Hard carbon material, hard carbon negative electrode material, battery and preparation method of hard carbon material

Abstract

The application discloses a hard carbon material, a hard carbon negative material, a battery and a preparation method of the hard carbon material. Micropores of the hard carbon material include closed pores and open pores. The micropores refer to pore structures with a pore diameter less than 2 nm. The closed pores refer to pore structures isolated from the outside world. The open pores refer to pore structures in communication with the outside world. The micropore volume of the open pores of the hard carbon material is 0.008 cm 3 / g to 0.015 cm 3 / g. The specific surface area of the micropores of the open pores of the hard carbon material is 30 m 2 / g to 70 m 2 / g. According to the hard carbon material, the battery has a high discharge platform and a high capacity, and the high discharge platform is beneficial to the long cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a hard carbon material, a hard carbon negative electrode material, a battery and a preparation method of the hard carbon material. BACKGROUND

[0002] In the related art, the preparation process of the hard carbon material in the hard carbon negative electrode material is as follows: the hard carbon raw material is pre-carbonized to obtain a hard carbon precursor, and then the hard carbon precursor is high-temperature carbonized to obtain the hard carbon material. However, the hard carbon material prepared in the related art has a relatively high capacity, but a relatively low discharge platform, which leads to the phenomenon of sodium precipitation in the negative electrode of the battery, and is not conducive to the long cycle performance of the battery. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the prior art. To this end, one object of the present application is to provide a hard carbon material having a relatively high discharge platform and a relatively high capacity, which can enable the battery to have a relatively large capacity, and the relatively high discharge platform is conducive to the long cycle performance of the battery.

[0004] The present application also provides a hard carbon negative electrode material having the above-mentioned hard carbon material.

[0005] The present application also provides a battery having the above-mentioned hard carbon negative electrode material.

[0006] The present application also provides a preparation method of the hard carbon material.

[0007] According to the hard carbon material of the first aspect of the present application, the micropores of the hard carbon material include closed pores and open pores, the micropores refer to pore structures with a pore size less than 2 nm, the closed pores refer to pore structures isolated from the outside world, and the open pores refer to pore structures in communication with the outside world; wherein the micropore volume of the open pores of the hard carbon material is 0.008 cm 3 / g~0.015 cm 3 / g and / or the specific surface area of the micropores of the open pores of the hard carbon material is 30 m 2 / g~70 m 2 / g.

[0008] According to the hard carbon material of the present application, by optimizing the microstructure of the hard carbon material, the micropores of the hard carbon material include open pores and closed pores, the closed pores in the hard carbon material can improve the capacity of the hard carbon material, the open pores in the hard carbon material can improve the discharge platform of the hard carbon material, and by setting the micropore volume of the open pores of the hard carbon material to 0.008 cm 3 / g~0.015 cm 3 / g and / or setting the specific surface area of the micropores of the open pores of the hard carbon material to 30 m 2 / g~70 m2 / g, so that a larger proportion of open pores is present in the hard carbon material per unit mass, so that the hard carbon material has a higher discharge plateau and at the same time has a higher capacity, so that the battery has a larger capacity, and the higher discharge plateau is conducive to the long cycle performance of the battery.

[0009] According to some embodiments of the present application, the hard carbon material has an interlayer spacing d002 of 0.38 nm to 0.40 nm.

[0010] According to some embodiments of the present application, the hard carbon material has a specific capacity of 290 mAh / g to 300 mAh / g.

[0011] According to some embodiments of the present application, the powder conductivity of the hard carbon material at 5 MPa is greater than 8 S / cm.

[0012] The hard carbon negative electrode material according to the second aspect of the embodiments of the present application comprises the hard carbon material according to the first aspect of the embodiments of the present application.

[0013] The hard carbon negative electrode material according to the embodiments of the present application, by providing the above-mentioned hard carbon material, can make the hard carbon negative electrode material have a higher discharge plateau and at the same time have a higher capacity, so that the battery has a larger capacity, and the higher discharge plateau is conducive to the long cycle performance of the battery.

[0014] According to some embodiments of the present application, a half-cell negative electrode sheet is prepared by taking metal as a negative electrode material, a half-cell positive electrode sheet is prepared by taking the hard carbon negative electrode material as a positive electrode material, and the half-cell negative electrode sheet and the half-cell positive electrode sheet are assembled into a half-cell; wherein the discharge plateau of the half-cell is greater than 38 mV.

