Composite carbon material, preparation method thereof, negative electrode sheet and secondary battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to a composite carbon material, which comprises a solid electrolyte and an amorphous carbon material, the solid electrolyte is coated on the surface of the amorphous carbon material, the solid electrolyte accounts for 1% to 10% of the composite carbon material in terms of weight fraction, and the amorphous carbon material accounts for 90% to 99% of the composite carbon material in terms of weight fraction. The composite carbon material has a stable structure and good rate performance, cycle performance and safety performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a composite carbon material, a preparation method thereof, a negative electrode sheet and a secondary battery. BACKGROUND

[0002] With the rapid development of automobile electrification, the demand for lithium-ion power batteries in the society is increasing, leading to the increasingly tight supply of lithium resources and the high price. In another direction, with the rapid advancement of the national "carbon peak and carbon neutral" strategy, cheap, sustainable and safe energy storage batteries have become the main development force. And the lithium-ion battery is the dominant position in the energy storage battery, therefore, the rapid development of the energy storage industry also intensifies the rapid consumption of lithium resources, leading to a supply and demand imbalance. Therefore, it is urgent to develop new energy storage batteries based on non-lithium-ion batteries. Sodium-ion batteries have the advantages of low cost, abundant resources, good safety and environmental friendliness, and are suitable for large-scale energy storage. However, the radius of sodium ions is large, and they are not compatible with graphite layers, making it difficult to embed them in graphite materials, so it is crucial to develop suitable non-graphite negative electrodes.

[0003] Unlike graphite, hard carbon or soft carbon materials have long-range disorder and short-range order structure, have a larger interlayer spacing, and contain pores, which are suitable for sodium ion insertion and extraction. However, it is difficult to form a stable SEI film on the surface of hard carbon or soft carbon materials, leading to the co-embedding of solvents. In addition, unlike the structure of lithium in graphite, sodium in hard carbon or soft carbon generally exists in a metallic state, has strong reducing properties, and is prone to react with organic solvents to produce hydrogen and other gases. The continuous formation of a thick SEI layer will inhibit sodium insertion and easily cause surface sodium precipitation, posing a safety hazard. Therefore, the surface needs to be modified to inhibit the occurrence of side reactions and improve the cycle life and safety performance of the battery. SUMMARY

[0004] One of the purposes of the present application is to provide a composite carbon material with a stable structure, good rate performance, cycle performance and safety performance to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A composite carbon material, comprising a solid-state electrolyte and an amorphous carbon material, the solid-state electrolyte being coated on the surface of the amorphous carbon material, the solid-state electrolyte accounting for 1% to 10% by weight in the composite carbon material, and the amorphous carbon material accounting for 90% to 99% by weight in the composite carbon material.

[0007] The solid-state electrolyte comprises a sodium ion conductor and a conductive carbon, and the sodium ion conductor comprises a sulfide ceramic and an oxide ceramic.

[0008] The oxide ceramic is a NASICON type material, and a molecular formula is Na 3+2x Zr 2-x M x Si2PO 12 , wherein M is a divalent element, M is at least one selected from Mg, Ca, Sr, Ba and Zn, 0<=x<=0.5; or a molecular formula is Na 3+x Zr 2- x M x Si2PO 12 , M is a trivalent element, M is at least one selected from La, Y, Nd and Sc, 0<=x<=0.5; or a molecular formula is Na3Zr 2- x M x Si2PO 12 , wherein M is a tetravalent element, M is at least one selected from Ce, Ti, Hf and Ge, 0<=x<=0.5; or a molecular formula is Na 3-x Zr 2-x M x Si2PO 12 , M is a pentavalent element, M is at least one selected from Nb, Ta, V and Sb, 0<=x<=0.5.

[0009] The weight fraction ratio of the oxide ceramic, the sulfide ceramic and the conductive carbon is 90-97:2-6:1-4.

[0010] The second purpose of the present application is to provide a preparation method of a composite carbon material, which is simple, controllable and easy to operate.

