do not limit the scope of the application in any way. In addition, unless otherwise specified, the conditions are not specifically recorded. Or the steps are all conventional methods, and the reagents and materials used can be obtained from commercial sources.

Example 1 Preparation of Anode Material

With glucose as the carbon source, glucose and deionized water were mixed uniformly at a ratio of 1:30 by mass, and then placed in a 100 ml reaction kettle. The reaction kettle was then held at 180 ° C for 6 hours, and then the reaction product It was filtered and dried in a blast drying box at 80 ° C. The dried precursor was kept in a high-temperature inert atmosphere reaction furnace at 650 ° C for 8 hours to obtain hollow carbon-carbon spheres. The hollow carbon-carbon spheres had a porosity of 55%. The specific surface area is 25m ² / g.

Hollow carbon spheres are used as the positive electrode active material, and Li sheets are used as the negative electrode to form a lithium ion battery. Constant current discharge is performed at a current density of 0.15 mA / cm ^{2 for} 15 hours. Metal lithium is deposited in the hollow carbon spheres. The mass ratio of the hollow carbon spheres is 1:15, forming a final metal lithium / hollow carbon sphere composite anode material with high energy density. The anode material has a porosity of 30% and a specific surface area of 9.6 m ² / g.

Example 2 Preparation of Anode Material

Take glucose as the carbon source, mix glucose and deionized water at a ratio of 1:30 by mass to obtain a glucose solution, and then add nano-silicon to the glucose solution at a ratio of 1:10 by mass of glucose, and drop a few drops. Alcohol was sonicated for 15 minutes, and then spray dried on a spray drying device to form a precursor. The precursor was kept at 650 ° C for 8 hours in a high-temperature reaction furnace under an inert atmosphere to obtain a hollow sphere. The main structure of the hollow sphere was made of carbon and silicon balls. The composition has a porosity of 48% and a specific surface area of 20 m ² / g.

The remaining steps are the same as in Example 1. The mass ratio of the deposited lithium metal to the mass of the composite hollow sphere is 1:15, and a final high-energy density metal lithium / composite hollow sphere anode material is formed. The anode material has a porosity of 26. %, And the specific surface area was 7.4 m ² / g.

Example 3 Preparation of Anode Material

With glucose as the carbon source, glucose and deionized water were mixed uniformly at a ratio of 1:30 by mass, and then placed in a 100 ml reaction kettle. The reaction kettle was then held at 180 ° C for 6 hours, and then the reaction product It was filtered and dried in a blast drying box at 80 ° C. The dried precursor was kept at 650 ° C for 8 hours in a high-temperature reaction furnace under a warm inert atmosphere to obtain hollow carbon spheres with a porosity of 55. % And specific surface area is 25 m ² / g.

Hollow carbon spheres are used as the positive electrode active material, and Li sheets are used as the negative electrode to form a lithium ion battery. A constant current discharge is performed at a current density of 0.5 mA / cm ^{2 for} 10 hours. Metal lithium is deposited in the hollow carbon spheres. The mass ratio of the hollow carbon spheres is 1: 5, forming a final metal lithium / hollow carbon sphere composite anode material with high energy density. The anode material has a porosity of 21% and a specific surface area of 5.4 m ² / g.

Comparative Example 1

Amorphous carbon was obtained by incubating glucose at 650 ° C for 8 hours. The result is a carbon skeleton material with no specific morphology, rather than a hollow carbon shell. The remaining steps are the same as in Example 1. The mass ratio of the deposited metal lithium to the mass of the amorphous carbon is 1:15, forming a final composite material. Lithium metal is deposited on the surface of the carbon skeleton material, not the inner surface of the hollow carbon shell.

The morphology of the samples obtained in the above examples was observed using a scanning electron microscope. Fig. 3 is a scanning electron microscope (SEM) image of the product after the hydrothermal reaction of glucose prepared in Example 1 (voltage 25 kV, 2000 magnification, instrument model JSM-5610LV). It can be seen from the figure that after 6 hours of reaction at 180 ° C, glucose formed a spherical particle structure with an average particle diameter between 5-10 microns.

Figure 4 shows the surface morphology of the material after the spherical precursor is carbonized at high temperature, and then made into a button battery for lithium insertion. After inserting the pole pieces in a blast oven at 100 ° C for 24 hours. It can be seen that after high-temperature carbonization, the morphology of the spherical precursor remains very good and still has a spherical structure. The density test of this carbonized sphere has a porosity of 50%. Based on the analysis of the morphology of the sphere, the spherical structure is carbon. Hollow spheres with a shell thickness of about 1-2 microns.