[0015] The battery according to the third aspect of the embodiments of the present application comprises: a shell; an electrode assembly arranged in the shell, the electrode assembly comprising a negative electrode sheet and a positive electrode sheet, the negative electrode sheet comprising a negative electrode current collector and an active material layer coated on the negative electrode current collector, and the active material layer comprising the hard carbon negative electrode material according to the second aspect of the embodiments of the present application.

[0016] The battery according to the embodiments of the present application, by using the above-mentioned hard carbon negative electrode material, can make the battery have a higher discharge plateau and a higher capacity, so as to improve the cycle performance of the battery.

[0017] The preparation method of the hard carbon material according to the fourth aspect of the embodiments of the present application comprises: pre-carbonizing a hard carbon raw material to obtain a hard carbon precursor; high-temperature carbonizing the hard carbon precursor, and heating to a high-temperature carbonization temperature at a first heating rate and maintaining for a first time length, wherein the first time length ranges from 5 min to 30 min.

[0018] According to the preparation method of the hard carbon material, the holding time of the high-temperature carbonization stage is limited to 5 min to 30 min, so that the holding time of the high-temperature carbonization stage is short, which can avoid that a large number of open pores are completely closed and form closed pores in the high-temperature carbonization stage, so that a large proportion of open pores can be ensured in the prepared hard carbon material, so that the hard carbon material has a high discharge platform and at the same time has a high capacity, and the battery has a large capacity, and the high discharge platform is beneficial to the long cycle performance of the battery.

[0019] According to some embodiments of the present application, the first heating rate ranges from 50℃ / min to 150℃ / min, and the high-temperature carbonization temperature ranges from 1100℃ to 1400℃.

[0020] According to some embodiments of the present application, the pre-carbonization of the hard carbon raw material comprises: heating to a pre-carbonization temperature at a second heating rate and holding for a second time, wherein the second heating rate ranges from 1℃ / min to 3℃ / min, the pre-carbonization temperature ranges from 600℃ to 800℃, and the second time ranges from 1h to 4h.

[0021] According to some embodiments of the present application, the hard carbon raw material comprises starch, pitch or phenolic resin.

[0022] According to some embodiments of the present application, the preparation method of the hard carbon material further comprises: after the high-temperature carbonization of the hard carbon precursor and cooling to a set temperature, heating to a medium-temperature holding temperature at a third heating rate and holding for a third time to obtain the hard carbon material, wherein the medium-temperature holding temperature is higher than the pre-carbonization temperature and lower than the high-temperature carbonization temperature.

[0023] According to some optional embodiments of the present application, the third heating rate ranges from 1℃ / min to 5℃ / min, the medium-temperature holding temperature ranges from 1000℃ to 1100℃, and the third time ranges from 6h to 18h.

[0024] According to some embodiments of the present application, the hard carbon material is the hard carbon material according to the above-mentioned first aspect of the embodiments of the present application.

[0025] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0026] The embodiments of the present application are described in detail below, and the embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0027] The micropores of the hard carbon material according to the first aspect of the present application include closed pores and open pores, the micropores refer to pore structures with a pore size less than 2 nm, the closed pores refer to pore structures isolated from the outside world, and the open pores refer to pore structures in communication with the outside world.

[0028] The inventors have found that, when the hard carbon material is used in a sodium ion battery, the micropores in the hard carbon material can provide embedding positions for sodium ions, thereby providing capacity, i.e., increasing the capacity. The closed pores can provide more capacity than the open pores, i.e., the closed pores have more advantages than the open pores in increasing capacity. When the closed pores are relatively more, the hard carbon material can have a larger capacity, but the capacity of the closed pores that is increased needs to be exerted at a very small current. That is, the increase of the closed pores will lead to a decrease in the discharge platform. Although the capacity provided by the open pores is less than that provided by the closed pores, the open pores can relatively increase the discharge voltage in the low platform region. When the open pores are increased, the discharge platform of the hard carbon material can be improved, so that the hard carbon material has a higher discharge platform.

[0029] By optimizing the microstructure of the hard carbon material, the micropores of the hard carbon material include open pores and closed pores. The closed pores in the hard carbon material can increase the capacity of the hard carbon material, and the open pores in the hard carbon material can improve the discharge platform of the hard carbon material.