[0011] In order to achieve the above purpose, the following technical scheme is adopted in the present application:

[0012] A preparation method of a composite carbon material, characterized in that the method comprises the following steps:

[0013] Step S1, crushing an oxide ceramic and a sulfide ceramic, and mixing the oxide ceramic and the sulfide ceramic with conductive carbon to obtain a solid electrolyte coating layer precursor;

[0014] Step S2, coating the solid electrolyte coating layer precursor on the surface of an amorphous carbon material to form a coating layer, and obtaining a pretreated material with a core-shell structure;

[0015] Step S3, performing heat treatment on the pretreated material with the core-shell structure in an inert atmosphere to obtain a composite carbon material.

[0016] In the step S1, the particle size of the crushed oxide ceramic is 50-100 nanometers, and the particle size of the crushed sulfide ceramic is 10-50 nanometers.

[0017] The thickness of the coating layer in step S2 is 50-100 nm.

[0018] The heating rate of the heat treatment in step S3 is 1-10℃ / min, the heat treatment temperature is 200-400℃, and the heat treatment time is 1-5 hours.

[0019] A third object of the present application is to provide a negative electrode sheet having good structural stability and electrochemical performance.

[0020] To achieve the above object, the present application adopts the following technical scheme.

[0021] A negative electrode sheet comprises the composite carbon material.

[0022] A third object of the present application is to provide a secondary battery having good rate performance, cycle performance and safety performance, and the battery does not swell.

[0023] To achieve the above object, the present application adopts the following technical scheme:

[0024] A secondary battery comprises the negative electrode sheet.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The composite carbon material has good structural stability and electrochemical performance, the solid-state electrolyte layer on the surface plays the role of artificial SEI film, can effectively protect amorphous carbon, inhibit the occurrence of side reactions, and is beneficial to the optimization balance of capacity, coulombic efficiency and cycle life, and the obtained sodium ion battery has the advantages of long cycle life, excellent rate performance, high coulombic efficiency and no swelling.

[0027] 2. The raw material and preparation method of the composite carbon material are simple, low in energy consumption, low in cost, short in cycle, and beneficial to large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is an SEM image of the composite carbon material of the present application.

[0029] Figure 2 is an SEM image of the composite carbon material of Example 1 of the present application.

[0030] Figure 3 is a schematic diagram of the prepared secondary battery of the present application. DETAILED DESCRIPTION

[0031] The present application will be further described in detail below in combination with specific embodiments and the drawings of the specification, but the embodiments of the present application are not limited thereto.

[0032] A composite carbon material, comprising a solid-state electrolyte and an amorphous carbon material, the solid-state electrolyte being coated on the surface of the amorphous carbon material, the solid-state electrolyte accounting for 1-10% by weight in the composite carbon material, and the amorphous carbon material accounting for 90-99% by weight in the composite carbon material.

[0033] The solid-state electrolyte accounts for 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight in the composite carbon material, and the amorphous carbon material accounts for 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% by weight in the composite carbon material. The mass range of the solid-state electrolyte is set to control the thickness and compactness of the coating layer. If the coating layer is too thick, the performance of the amorphous carbon material is affected, and if the coating layer is too thin, the structural stability is affected, and the coating layer is easily peeled off.

[0034] In some embodiments, the solid-state electrolyte comprises a sodium ion conductor and a conductive carbon, and the sodium ion conductor comprises a sulfide ceramic and an oxide ceramic. The sodium ion conductor and the conductive carbon can form a mixed conductive structure to improve the conductive performance of the solid-state electrolyte. The sodium ion conductor comprises a sulfide ceramic and an oxide ceramic to form a stable structure.

[0035] In some embodiments, the oxide ceramic is a NASICON-type material, and the molecular formula is Na 3+2x Zr 2-x M x Si2PO 12 , wherein M is a divalent element, M is selected from at least one of Mg, Ca, Sr, Ba, and Zn, and 0≤x≤0.5; or the molecular formula is Na 3+x Zr 2- x M x Si2PO 12 , M is a trivalent element, M is selected from at least one of La, Y, Nd, and Sc, and 0≤x≤0.5; or the molecular formula is Na 2- x M x Si2PO 12 , wherein M is a tetravalent element, M is selected from at least one of Ce, Ti, Hf, and Ge, and 0≤x≤0.5; or the molecular formula is Na 3-x Zr 2-x M x Si2PO 12 , M is a pentavalent element, M is selected from at least one of Nb, Ta, V, and Sb, and 0≤x≤0.5.

