A hard carbon material, its preparation method, and a negative electrode sheet

Abstract

The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a hard carbon material, a preparation method thereof, and a negative electrode sheet. A preparation method of a hard carbon material of the present invention comprises the following steps: S1, a mixture of terpene resin, graphene oxide, and a crosslinking agent is pretreated to obtain a hard carbon precursor; S2, the mixture of the hard carbon precursor and a pore-forming agent is subjected to high-temperature carbonization treatment to obtain the hard carbon material. The present invention uses terpene resin and graphene oxide as raw materials, and under the action of a crosslinking agent and a pore-forming agent, a hard carbon material with low production cost, adjustable pore size and pore volume, excellent first-cycle performance, capacity performance, and capacity retention rate can be obtained; when used as a negative electrode material for sodium-ion batteries, it can further reduce the production cost of the battery and endow the battery with excellent rate performance and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and in particular to a hard carbon material, a preparation method thereof, and a negative electrode sheet. Background Art

[0002] With the increase in the price of lithium carbonate, the demand for sodium-ion batteries has increased. At present, the graphite negative electrode used in lithium-ion batteries cannot be directly used in sodium-ion batteries. The radius of sodium ions is larger than that of lithium ions, and the layer spacing of the graphite negative electrode is relatively narrow, making it impossible to embed a sufficient amount of sodium ions, resulting in a very low specific capacity of the battery. Amorphous carbon is a commonly used negative electrode material for sodium-ion batteries, among which hard carbon negative electrodes are mainly used and soft carbon negative electrodes are supplemented.

[0003] Hard carbon materials can generally be divided into three types: resin-based, pitch-based, and bio-based. Among them, resin-based hard carbon materials have reliable performance, meet the standard of consistency, and relatively few impurities. The disadvantages are high raw material costs and low carbon extraction efficiency due to easy volatilization during the processing. Pitch-based hard carbon materials have wide access channels and low cost, and the unit price per ton can reach about 20,000 yuan, but the first-cycle efficiency and energy density performance are average. Bio-based hard carbon materials have the characteristics of mature technology, excellent performance, and acceptable consistency. Carbon-containing biomass such as coconut shells, starch, and distiller's grains can be selected as the precursor. The disadvantage is relatively high cost. Therefore, it is urgent to find a sodium-ion battery hard carbon material with low cost, high performance, and stable batches.

[0004] Conventional resin-based hard carbon refers to phenolic resin, including phenol-formaldehyde resin, resorcinol-formaldehyde resin, hydroquinone-formaldehyde resin, and phenol-furfural resin, etc. Using such resins to produce hard carbon has high costs and cannot meet the current market demand.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a preparation method of a hard carbon material, which can greatly reduce the production cost and obtain a high-performance hard carbon material with adjustable pore size and pore volume.

[0007] The second object of the present invention is to provide a hard carbon material, which is inexpensive and has excellent first-cycle efficiency performance, capacity performance, and capacity retention rate.

[0008] The third object of the present invention is to provide a negative electrode sheet, which includes the above-mentioned hard carbon material.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are adopted:

[0010] The present invention provides a preparation method of a hard carbon material, including the following steps:

[0011] S1. A mixture of terpene resin, graphene oxide and crosslinking agent is pretreated to obtain a hard carbon precursor;

[0012] S2. The mixture of the hard carbon precursor and the pore-forming agent is subjected to high-temperature carbonization treatment to obtain the hard carbon material.

[0013] Further, in step S1, the softening point of the terpene resin is 50-140 °C, and the residual carbon rate is 5%-12%.

[0014] Preferably, in step S1, the number of layers of the graphene oxide is 1-5 layers, the sheet diameter <20 μm, the oxygen content <30 wt%, and ID / IG > 0.8.

[0015] Preferably, in step S1, the crosslinking agent includes at least one of ammonium dihydrogen phosphate, phosphorus pentoxide, dopamine, thiourea and maleic anhydride.