[0030] The micropore volume of the open pores of the hard carbon material is 0.008 cm 3 / g to 0.015 cm 3 / g, and / or the specific surface area of the micropores of the open pores of the hard carbon material is 30 m 2 / g to 70 m 2 / g, which can include the following cases:

[0031] For example, the micropore volume of the open pores of the hard carbon material is 0.008 cm 3 / g to 0.015 cm 3 / g, for example, the micropore volume of the open pores of the hard carbon material can be 0.008 cm 3 / g, 0.009 cm 3 / g, 0.010 cm 3 / g, 0.011 cm 3 / g, 0.012 cm 3 / g, 0.013 cm 3 / g, 0.014 cm 3 / g, 0.015 cm 3 / g, etc.

[0032] For another example, the specific surface area of the micropores of the open pores of the hard carbon material is 30 m 2 / g to 70 m 2 / g, for example, the open micropore specific surface area of the hard carbon material is 30 m 2 / g, 35 m 2 / g, 40 m 2 / g, 45 m 2 / g, 50 m 2 / g, 55 m 2 / g, 60 m 2 / g, 65 m 2 / g, 70 m 2 / g, etc.

[0033] For another example, the open micropore pore volume of the hard carbon material is 0.008 cm 3 / g~0.015 cm 3 / g and the open micropore specific surface area of the hard carbon material is 30 m 2 / g~70 m 2 / g.

[0034] By limiting the open micropore pore volume to be no less than 0.008 cm 3 / g and / or by limiting the open micropore specific surface area to be no less than 30 m 2 / g, a larger proportion of the open pores in the hard carbon material per unit mass is ensured, and by limiting the open micropore pore volume to be no more than 0.015 cm 3 / g and / or by limiting the open micropore specific surface area to be no more than 70 m 2 / g, the decrease of the compaction density of the hard carbon material due to too many open pores can be avoided, or the increase of the consumption of part of the sodium ions due to the decomposition of the electrolyte to form the solid electrolyte interface (SEI) film caused by the too large open micropore specific surface area, and the increase of the irreversible side reactions caused by the high specific surface area, can be avoided, so as to reduce the first coulombic efficiency and the cycle stability of the battery.

[0035] By setting the open micropore pore volume of the hard carbon material to be 0.008 cm 3 / g~0.015 cm 3 / g and / or setting the open micropore specific surface area of the hard carbon material to be 30 m 2 / g~70 m 2 / g, a larger proportion of the open pores in the hard carbon material per unit mass is ensured, so that the hard carbon material has a higher discharge platform and at the same time has a higher capacity, and the compaction density of the hard carbon material is higher and has better first coulombic efficiency and cycle stability. The battery using the hard carbon material can make the negative electrode not easy to appear sodium precipitation due to the higher discharge platform, which is beneficial to improve the long cycle performance of the battery and improve the cycle performance of the battery.

[0036] The open micropore volume of the hard carbon material and the open micropore specific surface area of the hard carbon material can be obtained by CO2 adsorption test.

[0037] According to the hard carbon material of the embodiment of the present application, by optimizing the microstructure of the hard carbon material, the micropores of the hard carbon material include open pores and closed pores, the closed pores in the hard carbon material can improve the capacity of the hard carbon material, the open pores in the hard carbon material can improve the discharge platform of the hard carbon material, and by setting the micropore volume of the open pores of the hard carbon material at 0.008 cm3 / g~0.015 cm3 / g and / or setting the open micropore specific surface area of the hard carbon material at 30 m2 / g~70 m2 / g, the hard carbon material has a larger proportion of open pores per unit mass, so that the hard carbon material has a higher discharge platform and at the same time has a higher capacity, which can make the battery have a larger capacity, and the higher discharge platform is beneficial to the long cycle performance of the battery. 3 3 2 2 The higher discharge platform is beneficial to the long cycle performance of the battery.

[0038] According to some embodiments of the present application, the interlayer spacing d002 of the hard carbon material is 0.38 nm~0.40 nm, for example, the interlayer spacing d002 of the hard carbon material can be 0.38 nm, 0.39 nm, 0.40 nm, etc. If the interlayer spacing d002 of the hard carbon material is greater than 0.40 nm, the conductivity of the hard carbon material will be poor; if the interlayer spacing d002 of the hard carbon material is less than 0.38 nm, it is not conducive to the insertion and extraction of sodium ions, and increases the ion migration resistance.

[0039] By setting the interlayer spacing d002 of the hard carbon material at 0.38 nm~0.40 nm, the open pores and closed pores in the hard carbon material can be within a suitable proportion range, which can further ensure that the hard carbon material has a higher capacity, at the same time has a higher discharge platform and better conductivity, and the ion migration resistance is lower, and the overall impedance is reduced.