[0036] In some embodiments, the weight fraction ratio of the oxide ceramic, the sulfide ceramic and the conductive carbon is 90-97: 2-6: 1-4.

[0037] A preparation method of a composite carbon material, comprising the following steps:

[0038] Step S1, crushing the oxide ceramic and the sulfide ceramic, and adding the conductive carbon to mix to obtain a solid electrolyte coating layer precursor;

[0039] Step S2, coating the solid electrolyte coating layer precursor on the surface of the amorphous carbon material to form a coating layer, and obtaining a pretreated material with a core-shell structure;

[0040] Step S3, heat treating the pretreated material with the core-shell structure in an inert atmosphere to obtain the composite carbon material.

[0041] In some embodiments, the particle size of the oxide ceramic after crushing in the step S1 is 50-100 nanometers, and the particle size of the sulfide ceramic after crushing is 10-50 nanometers.

[0042] In some embodiments, the thickness of the coating layer in the step S2 is 50-100 nanometers. The thickness of the coating layer is 50 nanometers, 60 nanometers, 70 nanometers, 80 nanometers, 90 nanometers or 100 nanometers.

[0043] In some embodiments, the heating rate of the heat treatment in the step S3 is 1-10℃ / min, the heat treatment temperature is 200-400℃, and the heat treatment time is 1-5 hours. The heating rate of the heat treatment is 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min; the heat treatment temperature is 200℃, 250℃, 300℃, 350℃ or 400℃, and the heat treatment time is 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.

[0044] A negative electrode sheet has good rate performance, cycle performance and safety performance.

[0045] A secondary battery includes the above negative electrode sheet. The secondary battery has good rate performance, cycle performance and safety performance, and the battery does not swell.

[0046] Example 1

[0047] First, Na3Zr2Si2PO 12 and Na3PS4 are prepared by ball milling combined with solid phase reaction, and sand milling is performed to reduce the particle size to 100 nanometers and 50 nanometers, respectively, and then mixed uniformly with acetylene black, wherein, Na3Zr2S i2 PO 12, and acetylene black is 94:4:2, to obtain a coating precursor of the solid electrolyte layer, the solid electrolyte layer is uniformly, completely, and conformally coated on the surface of the commercial hard carbon particles by using a mechanical fusion method, and finally the surface-modified hard carbon material is obtained by heating at 300°C for 2 hours in argon. The product is analyzed by SEM, and the solid electrolyte layer is uniformly, completely, and conformally coated on the surface of the hard carbon particles to obtain a solid electrolyte layer / hard carbon core-shell structure, as shown in Figure 1 .

[0048] The surface-modified hard carbon material prepared in this example is used as a negative electrode, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as a positive electrode, Celgard film as a separator, and NaPF6 PC / EMC solution as an electrolyte (4% FEC additive) to perform constant current charge and discharge tests (current density 0.5C charge / 1C discharge, voltage range 1.5-4V). The test results show that the capacity retention rate is 90% after 500 cycles, and the battery does not swell, as shown in Figure 2 . Figure 3 .

[0049] Example 2

[0050] Na3Zr2Si2PO 12 and Na3PS4 are prepared by using ball milling combined with a solid phase reaction, and sand milling is performed on both to reduce the particle size to 100 nanometers and 50 nanometers, respectively, and then they are uniformly mixed with nanometer carbon tubes. The weight ratio of Na3Zr2Si2PO 12 , Na3PS4, and nanometer carbon tubes is 94:4:2, to obtain a coating precursor of the solid electrolyte layer, the solid electrolyte layer is uniformly, completely, and conformally coated on the surface of the commercial hard carbon particles by using a mechanical fusion method, and finally the surface-modified hard carbon material is obtained by heating at 300°C for 2 hours in argon. The product is analyzed by SEM, and the solid electrolyte layer is uniformly, completely, and conformally coated on the surface of the hard carbon particles to obtain a hard carbon / solid electrolyte layer core-shell structure.

[0051] The surface-modified hard carbon material prepared in this example is used as a negative electrode, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as a positive electrode, Celgard film as a separator, and NaPF6 PC / EMC solution as an electrolyte (4% FEC additive) to perform constant current charge and discharge tests (current density 0.5C charge / 1C discharge, voltage range 1.5-4V). The test results show that the capacity retention rate is 90% after 500 cycles, and the battery does not swell.

