Hard carbon material for storing alkali metal ions and preparation method therefor

Abstract

Disclosed in the present invention are a hard carbon material for storing alkali metal ions and a preparation method therefor. Specifically, the hydrogen content of the hard carbon material for storing alkali metal ions is less than 2 wt%; the range of order is 0-20 nm; the interlayer spacing is greater than 0.36 nm; and the ratio of the intensities of the D-band and G-band of the Raman spectrum thereof is between 1.0 and 1.3. In particular, the operating temperature of the preparation method of the present invention is lower than 1800°C, and therefore the method is an energy-saving process.

Description

A hard carbon material for storing alkali metal ions and its preparation method Technical Field

[0001] The present invention discloses a hard carbon material for storing alkali metal ions and a method for preparing the same. The hard carbon material has a hydrogen content of less than 2 wt.% and an interlayer spacing greater than 0.36 nm. Specifically, the present invention achieves control over the hydrogen content and interlayer spacing by adjusting the processing temperature and doping additives. Background Art

[0002] With the rapid development of electronics, electric vehicles, and green energy-related industries, market demand for high-energy ion batteries with high metal ion storage capacity and high efficiency has also increased. Currently, graphite and its derivatives are the primary anode materials used in ion batteries. However, the low theoretical gram capacity and low discharge efficiency of existing anode materials have been technical bottlenecks that have been difficult to overcome. Furthermore, the small interlayer spacing and inability to form a stable intercalation structure in metal ion batteries have significantly limited their subsequent application.

[0003] In view of the above, the development of a new type of composite negative electrode material with high storage capacity and long cycle life is a technical target that urgently needs breakthroughs and development in current ion batteries.

[0004] Summary of the Invention

[0005] In view of the above technical background, in order to meet the needs of the industry. The present invention discloses a novel hard carbon material for storing alkali metal ions and a preparation method thereof. Specifically, the hydrogen content of the hard carbon material for storing alkali metal ions of the present invention is less than 2wt.%, and its ordered length (La) range is 0-20nm and its interlayer spacing is greater than 0.36nm. In particular, the hard carbon material for storing alkali metal ions of the present invention has higher alkali metal ion storage capacity and coulombic efficiency, which can greatly improve the shortcomings of traditional hard carbon materials. The preparation method provided by the present invention adopts a low-temperature sintering process, and at the same time achieves the material structure characteristics of less than 2wt.% hydrogen content, ordered length (La) range of 0-20nm and interlayer spacing greater than 0.36nm by temperature adjustment and doping additives.

[0006] The technical solutions adopted by the present invention and the technical effects achieved are described as follows.

[0007] A first objective of the present invention is to disclose a hard carbon material for storing alkali metal ions. The hard carbon material for storing alkali metal ions is prepared using phenolic resin, petroleum coke, coal, biomass, or a mixture thereof as a precursor, and then undergoes a manufacturing process at different temperatures and a doping procedure to produce the hard carbon material for storing alkali metal ions.

[0008] Specifically, the hydrogen content of the hard carbon material for storing alkali metal ions is less than 2 wt.%. More specifically, the ordered length (La) of the hard carbon material for storing alkali metal ions is in the range of 0-20 nm and the interlayer spacing is greater than 0.36 nm. Due to the above-mentioned material characteristics, the hard carbon material for storing alkali metal ions of the present invention is a hard carbon material with a high alkali metal ion storage capacity.

[0009] The second object of the present invention is to provide a method for preparing a hard carbon material for storing alkali metal ions. Specifically, the preparation method includes but is not limited to the steps of pre-carbonization, crushing, doping and carbonization, thereby preparing the hard carbon material for storing alkali metal ions. More specifically, the preparation method adopts two-stage process technology with different temperatures, and controls the hydrogen content to be less than 2wt.% by temperature regulation. More specifically, the process temperature of the preparation method of the present invention is controlled within 1800°C to avoid a significant narrowing of the interlayer spacing of the material due to high temperature, and at the same time, further hinders the process of narrowing the interlayer spacing by doping with different additives, thereby controlling the ordered length (La) of the hard carbon material for storing alkali metal ions of the present invention to be in the range of 0-20nm and its interlayer spacing to be greater than 0.36nm.