[0040] According to some embodiments of the present application, the gram capacity of the hard carbon material is 290 mAh / g~300 mAh / g, for example, the gram capacity of the hard carbon material can be 290 mAh / g, 292 mAh / g, 294 mAh / g, 296 mAh / g, 298 mAh / g, 300 mAh / g. By setting the gram capacity of the hard carbon material at 290 mAh / g~300 mAh / g, the hard carbon material can have a higher gram capacity, so that the energy density of the battery with the hard carbon material can be improved.

[0041] ​​​According to some embodiments of the present application, the powder conductivity of the hard carbon material at 5 MPa is greater than 8 S / cm. Thus, the hard carbon material has good electrical conductivity, improves the kinetic performance of the hard carbon material, and reduces the sodium precipitation problem during battery cycling.

[0042] According to the hard carbon negative electrode material of the second aspect of the embodiments of the present application, the hard carbon material according to the first aspect of the embodiments of the present application is used.

[0043] For example, a negative electrode sheet of a half-cell is prepared by using a metal as a negative electrode material, a positive electrode sheet of a half-cell is prepared by using the hard carbon negative electrode material as a positive electrode material, and the negative electrode sheet of the half-cell and the positive electrode sheet of the half-cell are assembled into a half-cell; wherein the discharge platform of the half-cell is greater than 38 mV. The hard carbon negative electrode material of the present embodiment can be used to measure the discharge platform of the half-cell to be greater than 38 mV in the half-cell test, thereby indicating that the battery with the hard carbon negative electrode material has a high discharge platform, the negative electrode is not prone to sodium precipitation, and the long cycle performance of the battery is improved.

[0044] Sodium precipitation of the negative electrode often occurs at 0 V or even lower negative potential, so the hard carbon material with a high discharge platform can avoid or reduce the occurrence of sodium precipitation. In addition, the amount of sodium ion source in the battery chemical system is constant, and when sodium precipitation occurs, the amount of sodium ion available for battery cycling decreases sharply, which results in low long cycle performance. Therefore, increasing the discharge platform can make the negative electrode not prone to sodium precipitation, which is beneficial to the long cycle performance of the battery.

[0045] According to the hard carbon negative electrode material of the embodiments of the present application, the hard carbon material is used, so that the hard carbon negative electrode material has a high discharge platform and a high capacity, the battery has a large capacity, and the high discharge platform is beneficial to the long cycle performance of the battery.

[0046] According to the battery of the third aspect of the embodiments of the present application, the hard carbon negative electrode material is used, so that the battery has a high discharge platform and a high capacity, thereby improving the cycle performance of the battery.

[0047] The battery can be a sodium ion battery.

[0048] According to the battery of the embodiments of the present application, the hard carbon negative electrode material is used, so that the battery has a high discharge platform and a high capacity, thereby improving the cycle performance of the battery.

[0049] The preparation method of the hard carbon material according to the fourth aspect of the embodiment of the present application comprises:

[0050] The hard carbon raw material is pre-carbonized to obtain a hard carbon precursor;

[0051] The hard carbon precursor is high-temperature carbonized, and the temperature is raised to a high-temperature carbonization temperature at a first temperature raising rate and kept for a first time length, wherein the first time length ranges from 5 min to 30 min, for example, the first time length can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc.

[0052] Optionally, the particle size of the hard carbon raw material ranges from 3 μm to 20 μm, for example, the particle size of the hard carbon raw material can be 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc.

[0053] Optionally, in the high-temperature carbonization stage, a discharge plasma sintering process or a microwave sintering process with extremely fast temperature raising rate can be used to high-temperature carbonize the hard carbon precursor, so that the high-temperature carbonization time is relatively short. The discharge plasma sintering process requires vacuum and pressure applied at both ends of the mold, and the microwave sintering process requires vacuum or a protective atmosphere, for example, the protective atmosphere can be a nitrogen atmosphere.

[0054] Before the high-temperature carbonization of the hard carbon precursor, the main type of micropore in the hard carbon precursor is open pore, and through short-time high-temperature carbonization, part of the open pores can be closed to convert part of the open pores into closed pores, increase the number of closed pores, and improve the capacity. By controlling the holding time in the high-temperature carbonization stage, the amount of open pores converted into closed pores can be controlled.