[0052] Example 3

[0053] Na3Zr2Si2PO 12 and Na3PS4, and the particle sizes of both were reduced to 100 nm and 50 nm respectively by sand milling, and then mixed with nanometer carbon fibers. The weight ratio of Na3Zr2Si2PO 12 , Na3PS4 and nanometer carbon fibers was 94:4:2, to obtain a coating precursor of the solid electrolyte layer. The solid electrolyte layer was uniformly, completely and conformally coated on the surface of the commercial hard carbon particles by mechanical fusion, and then heated at 300°C for 2 hours in argon to obtain the surface-modified hard carbon material. The product was analyzed by SEM, and the solid electrolyte was uniformly, completely and conformally coated on the surface of the hard carbon particles to obtain a hard carbon / solid electrolyte layer core-shell structure.

[0054] The surface-modified hard carbon material prepared in this example was used as the negative electrode, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode, Celgard film as the separator, and NaPF6 PC / EMC solution as the electrolyte (4% FEC additive). The constant current charge and discharge test (current density 0.5C charge / 1C discharge, voltage range 1.5-4V) was carried out. The test results showed that the capacity retention rate was 89% after 500 cycles, and the battery did not swell.

[0055] Example 4

[0056] Na 3.05 Zr 1.95 La 0.05 Si2PO 12 and Na3PS4, and the particle sizes of both were reduced to 100 nm and 50 nm respectively by sand milling, and then mixed with nanometer carbon fibers. The weight ratio of Na3Zr2Si2PO 3.05 Zr 1.95 La 0.05 Si2PO 12 , Na3PS4 and nanometer carbon fibers was 94:4:2, to obtain a coating precursor of the solid electrolyte layer. The solid electrolyte layer was uniformly, completely and conformally coated on the surface of the commercial hard carbon particles by mechanical fusion, and then heated at 300°C for 2 hours in argon to obtain the surface-modified hard carbon material. The product was analyzed by SEM, and the solid electrolyte was uniformly, completely and conformally coated on the surface of the hard carbon particles to obtain a hard carbon / solid electrolyte layer core-shell structure.

[0057] The surface-modified hard carbon material prepared in this example was used as the negative electrode, NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O2 cathode, Celgard membrane as separator, NaPF6 PC / EMC solution as electrolyte (4% FEC additive), constant current charge and discharge test (current density 0.5C charge / 1C discharge, voltage range 1.5-4V), test results show that after 500 cycles, the capacity retention rate is 91%, and the battery does not swell.

[0058] Example 5

[0059] First, Na3Zr2Si2PO 12 and Na 3.1 P 0.9 Sn 0.1 S4 were prepared by ball milling combined with solid phase reaction, and then sand milling was performed to reduce the particle size to 100 nm and 50 nm respectively, and then mixed with acetylene black, wherein the weight ratio of Na3Zr2Si2PO 12 , Na 3.1 P 0.9 Sn 0.1 S4 and acetylene black was 94:4:2, to obtain a coating precursor of the solid electrolyte layer, and then the mechanical fusion method was used to uniformly, completely and conformally coat the solid electrolyte layer on the surface of the commercial hard carbon particles, and finally heated at 300°C for 2 hours in argon, to obtain the surface modified hard carbon material. The product was analyzed by SEM, and the solid electrolyte was uniformly, completely and conformally coated on the surface of the hard carbon particles, to obtain a hard carbon / solid electrolyte layer core-shell structure.

[0060] The surface modified hard carbon material prepared in this example was used as the negative electrode, and the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cathode, Celgard membrane as separator, NaPF6 PC / EMC solution as electrolyte (4% FEC additive), constant current charge and discharge test (current density 0.5C charge / 1C discharge, voltage range 1.5-4V), test results show that after 500 cycles, the capacity retention rate is 92%, and the battery does not swell.