[0010] According to the above-mentioned purpose of the invention, in order to overcome the shortcomings of low metal ion storage capacity of existing conventional negative electrode materials, the present invention discloses a technical solution for a hard carbon material for storing alkali metal ions. Specifically, the hydrogen content of the hard carbon material for storing alkali metal ions is less than 2wt.%, its ordered length (La) range is 0-20nm, and its interlayer spacing is greater than 0.36nm. In particular, the hard carbon material for storing alkali metal ions of the present invention achieves the technical effect of controlling the upper limit of the hydrogen content of the hard carbon material and preventing its interlayer spacing from narrowing by means of low-temperature processes and doping additives, thereby achieving the technical effect of improving the alkali metal ion storage capacity of the material. Accordingly, the hard carbon material for storing alkali metal ions of the present invention has a higher alkali metal ion storage capacity and can be widely used as a negative electrode material for lithium-ion batteries, sodium-ion batteries or potassium-ion batteries. Second, the present invention provides a method for preparing a hard carbon material for storing alkali metal ions. Specifically, the preparation method uses low-temperature pre-carbonization, pulverization, doping, and carbonization steps to produce a hard carbon material with a high alkali metal ion storage capacity, having a hydrogen content of less than 2 wt.%, an ordered length (La) in the range of 0-20 nm, and an interlayer spacing greater than 0.36 nm. The preparation method of the present invention utilizes a low-temperature sintering process, with the operating temperature throughout the entire process being less than 1800°C. This technical approach achieves the technical effect of controlling the upper limit of the hydrogen content and the lower limit of the interlayer spacing. Simultaneously, doping with additives before carbonization prevents the interlayer spacing from narrowing significantly at the carbonization operating temperature, thereby achieving a multiplying effect. Thus, the preparation method of the present invention utilizes temperature control and additive doping to produce a hard carbon material with a high alkali metal ion storage capacity. Compared to existing processes that produce hard carbon materials at high temperatures exceeding 2000°C, the process of the present invention operates at temperatures below 1800°C. Therefore, the preparation method of the present invention also has the technical advantages of being environmentally friendly and energy-saving, and can be more widely applied in the hard carbon material and negative electrode material related industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the parameters and structure of graphite crystal.

[0012] FIG2 is an X-ray diffraction pattern of the hard carbon material prepared at different temperatures according to the present invention.

[0013] FIG3 is a Raman spectrum of the hard carbon material prepared at different temperatures according to the present invention.

[0014] FIG4 is a graph showing the relationship between cycle number and specific capacity of batteries using the hard carbon material prepared at different temperatures of the present invention as negative electrode material.

[0015] FIG5 is an impedance diagram of a battery using the hard carbon material prepared at different temperatures of the present invention as a negative electrode material.

[0016] FIG6 is a graph showing the relationship between voltage and specific capacity of a battery using the hard carbon material prepared at 1500° C. of the present invention as a negative electrode material.

[0017] FIG7 is a graph showing the relationship between cycle number and specific capacity of a battery using the hard carbon material prepared at 1500° C. of the present invention as a negative electrode material.

[0018] FIG8 is a graph showing the relationship between specific capacity and current density of hard carbon materials doped with different nitrogen contents according to the present invention. DETAILED DESCRIPTION

[0019] A first embodiment of the present invention discloses a hard carbon material for storing alkali metal ions. The technical characteristics of the hard carbon material for storing alkali metal ions include a hydrogen content of less than 2 wt.% and an ordered length (La) in the range of 0-20 nm. Preferably, the hard carbon material for storing alkali metal ions has a hydrogen content of 0.3-1 wt.%, and an ordered length (La) in the range of 2-8 nm.

[0020] In a specific example, the interlayer spacing of the hard carbon material having a hydrogen content of less than 2 wt.% is greater than 0.36 nm. Preferably, the interlayer spacing of the hard carbon material storing alkali metal ions is 0.37-0.4 nm.