[0016] Further, in step S1, the mass ratio of the terpene resin, the graphene oxide and the crosslinking agent is (2-6):(0.5-1.5):(0.5-1.5).

[0017] Further, in step S1, before the pretreatment, grinding is also included.

[0018] Preferably, in step S1, the grinding includes ball milling.

[0019] Preferably, in step S1, the rotation speed of the grinding is 100-800 rmp, and the grinding time is 1-3 h.

[0020] Further, in step S1, the pretreatment includes: heating to 280-410 °C under an inert atmosphere, holding for 0.5-4 h, and then cooling.

[0021] Preferably, in step S1, the heating rate is 1-10 °C / min.

[0022] Further, in step S2, the pore-forming agent includes at least one of KOH, NaOH, C2H5ONa and C2H5OK.

[0023] Preferably, in step S2, the mass ratio of the hard carbon precursor and the pore-forming agent is (3-8):1.

[0024] Further, in step S2, before the high-temperature carbonization treatment, grinding is also included.

[0025] Preferably, in step S2, the grinding includes ball milling.

[0026] Preferably, in step S2, the rotation speed of the grinding is 200 - 1500 rmp, and the grinding time is 1 - 3 h.

[0027] Further, in step S2, the high-temperature carbonization includes: under an inert atmosphere, heating to 1300 - 1600 °C and holding for 2 - 12 h.

[0028] Preferably, in step S2, the heating rate is 3 - 15 °C / min.

[0029] The present invention also provides a hard carbon material prepared by the preparation method of the hard carbon material as described above.

[0030] The present invention also provides a negative electrode sheet including the hard carbon material as described above.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The present invention uses terpene resin as the skeleton and composes graphene oxide. Under the action of a cross-linking agent and a pore-forming agent, a high-performance hard carbon material with adjustable pore size and pore volume can be obtained; using terpene resin as the raw material, the price is low, and the production cost can be greatly reduced; the prepared hard carbon material has excellent first-cycle performance, capacity performance, and capacity retention rate; using the hard carbon material of the present invention as the negative electrode material of a sodium-ion battery can further reduce the production cost of the battery and endow the battery with excellent rate performance and cycle performance. Specific Embodiments

[0033] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0034] A hard carbon material, its preparation method, and a negative electrode sheet according to embodiments of the present invention will be specifically described below.

[0035] In some embodiments of the present invention, a preparation method of a hard carbon material is provided, including the following steps:

[0036] S1. A mixture of terpene resin, graphene oxide, and a cross-linking agent is pretreated to obtain a hard carbon precursor;

[0037] S2. The mixture of the hard carbon precursor and the pore former is subjected to high-temperature carbonization treatment to obtain the hard carbon material.

[0038] As a petrochemical product, terpene resin has a certain degree of polymerized carbon components and can be used alone as the precursor skeleton for preparing hard carbon. When combined with graphene oxide material, it can be fully combined to improve the performance of hard carbon. Adding a cross-linking agent for doping and cross-linking reactions can further improve the cross-linking degree and polymerization degree of the product, ensuring the yield and performance of the hard carbon material. At the same time, for the composite product of cross-linked terpene resin and graphene oxide, adding a pore former for pore formation can assist in improving the pore size distribution and pore volume.

[0039] The present invention uses terpene resin as the raw material, which is inexpensive and can greatly reduce the production cost.

[0040] The hard carbon material prepared by the preparation method of the hard carbon material of the present invention has excellent first-cycle performance, capacity performance, and capacity retention rate.

[0041] The preparation method of the hard carbon material of the present invention can regulate the pore volume and pore size of the hard carbon through the pore former.

[0042] In some embodiments of the present invention, in step S1, the softening point of the terpene resin is 50-140°C, and the residual carbon rate is 5%-12%; preferably, the softening point of the terpene resin is 80-140°C; more preferably, the softening point of the terpene resin is 120-140°C, and the residual carbon rate is 8%-12%.