[0061] Example 6

[0062] First, Na 3.05 Zr2La 0.05 Si2PO 12 and Na 3.1 P 0.9 Sn 0.1 S4 were prepared by ball milling combined with solid phase reaction, and then sand milling was performed to reduce the particle size to 100 nm and 50 nm respectively, and then mixed with acetylene black, wherein the weight ratio of Na 3.05 Zr 1.95 La0.05 Si2PO 12 , Na 3.1 P 0.9 Sn 0.1 S4 and acetylene black with a weight ratio of 94:4:2 to obtain a coating precursor of the solid electrolyte layer, and then the solid electrolyte is uniformly, completely and conformally coated on the surface of the commercial hard carbon particles by mechanical fusion, and finally heated at 300°C for 2 hours in argon to obtain the surface-modified hard carbon material. The product is analyzed by SEM, and the solid electrolyte is uniformly, completely and conformally coated on the surface of the hard carbon particles to obtain a hard carbon / solid electrolyte layer core-shell structure.

[0063] The surface-modified hard carbon material prepared in this example is used as a negative electrode, and a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode, Celgard film as a separator, and NaPF6 PC / EMC solution as an electrolyte (4% FEC additive), and then constant current charge and discharge test is carried out (current density 0.5C charge / 1C discharge, voltage range 1.5-4V). The test results show that after 500 cycles, the capacity retention rate is 94%, and the battery does not swell.

[0064] Example 7

[0065] First, Na 3.1 Zr 1.95 Zn 0.05 Si2PO 12 and Na 2.95 PS 3.95 Cl 0.05 and sand milling to reduce the particle size to 100 nanometers and 50 nanometers respectively, and then mixed uniformly with nanometer carbon tubes, wherein, Na 3.1 Zr 1.95 Zn 0.05 Si2PO 12 , Na 2.95 PS 3.95 Cl 0.05The weight ratio of Na3PS3.95Se0.05, Na2PO4, and nanometer carbon tube is 97:2:1 to obtain the coating precursor of solid electrolyte layer. The solid electrolyte is uniformly, completely, and conformally coated on the surface of commercial soft carbon particles by mechanical fusion method. Finally, the surface modified soft carbon material is obtained by heating at 300°C for 2 hours in argon. The product is analyzed by SEM, and the solid electrolyte is uniformly, completely, and conformally coated on the surface of soft carbon particles to obtain the core-shell structure of soft carbon / solid electrolyte layer.

[0066] Example 8

[0067] Na2PO4 is first prepared by ball milling combined with solid phase reaction. 3.2 Zr 1.9 Mg 0.1 Si2PO 12 and Na3PS3.95Se0.05, and the particle sizes are reduced to 100 nanometers and 50 nanometers respectively by sand milling, and then mixed uniformly with nanometer carbon tube. The weight ratio of Na3PS3.95Se0.05, Na2PO4, and nanometer carbon tube is 97:2:1 to obtain the coating precursor of solid electrolyte layer. The solid electrolyte is uniformly, completely, and conformally coated on the surface of commercial soft carbon particles by mechanical fusion method. Finally, the surface modified soft carbon material is obtained by heating at 300°C for 2 hours in argon. The product is analyzed by SEM, and the solid electrolyte is uniformly, completely, and conformally coated on the surface of soft carbon particles to obtain the core-shell structure of soft carbon / solid electrolyte layer. 3.2 Zr 1.9 Mg 0.1 Si2PO 12 , Na3PS 3.95 Se 0.05 and nanometer carbon tube is 97:2:1 to obtain the coating precursor of solid electrolyte layer. The solid electrolyte is uniformly, completely, and conformally coated on the surface of commercial soft carbon particles by mechanical fusion method. Finally, the surface modified soft carbon material is obtained by heating at 300°C for 2 hours in argon. The product is analyzed by SEM, and the solid electrolyte is uniformly, completely, and conformally coated on the surface of soft carbon particles to obtain the core-shell structure of soft carbon / solid electrolyte layer.

[0068] The surface modified soft carbon material prepared in this example is used as the negative electrode, Na2MnFe(CN)6 is used as the positive electrode, Celgard film is used as the separator, and PC / EMC solution of NaPF6 is used as the electrolyte (4% FEC additive). The constant current charge and discharge test (current density 0.5C charge / 1C discharge, voltage range 1.5-4V) is carried out. The test results show that the capacity retention rate is 87% after 500 cycles, and the battery does not swell.

[0069] Comparative Example 1

[0070] The commercial hard carbon in Example 1 is directly used as the negative electrode, NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O2 as cathode to assemble sodium ion battery for electrochemical test, the test conditions are same as example 1. After 500 cycles, the capacity retention rate is 71%, and the battery is swollen.