[0055] By setting the holding time in the high-temperature carbonization stage to 5 min to 30 min, a certain amount of open pores can be closed and converted into closed pores by setting the holding time in the high-temperature carbonization stage to no less than 5 min, and a large amount of open pores can be prevented from being closed and converted into closed pores by setting the holding time in the high-temperature carbonization stage to no more than 30 min, so that a certain amount of open pores can be retained.

[0056] In this way, after the hard carbon precursor goes through the high-temperature carbonization stage, by controlling the holding time in the high-temperature carbonization stage, the hard carbon precursor can go through the high-temperature carbonization stage, part of the open pores can be closed and converted into closed pores, and part of the open pores can also be retained, so that the capacity can be increased, and the discharge platform can be improved, so that the hard carbon material obtained by the preparation method has a higher discharge platform and a higher capacity.

[0057] Optionally, the obtained hard carbon material can be crushed and sieved (for example, sieved through a 325-mesh sieve) to obtain a hard carbon material with a desired particle size.

[0058] Optionally, the hard carbon material obtained by the preparation method described above can be the hard carbon material according to the first aspect of the application.

[0059] According to the preparation method of the hard carbon material of the embodiments of the application, the holding time of the high-temperature carbonization stage is limited to 5 min to 30 min, so that the holding time of the high-temperature carbonization stage is relatively short, which can avoid that a large number of open pores are completely closed and form closed pores in the high-temperature carbonization stage, thereby ensuring that the prepared hard carbon material has a relatively large proportion of open pores, so that the hard carbon material has a relatively high discharge platform and at the same time has a relatively high capacity.

[0060] According to some embodiments of the application, the first heating rate ranges from 50℃ / min to 150℃ / min, for example, the first heating rate can be 50℃ / min, 70℃ / min, 90℃ / min, 110℃ / min, 130℃ / min, 150℃ / min, etc., and the high-temperature carbonization temperature ranges from 1100℃ to 1400℃, for example, the high-temperature carbonization temperature can be 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, etc. By setting the first heating rate to 50℃ / min to 150℃ / min and the high-temperature carbonization temperature to 1100℃ to 1400℃, a relatively high heating rate is achieved in the high-temperature carbonization stage, which can shorten the high-temperature carbonization time, avoid a large number of open pores from being closed to form closed pores, and ensure the carbonization effect.

[0061] According to some embodiments of the application, the pre-carbonization of the hard carbon raw material comprises: heating to a pre-carbonization temperature at a second heating rate and holding for a second time, wherein the second heating rate ranges from 1℃ / min to 3℃ / min, for example, the second heating rate can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, etc., the pre-carbonization temperature ranges from 600℃ to 800℃, for example, the pre-carbonization temperature can be 600℃, 630℃, 660℃, 690℃, 720℃, 750℃, 780℃, 800℃, etc., and the second time ranges from 1h to 4h, for example, the second time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc. By fine pre-carbonization control of the hard carbon raw material, the obtained hard carbon precursor has a suitable microporous structure and specific surface area.

[0062] According to some embodiments of the application, the hard carbon raw material comprises starch, pitch or phenolic resin. Starch, pitch or phenolic resin has no or less pore structure as a hard carbon raw material, and the microporous structure of the hard carbon precursor obtained after pre-carbonization is less, and the micropore volume is smaller, which can make the hard carbon material have a larger compaction density.

[0063] In the case of using starch or pitch as the hard carbon raw material, the starch or pitch is mixed with the cross-linking agent and then subjected to a pre-carbonization treatment. In the case of using phenolic resin as the hard carbon raw material, the cross-linking agent is not needed.

[0064] According to some embodiments of the present application, after the pre-carbonization is completed and before the high-temperature carbonization, the hard carbon precursor can be subjected to an acid washing purification to remove ash. The acid washing conditions can be as follows: 1 mol / L-3 mol / L hydrochloric acid or hydrofluoric acid, 1 h-4 h, and 25°C-80°C.

[0065] According to some embodiments of the present application, the method for preparing the hard carbon material further comprises: after the hard carbon precursor is subjected to the high-temperature carbonization and cooled to a set temperature, the hard carbon precursor is subjected to a third temperature increasing rate to increase the temperature to a medium-temperature holding temperature and held for a third time length in a protective atmosphere to obtain the hard carbon material, wherein the medium-temperature holding temperature is higher than the pre-carbonization temperature and lower than the high-temperature carbonization temperature. After the hard carbon precursor is subjected to the high-temperature carbonization, the process of the medium-temperature long-time holding can improve the powder conductivity of the hard carbon. Through the long-time medium-temperature calcination holding, the regularity of the arrangement of carbon atoms is improved, and thus the powder conductivity of the material is improved, the kinetic performance of the material is improved, the sodium precipitation is reduced, and the cycle performance of the battery is improved.