[0021] In another specific example, the hard carbon material having a hydrogen content of less than 2 wt.% exhibits a Raman spectrum intensity ratio of the D-band to the G-band (ID / IG) of 1.0 to 1.3. Preferably, the D-band to G-band intensity ratio is 1.0 to 1.2. This D-band to G-band intensity ratio is used to quantify the structural crystalline characteristics of the hard carbon material for alkali metal ion storage of the present invention. By controlling this D-band to G-band intensity ratio within a specific range, the metal ion storage capacity of the hard carbon material of the present invention can be enhanced.

[0022] In a specific example, the hard carbon material having a hydrogen content of less than 2 wt.% is used to store lithium ions, sodium ions, potassium ions, or a combination thereof.

[0023] In a specific example, the hard carbon material having a hydrogen content of less than 2 wt.% is one of the components of the negative electrode material of a lithium ion battery, a sodium ion battery or a potassium ion battery.

[0024] A second embodiment of the present invention provides a method for preparing a hard carbon material for storing alkali metal ions. The method includes but is not limited to the following steps.

[0025] Step 1: Perform a pre-carbonization process to convert the precursor into a first intermediate product.

[0026] Step 2: performing a crushing process to convert the first intermediate product into a second intermediate product.

[0027] Step 3: Perform a doping process to mix the second intermediate product with the additive to form a third intermediate product; the weight percentage of the additive is 0.5-10 wt.% based on the weight of the second intermediate product.

[0028] Step 4: performing a carbonization process to transform the third intermediate product into the hard carbon material storing alkali metal ions.

[0029] In a specific example, the operating temperature of the pre-carbonization process is 300-800° C. Preferably, the operating temperature of the pre-carbonization process is 500-700° C.

[0030] In one embodiment, the precursor comprises resin, anthracite, petroleum coke, cellulose, or a combination thereof.

[0031] In a specific example, the additives mixed in the doping process include the following compounds: oxygen-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, boron-containing compounds, or combinations thereof. Preferably, the additives are hexamethyltetramine, air, boric acid, or combinations thereof.

[0032] In a specific example, the operating temperature of the carbonization process is 1100-1600° C. Preferably, the operating temperature of the carbonization process is 1150-1400° C.

[0033] In a representative example, a phenolic resin or biomass is first subjected to a pre-carbonization process at 600°C to obtain a first intermediate product; the first intermediate product is crushed by a grinding and pulverizing device to obtain a second intermediate product; then a doping process is performed, and the additives in the doping process include but are not limited to 5wt.% hexamethyltetramine or 5wt.% boric acid; or the second intermediate product is directly oxidized in air at 400°C for four hours to dope oxygen or moisture in the air into the second intermediate product, and the third intermediate product is obtained by the above-mentioned doping process; finally, a carbonization process is performed at 1150°C to obtain the hard carbon material for storing alkali metal ions of the present invention.

[0034] In one embodiment, the hard carbon material for storing alkali metal ions prepared according to the above method has a hydrogen content of less than 2 wt.%, and an ordered length (La) in the range of 0-20 nm. Preferably, the hard carbon material for storing alkali metal ions has a hydrogen content of 0.3-1 wt.%, and an ordered length (La) in the range of 2-8 nm.

[0035] In a specific example, the interlayer spacing of the hard carbon material for storing alkali metal ions obtained according to the above preparation method is greater than 0.36 nm. Preferably, the interlayer spacing of the hard carbon material for storing alkali metal ions is 0.37-0.4 nm.

[0036] In one specific example, the hard carbon material for storing alkali metal ions obtained according to the above preparation method exhibits a Raman spectrum intensity ratio of the D-band to the G-band of 1.0 to 1.3. Preferably, the Raman spectrum intensity ratio of the D-band to the G-band is 1.0 to 1.2. This D-band to G-band intensity ratio is used to quantify the structural crystalline characteristics of the hard carbon material for storing alkali metal ions of the present invention. By controlling this D-band to G-band intensity ratio within a specific range, the metal ion storage capacity of the hard carbon material of the present invention can be enhanced.

[0037] In a specific example, the method for preparing the hard carbon material for storing alkali metal ions is used as a negative electrode material for lithium-ion batteries, sodium-ion batteries, or potassium-ion batteries.

[0038] The following experimental examples further illustrate the technical features and effects of the present invention.