[0071] Comparative Example 2

[0072] The hard carbon surface modification process is same as example 1, the difference is that no sulfide ceramic is added, the weight ratio of Na3Zr2Si2PO 12 and acetylene black is 94:2, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as cathode to assemble sodium ion battery for electrochemical test, the electrochemical test conditions are same as example 1, the test results show that after 500 cycles, the capacity retention rate is 79%, and the battery is swollen.

[0073] Comparative Example 3

[0074] The hard carbon surface modification process is same as example 1, the difference is that no oxide ceramic is added, the weight ratio of Na3PS4 and acetylene black is 4:2, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as cathode to assemble sodium ion battery for electrochemical test, the electrochemical test conditions are same as example 1, the test results show that after 500 cycles, the capacity retention rate is 75%, and the battery is swollen.

[0075] Comparative Example 4

[0076] The hard carbon surface modification process is same as example 1, the difference is that no acetylene black is added, the weight ratio of Na3Zr2Si2PO 12 and Na3PS4 is 94:4, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as cathode to assemble sodium ion battery for electrochemical test, the electrochemical test conditions are same as example 1, the test results show that after 500 cycles, the capacity retention rate is 80%, and the battery is swollen.

[0077] Comparative Example 5

[0078] The hard carbon surface modification process is same as example 1, the difference is that Na3Zr2Si2PO 12 is not used, but inert oxide ZrO2 is used, the weight ratio of ZrO2, Na3PS4 and acetylene black is 94:4:2, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was used as the positive electrode to assemble sodium ion batteries for electrochemical test. The electrochemical test conditions were the same as in Example 1. The test results showed that after 500 cycles, the capacity retention rate was 76%, and the battery swelled.

[0079] Comparative Example 6

[0080] The hard carbon surface modification process was the same as in Example 1, except that Na3PS4 was not used, but an inert sulfide P2S5 was used, and the weight ratio of Na3Zr2Si2PO 12 , P2S5 and acetylene black was 94:4:2, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was used as the positive electrode to assemble sodium ion batteries for electrochemical test. The electrochemical test conditions were the same as in Example 1. The test results showed that after 500 cycles, the capacity retention rate was 77%, and the battery swelled.

[0081] Comparative Example 7

[0082] The hard carbon surface modification process was the same as in Example 1, except that after coating, no heat treatment was performed, and NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2 was used as the positive electrode to assemble sodium ion batteries for electrochemical test. The electrochemical test conditions were the same as in Example 1. The test results showed that after 500 cycles, the capacity retention rate was 82%, and the battery swelled.

[0083] Comparative Example 8

[0084] The hard carbon surface modification process was the same as in Example 1, except that the heat treatment temperature was 150°C, and NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2 was used as the positive electrode to assemble sodium ion batteries for electrochemical test. The electrochemical test conditions were the same as in Example 1. The test results showed that after 500 cycles, the capacity retention rate was 83%, and the battery swelled.

[0085] Comparative Example 9

[0086] The hard carbon surface modification process was the same as in Example 1, except that the weight ratio of Na3Zr2Si2PO 12 , Na3PS4 and acetylene black was 97:1:2, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was used as the positive electrode to assemble sodium ion batteries for electrochemical test. The electrochemical test conditions were the same as in Example 1. The test results showed that after 500 cycles, the capacity retention rate was 83%, and the battery swelled.

[0087] Comparative Example 10

[0088] The hard carbon surface modification process is as in Example 1, except that the particle size of Na3Zr2Si2PO 12 and Na3PS4is reduced to 50 nm and 100 nm, respectively, and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2as the positive electrode to assemble a sodium ion battery for electrochemical testing. The electrochemical testing conditions are the same as in Example 1. The test results show that the capacity retention rate is 79% after 500 cycles, and the battery swells.

[0089] The capacity retention rate test and the swelling test are performed on the above Examples 1-10 and Comparative Examples 1-10, and the test results are recorded in Table 1.