FIG. 5 is an atomic oxygen distribution diagram of FIG. 4 after elemental analysis energy spectroscopy (EDS) surface scanning. Because the lithium atom is light and cannot be detected by scanning electron microscopy, the anode material needs to be oxidized in the air to oxidize metal lithium to lithium oxide. The distribution of lithium is characterized by testing the distribution of oxygen. From the EDS surface scan results of oxygen element, it can be known that metallic lithium (lithium oxide at this time, the white bright spot in Figure 5 is lithium oxide, as shown in the dashed box in the figure) is mainly distributed inside the carbon sphere, which is very good. It is illustrated that the lithium metal is embedded in the hollow sphere: FIG. 6 is an EDS surface scanning result chart of the oxygen element of Comparative Example 1 (the white bright spot is the O element). Comparing FIG. 5 and FIG. 6, if the lithium metal is distributed outside the carbon sphere, the scanning distribution of the EDS surface of the oxygen element should be the same as the distribution of the O element in FIG. 6, and it is distributed at each position on the scanning surface. When the metallic lithium is embedded in the hollow sphere, a distribution diagram as shown in FIG. 5 appears, and the oxygen element is mainly distributed in a spherical shape and does not cover the entire scanning surface.

The laminated battery was used to test the cycle performance of the negative electrode materials prepared in the above examples and comparative examples: a lithium iron phosphate was used as a positive electrode, and a metal lithium / hollow carbon ball composite material was used as a negative electrode to make a laminated battery. The specific charging and discharging system is: a system that uses 0.5mA / cm ² constant current charging and discharging.

FIG. 7 is a charge-discharge performance chart of the battery made in Experiment 1. It can be seen that after about 100 cycles, the capacity retention rate of the material prepared in Example 1 is very good, at about 98%, indicating that the anode material can effectively prevent lithium. The growth of dendrites. The charge and discharge performance of Examples 1-3 and the comparative example are shown in Table 1. Although the first discharge specific capacitance and the first coulomb efficiency of the comparative example can be kept the same as those of Example 1, the cycle performance is extremely poor, and the capacity retention rate of 100 cycles is only Is 27%. This shows that the negative electrode material prepared in the comparative example cannot effectively prevent the growth of lithium dendrites: the amorphous carbon in the comparative example is not a hollow structure, and lithium metal is not formed inside the hollow carbon shell.

Table 1: Charge and discharge performance

Zh	First discharge specific capacity	Coulomb efficiency for the first time	Capacity retention for 100 cycles
Example 1	420 (mAh / g)	95%	98%
Example 2	670 (mAh / g)	92%	90%
Example 3	910 (mAh / g)	91%	85%
Comparative example	420 (mAh / g)	95%	27%

In the description of this specification, the description with reference to the terms "one embodiment", "another embodiment", etc. means that a specific feature, structure, material, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application . In this specification, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of the different embodiments or examples without conflicting one another.

Although the embodiments of the present application have been shown and described above, the above embodiments are exemplary and should not be construed as limiting the present application. Those skilled in the art can make changes to the above embodiments within the scope of the present application Modifications, replacements, and variations.

Claims (18)

1. A negative electrode material includes:

   A hollow shell containing carbon; and

   Metal lithium located inside the hollow casing.
2. The negative electrode material according to claim 1, wherein the hollow case is a porous case, and the porosity of the hollow case is 30-80%.
3. The negative electrode material according to claim 1 or 2, wherein the specific surface area of the hollow case is 10-80 ^m2 / g.
4. The negative electrode material according to any one of claims 1 to 3, which has a porosity of 5-30%. The specific surface area is 2-10 m ² / g.
5. The negative electrode material according to any one of claims 1 to 4, based on the total mass of the negative electrode material, the content of the metallic lithium is 0.1 wt% to 80 wt%.
6. The negative electrode material according to any one of claims 1 to 5, based on the total mass of the negative electrode material, the content of the hollow case is 20 wt% to 99.9 wt%.
7. The negative electrode material according to claim 1, wherein a mass ratio of the metallic lithium and the hollow case is (0.5 to 3): (12 to 18).
8. The negative electrode material according to claim 1, wherein the hollow case further comprises at least one of Si, Al ₂ O ₃ , SiOx (0.1 ≦ x ≦ 1.99), and TiO ₂ .
9. The negative electrode material according to any one of claims 1 to 8, wherein the hollow case has an average diameter of 3 to 50 microns.
10. The negative electrode material according to any one of claims 1-9, wherein the thickness of the hollow case is 1-10 microns.
11. The negative electrode material according to any one of claims 1 to 10, wherein the average diameter of the negative electrode material is 3 to 50 microns.
12. A method for preparing a negative electrode material includes:

    Forming a hollow shell containing carbon,

    Through electrodeposition, metal lithium is filled inside the hollow case to obtain the negative electrode material.
13. The method according to claim 12, the method of forming the hollow shell comprises:

    Forming a hollow shell precursor,

    The hollow shell precursor is annealed to form the hollow shell.
14. The method according to claim 12 or 13, wherein the hollow shell precursor is formed by a solvothermal method or a template method.
15. The method according to any one of claims 12 to 14, the electrodeposition is performed by performing a constant current deposition under an inert atmosphere.
16. The method according to any one of claims 12-15, wherein the electrodeposition comprises:

    The hollow case is used as a positive electrode, and metal lithium is used as a negative electrode to form a lithium ion battery, and a constant current discharge treatment is performed under a constant current.
17. The method according to claim 16, wherein a current density of the constant current discharge treatment is 0.1 mA / cm ² to 1 mA / cm ² ;

    The processing time of the constant current discharge treatment is 1-30 hours.
18. A lithium ion battery, comprising a negative electrode material prepared according to any one of claims 1-11 or a method according to any one of claims 12-17.

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