[0066] According to some optional embodiments of the present application, the third temperature increasing rate is 1°C / min-5°C / min, for example, the third temperature increasing rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, etc., the medium-temperature holding temperature is 1000°C-1100°C, for example, the medium-temperature holding temperature can be 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, etc., and the third time length is 6 h-18 h, for example, the third time length can be 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, etc. If the medium-temperature holding temperature is too low, for example, lower than 1000°C, the carbon atom thermal motion ability is insufficient, and the powder conductivity cannot be improved. If the medium-temperature holding temperature is too high, for example, higher than 1100°C, the remaining open pores are closed at high temperature, and the necessary open pores need to be reserved to improve the platform voltage. By controlling the temperature increasing rate, the holding temperature, and the holding time length in the medium-temperature holding stage in the above ranges, the regularity of the arrangement of carbon atoms can be improved, the powder conductivity of the material is improved, and the closure of some open pores is avoided, and some open pores are reserved to ensure a high platform voltage.

[0067] According to some embodiments of the present application, by fine pre-carbonization control on the hard carbon raw material, the obtained hard carbon precursor has a suitable microporous structure and specific surface area; then by short-time high-temperature carbonization of the hard carbon precursor through discharge plasma sintering or microwave sintering with extremely fast heating rate, the effect of closing the pores of the hard carbon precursor is achieved, but at this time the powder conductivity of the hard carbon material is still relatively low, and the conductivity needs to be improved through medium-temperature long-time heat preservation, and finally the required hard carbon material is obtained, which has high capacity, high conductivity and high discharge platform.

[0068] The hard carbon material, the hard carbon negative electrode material and the battery of the present application are further described below in combination with multiple examples and comparative examples.

[0069] Example 1,

[0070] The preparation method of the hard carbon material of the present example is as follows: after 10 um or so starch is fully mixed with 20% crosslinking agent maleic anhydride, it is loaded into a graphite crucible for pre-carbonization, and the pre-carbonization condition is 1 ℃ / min heating to 700 ℃ under nitrogen atmosphere and heat preservation for 2 h; after the pre-carbonization is completed, the obtained hard carbon precursor is transferred to a vacuum microwave sintering furnace for high-temperature carbonization, and the high-temperature carbonization condition is 80 ℃ / min heating to 1300 ℃ under nitrogen atmosphere and heat preservation for 20 min; after the high-temperature carbonization is completed, the obtained hard carbon is transferred to a box furnace for 1000 ℃ heat preservation for 12 h, and the heating rate during the heat preservation is 3 ℃ / min under nitrogen atmosphere; after the heat preservation is completed, the hard carbon powder is crushed and sieved, the mesh size of the sieve is 325 meshes, and finally the required hard carbon material is obtained.

[0071] Example 2,

[0072] The difference from Example 1 is that the heating rate in the pre-carbonization stage is 2 ℃ / min, and the others are the same.

[0073] Example 3,

[0074] The difference from Example 1 is that the heat preservation time in the high-temperature carbonization stage is 10 min, and the others are the same.

[0075] Example 4,

[0076] The difference from Example 1 is that the heating rate in the high-temperature carbonization stage is 120 ℃ / min, and the others are the same.

[0077] Example 5,

[0078] The difference from Example 1 is that the heat preservation temperature in the medium-temperature long-time heat preservation stage in the box furnace is 1050 ℃, and the others are the same.

[0079] Example 6,

[0080] The difference from example 1 is that the holding time of the medium temperature long time holding stage in the box furnace is 16h, and the others are the same.

[0081] Example 7,

[0082] The difference from example 1 is that the starch is replaced by 10um or so of asphalt, the crosslinking agent is citric acid, and the others are the same.

[0083] Example 8,

[0084] The difference from example 1 is that the starch is replaced by 10um or so of phenolic resin, and there is no crosslinking agent, and the others are the same.

[0085] Comparative example 1,

[0086] The difference from example 1 is that the heating rate of the pre-carbonization stage is 5℃ / min, and the others are the same.