[0039] Hydrogen content determination

[0040] The hard carbon material of this invention is tested for repeatability using a carbon-hydrogen ratio (compliant with GB / T476-2008). A hard carbon sample is burned in an oxygen stream. The generated water reacts with phosphorus pentoxide to form metaphosphoric acid, which is then electrolyzed. The hydrogen content is calculated based on the amount of electricity consumed. The generated carbon dioxide is absorbed by a carbon dioxide absorber, and the carbon content is calculated based on the increase in carbon dioxide. Trace amounts of sulfur oxides and chlorine in the hard carbon sample are removed using the pyrolysis product of silver permanganate, and nitrogen oxides are removed using granular manganese dioxide to eliminate interference with carbon determination.

[0041] Interlayer spacing and ordered length measurements

[0042] As shown in Figure 1, the C=C double bonds of graphite crystals form a hexagonal structure, forming a plane (graphite surface). These surfaces are stacked together to form graphite crystals. 2 Hybridized large π bond, bonding energy is 345kJ / mol. The interlayer is van der Waals force, bonding energy is 16.7kJ / mol. Crystallite parameters include interlayer spacing (d 002 ), the distance between graphite flakes. Ideal single crystals have a value of 0.3354 nm, while amorphous carbon has a value of up to 0.37 nm. La is the average size of a graphite crystal along the a-axis, also known as the order length. Lc is the thickness of the graphite flakes stacked along the perpendicular c-axis, typically ranging from 1 nm to 10 μm.

[0043] Interlayer distance (d 002 ), the calculation formulas of the axial size of graphite crystallite (Lc), the number of microcrystalline layers (n) and the radial size of graphite crystallite (ordered length La) are as follows, where λ is 1.54182A (angstroms), β 002 and β 100 is the half-height width of Peak 002 and Peak 100.

[0044] Ion battery performance evaluation

[0045] The performance evaluation steps for the hard carbon material of the present invention as a negative electrode material for an ion battery are as follows: the hard carbon material of the present invention, a conductive agent, and a binder are dissolved in NMP solvent at a weight ratio of 92:3:5; a sodium / lithium counter electrode is used; the electrolyte is 1M sodium hexafluorophosphate (EC:PC:DEC = 1:1:1) or 1M lithium hexafluorophosphate (EC:EMC:DMC = 1:1:1). After the test cell is assembled, the performance test is performed using the following test procedure: 2 hours of rest; discharge: constant rate 0.1C (1C = 300mA / g) to a voltage of less than 0.001V, constant current 50uA to a voltage of less than 0.001V, and constant current 10uA to a voltage of less than 0.001V; rest for 15 minutes; charge: constant rate 0.1C to a voltage greater than 2V.

[0046] Experimental Example 1: Hard carbon materials prepared at different carbonization temperatures

[0047] This experimental example used a resin as a precursor. After pre-carbonization at 600°C, the sample was crushed and subsequently carbonized at different temperatures to produce a hard carbon material. The experimental results are shown in Table 1, the XRD patterns used to calculate the interlayer spacing are shown in Figure 2, and the Raman shift is shown in Figure 3. The intensity ratios of the D and G bands in the Raman spectrum of the hard carbon materials produced at carbonization temperatures of 800°C and 2000°C were 1.251 and 0.924, respectively. As anode materials for sodium-ion batteries, their first coulombic efficiencies were both below 50%. When the hard carbon material was carbonized at 800°C, its first coulombic efficiency was also below 50% as anode materials for lithium-ion batteries. This demonstrates the structural characteristics of the hard carbon material and the technical benefits of its preparation method.

[0048] As shown in Figure 4, the ion batteries using the hard carbon materials HC1150 and HC1500 prepared at 1150 and 1500°C as negative electrode materials still maintained their original specific capacity after 20 cycles of charge and discharge tests. However, the ion batteries using the hard carbon materials HC800 and HC2000 prepared at 800 and 2000°C as negative electrode materials experienced a significant decrease in specific capacity after 20 cycles of charge and discharge tests, thereby confirming the technical efficacy of this case.

[0049] FIG5 is an impedance diagram of an ion battery using hard carbon materials HC800, HC1150, HC1500, and HC2000 as negative electrode materials.