[0043] Terpene resin is processed from natural turpentine, and its softening point is 50-140°C; terpene is prone to cyclization, oxidation, reduction, polymerization and other reactions; terpene can also undergo intramolecular rearrangement and double bond transposition; an ideal hard carbon material can be obtained.

[0044] The structure of the terpene resin is as follows:

[0045]

[0046] In some embodiments of the present invention, in step S1, the terpene resin includes liquid terpene resin and / or solid terpene resin.

[0047] In some embodiments of the present invention, in step S1, the number of layers of graphene oxide is 1-5 layers, the sheet diameter <20 μm, the oxygen content <30 wt%, I D / I G > 0.8; preferably, the number of layers of graphene oxide is 1-3 layers, the sheet diameter <12 μm, the oxygen content <25 wt%, I D / I G > 1.1; I D / I GIt is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum.

[0048] The present invention uses terpene resin and graphene oxide as raw materials to prepare hard carbon materials. Using terpene resin and graphene oxide with the above parameters is beneficial to improving the performance of the hard carbon materials.

[0049] In some embodiments of the present invention, in step S1, the crosslinking agent includes at least one of ammonium dihydrogen phosphate, phosphorus pentoxide, dopamine, thiourea, and maleic anhydride; preferably, the crosslinking agent includes ammonium dihydrogen phosphate ((NH4)2HPO4) and / or maleic anhydride.

[0050] Using a crosslinking agent for doping and crosslinking can improve the degree of polymerization of the prepared hard carbon materials.

[0051] In some embodiments of the present invention, in step S1, the mass ratio of terpene resin, graphene oxide, and crosslinking agent is (2 - 6):(0.5 - 1.5):(0.5 - 1.5); preferably, the mass ratio of terpene resin, graphene oxide, and crosslinking agent is (2 - 4):(0.8 - 1.2):(0.8 - 1.2).

[0052] In some embodiments of the present invention, in step S1, before the pretreatment, grinding is also included.

[0053] In some embodiments of the present invention, in step S1, the grinding includes ball milling; preferably, the rotation speed of the grinding is 100 - 800 rmp, and the grinding time is 1 - 3 h; preferably, the rotation speed of the grinding is 300 - 500 rmp, and the grinding time is 1.5 - 3 h.

[0054] In some embodiments of the present invention, in step S1, the pretreatment includes: under an inert atmosphere, heating to 280 - 410 °C for heat preservation treatment for 0.5 - 4 h, and then cooling; typically but not limited to, for example, the pretreatment temperature can be 280 °C, 300 °C, 320 °C, 340 °C, 360 °C, 380 °C, 400 °C, 410 °C or any range value composed of any two of them; the pretreatment time is 0.5 h, 1 h, 1.5 h, 2.5 h, 3 h, 3.5 h, 4 h or any range value composed of any two of them. Preferably, the pretreatment temperature is 300 - 410 °C, and the pretreatment time is 0.5 - 2 h.

[0055] In some embodiments of the present invention, in step S1, the heating rate during the pretreatment process is 1 - 10 °C / min; preferably, the heating rate during the pretreatment process is 4 - 6 °C / min.

[0056] In some embodiments of the present invention, in step S1, the inert atmosphere includes nitrogen; preferably, nitrogen is introduced during the pretreatment process; the flow rate of nitrogen is 5 to 300 mL / min, preferably 100 to 200 mL / min.

[0057] Through ball milling in the present invention, terpene resin, graphene oxide, and crosslinking agent can be brought into full contact and mixed evenly; after mixing, carbonization pretreatment is carried out, which can remove most of the moisture and easily breakable elements; moreover, carbonization pretreatment can form pores on the surface of the carbon material; under the initiation of the crosslinking agent, a crosslinking reaction occurs, and a macromolecular compound with a porous structure and more macropores can be formed.