[0087] Comparative example 2,

[0088] The difference from example 1 is that the heating rate of the high temperature carbonization stage is 30℃ / min, and the others are the same.

[0089] Comparative example 3,

[0090] The difference from example 1 is that the holding time of the high temperature carbonization stage is 60min, and the others are the same.

[0091] Comparative example 4,

[0092] The difference from example 1 is that the holding temperature of the medium temperature long time holding stage is 800℃, and the holding time is 6h, and the others are the same.

[0093] The parameters of the preparation method of the hard carbon material of the above example 1 to example 8 and comparative example 1 to comparative example 4 are as follows table 1.

[0094] Table 1

[0095]

[0096]

[0097] The hard carbon precursor obtained in the pre-carbonization stage, the hard carbon obtained in the high temperature carbonization stage, and the hard carbon material obtained in the medium temperature long time holding stage in the above example 1 to example 8 and comparative example 1 to comparative example 4 are respectively subjected to CO2 adsorption test, powder conductivity test.

[0098] The open micropore volume of the hard carbon material is obtained by CO2 adsorption test, and the specific method is as follows:

[0099] (1) The adsorption amount of the material at each partial pressure point is tested, and the maximum partial pressure point is 0.03;

[0100] (2) The correspondence between the partial pressure-pore size-pore volume is established under the Horvath-Kawazoe analysis model (HK) ;

[0101] (3) The cumulative pore volume in the current pore size range is obtained through the pore volume at each partial pressure point.

[0102] The open-pore specific surface area of the hard carbon material is also obtained by CO2 adsorption testing, and the specific method is as follows:

[0103] (1) The limiting volume obtained by the Dubinin-Radushkevich (DR) equation is used as the monolayer saturated adsorption amount;

[0104] (2) The micropore specific surface area is calculated by the following formula:

[0105] where V m is the monolayer adsorption volume, V g is the molar volume of gas under standard conditions, N a is the Avogadro constant, w is the sample mass, and σ A is the cross-sectional area of the adsorbate molecule.

[0106] Powder conductivity test of the hard carbon material: The powder resistivity & compaction density instrument of Yuan Neng Technology is used, and the sampling point is taken every 5 MPa, the pressure is maintained for 10 s, and the automatic measurement is performed.

[0107] The hard carbon materials, conductive agents, binders, etc. of Examples 1 to 8 and Comparative Examples 1 to 4 described above are dispersed into the solvent in a set proportion, mixed uniformly to obtain a negative electrode slurry, and then coated onto a negative electrode current collector, and after drying and punching, a negative electrode sheet is obtained. The positive electrode sheet and the negative electrode sheet are assembled to prepare a button cell.

[0108] The button cells for testing prepared in each of the above examples and comparative examples are subjected to electrochemical performance testing. The testing is as follows:

[0109] First circle: 0.1C discharge to 5mV; stand for 10min; 0.01C discharge to 5mV; stand for 10min; 0.1C charge to 2V;

[0110] The second circle is a cycle test: 0.2C discharge to 5mV; stand for 10min; 0.2C charge to 2V.

[0111] The first cycle test can obtain the first coulombic efficiency; the cycle test can obtain the 50 cycle retention rate; the discharge platform, the first discharge gram capacity, the first charge gram capacity and the first coulombic efficiency can be obtained by the discharge test. Among them, the discharge platform refers to the platform voltage in the interval of 0.1V-5mV in the 0.1C discharge stage; the total area of the discharge interval / the total capacity of the discharge interval=platform voltage.

[0112] The CO2 adsorption test, powder conductivity test data of the hard carbon precursor obtained in the pre-carbonization stage, the hard carbon obtained in the high-temperature carbonization stage and the hard carbon obtained in the medium-temperature long-time holding stage in the above-mentioned examples 1 to 8 and comparative examples 1 to 4, and the test parameters and test results of the button cells prepared in each of the above-mentioned examples and comparative examples for testing are shown in Table 2 below.

[0113] Table 2

[0114]

[0115]

[0116] From the analysis of Table 2, it can be seen that when the open micro-pore volume of the hard carbon material is in the range of 0.008cm 3 / g~0.015cm 3 / g and the open micro-pore specific surface area of the hard carbon material is in the range of 30m 2 / g~70m 2 / g, the gram capacity, the first coulombic efficiency, the discharge platform and the 50 cycle retention rate are all high (see examples 1 to 8 in Table 2). When the open micro-pore volume of the hard carbon material is less than 0.008cm 3 / g or greater than 0.015cm 3 / g (see comparative examples 1 to 3 in Table 2), the discharge platform and the 50 cycle retention rate are both low. When the open micro-pore specific surface area of the hard carbon material is less than 30m 2 / g or greater than 70m 2 / g (see comparative examples 1 to 3 in Table 2), the discharge platform and the 50 cycle retention rate are both low.