[0050] Figures 6 and 7 show the relationship between voltage and specific capacity, and the relationship between specific capacity, coulombic efficiency, and cycle number, respectively, for an ion battery using hard carbon material HC1500, prepared at 1500°C, as the negative electrode material. Remarkably, the test battery still maintained a coulombic efficiency of 90% after 500 cycles, demonstrating the technical efficacy of this application.

[0051] Table 1

[0052] 1:d (002) Represents the interlayer distance in nm.

[0053] 2:La represents the ordered length, in nm.

[0054] 3: ID / IG represents the intensity ratio of the D band to the G band of the Raman spectrum.

[0055] 4: First efficiency represents the first coulombic efficiency.

[0056] Experimental Example 2: Hard carbon materials prepared from different precursors

[0057] In this experimental example, precursors including resin, anthracite, pitch coke, starch, and cellulose were pre-carbonized at 600°C, crushed, and then carbonized at 1150°C to produce hard carbon materials. The experimental results are shown in Table 2. This experimental example demonstrates that the preparation method of the present invention is applicable to a variety of precursors. The resulting hard carbon materials all have a hydrogen content (H content) of less than 0.5% and an ordered length of 2-8 nm, demonstrating excellent technical performance as negative electrode materials for ion batteries.

[0058] Table 2

[0059] 1:d (002) Represents the interlayer distance in nm.

[0060] 2:La represents the ordered length, in nm.

[0061] 3: ID / IG represents the intensity ratio of the D band to the G band of the Raman spectrum.

[0062] 4: First efficiency represents the first coulombic efficiency.

[0063] Experimental Example 3: Hard Carbon Materials Prepared by Doping Different Additives

[0064] In this experimental example, a resin was pre-carbonized at 600°C, followed by sample crushing, doping, and finally high-temperature carbonization at 1150°C to produce a hard carbon material. The experimental results are shown in Table 3. This experimental example demonstrates that doping with various additives, such as hexamethyltetramine, air, or boric acid, can better control the hydrogen content, interlayer spacing, order length, and intensity ratio of the hard carbon material's D-band and G-band in the Raman spectrum within a narrower range, resulting in more uniform quality of the hard carbon material of the present invention. This demonstrates that the doping step has an unexpected technical effect on the structural control of the hard carbon material. Furthermore, when this hard carbon material is used as the negative electrode material for an ion battery, the ion battery's gram capacity and first coulombic efficiency both maintain good battery performance.

[0065] Table 3

[0066] 1:d (002) Represents the interlayer distance in nm.

[0067] 2:La represents the ordered length, in nm.

[0068] 3: ID / IG represents the intensity ratio of the D band to the G band of the Raman spectrum.

[0069] 4: First efficiency represents the first coulombic efficiency.

[0070] Experimental Example 4: Hard Carbon Materials Doped with Different Nitrogen (N) Contents

[0071] In this experimental example, a hard carbon material was obtained by doping with varying nitrogen contents (0%, 7%, 9%, and 15%), followed by carbonization at 1150°C. The experimental results are shown in Table 4. This experimental example demonstrates that doping with varying amounts of nitrogen-containing additives can effectively control the interlayer spacing to greater than 0.36 nm and the intensity ratio of the D-band and G-band in the Raman spectrum of the hard carbon material. Figure 8 plots the current density and specific capacity of the hard carbon materials R0-1150, R7-1150, R9-1150, and R15-1150 prepared at 1150°C with varying nitrogen doping contents.

[0072] Table 4

[0073] 1:d (002) Represents the interlayer distance.

[0074] 2: Specific surface area, in m 2 g -1 .

[0075] 3: ID / IG represents the intensity ratio of the D band to the G band of the Raman spectrum.

[0076] The hard carbon materials prepared in Experimental Examples 1 and 4 have electrical properties as shown in Tables 5 and 6.