[0058] In some embodiments of the present invention, in step S2, the pore-forming agent includes at least one of KOH, NaOH, C2H5ONa, and C2H5OK.

[0059] In some embodiments of the present invention, in step S2, the mass ratio of the hard carbon precursor to the pore-forming agent is (3 to 8):1; typically but not restrictively, for example, the mass ratio of the hard carbon precursor to the pore-forming agent can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or any range composed of any two of them.

[0060] In the present invention, by using a pore-forming agent to regulate the pore volume and pore size of the hard carbon material, the porous structure of the hard carbon material, and the appropriate pore volume and pore size are beneficial to improving the performance of the hard carbon material such as the specific capacity and the first efficiency.

[0061] In some embodiments of the present invention, in step S2, before the high-temperature carbonization treatment, grinding is further included.

[0062] In some embodiments of the present invention, in step S2, the grinding includes ball milling; preferably, the rotation speed of the grinding is 200 to 1500 rmp, and the grinding time is 1 to 3 h; preferably, the rotation speed of the grinding is 600 to 1000 rmp, and the grinding time is 2 to 3 h.

[0063] In some embodiments of the present invention, in step S2, the high-temperature carbonization includes: under an inert atmosphere, heating to 1300 to 1600 °C and holding for 2 to 12 h; typically but not restrictively, for example, the temperature of the high-temperature carbonization can be 1300 °C, 1350 °C, 1400 °C, 1450 °C, 1500 °C, 1550 °C, 1600 °C, or any range composed of any two of them; the time of the high-temperature carbonization is 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, or any range value composed of any two of them. Preferably, the temperature of the high-temperature carbonization is 1400 to 1500 °C, and the time of the high-temperature carbonization is 2 to 8 h.

[0064] In some embodiments of the present invention, in step S2, the heating rate during the high-temperature carbonization process is 3 to 15 °C / min; preferably, the heating rate during the high-temperature carbonization process is 5 to 10 °C / min.

[0065] Based on the carbonization pretreatment, the present invention further performs high-temperature carbonization to further deepen pore formation, remove moisture and most oxygen-containing groups, and create internal pores in the cross-linked macromolecules to form a structure with large pores at the edges, hollow spaces between layers, and micropores inside.

[0066] The present invention adopts an appropriate carbonization temperature, carbonization time, and heating rate, which is beneficial to ensuring the performance of the obtained hard carbon material.

[0067] In some embodiments of the present invention, in step S2, it further includes crushing the hard carbon material; preferably, the D50 of the crushed hard carbon material is 5 to 15 μm.

[0068] In some embodiments of the present invention, there is also provided a hard carbon material prepared by using the above-mentioned preparation method of the hard carbon material.

[0069] In some embodiments of the present invention, the particle size D10 of the hard carbon material is 2 to 4.5 μm, and D90 is 10 to 15 μm.

[0070] In some embodiments of the present invention, the moisture content of the hard carbon material is 0.1 to 0.2 wt%, and the ash content is 0.5 wt% to 0.6 wt%.

[0071] In some embodiments of the present invention, the specific surface area (BET) of the hard carbon material is 2.5 to 3.5 m 2 / g.

[0072] In some embodiments of the present invention, the first efficiency of the hard carbon material is ≥92%, the capacity is ≥300 mAh / g, and the capacity retention rate after 50 cycles at 1C is >98%.

[0073] In some embodiments of the present invention, there is also provided a negative electrode sheet including the above-mentioned hard carbon material.

[0074] In some embodiments of the present invention, there is also provided a sodium-ion battery including the above-mentioned negative electrode sheet.

[0075] The sodium-ion battery obtained by using the hard carbon material of the present invention as the negative electrode material has excellent first efficiency, cycle performance, and rate performance.