[0090] Table 1

[0091]

[0092] From the above Table 1, it can be seen that the secondary battery performance of Examples 1-6 is better than that of Comparative Examples 1-10, and the capacity retention rate is as high as 94%. From the comparison of Example 1 and Comparative Examples 1-10, it can be seen that when sulfide ceramics, oxide ceramics, and conductive carbon are used at the same time, and the particle size and proportion of the oxide ceramics and the sulfide ceramics are controlled and heat treatment is performed at a reasonable temperature, the coating effect is better, the cycle life of the obtained battery is longer, and the battery does not swell after cycling; the use of sodium ion conductive oxide ceramics and sulfide ceramics is better than that of ordinary inert oxides and sulfides, the cycle life of the obtained battery is longer, and the battery does not swell after cycling, and the above conditions are interrelated, and any deviation from the above conditions will not improve the performance of the battery.

[0093] From the comparison of Example 1 and Examples 2-3, it can be seen that the use of nanometer carbon tubes and nanometer carbon fibers with better conductivity is better, and the cycle life of the obtained battery is longer. From the comparison of Example 1 and Examples 4-6, it can be seen that the use of doped oxide ceramics and sulfide ceramics is better, and the use of doped oxide ceramics and sulfide ceramics at the same time is better, and the cycle life of the obtained battery is longer, and the above conditions are interrelated, and any deviation from the above conditions will not improve the performance of the battery. From Examples 7-8, it can be seen that after the surface solid-state electrolyte modification of amorphous carbon, the cycle stability of sodium ion batteries based on layered oxides / hard carbon, polyanion / soft carbon, and Prussian blue / soft carbon is also good, and the battery does not swell.

[0094] Those skilled in the art can make various modifications and variations to the above embodiments based on the disclosure and teachings of this specification. Therefore, the present application should not be limited to the above specific embodiments, and any obvious modifications, replacements or variations made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation on the present application.

Claims

1. A composite carbon material, characterized in that, The composite material includes a solid electrolyte and an amorphous carbon material, wherein the solid electrolyte is coated on the surface of the amorphous carbon material; the solid electrolyte accounts for 1% to 10% of the composite carbon material by weight, and the amorphous carbon material accounts for 90% to 99% of the composite carbon material by weight; the solid electrolyte includes a sodium ion conductor and conductive carbon, wherein the sodium ion conductor includes oxide ceramics and sulfide ceramics, and the weight ratio of oxide ceramics, sulfide ceramics and conductive carbon is 90 to 97: 2 to 6: 1 to 4; The preparation method of the composite carbon material includes the following steps: Step S1: Pulverize oxide ceramics and sulfide ceramics, add conductive carbon and mix to obtain a solid electrolyte coating layer precursor; Step S2: Coat the surface of the amorphous carbon material with the solid electrolyte coating precursor to form a coating layer, and obtain the pretreated material with a core-shell structure. Step S3: Heat-treat the core-shell structured pretreated material in an inert atmosphere to obtain composite carbon material; The particle size of the oxide ceramic after pulverization in step S1 is 50~100 nanometers, and the particle size of the sulfide ceramic after pulverization is 10~50 nanometers. In step S3, the heating rate of the heat treatment is 1~10℃ / minute, the heat treatment temperature is 200~400℃, and the heat treatment time is 1~5 hours.

2. The composite carbon material according to claim 1, characterized in that, The oxide ceramic is a NASICON-type material with the molecular formula Na. 3+2x Zr 2-x M x Si2PO 12 In the formula, M is a divalent element, selected from at least one of Mg, Ca, Sr, Ba, and Zn, where 0 ≤ x ≤ 0.5; or, the molecular formula is Na. 3+x Zr 2-x M x Si2PO 12 M is a trivalent element, selected from at least one of La, Y, Nd, and Sc, with 0 ≤ x ≤ 0.5; or, the molecular formula is Na3Zr. 2-x M x Si2PO 12 In the formula, M is a tetravalent element selected from at least one of Ce, Ti, Hf, and Ge, where 0 ≤ x ≤ 0.5; or, the molecular formula is Na. 3-x Zr 2-x M x Si2PO 12 M is a pentavalent element, and M is selected from at least one of Nb, Ta, V, and Sb, where 0 ≤ x ≤ 0.

5.

3. The composite carbon material according to claim 1, characterized in that, The thickness of the coating layer in step S2 is 50~100 nanometers.

4. A negative electrode sheet, characterized in that, The composite carbon material includes any one of claims 1 to 3.

5. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 4.

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