[0077] Table 5

[0078] Table 6

[0079] In summary, the present invention discloses a technical solution for a hard carbon material for storing alkali metal ions. Specifically, the hard carbon material for storing alkali metal ions has a hydrogen content of less than 2 wt.%, an ordered length (La) in the range of 0-20 nm, and an interlayer spacing greater than 0.36 nm. In particular, the hard carbon material for storing alkali metal ions of the present invention achieves the technical effect of controlling the upper limit of the hydrogen content of the hard carbon material and preventing the interlayer spacing from narrowing by means of low-temperature processes and doping additives, thereby achieving the technical effect of improving the alkali metal ion storage capacity of the material. Accordingly, the hard carbon material for storing alkali metal ions of the present invention has a higher alkali metal ion storage capacity and can be widely used as a negative electrode material for lithium-ion batteries, sodium-ion batteries, or potassium-ion batteries. Second, the present invention provides a method for preparing a hard carbon material for storing alkali metal ions. Specifically, the preparation method is to prepare a hard carbon material with a high ability to store alkali metal ions, having a hydrogen content of less than 2 wt.%, an ordered length (La) in the range of 0-20 nm, and an interlayer spacing greater than 0.36 nm, by steps such as low-temperature pre-carbonization, pulverization, doping, and carbonization. The preparation method of the present invention uses a low-temperature sintering process, and the operating temperature in the entire process is less than 1800°C. This technical means is used to achieve the technical effect of controlling the upper limit of hydrogen content and the lower limit of interlayer spacing. At the same time, additives are doped before carbonization to prevent the interlayer spacing from being significantly narrowed at the carbonization operating temperature, thereby achieving a multiplying effect.

[0080] While the present invention has been described above using specific experimental examples, this does not limit the scope of the invention. Those skilled in the art will appreciate that various modifications and variations may be made without departing from the spirit and scope of the invention. Furthermore, no embodiment or claim of the present invention is required to achieve all of the objects, advantages, or features disclosed herein. The abstract and title are intended solely to assist in searching patent documents and are not intended to limit the scope of the present invention.

Claims

1. A hard carbon material for storing alkali metal ions, characterized in that: The hard carbon material has a hydrogen content of less than 2 wt.%, an ordered length range of 0-20 nm, and an interlayer spacing of greater than 0.36 nm.

2. The hard carbon material for storing alkali metal ions according to claim 1, characterized in that The hard carbon material having a hydrogen content of less than 2 wt.% has an intensity ratio of the D band to the G band in a Raman spectrum of 1.0 to 1.

3.

3. The hard carbon material for storing alkali metal ions according to claim 1, wherein The hard carbon material having a hydrogen content of less than 2 wt.% is used to store lithium ions, sodium ions, potassium ions or a combination thereof.

4. The hard carbon material for storing alkali metal ions according to claim 1, wherein The hard carbon material with a hydrogen content of less than 2 wt.% is one of the components of the negative electrode material of lithium ion batteries, sodium ion batteries or potassium ion batteries.

5. A method for preparing a hard carbon material for storing alkali metal ions, characterized in that: The following steps are included:

1. Performing a pre-carbonization process to convert the precursor into a first intermediate product; 2. performing a comminution process to form a second intermediate product from the first intermediate product; 3. performing a doping process to dope the second intermediate product with an additive to form a third intermediate product; wherein the weight percentage of the additive is 0.5 to 10 wt.% based on the weight of the second intermediate product; and 4. Performing a carbonization process to transform the third intermediate product into the hard carbon material storing alkali metal ions.

6. The method for preparing a hard carbon material according to claim 5, wherein: The operating temperature of the pre-carbonization process is 300-800°C.

7. The method for preparing a hard carbon material according to claim 5, wherein: The precursor comprises resin, anthracite, petroleum coke, cellulose or a combination thereof.

8. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, characterized in that: The additive comprises: an oxygen-containing compound, a nitrogen-containing compound, a phosphorus-containing compound, a boron-containing compound or a combination thereof.

9. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, wherein: The operating temperature of the carbonization process is 1100-1600°C.

10. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, characterized in that: The hard carbon material has a hydrogen content of less than 2 wt.%.

11. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, wherein: The hard carbon material has an order length (La) ranging from 0 to 20 nm and an interlayer spacing greater than 0.36 nm.

12. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, wherein: The hard carbon material has an intensity ratio of a D band to a G band in a Raman spectrum of 1.0 to 1.

3.

13. The method for preparing a hard carbon material for storing alkali metal ions according to claim 5, wherein: The hard carbon material is used as a negative electrode material for lithium ion batteries, sodium ion batteries or potassium ion batteries.

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