[0076] Example 1

[0077] The preparation method of the hard carbon material provided in this example includes the following steps:

[0078] S1. Mix terpene resin (softening point: 135 °C, residual carbon rate: 10%) and graphene oxide (number of layers: 3 layers, sheet diameter: 15 μm, oxygen content: 20%, I D / I G = 1.5) in a mass ratio of 3:1 to obtain a mixed material. Mix the mixed material and ammonium dihydrogen phosphate in a mass ratio of 4:1 in a ball mill tank. The rotation speed of the ball mill is 400 rpm and the time is 2 h. After ball milling, place it in a corundum crucible in a tubular furnace, introduce an inert N2 atmosphere with a flow rate of 130 mL / min (purity > 99.9%), heat it to 400 °C at a rate of 5 °C / min, hold for 1 h, and then cool to room temperature to obtain a hard carbon precursor;

[0079] S2. Ball mill and mix the above hard carbon precursor and KOH powder in a mass ratio of 5:1. The rotation speed of the ball mill is 800 rpm and the time is 2 h. After ball milling, put it into a graphite crucible in a tubular furnace. Under an inert N2 atmosphere (purity > 99.9%), heat it to 1450 °C at a rate of 8 °C / min, hold for 5 h, and then cool. Then pulverize it to obtain a hard carbon material with a D50 of 10 μm.

[0080] Example 2

[0081] The preparation method of the hard carbon material provided in this example refers to Example 1. The only difference is that in step S1, the number of layers of graphene oxide is 2 layers, the sheet diameter is 10 μm, the oxygen content is 22%, I D / I G = 2.

[0082] Example 3

[0083] The preparation method of the hard carbon material provided in this example refers to Example 1. The only difference is that in step S1, the softening point of terpene resin is 75 °C and the residual carbon rate is 7%; the number of layers of graphene oxide is 10 layers, the sheet diameter is 15 μm, the oxygen content is 30%, I D / I G = 0.8.

[0084] Example 4

[0085] The preparation method of the hard carbon material provided in this example refers to Example 1. The only difference is that in step S1, the mass ratio of terpene resin to graphene oxide is 5:2; the mass ratio of the mixed material to ammonium dihydrogen phosphate is 3:1.

[0086] Example 5

[0087] The preparation method of the hard carbon material provided in this example refers to Example 1. The only difference is that in step S1, heat it to 360 °C at a rate of 3 °C / min, hold for 4 h, and then cool to room temperature.

[0088] Example 6

[0089] The preparation method of the hard carbon material provided in this example refers to Example 1, the difference is only that in step S1, the rotation speed of ball milling is 350 rpm and the time is 1.5 h; after ball milling, it is placed in a corundum crucible of a tubular furnace, and an inert N2 atmosphere with a flow rate of 100 mL / min (purity > 99.9%) is introduced, and it is heated to 430 °C at a rate of 6 °C / min for heat preservation treatment for 1.5 h, and then cooled to room temperature to obtain a hard carbon precursor.

[0090] Example 7

[0091] The preparation method of the hard carbon material provided in this example refers to Example 1, the difference is only that in step S2, it is heated to 1350 °C at a rate of 8 °C / min for heat preservation treatment for 6.5 h, and then cooled to room temperature.

[0092] Example 8

[0093] The preparation method of the hard carbon material provided in this example refers to Example 1, the difference is only that in step S2, after ball milling, it is put into a graphite crucible of a tubular furnace, and under an inert N2 atmosphere (purity > 99.9%), it is heated to 1280 °C at a rate of 8 °C / min for heat preservation treatment for 6 h, and then cooled; then it is pulverized to obtain a hard carbon material with D50 of 10 μm.

[0094] Comparative Example 1

[0095] The preparation method of the hard carbon material provided in this comparative example refers to Example 1, the difference is only that in step S1, graphene oxide is not added, and terpene resin and ammonium dihydrogen phosphate are ball milled and mixed in a ball milling tank according to a mass ratio of 4:1.