[0117] In addition, it can be seen from Table 1 and Table 2 that the powder conductivity of the hard carbon formed after high-temperature carbonization is obviously improved after the long-time middle-temperature holding. In addition, it can be seen from Comparative Example 4 in Table 1 and Table 2 that if the holding temperature is too low and the holding time is too short during the long-time middle-temperature holding, the powder conductivity of the hard carbon is relatively low compared with that of Examples 1 to 8 and Comparative Examples 1 to 3. Therefore, the long-time middle-temperature holding needs a sufficient holding temperature and holding time to obviously improve the powder conductivity of the hard carbon.

[0118] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0119] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made hereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A hard carbon material, characterized in that, The micropores of the hard carbon material include closed pores and open pores, the micropores refer to pore structures with a pore size less than 2 nm, the closed pores refer to pore structures isolated from the outside world, and the open pores refer to pore structures in communication with the outside world. The micropore volume of the opening in the hard carbon material is 0.011 cm³. 3 / g~0.015cm 3 / g and the specific surface area of ​​the micropores in the hard carbon material is 30m². 2 / g~70m 2 / g.

2. The hard carbon material of claim 1, wherein, The interlayer spacing d002 of the hard carbon material is 0.38 nm to 0.40 nm.

3. The hard carbon material of claim 1, wherein, The specific capacity of the hard carbon material is 290 mAh / g to 300 mAh / g.

4. The hard carbon material of claim 1, wherein, The powder conductivity of the hard carbon material at 5 MPa is greater than 8 S / cm.

5. A hard carbon negative electrode material, characterized in that, The hard carbon material according to any one of claims 1-4. Preparation of a negative electrode sheet of a half-cell with a metal as a negative electrode material, preparation of a positive electrode sheet of a half-cell with the hard carbon negative electrode material as a positive electrode material, and assembly of the negative electrode sheet of the half-cell and the positive electrode sheet of the half-cell into a half-cell. 6.The hard carbon negative electrode material of claim 5, characterized in that, The discharge platform of the half-cell is greater than 38 mV. The hard carbon material according to any one of claims 1-4.

7. A battery, characterized by The hard carbon material according to any one of claims 1-4. The preparation method comprises: Pre-carbonization of a hard carbon raw material to obtain a hard carbon precursor; 8. A method for producing a hard carbon material, characterized by, High-temperature carbonization of the hard carbon precursor, heating to a high-temperature carbonization temperature at a first heating rate and maintaining for a first time period, wherein the first time period ranges from 5 min to 30 min, the first heating rate ranges from 50 ℃ / min to 150 ℃ / min, and the high-temperature carbonization temperature ranges from 1100 ℃ to 1400 ℃. The pre-carbonization of the hard carbon raw material comprises: heating to a pre-carbonization temperature at a second heating rate and maintaining for a second time period, wherein the second heating rate ranges from 1 ℃ / min to 3 ℃ / min, the pre-carbonization temperature ranges from 600 ℃ to 800 ℃, and the second time period ranges from 1 h to 4 h. The hard carbon raw material comprises starch, pitch, or phenolic resin.

9. The method of claim 8, wherein the hard carbon material is prepared by a process comprising: The hard carbon material according to any one of claims 1-4.

10. The method of claim 8, wherein the hard carbon material is prepared by a process comprising: After high-temperature carbonization of the hard carbon precursor and cooling to a set temperature, heating to a medium-temperature holding temperature at a third heating rate and maintaining for a third time period to obtain the hard carbon material, wherein the medium-temperature holding temperature is higher than the pre-carbonization temperature and lower than the high-temperature carbonization temperature.

11. The method of producing a hard carbon material according to any one of claims 8 to 10, characterized in that, The third heating rate ranges from 1 ℃ / min to 5 ℃ / min, the medium-temperature holding temperature ranges from 1000 ℃ to 1100 ℃, and the third time period ranges from 6 h to 18 h. ​ 12. The method of claim 11, wherein the hard carbon material is prepared by a process comprising: ​

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