[0096] Comparative Example 2

[0097] The preparation method of the hard carbon material provided in this comparative example refers to Example 1, the difference is only that in step S1, ammonium dihydrogen phosphate is not added, and terpene resin and graphene oxide are ball milled and mixed in a ball milling tank according to a mass ratio of 3:1.

[0098] Test Example Ⅰ

[0099] The preparation method of 2032 button cell includes the following steps:

[0100] The negative electrode material: conductive agent SP: binder SBR: binder CMC are homogenized according to a mass ratio of 95.5:1.5:1.5:1.5, coated and then dried to obtain a negative electrode sheet with a compaction degree of 1.05 g / cm 3, the negative electrode uses a lithium sheet with a thickness of 600 μm, adds electrolyte, assembles it into a 2032 button cell, and after encapsulation, conducts charge and discharge tests.

[0101] Charge and discharge regime: In the range of 0 - 2.5 V, first, constant current at 0.1 C until 2.5 V, then constant voltage at 2.5 V until the current is less than 0.02 C. After 2 cycles, change to 1.0 CC / 1.0 CD, and continue to cycle 50 times, then remove the button cell.

[0102] Use the hard carbon materials of Examples 1 - 8 and the hard carbon materials of Comparative Examples 1 - 2 respectively to assemble 2032 button cells according to the above preparation method, and test their electrochemical performance. The results are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, It includes the following steps: A mixture of terpene resin, graphene oxide and a crosslinking agent is pretreated to obtain a hard carbon precursor; The softening point of the terpene resin is 80-140°C, and the residual carbon rate is 8%-12%; The number of layers of the graphene oxide is 1 to 3 layers, the sheet diameter is <12 μm, the oxygen content is <25 wt%, and I D / I G > 1.1; The crosslinking agent is at least one of ammonium dihydrogen phosphate, phosphorus pentoxide, dopamine, thiourea and maleic anhydride; The mass ratio of the terpene resin, the graphene oxide and the crosslinking agent is (2-6):(0.5-1.5):(0.5-1.5); The pretreatment includes: under an inert atmosphere, heating to 300-410°C and holding for 0.5-2 h, and then cooling; The mixture of the hard carbon precursor and a pore-forming agent is subjected to high-temperature carbonization treatment to obtain the hard carbon material; The high-temperature carbonization includes: under an inert atmosphere, heating to 1400-1600°C and holding for 2-12 h.

2. The preparation method of the hard carbon material according to claim 1, wherein In step S1, before the pretreatment, grinding is also included.

3. The preparation method of the hard carbon material according to claim 2, wherein In step S1, the grinding includes ball milling.

4. The preparation method of the hard carbon material according to claim 2, characterized in that, In step S1, the rotation speed of the grinding is 100-800 rmp, and the grinding time is 1-3 h.

5. The preparation method of the hard carbon material according to claim 1, wherein In step S1, the heating rate is 1-10°C / min.

6. The preparation method of the hard carbon material according to claim 1, characterized in that In step S2, the pore-forming agent includes at least one of KOH, NaOH, C2H5ONa and C2H5OK.

7. The preparation method of the hard carbon material according to claim 1, characterized in that, In step S2, the mass ratio of the hard carbon precursor and the pore-forming agent is (3-8):

1.

8. The preparation method of the hard carbon material according to claim 1, characterized in that, In step S2, before the high-temperature carbonization treatment, grinding is also included.

9. The preparation method of the hard carbon material according to claim 8, wherein In step S2, the grinding includes ball milling.

10. The preparation method of the hard carbon material according to claim 8, characterized in that, In step S2, the rotation speed of the grinding is 200-1500 rmp, and the grinding time is 1-3 h.

11. The preparation method of the hard carbon material according to claim 1, wherein, In step S2, the heating rate is 3-15°C / min.

12. A hard carbon material, characterized in that, It is prepared by the preparation method of the hard carbon material according to any one of claims 1-11.

13. A negative electrode plate, characterized in that, It includes the hard carbon material according to claim 12.

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